United States Patent (19) 11 Patent Number: 4,609,535 Thomas 45 Date of Patent: Sep. 2, 1986

(54 EXTRACTING SOLUBLE PHOSPHATES 2,430,863 1/1947 Colton et al...... 423/312 FROM NATURALLY OCCURRING RON 4,113,184 9/1978 Loughrie ...... 423/167 AND ALUMNUMPHOSPHATES USING 4,167,406 9/1979 Hauschild et al...... 423/167 SOLUTIONS OF ALKAL METAL 4,321,244 3/1982 Magnier et al...... 423/150 CARBONATES AND HYDROXOES 4,374,817 2/1983 Lehman et al...... 423/167 76 Inventor: Griffith Thomas, 81 Lynbara Ave., FOREIGN PATENT DOCUMENTS St. Ives, New South Wales, 606795 10/1960 Canada ...... 423/32 Australia, 2075 804292 11/1958 United Kingdom . 21 Appl. No.: 636,601 345938 2/1979 U.S.S.R...... 423/167 Primary Examiner-John Doll 22 Filed: Aug. 1, 1984 Assistant Examiner-Wayne A. Langel 30 Foreign Application Priority Data Attorney, Agent, or Firm-Cushman, Darby & Cushman Aug. 4, 1983 AU Australia ...... PGO662 57 ABSTRACT 51 int. Cl...... CO1B 25/6 A process for production of alkali metal phosphates 52 U.S. C...... 423/167; 423/131; from material containing iron and aluminium phos 423/150; 423/312 phates comprises leaching the said material with alkali 58 Field of Search ...... 423/167, 312, 150, 131 metal carbonate solution to produce a leachate contain 56 References Cited ing dissolved phosphates, and recovering alkali metal phosphates from the leachate. In a preferred embodi U.S. PATENT DOCUMENTS ment, the carbonate leach is followed by further leach 1,252,318 1/1918 Blumenberg ...... 423/167 ing with alkali metal hydroxide to effect further dissolu 1,799,882 4/1931 Brenek ...... 7/47 tion of phosphates from the material, before recovering 1,935,474 11/1933 Laubi ..... 423/150 1,961,127 6/1934 Coleman ... 423A312 alkali metal phosphates from the leachate. 2,220,790 1 1/1940 McCullough ...... 423/312 2,221,356 l/1940 Michels ...... 423/312 8 Claims, No Drawings 4,609,535 1. 2 EXTRACTING SOLUBLE PHOSPHATES FROM NATURALLY OCCURRING RON AND ALUMNUM PHOSPHATES USENG SOLUTIONS OF ALKAL METAL CARBONATES AND 5 HYDROXDES This invention relates to the extraction of soluble phosphates from naturally occurring iron and alumin ium phosphates. 10 Previous art involves dissolving complex iron and In a third form of the invention, a calcium phosphate aluminium phosphates in sodium hydroxide, as will be rock contaminated with minor amounts of iron and discussed in more detail below. aluminium phosphates which make it undesirable for The present invention is characterised by the use of conventional fertilizer manufacture, is treated to reduce alkali metal carbonate solutions to leach naturally oc 5 the iron and aluminium content. Low-grade Florida curring phosphates. In a preferred embodiment of the rock is a rock of this type. After leaching with hot invention the carbonate leach is followed by further sodium carbonate solution, the resulting sodium carbon leaching with alkali metal hydroxide. The process of the ate and phosphate solution is separated from the unre invention may be applied to many types of naturally acted rock and iron hydroxide. The insoluble material is occurring phosphates, including those from Christmas 20 classified to remove as much colloidal iron hydroxide as Island, Senegal, Brazil and other sources. possible and it is then suitable for conventional fertilizer The carbonate leach is preferably carried out at ele manufacture. vated temperature, for example from 70° C. and the The solution of sodium phosphate and sodium alumi boiling point at atmospheric pressure, or under imposed nate is cooled to crystallize out sodium orthophosphates pressure from 100 to 150° C. 25 and the remaining solution carbonated to produce so In one form of the invention, barrandite, a naturally dium carbonate and aluminium hydroxide. The sodium occurring iron and aluminium phosphate, is leached carbonate is recycled to leach more low grade Florida under pressure at 100-150 C. with potassium carbon rock. ate solution to form a solution of potassium orthophos In a simplified form the reactions taking place are phate and potassium aluminate. The residual solids are 30 leached further with potassium hydroxide solution at believed to be represented by the equations outlined for 70°-90° C. to give essentially complete extraction of the second form of the invention. phosphorus and aluminium in the original