March 19, 1963 G, CEVIDALL ETAL 3,082,063 PROCESS FOR THE PREPARATION OF POTASSIUM SULPHATE AND HYDROUS POTASSIUM-MAGNESIUM SULPHATES FROM NATURAL. KAINTE Filed Dec. 8, 1959 722 A/2002As afely SA/. A. Was 72 INVENTOR. 2. Caw/A-1ZZ/ 47 14. BY 4%-44, 2444 f2. 47-721%%r 3,082,063 United States Patent Office Patented Mar. 19, 1963 1. 2 flotation, prior to the treatment, in the same way as it has 3,082,063 been done for separating the NaCl from the KCl in the PROCESS FORTHE PRiff ARATION of PoTASSIUM Sylvinite minerals. But whereas for the sylvinite, the SULPHATE AND HYDROUS POTASSIUM-MAG flotation produce (i.e. the KCl) is a potassium salt of very NESUMSULPHATES FROM NATURAL, KAENTE Guidobaldo Cevidalli, Fulvio Marchi, Pietro Saccardo, high grade directly usable as a fertilizer, the direct flota and Alberto Scarfi, al.9%. Sincat Societa industriale tion of kainite minerals yields only a product of low K2O Catanese S.p.A., Via Principe Eugenio 5, Milan, Italy content, that has to undergo a further treatment, such as Filed Dec. 8, 1959, Ser. No. 858,011 for instance the one outlined above. In this way the cost Claims priority, application Italy Dec. 5, 1956 of flotation of the excessively increases the cost of the 4 Claims. (Cl. 23-117) KO produced. 10 It is an object of the present invention to produce mag The present invention relates to the production of nesium-potassium sulphate and potassium sulphate start potassium sulphate and magnesium-potassium Sulphate, ing from raw natural kainite, containing even large starting from natural kainite. amounts of sodium chloride. Since the early times of the potassium salts industry, 5. It is a further object of the present invention to produce in Germany, kainite, KCl.MgSO4.3H2O, has been the magnesium-potassium sulphate and potassium sulphate object of the investigation as a starting material for pro starting from raw kainite in a process which provides a ducing potassium containing fertilizers. Having in itself high potassium yield. the necessary components for obtaining K2SO4 according The present process is based on the discovery that when to the classic method, it looked at first as the most suitable 20 raw kainite containing more than 12% of NaCl has been mineral for this purpose. treated with water, or mother liquors of potassium sul Instead it was found very soon that the use of kainite phate, with the lowest water/kainite ratio sufficient to was complicated by difficulties deriving mainly from the carry in solution the magnesium chloride obtained from presence of NaCl mixed with the mineral, in larger or the decomposition of the kainite, after filtering, there is smaller amounts, and very difficult to separate. 25 obtained a solid phase constituted by a mixture of schoe Several were the processes suggested to obviate such a nite and sodium chloride. difficulty, some of them actually had also an industrial The solid phase thus obtained, constituted by schoenite application. All were however discontinued and the proc mixed with NaCl, would be unsuitable for supplying potas essing of kainite has been completely disregarded since the sium sulphate by treating it with water just because of first years of this century, on various grounds. 30 the presence of NaCl. But we have found that this NaCl It has long been known that by treating "pure' kainite can be easily separated from the schoenite if the mixture with water in suitable quantity, the kainite undergoes a of schoenite and NaCl such as it is obtained by filtering, transformation forming two different products: (1) a solid is subjected to flotation in the presence of suitable flota phase constituted by schoenite crystals, and (2) a liquid tion reagents. phase constituted by a magnesium chloride solution, con 35 Still better, the NaCl can be separated from the schoe taining, in solution, also some potassium chloride and nite if the pulp, as obtained from the transformation of potassium sulphate. The schoenite can be separated by the kainite and constituted by schoenite plus solid NaCl filtering and the brine discharged as waste. suspended in the magnesium chloride solution deriving In its turn the schoenite can be treated with water in a from the conversion, is directly subjected to the flotation calculated amount, separating in a solid phase constituted 40 process. by potassium sulphate, and in a liquid phase formed by Contrary to prior opinion the brine rich in magnesium an aqueous solution of potassium sulphate and magnesium chloride obtained from the conversion of the raw kainite sulphate. into schoenite, has proved fit, in the presence of suitable The potassium sulphate can be separated by filtering flotation reagents, for the use as flotation brine for the and the magnesium sulphate and potassium sulphate solu 45 separation, through flotation, of the schoenite from NaCl. tion can be