巴西专利BR112014006571B1 METHOD FOR THE TREATMENT OF WASTE WATERS CONTAINING PHOSPHATE

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method and system for the treatment of waste water, appliances, and systems. method for the treatment of waste water containing phosphate, such as water from the phosphogipsite reservoir. the method includes the steps of: (a) adding a first cation to the wastewater to precipitate the fluorosilicate from the wastewater; (b) the addition of a second cation to the wastewater to precipitate the fluoride from the wastewater; (c) the elevation of the wastewater ph to precipitate the second wastewater cation; (d) the removal of residual silica from wastewater and (e) the precipitation of phosphate from wastewater. the precipitated fluorosilicate can be sodium fluorosilicate. the precipitated phosphate may be struvite.
公开号:BR112014006571B1
申请号:R112014006571-3
申请日:2012-09-21
公开日:2020-09-29
发明作者:Pierre Cote；Ahren Britton；Ram Prasad Melahalli Sathyanarayana；Rhonda Maria Hyslop；Donald Robert Clark
申请人:Ostara Nutrient Recovery Technologies Inc；
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Cross Reference to Related Patent Applications
[0001] This patent application claims priority for U.S. patent application No. 61 / 537,496 filed on September 21, 2011 entitled: “TREATMENT OF FOSFATO-CONTAINING WASTEWATER WITH FLUOROSILICATE AND FOSFATO RECOVERY” and for U.S. patent application No. 61 / 562,388 filed on November 21, 2011 entitled: “TREATMENT OF FOSFATO-CONTAINING WASTEWATER WITH FLUOROSILICATE AND FOSFATO RECOVERY”. For the purposes of the United States of America, this patent application claims the privilege under 35 U.S.C. § 119 of U.S. patent application No. 61 / 537,496 filed on September 21, 2011 entitled: “TREATMENT OF FOSFATO-CONTAINING WASTEWATER WITH FLUOROSILICATE AND FOSFATO RECOVERY” and U.S. Patent Application No. 61 / 562,388 filed on November 21, 2011, which are incorporated in this case as a reference for all purposes. Technical Field
[0002] The invention relates to the treatment of phosphate-containing wastewater, such as reservoir water with phosphogipsite, and the recovery of useful compounds fluorosilicate and phosphate, such as sodium and struvite fluorosilicate (magnesium and ammonium phosphate) from such wastewater . Fundamentals of the invention
[0003] Phosphogypsite reservoir water is a waste water by-product of phosphoric acid production. Phosphogypsite reservoir water is contaminated with a variety of chemicals that include phosphates, fluorides and silica. Phosphogypsite reservoir water is also highly acidic. Tanks that contain large amounts of reservoir water with phosphogipsite pose significant risks to the environment.
[0004] Processes for the treatment of phosphate-containing wastewater, such as phosphogipsite reservoir water, which reduce or eliminate contaminants while recovering commercially useful compounds would be desirable. summary
[0005] This invention has several aspects. One aspect provides methods for treating wastewater containing phosphate. Some embodiments of the methods are particularly advantageous in allowing the recovery of materials from wastewater that have value and are useful in a wide range of industrial and commercial methods. In some embodiments, struvite or other materials useful as fertilizers are produced. Some methods of carrying out the methods can be applied to the treatment of waste water from reservoirs with phosphogipsite that would otherwise avoid very significant damage to the environment. Other aspects provide systems for the treatment of wastewater.
[0006] Some embodiments of the invention relate to methods for treating wastewater containing phosphate while recovering fluorosilicate compounds and commercially useful phosphate compounds. Phosphate compounds can, for example, be recovered in the form of struvite. Struvite is used, among others, as a fertilizer.
[0007] Some embodiments provide methods that sequentially remove substances from phosphate-containing wastewater (such as, for example, phosphogipsite reservoir water) in a sequence such that the removed substances are supplied in a relatively pure form. The process generally improves wastewater. Bases can be introduced to increase the pH of phosphate-containing wastewater. Cations can be introduced to 1) remove contaminants, 2) recover fluorosilicate and / or 3) recover phosphate compounds. In some embodiments, cations and / or alkalis are recirculated to maximize the removal of contaminants and the recovery of fluorosilicate and phosphate compounds while maintaining a process that has a better overall cost-benefit ratio.
[0008] Some embodiments of the invention relate to treatment processes in which the phosphate-containing wastewater consists of phosphogipsite reservoir water, the fluorosilicate is recovered in the form of sodium fluorosilicate and the phosphate compound is recovered in granular struvite form (eg struvite pellets). These embodiments coincide with aspects of the invention that have significant commercial utility. The scope of the invention, however, is not limited to these embodiments.
[0009] A non-limiting example aspect provides a method for treating waste water containing phosphate. The method comprises: adding a first cation to the wastewater to precipitate the fluorosilicate from the wastewater; the addition of a second cation to the wastewater to precipitate the fluoride from the wastewater; increasing the pH of wastewater to precipitate the second wastewater cation; the removal of residual silica from wastewater and the precipitation of phosphate from wastewater.
[00010] A non-limiting example aspect provides a system for treating phosphate-containing wastewater, for example, from a phosphogipsite reservoir. The system comprises a connected inlet to remove phosphate-containing wastewater from a wastewater source such as a phosphoglyphite reservoir. A fluorosilicate precipitation stage comprising one or more first containers is connected to receive the wastewater containing phosphate from the inlet. The fluorosilicate precipitation stage comprises a first reagent injection mechanism arranged to release a first reagent which comprises a first cation for wastewater in one or more of one or more first containers to precipitate fluorosilicate from wastewater. A fluoride removal stage comprising one or more of the second containers is connected to receive the liquid effluent from the fluorosilicate precipitation stage. The fluoride removal stage comprises a second reagent injection mechanism arranged to release a second reagent comprising a second cation and a waste water base in one or more of one or more second containers to precipitate the waste water fluoride. A settling tank connected to receive liquid effluent from the fluoride removal stage. A phosphate removal mechanism, which in some embodiments comprises a recirculating crystallizer, is connected to receive liquid effluent from the settling tank. The crystallizer can be configured to precipitate a phosphate-containing compound from wastewater and comprises a mechanism for collecting particles of the phosphate-containing compound.
[00011] Other aspects and characteristics of the invention in non-limiting ways of carrying out the invention are described below illustrated in the accompanying drawings. Brief Description of Drawings
[00012] The accompanying drawings illustrate the embodiments of the non-limiting example of the invention.
[00013] Figure 1 is a flow chart illustrating a process for the treatment of waste water containing phosphate according to an embodiment of the present invention.
[00014] Figure 2 is a flow chart illustrating a process for the treatment of reservoir water with phosphogipsite according to an embodiment of the present invention.
[00015] Figure 3 is a graph that illustrates an example of changes in pH during the treatment of reservoir water with phosphogipsite according to the process illustrated in Figure 2.
[00016] Figure 4 is a graph that illustrates an example of the variations in the concentrations of chemical substances during the treatment of reservoir water with phosphogipsite according to the process illustrated in Figure 2.
[00017] Figures 5a and 5b together are a block diagram illustrating a process for the treatment of reservoir water with phosphogipsite according to another embodiment of the present invention.
[00018] Figures 6a and 6b together are a block diagram illustrating a process for the treatment of reservoir water with phosphogipsite according to another embodiment of the present invention.
[00019] Figures 7a and 7b together are a block diagram illustrating a process for the treatment of reservoir water with phosphogipsite according to another embodiment of the present invention.
[00020] Figure 8 is a flow chart illustrating a process for the treatment of reservoir water with phosphogipsite according to another embodiment of the present invention. Detailed Description
[00021] Throughout the description below, specific details are provided to provide a more complete understanding of the invention. However, the invention can be carried out without these particulars. In other cases, well-known elements have not been presented or described in detail to avoid unnecessarily obscuring the invention. Consequently, the specification and drawings need to be considered in an illustrative rather than a restrictive sense.
[00022] Figure 1 illustrates in general a water treatment process 1 according to an embodiment of a non-limiting example of the invention. In process 1, phosphate-containing wastewater from a wastewater source is subjected in sequence to a fluorosilicate recovery step 10. to a fluoride removal step 20, to a residual cation removal step 30, to a residual silica removal step 40 and a phosphate recovery step 50. The waste water can then optionally be subjected to a post-treatment step 60 to provide ready-to-discharge effluent L or other uses, to recover a solution of alkaline cation from the effluent for recycling for steps 10, 20, 30, 40 and / or 50 as a substitute for the source of new reagent or alkaline material cation and / or to recover phosphate fines for recycling for step 50.
