Abstract: The air cooling of exothermic reaction vessels is improved by providing a cooling air recirculation loop wherein substantial amounts of the cooling air are recycled through the system with but a small fraction thereof being discharged to ambient, and after the condensable/soluble off-gases are depleted therefrom and with addition thereto of but minor amounts of additional feed air. Such technique is well suited for controlling the temperature of the digestion of phosphate rock with sulfuric acid, in the known wet-process for the production of phosphoric acid.

Abstract: An improved method for the production of wet process phosphoric acid wherein the addition of relatively small amounts of gelatin to the reaction system substantially increases the filtration rate of the calcium sulphate crystals without adversely affecting the quality of the acid.

Abstract: A process, for removing solid impurities from impure phosphoric acid containing solids, comprising:(a) passing said acid at an elevated temperature through a filter cake of a phosphoric acid-resistant filter aid supported on a porous medium, thereby to cause at least a portion of said solid impurities of said acid to be filtered therefrom and to be retained by said filter cake;(b) contacting at least a portion of said filter cake with a displacing liquid, maintained at a temperature and in an amount sufficient to cause at least a portion of the acid which remains in said filter cake to pass through said filter cake without fracturing said filter cake;(c) collecting said filtered acid which passes through said filter cake; and(d) removing an impurity-containing portion of said filter cake after contact with said acid and displacing liquid, thereby to present a fresh surface for subsequent filtration.

Abstract: The invention relates to a method for the preparation of phosphoric acids by the wet process by reaction of at least one natural phosphate on at least one strong acid, such as, preferably, sulphuric acid, characterized in that said reaction is effected in the presence of 50 to 500 g/t of phosphate consumed, of at least one non-ionic surface-active agent obtained by condensation of 2 to 30 molecules of ethylene oxide per molecule of at least one branched fatty alcohol.

Abstract: An improved process for the wet-acid process for manufacture of phosphoric acid with recovery of valuable co-products is provided. Phosphate rock is digested in a sulfuric acid/phosphoric acid mixture. Phosphoric acid is filtered from the digested rock, the gypsum thus formed, and sludge from the phosphoric acid, are second-stage acid treated, washed, and heated in a drier-calciner at 900.degree. to 1300.degree. C. Sulfur dioxide evolved from the gypsum and the fossil fuel is used to replenish the sulfuric acid. The hot impure lime remaining is fused in an electric furnace to form valuable calcium aluminum silicate products, which are then tapped, cooled, stored, and sold. The only waste products from the process are common, sulfur dioxide free combustion gases from the high sulfur content fossil fuel. Nearly 100% recovery of all phosphorus and fluorine values is claimed.

Abstract: Phosphoric acid and gypsum are produced from phosphate rock by digesting same with sulfuric acid to produce a high concentration of phosphoric acid and calcium sulfate hemihydrate. The solubilized uranium in the rock is rendered recoverable by reducing same from the +6 valence state to the +4 valence state during the digestion step followed by oxidizing back to the +6 valence state in a subsequent step.

Abstract: A process is described for producing high purity phosphoric acid of 40% P.sub.2 O.sub.5 concentration from phosphate rock. The process is controlled to achieve the desired results by monitoring and controlling the sulfuric acid content at various processing stations resulting in the control of gypsum formation and the minimization of freed impurities in the phosphate rock.

Abstract: A method according to this invention is used for washing waste phosphogypsum produced at decomposition of a mineral phosphoric raw material with sulphuric acid, wherein the said washing is carried on in countercurrent on a multi-zone filter; to the last zone of this filter there is supplied water while filter washings with highest concentration of the component being washed-off are returned to the decomposition stage. The essence of this method consists in that to the washing liquids there is introduced sulphuric acid solution of a concentration of sulphuric acid ranging within the limits from 20 up to 98 percent by weight of sulphuric acid in the amount of 1 to 30 percent of sulphuric acid amount used for decomposition of a phosphoric raw material.

