Abstract: Apparatus and methods are related to treating waste water containing ammonium salts, which contains NH4+, SO42?, Cl?, and Na+. In such a method, the pH value of the waste water to be treated is adjusted to a specific range in advance; sodium sulfate crystal and relatively concentrated ammonia are obtained by first evaporation, and then sodium chloride crystal and relatively dilute ammonia is obtained by second evaporation; alternatively, sodium chloride crystal and relatively concentrated ammonia is obtained by third evaporation, and then sodium sulfate crystal and relatively dilute ammonia are obtained by fourth evaporation. Ammonia, sodium sulfate, and sodium chloride from the waste water are recovered so that the resources in the waste water can be reused.

Abstract: A mine safety dust exhibiting improved dispersion in water. The rock dust includes dolomitic limestone particles which, when mixed at the mine site to form a slurry, stay in suspension during intermittent operation of spray machinery and with a reduced need for continuous mixing. The rock dust composition includes an inorganic salt that acts as a dispersant to improve dispersion of the rock dust in water and further acts as a deflocculant to keep the dust particles in suspension in the resultant slurry.

Abstract: A mine safety dust exhibiting improved dispersion in water. The rock dust includes dolomitic limestone particles which, when mixed at the mine site to form a slurry, stay in suspension during intermittent operation of spray machinery and with a reduced need for continuous mixing. The rock dust composition includes an inorganic salt that acts as a dispersant to improve dispersion of the rock dust in water and further acts as a deflocculant to keep the dust particles in suspension in the resultant slurry.

Abstract: Embodiments of the present disclosure are directed to systems and methods of removing carbon dioxide from a gaseous stream using magnesium hydroxide and then regenerating the magnesium hydroxide. In some embodiments, the systems and methods can further comprise using the waste heat from one or more gas streams to provide some or all of the heat needed to drive the reactions. In some embodiments, magnesium chloride is primarily in the form of magnesium chloride dihydrate and is fed to a decomposition reactor to generate magnesium hydrochloride, which is in turn fed to a second decomposition reactor to generate magnesium hydroxide.

Abstract: The present invention relates to an energy efficient carbon dioxide sequestration processes whereby Group 2 silicate minerals and CO2 are converted into limestone and sand using a two-salt thermolytic process that allows for the cycling of heat and chemicals from one step to another.

Abstract: The invention is directed to a process of combining an aqueous solution of a fluoride with an aqueous solution of a host multi-valent metal salt and an aqueous solution of a salt forming a reactant mixture resulting in a precipitate of aqueously insoluble rare-earth doped multi-valent metal fluoride nanoparticles.

Abstract: In an exhaust gas treatment, the amount of a highly corrosive mercury-halogenating agent to be added is reduced with the mercury-removing efficiency maintained high. A mercury-halogenating agent (40) and ammonia (30) are added to combustion exhaust gas from a boiler, the exhaust gas containing NOx, SOx and mercury. The exhaust gas is brought into contact with a CO/HC oxidation catalyst (50) and is then subjected to reduction denitration (60) in the presence of a solid catalyst. Thereafter, metallic mercury is oxidized to halogenated mercury. Then, the exhaust gas is wet-desulfurized (100) with the alkaline absorbing solution, and the halogenated mercury is removed.

Abstract: The present invention relates to a method for making pure salt comprises recapturing post-drilling flowback water from hydro-fracturing; removing oil from the flowback water; filtering the flowback water using an ultra filter with a pore size of about 0.1 microns or less to remove solid particulates and large organic molecules, such as benzene, ethylbenzene, toluene, and xylene, from the water; concentrating the flowback water to produce a brine that contains from about 15 wt % to about 40 wt % of salt relative to the total weight of the flowback brine; performing one or more chemical precipitation process using an effective amount of reagents to precipitate out the desired high quality commercial products, such as, barium sulfate, strontium carbonate, calcium carbonate; and crystallizing the chemically treated and concentrated flowback brine to produce greater than 99.5% pure salt products, such as sodium and calcium chloride.

Abstract: The present invention relates to a method for making pure salt comprises recapturing post-drilling flowback water from hydro-fracturing; removing oil from the flowback water; filtering the flowback water using an ultra filter with a pore size of about 0.1 microns or less to remove solid particulates and large organic molecules, such as benzene, ethylbenzene, toluene, and xylene, from the water; concentrating the flowback water to produce a brine that contains from about 15 wt % to about 40 wt % of salt relative to the total weight of the flowback brine; performing one or more chemical precipitation process using an effective amount of reagents to precipitate out the desired high quality commercial products, such as, barium sulfate, strontium carbonate, calcium carbonate; and crystallizing the chemically treated and concentrated flowback brine to produce greater than 99.5% pure salt products, such as sodium and calcium chloride.

