FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10; Rule 13)
1. TITLE OF THE INVENTION:
Process For Production of Potassium Chloride From Syngenite
2. APPLICANT(S)
(a) NAME: Agrocel Industries Limited
(b) NATIONALITY: An Indian Company
(c) ADDRESS:
Agrocel Industries Limited
4th Floor, Doctor House,
Opp. G K General Hospital,
Bhuj,
Gujarat 370 001,
INDIA.
3. PREAMBLE TO THE DESCRIPTION:
The following COMPLETE specification particularly describes the nature of this invention and the manner in which it is to be performed.

PROCESS FOR PRODUCTION OF POTASSIUM CHLORIDE
FROM SYNGENITE
FIELD OF INVENTION
This invention relates to a process for production of potassium chloride and magnesium oxide from bittern. More particularly, this invention relates to production of potassium chloride by fractional crystallization of bittern to obtain kainite type mix salt 86 mother liquor containing MgC12, treating mix salt with gypsum to obtain syngenite and treating syngenite with calcium chloride to obtain potassium chloride; treating mother liquor containing MgC12 with Ca(OH)2 to obtain Mg(OH}2 and calcination of Mg(OH)2 to obtain MgO.
BACKGROUND AND PRIOR ART
Potassium containing minerals are mined from underground ore
deposits, salt lakes and brines. Most abundant mineral in the
commercial deposits is sylvinite (NaCl + KC1). Kainite ores
(KCl.MgS04.2.75H20) are less common. In brines, carnalite
(KCl.MgC12.6H2O) is present with halite (NaCl). Potassium values are recovered from these resources by conventional shaft mining or solution mining. It can also be recovered from bittern/brine.
Processes for recovery of potassium chloride from bittern as reported in the literature involve heating and/or cooling and they are energy consuming and complex.
US3615174 describes a process for selective recovery of potassium and magnesium values from aqueous solutions. The method involves fractional solar evaporation of naturally occurring brines for eliminating

the bulk of sodium chloride and then precipitating crude kainite salt upon further concentration, kainite is retained under the mother liquor [ML] from which it is precipitated and the mother liquor is cooled to a sufficiently low temperature to convert the kainite salt into carnallite. Carnallite is harvested and purified by flotation in a cold system, i.e., at about 0°C. employing the flotation agents. The mother liquor is then withdrawn and the crude carnallite salt is harvested. Carnallite salt is leached with water to obtain KC1 salt and brine containing MgCb.
US3528767 discloses a process wherein raw brine is first evaporated to crystallize out bulk of sodium chloride. The remaining brine is then evaporated in a controlled manner to separate out first schoenite (MgSO4.K2SO4.6H2O), then Kainite (KCl.MgSO4.2.75 H2O) and finally Carnalite (KCl.MgCl2.6H2O). Carnalite is decomposed to obtain potassium chloride in a known manner as described in IL 10603, or German patent 10754. The process disclosed in said US3528767 is very tedious and comparatively more energy consuming than present invention.
A study on manufacture of potassium chloride by treating brine with
waste CaCl2 liquor has been reported by Guo Guilan et al. [Haihuyan Yu
Hungong 1996, 25(3), 7-10]. In this process, carnalite is first produced
by treatment of bittern with waste CaCl2 liquor followed by solar
evaporation in solar pond. Potassium chloride is then produced from
carnalite. Manufacture of potassium chloride by carnalite
decomposition is also reported by Xia Shu-ping et al [Haihuyan Yu Huagong 1994, 232, 10-15].
Process for manufacturing potassium chloride from chloride type potassium brine has been reported in CN1063663. The process comprises preparing brines with NaCl-KCl-carnalite (I) and NaCl-

