BE623008A - - Google Patents

Description

       

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 EMI1.1
 

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    Removal of impurities and separation of potassium hydroxide during the production of potassium permanganate.



   The present invention relates to a process for removing impurities during the production of potassium permanganate and also for separating potassium hydroxide. In particular, a large proportion of the impurities in a product stream is converted into potassium hydroxide and the resulting caustic solution is of great utility as a recycle in the overall process of producing potassium permanganate.



   In the known procedures, the manufacture of potassium permanganate (KHnO4) from manganese material, such as manganese dioxide (EnO2) contained in many natural minerals, essentially requires two different types of oxidation stages. which all require the presence of hydroxide

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 EMI3.1
 potassium and an oxidizer. 1 aert r a cor stages cohort the production of potassium ae rsncanate VI (K2MnO 4) and t. vauel-
 EMI3.2
 lly the formation had l! U1ngéJlllitt: V of potassium (Kl1n04) intermrd1a1.1
 EMI3.3
 re.

   The second of these stages consists of an electrolytic oxidation transforming the mangtU1.d.t.> VI of potassium into a small quantity of potassium. These two oxidation studies can be represented
 EMI3.4
 in substance by the following equations:
 EMI3.5
 
 EMI3.6
 The operation represented by the içuration (1) is an oxidation
 EMI3.7
 high temperature tion which is carried out using air or other
 EMI3.8
 gons containing oxygen and which is carried out in the presence of relatively concentrated potnSdUl.1 hydroxide.

   We know various procô-! ds for this ox: rdntion; for example, a process de za.bitzz: x consists of. produce the seen r.lpnfllnnte of potassium in -r111E; nt of the 3) -lfnges of! Solids formed from the minorai of 1'a.ngBu fe aloxide and potassium hydroxide, the solids having been ground into finer particles after an initial meiosis of the two components. The rr1..7.,: E is usually carried out at IIF-ir at about 2.15 C oc the water so sprayed internally on the ground solids. The oxidation according to {quE <t1on (1) is preferably carried out by conforming to more recent r! 'Oc {dS (it consists in adding the
 EMI3.9
 hydroxide ore of pot & if molten very concentrated and at
 EMI3.10
 introduce at high tonprture a g4z cor4-1-tr., t oa:, yyne.

   This
 EMI3.11
 oxidation to liquid phse is described in detail in the patents
 EMI3.12
 8r1cins n s 2,940,821; 2.9A0.822 and: .9.O.E.



  Whichever way the ore is o: xy ': 1' according to 7. 'Equation (1), the desired product is: 41 "1111" (nnte VI of potassium which then serves as raw material1: rI'; where Tf: & ct1f initiult for the lp.ctrolJ.t1que oxidation represented by the 4qurticn (2). It has been found extremely .fI.v.rntDgeux to perform this electrolytic oxydr.ticn by conforming to US Patents Nos. 2,843-517 and
 EMI3.13
 2.008.620.

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 EMI4.1
 The end product of electrolytic oxidation is
 EMI4.2
 ppnaaneanate from gata.iu :: qu. is obtained in the form of crystals from a concentrated mother liquor.

   This aqueous mother liquor,
 EMI4.3
 which is a saturated solution of potassium permanganate, also contains relatively high amounts of potassium hydroxide as well as alkali soluble impurities consisting of
 EMI4.4
 predominantly in potessiuri carbonate and in medium quantities
 EMI4.5
 neural or in traces of compounds such as potassium silicates.
 EMI4.6
 



  , potassium aluminates, potassium phosphates. deß van.a.-; potassium dates, potr-ssium molybdates, potassium a.rsdniates, etc. The separation of the potassium hydroxide and the other impurities of the peznnr, n4nate de notas .it does not raise any particular problem so much, that the crystals of the potassium permanganate are easily isolated, for example by centrifugation. , of the mother liquor in Inquelle the in.purities are dissolved, your
 EMI4.7
 
 EMI4.8
 However, the treatment of the mother liquor poses a very serious problem.
 EMI4.9
 serious because it is extremely important to recover the hydra-
 EMI4.10
 # potassium oxide it contains, as well as 1 non-crystallized potassium permanganate and small amounts of -manger-ate VI
 EMI4.11
 
 EMI4.12
 of potassium included.

   2 Therefore, it is necessary to recy- ring the mother liquor at other points of the sown process, if this mode j
 EMI4.13
 operation leads to an accumulation of unwanted impurities in the overall process.



  We know that in the industrial production of permanga-
 EMI4.14
 potassium hydroxide, only about 40p of the total amount of potassium hydroxide initially introduced, usually under
 EMI4.15
 form of technical caustic potash, serve \ shoe product
 EMI4.16
 final. The remaining 60% n'hydroxide potssiur: circu !, E7n. in the process, for example in aqueous solution, as a reaction medium. The reuse of this considerable a.cês ah.'ro'de of potassium is important from an economic point of view cLs it is necessary, moreover, to separate the p'.r: C :: 3naZ2é tC and the inanrinrtc- from -pot - r;, 'a
 EMI4.17
 

 <Desc / Clms Page number 5>

 
 EMI5.1
 which remain in solution in the, qeumza subjected to crystallization.

   This mother liquor cannot, however, be rpeyclde directly, without having been partially freed of the alkali-soluble purc t.es such as carbonate.
 EMI5.2
 potassiua, which accumulate during each operating cycle *
 EMI5.3
 For example, if the concentration of eartK> ftj <1; e of potassium dÓ, pa: 18e 45 g per liter or already 40 g per liter, '-e. yield of desired product and the purity of the latter unfavorable etrect6p bridge. It is preferable that the concentrations of 11r.pureMs are much lower. Therefore, a continuous operation to remove these impurities has long been considered essential for the production of potcsQ, uzn permsnganste.