Abstract: The invention relates to the production of calcium compounds containing water of crystallization by means of a chemical reaction between an aqueous alkaline sodium aluminate solution and solid or dissolved or suspended calcium (hydr)-oxide in the presence of carbon dioxide or carbonate; and to the use of these compounds. The resulting precipitate is separated by sedimentation, dehydration, drying and/or clacination and/or grinding or suspending the resulting filter cake and reacted with at least one mineral acid and/or at least one salt of the same. The resulting precipitate, which contains water of crystallization, is separated by sedimentation, dehydration, drying and/or grinding.

Abstract: The invention provides a process for the production of amorphous silica from a silica-based material having a silica content of at least 90% comprising: a) heating said silica-based material with CaCl2, at a temperature in the range of about 900° C. to about 1,200° C. and in the presence of water vapor in excess of the stoichiometric amount needed for the reaction: x CaCl2+y SiO2+x H2O→(CaO)x·(SiO2)y+2x HCl wherein x is equal to or greater than y to obtain a conversion of said silica-based material to calcium silicates in excess of 99.9%; b) Leaching said calcium silicates with HCl to form a solution of CaCl2 with insoluble silica; c) separating said insoluble silica from solution; and d) recycling the CaCl2 solution from step “c” to step “a”.

Abstract: The present invention provides methods for the isolation and production of magnesium products from leaching of laterite material with acid. A magnesium compound is formed by downstream treatment of a leach stream after at least one of nickel or cobalt have been brought into solution. Magnesite is then obtained by adding at least one of alkali metal or alkaline earth metal carbonate to the leach stream. The magnesite may be converted into magnesium chloride by adding an acid, such as HCL.

Abstract: The present invention provides a two stage process of thermal separation of CFCs and HCFCs followed by vitrification of the waste into a commercially viable glass. In the first stage, the hydrogenated compounds are reacted at elevated temperature with water and a metal oxide such as calcium oxide to form a halide salt and carbon dioxide. In the second stage of the process, the brine slag is reacted at elevated temperature with the carbon dioxide from stage one and glass-forming raw materials such as silicon dioxide to produce a glass. The final glass product incorporates the halide into the glass.

Abstract: A new process for producing calcium chloride and other metal halides from the carbonates, bicarbonates, oxides of these metals. The process utilizes the discovery that hydrogen halides, when used in a true or conventional fluidizing medium in shallow beds of the aforementioned solids at moderately elevated temperatures in a continuous counter current process results in the conversion of the metal carbonates, bicarbonates, and oxides, into metal halides and carbon dioxide gas and/or water vapor. The process is carried out in a series of true or conventional fluidized beds preferable but not necessarily arranged in a vertical configuration so that the solids flow downward due to the fluidized process and the hydrogen halides flow counter currently in an upward direction producing metal halides at the bottom and pure carbon dioxide gas and/or water vapor at the top.

Abstract: Methods and apparatus for the production of low sodium lithium carbonate and lithium chloride from a brine concentrated to about 6.0 wt % lithium are disclosed. Methods and apparatus for direct recovery of technical grade lithium chloride from the concentrated brine are also disclosed.

Abstract: A method of treating solid containing material derived from effluent or sludge from a plant for de-inking paper, the material containing calcium in the form of one or more insoluble calcium compounds, the method including the steps of treating the material with an acid to cause dissolution of the calcium thereby forming a calcium ion-containing solution in which insoluble solids are suspended, separating the solution from the insoluble solids and incinerating the separated solids. The solution containing calcium ions may be treated by adding one or more reagents to form a calcium compound precipitate, eg calcium carbonate. The particulate solids produced following the incineration step and following the precipitate formation may be employed as pigments or fillers in paper making or paper coating.

Abstract: Method of recovering calcium carbonate from waste material or contained natural calcic material. Calcium is recovered by prepariag an aqueous suspension the material containing calcium to be recovered and by lowering the pH of the suspension to pH<6, preferably pH<4, for providing a spension including an acidic liquid phase containing the calcium compounds in soluble form. Thereafter the pH of the liquid is raised to pH>6, preferably pH>7, by mixing a base therein, for precipitating the main portion of aluminium therein. Thereafter the neutral or basic liquid phase is carbonized by introducing Na2CO3 or NaHCO3 therein, for precipitation of the calcium compounds as CaCO3.

