Patented Oct. 9, 1934 1,75,798 ~ UNITED STATES PATENT OFFICE 1,975,798 PROCESS FOR RECOVERING POTASSIUM SALTS FROM MINERALS Everett P. Partridge,‘ Park View Estates, and Foster Fraas, New Brunswick, N. J ., assignors to the United States of America, as represented by the Secretary of Commerce No Drawing. ApplicationJuly 21, 1932, Serial No. 623,810 11 Claims. (CI. 23-27) (Granted under the act of March 3, 1883, as amended April 30,1928; 37,0 0. G. 757) This invention described herein may be manu For example, when polyhalite, ground to pass a factured and used by or for the Government for screen with 10 meshes to the linear inch, is heated governmental purposes, Without the payment' to in contact with a stream of hydrogen, the poly us of any royalty thereon. _ ‘ halite is decomposed, with hydrogen sulphide, wa This invention relates to a method of treating ter vapor and free sulphur present in the waste 6 complex potassium minerals or salts for the gas. While‘reduction may take place slowly at’ purpose of manufacturinga product of relatively lower temperatures, it ?rst becomes evident at a high potassium content. _ temperature or approximately 650° C. The rate of reduction increases with increase in tempera The primary'object of the invention is the re 65 covery of potassium salts in ‘a valuable concen ture. This increase is particularly noticeable in trated form from the mineral polyhalite the range from 800 to 900° C. The volatilization of potassium compounds is small in this tempera (K2804.MgSO42CaSO42H2O) ture range, but increases rapidly with increase in temperature above approximately 1000° C. It which is known to exist in extensive deposits in 70 a region in the southwestern United States. The is therefore desirable to' maintain a temperature method of recovery disclosed may, however, also between 800° and 10000 C. during reduction. A be applied to similar potassium minerals or salts, temperature of 900° C. has been found suitable such as krugite, langbeinite, schiinite, leonite, since’ it results‘ in a rapid rate of reduction with syngenite, or to any mixture comprising potas little loss of potassium compounds by volatiliza sium sulphate with magnesium sulphate and/or tion. It is obvious, however, that the reduction might be‘ carried out in practice at a somewhat calcium sulphate. , _ ' ‘ The reduction-of simplesulphates, such for higher or somewhat lower temperature. example as barium sulphate, by means of suitable ' Experimentshave shown that when polyhalite reducing agents is old art, but no evidence con is heated at'approximately 900° C. in‘a stream cerning the behavior of ‘double or triple salts of‘dry carbon monoxide, practically no reduction containing potassium sulphate upon reduction takes place although‘ the polyhalite is in the ?uid is known with the exception of one laboratory state. If, however, a mixture of carbon mon . referencev vby Schumann (Ann. 187, 286-321 oxide and water vapor is used under otherwise (‘1877) p. 306) .‘ Schumann noted that the dou similar conditions the polyhalite is readily re ble sulphate of potassium and magnesium was duced; Satisfactory reduction is likewise accom reduced by hydrogen at a red heat and assumed plished by the similar use of a mixture of carbon from his qualitative experiments that K28 and monoxide and hydrogen or a mixture of carbon MgO were the‘products obtained. No quantita monoxide, hydrogen and water vapor. 'We have also discovered that when natural gas tive data were recorded by this investigator. 0 35 ‘ It is not possible to state de?nitely. from this in which methane is the chief constituent is passed experiment or from any other disclosure in the over polyhalite heated at approximately 900° C. prior art that a satisfactory recovery of potas in the substantialabsence of water vapor, poly sium compounds'would be, obtained by a reduc halite is reduced, but carbon is deposited in con tion method even in thecase of the double vsul siderable quantities. If, however, a mixture of 40 phateo‘f potassium and magnesium. In the case this natural gas and water vapor is used under of polyhalite, which is a' triple sulphate of potas otherwise similar conditions the polyhalite is re sium, magnesium, and calcium, prediction of re duced without appreciable carbon deposition. sults could be no more than a hypothesis. Experiment has further shown that when an intimate mixture of polyhalite and carbon is We have discovered that by maintaining a re 100 45 ducing agent in contact .with polyhalite at a heated at approximately 900° C. the polyhalite moderately high degree of heat for a desirable is reduced, andthat this process of reduction may period of time the polyhalite is so modi?ed that be facilitated by blowing water vapor through on subsequent extraction with water practically the heated mixture. ‘ We have found that the potassium compounds all‘of the potassium compounds contained in the 105 reduction product goes readily into solution, while present in the reduced material are easily and practically no calcium or magnesium compounds completely extracted by water.