Process for treating a sodium carbonate purge

A concentrated aqueous sodium hydroxide solution comprising:

• at least 25% by weight of NaOH,
• sodium chloride (NaCl) and/or sodium sulfate (Na2SO4),
• and at least one soluble salt or one soluble impurity from a sodium carbonate or 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, Mg, Mo, P, Pb, Se, Si, Sr, Te, Tl, Ti, V, and W,
• wherein:
• the at least one element is at a concentration expressed in mg of element per kilogram of the aqueous sodium hydroxide solution, in the following ranges:
• As at least 18 and at most 31.4,
• Ba at least 0.04 and less than 0.17,
• B at least 560 and at most 1160,
• Ca at least 5.9 and at most 21.7,
• Co at least 0.52 and at most 1.24,
• K at least 6187 and at most 12360,
• Li at least 29.0 and at most 47.4,
• Mg at least 2.4 and at most 3.4,
• Mo at least 64 and at most 74.1,
• P at least 114 and at most 460 expressed as PO4,
• Pb at least 1.2 and at most 2.4,
• Se at least 1.1 and at most 9.2,
• Si at least 187 and at most 1970,
• Sr at least 0.06 and at most 0.17,
• Te at least 0.7 and at most 6.2,
• Tl at least 0.5 and at most 0.6,
• Ti at least 0.34 and at most 0.74,
• V at least 21 and at most 26.1,
• W at least 2.6 and at most 2.7.