CA2203510C - Co-production of potassium sulfate, sodium sulfate and sodium chloride - Google Patents

Abstract

A process for producing potassium sulfate, sodium sulfate, and sodium chloride from potash and a sodium sulfate/water source, wherein potash (12), sodium sulfate (14), slurry (34) from the recovery stage and brine (18) from the gaserite decomposition stage (20) are introduced to a first stage (10), wherein the sodium sulfate and potash dissolve, such that glaserite is precipitated. The slurry is concentrated and delivered (22) to the glaserite decomposition stage (20) along with water (24). Potash is introduced directly (8) and/or via stream (22) by introducing excess potash into stage (10). The potassium sulfate solids are separated, washed and dried to give a potassium sulfate product (27). The mother liquor (18) removed from the reactor is returned to the glaserite production stage (10). The brine (26) produced in the production of glaserite (10) is evaporated in an evaporative crystallizer (28). The removal of water (30) produces a supersaturation of sodium chloride, which precipitates out of solution.

Description

W O 96/16900 PCT~US95/14961 CO-PRODUCTION OF POTASSIUM SULFATE, SODIUM
SULFATE AND SODIUM CHLORIDE

EIELD AND BACKGROUND OF THE INVENTION

The present invention relates to p~oce~..es for producing puts~

5 sl~lf~e, and more particularly, to ploc~,.es for pluJ~ L pot~cci--m sl-lf~'e, so-~ .. sulfate and so.li~u chloride from potash and a source of so~l;.---.
sulfPte.

Sodium Sulfate Production:
Various ~ oces~es are known for pro~l~--;-.g so~iun sulfate from 10 lly~lraled sources of sodium sl~lf~'e. High-quality coll~ ;;al grades of so~linm sulfate are usually ~ odl.ce.l from Glauber's salt (Na2SO4*10H20).
Gl~ulJ~'s salt is oblalucd from natural deposits ("mirabilite") r~ , in various cold ~ s. Glauber's salt is also produced by co~'ing a natural brine, a solution o~tPined by solution-..~ g, or a l, oce stream. The 15 cooling is effected in ponds or in cryst~ rs (surface-cooled or vacuum-cooled).
Anllyllruus SO.]i~ll sulfate is typically pro~l--(~e-l from Glauber's salt by evaporative crysPlli~ n in a -p'e-cffect or mech~n;~l vapor recoml es~ion ~VR) evaporator, by dehydration in a rotary dryer, or by 20 m~lting followed either by evalJ~.alion or by salting out with sodium chloride. The m~ltin~ of Glauber's salt to precipitate anhy~ s sodium sulfate generally produces an nn~rce~ hly fine product 1ll~ ial.
Mo eovel, Glauber's salt often cont~inC in~ol--hle matter which is ~m^ccert~hle in high grade anhydrous so.liulll s--lf~te. Hence, rlicco'nt:-n~

-W O 96/16900 PCTfUS95/14961 filtration (and ~..x;l:~.y s~a dtion methods such as ~ ), and evaporative crys~ n operations are ..~ . y to obtain material of the proper quality. Generally, some mother liquor is purged in order to keep impurities from ~re p~ting out with the product. Alternatively, the 5 (~Jl~llbPr~s salt can be melted to ~ oduce low-quality "salt-cake" grade sodi~ slllf~e. The SalU1aled mother liquor is then filtered and evaporated to l, oduce high-grade so~linm slllf~t~.

Pot~ lm Sulfate Pro~lrrti^n:
In the production of potassium sulfate from potash and sodiulu 10 slllf~te, thermodylla.luc and ecQno~ con~ s dictate that the po~
sulfate be produced in two stages. In cull~r..l;cll~l p~oc~Ps~, these stages consist of:
1) Production of ~lasel;le ~K3Na(SO~ from sodiuul slllf~t~P, pot~h, and Stage 2 liquor;

