Process for control of crystallization of inorganics from aqueous solutions

Abstract

Process of crystallization of sodium bicarbonate from solution mined Nahcolite pregnant liquor comprising the use of from about 2 to 100 parts per million of lecithin, introduced full strength, made miscible in water with a soap or detergent, saponified with NaOH at a pH of 10-12, or preferably as a mixture of lecithin in pregnant or barren liquor containing HCO3−/CO3= ions at a pH in the range of from about 8 to 12, preferaby 8-10. The lecithin functions as a crystal growth modifier, producing improved crystal yields, product size classification, improved crystal shape including reduction in dendritic, branched and twinned forms, very significant scale reduction, reduction in wet cake moisture, increase in product bulk density, reduction in both oversize and undersize fractions (the classification phenomenon) and less breakage during drying and handling. The aqueous lecithin premix is preferably added to a pregnant liquor tank, and may also be added in one or more crystallizers in the circuit in batch (timed aliquots) or continuously metered in proportion to throughput. The process may also be applied to crystallization of carbonates, bicarbonates, phosphates, nitrates, sulfates, hydroxides and borates of Na, Li, K, Ca and Mg from aqueous solutions including brines. For commercial scale bicarbonate production the presently preferred range is 2-30 ppm, and for product −425 μm+45 μm the range is about 5-15 ppm. Coarse product (+425 μm) is preferably produced in the range of about 12-30 ppm.

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