Abstract: A method for producing lithium carbonate by precipitating magnesium as the hydroxide from a brine concentrated to a lithium concentration of about 6%. Lithium is then precipitated from the brine by addition of recycled limed mother liquor from a previous lithium precipitation step.

Abstract: A process for producing anhydrous magnesium chloride comprising steps of selective calcination of Mg-containing minerals, selective leaching of magnesium, separation of insoluble impurities, precipitation of magnesium chloride hexammoniate and thermal decomposition of the magnesium chloride hexammoniate crystals into magnesium chloride and ammonia.

Abstract: Method of treatment of environmentally hazardous waste material and recovering MgCl.sub.2 brine, based on dissolving of the waste material in water and hydrochloric acid and simultaneous removal of ammonia at elevated temperatures, destruction of residual aqueous ammonia and removal of Mn, where the material is pre-treated in a special mixing unit adding water to provide a slurry and where hydrogen and other evolved gases are continuously diluted.

Abstract: The present invention is concerned with a method for the extraction of magnesium from magnesium-containing materials such as magnesite, dolomite and silicates materials like serpentine residues, products from the amphibole or pyroxene group. The magnesium-containing material is first leached in at least one leaching reactor, and subsequently submitted to a series of neutralizing steps in separate reactors under controlled pH and oxydo-reduction potentials. The slurry produced is filtered to produce a substantially pure magnesium chloride solution containing less than 1 ppm of each contaminant present therein.

Abstract: The present invention relates to a process for reducing and/or removing inorganic matter from a material containing inorganic matter which comprises the steps of:(i) (a) treating the material with a source of hydrogen fluoride so as to form a first residue and a first solution containing inorganic matter;(b) separating the first residue from the first solution containing the inorganic matter;(c) treating the first residue with an acid so as to form a second residue and a second solution containing further inorganic matter; and(d) separating the second residue from the second solution containing the further inorganic matter; or(ii) (a) treating the material with an acid so as to form a first residue and a first solution containing inorganic matter;(b) separating the first residue from the first solution containing the inorganic matter;(c) treating the first residue with a source of hydrogen fluoride so as to form a second residue and a second solution containing further inorganic matter; and(d) separating the

Abstract: In a process for producing anhydrous magnesium chloride, the following combination of steps: drying impure salt containing hydrated magnesium chloride; establishing a solution of the hydrated magnesium chloride; removing insoluble impurities; reacting the solution of hydrated magnesium chloride at substantially ambient temperature and pressure by feeding it into an ammonia saturated very low boiling point alcohol solution and in the presence of ammonium chloride while maintaining the last-mentioned solution saturated in ammonia thereby to form a precipitate of ammoniated magnesium chloride; separating the precipitate and heating it to obtain anhydrous MgCl.sub.2 and ammonia for recycling.

Abstract: Calcium fluoride with high purity of very small content of unreacted calcium carbonate and silica is recovered from an etchant mainly composed of hydrogen fluoride or hydrogen fluoride and ammonium fluoride. The etchant is reacted with calcium carbonate with transfer directions of the etchant and calcium carbonate being controlled within a composition region in which mole equivalent ratio of ammonium fluoride/hydrogen fluoride is specified.

Abstract: The invention relates to a method for separating sulphate from an aqueous electrolyte in an alkali metal chlorate process, thereby reducing the operating cost and increasing the possibility of further closing the electrolytical production of alkali metal chlorate. Calcium ions are added to a portion of the electrolyte, for precipitating calcium sulphate. By adjusting the pH within the range of from 4.6 up to about 7, and combining the temperature, content of ions and the molar ratio between sulphate and calcium ions added in a suitable manner, the calcium sulphate will precipitate predominantly as gypsum and essentially without inclusions and/or co-precipitation of chromium-containing compounds or chlorate. The precipitate is subsequently removed from the portion of electrolyte, whereafter the thus purified portion of electrolyte is recycled to the chlorate process.

Abstract: A process for destroying alkali metal and alkaline earth metal-containing wastes, such as sodium, by feeding such waste into a molten bath containing a molten salt such as sodium carbonate, or a mixture of salts having a lower melting point, such as a mixture of sodium carbonate and an alkali metal halide, e.g. sodium chloride, or mixtures of alkali metal chlorides, feeding a mixture of carbon dioxide and oxygen into the molten salt bath and reacting the alkali metal or alkaline earth metal such as sodium in the waste with the carbon dioxide and oxygen to form alkali metal carbonate, e.g. sodium carbonate, in the molten salt bath.

