Patent ID: 6280630
Filing Date: 2001-08-28
Classification: C02F,Y10S

Abstract:
A process for the removal of sulphates and calcium from a water stream, said process comprising the steps of:(a) adding an alkali to the water stream to raise the pH of the water stream to between 11 and 12.6;(b) combining the water stream with amorphous aluminum trihydroxide (Al(OH).sub.3) to cause formation of ettringite (3CaO.Al.sub.2 O.sub.3.3CaSO.sub.4.31/32H.sub.2 O) as a precipitate;(c) removing the precipitated ettringite from the water stream; and(d) decomposing the removed ettringite to recover amorphous aluminum trihydroxide, said decomposing comprising (a) treating the ettringite with a saturation calcium sulphate solution in an amount sufficient to form a suspension of amorphous aluminum trihydroxide in a supersaturated solution of calcium sulphate and (b) recovering the suspended amorphous aluminum trihydroxide while leaving the calcium sulphate remaining in the supersaturated solution.