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July 2, 1963 A K. SCHMIDLAPP 3,096,034 METHOD AND APPARATUS FOR PURIFYING POTASSIUM SALT-CONTAINING MATERIALS Filed Dec. 28, 1960 INVEN TOR. IWSQW‘L» WW1 United States Patent 0 an» ce sagas-354 Patented July 2, 1963 1 2 3,096,034 ers, whereby large quantities of waste Waters are pro duced which it is sometimes di?icult to dispose of. Vari ous other modi?cations of dry and wet clay separation Kurt Schmidlapp, Neuhof, Kreis Fuld'a, Germany, as signor to Wintershall Aktiengesellschaft, Kassel, Ger have been proposed all of which, however, are quite in volved, and uneconomical, and at best only of limited METHOD AND APPARATUS FOR PURIFYING POTASSIUM SALT-CONTAINING MATE many Filed Dec. 28, 1960, Ser. No. 79,073 16 Claims. (Cl. 241-14) effectiveness. Thus, frequently one has to resort to the old method of manually separating the larger clay par ticles from the crushed raw material and to’ attempt in this manner to keep during subsequent working up of the The present invention relates to the working up of po 10 potassium salts the content of clay constituents at a tassium salts-containing raw material and particularly manageable low level. It may be noted that in order to the separation of sludge~forming clay constituents from to be effective, the separation of clay or sludge-forming the crude potassium salts or potassium salts containing constituents should be carried out to such an extent that raw materials so as to facilitate the further processing of no more than 1.5% by weight, and preferably less, of 15 the sludge-forming constituents remain in the potassium the material. Natural potassium salt deposits contain clay-like and salt-containing fraction. other water insoluble accompanying materials all of which will be referred to herein as clay constituents. These It is therefore an object of the present invention to overcome the above-discussed di?iculties in the separation water insoluble and sludge-forming clay constituents of sludge-forming constituents from the main body of cause great difficulties in the working up of the potassium 20 potassium salts-containing raw materials. salts, for instance by ?otation processes. Clay constituents It is another object of the present invention to provide of sylvitic hard salt deposits may amount to about 2% a simple and economical method for the effective separa of the weight thereof and the amount of clay constituents tion of sludge-forming constituents such as clay from in other sylvitic raw materials may exceed 10%. the potassium salts-containing portion of raw materials, These sludge-forming impurities cause considerable 25 for instance sylvitic minerals. Other objects and advan di?iculties during formation of hot potassium salt solu tages of the present invention Will become apparent from tions. The hot solution is contaminated with ?nely sub a further reading of the description and of the appended divided sludge-forming insoluble particles which tend to claims. remain in suspension and frequently can be caused to With the above and other objects in view, the present thicken and to form a sediment only with the assistance 30 invention contemplates in a method of separating sludge of auxiliary precipitating agents. Nevertheless, fre quently it is extremely di?icult to free the hot solution from sludge particles remaining in suspension and this will result upon cooling of the hot potassium solution in the recovery of ?nely granulated low-purity end products. In addition, even when it is possible adequately to separate the sludge from the major portion of the hot forming constituents from crude potassium salt containing the same, the steps of subjecting the sludge-forming con stituents containing crude potassium salt to a series of successive impact comminutions at varying impact velo cities, with the impact velocity of the ?rst and last impact comminution steps being smaller than the impact velocity of the intermediate impact comminution. solution further diiiiculties arise in the separation of the Surprisingly, it has been found that according to the sludge cake from the adhering residual salt solution. The present invention the content of sludge-forming constit sludge may contain bentonite and may display thixotropic uents of the crude potassium salt containing material tendencies. Thus, potassium containing solution will be can be reduced down to about 1.5% or even lower bound by the sludge cake and losses of potassium will be by continuously passing the raw material through a series incurred due to the unsatisfactory separation of solution of successively arranged impact comminutors operating from the sludge cake. 45 at predetermined rotational speeds, whereby the material Separation by ?otation is also unfavorably in?uenced is sifted or screened while passing from one impact com by sludge-forming constituents of the raw material, since minutor to the next. It has been found that in each of sludge particles will be retained in the concentrate frac these impact comminutions the material will be broken tions and will reduce the purity thereof. Furthermore, down into clay or the like particles of relatively large size the ?nely subdivided sludge particles impair the effective 50 and potassium salt-containing particles of relatively ness of ?otation improving agents. In addition, the pres ence of the ?nely subdivided sludge particles will stabilize and prevent easy destruction of the foam formed on the liquid leaving the ?otation process. Thus, an excess of smaller size so that- the clay particles can be separated from the potassium salt containing particles by screening prior to subjecting the thus separated larger clay-contain sludge-forming particles will not only render the ?otation process uneconomical but, in fact, will make it impossible ing particles to the next impact comminution. The present invention requires