  The potassium carbonate and the putrem impurities come in part from the ore, from Btigenpe oxide which is never absolutely sterile infancanese dioxide: in fact, when air comes into contact with the solutions of Potassium hydrochloride during the process, new amounts of: .At.s: aur carbonate are formed.

   The ore contains small amounts of other inpurets which are insoluble in the solution of hyc]; roxr4e of potcssiuij sour.:ise the oxidation in the ol1ftit \ H and which are elif thin in this st & by a classical filtrate. These soluble iwpuretis tn "riinerai are in particular Poe CaO, MgQ, 8aQ, Cu, k'la, P,
 EMI5.4
 Ni and CO as is or combined *
 EMI5.5
 one proposed various processes to eliminate the colublen impurities in the alkalis and in partteu..r the carbonate of potap, # siur.!? all these processes:; 13 resort to a salting of the carbonate of pct! -. SS1UCl using lime, that is to say <3a0 or Cr, (Ol) ze follows
 EMI5.6
 the following equation goes:
 EMI5.7
 
 EMI5.8
 For example we proposed de) tt .. 'ls.n.E #' r 9 the ehnux to raw D1inf.trl1i, or Ir.pur, before the prenier stc-de d1oxyq.úttç.n.

   This rrcao.d: would be

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 EMI6.1
 very impractical because of the difficulties offered by the mipul & - #tion of large quantities Cxt ninersi during cactst.f.ldt3, on and removal of impurities, far elsewhere a preliminary processing of the raw rainerai does not elitninerlit not the bus. bonito de potsssiun nor other impurities 4llor.,. 'e: s During oxidation it, meie.



  A more common method of removing carbnte from? potassium and others i) 'soluble ipuretus riar.µ ,, les rz.c..7.i consists in concentrating the recycled potassium hydroxide solution to evaporate the enu to a dennit4 of about 1.575-1.585 to which
 EMI6.2
 the natural proportion of the impurities precipitates from the solution.
 EMI6.3
 



  Mange.na.te and potassium permanganate also precipitating from solution. precious materials are like the precipitated impurities, by filtr.tîo.-t in the form of solids which can be called "vapor salts". To avoid the loss of precious products and recover as much 'hydra: yae of potassium as possible, the salts collected by filtration, or salts: evaporators' *, are redissolved in water and csustift''s by Ca (OI4) 2 at, lbu ... t3Cax.

   The KOH solution obtained must be relatively c3.ue, '$ tent given that the cs-uctification reaction' (3) is reversible and that the trr: ri.sfor.x.tion of ir-puretr's in KCH 'decreases when the augneute KOH concentration. Consistent Éar
 EMI6.4
 
 EMI6.5
 after m: pzrttirr impure solids such as Ca3o 3 $ of the solution> concentration by evaporation is necessary to obtain a solution of K03 sufficiently concentrated to reuse it in the prci .: overall.



  An objection that can be raised arropos de la caustifica-. The main reason for the salts of the vaporizers is that the level of impurities in the whole product is relatively high. It is not possible to carry out a sufficient -vzportation to separate all the products. iripure salts, and relatively large amounts of impurities continue to be recycled. In addition, hydrochloride is at the heart of the rationale for "evaporator salts"

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 EMI7.1
 results in a significant loss of K2L.rno4 "In addition, it is necessary to immobilize these capital i" 'roTnts for the equipment of watering, filtration, calcium carbonate formed, unchanged lime and other, - - i, ^ :, urt. =:;: mi lc * jfue ± 5, and Ptv, 'r'oN1.t10n of water in order to rc: concentrate the solution of n.0ü.

   The thoughts of, v "r ('! Rlit1on eu'entr'nh7 these are particularly high because of the .'round that" nt; ft, of water which must be \ 11I1hl' (! - ' Abor. to precipitate the fes salts ('v :: porl! túurcff, then to reconcentrate the solution of KOB in order to recycle it to the process of. i. Ct1use of these numerous drawbacks, we have also proposed s ..p:., rer so: tr.nousc: 1ent the "salts of ;. éV: 1!, or tpursl '/ of xn3ere to obtain caroonate ie potassium cosi # e final product. However, this way of procyutr is of little interest, since it does not stop the complete carbonization of all the adherent rot hydroxide, seium, reduction and 1 ', 11'11trir.t1on of the rennate- as well as the' 1; 11I1im. tlon due "des l'1u :: dnates, etc.

   Not only was part of the manganate perished, but in addition the fuel, the pot & stiuri obtained did not have a value sviffisfjrxtc: ;; 01.1: 'to compensate the expenses incurred to prepare it The present invention aims ; of procures.- a procedure for Ü1t. \ 1ner las 1 '-: PUN-t.ÚS and to separate the hyuroxide of j! otassl'W: .1 during the oxidation of a mine- r: 1.1. oxide of.: =:,. nganè :: l (> en; '; l.?r=tangogén.u:.te pot, s! -4um, which significantly avoids the various disadvantages of prou nnte-
 EMI7.2
 laughing;
 EMI7.3
 from a1 :: rl.i'lUCr senfiblet1..nt the rate of i ^ purc: tw: soluble in alcnl1s during the procf.d, globrl of production of per- E.'F.: 2, C ', T; 7 ^ t'G 'of potassium;
 EMI7.4
 to avoid the loss of valuable products in the whole
 EMI7.5
 system, for example psr hydrolysis that K.:.-no 4 ru course of 1, crusti-
 EMI7.6
 fraction;

   

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 EMI8.1
 to carry out in the best conditions the separation and recycling of the hydroxide of: 9otssiu :: J. while avoiding high expenditure S: 'fV;' Or ';' 'Cnj d' (; vi ter difficult and costly filtrations aimed at separating ir.purites s 'n;.' sir4 clec in c.if drills points of the pro- c .; "production loORi ... I '; 1. :: Jlznate de potassiun.