[00023] In some embodiments, process steps 1 are performed on a device that receives wastewater (for example, wastewater can be pumped from a reservoir with phosphogipsite) and processes such wastewater to remove chemicals such as described in this case. The effluent from the method can be taken back to the tank and / or, if sufficiently purified, it can be discharged to the environment, and / or taken back to a wet phosphoric acid process plant as replacement water for use in cooling water or in ■ boilers. The apparatus may comprise tanks, chambers, suitable reactors or similar to receive the wastewater, dispensers and / or mixtures for adding reagents to the wastewater as described below together with the apparatus for monitoring and controlling the process for treating the wastewater. . In some embodiments, solids generated during process steps 1 can be removed. Such solids can be removed by one or more devices suitable for separating solids such as a clarifier, settling tank, lamella clarifier, sediment supernatant blanket clarifier, disc filter, centrifuge, vacuum filter, flotation device with dissolved air or the like. The removed solids can be further dehydrated using a suitable dehydration device, if desired. The separation of solids and dehydration can be aided by the use of certain polymers or coagulants to increase the concentration of solids removed in the suspensions and reduce the required decantation / separation time.
[00024] In some embodiments, different stages are carried out in different containers. For example, the fluorosilicate recovery step 10 can be performed by receiving wastewater in one or more tanks. After each stage, the wastewater can be transferred to a subsequent tank for the next processing stage. In other embodiments, two or more of the steps can be performed while the waste water is retained in a container. The embodiments can provide batch processing modes or continuous processing modes.
[00025] For example, the fluorosilicate recovery step 10 can be performed in a batch of wastewater kept in one or more tanks. The waste water can then be transferred to another tank (or set of tanks) for the fluoride removal step 20. In some embodiments, fluoride containing solids from the fluoride removal step 20 are recovered in a clarifier. In some embodiments, more than one clarifier or the like can be used to recover the solids from the fluoride removal step 20. The residual cation removal step 30 can be done using one or more mixers. Mixers can add one or more bases to raise the pH in the residual cation removal step 30. In some embodiments, the residual cation removal step 30 is done in one or more tanks. The wastewater can be transferred to an aging tank for the residual silica removal step 40. In some embodiments, the aging tank has a greater capacity than the tanks used for the previous steps in the process. The solids from the residual cation removal step 30 and the residual silica removal step 40 can be decanted together in a settling tank, for example. In other embodiments, the solids from the residual cation removal step 30 and the residual silica removal step 40 can be decanted into separate settling tanks after each step.
[00026] In some embodiments, in which the phosphate is recovered as struvite, for example, the phosphate recovery step 50 is performed using a reactor with struvite in a fluidized bed. An example of such a reactor is the apparatus as described by Koch et al., in US 7,622,047, hereby incorporated by reference. In some embodiments, the phosphate-containing compounds precipitated in the reactor are dehydrated and dried in a dryer.
[00027] In some embodiments, the post-treatment step 60 may include the capture of precipitated phosphate fines. The fines can be efficiently ■ captured in a device for decanting or thickening (for example, a clarifier, settling tank, lamella clarifier, gravity thickening, sediment supernatant mat clarifier, mat thickener, disc filter or another effective device for separating solids). The fines can be filtered through a conveyor filter or another suitable filter, for example. The filtered solids can be dried in a dryer. The filtered solids can be pelletized for use as a fertilizer or for some other application. Alternatively the captured fines can be dissolved by adding a suitable acid. In some embodiments, a mineral acid is added that provides the desired pH range to reduce the pH to dissolve captured fines. In some embodiments, sulfuric acid may be suitable because of its availability in a phosphoric acid production complex and because it does not introduce undesirable elements such as chloride in the process that could lead to an increase in the corrosivity of the processed water and are not otherwise discarded in the produced solids. The acidified phosphate fines solution will then contain the substances dissolved in the phosphate product and can be reintroduced in the phosphate recovery step 50 together with additional alkali (any alkali can be used, but alkalis that do not contain calcium are desirable for the struvite recovery). It has been shown that sodium hydroxide is particularly effective, while also adding a sodium source that can be reused later to form sodium fluorosilicate in step 10 by recycling post-treatment concentrate as discussed below.
[00028] In some embodiments, the post-treatment step 60 includes treatment with lime. Lime sediment from the lime treatment step can be removed in a clarifier, for example. In some embodiments, the post-treatment step 60 may include a membrane treatment, for example, which includes one or more stages of membranes which may each comprise a reverse osmosis or a nano filtration membrane, for example. In some embodiments, the post-treatment step 60 may comprise the passage of the clarified effluent from the fines separation step through a pre-filtration stage (one or more of a cartridge filter, a disc filter, a filter with granular medium, an ultrafilter, a microfilter or the like) to remove suspended residual solids and reduce the soot density index of the solution. This filtered solution can then be passed through a membrane for nano filtration (for example, a membrane for selective nano filtration for sulphate) to produce a concentrate with a high concentration of sodium and sulphate and a permeate with a sodium level, of sulfate and other ions very reduced. This permeate stream can then be treated with a reverse osmosis membrane to produce a permeate with the remaining ions dissolved below applicable limits for discharge to receive water or for reuse in industrial processes such as cooling boilers or towers and a concentrate stream. which can be recirculated to one or more pre-treatment stages (10, 20, 30, 40) of the treatment process as described below optionally mixed with the nanofiltrate concentrate.
[00029] In some embodiments the membrane for reverse osmosis is operated at a relatively low pressure, for example, 1 MPa-2 MPa. The pH control can be used before the membrane for nano filtration or between the membrane for nano filtration and the membrane for reverse osmosis to improve selectivity for certain ions such as ammonia and / or to reduce the potential for dirt to form on the membrane. In some embodiments, pL1 control includes lowering the pH before one or more membranes. The reduction in pl-f can have one or more of the following effects: (i) shift the NH3 balance <-> NH / towards NH4 as many membranes will reject NHf more strongly than NH3 and (ii) reduce the saturation of cations in solution (as the solubility of many salts increases when the pH decreases) and thereby reducing the precipitation of salts that could clog the membrane (s). In some embodiments, the pH can be raised to (a) subsequent membrane (s) as some ions are better rejected at a higher pH.
[00030] The nano filtration concentrate alone or mixed with the reverse osmosis concentrate, which contains high concentrations of sodium and sulfate and lower concentrations of other ions, can then be treated with an alkali, such as lime, to produce a precipitate of gypsum (CaS04) and a sodium hydroxide solution at a relatively high concentration with a pH of 10-13. A solids separation step (clarifier, filter or the like) is then used to separate the solids from the solution. The gypsum precipitate will likely contain some unreacted lime and this suspension can be used as a substitute for at least part of the new lime used in the fluoride removal step 20 to precipitate calcium fluoride. The high concentration sodium hydroxide solution with a 10-13 pEI can be used as a source of alkaline solution to precipitate sodium fluorosilicate in the fluorosilicate recovery step 10 or for pH control in one or more of the steps 10, 20, 30 and 40. The post-treatment membrane treatment and the alkali treatment (for example, lime treatment) of the concentrate from the membrane treatment regenerates the sodium hydroxide used in the upstream processes to prevent need to add new sodium hydroxide to the process. In this way, the use of lime as the main alkaline source for the process reduces or avoids any need to introduce calcium ions in the stages where the introduction of calcium would result in greater phosphate precipitation in the pretreatment (steps 20, 30, 40) and therefore reduction in the yield of phosphate product recovered in step 50.
