" ce 2,902,343 United States Patent 1 Patented Sept. 1, 1959

‘1 . s 2' . point of view; as prior to theppresent invention it has been the only' one by'which almost pure kainite can be 2,902,343 - ' _ prepared in a very simple mannen-it is not so attractive PROCESS FOR THE PREPARATION_ HYDRUUS economically, for it merely‘ removes the NaCl and yields POTASSIUM MAGNESIUM 7 SULFATE 7 FROM kainite with a high percentage of KCl.MgSO4.3H2O, but KAINITE CONTAINING SODIUM CHLORIDE it does not change the chemical composition of the po Pietro Saccardo, Milan, Italy, ‘assignor-to Sincat Societa tassium magnesium salt. Therefore, the latter has still - _ Industriale Ca'tanese. S.p.A.-, Milan, Italy to be chemicallyconverted‘with a view to manufacturing 1 No Drawing} Application-Mareh1ii,_"1957 a commercially accepted product. Hence the ?otation of ‘ Serial No. 644,206‘ , ' 10 crude‘ kainite merely produces an intermediate product, and this in a rather expensive manner because of the Claims'p'riority, application Italy September "14, 1956 consumption of ?otating agents and the high operating costs. The cost of the ?nal product (potassium sulfate 6 Claims. ((143-121) ~ I or potassium magnesium sulfate) made from the ?otated The present invention relates to a ‘process for preparing 15 kainite will accordingly be high. hydrous magnesium potassium sulfate, e.g. schoenite or The various disadvantages of the known processes dis leonite, substantially free from sodiumchloride, by the cussed above are overcome by the present invention. processing of naturally occurring kainite. This has the object to provide a simple and cheap proc Kainite, being KCl.MgSO4.3H2O, has been largelyused ess for producing potassium magnesium sulfate from for some time as a starting material for the manufacture 20 crude kainite or similar potassium magnesium minerals of potassium fertilizers. However, the usefulness of containing NaCl, e.g. halite, as impurity, even a high pro kainite for this purpose is'considerably‘ impaired by the portion thereof, and this without any previous enrichment more or less considerable quantity of NaCl which is nat of the mineral. W > . ‘ urally contained ‘therein as an impurity and is dif?cult to It is known that kainite can be- converted into schoenite‘ separate. Many purifying processes have been suggested 25 by treatment with water at room temperature according to to overcome this di?‘iculty; some have also been used in the equation: the industry. However, all of them have been given up and for various reasons the processing of the kainite has axorngsotsnto E5» KisotMgsotenio + Mgon been abandoned since the early part of this century. The By a similar reaction, ‘leonite can be produced instead purifying processes of some importance were those in of schoenite. which the mineral was dissolved in the heat and a po The quantity of water used for this reaction will be cal tassium magnesium salt was precipitated by cooling, such culated in accordance with the solubility of the amount as the Douglas, Dupré; Hake, Borsche and Gruneberg of MgCl2 which is liberated by the reaction under equi and similar processes. In these processes, either-the en librium conditions. tire mineral was dissolved or the NaCl was left» behind 35 From kainite contaminated with NaCl one obtains in undissolved. The dissolving liquorv used was a brine this way schoenite containing some NaCl as impurity. of kainite, MgSO4 or NaCl saturated at room tempera- I The solubility of the NaCl in the chemically balanced ture. By cooling the heat-saturated solution, they potassi reaction liquors is very low, from about 3 to 6% by um magnesium salt was crystallized and could be sep weight. arated.v The mother liquors were recycled to dissolve 40 For the production ofpotassium magnesium sulfate free new batches of the mineral._ As the heat consumption in from NaCl so much water could be used for the reaction these processes was very high owing to the large quanti aforesaid that all the NaCl isldissolved, but in that case ties of circulating brine relative to the quantity of potas so much potassium salt would also be dissolved that the sium magnesium salt produced, these processes were process would have very low yields. If, instead, the NaCl rather expensive. Moreover, the degree of purity of the 45 containing potassium magnesium