  These and other objects of the invention, thus its advantages, will become apparent from its description below given with reference to the appended drawing which illustrates, in the form of a table of :; arche, the overall production process for potasium perwan ^ Fnate., and notes the specific treatment aimed at removing impurities and s6pring the hydroardium from pot & ssiua ..
 EMI8.2
 



  The present invention is based on the discovery
 EMI8.3
 that it is possible to: t1.fie directly the 11q1.1eUr-llère whose
 EMI8.4
 potassium permanganate is crystallized after oxidation
 EMI8.5
 in two stages of the ore of o: cananse cycle. This mother liquor consists essentially of an aqueous solution of potassium hrrr1ro.rJde, potassium permanganate, potassium rvmi1arate VI and potassium carbonate. Small amounts of silicates, alundants , vanadates, phosphates, i: tl.y1> â.a-tes, arsenates and other potash builders can also be dissolved in this mother liquor and taken with lt; carbo n, te of potassium, they constitute the solublec impurities in the alkalis which are transformed into potassium hydroxide by
 EMI8.6
 
 EMI8.7
 caustificat10n by CaO or Ca (OH2).

   Preferably, the crystalline mother liquor is made with water before causticizing.
 EMI8.8
 tion, in order to regulate self gneuc kill the concentration of K011 and ia- puret0s. Testing should be carried out at a pot hydroxide concentration <': S: 3.!. U:.! 4 * at 1: oins 30 and preferably "'; rf:; This of at least 60 g per liter, these concentrations are those of 7. your initial li, ueur - ::: rc after 1' # 'ilution r-¯3 -.' c?: 1. ;;. '. v ::!: +; ue le i! npuretles soluble dais les;'. Lc '\ lis be t: rl1n ::: fo ,:,.': ,: in

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 EMI9.1
 , potassium hydroxide.

   During there cr-, ustiCietLttn, the concentration
 EMI9.2
 in must remain general.i'ënt between -e, 0 and.;: 0 g per liter and preferably between about 60 and here gp; .r liter, the rutction ctenl carried out at 55-9: C and of: r6f. .rf'nc4 1 about 70-80 C This bond is ::. v:, nt; 1.Z (; Uer1únt efi'ectu,: e we about the normal pres- ion, under about 1 atmosphere, and under
 EMI9.3
 suitable agitation *
 EMI9.4
 Another 0.; couverturel :! ,: the art on which the invention is based is that after its cal.1t: lf; tcú.t1on take the aforementioned process, the lif'ueur - ?: er-3 'l1Juf; e can be \ ltUÜS'1Q directly oo "Me n1l1eu of leaching for the eiit treatment of 4ZHnO 4 obtained cortne product cte Itl preisicre oxidation 5trLvr, nt .'v.aurtion (1) above.

   This leaching should have a concentration on oh of about 40 to 130 g pt.r liter and prcr.rc: nce of about 70 to 110 g per liter, this condition can be easily fulfilled for the liqueur .. ;; èrc cu: .tü'.e. Thus, 1 rh ... ns the Frac: ci glo ... ber, it is possible to recycle part of the 1:!. QueUT-! F. :: L '(1 to lixivier the Y .: 4: 'In 4J1 before its ulectrolytic oxidation, and of tr.n:; 1'or.1Gr in r.:.;e ter, 1P1: I the soluble iapuret-is ut: t1:> the alkali, COlr .... (: potassium carbonate | 3iu.-n, in hydroxide of P () ts: liu '(l, de :: 1.: ni0re o "inintenip a level of impurities during the stage of electrolysis of rro: d :. addition of CaO or a (Ca {! aH) 2 for cHust1ficfltlon does not adversely affect the release,: .. l: ne in the case of excess considerable, and these arntï. ¯zr c;

   ustf.ficut3.cn are separated fttc..c¯r: ent pHr x ult 1 "h: ur" filtration, so that they do not undergo the oxidation stage; electrolytic.



  The excess J.'Ç;!. Í ':,. Nt custirtMl, t is dc filtrated, - in nLw t': 1; Js que 1 (. I''ï) uretos .n. = O.uia. F.;: For.ue3 during the cc.ustli'Lcatl (1n and in mô ,, '1c time that the insoluble iapurettis of the ore, which -avit flitratjions S'} J :.) '"2 ± difficult.

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   The overall process for the production of potassium permanganate and the use of causticization according to the invention, in conjunction with carrying out the process, are illustrated by the accompanying process chart which represents a preferred embodiment of the invention. invention. It goes without saying that the stages of the overall process other than the causttfication according to the invention and its combination with the overall process are known and that it is therefore possible to modify the embodiments or to resort to variants of execution of these known stages without departing from the scope of the invention.



  For example, the specific oxidation operations according to equations (1) and (2) above can be carried out in any known manner and under a relatively wide range of reaction conditions, without avoiding the need to eliminate. alkali-soluble impurities and to separate the potassium hydroxide. For this reason, in the description of the operating table, particular reference is made to the conditions which relate essentially to the new processes for caustitizing and recycling the mother liquor according to the invention. Furthermore, the overall process is described here only by way of illustration.



   According to the operating chart, the overall process is essentially continuous and can easily be adapted to automatic control. The first stage of the process is represented by the oxidation of a manganese oxide ore in a suitable reaction vessel 1, or in a series of such vessels, preferably by liquid phase oxidation carried out in sodium hydroxide. molten potassium with a concentration of 65-90% (by weight). Air, or other oxygen-containing gas, is used for this oxidation, and fresh KOH and recycle KOH can be introduced and adjusted to the desired concentration.