Abstract: A process is disclosed for treating salt-containing aluminum dross to remove potassium and sodium chloride salts therefrom. The process generally comprises treating the dross in a first treating step with a leaching solution having a pH maintained in the range of about 6-7 to remove a portion of the salt content thereof; filtering the residual solids from the first leaching solution; and treating the filtered solids in a second treating step with a second leaching solution having a pH maintained above about 8, and preferably above about 9. The pH of the first leaching solution is maintained in the desired range by the addition of hydrochloric acid, and the pH of the second leaching solution is maintained in the desired range by the addition of potassium and/or sodium hydroxide.

Abstract: Process for production of magnesium chloride with sufficient purity for the production of magnesium metal, by leaching a magnesium containing raw material in hydrochloric acid. It is essential to keep the ratio between acid soluble iron and nickel greater than 120 and the ratio between acid soluble iron and phosphorus greater than 20 in the primary magnesium chloride solution, to obtain a sufficiently pure product. The acid soluble iron can partly or completely be substituted by an equal, molar amount of acid soluble aluminium. It is especially preferred to use mixtures of macro- and crypto-crystalline magnesites in the ratio 1:10-10:1 as raw material.

Abstract: A two-stage process for treating acidic gypsum pond water for reuse or for discharge is disclosed. The first stage blends raw acidic pond water with recycled lime-treated slurry from the second stage of the process. The resulting elevation in pH causes CaF.sub.2 and SiO.sub.2 to precipitate and the precipitated material is discarded onto the gypsum storage area. The supernatant water can be used in the wet grinding mill and/or further treated in a second stage with lime to produce treated water which meets government environment standards for discharge. The slurry of calcium phosphate formed in the second (liming) stage is recycled to the first stage.

Abstract: Method for production of magnesium chloride, to be used for production of magnesium, by leaching of magnesite in hydrochloric acid. A two-stage leaching process is used where in a first reactor magnesite lumps are dissolved in hydrochloric acid. The magnesium chloride containing solution is led to a second reactor, where finely ground magnesite or hydrochloric acid is added to obtain approximate equivalence between magnesium and chlorine. To precipitate the impurities an excess of magnesium oxide or magnesium hydroxide is added in one or several purification stages.

Abstract: The invention relates to a process for the removal of fluoride from waste water in the form of a slightly soluble salt by mixing the waste water with a reagent. According to the invention the fluoride containing waste water is thoroughly mixed with the water soluble reagent at a suitable pH in a reactor of the fluidized bed type, which is provided with an appropriate seed material, on which the fluoride salt crystallizes out, whereby the thus obtained pellets comprising the seed material with the crystalline fluoride salt, is removed from and new seed material is added to the reactor from time to time. According to the present process as reagent CaCl.sub.2 is used, whereas the pH is adjusted to an appropriate value.

Abstract: A method for reducing impurity levels of calcium, magnesium and/or silicon in hexammine cobalt halide compounds involves the addition of ferric ions and, optionally, soluble fluorides to an aqueous hexammine cobalt (III) chloride solution having a pH of at least 9. Insoluble compounds of magnesium fluoride, calcium fluoride, and/or ferric hydroxide and silicon coprecipitates are removed from the solution by filtration.

Abstract: A process for the production of pure magnesium chloride liquor from siliceous magnesium minerals comprises the steps of continuously leaching the siliceous magnesium mineral with a hydrochloric acid solution at a temperature higher than 50.degree. C. but below the boiling point and in such a manner as to maintain the pH of the slurry below 1.5 to prevent the formation of silica gel, continuously reacting such slurry with a reactive magnesia in order to raise the pH to 4.0-7.0 to precipitate substantially all the impurities from solution while preventing silica gel formation, and performing a solid/liquid separation of the slurry on suitable filtration equipment to obtain pure magnesium chloride liquor.

