Method of recovering minerals from papermaking sludge and sludge-derived ash

Abstract

Extraction of minerals from papermaking sludge or sludge-derived ash is accomplished by mixing with a solution of an inorganic or organic acid--generally 0.1% to 35% by weight, preferably 2% to 20%, and most preferably 3% to 8% by weight. In preferred embodiments, the material is carried as an aqueous solution and combined with 2% to 20%, and most preferably 3% to 6%, HCl; 2% to 25%, and most preferably 8%, HNO.sub.3 ; 2% to 30%, and most preferably 8%, acetic acid. Generally, the amount of acid added into the reaction mixture preferably is 0.8 to 2.0 times the stoichiometric calcium carbonate content in the mixture, more preferably 0.8 to 1.2 times the stoichiometric content, and most preferably matched to the stoichiometric content of calcium carbonate in the mixture. The acid-containing mixture is incubated (with agitation, if desired, to shorten the reaction time) to solubilize the desired minerals, following which the liquid phase is isolated, and mineral salts recovered therefrom.

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