[00031] An alternative arrangement for nano filtration followed by the reverse osmosis process is to pass the clarified and filtered fines directly through a reverse osmosis system at a higher pressure (the operating pressure can be, for example, from 2 to 5.5 MPa with the same lime treatment process used over the concentrate used to produce a solid gypsum / lime fraction and an alkaline sodium hydroxide solution.
[00032] In some embodiments, one or more of the steps in process 1 can (m) be done in a batch process or as a continuous process. In some embodiments, in the case of reservoir water treatment with phosphogipsite, one or more of the steps in process 1 can be done directly in the phosphogipsite reservoir or in settling tanks used to retain the formed solid reaction products. In some embodiments, in the case of treatment of a reservoir with phosphogipsite, the effluent from one or more of the steps of process 1 can be recirculated back to the reservoir with phosphogipsite.
[00033] In some embodiments, waste water containing phosphate may be reservoir water with phosphogipsite. In other embodiments, wastewater containing phosphate may be agricultural wastewater, municipal sewage, wastewater from other industrial processes or the like.
[00034] The fluorosilicate recovery step 10 can be performed by adding a cation source and raising the pH to a level sufficient to precipitate fluoride and silica from the wastewater as a cation fluorosilicate. The cation can, for example, be sodium, calcium or magnesium, to provide sodium fluorosilicate, calcium fluorosilicate or magnesium fluorosilicate, respectively. Sodium fluorosilicate is a useful material. Sodium fluorosilicate is used, for example, in the fluoridation of drinking water and in the manufacture of silicon. In some embodiments, two or more different cations can be added in the fluorosilicate recovery step to provide different fluorosilicates or different mixtures of fluorosilicates (for example, a mixture of sodium fluorosilicate and calcium fluorosilicate or the mixture of sodium fluorosilicate, calcium fluorosilicate and potassium fluorosilicate).
[00035] The amount of cation source added may be based on the measured concentrations of fluoride and silica in the waste water. In some embodiments, the cation source can be added in a stoichiometric amount to precipitate the cation fluorosilicate. In still other embodiments, the cation source can be added in excess to precipitate the cation fluorosilicate.
[00036] When fluorosilicate recovery step 10 includes adding a cation source and raising the pH to a predetermined level, in some embodiments a cation base can be added to provide both the cation source and raise the pH. In other embodiments, the cation source and base can be added as separate chemicals. The base in such embodiments can be dosed in a stoichiometric ratio with the phosphate in the wastewater to preload the base for subsequent precipitation in the phosphate recovery step 50. For example, if the phosphate compound to be recovered in the step for phosphate recovery 50 is or comprises struvite, suitable bases may include bases containing magnesium and / or ammonium bases such as magnesium oxide, magnesium hydroxide, ammonium hydroxide and anhydrous ammonia. The addition of a base containing magnesium can also promote precipitation of fluoride such as magnesium fluorosilicate.
[00037] At the end of the precipitation step of fluorosilicate 10, solids (for example, precipitated fluorosilicates) can be recovered, for example, by decantation. The precipitated fluorosilicates can be removed by other mechanisms, such as filtration, centrifugation, etc. The precipitated fluorosilicates can then be collected and dried, with subsequent processing to increase their purity as necessary for their designated use. In some embodiments, the predetermined pH for the fluorosilicate precipitation step 10 can be maintained until the recovery of the solids is complete.
[00038] Fluorosilicate precipitation step 10 typically does not remove all fluoride from the phosphogipsite reservoir water. Most or all of the remaining fluoride can be removed in the fluoride removal step 20.
[00039] The fluoride removal step 20 in some embodiments includes adding a cation source and raising the pH in two stages to precipitate the remaining fluoride in the waste water. The cation can, for example, be calcium, magnesium, sodium or a mixture thereof and the precipitated fluoride can be calcium fluoride (fluoride), magnesium fluoride (saddle), sodium fluoride or a mixture thereof. If the cation is added dry, the cation is mixed with the waste water for a time sufficient to dissolve the cation. The pfl is initially raised to, and maintained at, a level high enough for substantial precipitation of the added cation fluoride but low enough to avoid any significant precipitation of the added cation phosphates. For example, when the cation used in the fluoride removal step 20 comprises calcium ions the pH can be approximately 3.5-4.0. The pH can be raised before, during or after adding the cation. The cation can be introduced by adding a cation base, such as lime or limestone, in which case it may not be necessary to separately add a base to initially raise the pH. After the initial fluoride precipitation stage of the fluoride removal step 20, the pH is subsequently raised to, and maintained at, a lower solubility level for the added cation fluoride.
[00040] In the initial and / or subsequent stages of the fluoride removal step 20, a free base of the added cation can be added to simultaneously raise the pH when necessary and the wastewater dose in a stoichiometric proportion with the phosphate for pre- base charge for subsequent precipitation in phosphate recovery step 50. For example, if the phosphate compound to be recovered is or comprises struvite and the added cation is calcium, suitable calcium free bases may include bases containing magnesium and / or ammonium such as magnesium oxide, magnesium hydroxide, ammonium hydroxide and anhydrous ammonia. The addition of a base containing magnesium can also assist in the removal of fluoride by promoting precipitation of fluoride such as magnesium fluoride (saddle). In this example, the mixture of two or more calcium-free bases can be used to raise the pH in the fluoride removal step 20.
[00041] Bases can be added in a sequence that takes into account pH-dependent differences in the solubility of the bases. For example, the base with better dissolution at a lower pH can be added before the base with less dissolution at a lower pH. For example, if magnesium oxide and ammonium hydroxide are used as bases, then magnesium oxide can be added first (because it is better dissolved at a lower pH) and then the added ammonium hydroxide next to achieve the Desired pH for fluoride removal.
[00042] The fluoride removal step 20 may alternatively include sufficient cation to wastewater at a rate such that the product of the concentration of the cation, the concentration of ionic species containing fluorine and the concentrations of any other components of the cation salt exceeds the ksp for the cation salt without being so high as to cause significant precipitation of the cation phosphate in the form of relatively insoluble phosphate compounds.
[00043] At the end of the fluoride removal step 20, precipitated solids (for example, the added cation fluorides) can be removed, for example, by decantation, by filtration, by centrifugation or the like. The precipitated solids can be decanted into the sediment form, which can be transferred to a sediment reservoir. The supernatant from the sediment reservoir can be combined with the supernatant from the decantation step before the residual cation removal step 30. In some embodiments, the fluoride precipitation step 20 may be absent (for example, when it does not remain too much fluoride after the fluorosilicate precipitation step 20).
[00044] The residual cation removal step 30 includes raising the pH to remove residual amounts of the cation added in the fluoride removal step 20 but not yet removed. In some embodiments, the pH is raised with a base that does not precipitate and / or a base that precipitates in a stoichiometric proportion with the remaining phosphate to preload the base that precipitates for the 50 phosphate recovery step. which does not precipitate may, for example, be sodium hydroxide. The precipitating base can, for example, be anhydrous ammonia or ammonium hydroxide when the phosphate to be precipitated in the phosphate recovery step 50 is struvite.
[00045] At the end of the residual cation removal step 30, the precipitated solids can be removed, for example, by decantation (or by another suitable process). The precipitated solids can be decanted into the sediment form, which can be transferred to a sediment reservoir. The supernatant from the sediment reservoir can be combined with the supernatant from the decantation step before the residual silica removal step 40. In some embodiments, precipitated solids from the residual cation removal step 30 can be decanted and removed along with the solids from the residual silica removal step 40. In some embodiments, the residual cation precipitation step 30 may be absent.
[00046] The step of removing residual silica 40 may comprise the aging of waste water to form silica gel. After aging, the wastewater is mixed to break the gel structure of the silica polymers and then decanted. In some embodiments, a suitable flocculant may be added to better promote the gelation and decantation of the silica polymers. In some embodiments the mixing times can be prolonged sufficiently to allow the silica polymers to settle in dense beds.
[00047] At the end of the residual silica removal step 40, the decanted solids are removed. In some embodiments, the step of removing residual silica 40 may be absent. As the formation of silica gel tends to occur at high concentrations of silica, the embodiments of the invention for processing wastewater with low concentrations of silica can result mainly in the complete removal of silica in the fluorosilicate precipitation step 10 and do not require the step of removing residual silica 40.