   The K2MnO4 produced by the reaction precipitates and forms a suspension which can be fed to separator 2 to collect the solid product.



  At the high concentrations of KOH used for an oxy-

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 EMI11.1
 dation in liquid phase, X e 0 4 is relatively insoluble, more than 1Ilm.e certain impurities such as x2co3 and other analogous salts. Consequently, the KZHn 4 obtained is not present in pure form, but contains the so-called "alkali-soluble" impurities, that is to say potassium carbonate and cPautI'C8 minor impurities such as silicates, potassium illuminants and / or phosphates. In addition, there is normally a small amount of completely insoluble impurities or by-products from elements such as iron, calcium, magnesium, barium,
 EMI11.2
 copper, plo-rbp phosphorus, nickel or cobalt present in minor proportions in the ore.

   These insolubles are hereinafter referred to as "ore impurities".



     The liquid phase oxidation in the container 1 usually makes it necessary to separate the concentrated KOH solution from the solid product, and this solution can then be recycled.
 EMI11.3
 on liquid phase oxidation, C0! l1! 1e indicated. When the ore is roasted in an almost dry state, it is clear that the product obtained is relatively dry and does not require such additional treatment.
 EMI11.4
 



  The impure r6eo4 obtained is then confined with a more dilute solution ae KOR in which dissolve the manganate and the impurities such as potassium carbonate, but not the impurities of the Muerai This operation is carried out in a suitable mixing vessel 3 by adding a Diluted and caustic mother liquor from a heated vessel 11. This mother liquor used for leaching is described in more detail below, but with regard to leaching, it is prepared in such a manner.
 EMI11.5
 that its g0i3 content is 30 to 120 and preferably 60 to 100 g per liter.

   The crude K2y'no4 produced is added to this 11 (urea so as to obtain a K.v04 concentration of cpvron 100 to 200 g and preferably of about 10 to z0 g per liter. Leaching of the crude # Xiffi04 can be obtained. be driven to a t1tpÚ'ature of approximately 1.5-9 "C.

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 EMI12.1
 and preferably about 6O-S0 C. Under these conditions; the hydrolysis of Ki'.nO 4 is minimum, being leached in a concentrated solution suitable for electrolysis. the leaching solution is brought from vessel 3 by a suitable pump 4. into a filter or a series of filters 5 for separate all solid impurities, including those produced during causticization from the mother liquor.

   If only one filter is used, the filtered leach solution containing the
 EMI12.2
 "Dissolved 2MnO4 must be collected separately from the wash water to allow better control of the concentration of the dissolved substances. Separate filtrates can of course be easily obtained also by using a series of two or more filters of the Conventionally, the filtered leach solution from filter 5 is fed to mixing vessel 6 where the concentration of the different constituents can be precisely controlled to obtain the best results during electrolysis.



  The solids of filter 5 are washed and discarded, and the wash water
 EMI12.3
 is preferably recovered and reused for the causticization.



  The solid impurities of filter 5 consist mainly of CaCO1 in Ca (OH) 2 in excess and insoluble impurities of the ore, Virtually all other alkali soluble impurities eg calcium silicates are also removed at this stage .



   In mixing vessel 6, the leaching solution
 EMI12.4
 is preferably diluted with at least part of the mother liquor L and the third precipitated salts, from an evaporator 12, can also be added. If necessary, a little more water can be added at this time to reduce the amount of 7.if; un: i '-: rz: w recycled directly to the mixing vessel * However, the amounts above 'p: .Ú "water entries are advantageously reduced to ninimun to avoid excessive costs of evaporation.



  The siclange in the rcci? 3er.t 6 must be carried out so that the obtained solution has a KOH concentration of about 80 to 190

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 and preferably 120 to 170 g per liter, and a concentration of
 EMI13.1
 2Mn0 of about 35 to 80 and preferably 50 to 60 g per liter. The amount of WMO 4 in this solution is kept as low as possible, preferably less than 20 g per liter.
 EMI13.2
 



  Therefore, the amount of impurities soluble in alkalis, such as K2co3e, must be reduced to a minimum to avoid poor yields,
 EMI13.3
 electrolysis and the formation of an impure product, and the solution of the mixing vessel 6 should not contain more than
 EMI13.4
 40 g per liter of such impurities and it will preferably contain less than 30 g per liter.



   The solution of the mixing vessel 6 is then sent by a pump into the electrolytic cell 7 to oxidize the
 EMI13.5
 K2MnO4 to M.INO4 at a temperature of about 55 to 80 ° C, and preferably 60 to 5 ° C. As causticization and leaching are usually carried out at somewhat lower temperatures than those of electrolytic oxidation. , it is generally advisable to provide a means of heating the receptacle 6, this heating being possible, for example, by indirect heat exchange or by admitting live steam into the mixture. The construction and operation of cell 7 are described in detail in U.S. Patent Nos. 2,843,537 and 2,908,620.

   It is Important to avoid precipitation or crystallization of the permanganate of
 EMI13.6
 potassium in the cell itself, since this would result in a rapid decrease in the capacity and efficiency of the cell. In this connection, such undesirable precipitation increases with the amounts of alkali-soluble impurities which are present. in the cell, so that the efficiency during electrolytic oxidation is strongly influenced by the way impurities are removed :) in the overall process,
 EMI13.7
 The solution obtained in the electrolytic cell 7 is then brought into a crystallizer 8. or in a similar apparatus.
 EMI13.8
 to cool and crystallize the E²ùl04 produced.