Abstract: A wet phosphoric acid production process comprising the attack on phosphate rock by sulfuric acid and phosphoric acid utilizing a vacuum cooling and a recirculation of the reaction slurry. The flow rates of the materials within the system are maintained at a level, relative to the rate of withdrawal of the slurry from the system, of between 300% and 4000% for the cyclic flow, between 2000% and 4000% for the vacuum cooling flow and between 500% and 2200% for the local agitation flow. Control of the flow rates according to factors including the rock analysis allows maximization of the yield of H.sub.3 PO.sub.4.

Abstract: For settling suspended solids in phosphoric acid product solutions, a copolymer of 95 mole percent ammonium acrylate monomer, 5% acrylamide monomer is shown to remove more solids than prior art flocculants when used in equivalent dosage, and to remove equivalent solids at much less dosage.

Abstract: High quality phosphoric acid is produced from phosphate rock and high alumina pebble which is a byproduct of phosphate rock mining operations. The rock or pebble with or without comminution is digested in phosphoric and sulfuric acid and the resultant phosphoric acid contains the metallic ions normally present in the treated rock and pebble. The metallic ions are then extracted from the acid by ion exchange with a water-immiscible organic sulphonic acid compound (preferably in the presence of an organophosphate or phosphonate). After phase separation the organic phase containing the extracted metallic ions can be regenerated. The process is especially useful when the digestion is done at a P.sub.2 O.sub.5 concentration and temperature which produces calcium sulfate hemihydrate.

Abstract: A process is disclosed for improving the dispersability of siliceous (preferably diatomite) filter aid particles in hot (i.e., 140.degree. F. or higher) aqueous acid systems used in the "wet process" formation of orthophosphoric acid from phosphate rock. In this process the filter aid particles are prewetted with water to cause the adsorption of 15 to 75 weight percent of water on the filter aid prior to dispersing the prewetted filter aid in the acid system.

Abstract: Methods for control of excessive corrosion in wet process phosphoric circuits are effected by oxidation of reduced ion species in the acid with maintenance of EMF value of the acid above about 190 millivolts (S.C.E. reference) through the digestion circuit. Supplementary monitoring is by a ceric red-ox titration procedure. In one embodied form, the present invention is utilized to control corrosion in a phosphoric acid plant digestion system (and subsequent processing equipment) operating by a dihydrate (gypsum) process even when such a process employs a calcined western U.S. phosphate ore feed from a relatively highly carbonaceous ore. The invention is also applicable for treating wet process phosphoric acid in phosphoric acid plants having a digester system operating by a hemihydrate process.

Abstract: Phosphoric acid is prepared from phosphate rock and sulfuric acid by using a reaction train comprising a dissolving slurry and a crystallization slurry maintained at different sulfate levels. Both inter and intra vessel circulation are used at high rates to minimize reagent concentration gradients and temperature gradients and provide a suitable crystallization environment. Preferably, the intra vessel circulation is substantially in plug flow, as through a draft tube.

Abstract: In a multi-stage, multi-vessel phosphoric acid production system where a first reaction vessel contains a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid and a second reaction vessel contains a second slurry comprising calcium sulfate hemihydrate, sulfuric acid and phosphoric acid, in which the reaction slurry undergoes intra- and inter-vessel circulation, preferably through a draft tube, an improved start-up procedure involves filling the system with heated phosphoric acid having a P.sub.2 O.sub.5 analysis in the range of about 28 to about 38% (e.g. 31%), then feeding phosphate rock to the system, preferably in a separate reaction vessel, while phosphoric acid is recycled from a fourth, filter feed vessel, until the solids content in said slurry is in the range of 25-35% (e.g. about 30%) while the sulfate content in the first vessel is maintained at a negative level (e.g. excess calcium ion) and at a positive level in the second, crystallizer vessel.