[00048] The phosphate recovery step 50 includes precipitation of the phosphate in the waste water, for example, according to the methods and apparatus as described by Koch et al., In US 7,622,047. The phosphate can be recovered in a commercially useful form such as struvite, struvite analogs or other phosphate compounds. In some embodiments in which the desired phosphate to be recovered is struvite or a struvite analog, the supersaturation conditions for the phosphate compound can be maintained during the phosphate recovery step 50. Maintaining the supersaturation conditions can , for example, include: maintaining an adequate oversaturation ratio; maintaining an adequate pH; maintaining a higher phosphate concentration than concentrations of other components of the phosphate compound and / or controllably introducing compounds that comprise at least one of the other components of the desired phosphate compound.
[00049] Post-treatment step 60 may include recovering fine particulates from commercially available precipitated phosphate forms. The post-treatment step 60 may additionally or alternatively include one or more polishing steps, the extent and nature of which may depend on the use or the discharge point of the treated effluent. For example, polishing steps can reduce residual phosphate, ammonia, metals, conductivity or other parameters. In some embodiments, the material recovered from one or more polishing steps can be recirculated to one or more of the polishing steps described above. For example, cations can be recovered in one or more polishing steps and recirculated to the fluorosilicate precipitation step 10 and / or to the fluoride precipitation step 20 as a source of cations and / or alkalinity. In some embodiments, the post-treatment step 60 may be absent.
[00050] Figure 2 illustrates process 100 and Figure 8 illustrates process 500. Both process 100 and process 500 are embodiments of the invention according to process 1, but more specifically exemplifying the treatment of reservoir water with phosphogipsite and the recovery of sodium fluorosilicate and struvite. The pH of the reservoir water with phosphogipsite is typically from 1.2 to 1.7, the pH of the reservoir water in some cases is in the range of 1.3 to 1.4.
[00051] The step of recovery of sodium fluorosilicate 110 includes raising the pH of the wastewater to around pH 2.0 with a sodium source. Mixing at the sodium source causes fluoride and silica to precipitate as sodium fluorosilicate. The sodium source may, for example, be a base containing sodium such as sodium hydroxide, sodium carbonate or sodium bicarbonate or another source of sodium such as sodium chloride or recovered sodium hydroxide solution produced by treatment with lime after membrane concentrate. The precipitated sodium fluorosilicate can be recovered, for example, by decantation. The recovered sodium fluorosilicate can be filtered and then dried to a powder form. The precipitated sodium fluorosilicate needed to be removed before proceeding to the next step, as the residual solids can redissolve and increase the unal fluoride and silica concentrations in the downstream processes. The sodium fluorosilicate recovery step 110 can reduce the fluoride concentration in wastewater up to around 4000-5000 mg / L for example and can reduce the silica concentration up to around 500-600 mg / L, for example .
[00052] The fluoride removal step 120 includes dosing with calcium. The calcium dose can be based on a residual calcium concentration (that is, the calcium concentration of the waste water entering the fluoride removal step 120 can be measured and the calcium dosage can be controlled to add the amount of additional calcium needed to achieve a desired calcium concentration). The calcium concentration from approximately 0.08 to 0.16 mol / L in excess stoichiometric demand to form CaF2 was presented by the inventors to remove fluoride up to 50-150 mg ZL, with or without the fluorosilicate precipitation step 110 .
[00053] Calcium can be added as lime or as limestone, for example, and mixed for a period of time sufficient to dissolve the calcium, for example, 1 hour to dry the lime. Suspensions may require less dissolution time, as they are already fully moistened. Calcium can be supplied to step 110 as a solution.
[00054] The pH is initially raised to around 3.5-4.0. for example, and maintained for at least 2 hours for optimal fluoride removal. Other embodiments may involve longer mixing times. The pH at this stage is preferably not raised above approximately 4.0, as calcium phosphate begins to precipitate at a pH of or above approximately pH 4.0. In such embodiments, fluoride precipitation at this stage can take place "quickly", as calcium phosphate precipitates slowly.
[00055] The initial fluoride removal stage of fluoride removal step 120 removes a substantial amount of fluoride without phosphate interference. The pH is then raised to a level of less solubility of calcium fluoride; The target pH can be approximately 5.5, for example.
[00056] Reaching the target pH will further reduce fluoride levels. The target pH can be maintained, for example, for approximately 20-30 minutes. This reduces the fluoride concentration to approximately 50-150 mg / L, for example, and approximately 600 mg / L, for example, comes out of calcium in solution.
[00057] The solids from the fluoride precipitation step 120 are then removed, for example, by decantation. Again, residual solids can redissolve in downstream processes, so the separation needed to be as complete as possible.
[00058] The calcium removal step 130 involves removing calcium to below interference levels for struvite production in the phosphate precipitation step 150. The calcium removal step 130 may involve raising the pH to above 7.0. For example, the pH range for this step can be approximately 7.0-7.5. The pH can be raised with any base that does not precipitate or base deficient in calcium, for example, a combination of gaseous ammonia or liquid ammonium hydroxide with sodium hydroxide. The ammonia can be dosed in a stoichiometric ratio with the remaining phosphate to preload the ammonia for struvite production in the 150 phosphate recovery step. Sodium hydroxide can then be added when necessary to reach the target pH. Since removing calcium also removes phosphate, a 0.7-0.9: 1 molar ratio can be used to minimize the addition of excess ammonia that can be accomplished through the phosphate recovery step 150. Approximately 10-20 % of phosphate can be lost based on the residual calcium concentration.
[00059] The fluoride concentration may rise slightly due to the redissolution of any of the residual solids after separation. Silica is typically below 100 mg / L, for example, after the calcium removal step 130.
[00060] The solids can optionally be removed, for example, by decantation, after the calcium removal step 130. The removed solids can comprise useful materials. For example, solids can comprise calcium phosphate or compounds containing phosphate and calcium. Such materials can be used, for example, as fertilizers or fertilizer components, as phosphate substitutions are in the production of phosphoric acid.
[00061] The residual silica removal step 140 involves the aging of the waste water to allow silica gel to form. For example, wastewater can be left to age for 8 to 12 hours or longer. After aging or during aging, the solution is mixed vigorously to disrupt the gel structure of the silica polymers and allow them to settle. Longer mixing times allow the silica to settle to a denser bed. The decanted solids are removed and the remaining pre-treated solution can now have low levels of silica, fluoride and calcium and 5000-8000 mg / L of phosphorus, for example, and a stoichiometric amount of ammonia combination. The solution can now be used for struvite recovery.
[00062] The struvite recovery step 150 involves introducing wastewater into a struvite recovery system. For example, a struvite-forming reactor can be used. The reactor may comprise a reactor with a fluidized bed in recirculation, for example. Super saturation conditions for the phosphate compound can be maintained to recover the struvite. Maintaining supersaturation conditions can, for example, include: maintaining a supersaturation ratio of 2 to 5; maintaining an adequate pH; the maintenance of a higher phosphate concentration than ammonia and magnesium concentrations and / or the controlled introduction of ammonia and magnesium. Ammonia can be added, for example, as an ammonium hydroxide solution or as anhydrous ammonia, magnesium can be added as magnesium chloride, magnesium hydroxide or preferably as magnesium sulfate. The addition of magnesium chloride in a phosphogipsite application may lead to the formation of chloride ions in the system, leading to an increased risk of corrosion, while the addition of magnesium hydroxide has been found to react incompletely at the pH of the operation for the struvite recovery, requiring additional reagent and also acting as nucleation sites for struvite crystals, which results in the difficulty of producing larger struvite pellets (ie, with a diameter of 0.5-5 mm). The magnesium sulfate solution can be obtained at the site by reacting stoichiometric amounts of sulfuric acid with magnesium oxide or magnesium hydroxide appropriate engineering controls to control the reaction temperature. In some embodiments, the struvite recovery reactor can be controlled to produce struvite granules with a size range from 0.5 to 5 mm in diameter and sufficient mechanical strength to withstand downstream processing such as grading, blending with other fertilizer, transport and diffusion components.