barrandite. In the above description of the invention it should be Residual solids are separated from the solutions and the clearly understood that where potassium compounds solutions cooled to separate out potassium orthophos 35 are mentioned sodium compounds are also applicable phates. The remaining solution is cooled to precipitate and vice versa. aluminium trihydrate and the resulting potassium car ADVANTAGES bonate recycled to leach more barrandite. In a simplified form the reactions taking place are Previous art involves dissolving complex iron and believed to be: aluminium phosphates in sodium hydroxide. The result ing solution is freed from residual solids, cooled to crys tallize out sodium phosphate, and the resulting sodium aluminate solution decomposed into aluminium hydrox ide and sodium hydroxide, see Rothbaum and Reeve, 45 - "Recovery of Alumina and Phosphate from Christmas Island C Phosphate' N. Z. Journal of Science Vol. II No. 4, December, 1968. This technique has the apparent advantage that the sodium associated with aluminium in solution can be 2KAlO2-3H2O-CO2-3K2CO3--2Al(OH)3 5. 50 recovered as sodium hydroxide. However the decom In another form of the invention Christmas Island G position of sodium aluminate, the Bayer process, re grade rock, a naturally occurring complex calcium iron quires large decomposition vessels, the recirculation of aluminium phosphate is leached with hot sodium car large volumes of seed aluminium hydroxide and the use bonate solution to form a solution of sodium orthophos of relatively dilute solutions to promote the decomposi phates and sodium aluminate. The residual solids are 55 tion of sodium aluminate. The recovered sodium hy leached with hot sodium hydroxide solution to bring droxide solution from Bayer decomposition essentially all the phosphorus and aluminium associated with the iron and aluminium in the original rock into NaAlO2-2H2OeNaOH--Al(OH)3 solution. Residual solids essentially calcium phosphate has to be evaporated for reuse. It will be observed from and iron hydroxide are separated from the solution equation 2 that only 25% of the sodium hydroxide re which is then cooled to crystallize out sodium ortho acting with aluminium phosphate is recovered by the phosphates. The remaining solution is carbonated to Bayer process and none from iron phosphates (equation precipitate aluminium hydroxide and the resulting so 3). dium carbonate solution recycled to leach more Chris My process has the advantage that capital and operat tmas Island C grade rock. 65 ing cost of the large decomposers, evaporators and seed In a simplified form the reactions taking place are recycle equipment is eliminated. The relatively small believed to be: amount of alkali metal carbonate produced in decom 4,609,535 3 4. posing the alkali metal aluminate is recycled to dissolve subsequent leaching was reduced to 90% of stoichio more phosphate rock by reactions 1 and 2. metric. My process has the additional advantage that potas sium carbonates and hydroxide can be used to produce EXAMPLE 3 valuable potassium phosphate. If potassium hydroxide 5 In this experiment potassium carbonate and potas is used to dissolve iron and aluminium phosphates the sium hydroxide were used instead of the sodium com resulting potassium aluminate is not suitable for recov pounds in Example 2. Because of the greater causticity ery of potassium hydroxide by a process analagous to of the potassium salts approximately 20% of the caustic the Bayer process with sodium aluminate, but potassium available phosphate was solubilised during grinding and O the amount of potassium hydroxide used for subsequent aluminate can be readily decomposed by carbon diox leach was reduced to 85% of stoichiometric. The over ide. all effect was that no byproduct potassium carbonate The invention will be further illustrated by the fol was produced and the solution after aluminium hydrox lowing non-limiting examples. ide precipitation could be recycled direct to grinding. EXAMPLE 1. 