Sodium hydroxide soln. purification - by lime addn. and concn. by evaporation esp. for treating Bayer process recycle soln.

摘要

An alkaline soln. contg. Free NaOH, Na2CO3, Na2SO4, NaAlO2 and impurities of mineral or organic origin is purified by treatment at up to the b.pt. with lime, followed by sepn. of a first ppte. consisting mainly of CaCO3 and a mixt. of other (in)organic salts of Ca, concentrating the liquor by evapn. to a free NaOH content of 50% to ppte Na2SO4 and sepg. Na2SO4 crystals to leave a free NaOH-rich liquor. The method can be used to treat recycled NaOH solns., e.g. in bauxite digestion processes, to prevent impurity build-up.