[00063] Figure 3 shows an example of the changes in pH during the process period 100 of the water recovery step from phosphogipsite to crude struvite 150. In some example of the embodiments the pH can vary up to ± 0.1 of the pH levels shown in Figure 3. In other examples of embodiments the pH can vary up to ± 0.25 from the pH levels shown in Figure 3. In other examples of embodiments the pFI can vary up to ± 0.50 of the pH levels shown in Figure 3. In other examples of embodiments the pH can vary by more than 0.50 from the pH levels shown in Figure 3.
[00064] Figure 4 shows an example of variations in the concentrations of phosphate, fluoride, silica and calcium during the period of period 100 of the reservoir water with crude phosphogypsite for the struvite recovery step 150. In some examples of embodiments the concentrations of chemicals can vary up to ± 10% of the levels shown in Figure 4. In another example of the embodiments the concentrations of chemicals can vary up to ± 20% of the levels shown in Figure 4. In other embodiments of the example chemical concentrations can vary by more than 20% from the levels shown in Figure 4.
[00065] Post-treatment steps 160 may include, for example, a fines recovery step 162 in which particulate struvite particles recovered by washing the reactor forming struvite are recovered. These recovered fines can then be redissolved by reducing the pH of the suspension of fines to approximately 5-6 or such a pH as is sufficiently low to dissolve the struvite present, using a mineral acid such as sulfuric acid. As shown in Figure 8, the dissolved struvite fines solution can then be reintroduced by the recirculation step to the struvite formation reactor for further reaction to form new struvite pellets with the addition of a base to neutralize the mineral acid that was used to dissolve the fines. This acts effectively as a "closed loop to destroy the fines" in which the fine particles formed in the struvite formation step are dissolved and reintroduced into the reactor where they are allowed to grow until the desired pellet product.
[00066] Post-treatment steps 160 may optionally involve other steps, for example, depending on the use or the discharge point at which the treated water in the reservoir is used, which reduce residual phosphate, ammonia, metals, conductivity or other parameters. As shown in Figure 2, this may involve a lime treatment step 164 that involves adding sufficient lime to bring the pH of the effluent from the fines recovery step 162 to the range of 9.0 to 11.0 depending on treatment goals. The lime sediment from the lime treatment step 164 could be returned by the recirculation step 165 to the fluoride removal step 120 as a calcium source for fluoride removal and as a means to resolubilize any precipitated phosphate during the fluoride removal 120 for recovery in the struvite recovery step 150. For stricter discharge limits, additional post-treatment such as pre-filtration followed by a nano filtration and / or a reverse osmosis step 166 can be provided. shown in Figure 2 in some embodiments the concentrated waste water can advantageously be taken up by the recirculation step 167 for a sodium fluorosilicate recovery step 110 as a source of recovered sodium ions and alkalinity and / or one or more of the steps 120, 130 or 140 as a source of alkalinity. In this way any excess sodium added in the previous steps can be reused as a substitute for newly added sodium in the sodium fluorosilicate recovery step 110 and to reduce the potential for sodium ion formation in the system when reverse osmosis is required. As shown in Figure 8, in other embodiments the concentrated residual streams from the nano filtration and / or reverse osmosis step 166 can be treated with an alkali such a lime in an alkali treatment step 168 to precipitate and decant the sulfate present in the concentrate as gypsum and provide a solution with a relatively high concentration of sodium hydroxide. Precipitation and separation of gypsum / drop solids can be carried out in a suitable decantation / filtration device.
[00067] The alkali treatment step 168 provides both a drain for the sulphate added to the system as sulfuric acid and / or magnesium sulphate and an alkaline sodium solution with a relatively high concentration that can be resumed by the recirculation stage 172 for be used both as a source of sodium for step 110 as a reagent for pH control in one or more of steps 110 through 140. The concentration of residual calcium in this recirculation stream will make it less desirable as a source of alkali for pH control in steps 140 and 150 where high calcium concentrations will result in the loss of phosphate as calcium phosphate compounds. For this reason, in some embodiments, new sodium hydroxide solution is added to steps 140 and 150 when necessary for pH control. maintaining the recirculation of the concentrate stream to step 110 as a source of sodium for the production of sodium fluorosilicate and for one or more of steps 110, 120 and 130 for pH control. When the gypsum / lime solids are separated from the alkaline sodium solution, these solids can be taken up by the recirculation step 174 for the fluoride removal step 120 where the unreacted lime in the solids can be used for pH adjustment and as a source of calcium while the gypsum remains in solution and any calcium phosphate compounds can be left to redissolve for recovery in the 150 phosphate recovery step. In other embodiments, the concentrated waste water can be taken up to the reservoir with phosphogipsite,
[00068] In some embodiments, for one of the precipitation stages in which the precipitate is not important (for example, when the precipitate is not desired to be recovered or recirculated), the reagents can be mixed in one or more tanks and then directed to one or more precipitation reservoirs. For example, the precipitation steps involved can be one or more of the fluoride removal step 120, the residual calcium removal step 130 and the residual silica removal step 140. The supernatant can be removed from the reservoir for processing in the step subsequent and the sediment decanted can be left as a layer at the bottom of the reservoir or optionally removed for further processing or disposal. This process can be repeated so that the settled sediment layers form at the bottom of the reservoir before being optionally removed for further processing or disposal.
[00069] The treatment processes of example 100, 500 as shown in Figures 2 and 8 have several characteristics that are advantageous. These include, for example: - The recovery of two commercially valuable product streams, ie fluorosilicates (eg sodium fluorosilicate) and phosphates (eg struvite) from wastewater while simultaneously treating wastewater by reducing their concentrations of fluoride, silica, ammonia, sulfate and phosphate; - The elevation of the pFI in each step of recovery of sodium fluorosilicate, step of fluoride removal and step of calcium removal facilitates the reactions in each step and also, at the end of these three steps, supplies waste water to a range of pFI range suitable for struvite recovery; - The reduction or elimination of silica in wastewater since silica gels can interfere with the reactions, the separation of solids and the proper operation of the apparatus used in the treatment of wastewater; - When the post-treatment includes a lime step treatment, recycling lime sediment as a source of calcium to remove fluoride to reduce the need to add new calcium, and as a means to resolubilize any precipitated phosphate during the removal of fluoride for recovery during struvite recovery; - When the post-treatment includes nano filtration and / or reverse osmosis, the recycling of sodium-containing concentrate for the sodium fluorosilicate recovery step as a source of sodium ions and alkalinity and the steps for removing fluoride and calcium as a source of alkalinity, significantly reducing the need to add new sodium and base e; - When the post-treatment includes nano filtration and / or reverse osmosis with lime treatment of the concentrate to precipitate gypsum, the system provides both a drain for the sulfate present in the reservoir water and that added in the process reagents, while allowing that the main source of alkalinity is removed from lime instead of sodium hydroxide, thereby significantly reducing the cost of chemicals to operate the process.
[00070] Figures 5a and 5b illustrate process 200, another example of an embodiment of the invention according to process 1, in which the post-treatment includes a step of recovering precipitated phosphate fines.
[00071] Figures 6a and 6b illustrate process 300, another example of embodiment of the invention according to process 1, in which the post-treatment includes a step of recovering precipitated phosphate fines, a treatment step with lime and two-stage membrane filtration (pre-filtration stage and reverse osmosis stage). Figures 7a and 7b illustrate a process 400 similar to process 300, but including a closed circuit for destroying fines.
[00072] The processes according to any of the embodiments as described in this case can include one or more steps in which precipitated or unreacted solids are separated from a fluid. A flocculant, for example, a suitable polymer can optionally be added during or before the step in which precipitated or unreacted solids are decanted or separated. For example, suitable flocculants can be added to accelerate and / or increase the efficiency of any one or more of settling or removing: sodium fluorosilicate; calcium fluoride, silica; precipitated phosphate; precipitated gypsum and unreacted lime.
[00073] The following are examples of vessel scale and pilot scale testing of embodiments of the invention up to, but including, the phosphate recovery step. Table 1