certain relationships be to carry out such process. In order to overcome the above-described and very tween the rotational speeds of the individual impact com minutors through which the material passes. The rota tional speed increases from the ?rst to the second step and serious di?'iculties in the recovery of potassium salts from raw materials including sludge-forming constituents, at 60 is then reduced again in subsequent impact comminution tempts have been made to separate the sludge-forming steps, as will be more ‘fully described below. constituents of the raw material from the potassium con By comminuting the raw material in a hammer mill, it taining remainder thereof prior to ?otation or hot dissolu will not be possible to form the fractions of considerably tion of the potassium containing fraction. Thus, it has increased or reduced clay content. For instance, by sub been attempted to separate coarse clay particles by hand 65 jecting the crude potassium salt containing 2.5% insoluble from the crushed raw material. According to a rather expensive method, the dry comminuted material is sub jected to electrostatic separation. The wet methods of clay separation are modi?ed ?otation processes with sludge thickening devices such as counter current wash-thicken 70 constituents to comminution in a conventional hammer mill having a rotational speed of 29 meters per second at its peripheral beater portion, the material may be com minuted into particles of varying sizes ranging up to 4 mm. Upon sepmation of the thus comminuted material into ...~. . 3,096,034 . 4 various size ranges, the following percentage of clay was tain on the one hand clay particles which contain only a very small percentage of potassium salt and on the other found in the respective particle sizes: hand potassium salt enriched particles which contain only very little clay. TABLE I Particle size, mm.: clziiiivliéigiftent -It is important to note that, as shown in Table IlA, when impact comminution for instance with the Andreas im 075-1 _ 11-73 pact breaker shown in U.S. Patent No. 2,889,119 is carried 0.6-0.75 12-24 out at considerably higher impact velocities for instance 0.54m 10-91 at a circumferential velocity of the impact comminutor 0.4-0.5 _ 9-46 10 of 60 meters per second, that under such conditions maxi~ 0.3-0.4 _ 12.67 mum concentration will be shifted to a relatively smaller 0.2-0.3 8-44 particle size such as between 0.4 and 0.75 mm. so that it o.1_o.2 ___ 10.19 is not possible thereafter to separate the clay enriched O.6—0.1 _ 10.99 particles from the remainder in an economical manner. 0.06 ___ 12.27 It is therefore important according to the present inven tion to so adjust the circumferential speed or velocity of Obviously, the above-described process is not suitable the impact comminutor that with reducing particle size for effectively reducing the clay content of the crude of the material which is fed into the impact comminutor potassium salt. In contrast thereto sequentially arranged the further comminution will still result in larger particles impact comminutors, preferably at least 3, and most preferably 4, impact comminutors with sifting of the 20 of increased clay content and smaller particles of reduced 1-4 5 - clay content. For instance, the impact velocity during the second comminution may begreater than during the ?rst comminution, while in subsequent comminution steps material while it passes from one impact comminutor to the next and with a de?nite relationship between the rota tional speeds of the individual impact comminutors, will the impact velocity may again be reduced in order to achieve the desired result. result in a selective breakdown of the material into larger predominantly clay containing particles and smaller potas— sium salt enriched particles. Thus, according to the present invention, it is possible TABLE IIA Impact velocity, m./sec.: to comminute the raw material for instance to a‘ maximum particle size of 4 mm. while at the same time carrying out Percent1 15 an effective clay separation with small, economically 30 feasible loss of potassium salt. The process of the present 88 25 _ 30 ___ invention will result in a product containing not more than 40 about 1.5% and preferably only about 1.2% of insoluble constituents, which product is eminently suitable for further puri?cation by ?otation or the like. Surprisingly, it has been found that the somewhat plastic 60 ___ _ 70 38 ___ __ 3 0.5 1‘Percent clay content of larger particles (greater than 3 mm.). The dependency of the loss of potassium salt on the clay constituents will offer more resistance to comminu tion in an impact comminutor than the potassium salt constituents of the raw material. This is particularly impact velocity is shown in Table HI with one raw ma terial, by way of example: ' TABLE III 40 so when the impact velocity is relatively low. Thus, it is Impact veloctiy, m./sec.: possible to separate the sludge-forming clay constituents K20 percent1 to a considerable extent in dry form fromthe more brittle 15 0.85 salt and to enrich the clay content of certain particle sizes while the clay content of other particle sizes is reduced. For instance, by subjecting a raw material having a 45 maximum particle size of 40 mm. and containing 2.5% 20 _ 0.61 35' _________ __ 0.35 insolubles to impact comminution in an'impact breaker 40 ______ ._ 0.29 25 30 _______ __ 0.51 ____ ‘_ 0.43 such as disclosed in US. Patent 2,889,119 to Andreas, at 1 Percent lost with clay enriched fraction. an impact velocity of 24 m./sec., it will be found that the For best separation of the raw material used according clay content of the various size fractions will be as 50 to Table III, the selective comminution of the same and follows: separation of the clay constituents from the residue will TABLE 11 be carried out in four impact comminution steps at impact Clay in percent Particle size, mm.: by weight velocities as indicated in Table IV: Up to 4 20.52 TABLE IV. 1-4 39.34 0.75-1 0.5——0.6 _____. 