GB951643A - Process and apparatus for the purification of brine - Google Patents

Abstract

A two step process for continuously purifying brine by consecutively adding lime and an alkali-metal carbonate to continuously upward-flowing brine, whereby flakes are formed that settle out, the velocity of the brine flowing upwardly through the first reaction zone decreasing on account of the cross-section of the zone widening, the addition of the brine occurring where the flakes begin to form a sludge, comprises the steps of (1) continuously adding to the upward flowing brine in a first reaction zone and at a temperature between 50 DEG C. and 100 DEG C., lime in countercurrent flow, (2) regulating the lime feed rate to maintain the pH of the brine at at least 10.0 at the place where it leaves the first reaction zone, (3) regulating the flow velocity of the brine and removal rate of the sludge to prevent sludge or flakes carrying over to the second reaction zone, (4) adding, in a second reaction zone, an alkali metal carbonate in excess of that required for purification, and (5) regulating the flow velocity in the second zone to prevent flake or sludge removal therefrom. The lime may be in the form of calcined lime or milk of lime. Sodium sulphate may be added to the brine prior to entering the second zone to reduce the alkali metal carbonate requirement, for example in the form of a mother liquor obtained by the evaporation of a sodium sulphate containing brine. There may be added before or simultaneously with the alkali metal carbonate, alkali bicarbonate in an amount such that the hydroxyl ion concentration remains at at least 10-6 g/l. Similarly CO2 may be introduced between the two zones for the same purpose. The second zone may be situated above the first zone, and the sludge precipitated in the second zone may pass through the first zone.