[00074] Table 1 above presents results of pretreatment in a phosphogipsite water tank test, which shows the concentrations of the three compounds to be removed before the phosphate precipitation / recovery step, as well as the concentration of phosphate, of which as much as possible should be left in solution immediately before the phosphate precipitation / recovery step.
[00075] Table 2 below presents a pretreatment in a second vessel with a water reservoir containing phosphoglypse from another source: Table 2

[00076] It can be seen that this second water sample from the reservoir behaves similarly to the first water in the reservoir, although the starting concentrations vary considerably.
[00077] The majority of phosphate loss occurs in the fluoride removal step, with a significant amount also lost in the calcium removal step.
[00078] The amount of fluoride removed in the sodium fluorosilicate recovery step will depend on the initial silica levels. Other pot tests used a reservoir water sample with a higher proportion of Si: F in solution and resulted in lower concentrations of F after the first stage. Table 3: Results of pilot batch feeding test:
Table 4: Results of the pilot test for phosphate recovery

[00079] Destruction of fines was tested by acidifying a suspension of fines from the phosphate recovery pilot reactor (mainly micron-sized struvite particles) with sulfuric acid to a pH endpoint of approximately 5.65. This resulted in an almost complete dissolution of the solids present in the suspension together with increased concentrations of phosphate, ammonia and magnesium in solution as expected. The acidified solution was then dosed with sodium hydroxide (NaOH) to bring the pH back to 7.1 and the dissolved struvite fines were re-precipitated as visually larger particles than the original fines sample. Table 5: Destruction of fines and recrystallization experience