2) Pro~lurtion of pul~ ..... sulfate from potash, water, and glaserite from Stage 1;
The mother liquor produced in Stage 1 co-.~e;l.~ s~lhst~nti~l q~
of dissolved pot~inm and snlf~te, which generally W~~ i a recovery operation. The ~ uLly-known ~ oces~es differ primarily in the s~ hPmP
20 used to retrieve these pot~c~inm and sulfate values.
Several ~ oce~es (hereinafter "Type I" ~.oc~es) take adva-~lage of the different solllhility behaviors of pol~i.. chloride, sodium chloride, and so~linnn snlf~t~/Glauber's salt at high and low t~lu~ ules. The -W O96/16900 PCTrUS95/14961 el 11.. ..~ from Stage 1, of composition 'a' (at 25C) (see Figure lb), is cooled to about 0C, precipitating Glauber's salt for reuse and possibly some SOl]i~l chloride, dep~n~lin~ on the water l~ ..cc in the system. The potassium values are concclllraled in the aqueous phase.
S After se~udtion, the solution is c~por~ted at high t~ tldtul~e, yielding sodium chloride and lu~lh~l concelllralil.~ the popc~ ~ ions in solution. The sollinm chloride is removed as the ~ oces~ by-product, and the hot liquor is cooled, ~ e~ iLdting pO~ . as KCI and/or glss_.ite, which is subsequcnlly lclullled to the re~rti~n stages. Alltl~l~div~ly, the hot 10 brine is reacted with Glauber's salt reco~ed from the cooling crysf~ ?'i-ln stage to produce a glaserite ~ on, which is l~lurll~ to Stage 1.
Other cyclic processes (hel~il.drl~l "Type II" I. oc~es) take adv~.Ldg~ of the different solubility behaviors of l.ot~ .. chloride and 15 SOdiulll chloride at high te l-pC. atures. The lu~llily of water added to the ~ -rffon stages is set such that ~l~cl~le and solution 'b' (at 25C) are lJ o-h,ce~l (Figure lb). The glaserite is then reacted with potash and water to produce the pot~ ;.. sulfate product and a liquor of composition 'c' (at 25C). The liquor is l~lul-lcd to Stage 1. The t~rllu .~1 liquor from Stage 20 1 is evaporated at high t~nl~eldlul~es (75-110C), ~ ~o~lu~ pure NaCl, and the end liquor is rclulned to Stage 1.
It must be Pmph~ci~e~ that the production of ~ot~ -.. sulfate from potash and sodium sulfate is a low value-added l- oc~, even when the W O96/16900 PCTrUS95114961 so~ m chloride by~ lu~l can be I11~heted. The multi-stage ~roces~es described above are both capital-h1l~llsive and energy-h~ ~ive.
The Type I l, oc~s~ are ~)~Li~ll~ly co~nrlPY, 1e4uil~g a large number of unit operations. These in~ de 4 to 6 filtration steps, not 5 in~ Aing f~tration of the ~hed 1,ot~x~ -.- sulfate product. Mo.~"
cooling cryst~lli7~ n is used to bring the t~ e1diule of the Stage 1 er~ to 0C. The heat of cryst~lli7~ion of Glauber's salt, which is ..I;ql (18.4 kcal/m), must also be 1~l~lov~d at low lelll~ ures~ The cooling and 1.P ~;~.g costs associated with this stage, coupled with ~ ;ve 10 equipment (such as cryst~lli7-Prs, heat eY~hqngPrs, coo'qnt system, and the like) are a serious disadv~1lage.
The Type II processes have no coo'ing stage below ambient conditions. However, the recycle stream is much larger ( ~ 10 tons per ton K2SO4 produced), which h1~eases energy co..~ -l;^m The low ratio of 15 water evaporated to Ihro~l1put in the ~v~ dlive cryst-qlli7q~ion stage dr~ti~lly reduces the natural slurry density, requiring larger cryst~lli7Prs and/or more sol,h;!i~;r~ted cryst~ ;o.~ techn~!ogy.
Although Glauber's salt is a relatively inPxpPn~ive source of so~linm s~llf~tP, the ~rl(lition~l water from the Glauber's salt decreases the 20 co 1v~1 ~ion in the reaction stages and increases the sulfate composition of the Stage 1 pr~ Some cyclic ~ oces~es cannot be operated using Glauber's salt while others require ~d-litioll~l unit operations (for PY~mp evaporation).

W O 96/16900 PCTrUS95tl4961 To date, there is no economically viable industrial process for pror~ ing a~ ulLu~ grade potq-ccinm sulfate from sodillm sulfate or Glauber's salt.
Thus, there is a widely leco~ ; e(l need for, and it would be highly 5 a~lv~llabcous to have, a process for p~ol~.~;..g ~ot~ ... sulfate from S(idium sulfate which would be more ~tr,~ and more ecolo~llical that heretofore known.