   A suspension of

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 crystalline product in the mother liquor can be withdrawn continuously from the crystallizer and passed through a centrifuge 9, or a dialogue device, to filter or separate the crystals, the mother liquor (ML filtrate) being returned to the crystallizer. The cria- tou can be further washed in the centrifuge and then dried in dryer 10 to obtain KMnO4. The first wash water from the centrifuge 9 is preferably recycled to the process at a point where the solution must be diluted to avoid possible loss of adherent mother liquor. It is very advantageous to combine this wash water with the filter wash water to dilute the mother liquor (MMI) for causticization.



   Crystallizer 8 is also constructed and preferably used as described in U.S. Patents Nos. 2,843,537 and 2,908,620, according to which the hot solution of cell 7 is first fed to a gas separator, then raised, using a pump, via a riser, connected to the crystallization vessel, and introduced into an evaporator maintained under reduced pressure by a condensing and vacuum installation.



   Evaporation and refluxing of the hot product solution creates a state of supersaturation with KMn O4 in the solution, which then disappears as the solution from the evaporator descends into the mother liquor of the crystallizer. Seeds or small crystals of KMnO4 are always present in the mass of mother liquor of the crystallizer, crystal growth being able to continue on these checks. Larger crystals settle to the bottom of the crystallizer to be withdrawn as a suspension, while the recycle mother liquor can be withdrawn near the top or the liquid surface of the crystallizer.

   The mother liquor from the crystallizer is cooled to about 50 to 30 C and preferably to about 38 C,
In general, the mother liquor withdrawn from the crystallizer as a recycle stream has a composition which varies within certain limits depending on various factors, especially the proportions.

 <Desc / Clms Page number 15>

 
 EMI15.1
 Reactive tones allowed Onn, the cell the <:: trolyt1qte, the rer.4e * & Kt of the cell itself, the concentration of potassium hydroxide and the temperature of the solution, the amount of soluble impurities in the alkalis which can accumulate and the amount of KMnO that is actually crystallized and separated from the mother liquor.



  It goes without saying that it is advantageous to separate as much potassium permanganate as possible from the crystallizer, but in practice it is impossible and not necessarily desirable to completely free the mother liquor of potassium permanganate. Thus, it is advantageous to recycle small amounts of KMnO4 to various
 EMI15.2
 stages of the process, for example to avoid hydrolysis of K2Mn 4 "The main consideration is therefore to operate the crystalliser so as to separate a maximum amount of potassium permanganate without precipitating other solids, in particular impurities, and thus avoiding complicated and tedious operations of purifying
 EMI15.3
 cation of the isolated product.

   In other words, the purification of potassium permanganate is substantially complete after crystallization and centrifugation of this product from the mother liquor. !
During the normal performance of the electroly- oxidation
 EMI15.4
 crude IClfu 4 ctu tick which has been 11x1V1é in a solution of potassium hydroxide, the boron liquor withdrawn from the crystallizer in order to be recycled can have in accordance with the invention, approximately the following composition
 EMI15.5
 
<tb> Concentration <SEP> Crabs <SEP> per <SEP> liter
<tb>
 
 EMI15.6
 General preferred gcame range Koli 120-200 130-170 A.

   0+ l - 65 20-40
 EMI15.7
 
<tb> KKnO <SEP> 10-30 <SEP> 15-20
<tb> Soluble <SEP> impurities <SEP> in <SEP> the
<tb> alkalis <SEP> 5-40 <SEP> 10-25
<tb>
 
 EMI15.8
 It should of course be noted that these concentration values are taken after establishing a certainty in equilibrium in continuous operation. The amounts of 10u, K.nO 4 and KMnO 4 are relative. stable and determined by the good

 <Desc / Clms Page number 16>

 operation of the cell and the crystallizer, while there may be a large fluctuation in the amount of soluble impurities in alkalis, such as potassium carbonate and potassium silicates, aluminates and phosphates and other similar salts, due to the quality of the manganese oxide ore used in the process.



   The recycled mother liquor is preferably separated into three streams, one part, Ml¯I, being recycled directly from crystalline 8 to mixing vessel 6 to adjust the aqueous mixture just prior to electrolysis. A second part of the mother liquor, ML-II, is recycled to the causticization vessel 11 and used for leaching in the vessel 3, as described in detail below.



   The third part of the mother liquor, ML-IJI, is recycled to an evaporator 12 where a sufficient quantity of water is withdrawn to precipitate in the usual manner, the "salts of the evaporators", these precipitated salts being returned to the mixing vessel. 6 directly or after redissolution. The concentrated KOH solution formed can be reused in the process, preferably by recycling to the first stage of oxidation of. manganese oxide ore, and it can be stored temporarily in any suitable container 13.



   It will be found that dividing the mother liquor from recycle into three separate recycle streams provides great flexibility in carrying out the overall process under optimum conditions. Even more important thing is that the level of impurities in the system can be. carefully regulated by causticizing the second stream, ML-II, so that the alkali-soluble impurities turn into potassium hydroxide. The proportions in which the mother liquor is divided into three recycle streams are best established on the job by continuous determination of the level of impurities and the leaching roll concentration.

   It is desirable to minimize the amount of mother liquor recycled to evaporator 12 to avoid excessive evaporation expense.

 <Desc / Clms Page number 17>

 



  The operation of the recycling system can be such
 EMI17.1
 that all the mother liquor from the 8% crystallizer; first recycled without any treatment, such as the ML-I iridic, to mixing vessel 6 until the level of impurities reaches the maximum allowable value. The ML-II causticizing stream and / or the ML-111 evaporating stream can be used intermittently as the level of impurities must be again reduced, and the KOH concentration raised.

