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EP-4486699-B1 - PROCESS FOR MAKING CRYSTALLINE SODIUM SULFATE

EP4486699B1EP 4486699 B1EP4486699 B1EP 4486699B1EP-4486699-B1

Inventors

  • RYLL, Thomas Michael
  • Volkov, Aleksei
  • RAULS, MATTHIAS

Dates

Publication Date
20260506
Application Date
20230316

Claims (8)

  1. 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 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 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. Process according to claim 1 wherein the filtrate in step (c) has a pH value in the range of from 10 to 13.
  3. Process according to claim 1 or 2 wherein the evaporation method in step (e) is selected from spray drying and evaporation crystallization.
  4. Process according to any of the preceding claims 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. Process according to any of the preceding claims wherein in step (a), additionally at least one of aluminum and magnesium is included in the precipitation by introducing at least one of MgSO 4 , Al 2 (SO 4 ) 3 , NaAl(OH) 4 , NaAl(SO 4 ) 2 , and KAl(SO 4 ) 2 .
  6. Process according to any of the preceding claims wherein in step (d), a pressure of up to 5 atm is used.
  7. Process according to any of the preceding claims wherein between steps (d) and (e) a reverse osmosis (d') is performed.
  8. Process according to any of the preceding claims 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

The present invention is directed towards 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 cobalt and manganese with an aqueous solution of sodium hydroxide or sodium carbonate, respectively, 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 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. Alkali metal sulfates like sodium sulfate are useful products in many applications, for example, they may serve as builders in laundry detergents. However, in order to be a suitable builder such sulfates need to fulfil several criteria. They must not contain critical impurities. They need to be colorless and should not offer an unpleasant odor to the laundry detergent. Furthermore, they must not be a cost factor for the laundry detergent. Major quantities of sodium sulfate are obtained from mineral resources, for example from mirabilite. However, alternative methods are interesting as well. In CN 112299638 A1, a method is described for obtaining sodium sulfate from a filtrate of a ternary precursor precipitated from sulfates with sodium hydroxide. The resulting sodium sulfate may still not be suitable for builders or other home care applications. In WO 2019/117411, a process for working up filtrates is described where ammonia, a commonly used complexing agent in precursor manufacture, is recovered as ammonium sulfate. In US 6,001,246, a process is disclosed wherein sodium sulfate is produced from wastewater. The sodium sulfate contains about 0.200% by weight of NaCl. It was the objective of the present invention to provide a process for making sodium sulfate from a cheap source that fulfils the above requirements of purity, free from smell, and colorless, without having the disadvantages of the prior art methods. It was further an objective of the present invention to provide a set-up in which the respective process may be carried out. Accordingly, process as defined at the outset has been found, hereinafter also referred to as inventive process. The inventive process comprises the steps (a) to (e), hereinafter also referred to as step (a) or in brief as (a), step (b)or in brief as (b), etcetera. The inventive process will be described in more detail below. Step (a) includes 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 in a stoichiometric ratio of about 1 : 2 or 1 : 1, respectively, in the presence of ammonia or a salt of ammonia. The relative amounts of nickel and the at least one metal selected from cobalt and manganese may be selected in wide ranges. Nickel may amount from 25 to 97 mol-% of the metals other than alkali metal. Cobalt may be absent or present and may then amount from 1 to 33 mol-%, preferably 2 to 20 mol-% of the metals other than alkali metal. Manganese may be absent or present and may then amount from 1 to 75 mol-% preferably 2 to 68 mol-% of the metals other than alkali metal. Further metals that may be present in step (a) are magnesium or aluminum, for example up to 2 mol-% of magnesium, or up to 10 mol-% of aluminum. When aluminum is present in amounts of 3 to 10 mol-%, it is preferred that cobalt is present as well. In the course of step (a), a precipitation is performed. In one embodiment of the present invention, at least one of aluminum and magnesium is included in the precipitation in step (a) by introducing at least one of MgSO4, Al2(SO4)3, NaAl(OH)4, NaAl(SO4)2, and KAl(SO4)2. Sodium hydroxide is able to absorb carbon dioxide from air, and frequently, technical grade sodium hydroxide contains some sodium carbonate, for example up to 0.5 by weight, preferably 0.1 to 0.4% by weight. By applying such technical grade sodium hydroxide, mixed hydroxides/carbonates are precipitated. In one embodiment of the present invention, in step (a), the stoichiometric ratio of sodium hydroxide to the sum of nickel and other metals is about 2:1. The term "about" in this context refers to ± 2 mol-% deviation of the hydroxide content to the ratio that would correspond to an exact stoichiometric ratio. In case aluminum is present, the amount of hydroxide may vary, also depending on the nature of the source of aluminum. In one embodiment of the present invention, the stoichiometric ratio of sodium carbonate to the sum of nickel and other metals is about 1:1. The term "about" in this context refers to ± 2 mol-% deviation of the c