15 It will be clearly understood that the invention in its general aspects is not limited to the specific details re One hundred grams of Barrandite from Christmas ferred to hereinabove. Island was ground in hot sodium carbonate solution The claims defining the invention are as follows; I recycled from previous experiments and leached in claim: agitated vessels for one hour at 70° C. This dissolved 1. A process for production of alkali metal phos about 13% of phosphate present in the original rock. phates from naturally occurring phosphate rock which The ground barrandite slurry was further reacted has not been chemically treated to extract phosphates, with sodium hydroxide in agitated vessels. the phosphate content of the rock being predominantly This sodium hydroxide was added as a 50% solution iron phosphates and aluminum phosphates, the process and the barrandite suspension agitated for 30 minutes at 25 comprising leaching the phosphate rock with alkali 80' C. The amount of sodium hydroxide added was metal carbonate solution to produce a leachate contain calculated to be stoichiometrically equivalent to the ing dissolved alkali metal phosphates, separating the “caustic available' phosphate present in the original leachate from undissolved residual solids, and recover barrandite. “Caustic available' phosphate is defined as ing the alkali metal phosphates from the leachate. total phosphorous less 0.5 times the calcium present e.g. 30 2. A process as in claim 1 including leaching said roughly equivalent to calcium phosphate. residual solids with alkali metal hydroxide to effect Residual solids, consisting largely of insoluble iron further dissolution of phosphates, and recovering alkali compounds and calcium phosphate, were filtered from metal phosphates from the hydroxide leachate. the leach solution at 70° C. This clarified solution was 3. A process according to claim 1 in which the leach then cooled to 20 C, when practically all the phosphate 35 ing with alkali metal carbonate solution is carried out at present crystallized as sodium orthophosphates. elevated temperature. The sodium orthophosphates were filtered off and 4. A process according to claim 3 in which the leach ing with alkali metal carbonate solution is carried out the residual sodium aluminate solution reheated to 35 under pressure at 100 to 150 C. C. and a small amount of aluminium hydroxide added to 5. A process for production of alkali metal phos promote subsequent precipitation. Carbon dioxide was phates from naturally occurring phosphate rock con bubbled into the solution to suspend the aluminium taining predominantly iron phosphates and aluminum hydroxide and decompose the sodium aluminate to phosphates which comprises leaching the rock with sodium carbonate and aluminium hydroxide. After alkali metal carbonate solution at 70°-100° C. to effect three hours carbonation the aluminium hydroxide was 45 dissolution of phosphate from the rock, separating the filtered off at 35° C. and the resulting sodium carbonate leachate from undissolved residual solids, adding alkali solution cooled to 20 C. to crystallize out and recover metal hydroxide solution to the residual solids and con sodium carbonate. The residual solution containing tinuing the treatment to effect further dissolution of sodium carbonate and a small amount of sodium phos phosphates from the rock, removing residual solids phate was recycled for leaching more barrandite. 50 from the eachate, and cooling the leachate to precipie By this technique I was able to recover over 90% of tate phosphates therefrom. the soluble phosphate in barrandite. Of the sodium re 6. A process according to claim 5, in which the solu acting to form sodium aluminate, approximately 20% of tion from which the phosphates have been precipitated the sodium hydroxide used, over 90% of it was recov is carbonated with carbon dioxide to precipitate alumi ered in the form of sodium carbonate. 55 num hydroxide therefrom, and the precipitated alumi num hydroxide is removed to produce a solution of EXAMPLE 2 alkali metal carbonate which may be recycled to the In this experiment the same technique was used as in initial leaching step. Example except that after grinding and eaching in 7. A process according to claim 5 in which the alkali recycled sodium carbonate, the ground barrandite 60 metal carbonate is sodium carbonate. slurry was heated to boiling point to drive off some of 8. A process according to claim 5 in which the alkali the carbon dioxide present as sodium bicarbonate. By metal carbonate is potassium carbonate. this means the amount of sodium hydroxide used for t k s s 65