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Abstract
Industrial and laboratory kraft black liquors were precipitated with a) water-soluble solvents (alcohols and acetone), b) calcium and aluminum salts, and c) alcohol-calcium solutions. Volume of solvent and the amount of Ca (or Al) were varied over wide intervals, and their effect on the amount and composition of precipitate was studied. Alcohol-calcium solutions were the best precipitating agent (90% of the lignin was recovered with good filterability). The pollutant load of the resulting filtrate showed considerable reductions in some parameters. Precipitation of black liquors with alcohol-calcium solution instead of acid precipitation or ultrafiltration may be an alternative to combustion.