Abstract: The invention comprises a multi-vessel reaction apparatus useful for reacting phosphate rock and sulfuric acid in which the reaction slurry undergoes intra- and inter- vessel circulation (preferably through a draft tube). The solution portion of the slurry in a first vessel or set of vessels (the "dissolver") is preferably maintained at at lower sulfate ion concentration and the solution portion of the slurry in the second vessel or system of vessels (the "crystallizer") is preferably maintained at a positive sulfate ion concentration. Also preferred are means for maintaining the second vessel or set of vessels at a reduced pressure. Most preferred is that means be included in at least one said vessel for incorporating a crystal modifier (e.g. a sulfonic acid, a sulfonic acid salt, tall oil fatty acids or alkoxylated or esterified tall oil fatty acids) in the crystallizer. The system can be used in the anhydrite, hemihydrate or gypsum types of processes.

Abstract: A system for the preparation of phosphoric acid from phosphate rock and sulfuric acid, includes in combination a first reaction vessel containing a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid, a second reaction vessel containing a second slurry comprising calcium sulfate hemihydrate, circulation means including a draft tube disposed centrally in each of said vessels and an agitator positioned axially in each of said vessels within said draft tube, a first conduit interconnecting said first and second reaction vessels for conducting said first slurry from said first reaction vessel to said second reaction vessel, a second conduit interconnecting said vessels for conducting said second slurry from said second reaction vessel to said first reaction vessel, an inlet pipe for introducing phosphate rock and phosphoric acid to said first reaction vessel, and wherein a vent is connected to said inlet pipe to permit escape of gases and, thus, increasing the rate of fl

Abstract: Apparatus for the continuous production of phosphoric acid from phosphate-containing rock and sulfuric acid, consisting of a reaction tank with a cylindrical side wall and a planar horizontal bottom and cover, wherein the improvement comprises a rigid vertical internal S-shaped baffle with one end smoothly merging into the said cylindrical side wall of the reaction tank and the other end freely projecting into the tank so as to permit of free circulation and flow of the reaction mixture from one side of the baffle to the other but dividing the reaction tank into two distinct zones.

Abstract: A method for removing impurities from wet process produced phosphoric acid and recovering phosphate values retained by the impurities is disclosed. The wet process produced phosphoric acid is filtered through a diatomite filter cake in a porous medium at a temperature from about 57.degree. C. to about 77.degree. C. During filtering an impurity-containing upper portion of the filter cake is removed exposing a fresh surface of the filter cake. An aqueous slurry is formed with the removed portion of filter cake. The slurry is filtered to recover a filtrate containing a major portion of the phosphate values retained by the removed portion of the filter cake.

Abstract: Various stages of the process of producing phosphates are subject to a vacuum produced by a liquid ring pump in various materials of construction using relatively high concentrations of sulfuric acid as the compressant liquid.

Abstract: The anti-scaling effect of additives added to control the formation of scale during the washing of calcium sulphate anhydrite or hemihydrate crystals is increased when the additives are added as soon as possible after the wash liquors leave the crystals. The invention is of especial use in the washing of calcium sulphate hemihydrate produced during the production of phosphoric acid and is carried out by adding the additives via the central valve of the rotating pan filter on which the hemihydrate crystals are washed.

Abstract: When sulfate ions and a solution of monocalcium phosphate are reacted under conditions which result in the formation of a slurry comprising calcium sulfate hemihydrate and phosphoric acid of about 35% to about 55% P.sub.2 O.sub.5, filtration is improved when a sulfonic acid, a sulfonic acid salt, tall oil fatty acid or alkoxylated or esterified tall oil fatty acid and mixtures thereof is present in the slurry (preferably at 1-1000 ppm). Preferably a two vessel reaction system is used in which the reaction slurry undergoes intra- and inter- vessel circulation (preferably through a draft tube). The solution portion of the slurry in the first vessel (the "dissolver") is preferably maintained at a negative sulfate concentration (i.e. excess Ca.sup.+2) and the solution in the second vessel (the "crystallizer") is preferably maintained at a positive sulfate ion concentration, most preferably at a reduced pressure, (e.g. to provide evaporative cooling).

