Patent ID: 6193945
Filing Date: 2001-02-27
Classification: C01F,C01P,D21H

Abstract:
A method of recovering calcium compounds from waste material comprising the steps of:(a) providing waste material containing calcium compounds in an acid soluble form from at least one waste material source selected from the group consisting of (i) industrial reject material, (ii) recycled waste material, and (iii) pigment-discolored natural calcic material;(b) preparing an aqueous suspension of said waste material provided in step (a);(c) lowering the pH of said aqueous suspension prepared in step (b) to a pH less than 6 by mixing an acid therein to provide a suspension including an acidic liquid phase containing said calcium compounds and other acid-soluble non-calcium compounds;(d) raising the pH of said acidic liquid phase obtained in step (c) to a pH greater than 6 by mixing a base therein to precipitate a major portion of the non-calcium compounds present in said liquid phase and thereby provide,(1) a solid phase, including the precipitated non-calcium compounds and other non-soluble impurities, and(2) a neutral or basic liquid phase, including a major portion of said calcium compounds in soluble form;(e) separating said solid phase from said neutral or basic liquid phase obtained in step (d);(f) carbonizing said neutral or basic liquid phase separated in step (e) to precipitate said calcium compounds as CaCO.sub.3 ; and(g) separating the CaCO.sub.3 precipitated in step (f) from said neutral or basic liquid phase.