sulfate is washed with p'otassiurnrmagnesium salt obtained was not high enough water, the NaCl can be removed but again, a considerable for the further processing of the salt to produce K2804, quantity of potassium sulfate will dissolve in the washing as it still contained NaCl in a proportion from 10% to waters. ' ' ' 22% and even more. The yields were ‘low as consider This invention consists in a process for the manufac able amounts of potassium were lost in the undissolved ture of highly pure hydrous potassium magnesium sul residues and the ?nally rejected mother liquors. fate from NaCl-containing natural ‘potassium chloride Another process that had an industrial application was magnesium sulfateminerals, especially kainite, wherein the one by Precht (process of Neustassfurt), consisting the crude mineral, preferably ground ?nely, is treated with vigorous agitation with waterused in an amount in decomposing the kainite with an MgCl2 brine at tem 55 peratures ranging from 120° to 150° under pressures from equal to or slightlyvlarger than the amount required for 2 ,to 5 atmospheres. This process produces langbeinite dissolving the MgClz liberated by the treatment under (K2SO42MgSO4) in the form of a very ?ne, dust-like equilibrium conditions so as to produce ?nely divided powder which can be separated from the mineral me potassium magnesium sulfate while the NaCl is left vir chanically, e.g. by means of rotating sieve drums. This tually unaffected;,the salt‘ mixture is suspended in a sep process has the disadvantage that it requires MgClz brines arating liquid in which the settling speed of the NaCl whose contents of MgClz' are comprised within ?xed lim is greater than that of the potassium magnesium sulfate; its, and that the ?nally rejected mother liquors contain and the latter is separated from the former by decanta a high proportion of potassium, which makes necessary tion or the like._ I; -‘ . ' . Y - ' to utilize these mother liquorsin-other processes in order Recycled mother liquor from a preceding cycle of op to keep the losses within reasonable limits. Even this 65 eration may be used as a separating ‘liquid. fairly expensive process does'not‘yield a product com This process can be designed‘for the continuous pro pletely free from NaCl and has, therefore, been given up. ‘ duction of virtually pure schoenite from crude kainite More recently it has been suggested to use the known contaminated with NaCl. ' > alkali salt ?otation methods for the separation of the Morevor', as this process uses only the ‘minimum of kainite-from the accompanyingNaCl, whereby almost 70 water required for the conversion of'kainite into hydrous pure kainite can be obtained in yields of about 90%. potassium magnesium sulfate, a high yield of pure sulfate Although this method is attractive from the technological‘ - can ‘be obtained even-from poor‘kainite. 2,902,343 3 Further, this process requires no chemical reagents of Example 3.. . any kind and practically noysteam, the electrical power requirements are low, and .the necessary equipment is 3000 g. of kainite of the following composition: very simple. _ 7' - . ‘ 1 By a modi?cation of the invention the most character CH K- Mg" s04" Oai' ‘- 01' Na’ 1110 istic feature of the latter, i.e. the separation of potassium magnesium sulfate ?nes from a coarser NaCl sediment by 9.28 5.72‘ 23.13 0.15 33.01 10.10 12.74 means of an appropriate separating liquid, especially a re cycle brine, is applied to crude schoenite, leonite or an ground to a ?neness such as to pass through a 50 mesh other NaCl containing potassium magnesium sulfate other 10 sieve, is vigorously shaken with 1650 g. of water at room than produced by the conversion of kainite. temperature. Then 3000 g. of mother liquor recycled The process according to the invention is illustrated from a previous cycle is admixed to the suspension. The by the following examples to which it is not, limited. suspension of ?nes is then separated from the coarser crys~ Example I talline sediment. The two salts are separately suction 15 ?ltered, the ?ne schoenite'is Washed on the ?lter with cold Kainite containing (in percent by weight) water, and the NaCl sediment is similarly washed with warm water. The salts are dried and consist of: K’ Mg" S04" 01’ Na‘ Ca." E20 (a) 1060 g. of schoenite containing: , ,.