Abstract: A process for introducing and mixing a liquid, in a substantially liquid medium, comprising a rotary agitator whose axis is vertical and which is capable of creating a zone of turbulence above the liquid level, the liquid is introduced in the form of a vertical jet which is converted above the level of the liquid medium into a horizontal sheet of droplets to which there is imparted a centrifugal movement, by causing the jet to impinge on a surface that is fixed perpendicularly to the axis of the agitator, and mixing being effected above said level. In its preferred embodiment the apparatus is particularly suited for introducing corrosive liquids into a liquid medium containing solid particles in suspension. It is advantageously used for the wet-process production of phosphoric acid.

Abstract: Phosphate rock and sulfuric acid are reacted under conditions which result in the formation of calcium sulfate hemihydrate and phosphoric acid of about 35% to about 55% P.sub.2 O.sub.5. A two vessel reaction system is used in which the reaction slurry undergoes intra- and inter- vessel circulation (preferably through a draft tube). The solution portion of the slurry in the first vessel (the "dissolver") is preferably maintained at a negative sulfate concentration (i.e. excess Ca.sup.+2) and the solution in the second vessel (the "crystallizer") is preferably maintained at a positive sulfate ion concentration. Also preferred is that the second vessel be maintained at a reduced pressure, (e.g. to provide evaporation cooling). Better filtration rates can thus be obtained due to the favorable shape, dominant size and size distribution of the hemihydrate crystals. Most preferred is that a crystal modifier (e.g.

Abstract: Substantially fluoride-free phosphoric acid is produced by the acidulation of phosphate rock with sulfuric acid wherein the acidulation reaction is conducted in the presence of added potassium as K.sub.2 O bearing compounds, e.g. KHSO.sub.4, K.sub.2 SO.sub.4, KH.sub.2 PO.sub.4 or KOH, and additional silica, to precipitate fluorides and silica as potassium silicofluoride and then removed on separation of the gypsum formed. Optionally, additional silica may be added to the phosphoric acid solution recovered after precipitation and removal of the gypsum, to precipitate additional fluoride as potassium silicofluoride to further purify the phosphoric acid. In a further embodiment sufficient potassium may be added along with additional silica in the acidulation step to produce potassium dihydrogen phosphate and phosphoric acid as additional products.

Abstract: A multi-compartment reaction system for the manufacture of phosphoric acid by the wet process having a recirculation slurry flash cooler. The removal of heat from the reaction system is accomplished by circulating reaction zone slurry through an elevated vacuum flash cooler under the combined effect of differential liquid levels maintained in the system, and the vacuum in the flash cooler. The amount of reaction zone slurry passed to the flash cooler is sufficiently large so that the temperature differential experienced by the slurry is low and crystallization of calcium sulfate from the slurry liquid occurs in a favorable manner. There is also a substantial reduction in the pumping requirements compared with conventional operations in which the slurry is pumped to an elevated flash cooler, even though the large amount of slurry is passed to the flash cooler in accordance with the invention.

Abstract: Phosphoric acid with a high fertilizer-nutrient content is produced by decomposing phosphate rock with nitric acid followed by precipitation of calcium ions with sulfate. The steps of the process are as follows:A. Decomposing phosphate rock with (7-2x) to (17-2x) mol nitric acid and x mols sulfuric acid per mol phosphorous pentoxideA.sub.1 whereby x may take on any values between 0 and a maximum value X, which is limitedA.sub.2 by the condition that the mol ratio H.sub.2 SO.sub.4 :HNO.sub.3 may never exceed the value 8:1 andA.sub.3 by the condition that in the decomposition solution, into which, if need be, also ammonium sulfate is introduced, the content of sulfate ions after precipitation of the semihydrate gypsum is between 10 to 150 g/l solution;B. Adding--if no or not enough sulfuric acid has been used for precipitating calcium sulfate--ammonium sulfate in amounts corresponding to condition A.sub.