‘ Water at ordi are'dissolved; that an extract solution highly con nary atmospherictemperature may be used, but centrated with'respect to potash may thereby be hot waterhas been found to be preferable. The obtained; and that evaporation of this extract potassium concentration‘ of the extract liquor solution yields desirable potash compounds. is limited by mechanical problems in the'sep 110 2 1,975,798 aration of the extracted solid, rather than by halite. Mixtures of such minerals or salts, or the solubility of the potassium compounds pres of the constituent simple sulphates would not ent, which is very high. For ‘example, we ex differ essentially in behavior. Satisfactory sep tracted ‘l0 grams of reduced polyhalite with 50 aration of potassium compounds by reduction and grams of water at 100° C. for 30 minutes. The extraction of any such minerals or salts or mix 80 solid residue was separated by ?ltration, and the tures would be reasonably expected by any person ?ltrate was then used to extract an additional skilled in the art. 36 grams of reduced polyhalite. The ?ltrate from The method of treatment, examples of which this second stage contained 28 per cent K, 16.9 are given above, comprises relatively simple op 10 per cent total sulphur, and no Ca, Mg, or S04. erations which may be performed eiiiciently and The solid residue from the ?rst stage, after economically on an industrial scale by one skilled washing with 50 grams of water and drying at in the art. Since each one of the necessary op 110° 0., contained only 0.22 per cent K, showing erations may be performed by various means, and that the recovery of potassium compounds during since control of these operations within narrow 15 extraction was very complete. - , limits is not essential in obtaining desirable re 90 On evaporating the extract liquors rich in sults, the scope of the invention should not be potassium small amounts of such compounds- as ’ construed as being limited by the speci?c exam K2SO4 and K2803 are ?rst deposited. When ples used above in an illustrative manner. evaporated to dryness the major portion .of the We have shown that by reducing polyhalite and 20 potassium is obtained in the form of an essen subsequently extracting the reduction product tially sulphide‘material, which upon being dried with water it is possible to separate the potas at 110° C. may contain 50 per cent K, and when sium compounds from calcium and magnesium fused to drive off water may contain 64 per cent compounds in a simple and e?icient manner, K. For example, when 638 grams of, reduced yielding a product highly concentrated with 25 polyhalite were extracted with 630 grams of water respect to potassium. 100 at the boiling point for 10 minutes, and the solid Having described our invention, what we claim residue was separated by filtration, a concen as new and wish to secure by Letters Patent is: trated extract was obtained. After 80 per cent 1. The process of manufacturing potassium of the extract had been evaporated, only 6 grams salts which comprises reducing a material con of solid material, consisting of K280i and K2803‘ taining potassium sulphate, magnesium sulphate had been deposited from solution. On‘ evaporat and calcium sulphate by means of a suitable re ing the remaining solution to dryness and dry ducing agent ata moderately high degree of heat ing at 110° 0., 124 grams of material were ob-. to yield a reduction product containing potas tained which contained 51.0 per cent K, 26.3, sium sulphide together with calcium compounds 35 per cent total sulphur, 20.4 percent H20, and and magnesiumcompounds substantially insolu 110 no compounds of calcium or magnesium. ble inv water; extracting this reduction product Similar results were obtained by washing the with water to yield a liquor containing essentially solid residue from the above extractionwith 630 potassium sulphide with practically no com grams of cold water, and ?ltering oil? the ?nal pounds of-calcium or of magnesium; and recov 40 solid residue. After 80 per cent of the wash ering solid potassium salts from this liquor by 115 ?ltrate had been evaporatedonly 3 grams of known means. - solid material, consisting of K260; and K2803, 2. The process of manufacturing potassium had been deposited from solution. On further salts which comprises reducing a material con evaporation until 95 per cent of the ?ltrate has taining potassium sulphate and magnesium sul been evaporated, an additional 2 grams of solid phate by means of a suitable reducing agent at ' material had deposited. On evaporation of the a moderately high degree of heat to yield a re remaining solution to dryness and drying at 110? duction product containing potassium sulphide C.