   In varinte one profes to carry out all the procedure in a continuous way in the conditions of equilibrium in order to maintain a relatively constant level of impurities, between the limits indicate and to supplement in a continuous way the contribution of concentrated solution of KOH free of impu-, rotés. This variant allows more precise control of the process and avoids difficulties in correcting the concentration of the solution with a view to electrolysis. When working in these equilibrium conditions,

     the recycle mother liquor is advantageously divided into three separate streams in the following approximate proportions
 EMI17.2
 1 in VQll1ln'l 14L-I (recycling C.r84 '.. w. Waw. S. W ..... 78 Mi-11 (recycling of caust1t1cat1on) ......... 10 MOL-111 (evaporation recycling) ............ 12
 EMI17.3
 Causticizing the liquor recycle stream-more
 EMI17.4
 (ML-11) and its re-admission to the process as a medium here.

     viation constitute the essential improvements according to the invention and these operations are carried out in the following manner
The mother liquor of crystallizer 8 which has the concentration
 EMI17.5
 above in dibsousp components is combined with washing water from the ore impurity separator to one or more filters 5 and supplied to a suitable reaction vessel there *
 EMI17.6
 Wash water from the centrifuge 9 can also be combined with this liquor-more to allow maximum recovery of materials of interest. The mother liquor is thus diluted by

 <Desc / Clms Page number 18>

 way

  adjusted to establish the various concentrations required
 EMI18.1
 in order to properly water and convert the alkali-soluble L..I, urt4s to potassium hydroxide and to use the purified solution obtained for the leaching * 2n:.; rra, 7.,, to 5 parts of mother liquor are diluted with 5 to 7 parts z 't4U, parts being by volume.



  The dilution of the mother liquor before the caustication is therefore carried out so that the aqueous solution obtained has the following concentrations of dissolved constituents:
 EMI18.2
 0: axr, zes .r I t "" 2 = e. rL .Qi! l :: y; .o rbf6rJ9 KOH 30-110 60-100 XzMn 4 - 6ü 25-35 KMno 4 10- 70 20- 50
 EMI18.3
 
<tb> Soluble <SEP> impurities <SEP> in <SEP> the
<tb>
<tb> alkalis <SEP> Up to <SEP> 40 <SEP> 10- <SEP> 20
<tb>
 
 EMI18.4
 The KOH concentration is preferably maintained at a value of at least 60 g per liter to avoid undesirable hydrolysis.
 EMI18.5
 of K04 and also to avoid additional evaporation costs when causticization might not give a sufficiently concentrated KOH solution.

   However, a high KOH concentration should be avoided, because this would adversely affect the equilibrium of the causticization reaction and, in most cases,
 EMI18.6
 Apart from cases> -it is advantageous that the KOH concentration does not exceed 100 g'par.litre, and is preferably less than eO g per liter. When the level of impurities is relatively low, higher KOH concentrations may be permitted. The concen-
 EMI18.7
 trations in z: z-r.n 4 and in KMn 4 depend essentially on the correct functioning of the electrolytic cell and the conditions
 EMI18.8
 saturation of KMn 4 in the mother liquor of the crystallizer.

   Impurities,. Soluble in alkalis, consisting mainly of
 EMI18.9
 X2C031 are governed by the amount of impurities of this nature introduced into the system and by the efficiency of the caustic treatment.

 <Desc / Clms Page number 19>

 
 EMI19.1
 ! 1cat; tone. Therefore, it is important to dilute the aerated liquor of the crystallizer so as to obtain the KOH concentration.
 EMI19.2
 essential while allowing .aux concentrations of other substances to vary over a relatively wide range.
 EMI19.3
 



  The diluted mother liquor is then put at xGsg3x in a r6ci <
 EMI19.4
 pient 11 with lime or calcium hydroxide, according to equation (3) above, at a temperature of about 50 to 9500 and; preferably 60 to 80 ° C. The watering vessel may be provided with a suitable agitation device to achieve satisfactory mixing and is preferably heated to ensure precise control of the temperature.

   For continuous caustification it is also useful to preheat the diluted mother liquor to a temperature close to that of the reaction. The causation reaction takes place more easily if lime or calcium hydroxide is used in excess. for example at a rate of approximately 0, 5à
 EMI19.5
 1.0 part by weight, as Ca (Ofi) .j, per part by weight of alkali soluble impurities expressed as K2CO3.



   Under the above conditions, the caustification of the mother liquor is capable of converting the soluble impurities in the
 EMI19.6
 alkalis to potassium hydroxide, and surprisingly the presence of KMnO 4, AtMnO, and relatively high concentrations of & OH does not adversely affect this reaction.

   Moreover, the hydrolysis of K2MnO4 is negligible and there is no noticeable loss of these valuable reagents. In normal operation, the causticization reaction should be carried out in about 4 to 24 hours, and preferably in about 4 to 10 hours depending on the amount of impurity to be converted to KOH. small modifications can be made to the causticizing apparatus and process without departing from the scope of the invention. For example, the overall work can be simplified if two separate vessels are provided for the causticization, so that the recycled mother liquor can be continuously supplied to one of the vessels while the reaction is taking place in one vessel. filled in beforehand.

   Alternatively, causticization can

 <Desc / Clms Page number 20>

 be carried out continuously in a reaction column or in a series of stirrer vessels.



   A particular advantage of the invention is that the caustified mother liquor can be used directly as a leach solution for the treatment of the crude K2MnO4 obtained during the first oxidation stage. The caustified liquor is therefore preferably supplied from the reaction vessel 11 into a reservoir (not shown) interposed between the vessel 11 and the leach vessel 3. When the overall process is not continuous, the caustified mother liquor serving. Make-up liquid can be drawn from the tank as required for leaching.



  In the case of a continuous feed of crude K2MnO4 and a continuous causticization there is always a fresh feed of leach liquid and the overall process is substantially continuous.



   To serve as an aqueous leach liquor, the mother liquor should be causticized so as to bring the KOH concentration to at least about 40 to 130 and preferably 70 to 110 g per liter.