Abstract: The process of treating insoluble phosphate ore in the form of calcium phosphate, such as phosphate rock or bone phosphate, at near ambient conditions with sulfur trioxide or sulfuric acid as reactants in the presence of a liquid anhydrous dispersion media of, preferably, sulfur trioxide, sulfur dioxide, or their mixtures in liquid form so that the contacting of the ore is made in the form of an anhydrous slurry, to make the phosphorous content available as a nutrient or as phosphoric acid, and subsequently separating the dispersion media from the contacted ore preceding aqueous contact or extraction of the phosphorous constituent. The presence of sulfur dioxide in the anhydrous dispersion media is desirable to minimize operational difficulties associated with the proximity of the vaporization and solidification points of sulfur trioxide.

Abstract: Phosphatic raw materials are treated with phosphoric acid to obtain monocalcium phosphate which is dissociated with an organic solvent to yield high grade phosphoric acid and fertilizer grade dicalcium phosphate.

Abstract: Phosphate rock and sulfuric acid are reacted to produce phosphoric acid and calcium sulfate by means of the hemihydrate wet process. In this improved process, the calcium sulfate hemihydrate is crystallized from solution in the presence of an organic sulfonic acid or a derivative thereof. The organic sulfonic acid or its derivative improves the growth of the calcium sulfate hemihydrate crystals and thus improves the filtration rate of the slurry produced in this improved process.

Abstract: Phosphate rock and sulfuric acid are reacted under conditions which result in the formation calcium sulfate hemihydrate and phosphoric acid of about 30% to about 55% P.sub.2 O.sub.5. A two vessel reaction system is used in which the reaction slurry undergoes inter- and intra- vessel circulation. This results in excellent dispersion of reactants and minimization of temperature and concentration gradients throughout the slurry.

Abstract: Diluted sulfuric acid used in the production of wet process phosphoric acid is obtained by the admixing of gypsum-containing waste water with concentrated sulfuric acid and subsequently cooling in a liquid-to-liquid heat exchanger. By maintaining the concentration of the diluted acid at from about 65 to 80% H.sub.2 SO.sub.4, harmful formation of scale in the heat exchanger is prevented. The process permits the recovery of P.sub.2 O.sub.5 values from gypsum-containing waste waters and does not require expensive dilution tanks or flash coolers.

Abstract: A method is disclosed for the manufacture of phosphoric acid directly from phosphate rock wherein the crushed phosphate rock is mixed with dilute phosphoric acid to form a slurry and the slurry is then heated to produce calcium monophosphate. Thereafter, oxalic acid is added to the slurry to precipitate the calcium therein as calcium oxalate which is separated. The liquid resulting therefrom which contains the phosphoric acid from the rock is then treated conventionally to recover the phosphoric acid therein.

Abstract: Phosphate ora matrix is treated to recover P.sub.2 O.sub.5 values. The matrix may be the phosphate ore as it is mined, or it may be residue formed upon dewatering benefication slimes. Without being subjected to beneficiation, this matrix is slurried with an organic solvent in a slurry vessel. When the slurry is mixed with a strong mineral acid, a system having a single liquid phase is formed with the organic solvent serving as a vehicle for distribution of the mineral acid which in turn solubilizes P.sub.2 O.sub.5 values for their extraction from the matrix. Thereafter the P.sub.2 O.sub.5 values are separated from the solid phase and then removed from the organic solvent.

Abstract: Substantially fluoride-free phosphoric acid is produced by the acidulation of phosphate rock with sulfuric acid wherein the acidulation reaction is conducted in the presence of added potassium as K.sub.2 O bearing compounds, e.g. KHSO.sub.4, K.sub.2 SO.sub.4, KH.sub.2 PO.sub.4 or KOH, and additional silica, to precipitate fluorides and silica as potassium silicofluoride and then removed on separation of the gypsum formed. Optionally, additional silica may be added to the phosphoric acid solution recovered after precipitation and removal of the gypsum, to precipitate additional fluoride as potassium silicofluoride to further purify the phosphoric acid. In a further embodiment sufficient potassium may be added along with additional silica in the acidulation step to produce potassium dihydrogen phosphate and phosphoric acid as additional products.