carnalite-bischolite (II) phases by evaporating water from the brine, mixing I 85 II in wt ratio l:(l-3) and separating NaCl from the mixture based on the crystal size difference, charging into a crystallizer with (1) the NaCl removed mixture at 300-800 Kg/h-m3, (2) enough water to dissolve the carnalite and (3) mother liquor obtained from later stage after removing MgCl2 and residue NaCl at carnalite / ML wt ratio l:(3-6), and separating the larger KCL crystals from the mixture to obtain the product while filtering MgC12 and residue NaCl out from ML, and recycling ML. This process is very tedious.
Cekinski E et al. have described a process for manufacture of KC1 from carnalite [Fertilizantes, 11(1), 6-8 (1989)]. Carnalite is reacted with NH3 or urea at a suitable temperature. The resulting solution contains KC1 and NH4Cl.MgC12.nH20. KC1 is separated from the solution by selective crystallization and dried.
DD251541 discloses a method for processing carnalite wherein the losses of potassium are decreased by carrying the reaction at 250-285 K and after separation of the crystallized KC1, recycling part of the process solution to reaction and using the remainder to pre-cool the process mixture. The process involves many steps.
In comparison to carnalite involved in the prior art processes mentioned above, present invention involves a process for preparation of potassium chloride wherein syngenite reacts with calcium chloride. Carnalite contains only 17% K20. On the other hand, syngenite contains 28.8% K20. Present invention provides a process for preparation of potassium chloride which utilizes only bittern and calcium hydroxide as raw materials. Gypsum used in the process is recycled. Calcium hydroxide used initially gets converted into calcium chloride, which is used for treatment of syngenite to produce KC1. The process of present invention

is more efficient and economic compared to processes reported in the prior art.
OBJECTS OF INVENTION
It is an object of this invention to provide a cost-effective process for production of potassium chloride from mix salt by treatment of mix salt with gypsum to obtain syngenite and treating syngenite with calcium chloride to obtain potassium chloride.
Another object of invention is to provide a process for production of potassium chloride which does not consume lot of energy.
Yet another object of invention is to provide a process for production of potassium chloride wherein effluent is minimized.
STATEMENT OF INVENTION
The present invention provides a process for production of potassium chloride comprising fractional crystallization of bittern to obtain kainite type mix salt & mother liquor containing MgCl2, treating mix salt with gypsum to obtain syngenite and treating syngenite with calcium chloride to obtain potassium chloride; treating mother liquor containing MgCl2 with Ca(OH)2 to obtain Mg(OH)2 and calcination of Mg(OH)2 to obtain MgO. The invented process utilizes bittern and calcium hydroxide as only raw materials. Calcium hydroxide gets converted into calcium chloride which is used for treatment of syngenite to obtain potassium chloride.

DESCRIPTION OF DRAWINGS
Fig. 1 is the flow diagram of overall process for preparation of potassium chloride and MgO.
Fig.2 is the flow diagram of the process for preparation of syngenite from mix salts.
Fig.3 is the flow diagram of the process for preparation of potassium chloride from syngenite.
DESCRIPTION OF INVENTION
Though the procedure described in present invention utilizes some chemical conversions known in the art, the overall process is not known and it presents significant practical and economic advantage over prior art.
The outline of the overall process for preparation of potassium chloride and MgO is shown in Fig.l. In this process, bittern is evaporated to 29-30°Be to separate out crude salt and epsum. It is further evaporated to 35-3 7°Be and filtered to obtain kainite type mix salt and mother liquor (1) containing MgCl2. Water is added to mix salt and subsequently gypsum is added whereupon syngenite formation takes place. The reaction mass is filtered to obtain mother liquor{2) and syngenite. CaC12 solution is added to syngenite and the mixture is filtered to obtain gypsum and mother Iiquor(3). Potassium chloride is recovered from mother liquor (3). Gypsum is recycled for syngenite formation.
Ca(OH)a is added to mother liquor(l) i.e., MgCl2 solution. The mixture is filtered to obtain Mg(OH)2 and mother liquor(4) i.e., CaC12 solutiion,

which is used for treatment of syngenite [which is separated form mother liquor(2) ] to obtain KC1 solution and gypsum. Mg(OH)2 is calcinated to obtain MgO.
Preparation of syngenite from mix salt:
As shown in Fig.2, water is added to kainite type mix salt and it is treated with gypsum. The reaction mass is stirred at room temperature, allowed to settle overnight and filtered to obtain syngenite cake and mother liquor (1). Syngenite cake is washed with water and filtered to obtain syngenite and mother liquor (2). Mother liquor 1 & 2 are evaporated to obtain mix salt which is recycled.
Preparation of potassium chloride from syngenite and calcium chloride:
As shown in Fig. 3, syngenite is treated with CaC12 followed by hot filtration to obtain gypsum cake and mother liquor (1) containing potassium chloride. Mother liquor(l) is concentrated by evaporation followed by crystallization and filtration to obtain potassium chloride. Water is added to gypsum cake separated from mother liquor(l). Gypsum cake is re-pulped in water followed by filtration to obtain gypsum which is used for syngenite preparation.
Example-1
Preparation of mix salt from bittern:
Bittern was evaporated to about 29°Be to separate out crude salt
and epsum. 200 lit of 29°Be bittern was evaporated further by
solar evaporation to 35-37°Be to obtain 15 Kg of kainite type mix
salt comprising 18% KC1, 31% MgS04, 3% MgC12 and 18% NaCl;
and mother liquor(l) containing MgCl2.