   The amount of soluble impurities in the alkalis transformed into
KOH must also be high enough to maintain a ni. veal impurities not exceeding 40 g, and preferably less than
25 g per liter of solution subjected to electrolytic oxidation.



   For example, it is particularly preferred to caustify to such an extent that the obtained leach solution has an impurity concentration of about 8 to 15 g per liter, calculated as K2CO3 At this time, the concentration of other soluble impurities in alkalis, such as potassium silicates and aluminates and the like, is practically negligible. '
The causticization reaction produces calcium carbonate (CaCO3) as an additional impurity, along with calcium ailicates and:

  } Calcium aluminates and other corresponding corresponding salts referred to as all calcium impurities. "However, these calcium compounds are insoluble in the caustic mother liquor.

 <Desc / Clms Page number 21>

 trusted and remained so during the leaching. Therefore, these new insoluble impurities are easily separated by the filter (s) 5 along with the usual insoluble impurities of the ore. In addition, any excess of Ca (OH) 2 is also removed in the form of a solid impurity by this filtration.



   One of the discoveries of the invention is the favorable coincidence which allows the dilute and causticized mother liquor to be readily used for leaching. This process is possible, according to the invention, because the degree of dilution of the mother liquor which is necessary for the causticization corresponds approximately to the concentration of KOH which is required for the leaching. In addition, the liquor -mother can be brought by dilution to
 EMI21.1
 a minimum: OH concentration for better caust1! 'ioat1on because the subsequent transformation of. 3 impurities into KOH restores the most suitable KOH concentration for leaching *
The invention is further illustrated by the following non-limiting examples of a preferred embodiment of the invention.
 EMI21.2
 



  EÁl'1-LP 1..1 :: ... L. = This example is carried out to establish the efficiency of the
 EMI21.3
 cauBtit1c8tion reaction and the usefulness of the resulting solution as a leaching agent *
About 1 liter of potassium permanganate mother liquor is diluted with an equal volume of water to obtain an aqueous solution of the following composition!
 EMI21.4
 'T2.5 gas.! .4Ull; 12.8 9 / 1- KMnO 8.3 rll. KMnO and lez g / l.

   K2CO3 "A quantity of 45 g of quicklime (CaO) is added to this dilute solution and the resulting mixture is then stirred for about 8 hours while maintaining the temperature between 60 and 65 C. The reaction mixture is analyzed periodically and the results are presented in the following table:

 <Desc / Clms Page number 22>

 
 EMI22.1
 
<tb> Time <SEP> elapsed <SEP> K <SEP> CO3 <SEP> KOH
<tb>
<tb>
<tb>
<tb> (hours). <SEP> zrams / liters
<tb>
<tb>
<tb> 0 <SEP> 17.4 <SEP> 72, <SEP> 5
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 2 <SEP> 13.0 <SEP> 78.9
<tb>
<tb>
<tb>
<tb>
<tb> 4
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 8 <SEP> 6.0 <SEP> $ 2,, 7
<tb>
 
During this 8 hour reaction time, there was noticeable no change in the initial concentrations of K, MnO4 and KMnO4.

   The K2CO3 concentration falls by 11 g per liter while that of KOH increases by 10.2 g per liter.



  Theoretical conversion of K2CO3 would give only 9.3 g of KOH per liter and it has been established that the additional 0.9. G of KOH per liter is obtained by reaction with silicates, aluminates, phosphates, vanadates, molybdates , arsenates and other potassium salts.



   The concentrations of dissolved constituents in the resulting causticized solution are well within the limits necessary for a leaching solution and the level of alkali-soluble impurities is low enough for a very satisfactory electrolytic oxidation after leaching a crude K2MnO4. * EXAMPLE 11 - According to the accompanying drawing, a continuous process for the production of potassium permanganate is carried out in the manner illustrated and after having reached a quasi-equilibrium of the various streams of the process.
The causticization operation of the overall process begins by withdrawing a mother liquor from crystallizer 8, this mother liquor being a saturated aqueous solution of KMnO4 at a temperature of about 38 ° C. and having the composition next:

   160 grams / liter KOH 20 K2MnO4 20 "KMnO4 20" "K2CO3

 <Desc / Clms Page number 23>

 One part of this liquor-pond (ML-II) is recycled at a rate of 22.7 liters per minute to the causticizing vessel 11 and diluted continuously with approximately 18.9 liters per minute of water for washing the filter 5. and an additional 7.6 liters per minute of water from another source, for example the wash water from the KMnO4 separated in the centrifuge 9.

   About 0.36 kg / minute of quicklime (CaO) is also added to the water-forming vessel 11, which represents an excess of about 100% for the reaction with potassium carbonate and other alkali-soluble impurities. which are present in relatively small amounts.



   The caustification reaction is carried out at a temperature of 70 ° C. by heating the vessel 11 with steam and maintaining constant agitation of the reaction mixture. The caustic product stream is withdrawn continuously so as to maintain a constant agitation of the reaction mixture. volume approximately constant in the reaction vessel, i.e. at a rate of approximately 49.2 liters per minute and fed into the leach vessel 3.

   The residence time in the causticizing vessel is long enough that the causticized product has the following composition!
80 grams / liter KOH
10 "" K2CO3
30 "" K2MnO4
30 'KMnO4
A crude K2MnO4 obtained in the first oxidation stage of the process is combined and mixed with the diluted and caustified mother liquor in the leach vessel 3 which is maintained at a TEMP of about 80 C. The mother liquor not only dissolves the liquid. KMnO, from the oxidation product, but also K2CO3 and other alkali soluble impurities that contaminate this crude product - In addition, a small amount of potassium hydroxide accompanies the crude K2MnO4 and increases the alkaline concentration of the solution leaching obtained.