Abstract: The present invention relates to a wet process for the manufacture of phosphoric acid, which process essentially comprises a digestion step in which phosphate rock is digested by means of phosphoric acid and sulfuric acid to form a slurry containing highly concentrated phosphoric acid together with calcium sulfate hemihydrate, and a separation step in which the slurry is filtered for separation of calcium sulfate hemihydrate from the highly concentrated phosphoric acid (in which the concentration of P205 in the product acid is higher than 40% by weight, based on the weight of the product acid) and which is characterized by supplying active silica at a ratio of 0.2-5% by weight, based on the weight of phosphate rock, in order that active silica may be present in the above mentioned digestion step.

Abstract: A method of making phosphoric acid and gypsum through a precipitated phosphate intermediary which comprises mixing a precipitated dicalcium phosphate with a highly dispersed reaction admixture of sulfuric acid and phosphoric acid, at a temperature between about 25.degree. and 80.degree. C; and withdrawing and separating phosphoric acid containing up to about 45% or more P.sub.2 O.sub.5 and gypsum containing generally less than 0.25% P.sub.2 O.sub.5. The resultant gypsum is highly filterable and very low in occluded phosphate value. Preferably, the process involves first obtaining a weak phosphoric acid solution from and by leaching as-mined phosphate mineral containing material to obtain the precipitated dicalcium phosphate; and then converting the precipitated phosphate by the process to the strong phosphoric acid solution.

Abstract: Wet-process phosphoric acid which is obtained by the acidulation of uncalcined phosphate rock with sulphuric acid and which typically contains 28-31% P.sub.2 O.sub.5 and measurable amounts of solid organic materials, such as, for example 0.1% or more, is treated to remove the solid organic materials contained therein by intimately contacting the acid with a liquid hydrocarbon so that the aqueous is the continuous phase, resulting in the solid organic materials being taken up by the organic phase.

Abstract: In the manufacture of phosphoric acid by the acidulation of phosphate rock detrimental foaming is reduced by the use of certain phosphate esters of aliphatic alcohols as defoaming agents. Aqueous emulsions of such esters comprise novel, useful compositions of matter.

Abstract: A continuous procedure is disclosed for the wet-process manufacture of phosphoric acid in a reaction zone and continuously cooled by means of evaporation into air circulating at the surface of the reaction zone. The evaporated gases are scrubbed by using part of the water needed for the methodic washing of the calcium sulfate, whereby the solution obtained is collected and passed into the reaction zone in such a way as to cause the soluble gaseous products to return to the reaction medium, from which they are collected with strong acid, which constitutes production. The procedure gives rise to no liquid pollutants, particularly fluorine, and does not increase the amount of water consumed.

Abstract: In a process for preparing phosphoric acid by contact of sulphuric acid and phosphate rock with filtration of the gypsum slurry and recycle of the rest for contact with fresh rock, a fraction of the recycle slurry is treated with sulphuric acid to convert at least some of the gypsum to calcium sulphate hemihydrate and the slurry comprising hemihydrate is returned to contact the mixture of phosphate rock, phosphoric acid and recycle gypsum slurry. The process gives an easily filtered gypsum slurry with low phosphate losses in the gypsum filter cake.

Abstract: Apparatus for manufacture of wet process phosphoric acid wherein phosphate rock and sulfuric acid are separately added to a combination reactor and cooler unit at a rate of addition such that the increase in calcium content and sulfate content in the slurry contained in the unit are small. Circulation of the slurry is provided and the rate at which sulfuric acid and phosphate rock are added is small compared to the rate of circulation of the reactor slurry.

Abstract: In a process for the reaction of phosphate rock and sulfuric acid in the presence of potassium ion to form a mixture of phosphoric acid and a precipitated gypsum wherein the presence of the potassium ion causes precipitation of fluorides from the phosphate rock as potassium silicofluoride as a coprecipitate with the gypsum, and the phosphoric acid is separated from the gypsum slurry, the potassium silicofluoride is separated from the gypsum by extraction with phosphoric acid which may contain from 0-25 weight percent of sulfuric acid based on the amount of gypsum to be extracted or such phosphoric acid which may contain some fluorine. This extraction procedure provides a substantially fluoride-free gypsum product and an extraction solution containing recoverable potassium silicofluoride.

