Removing sulphate from waste water - by pptn. with aluminium salt and lime, esp. for treating water from gas desulphurisation units

摘要

Sulphate-contg. waste water is treated by adding, as pptn. agents, a water-soluble Al (III) salt (A) plus Ca(OH)2 and/or CaO. (A) is AlCl3 or Al(NO3)3 and the pptn. agents can be used together with (a) NaOH and/or (b) water-soluble Fe (III) salt, esp. FeCl3. The mole ratio Al:sulphate (in the water):Ca is 2:3:6-12. The water is mixed vigorously, for 15-30 min, with the pptn. agents (and opt. NaOH and Fe salt), then a polyelectrolyte soln. (e.g. polyacrylamide at 1-10 mg/l) added with gentle stirring. The mxit. is allowed to settle for 30-60 min without stirring, and the settled ppte. and purified supernatant liq. sepd. Pref. part of the ppte. is recycled to the treatment zone. USE/ADVANTAGE - To remove sulphate (which is corrosive to concrete) from e.g. industrial waste or partic. water from combustion gas desulphurisation units. Provides high purificn. at low chemical cost. Addn. of the Fe salt improves the degree of purification.