Process for producing a concentrated aqueous sodium hydroxide solution

A method for producing a concentrated aqueous sodium hydroxide solution from a purge stream derived from an anhydrous sodium carbonate crystallizer, or a sodium carbonate monohydrate crystallizer, or a sodium carbonate decahydrate crystallizer, or a sodium sesquicarbonate crystallizer, or a wegsheiderite crystallizer, or a sodium bicarbonate crystallizer, said purge stream comprising:

• sodium carbonate and/or sodium bicarbonate from a sodium carbonate or sodium bicarbonate ore deposit selected from the group consisting of:
• trona ore, nahcolite ore, and wegscheiderite ore,
• at least 1% by weight of a sodium salt selected from the group consisting of sodium chloride, sodium sulfate and mixtures thereof, and
• at least one soluble salt or at least one soluble impurity from said sodium carbonate or sodium bicarbonate ore deposit, said soluble salt or soluble impurity comprising at least one of the following elements selected from the group consisting of:
• As, Ba, B, Ca, Co, K, Li, Mo, P, Pb, Se, Sn, Sr, Te, Tl, Ti, V, and W,
• said concentrated aqueous sodium hydroxide solution comprising:
• at least 25% by weight of NaOH,
• said method comprising the following steps:
• f) adding lime to the purge stream, in presence of water, to causticize at least 50 mol. % of the sodium from sodium carbonate and/or sodium bicarbonate, into an aqueous sodium hydroxide solution and into a calcium carbonate mud;
• g) separating the calcium carbonate mud from the aqueous sodium hydroxide solution;
• h) concentrating the aqueous sodium hydroxide solution by removing part of the water to obtain:
• the concentrated aqueous sodium hydroxide solution comprising at least 25% NaOH, and to crystallize a solid comprising sodium carbonate and comprising sodium chloride and/or sulfate,
• i) separating the crystallized solid comprising sodium carbonate and sodium chloride and/or sulfate from the concentrated aqueous sodium hydroxide solution;
• j) valorizing the concentrated aqueous sodium hydroxide solution as a salable sodium hydroxide solution or recycling at least one part of the concentrated aqueous sodium hydroxide solution to the anhydrous sodium carbonate crystallizer, or to the sodium carbonate monohydrate crystallizer, or to the sodium carbonate decahydrate crystallizer, or to the sodium sesquicarbonate crystallizer, or to the sodium bicarbonate crystallizer, or to processes upstream of the anhydrous sodium carbonate crystallizer, or of the sodium carbonate monohydrate crystallizer, or of the sodium carbonate decahydrate crystallizer, or of the sodium sesquicarbonate crystallizer, or of the sodium bicarbonate crystallizer;
• and wherein the at least one soluble salt or the at least one soluble impurity comprising at least one element selected from the group consisting of:
• As, Ba, Be, Bi, B, Ca, Co, Cu, F, K, Li, Mo, P, Pb, Se, Sn, Sr, Te, Tl, Ti, V, and W,
• is at least partially removed at steps f) to i) from the purge stream.