Process for treating a sodium carbonate purge

A method for producing a sodium carbonate salt or a sodium bicarbonate salt from a sodium carbonate/bicarbonate solution derived from a sodium carbonate/bicarbonate ore, wherein the sodium carbonate/bicarbonate ore is selected from a group consisting of trona, nahcolite, and wegsheiderite ores, or from a sodium carbonate/bicarbonate lake water, or from a reclaimed solid, or from a mine water, said ores, waters or solid comprising sodium carbonate/bicarbonate, comprising the following steps:

• a) pre-treating the sodium carbonate/bicarbonate solution in removing part of organics and/or changing the carbonate/bicarbonate molar ratio in order to obtain an optional pre-treated sodium carbonate/bicarbonate solution;
• b) crystallizing from the sodium carbonate/bicarbonate solution, or from the optionally pre-treated sodium carbonate/bicarbonate solution,
• a sodium carbonate salt or a sodium bicarbonate salt with one of the means selected from the list of:
• evaporation crystallization, cooling evaporation, carbonation crystallization and combinations thereof,
• said crystallization step of the sodium carbonate salt or the sodium bicarbonate salt generating a mother liquor, said mother liquor comprising sodium carbonate or bicarbonate, sodium chloride or sodium sulfate, and water;
• c) separating the sodium carbonate salt or the sodium bicarbonate salt from the mother liquor;
• d) recycling part of the mother liquor back into one of the step a), or step b) and removing part of the mother liquor in order to generate a purge stream to control the sodium chloride and/or the sodium sulfate concentration in the mother liquor of the crystallization step b), and
• e) treating the purge stream, wherein the treating comprises:
• f) causticizing 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 by reaction of the purge stream by adding lime, in presence of water;
• 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:
• a concentrated aqueous sodium hydroxide solution comprising at least 25 wt % NaOH, and
• a crystallized solid comprising sodium carbonate and comprising sodium chloride and/or sodium sulfate,
• wherein the lime added at step f) and water removed at step h) are controlled so that the weight ratio of sodium carbonate to the sum of the sodium chloride and/or sodium sulfate in crystallized solid is at most 2, recovering the water removed at step h) as condensates from an evaporator, and recycling the condensates to a calcined carbonate or bicarbonate ore leaching or to a carbonate or a bicarbonate ore solution mining;
• i) separating the crystallized solid comprising sodium carbonate and sodium chloride and/or sodium sulfate from the concentrated aqueous sodium hydroxide solution, said crystallized solid to be disposed of or to be further valorized;
• and
• j) 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.