10.50 _____________________________ __ _ 6.70 0.4-0.5 ___ _ ___-.. 0.3-0.4 ___ 0.2-0.3 ___--- 0.l-—0.2 0.06—0.1 0.06 5.13' 2.19 ___- ___ Preferred 1n./sec. 6.28 ___ ____._ _ Impact velocity mJsec 7.13 _ 1.31 ________________________________ __ 0.90 100.00 Thus, it can be seen that the clay content of the larger particles will increase while the smaller particles will show a reduced content of sludge-forming clay constituents. 'If the mixture resulting from such impact comminution is now classi?ed by size, for instance by screening, it will be possible to separate the larger particles of increased clay‘ content from the smaller particles of reduced clay content. By repeating this process at suitably arranged 60 First impact comminution __________________ __ 17-27 18—'22 Second impact comminution_____ 26-38 30-36 Third impact comminution ____ __ Fourth impact comminution ________________ __ 20-30 20-30 22-26 22-26 Considering the upper limit of the preferred range of impact velocity for the ?rst impact comminution and the lower limit of the preferred range of impact velocity for the second impact comminution, it will be apparent that preferably the impact velocity of the second impact com 70 minution will be at least about 35% greater than the im pact velocity during the ?rst impact comminution. Most of the clay will be found in the coarse fractions of 0.5 mm. or larger particle size and it is possible in this manner to remove without di?iculty for instance up to impact comminution velocities, it will ‘be possible to ob 75 60% of the initial clay content of the raw material, 3,096,034 5 6 This surprising result can be further improved by spray ing or wetting with ?nely subdivided polar or non-polar liquids, for instance water or salt solutions, or by treating minal portion. However, screening and wetting may also be carried out in separate devices, by passing the particles after screening over a vibrating table or the like and to spray or steam the material while it is intensively moved during passage across the vibrating table. It is desirable the material for a short period of time with warm air of 100% relative humidity. As polar liquids, aliphatic and aromatic alcohols, esters, ketones, ether and mixtures to closely control the amount of liquid which is imparted to the material and this is more easily accomplished by thereof may be used, and as non-polar liquids, for instance non-polar liquid hydrocarbons, such as benzene, or car bon tetrachloride. Apparently, by such treatment a sur steaming. without appreciable softening of the clay and in this man ner the plastic qualities of the clay are increased compared with the potassium salt-containing mineral constituent potassium salt enriched smaller particles of the individual which remains brittle. essing. After completion of the last impact comminution step, face impregnation of the clay constituents takes place 10 preferably the fourth impact comminution, the clay en riched fraction is withdrawn from the process while the impact comminution steps are collected ‘for further proc Consequently, upon subjecting the thus wetted raw material to impact comminution there > Comparison experiments which vwere carried out with the same raw material by hand separation and by selec tive impact comminution according to the present in will be an even more eifective separation into somewhat plastic clay particles and brittle potassium salt enriched particles. vention at the rate of 250 tons per hour gave the results It was then found that lesser quantities of liquid will be shown in Table VI: needed for the above purpose when the liquid is applied 20 TABLE VI in vapor form than when liquid is sprayed directly on to the material. Clay separation by— Table V illustrates a result obtained by application of 0.3% Water in the form of a spray or in the form of satu rated steam: TABLE V Particle size, mm. Untreated, percent insoluble 66. 6 10. 6 5. 6 4. O 3. 0 4. 2 68. 5 10.3 6. 1 2. 9 2. 9 4. 5 insoluble ‘ Separated clay mineral, t/h ________________ __ Sprayed with Steamed with 3% water, saturated percent steam, percent insoluble Manual Selective separation impact corn~ 25 3 3.15 13. 1 16. 14 34. 1 45 percent insoluble ________________________ __ 1. 2 0.91 K20 loss in separated clay, percent ________ __ 0.29 0.33 Insolubles in clay mineral, percent-.. Clay removal (on clay mineral), perce 30 82. 4 6. 1 3.8 1. 9 1. 5 2. 0 minution 1 Residual clay in potassium salt fraction, 1 According to the present invention. As shown above, the fully automatic selective impact comminuation according to the present invention will 6. 0 4. 8 2. 8 achieve a lesser residual clay content in the crude potas sium salt than can be achieved by manual separation, while, for all practical purposes, the loss of K20 in the Table V shows the remarkably favorable clay enrich ment in the coarse fraction of the Wetted clay containing clay fraction is the same in both cases. Furthermore, and this is most important, manual separation of 250 tons per potassium salt mineral and the better separation accom plished in this manner. It is interesting to note that the hour requires about 35 IWOI‘KCI'S which, of course, are not needed by proceeding in accordance with the present in clay content of the coarse fraction of above 3 mm. will vention. increase only by 1.9% upon spraying with water, how The effect of the present invention on subsequent salt ever, by steaming the increase will amount to 15.8%. Spraying took ?ve minutes while steaming was completed 45 ?otation is shown in Table V-II which clearly indicates a better K20 yield at higher concentration and with lesser in three seconds, which, of course, further increases the advantages of steaming over spraying. requirements of ?otation agents than by manual separa