used, in place of water, for treating fresh In this way there is the following remarkable advantage, quantities of kainite, with a higher overall yield. in respect. to the usual flotation processes of mineral, for This process however can be applied only, as mentioned instance kainite; while for the flotation of mineral these above, to a very high grade, pure kainite, free of or con have to be carefully ground down to a partial size such as taining only very small quantities of sodium chloride, 50 to assure the liberation of the single mineralogical con such as it is very seldom encountered in nature. stituents, in our process the liberation of the schoenite Indeed it is known that when it is desired to produce freshly formed from the previously existing halite is ob potassium sulphate, even starting from other types of tained without any particular expensive treatment. mineral (hartsalz and Sylvinite etc.) according to the Our process can be schematically described referring usual method, the presence of even only limited quantities 55 to the drawing: of NaCl in the intermediate compounds (schoenite, Sylvite The raw kainite, mixed with the mother liquors obtained etc.) makes the process impracticable. from the filtering of the potassium sulphate, is charged Should such process be applied to natural kainite, it in a suitable container provided with a stirring device, would be necessary to use such an amount of water (or of where it is converted into solid schoenite and solid NaCl, brine as derived from the filtering of the potassium sul 60 suspended in a brine of MgCl, etc. The pulp thus ob phate) as to dissolve, besides the MgCl2 deriving from the tained is subjected in 2 to a flotation process, following decomposition of the kainite, also all the NaCl present. which the NaCl is separated as a residue, and filtered In this way a large portion of the potassium sulphate, in 3. The schoenite obtained in the froths is filtered in 4; instead of remaining in the solid state as constituting the the mother liquor is partially discharged to waste, in schoenite, would be carried away in solution and lost in 65 order to eliminate the magnesium chloride deriving from the brines of magnesium chloride going to the waste. In the decomposition of the kainite, and partly is recycled practice the yield would be reduced to ever lower values to 1. The moist solid schoenite is partly dried in 5, to with increasing NaCl contents and the process becomes give hydrated potassium and magnesium sulphate, and impractical for NaCl contents over 25-30 percent such as partly converted with water in 6, in a suitable converter. are commonly found in the kainite minerals. 70 The result is a pulp of solid potassium sulphate in a solu To avoid this inconvenience it has recently been pro tion of potassium sulphate, and magnesium sulphate. posed to separate the NaCl from the kainite by means of After filtering in 7, the potassium sulphate is dried in 3,082,063 3 8. The mother liquor is used to convert new kainite into 4 Schoenite. gr. are decycled for the KSOA production. The total yield It has been found that saturated and unsaturated fatty of K2O, based on the kainite used, is the following: acids, with from 6 to 18 carbon atoms, free as well as combined to form salts, may be used as selective floatation reagents for Schoenite. In particular the unsaturated Gr. Percont acids, containing 10 or more carbon atoms have proved to be more efficient, while the acids having a shorter chain KO in the kainite-------------------------------- 42.37 100 KO in the K2SO4--------------------------------- 12,67 29.93 are more efficient if saturated. As coadjuvants of the fatty K20 in the Schoenite produced=(gr.92x22.6%) 20.79 49.02 acids there can be advantages used dispersing agents such 10 as Starch, dextrine, guar gum, tannin and the like. Total.---------------------------------------- 33.46 78.95 It is known that in all flotation processes, the flotation reagents have to be intimately mixed for a certain length of time, prior to flotation with the crystals of the mineral It is to be understood that all the data set out above to be treated. have no limiting value whatsoever, and the invention shall Such mixing operation is commonly called "condition 5 be limited only by the appended claims. ing.” We have discovered that such a conditioning is ob This application is a continuation-in-part of application tained very conveniently and in a way such as to then Serial No. 644,332, filed March 6, 1957, now abandoned. allow high flotation yields, in the flotation reagents and What we claim is: dispersing agents are introduced in the same container 20 1. A process for the conversion of natural kainite con and at the same time at which the transformation of the taining Sodium chloride as an impurity into schoenite kainite into schoenite takes place.