PROCESS FOR MAKING CRYSTALLINE SODIUM SULFATE

Abstract

Described herein is a process for making crystalline sodium sulfate, the process including the steps of (a) combining an aqueous solution containing sulfates of nickel and at least one metal selected from cobalt and manganese with an aqueous solution of sodium hydroxide or sodium carbonate, respectively, in a stoichiometric ratio of about 1:2, optionally in the presence of ammonia or a salt of ammonia, (b) removing the precipitated hydroxide or carbonate of nickel and the at least one metal selected from cobalt and manganese by filtration, (c) removing the ammonia from the filtrate from step (b) by stripping in a distillation column, (d) passing the remaining liquid phase through a membrane, thereby obtaining a permeate, and (e) removing water from the permeate from step (d) by an evaporation method.

Claims

1. A process for making crystalline sodium sulfate, said process comprising the steps of (a) combining an aqueous solution containing sulfates of nickel and at least one metal selected from the group consisting of cobalt and manganese with an aqueous solution of sodium hydroxide or sodium carbonate in a stoichiometric ratio of about 1:2 or 1:1, respectively, in the presence of ammonia or a salt of ammonia, (b) removing the precipitated hydroxide or carbonate of nickel and the at least one metal selected from the group consisting of cobalt and manganese by filtration, (c) removing the ammonia from the filtrate from step (b) by stripping in a distillation column, (d) passing the remaining liquid phase through a porous membrane, thereby obtaining a permeate, and (e) removing water from the permeate from step (d) by an evaporation method.

2. The process according to claim 1, wherein the filtrate in step (c) has a pH value in the range of from 10 to 13.

3. The process according to claim 1, wherein the evaporation method in step (e) is selected from the group consisting of spray drying and evaporation crystallization.

4. The process according to claim 1, wherein the chloride content of the filtrate of the sulfate after step (d) is in the range of from zero to 10 ppm by weight, referring to the filtrate.

5. The process according to claim 1, wherein in step (a), additionally at least one of aluminum and magnesium is included in the precipitation by introducing at least one of MgSO.sub.4, Al.sub.2(SO.sub.4).sub.3, NaAl(OH).sub.4, NaAl(SO.sub.4).sub.2, and KAl(SO.sub.4).sub.2.

6. The process according to claim 1, wherein in step (d), a pressure of up to 5 atm is used.

7. The process according to claim 1, wherein between steps (d) and (e) a reverse osmosis (d) is performed.

8. The process according to claim 1 wherein the pH value of the permeate from step (d) or the retentate from step (d), if applicable, is adjusted to 6.5 to 9.5 prior to step (e) with sulfuric acid.

Description

EXAMPLE

[0078] The following set-up is used: a 10-l stirred tank reactor (A.1) with baffles, overflow system, lamellar clarifier, and stirrer, connected to a filter press, (B.1). The filtrate may be transferred to a fractionating column (C.1). The low-boiling fraction is transferred to a first vessel with a porous ceramic filter, (D.1), a reverse osmosis unit (D.1) and the retentate from there to a crystallizer

[0079] (E.1) or to a spray dryer (E.2).

Step (a.1):

Synthesis of a precursor TM-OH.1

[0080] The stirred tank reactor (A.1) was filled with deionized water and 49 g of ammonium sulfate per kg of water. The solution was tempered to 55 C. and a pH value of 12 was adjusted by adding an aqueous sodium hydroxide solution.

[0081] The co-precipitation reaction was started by simultaneously feeding an aqueous transition metal sulfate solution and aqueous sodium hydroxide solution at a flow rate ratio of 1.8, and a total flow rate resulting in a residence time of 8 hours. The transition metal solution contained Ni, Co and Mn at a molar ratio of 8.5:1.0:0.5 and a total transition metal concentration of 1.65 mol/kg. The aqueous sodium hydroxide solution was a 25 wt. % sodium hydroxide solution and 25 wt. % ammonia solution in a weight ratio of 6. The pH value was kept at 12 by the separate feed of an aqueous sodium hydroxide solution. Beginning with the start-up of all feeds, mother liquor was removed continuously. After 33 hours all feed flows were stopped.

[0082] Step (b.1): The mixed transition metal (TM) oxyhydroxide precursor was obtained by filtration of the resulting suspension over a filter press (B.1), washing with a 1% by weight NaOH solution, drying at 120 C. in air and sieving.

[0083] The filtrate from step (b.1) is combined with the mother liquor withdrawn in step (a. 1) and the washing water. The combined filtrate so obtained had a pH value of 12.0.

Step (c.1):

[0084] The combined filtrate from step (b.1) is transferred to a fractionating column (C.1). A distillation column with trays that bear bubble caps and 15 theoretical plates serves as fractionating column (C.1). Step (c.1) is operated continuously. The low-boiling fraction is a 15% by weight aqueous solution of ammonia, the high-boiling fraction is a slightly turbid aqueous solution of Na.sub.2SO.sub.4 with a pH value of 12.

Step (d.1)

[0085] The slightly turbid solution from step (c.1) is cooled to 50 C. and transferred to a 20-l vessel (D.1) leading to a porous ceramic Al.sub.2O.sub.3 membrane unit: three membranes with average pore diameters 800 nm, then 400 nm and finally 100 nm. A pressure of 3 bar is exerted. A transparent and colorless permeate is obtained.

[0086] After step (d.1), sulfuric acid is added to permeate from step (d.1) to adjust the pH value to 7.0.

Step (d.1):

[0087] The neutralized permeate from step (d.1) is cooled to 25 C., and a reverse osmosis is performed. With a pressure of 100 bar, water is removed from the permeate of step (d.1), thereby obtaining a permeate of step (d.1) and a retentate. The retentate is then transferred to step (e.1).

Step (e.1)

[0088] The neutralized transparent and colorless filtrate from step (d.1) is then transferred to a tubular heat exchanger (E.1) that serves as a falling film evaporator. By repeated passage of the solution over the tubular heat exchanger it is heated to 100 to 110 C., and water evaporates. The thus concentrated but still crystal free solution enters a crystallizer unit. Here, the solution is pumped over another heat exchanger where it becomes superheated to 110 to 120 C. On reentering the crystallizer, water evaporates and crystals of Na.sub.2SO.sub.4 precipitate. The suspension is withdrawn from the crystallizer by means of a pump and crystals are separated from the suspension from a laboratory-scale belt filter. Their whiteness is excellent, and they do not have malodor.

Step (e.2)

[0089] The neutralized transparent and colorless filtrate from step (d.1) is then transferred to a laboratory spray dryer, single-effect type, through a spray nozzle. As gas for the nozzle, air used. A fog is formed. The spray tower is operated in a co-current mode with respect to gas flow and the fog. The gas temperature is 200 C. The filtrate is introduced through the nozzle with a pressure of 2500 kPa. A white odorless Na.sub.2SO.sub.4 powder, average particle diameter 10 m, is obtained.

[0090] The nickel content of the Na.sub.2SO.sub.4 is in each case below detection level.