It is also possible and sometimes advantageous to carry out the ?rst surface treatment, be it by steaming or spray tion of clay constituents: ing, below ground for instance during tilting and empty ing of the miner’s Wagon, whereby this thus introduced moisture will bind simultaneously undesirable dust. 50 . TABLE VII Method of clay separation Amount of ?otation agent, g./t. Of course, the wetting must not be carried out beyond the introduction of a certain upper percentage of mois ture. This maximum percentage is in the neighborhood 55 No separation crude salt containing of about 0.5% of the weight of the treated material, above 1.85% Water insolubles correspond which the plasticity of the clay is increased beyond desir ing to 2.5% clay substance ________ __ A further increase in the selective separation effect can be accomplished by the incorporation of a polar Wetting Yield, percent K20 75 57. 3 S4. 6 40 58. 3 90. 2 32 59. 0 91. 6 Manual separation crude salt con taining 1.31% water insolubles cor able limits and makes it di?icult to separate the same from the potassium salt increased fraction during the subse quent screening process. Concentration, percent K20 responding to 1.6% clay substance- 60 Repeated impact comminution (four times) crude salt containing 0.84% water insolubles corresponding to 0.9% clay substance _______________ __ agent, for instance a fatty acid amine in the aqueous wet The clay enriched residue of the ‘last impact comminu After the ?rst impact comminution step, the'oversize 65 tion is removed and may be used for instance as back ?lling. However, at least a portion thereof may also be clay enriched particles will be retained on the screen while used for granulating potassium salts. In the latter case the smaller particles of reduced clay content will pass separation of the clay constituents may be carried out through the same. After subsequent impact comminu selectively by varying ‘the rotational speed of the impact tion, screening is carried out in similar manner, whereby the clay enriched over?ow particles are Wetted by spray comminutors, since in this case it is not necessary to con ing or steaming in order to increase the selectivity of the trol and carefully limit the K20 losses in the clay fraction subsequent impact comminution step. which subsequently is used for granulating potassium It has been found to be advantageous to insert at the salts. terminal portion of the sieve or screen a blind bottom to If the clay enriched residue of the process of the pres ting liquid. carry out wetting while the material passes over this ter 75 ent invention is to be further processed into a fertilizer, 3,096,084 8 together with other constituents, then the clay fraction devices, i.e., the number of wetting devices and the loca: may be further comminuted by additional impact com minution of the same at higher rotational speeds, prefer ably between 25 and 70 meters per second, whereby it is advantageous during such further comminution of the clay fraction to heat the impact comminutor with hot air, Further processing may be carried out for instance in ac tion of the same, depends to some extent on the particu lar raw material and on the degree of comminution cordance with the method described in German Patent No. 1,022,241. achieved in the individual impact comminutors. ' ' Screen 19 is provided with two screening surfaces so that the material reaching screen 19 from'impact com minutor 18 will be divided into three fractions of which the ?nes will pass via chute 25 to elevator 32, while the intermediate fraction may optionally pass via chute The impact comminution of the raw material or of the 10 28 to elevator 32 or via chute 27 to the last impact com minutor 20. The coarse fraction, i.e., the over?ow from the upper screen 19, will then pass via chute 26 to im pact comminution is carried out in an impact crusher or pact comminutor '20. a breaker per se known in the art, one type of such impact The material which reaches impact comminutor 2G is breaker is for instance describedrin US. Patent No. 15 high in clay content and includes only a very small, por 2,889,119 to Andreas. ' > tion of the original potassium salt. Thus, the material The novel features which are considered as character which is passed through comminutor 20 serves no longer istic for the invention are set forth in particular in the for the recovery of potassium salt therefrom. It is fur appended claims. The invention itself, however both as larger particle, fraction resulting from the preceding im ther comminuted in comminutor 29,’ preferably until at to its construction and its method of’ operation, together with additional objects and advantages thereof, will be 20 least 85% of the material reaches a ?neness of 1.5 mm. or below and during comminution in impact comminutor best understood from the following description of speci?c 20, hot air is introduced via blower 30 and conduit 31, embodiments when read in connection with the accom paying drawing, in which the FIGURE shows a schematic illustration of a preferred arrangement according to the present invention. Referring now to'the drawing, it is schematically shown that the broken raw material as mined is conveyed under ground in haulage vehicles 1 to conveyor 3 and passes since the residual moisture of the material wouldother wise prevent ?ne crushing of the same. . T It is thus apparent that the relationship between the rotational speeds, i.e., theimpact velocities to which the material is exposed in the series of impact comminutors, is ‘of major importance in order to achieve the nearly from conveyor 3 through crusher 4 into underground complete separation of potassium salt from the sludge hopper 5. The ?rst wetting of the raw material is pref 30 forming insoluble or clay constituents of the raw ma erably carried out during passage of the raw material from terial. The process