SllMMARY OF THE INVENTION
Acco .li~g to the ~ l invention there is provided a process for 10 producing potqccinm sll1fqte, so-l;,.... sulfate, and sodium chloride from potash and a sodium sulfqte/water source, CV~ llg the steps of: (a) Lrealillg the sodium snlf~elwater source to produce a slurry CQ~ q-;..i..g anhydl ous sodium sulfate; (b) conccllLl dLill~ the slurry to form a cn .c~ . ale and a diluent; (c) Lr~dLhl~ the diluent to ~ P out anhydrous sodium 15 snlfqte; (d) subjecting the anhydrous sodium sulfate from steps (b) and/or (c) and/or from a different source to con~c~sioll with potash in an aqueous mP(linm to yield ~lasc.;le and a ffrst mother liquor, with any excess anhydrous sodium sulfate being taken as co-product; (e) co~lve Lhlg the glaserite with potash and water to produce a l~e ;l~ of lJoLas~iulll sulfate 20 and a second mother liquor; (f) r~Lul~lhlg the second mother liquor to step (d); (g) subjecting the first mother liquor to evaporative cryct-qlli7q~i~n such that snhst-qntiqlly pure sodium chloride is precipitated in a third mother W O96/16900 PCTrUS95/14961 liquor; and (h) rdu~ g the third mother liquor for COIlv~l ~ion to o1~i.. salts.
According to fu~ fedlules in prert;.led embo~ of the invention described below, the aqueous so-l;.. sulfate solution is treated by S evaporative crystallization or by outcqltin~ with So~ l chloride.
The l. eselll invention ~..rce~ fully addresses the shollcv...;..g. of the l es~lllly known co~rl~uldlions by providing a ~.oc~i, for the integrated prod~-cti~n of potqccil-ln sulfate and sodium chloride with soJiu~l sulfate, from potash and Glauber's salt, which is an i~ ive and available 10 source of sodium sulfate. The use of (~Jl-q---her's salt along with the co-producti~-l of high-grade so-li.. sulfate reduces raw ll~ .;al costs and boosts total product value, such that the value-added is very nearly doubled.
The l. es~llL invention makes use of salt-cake grade so~ n s--lf~e, which can be ~lv~luced in-situ, to obtain the potqc~inm sulfate product. In 15 ~dit:~n to re-lu~ing the ~d~uldlion load, the il,lc~l~led l.locess allows for a more çffi~ nt ntili~q~ion of energy leso~,.ces, intll~ding waste vapors. In ~ liti~n, the ~ illg of so~liulll sulfate lllulLe~ liquor is eliminq~e~l or s~l,slz~ qlly redl-ced.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of çYqmrle only, with lelel~llce to the ,qrcul~ q~nying dl~Wi~gS, wherein:

-FIGs. la, lb and 1c are solution phase diagrams for the Na2SO4/2NaCI/K2SO4/2KCI/H20 system at 0, 25 and 100C, rc~ye~tiv~ly;
FIG. 2 is a block dia~.~ schematically depicting proc~s~ according to the y ~l il~v~l~lion.