[00080] The effluent from the pilot phosphate recovery stage has been decanted and decanted. The decanted solution was then evaporated to approximately 50% by volume to produce the simulated nano filtration / reverse osmosis concentrate and dosed with hydrated lime at Ca: S04 molar ratios ranging from 0.5: 1 to 1.25: 1 to produce an alkaline sodium solution for recycling to the pre-treatment stages by gypsum precipitation. The results are shown in Table 6 below. This demonstrates that a lime dose of 0.5: 1 or less is likely to be optimal for this treatment, as a greater addition of lime would result in little additional reduction in sulfate concentrations, probably because the high pH would result in still lime solubility. more limited and the additional lime would simply remain in solid form. The solids formed in this test settle easily within 60 minutes. This test demonstrates that lime treatment of post-treatment membrane concentrates is an effective means of precipitating gypsum to remove sulfate from the solution and create a sodium solution with a concentration in excess of 5000 mg / 1 of Na to a pH between 11.7 and 12. The resulting solution also had relatively low levels of soluble calcium making it suitable for use as a source of sodium and as a source of alkalinity almost in the pre-treatment step of removing calcium. Table 6: Post-treatment of concentrate with results of the lime test.

[00081] The results of the pilot test are consistent with the results of the vessel test.
[00082] It is intended, therefore, that the appended claims and the claims introduced hereinafter be interpreted to include all such modifications, permutations, additions, omissions and sub-combinations as can be reasonably deduced. The scope of the claims should not be limited by the preferred embodiments presented in the examples, but the broadest interpretation consistent with the specification should be provided as a whole.
[00083] Although some examples of aspects of embodiments have been discussed before, those skilled in the art will recognize certain modifications, permutations, additions and subcombination thereof. It is intended, therefore, that the following appended claims and the claims introduced herein are interpreted to include all such modifications, permutations, additions, omissions and subcombination.