of the present invention is generally haulage vehicles 1 to crusher 4, for instance by means of a spraying device associated with conveyor 3. The crushed wetted and well mixed raw material is stored in hopper 5 and hauled from there above ground by means of haulage device 6. . The material now enters the crude salt comminution carried out at ambient temperatures. It has been found that best results according to the present invention are achieved by arranging, for separa tion of clay and salt between three and four impact com minutors, preferably the four impact comminutors indi installation and passes over screen '7 for separation into cated in the drawing reference numerals 8, 12, 161and 18, ?nes and into material of above about 4 mm. particle so that the rotational speed of the second impact com size. The thus separated ?nes, as well. as the subse 40 minutor is higher than the rotational speed of the ?rst quently separated ?nes fractions are collected on elevator impact comminutor, and the rotational speed of the third ‘ V 32. The over?ow from screen 7 is comminuted in ?rst impact comminutor 8 at relatively low circumferential speed. The crushed material leaving impact comminutor and fourth impact comminutors is lower than the rota? tional speed (or impact velocity) of the second impact comminutor. .At least two impact comminutors must be 8 passes over screen 9 where it is separated in ?nes which 45 used according to the present invention, in which case reach elevator 32 via chute 22, and into coarse material (the over?ow of screen 9) which passes to and is wetted ' the rotational speed of the second impact comminutor will be greater than that of the ?rst impact comminutor on vibrating table 10. Wetting‘ may be carried out by and, for all practical‘purposes, the maximum number of spraying or steaming as described further above. The impact comminutors for sequential comminution of the 50 wetted material is then introduced into the next or sec raw material with separation into coarse clay enriched ond impact comminutor 12 and here again broken into a particles and smaller potassium salt enriched particles, _ fraction of ?nes, consisting essentially of potassium salt will not exceed eight. and into a coarse fraction of enriched clay or insolubles content. From impact comminutor 12, the material Wetting agents which may be advantageously sprayed ‘passes to screen 13, the ?nes are separated and reach 55 or steamed on to the material include saturated steam elevator 32 via chute 23, and the coarse fraction passes under relatively low over pressure, or aqueous salt solu to vibrating table 14 and is again wetted, for instance by tions containing, for instance, between 150 and 250 grams The thus wetted'ma per liter of magnesium chloride, or, the so-called hard’v 'terial passes to the third impact comminutor 16. Here salt solution which accrues in the potassium salt recovery again, the material is broken down into ?nes and a coarse 60 and which contains about 80! grams per liter of potassium ,means such as a nozzle device 15. fraction and the ?nes are screened out on screen 17 and ‘guided to elevator 32 via chute 24. It is essential ac I cording to the present invention that the circumferential chloride, 100 grams per liter of sodium chloride, 1507' grams per liter of magnesium chloride and 50 grams per , liter of magnesium sulfate may also be advantageously comminutor of the series starting with impact comminu 65 used for wetting the material; prior to. further impact comminution. tor 8, is higher than the circumferential velocity of im The following example'is given as illustrative only of pact ,comminutor 8, while the circumferential speed of the present invention howeven'without limiting the same the third impact comminutor 16 preferably is less than to the speci?c details of the example. that of impact comminutor 12. The coarse fraction of the broken mixture produced in impact comminutor V16, 70 velocity of impact comminutor 12, i.e., the ‘second impact i.e., the over?ow of screen 17, is then introduced into the fourth. impact 'comminutor @18 and passes ‘from there to screen 19. Contrary to screens 10 and 14, screen 19 is not‘coordinated with a wetting device. However, it may be noted that the speci?c arrangement of wetting Example The material as mined is broken and wetted and thenv conveyed to screen 7.7 250 tons per hour of such’ ma~ terial containing 1.4% insoluble which equals 1.80% clay 3,096,034 10 0 mineral are thus introduced. Without further analysis, the vforegoing will so fully This material has the fol lowing particle sizes: reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the stand point of prior art, fairly constitute essential character TABLE VIII Percent 40-160 mm 18.1 4—40 14 0.6—1 0.3-0.6 24.7 15.8 11.4 15.0 0.2-0.3 istics of the generic or speci?c aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims. 4.2 10 11-0-3 _____ 10.8 What is claimed as new and desired to be secured by Letters Patent is: 1. In a method of separating sludge-forming clay con stituents from a particulate sludge-forming clay and potas sium salt containing mined raw material, the steps of 100.0 About 150 tons per hour of the material pass through screen 7 and are removed by conveyor 21. These 150 15 subjecting particulate sludge-forming clay and potassium salt-containing mined raw material including also par tons per hour have a particle size of less than 4 mm. 100 ticles within the size range of between 40 and 160 mm. tons per hour with a particle size which is generally at without prior impact comminution to impact comminu least 4 mm. and contains only very little of smaller par tion at a ?rst predetermined impact velocity so as to sepa ticles pass then into impact comminutor 8 and are there ‘rate said raw material into clay enriched larger particles 20 in selectively broken down under conditions such that and potassium