   The insoluble impurities of the ore, calcium carbonate and excess calcium hydroxide are carried away

 <Desc / Clms Page number 24>

 by the leach solution without being dissolved.



   The leach solution is passed through filter 5 and introduced as a filtrate into mixing vessel 5 at a rate of 56.9 liters per minute. This leach solution has approximately the following composition, with respect to dissolved substances).



   95 grades / liter KOH
20 "n K2CO3
130 '' K2MnO4
30 '"KMnO4 The insoluble impurities are separated by the 5 eT filter after separation of the filtrate they are washed with 26.5 liters per minute of water and discharged from the system. The washing water is recycled to the caustification at an appropriate rate. of 18.9 liters per minute as indicated above, the wash water being collected in a series of stages, so that only the water of the early stages must be recycled to retain the dissolved substances of interest.



   The filtered leach solution from filter 5 is continuously combined in mixing vessel 6 with recycle mother liquor (ML-II) from crystallisol 8 at 246 liters per minute. It is preferable to also add to this mixing vessel the small amount of salts precipitated in the evaporator 12. The combined streams are then heated to about 65 ° C and passed through cell 7 for the transformation of K2MnO4 into KMnO4, A suspension of KMnO4 crystals is separated from the eristallisor 8 and passed through the centrifuge 9, the filtered mother liquor being returned to the crystallizer.



  The crystals are then washed with about 7.6 liters of water per minute to separate the adherent mother liquor, and this wash water is recycled to the causticization in 11. After washing again followed by drying in the dryer 10 at about 120 ° C., a very pu KMnO4 is obtained at a rate of about 53 kg per minute.

 <Desc / Clms Page number 25>

 



   To again concentrate part of the mother liquor, a recycle stream (ML-III) is passed to evaporator 12 at a rate of about 34 liters per minute approximately to separate it from water, and then stored in the tank 13 to be reused in the first oxidation stage in 1.



   In the above description and examples, the term "alkali soluble impurities" denotes impurities such as potassium carbonate which are normally soluble in dilute caustic solutions, i.e. in aqueous solutions of potassium hydroxide, the R concentration of which does not exceed about 20% by weight. These alkali-soluble impurities are very troublesome in the overall process, because they precipitate in very concentrated caustic solutions' and even in more dilute caustic solutions, they tend to form on certain parts of the apparatus such as the cell. electrolytic deposits which are extremely difficult to remove.

   In. In addition, a build-up of soluble alkali impurities in the overall process ultimately leads to very impure KMnO4 and / or a substantial decrease in efficiency and yields.



   The present invention provides a very efficient means of removing alkali soluble impurities by the particular causticization process described herein, whereby the overall process of producing potassium permanganate can be carried out continuously and without costly interruptions. Further, the caustiflcation process of the invention eliminates the excessive filtration and filtration costs of separating soluble and insoluble impurities. As a result, a significant saving in capital and operating costs is achieved.


    

Claims (1)

CLAIMS. 1.- Process for removing impurities and separating potassium hydroxide during the production of potassium permanganate, characterized in that calcium hydroxide is reacted with a para-liquor consisting essentially of an aqueous solution of potassium hydroxide, mangante VI of potassium, potassium permanganate and at least one impurity-soluble in alkalis at a temperature of about 50 to 95 C to transform at least part of this impurity soluble in alkalis in potassium hydroxide. 2. A method according to claim 1, characterized in that reacting the alkali-soluble impurity with calcium hydroxide at a temperature of 60 to 80 C, 3. A method according to claim 2, characterized in that the alkali-soluble impurity is potassium carbonate. 4. A process according to claim 1, characterized in that the initial KOH concentration of the mother liquor, before the reaction with calcium hydroxide, is about 60 to 100 g per liter. 5. A process according to claim 1, characterized in that the KOH concentration of the aqueous solution during the reaction is maintained between 30 and 140 g per liter. 6. A process according to claim 1, characterized in that the KOH concentration of the aqueous solution during the reaction is maintained between about 70 and 110 g per liter. 7.- Process for the production of potassium permanganate by a two-stage oxidation of a manganese oxide ore, according to which a crude potassium manganate VI obtained in the first stage is dissolved in an aqueous medium of potassium hydroxide and potassium manganate VI is then electrolytically oxidized, in the second stage to potassium permanganate which is crystalline <Desc / Clms Page number 27> read and separated from a pond liquor consisting essentially of an aqueous solution of potassium hydroxide, potassium manganate VI, potassium permanganate and an impurity, soluble in alkalis and predominantly formed of carbonate of potassium, characterized by reacting calcium hydroxide with part of the mother liquor at a temperature of about 50 ° C to 95 ° C to convert the alkali soluble impurity to potassium hydroxide by caustification and the crude potassium manganate VI obtained in the first stage is leached using the caustified mother liquor. 8.- Process for the production of potassium permanganate by a two-stage oxidation of a manganese oxide ore according to which a crude potassium manganate VI obtained in the first stage is leached using a medium aqueous potassium hydroxide to dissolve potassium manganate VI and separate insoluble impurities from the ore, and potassium manganate VI is then electrolytically oxidized in the second stage to potassium permanganate which is crystallized and separated from a mother liquor consisting essentially of an aqueous solution of potassium hydroxide, potassium manganate VI, potassium permanganate and an alkali-soluble impurity predominantly formed from potassium carbonate, characterized in that calcium hydroxide is reacted with at least part of the liquor- mother by causticization at a temperature of about 60 to 80 C to transform the impurity soluble in alkalis into potassium hydroxide and into a product insoluble in alkalis and predominantly formed of calcium carbonate, the Crude potassium manganate VI obtained in the first stage with the aid of the causticized mother liquor and simultaneously separating the causticizing product insoluble in alkali and insoluble impurities of the ore from the leaching solution obtained.