权利要求:
Claims (67)
[0001]
1. Method for the treatment of waste water containing phosphate, the method characterized by the fact that it comprises: (a) the addition of a first cation to the waste water to precipitate the fluorosilicate of the waste water; (b) the addition of a second cation to the wastewater to precipitate the fluoride from the wastewater; (c) raising the pH of waste water with calcium-free bases to precipitate the second cation of waste water; (d) the removal of silica from wastewater; (e) the precipitation of phosphate from waste water; (f) wastewater polishing, comprising: (i) subjecting wastewater to nano filtration and / or reverse osmosis to obtain a liquid wastewater concentrate and treated wastewater effluent; (ii) recirculation of the liquid waste water concentrate for steps (a), (b), (c) and / or (d).
[0002]
2. Method according to claim 1 characterized by the fact that step (a) comprises raising the pH of the wastewater, from a pH below 2.0 to pH 2.0 to precipitate the fluorosilicate.
[0003]
Method according to claim 2 characterized by the fact that step (a) comprises the addition of a stoichiometric amount of the first cation to precipitate the fluorosilicate.
[0004]
Method according to claim 2 characterized by the fact that step (a) comprises adding an excess amount of the first cation to the stoichiometric amount of the first cation to precipitate the fluorosilicate.
[0005]
Method according to any one of claims 1 to 4, characterized by the fact that the first cation comprises a sodium compound and the fluorosilicate comprises sodium fluorosilicate.
[0006]
Method according to any one of claims 1 to 4, characterized in that the first cation of the step comprises a calcium compound and the fluorosilicate comprises calcium fluorosilicate.
[0007]
Method according to any one of claims 1 to 4, characterized in that the first cation comprises a magnesium compound and the fluorosilicate comprises magnesium fluorosilicate.
[0008]
8. Method according to claim 5, characterized in that the sodium compound of the step is selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium chloride and an alkaline sodium solution produced by post-treatment of effluent produced by the method.
[0009]
Method according to claim 8, characterized in that the sodium compound of the step is alkaline.
[0010]
10. Method according to claim 2, characterized in that the step that raises the pH to 2.0 comprises the addition of an ammonia source.
[0011]
Method according to claim 10, characterized in that the step ammonia source comprises anhydrous ammonia or ammonium hydroxide.
[0012]
Method according to any one of claims 1 to all, characterized in that step (a) comprises reducing the fluoride concentration of the wastewater to 4000 to 5000 mg / L.
[0013]
Method according to any one of claims 1 to 12, characterized in that step (a) comprises reducing the silica concentration of the wastewater to 500 to 600 mg / L.
[0014]
14. Method according to claim 5, characterized by the fact that after step (a) the sodium fluorosilicate is removed from the waste water by decantation.
[0015]
Method according to claim 14, characterized in that it comprises the addition of a first flocculant before the removal of sodium fluorosilicate.
[0016]
16. Method according to any one of claims 1 to 15, characterized by the fact that step (b) comprises: (b) (i) raising the pH of the wastewater from a pH less than 3.5 to pH 3 , 5 to 4.0; (b) (ii) maintaining the pH of the waste water at pH 3.5 to 4.0; (b) (iii) raising the pH of the wastewater to pH 5.5 and (b) (iv) maintaining the pH of the wastewater to pH 5.5.
[0017]
17. Method according to claim 16, characterized in that the second cation comprises a base cation, in which steps (b) (i) and (b) (iii) comprise the addition of the base cation.
[0018]
18. Method according to claim 17, characterized in that the base cation is selected from the group consisting of a base containing calcium and a base containing magnesium.
[0019]
19. Method according to claim 16, characterized in that the base cation is a base containing calcium.
[0020]
20. Method according to claim 17, characterized in that the base containing calcium comprises lime.
[0021]
21. Method according to claim 17, characterized in that the base containing calcium of the step comprises limestone.
[0022]
22. Method according to any one of claims 16 to 21, characterized in that step (b) (ii) comprises maintaining the pH of the waste water at a pH of 3.5 to 4.0 for at least 2 hours .
[0023]
23. The method of any one of claims 16 to 22, characterized in that step (b) (iv) comprises maintaining the pH of the waste water at a pH of 5.5 for 20 to 30 minutes.
[0024]
24. The method of any one of claims 16 to 23, characterized in that step (b) (iv) comprises reducing the fluoride concentration to less than 150 mg / L.
[0025]
25. Method according to claim 24, characterized in that step (b) (iv) comprises reducing the fluoride concentration to 50 to 150 mg / L.
[0026]
26. Method according to any of claims 16 to 25, characterized in that step (b) (iv) comprises reducing the concentration of the second cation to 600 mg / L.
[0027]
27. Method according to claim 19, characterized in that the fluoride from the step is precipitated as calcium fluoride.
[0028]
28. Method according to claim 27, characterized in that in the step after step (b) (iv), the precipitated calcium fluoride is removed from the waste water by decantation.
[0029]
29. The method of claim 28, characterized in that it comprises adding a second flocculant before removing the precipitated calcium fluoride.
[0030]
30. Method according to claim 19, characterized in that the step that raises the pH of the wastewater in step (b) (i) and / or in step (b) (iii) also comprises the addition of one or more calcium-free bases in an amount to satisfy the stoichiometric requirements to precipitate the phosphate in step (e).
[0031]
31. The method of claim 30, characterized in that one or more calcium-free bases are selected from the group consisting of: magnesium oxide, magnesium hydroxide, ammonium hydroxide and anhydrous ammonia.
[0032]
32. Method according to any one of claims 28 to 31, characterized in that the calcium-free base is sodium hydroxide or a sodium-rich alkaline solution produced by the post-treatment of the effluent from step (e).
[0033]
33. Method according to any one of claims 1 to 31, characterized in that step (c) comprises raising the pH of the wastewater from a pH below 7.0 to above pH 7.0.
[0034]
34. Method according to claim 33, characterized in that step (c) comprises raising the pH of the wastewater to a pH in the range of from pH 7.1 to pH 7.5.
[0035]
35. Method according to claim 34, characterized in that step (c) comprises raising the pH of the waste water with a base.
[0036]
36. The method of claim 35, characterized in that the base comprises one or more of ammonia gas, anhydrous ammonia or ammonium hydroxide.
[0037]
37. Method according to claim 36, characterized in that the one or more of ammonia gas, anhydrous ammonia or ammonium hydroxide is added in an amount to satisfy the stoichiometric requirements to precipitate the phosphate in step (e).
[0038]
38. Method according to claim 35, characterized in that the base additionally comprises sodium hydroxide or a sodium-rich alkaline solution produced by the post-treatment of the waste water from step (e).
[0039]
39. Method according to any one of claims 1 to 38, characterized by the fact that the second precipitated cation is removed by decantation.
[0040]
40. Method according to any one of claims 1 to 39, characterized by the fact that step (d) comprises: (d) (i) aging the waste water to allow the residual silica to form a gel; (d) (ii) mixing the gelled silica; (d) (iii) allowing silica to settle and (d) (iv) removing from the decanted silica.
[0041]
41. Method according to claim 40, characterized in that it comprises the addition of a third flocculant during or before step (d) (iii).
[0042]
42. The method of claim 40, characterized by the fact that step (d) (i) comprises the aging of waste water for 8 to 12 hours.
[0043]
43. The method of any one of claims 1 to 41, characterized in that step (e) comprises adding magnesium and / or ammonia in a controlled manner to precipitate the phosphate as struvite.
[0044]
44. Method according to claim 43, characterized in that step (e) additionally comprises maintaining a pH between 6.5 to 7.5.
[0045]
45. Method according to claim 44, characterized in that maintaining the pH between 6.5 and 7.5 comprises the addition of sodium hydroxide or a sodium-rich alkaline solution produced by the post-treatment of the effluent produced by the method .
[0046]
46. Method according to claim 43, characterized in that step (e) comprises maintaining a higher phosphate concentration than the concentrations of magnesium and ammonia.
[0047]
47. Method according to claim 46, characterized in that the magnesium in step (e) is selected from the group consisting of magnesium oxide, magnesium hydroxide, magnesium sulfate and magnesium chloride.
[0048]
48. The method of claim 46, characterized in that the ammonia in step (e) comprises ammonium hydroxide or anhydrous ammonia.
[0049]
49. Method according to any one of claims 1 to 48, characterized in that it additionally comprises a step (f) of recovering fine particles of the phosphate precipitated from step (e).
[0050]
50. Method according to claim 49, characterized in that the precipitated phosphate is recovered by a device for decanting or thickening.
[0051]
51. Method according to claim 50, characterized in that it comprises the addition of a fourth flocculant before recovery of the precipitated phosphate.
[0052]
52. Method according to claim 50, characterized by the fact that the settling or thickening device is selected from the group consisting of a clarifier, a settling tank, a lamella clarifier, a gravity thickener, a gravity clarifier supernatant sediment blanket, mat thickener and a disc filter.
[0053]
53. The method of any one of claims 49 to 52, characterized in that it also comprises dissolving the decanted and thickened fines by adding a mineral acid to form a phosphate-rich solution and returning the phosphate-rich solution to the step (e) for phosphate recrystallization.
[0054]
54. Method according to claim 53, characterized in that the mineral acid comprises sulfuric acid.
[0055]
55. Method according to claim 53, characterized in that it comprises reducing the pH of a suspension of thickened fines to a pH greater than 6.0 to 3.0 to 6.0 by adding mineral acid, resulting in dissolution of substantially all thickened product fines.
[0056]
56. Method according to claim 1, characterized by the fact that step (f) comprises raising the pH of the wastewater to between 9.0 and 11.0.
[0057]
57. Method according to claim 56, characterized by the fact that raising the pH of wastewater to between 9.0 and 11.0 comprises the addition of lime.
[0058]
58. Method according to claim 57, characterized by the fact that the lime sludge generated by step (f) is recycled to step (b).
[0059]
59. Method according to claim 1, characterized in that it comprises reacting the wastewater concentrate from step (f) with lime or with a calcium-rich alkaline substance to precipitate the gypsum and produce a sodium-rich alkaline solution.
[0060]
60. Method according to claim 59, characterized in that it comprises separating the precipitated gypsum and any unreacted lime from the alkaline sodium solution in a device for separating solids-liquid.
[0061]
61. The method of claim 60, characterized by the fact that it comprises the addition of a fifth flocculant prior to separating the unreacted gypsum from the alkaline sodium solution.
[0062]
62. The method of claim 60, characterized by the fact that it comprises the recirculation of a precipitated gypsum suspension and any lime that did not react to step (b) as a source of calcium.
[0063]
63. Method according to claim 60, characterized in that it comprises controlling the efficiency of the solids-liquid separation device for controlling the flow division between a solids suspension and the clarified sodium-rich alkaline solution to direct suspension sufficient for step (b) for both the calcium source and alkalinity while the clarified sodium-rich alkaline suspension is used as the sodium and alkalinity source for step (a).
[0064]
64. The method of claim 63, characterized in that the clarified sodium-rich alkaline suspension is used as a source of alkalinity for steps (c) and / or (d).
[0065]
65. Method according to any one of claims 1 to 42, characterized in that step (e) comprises the controlled addition of a third cation and / or a fourth cation to precipitate the phosphate as a struvite analogue.
[0066]
66. The method of claim 65, characterized in that the struvite analogue comprises iron and ammonium phosphate.
[0067]
67. Method according to claim 1, characterized by the fact that step (e) is carried out in a crystallizer for recirculation and includes collection of struvite particles or struvite analog from the crystallizer for recirculation.

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法律状态:
2018-03-27| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

2019-08-06| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

2020-03-24| B07A| Application suspended after technical examination (opinion) [chapter 7.1 patent gazette]|

2020-08-11| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

2020-09-29| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 21/09/2012, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

申请号 | 申请日 | 专利标题

US201161537496P| true| 2011-09-21|2011-09-21|

US61/537496|2011-09-21|

US201161562388P| true| 2011-11-21|2011-11-21|

US61/562388|2011-11-21|

PCT/CA2012/050665|WO2013040716A1|2011-09-21|2012-09-21|Treatment of phosphate-containing wastewater with fluorosilicate and phosphate recovery|

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