salt enriched smaller particles; recovering substantially no clay agglomerations are formed. The said potassium salt enriched particles from the thus material from comminutor 8 passes on to screen 9 where formed particulate mixture; subjecting said clay enriched again the portion having a particle size of less than 4 larger particles to impact comminution at a second veloc mm. is passing through the screen and is removed by conveyor 22. The material which does not pass through 25 ity being greater than said ?rst impact velocity so as to separate said clay enriched particles into further potas sium salt enriched smaller particles and larger clay en riched particles; recovering said further potassium salt enriched particles; and subjecting the thus separated clay screen 9 is then wetted as previously described in connec tion with the drawing. This process is repeated several times for instance as illustrated in the drawing, where by the degree of separation on each screen depends of course on the mesh Width thereof. enriched particles to impact comminution at a third im The ?ner the mesh 30 pact velocity being smaller than said second impact veloc width, the purer is the potassium salt material which is separated, however, the ‘greater is the amount of potas sium which remains with the coarse over?ow. ity so as to cause further separation into clay enriched larger particles and smaller potassium salt containing par ticles of greatly reduced clay content. Conse quently, when the potassium containing over?ow can 2. In a method of separating sludge-forming clay con be utilized for other purposes, then it is generally de stituents from a particulate sludge-forming clay and potas sium salt containing mined raw material, the steps of sirable to use a screen of lesser mesh width in order to obtain a ?ne product of higher purity. However, when it is desirable to obtain the largest possible yield calcu lated as potassium oxide in the ?ne product then, of course, a somewhat wider mesh will be used for the screen subjecting particulate sludge-forming clay and potassium salt-containing mined raw material including also particles 40 within the size range of between 40 and 160 mm. with out prior impact comminution to impact comminution at a ?rst predetermined impact velocity of between 17 and ing of the respective comminuted material. In any event, the clay concentration in the coarse material which does not pass through the respective screens will be enriched 27 m./sec. so as to separate said raw material into clay enriched larger particles and potassium salt enriched so that for instance if the material which reaches screen 7 smaller particles; recovering said potassium salt enriched contains 1.8% of clay mineral, then the coarse material 45 particles from the thus formed particulate mixture; sub or over?ow from screen 7 will show a clay concentration jecting said larger clay enriched particles to impact com of 3.6%, the over?ow from screen 9 a clay concentra minution at a second impact velocity of between 26 and tion of 7.6%, the over?ow from screen 13 a clay con 38 m./sec. being greater than said ?rst impact velocity centration of 20.5%, the over?ow from screen 17 a so as to separate said clay enriched particles into further clay concentration of 35% and the over?ow from screen potassium salt ‘enriched smaller particles and larger clay 19, i.e., the two over?ows which are indicated by refer enriched particles; separating said further enriched par ence numerals 26 and 27 will show a clay concentration ticles; subjecting said clay enriched particles to impact of 58.0% while over?ow 26 taken ‘alone will have a clay comminution at a third impact velocity of between 20 concentration of 63.0%. Under the given conditions, about 1.7 tons per hour of comminuted potassium ?ne 55 and 30 m./sec. being smaller than said second impact velocity so as to cause further separation into clay en salt will pass through double screen 19- to conveyor 25. The separated clay is contained in the over?ows 26 and 27, whereby over?ow ‘27 may be added to the crude salt and reintroduced into the screening process if desired. Under the given conditions, for instance 3.5 tons per 60 hour of clay enriched material will accrue in over?ows 26 and 27. The analysis of the combined over?ows 26 and 27 show about 34.1% insoluble substances which cor respond to about 58% of clay substance. riched larger particles and smaller potassium salt con taining particles of greatly reduced clay content, and re covering the thus formed potassium salt containing par ticles of greatly reduced clay content. 3. ‘In a method of separating sludge-forming clay constituents from a particulate mined raw material con taining a potassium salt and sludge-forming clay con stituents, the steps of subjecting particulate sludge-forming clay and potassium salt-containing mined raw material in Table IX gives the screen analysis of the coarse over 65 cluding also particles in the size range of between 40 and ?°W 26TABLE IX Percent 160 mm. without prior impact comminution to impact 4 mm. ___ 73.8 comminution at a ?rst predetermined impact velocity so as 3-4 _____________________________________ __ 22.1 to form of said raw material a mixture of clay enriched 1-3 1-1.5 O.5—1 O—0.5 __-_ _______ __ 2.5 70 larger particles and potassium salt enriched smaller par ____ __ 0.6 ticles; screening the thus-formed mixture so as to sepa rate the same into said smaller and larger particles; sub ____ __ ___________________________________ __ 0.6 0.4 jecting the thus separated clay enriched larger particles to impact comminution at a second velocity being greater 100.0 than said ?rst impact velocity so as to form a second mix 3,096,034 ll 12 ture of clay enriched larger particles and of potassium salt enriched smaller particles; screening the thus formed type which has a rotor which throws material against an impact