5 DESCRIPTION OF THE PREF~RR~l) EMBODIMENTS
The present invention is of a process for the hlle~l aled plodu~lion of pot~ccil-m sulfate and sodium chloride with so~lir~n sulfate, from potash and a sodium s~lf~P/water source, where the soJ;----. s~lf~tç/water source may be a low quality water cor l ~ so-l;---.. s--lf~te, such as Glauber's salt or 10 semi-anhydrous so~li--m sulfate, i.e., a Il~lu~e of so.l;.. sulfate and Glauber's salt or partially hydrated sodi~ll s--lf,~te.
The plh,~;l,les and oye~- Qn of a process according to the present invention may be better umlelsloo(l with reference to the dl~illg~ and the accQ~ -.yill~ description.
To illu~llale the a~lv~ g~s and benPfitc of the proposed invention, it is hlsll u_live to consider two separate pl ocesses in which pot~c~ .. sulfate is produced from potash and Glauber's salt and so-l;....- sulfate is pro~uce~l from Glauber's salt.
The use of Glauber's salt as the sole source of sodium sulfate in the 20 pro-l--ct an of po~cci-lm sulfate is ~ tic in Cu~ tly known 1~- ocesses.
Some cyclic processes cannot be operated using Glauber's salt, or require additional unit operations (for PY~ nple, evaporation). In other ~locesses, the use of Glauber's salt greatly h.(;leases the volume of internal sll~s W O96/16900 PCTrUS95/14961 and the amount of Glauber's salt that must be recuve~ed by ~X~ ive cooling-cryst-qlli~:qtion.
In c~ lly known IJ Oc~ P~ the evaporation load in the po1~;.....
l'eCOVt~ stage is incleased to ~3.0-3.5 tons per ton of l~~ sulfate 5 produced, all of which is evaporated at high le~ e~1ule in Chl(~ ? rich solutions and le~ eS ~xl~r~;ve c~ ction luat~;als~ such as monel or l;~ ...;.... Thus, the known processes which are able to utilize Glauber's salt are even more capital i"l~"~ive and energy h~ ive than processes which c~ ~....P anl~yllrou~ s~ iu.,l s~1f~te.
~ that the Glauber's salt is completely dissolved in order to produce high purity sodiull~ sulfate with the requisite size distribution, the W;1~O dlion load is ~ 2.3 tons per ton of anhy 1~ s sodium sulfate pro~nce~l The cu.,ll,h.cd evd~ dlion load is ~5.5 tons per ton of each product produced in separate l oc~
A block dia~ of the proposed ~oc~ is provided, by way of PY~mple, in Figure 2. The anhy-l, ûus so.liul" sulfate ~ duced in the melter is of snfflri~nt quality for pro~lnrin~ a~ ullulal grade pot~inm sulfate, such that the evaporation load for the h,le~l aled IJ- oces~ is only 4.6-4.8 tons per ton of each of pol~ sulfate and so~linm snlfate. In a~l~lition, the 20 evaporative cryst~ tiQn stages can be linked, with waste vapor from one stage being fed to the other, which reduces the total amount of waste vapor in the system. Moreover, in the ...~ll;..g stage, the heat re~uil~lllelll nearly doubles lel~live to each individual process. Thus, in a process according to the ~. es~"l invention described below, the available waste vapor and low-I. e~u e vapor requilelllents are much more hql~ncerl, le~ the cost of cooling water, con~l~..ce.~, and the like. Similarly, more fi~n~l~ ..-..111 energy- opli..~ n l,o~ibililies exist for the illl~.,ted 1~ ocess, in^l.l ling cogeneration of steam and electricity and/or use of ...e~h- ..ical vapor 5 recompression for at least one of the evaporation ~y~lellls.
In a process according to the present invention, the capital cost of services (such as steam, hot water, cooling water) and l-:oces~ control are reduced becdu~e a single system is needed rather than two. The dry-ing, storage, and t~ s~ l of so.l;.. sulfate produced in the melter are 10 Pli...;~.~tPd. No purging of the so~ lm sulfate solutions is rPerlPrl since impurities generally l eci~ildte out with the so.liu,ll sulfate ~ rerl in the melter. Thus, the sodium sulfate y-ield increases.
With reference to Figure 2, a l, occss according to the ~cs~nl invention is as follows: The conversion of potash and sodillm sulfate is 15 carried out in two stages. In the first stage 10, the reaction is effected at from about 15 to about 60C, with the preferred l~ pe.d~u.e range being from about 20 to about 40C. Potash 12, sodinm sulfate 14, slurry 34 from the lecovel y stage, and brine 18 from the glas~.ile ~lec~ -osilion stage 20 are intro~ ce~l. The sodium sulfate source is primarily or ~Aclu~i~ely 20 anhydr.--c sodium sulfate, but some Glauber's salt and/or aqueous sodium sulfate is added. Each of the above-referenced, alone or in combin~ rn, is ~referred to hereinafter singly or collectively as llsodiu~ll s--lf'-P./water source". The term 'potash' is meant to in~lic~te any pot ccil-m chloride C(i ~;--i--g Illal~lial in~ll-(ling, for ~ .le~ ~ylvhlile.

W O96/16900 PCTrUS95/14961 The sv~ sulfate and potash di~olve, generating a ~ul~el ~Lul dlion with r~v~e~:l to glaserite, such that ~las~lite is precipitated. The system can also be ~ulle.saturated with re~lJe~l to so.~ ... chloride, such that some so~ .... chloride is co-lJ. e.~ e~l. The slurry is co - ~..l aled and deliv~ êd 5 22 to the glaserite decompocitiQn stage 20. The lllvlhc. liquor 26 is luldled with rex~e~l to l~.ite and should approach sdtuldlion with sodi~ll chloride and/or l,ot~ ;.. chloride under ideal conllit;~ns. A typical --ol~ liquor cornpociti~n has the fo~owing co~ Q~;~;Qn.ll~ ~x~;------6 wt%;
soll;... - 8 wt%; chloride- 17wt%; sulfate- 1.5wt%; water- the balance. The 10 subst~n~iq~ ;PC of pot~cci-lm and sulfate in the mother liquor are relul~led to the process in the lèCO~..y stage.
The ~las~l;Le ~lrcc~ ..I-o~ r~n stage 20 is ~lr~ ,5led at from about 15 to about 60C, with thê y er~led te~ e~dlule range being from about 20 to about 35C. Water 24 is hlllvlluced along with the solids 22 obt~in~d 15 from the first st~ge 10. Potash is illllvduced vhec~ 8 and/or via stream 22 by hlll~ excess potash into stage 10. The potash and ~lasel;le solids dissolve, gell~ iu~ a ~u~e~ s;1lu~ ~lion solely with res~e~l to ~o~
s--lf~te, such that pot~innn sulfate is 3~1ecliv~ly pl~e~ l The m~x;.... ...cvllv~l;,ion is obtained when the mother liquor composition 20 approaches the KCI/K2SO4/glaserite/H2O illv~u;dlll point. The l,vl~
sulfate solids are separated, washed and dried to give a pot~inm sulfate product 27. The mother liquor 18 removed from the reactor is returned to the glaserite pro(ll- tisln stage 10. The spent wa~hwalél~ however, is used . =.~ =