Abstract: A method of producing wet process phosphoric acid comprises reacting, in a reactor system, calcium phosphate rock particles with a mixture of recycled phosphoric and sulfuric acids, preferably supplemented with added fresh sulfuric acid, to form additional phosphoric acid and calcium sulfate dihydrate (gypsum). The reactor environment is controlled so as to avoid appreciable coating of the rock particles with calcium sulfate. A gypsum slurry is withdrawn and product phosphoric acid is separated therefrom and withdrawn from the process. The gypsum may be washed with a dilute sulfuric acid wash solution which is then added to the reactor. The gypsum is passed to a first recrystallizer wherein sulfuric acid is introduced, and the gypsum is recrystallized to hemihydrate. A slurry of the hemihydrate is passed to a second recrystallizer, wherein water obtained as described below is added and the hemihydrate is recrystallized to gypsum.

Abstract: Substantially fluoride-free phosphoric acid is produced by the acidulation of phosphate rock with sulfuric acid wherein the acidulation reaction is conducted in the presence of added potassium as K.sub.2 O bearing compounds, e.g. KHSO.sub.4, K.sub.2 SO.sub.4, KH.sub.2 PO.sub.4 or KOH, and additional silica, to precipitate fluorides and silica as potassium silicofluoride and then removed on separation of the gypsum formed. Optionally, additional silica may be added to the phosphoric acid solution recovered after precipitation and removal of the gypsum, to precipitate additional fluoride as potassium silicofluoride to further purify the phosphoric acid. In a further embodiment sufficient potassium may be added along with additional silica in the acidulation step to produce potassium dihydrogen phosphate and phosphoric acid as additional products.

Abstract: A wet phosphoric acid process involving operation of two streams, substantially equivalent, one producing phosphoric acid of a particular level of concentration, and gypsum as a by-product, and the other phosphoric acid of a different concentration, producing calcium sulfate hemihydrate as a by-product, with means for interconnecting and coordinately operating the processes so as to produce a single acid product stream of a higher concentration than the sum of the individual streams. The method consists of employing acid from one process as a wash in the second and balancing the flow streams to produce the combined product acid of enhanced final concentration and the plants involved in carrying into effect this method of operation.

Abstract: A process for reducing formation of calcium sulphate scale during the washing of calcium sulphate hemihydrate crystals by washing the crystals with a liquor containing certain surface-active agents in sufficient amount to give a concentration of from 0.0002 to 1% by weight of surface-active agent in the wash liquors.

Abstract: Wet process phosphoric acid is made by grinding phosphate rock as a slurry in water, and digesting the ground rock slurry with sulfuric acid which has been diluted by spent calcium sulfate wash water before being combined with the ground slurry.

Abstract: In a method of treating clay-containing phosphate rock comprising at least mining the phosphate rock, reducing the phosphate rock to a predetermined size range, adding water to the phosphate rock, and storing the admixture containing at least the phosphate rock and water; the improvement characterized by adding to the admixture an amount effective to control problems associated with the swelling of residual clays of a chemical treatment selected from the class consisting of aliphatic hydroxy acids containing 2-6 carbon atoms, inclusive, of which citric acid and tartaric acid are members; the aliphatic hydroxy acid salts, and effective blends of the aliphatic hydroxy acid or the aliphatic hydroxy acid salts with a strong caustic, or base. The chemical treatment prevents a build up of viscosity such that the admixture remains pumpable even with a concentration of solids in excess of 66 percent by weight.

Abstract: Calcium sulphate produced by reacting crude phosphate with sulphuric acid is washed with aqueous solutions of condensed and complex aluminium fluorides of the general formulae MeAlF.sub.4, Me.sub.2 AlF.sub.5 and Me.sub.5 Al.sub.3 F.sub.14 as well as AlF.sub.3.nH.sub.2 O, in which Me represents an alkali metal, ammonium or thallium-I ion and n is a number between 1 and 9.