PROCESS FOR MANUFACTURE OF SODIUM HYDROXIDE AND SODIUM CHLORIDE PRODUCTS FROM WASTE BRINE

摘要

The present invention provides a process for the manufacture of sodium hydroxide and sodium chloride products from a waste brine stream containing sodium chloride, and at least sodium carbonate or sodium bicarbonate. The method of this invention comprises converting the sodium carbonate and/or sodium bicarbonate to sodium hydroxide through addition of lime to the brine, while simultaneously converting impurities to less soluble forms to facilitate their removal. The causticized brine is separated from unreacted lime, calcium carbonate and solid impurities to produce clean brine with reduced levels of impurities. The brine is then concentrated by evaporation, forming relatively pure sodium chloride crystals, which are extracted and rinsed to reduce alkali contaminants. The process continues until sodium hydroxide solution strength of about 46-50% is reached, with cooling of the solution and separation of crystallised salts further reducing impurities to a comparable level to diaphragm cell derived industrial grade sodium hydroxide.

主权项

1. A process for manufacture of sodium hydroxide and sodium chloride products from a brine stream containing at least sodium chloride, and sodium carbonate or sodium bicarbonate (or a mixture of sodium carbonate and sodium bicarbonate), which comprises at least the following steps:
a) converting (causticizing) the sodium carbonate and sodium bicarbonate present to sodium hydroxide through addition of lime to the sodium chloride rich brine; b) separating the causticized brine from unreacted lime and calcium carbonate formed; c) concentrating the causticized brine via evaporation of water such that sodium chloride crystals form; d) separating the sodium chloride crystals from the saturated solution; e) continuing the evaporation/crystallisation process until only a concentrated sodium hydroxide solution remains.