Abstract: In a process for the electrolytic production of magnesium by the molten salt electrolysis of magnesium chloride using a molten salt cell bath comprised mainly of one or more salts selected from alkali metal chlorides and alkaline earth metal chlorides, the molten salt bath is enriched with magnesium chloride by suspending a magnesium oxide and/or magnesium carbonate powder to form a molten suspension and passing a chlorine-containing gas through the molten suspension at a temperature of 600.degree.-900.degree. C. so as to react the suspended powder with chlorine to form magnesium chloride. The resulting molten salt enriched with magnesium chloride can be directly introduced into the cell for electrolysis, thereby eliminating moisture absorption by the highly hygroscopic magnesium chloride. A pure magnesium can be produced with a high yield and improved current efficiency.

Abstract: Halogenated hydrocarbons are reacted in a reactor at temperatures up to 1000.degree. C. with greater-than-stoichiometric amounts of calcium and/or magnesium silicates in a reactor for the chemical-thermal degradation of the halogenated hydrocarbons. Neither dioxins nor furans are formed in the waste gas in this process.

Abstract: A method for producing a magnesia powder for use as an electrical insulating material. A magnesia clinker powder is washed with an aqueous solution of an acid. The acid radical content of the powder is subsequently reduced to 0.015% by weight or less by washing the powder with water or by subjecting the powder to a heat treatment.

Abstract: A reaction product of at least one of magnesium carbonate and magnesium silicate, with a metal chloride at a temperature exceeding 300.degree. C. Such a product, when mixed with water, sets to be an immensely strong magnesium cement. It may have aggregates of various types mixed with it.

Abstract: A process for the production of Mg metal from impure Mg-containing materials is disclosed. The process comprises the steps of reacting a slurry of impure Mg-containing material with a hot HCl-containing gas stream to produce an impure MgCl.sub.2 slurry, purifying the MgCl.sub.2 slurry to form a substantially pure MgCl.sub.2 solution, drying the substantially pure MgCl.sub.2 solution to produce a MgCl.sub.2 powder containing up to about 5% each of MgO and H.sub.2 O, dehydration melting of the MgCl.sub.2 powder to produce molten anhydrous MgCl.sub.2, performing electrolysis of the molten anhydrous MgCl.sub.2 to produce Mg metal and Cl.sub.2, and recycling all of Cl.sub.2 produced during electrolysis to the above dehydration melting step for converting MgO and H.sub.2 O present in the MgCl.sub.2 powder into MgCl.sub.2 and HCl and for producing the hot HCl-containing gas stream. Dehydration melting is preferably done by feeding the MgCl.sub.2 powder into the feed end of a rotary kiln, and reacting Cl.sub.

Abstract: A process is described for the recovery of silicon from a reaction mixture comprising silicon and an alkali metal fluoride.

Abstract: A process for producing a substantially pure, concentrated MgCl.sub.2 solution suitable for subsequent molten salt electrolysis to magnesium metal from an impure magnesite ore or concentrate is disclosed. The process comprises the steps of calcining a magnesite ore or concentrate at a temperature greater than 600.degree. C. to decompose most of the magnesite and form a reactive magnesia, dissolving such reactive magnesia with either concentrated hydrochloric acid or hydrogen chloride gas with the addition of a surface active wetting agent to produce an impure concentrated MgCl.sub.2 solution, and reacting such impure concentrated MgCl.sub.2 solution with a minimum of excess magnesia to increase the pH of the solution to at least 5.5 to precipitate undesirable impurities from solution and produce a substantially pure MgCl.sub.2 solution.

Abstract: Essentially pure strontium carbonate is recovered from low to medium grade strontium sulfate containing ores by first treating the ore with a hydrochloric acid solution to remove extraneous materials including calcium, magnesium, barium, and iron. The remaining strontium sulfate containing residue is treated with ammonium carbonate to produce insoluble strontium carbonate and soluble ammonium sulfate. The strontium carbonate then is converted to soluble strontium chloride through treatment with a second, stronger hydrochloric acid solution. Any remaining extraneous barium or iron is removed from the second acid solution before the strontium chloride is reconverted to insoluble strontium carbonate and precipitated out of solution for recovery.

Abstract: A process is provided for hydrometallurgical processing of steel plant dusts containing cadmium, lead, zinc, and iron values, along with impurities such as chloride and fluoride salts of sodium, potassium, magnesium, etc. The first step in the process involves leaching the dust in a mixed sulfate-chloride medium that dissolves most of the zinc and cadmium. Any iron and aluminum dissolved in this step is precipitated by oxidation and neutralization. Zinc is recovered from the resulting solution by solvent extraction which provides a raffinate which is recycled to the leaching step with a bleed stream also provided for recovery of cadmium and removal of other impurities from the circuit. The lead sulfate residue from the leaching step is leached with caustic soda, and zinc dust is used to cement the lead out from the caustic solution, which then joins the main solution for zinc recovery.