member of the crusher, said ?rst impact crusher second mixture so as to separate the same into said last including means for rotating said rotor thereof at a pre formed smaller and larger particles; subjecting the thus determined speed for crushing said particulate raw ma terial into a relatively coarse clay enriched fraction and ' last formed separated clay enriched larger particles to im- ' pact comminution at a third impact velocity being smaller into arelatively line potassium salt enrichedfraction; feed than said second impact velocity so as to form a further means for feeding said particulate raw material to'said ?rst impact crusher; a second impact crusher of the same mixture of clay enriched larger particles and potassium salt enriched smaller particles; screening the thus formed further mixture so as to separate the same into said further formed smaller potassium salt enriched particles and clay enriched larger particles; and recovering said separated potassium salt enriched smaller particles formed in said several impact comminution steps. 4. In a method of separating sludge-forming clay con type as and operatively. connected to said ?rst impact crusher, said second impact crusher including means for rotating the rotor of said second crusher at aspeed greater than said predetermined speed for further crushing said relatively coarse clay enriched fraction into a further clay enriched relatively coarse fraction and a potassium enriched relatively ?ne fraction; a third impact crusher stituents from a particulate mined raw material contain of the same type as said ?rst impact crusher and opera ing a potassium salt and sludge-forming clay constituents, tively connected to said second impact crusher, said third impact crusher including means for rotating the rotor thereof at a speed which is less than the rotational speed of said rotor of said second impact crusher for separat ing the further clay enriched fraction from said second impact crusher into a relatively ?ne potassium salt en riched fraction and a relatively coarse clay enriched fraction; screening means operatively associated with each ' the steps of subjecting particulate sludge-forming clay and . potassium salt-containing mined raw material including also particles in the size range of between 40 and 160 mm. without prior impact comminution to a ?rst impact com minution at a ?rst predetermined impact velocity so as to form of said raw material a mixture of clay enriched larger particles and potassium salt enriched smaller par of said impact crushers for separating the relatively coarse from the relatively ?ne fraction formed in the respective impact crushers; conveying means for passing the thus separated relatively coarse fraction produced in said ?rst and second impact crushers to the second and third im greater than said ?rst impact velocity so as to form a sec ond mixture of clay enriched larger particles and of potas 30 pact crushers, respectively; and collecting means for col lecting the relatively ?ne potassium salt enriched fractions sium salt enriched smaller particles; screening after said produced by said impact crushers. second impact comminution the mixture of larger and ticles; screening the thus-formed mixture so as to separate the same into said smaller and larger particles; subjecting the thus separated clay enriched larger particles to a second impact comminution at a second velocity being smaller particles formed thereby so as to separate the same into smaller and larger particles; subjecting the thus ' separated clay enriched larger particles to impact coin-' minution at a third impact velocity being smaller than 12. In a device according to claim 11, wetting means operatively associated with at least one of said screening means for wetting at least one of said clay enriched frac tions prior to introduction of the same into the subsequent said second impact velocity so as to form a further mix impact crusher. ture of clay enriched larger particles and potassium salt enriched smaller particles; screening the thus formed 13. In a device according to claim 12, a last impact crusher of the same type as said ?rst impact crusher, said further mixture so as to separate the same into said further formed smaller potassium salt enriched particles _ and clay enriched larger particles; and recovering said separated potassium salt enriched smaller particles formed in said several impact comminution steps. 5. A method according to claim 4 wherein prior to the last impact comminution said potassium’ salt containing particles are treated with low pressure steam so as to form ‘ last impact crusher being adapted to receive the coarse . , fraction from the screening means associated with said third impact crusher for further comminution of said’ fraction, said last impact crusher including blower means for contacting said coarse fraction during comminution of the same with hot air. 14. ‘In a method of separating sludge-forming clay con stituents from. a particulate mined raw material contain ing a potassium salt and sludge-forming clay constituents, the steps of subjecting particulate sludge-forming clay and 6. A method according to claim 4, wherein said clay enriched particles obtained by impact comminution at 50 potassium salt-containing mined raw material including also particles in the size range of between 40 and 160 mm. said third velocity, after separation from. the potassium without prior impact comminution to impact comminu salt enriched fraction, are subjected to at least one further tion at a ?rst predetermined impact velocity so as to sepa impact comminution at an impactvelocity of between 25 rate said raw material into clay enriched larger particles and 70 m./sec. and potassium salt enriched smaller particles; recovering 7. A method according to claim 6, wherein during said said potassium salt enriched smaller particles from the further impact comminution of said clay enriched particles thus formed particulate mixture; subjecting said clay en the same are contacted with hot air so as to dry said a thin layer of. water on said particles. particles. ' 8. A method according to claim 4 wherein the material ‘to be treated is wetted at least once after the ?rst and before the last impact comminution.’ 