,`- `11 ,, in the ~ecn...~Qs;l ~n of glaserite. Some or all of portions of stages 10 and 20 may be er~:ied in a single cou~ .,l li~,clllisl contactor.

The brine 26 pro~lnce(l in the production of tlasel;le 10 is evaporated .~ ~
in an ev~ol~live cryst~ Pr 28, at about 70 to about 130C, with the S ~.ef~lled range being about 95 to about 110C. If ..~c~-cc~.y, the brine 26 can be filtered prior to ev~olalion to remove any ;--col~-ble matter. The removal of water 30 produces a ~u~e,~lulali~ll of eo~ Tn chloride, which ~le~ P-C out of solution. Care must be taken not to ov~l~v;ll,orate, which can result in the nnrlecirable co-~e~ ;on of glaserite.
After a solid/liquid separation, the wet sodium chloride product 32 is r~llloved from the system. The po~ enrlclled brine 34 is cooled 36 and returned to vessel 10.
The codillm sulfate i,ltlod-Jced to vessel 10 is pro-lucP-l in-situ in a melter 42 by m~ltin~ the Glauber's salt feed 40. Water 44 is added as ~~- 15 n~ede~l The product slurry 41 can be co.. ~ -aled in vessel 43. The .
concPntrate 14 is fed to vessel 10 and the diluent 45 is returned to evap.)lalol 48. The dilllent can be filtered before being ev;~ led to - remove the water 50. The solids 52 are dried to produce anhy-ll o~ sodi.~-- sulfate l o.lu~t.

- 20 While the invention has been described with ~ecl to a limited - ' number of embo.l;.. ~ e, it will be ap~ ;aled that many v~ ;o.. e, ~ .
- mo~ tinn~ and other applications of the illv~llliol~e can be made.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing potassium sulfate, sodium sulfate, and sodium chloride from potash and a sodium sulfate/water source, comprising the steps of:
(a) treating the sodium sulfate/water source to produce a slurry containing anhydrous sodium sulfate;
(b) concentrating said slurry to form a concentrate and a diluent;
(c) treating said diluent to precipitate out anhydrous sodium sulfate;
(d) taking a portion of said anhydrous sodium sulfate from steps (b) and/or (c) as co-product, leaving a remainder of said anhydrous sodium sulfate from step (b) and/or (c) and subjecting said remainder of said anhydrous sodium sulfate from step (b) and/or (c) to conversion with potash in an aqueous medium to yield glaserite and a first mother liquor;
(e) converting said glaserite with potash and water to produce a precipitate of potassium sulfate and a second mother liquor;
(f) returning said second mother liquor to step (d);
(g) subjecting said first mother liquor to evaporative crystallization such that substantially pure sodium chloride is precipitated in a third mother liquor; and (h) returning said third mother liquor for conversion to potassium salts.

2. A process according to claim 1, wherein said diluent is treated by evaporative crystallization.

3. A process according to claim 1, wherein said diluent is treated by outsalting with sodium chloride.

4. A process according to claim 1, wherein sodium sulfate produced from said diluent is used as raw material for step (d), with the excess solid sodium sulfate from steps (b) and (c) being removed as co-product.

5. A process according to claim 1, wherein Glauber's salt is added to said third mother liquor in, or prior to, step (d).

6. A process according to claim 1, wherein said sodium sulfate used in step (d) is a low-quality salt-cake, such that all the high-grade sodium sulfate produced in steps (a) and (c) is removed as co-product.

7. A process according to claim 1, wherein the sodium sulfate/water source is Glauber's salt.

8. A process according to claim 7, wherein said treating includes melting.

9. A process according to claim 1, wherein the sodium sulfate/water source is semi-anhydrous sodium sulfate.