6.98 4.03 19.20 38.50 21.9 0.44 8.95 20

is ground to a ?neness so as to pass a 35 mesh sieve. 18. 37 6. 43 50. 8 0. 58 0. 88' 0. 62 22.62 600 gr. thereof is vigorously shaken with 260 g. of water at room temperature. This operation produces a. sus 25 (b) 970 g. of crude NaCl'containing: " pension of very ?ne crystals of schoenite‘ and a heavy sediment of coarser crystals of NaCl. Upon addition of 300 g. of mother liquor recycled from a previous similar operation, the ?ne schoenite in suspension may be de 0. 66 O. 25 2. 3 0. 16 58. 23 canted from the coarse residue. The decanted schoenite 30 ‘suspension is then ?ltered by means of a suction ?lter, and the schoenite is washed on the ?lter with water. The The potassium yield is about 70%. coarse NaCl sediment is ?ltered and washed with Warm The washing waters are recycled to a subsequent cycle water. Both salts are separately dried. In the result one of operation in which they are admixed to the water of obtains 139 g. of schoenite containing (in percent by 35 reaction. weight): - Example 4 300 g. of kainite containing:

K‘ Mg" Ca" so," 01' Na‘ H1O 40 18. 08 G. 23 52. 8 0. 26 0. 8 2. 12 20. 6 11.43 7.10 0.1 28.78 20.1 0.4 16.55

and 277.8 g. of crude NaCl containing and ground to a ?neness so as to pass through a 35 mesh 45 sieve, is vigorously shaken with 180 g. of water, or with 140 g. of Water plus an appropriate quantitiy of washing waters recycled from a preceding cycle of operation. 0. 53 0. 20 3. 45 57. 8 38. 06 0. 4 The suspension of ?nes is separated by decantation from the coarser sediment. The two salts are washed and 50 dried separately, all this as described in Eaxmple 1. The The yield of potassium is about 60%. 1 products are: Example 2 (a) 130.2 g. of schoenite containing: If the same kainite as used in Example 1 is treated in K' Mg" sol" 01' Na‘ Ca" 11,0 the same manner as described but the quantity of 260 g. 55 of water is replaced by 180 g. of water plus the combined washing waters of a preceding cycle, amounting to 154 19. 79 6. 52 51. 07 0. 87 1. 22 0. 092 I9. 75 g. the products consist of: (a) 151.5 g. of schoenite of the following composition: (b) 55 g. of crude NaCl containing: 60

18.0 6. 26 51. 1 0. 35 1. 2 0. 85 22. 01 0. 92 0. 37 3. 27 57. 2 37 0. 081 65 (b) 244 g. of crude NaCl of the following composi The potassium yield is about 75%. tion: Example 5 202 g. of crude schoenite containing 18.3% of K20 70 and 20.8% of NaCl is suspended in a brine consisting of mother liquors from the preparation of schoenite as de 1. 27 0. 45 0. 4 5. l8 55.v 84 36. 64 scribed in the preceding examples. The suspension of the ?nes is separated from a coarser sediment and ?ltered, the ?lter residue is washed and dried. The product con The total potassium yield is about 65%. 75 sists of 151.5 g. of schoenite containing 23.2% of K20 2,902,343 5 6 and 0.8% of C1. The dried heavier sediirent consists of 3. The process of claim 1 in which the inert separating 45.7 g. of NaCl containing 0.45% of potassium. liquid comprises the mother liquors resulting from the The separation of the suspension of ?nes from the conversion of kainite to potassium-magnesium sulphate. coarser sediment may be effected by any suitable means 4. The process of claim 1 in which the inert separating known per se, e.g. tip cases, separating cones, hydrocy liquid suspending the NaCl and the produced potassium clones, centrifuges, shakeout tables, or by means of de salts are composed of brines that are in chemical equi vices whose operation is based on the different sizes of librium with a solid phase containing potassium-magne the ?nes and sediment crystals, e.g. sieves, hydraulic sium sulphate and sodium chloride. sieves, vibrating sieves, sieve drums or the like. 5. The process of claim 1 in which the NaCl and the What I claim is: 10 potassium-magnesium sulphate obtained are separately 1. The process of obtaining substantially pure potas washed with water, and the resulting washing waters are sium-magnesium sulphate from kainite containing ap employed together with fresh water for the further con preciable quantities of NaCl as an impurity comprising version of raw kainite. the steps of reacting the impure kainite under conditions 6. The process of claim 1 in which there is added as of vigorous agitation with a quantity of water su?icient 15 an auxiliary separating liquid a predetermined ratio of to convert the kainite into a thick aqueous suspension mother liquor brine to the water used for the conversion of ?nely divided potassium-magnesium sulphate and fur of kainite to potassium-magnesium sulphate. ther, at least suf?cient to dissolve the MgC12 produced under said reaction conditions, but insufficient to substan References Cited in the ?le of this patent tially dissolve the aforesaid NaCl, adding an inert aque 20 UNITED STATES PATENTS ous separating liquid to reduce the density of the said 229,249 Hake ______.._ June 29, 1880 thick suspension of ?nely divided potassium-magnesium 1,244,884 Nagelvoort ______... Oct. 30, 1917 sulphate, and then separating the said ?nely divided po 1,357,973 Giesecke ______Nov. 9, 1920 tassium-magnesium sulphate from the undissolved original 1,813,575 Janecke et a1. ______July 7, 1931 relatively coarse NaCl crystals. 2. The process of claim 1 in which separation of the OTHER REFERENCES ?nely divided potassium-magnesium sulphate from the Mellor: “Comprehensive Treatise on Inorganic and relatively coarse NaCl is e?ected through the differential Theoretical Chemistry,” vol. 4, pp. 240-344, 1923, Long speed of sedimentation of the respective crystals in the mans, Green and Co., New York. aqueous suspension.