50.5 Kg Mother liquor(l) containing MgCl2 was treated with 40%
calcium hydroxide slurry till complete precipitation of magnesium
hydroxide. It was filtered to obtain magnesium hydroxide and
mother liquor containing 23%CaCl2. Magnesium hydroxide was
washed with water and calcined by conventional method to obtain
MgO. Mother liquor containing 23% CaCl2 was concentrated to
35% and was used for preparation of KC1 from syngenite as
described in Example-3.
Example-2
Preparation of syngenite from mix salt:
5 Kg of kainite type mix salt comprising 18% KC1, 31% MgS04, 3% MgC12 and 18% NaCl was taken in the reactor. 7.5 lit water and 0.85 Kg of gypsum were added. The mixture was stirred for 1 hr. and the reaction mass was allowed to settle for 12 hrs. The slurry was filtered to obtain syngenite cake, which was washed with 2.5 lit of water for removal of NaCl. 1.6 Kg of syngenite was obtained comprising 32% K2S04, 40% CaS04, 1.2% NaCl, 1% MgS04, <1% MgC12.
10.6 lit filtrate was obtained comprising 4.5% K2S04, 5.7%
MgS04, 8% MgCl2 and 11% NaCl. The filtrate was evaporated to
give 2.0 Kg of mix salt comprising 17% KC1, 29% MgS04, 2%
MgC12 and 20% NaCl. Mix salt was recycled for preparation of
syngenite.
Example-3
Preparation of potassium chloride from syngenite:
500 gm syngenite obtained in Example-2 above was taken in the
reactor. 800 ml water and 290 gm 35% CaCl2 were added. The
mixture was stirred for 1 hr. at 30-50°C. The slurry was filtered to

obtain gypsum cake and mother liquor [ML], The ML was evaporated and cooled to room temperature to obtain KC1 crystals which was filtered to get 120 gm potassium chloride on dry basis having 97% purity and <2% sodium chloride content. The gypsum cake was re-pulped in 1050 ml water at 50°C and filtered to obtain 434 gm gypsum on dry basis, which was recycled.

CLAIMS:
1. A process for production of potassium chloride from syngenite comprising: (i) Evaporating bittern to about 28-30°Be to separate out crude
salt and epsum; (ii) Further evaporation of bittern obtained in step (i) above to
35-37°Be to obtain Kainite type mix salt and mother liquor
containing MgCl2; (iii) Treating mother liquor containing MgCl2 as obtained in step
(ii) above, with calcium hydroxide to obtain precipitate
containing magnesium hydroxide and mother liquor
containing CaCl2; (iv) Treating kainite type mix salt as obtained in step (ii) above
with water and gypsum followed by filtration to obtain
syngenite and mother liquor; (v) Treating syngenite as obtained in step (iv) above with mother
liquor containing CaC12 as obtained in step (iii) above,
followed by nitration to obtain gypsum and mother liquor
solution containing KC1.
2. A process as claimed in claim-1, wherein mother liquor which is
obtained in step (v) of said process is concentrated by evaporation
to crystallize out KC1.
3. A process as claimed in claim-1, wherein gypsum formed during step (v) is recycled for syngenite preparation described in step (iv).
4. A process as claimed in claim-1, wherein syngenite obtained in step(iv) is washed with water for removal of NaCl.
5. A process as claimed in claim-1, wherein mother liquor obtained in step(iv) is evaporated to crystallize out kainite type mix salt which is recycled for preparation of syngenite in step(iv).

6. A process as claimed in claim-1, wherein step (v) is carried out using fresh CaCl2 from any source.
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