Abstract: A process for recovering metallic values by putting the values into solution and separating undesired mineral matter from the solution using countercurrent flotation is provided. The process involves leaching metallic values from host rock, conditioning the resultant ore pulp with the required reagents to achieve selective flotation of mineral matter in the metallic values solution, introducing the conditioned ore pulp into flotation cells, along with counterflow of solution from an immediately subsequent flotation step, wherein simultaneous washing and flotation is achieved, and the mineral matter is removed leaving a solution of the metallic values. The resultant mineral matter froth product is subjected to subsequent stages of flotation and simultaneous washing with counterflow of solution removed from each subsequent stage of flotation, water and/or barren solution being used for washing in the final flotation stage.

Abstract: A process for the preparation of calcium fluoride from industrial waste waters which comprises treatment of the waste waters with potassium hydroxide, followed by lime precipitation, neutralization with carbon dioxide and filtration to provide the calcium fluoride product.

Abstract: A process for obtaining calcium fluoride from the pond water of phosphoric acid plants and recycling the high phosphate defluorinated water to the pond is disclosed. Sufficient calcium carbonate is added to a solution having a pH of about 0.8, containing about 1% fluoride, 1% phosphate and less than 0.4% sulfate, to raise the pH thereof to 2-3, whereby calcium fluoride is precipitated as a major component, calcium phosphates and calcium sulfates are precipitated as minor components. The calcium fluoride precipitate obtained is washed with raw pond water to reduce the phosphate content and with ammonium carbonate solution to reduce the sulfate content. In this manner an industrially useful fluorspar is obtained. The low fluoride supernatant liquid is then mixed with sufficient raw pond water to bring the pH into the range 1.5-2.0 and the resulting suspension is then held in a lagoon for 5-21 days to permit separation of silica.

Abstract: Method for producing purified and concentrated MgCl.sub.2 -brine by evaporation and crystallization from brines containing MgCl.sub.2, KCl, NaCl and MgSO.sub.4 involving recirculation of carnallite and part of the final product brine. The carnallite is recirculated to a decomposition step (1) into which the whole or part of the crude brine is also introduced while part of the final product brine is recycled to the evaporation step (2). The method results in a pure end product by a simple process comprising only one evaporation step and without any addition of chemicals.

Abstract: Method for neutralizing waste cooling pond waters of wet process phosphoric acid plants, and for neutralizing similar waste waters from phosphate complexes, wherein neutralization is performed in two stages and wherein the flocculent precipitate from the second neutralization stage is disposed of by dissolving it in incoming untreated waste water prior to the first neutralization stage. Neutralization in the first neutralization stage is accomplished by addition of limestone to the waste water, and neutralization in the second neutralization stage is accomplished by addition of limestone to the water phase from the first neutralization stage. The precipitate from the first neutralization stage is readily separable from the liquid phase, and is suitable for disposal in the gypsum stack of a wet process phosphoric acid plant. The fully neutralized water meets federal and state requirements for disposal in surface and underground water systems as to pH and as to fluoride and phosphate content.

Abstract: The addition of an excess of asbestos tailings in the course of the extraction of magnesium from asbestos tailings by digestion with an acid greatly facilitates the elimination of silica and other impurities by filtration of the resulting reaction mixture. The improvement reduces the filtration time and the filtration leaves a cake which is much easier to dispose.

Abstract: Metal ion impurities are removed from phosphoric acid by adding to the acid a precipitant comprising ions of calcium and fluorine to cause precipitation of a magnesium-containing precipitate. A preferred precipitant is one containing calcium flouride, such as the sludge obtained by treating pond water from a phosphoric acid plant with a calcium-containing compound. Preferably, the soluble sulfate content of the phosphoric acid is maintained at at least about 2% by weight. An animal feed can be prepared from the precipitate by combining the precipitate with phosphate rock, water, and a sodium-containing compound, and then calcining the combination.

Abstract: A process for purifying water containing fluoride which comprises precipitating fluoride from the water as fluorapatite in the presence of a bed of seeding composition. Fluoride is removed as fluorapatite by having sufficient available calcium for each mole of fluoride present in the water and sufficient available phosphate for each mole of fluoride in the water to form a precipitate which is or converts to sufficient fluorapatite to remove essentially all fluoride from the water.