9. A method according to claim 4 wherein a wetting ' agent is applied to the material to be treated at least once riched larger particles to impact comminution at a sec ond velocity being at least about 35% greater than said ?rst impact velocity so as to separate said clay enriched particles into further potassium salt enriched smaller par ticles and larger clay enriched particles; recovering said further potassium salt enriched particles; and subjecting the thus separated clay enriched particles to impact com after the ?rst and before the last impact comminution. 10. A method according toclaim 4 wherein a liquid is 65 minution at a third impact velocity being smaller than said second impact velocity by at least about 15%,v so as to applied to the surface of the separated clay enriched larger cause further separation into clay enriched larger particles vparticles formed in the, last of said second impact com and smaller potassium salt containing particles of greatly minutions prior to subjecting said particles to impact com reduced clay content. minution at said third impact velocity; and wherein said 15; ‘In a method of separating sludge-forming clay con ' liquid is applied in a quantity equal to about 0.5% of the 70 'weight of said larger particles. stituents from particulated sylvitic hard salt deposits as a 11. In a device for separating sludge-forming clay con . raw material containing a potassium salt and sludge-form ing clay constituents, the steps of subjecting particulate prising crude potassium salts and sludge-forming clay sludge-forming clay and potassium salt-containing mined constituents, in combination, a ?rst impact crusher of the 75 raw material including also particles in the size range of stituents from a particulate mined raw material com 3,096,034 13 14 between 40 and 160 mm. without prior impact comminu tion to impact comminution at a ?rst predetermined im respective second impact comminution so as to separate the same into smaller and larger particles; subjecting the pact velocity so as to separate said raW material into clay separated clay enriched larger particles formed in the last enriched larger particles and potassium salt enriched smaller particles; recovering said potassium salt enriched smaller particles from the thus formed particulate mix ture; subjecting said clay enriched larger particles to im of said second impact comminutions to impact comminu tion at a third impact velocity being smaller than said second impact velocities so as to form a further mixture of clay enriched larger particles and potassium salt en riched smaller particles; screening the thus formed further pact comminution at a second velocity being at least about 35% greater than said ?rst impact velocity so as to sepa mixture so as to separate the same into said further formed rate said clay enriched particles into further potassium 10 smaller potassium salt enriched particles and clay enriched salt enriched smaller particles and larger clay enriched larger particles; and recovering said separated potassium particles; recovering said further potassium salt enriched salt enriched smaller particles formed in said several im particles; and subjecting the thus separated clay enriched pact comminution steps. particles to impact comminution at a third impact velocity being smaller than said second impact velocity by at least 15 about 15%, so as to cause further separation into clay enriched larger particles and smaller potassium salt con taining particles of greatly reduced clay content. 16. In a method of separating sludge-forming clay con stituents from a particulate mined raW material contain 20 ing a potassium salt and sludge~forming clay constituents, the steps of Wetting particulate sludge-forming clay and potassium salt-containing mined particulate raw material including also particles Within the size range of between References Cited in the ?le of this patent UNITED STATES PATENTS 139,782 Goodhart ____________ __ June 10, 1873 256,073 368,900 1,147,211 Taggart ______________ __ Apr. 4, 1882 Ryerson ______________ __ Aug. 23, 1887 Coleman et al. ________ _. July 20, 1915 2,023,247 2,464,212 Senseman ____________ __ Dec. 3, 1935 Carter ______________ __ Mar. 15, 1949 v2,609,150 Bludeau _____________ __ Sept. 2, 1952 25 2,789,772 2,826,370 2,889,119 WilliarnSen __________ __. Apr. 23, 1957 Weston ______________ __ Mar. 11, 1958 Andreas ______________ __ June 2, 1959 screening the thus-formed mixture so as to separate the 30 20,115 Great Britain ______________ __ of 1913 40 and 160 mm. ; subjecting said Wetted raw material With out prior impact comminution to a ?rst impact comminu tion at a ?rst predetermined impact velocity so as to form of said raw material a mixture of clay enriched larger FOREIGN PATENTS particles and potassium salt enriched smaller particles; same into said smaller and larger particles; subjecting the thus separated clay enriched larger particles to a plurality of successive second impact comminutions at second ve locities being greater than said ?rst impact velocity so as to form successive mixture of clay enriched larger par ticles and of potassium salt enriched smaller particles; screening after each of said second impact comminutions the mixture of larger and smaller particles formed in the 76,400 Germany _____________ __ July 27, 1894 697,309 Germany _____________ __ Oct. 10, 1940 OTHER REFERENCES Dana’s Manual of Mineralogy, fourteenth edition, pp. 180, 186 and 323. Handbook of Chemistry, by Lange, ninth edition, pp. 1101 and 1102.