CALCIUM REMOVAL FROM PAPER MACHINE EFFLUENT BY PRECIPITATION/COPRECIPITATION

Abstract

In integrates pulp and paper mills, the effluent generated by the paper machine can be considered as a sector effluent, called white water, due to the high concentration of calcium. In this work, experiments were conducted to understand the behavior of the effluent in different pH values and to develop removal methods of calcium from the white water, aiming the reuse of water and the calcium recovery. Potentiometric titrations were carried out with HCl 0.022 mol L-1 and NaOH 0.025 mol L-1 standards, after adjusting the effluent pH at 12.0 and 2.0; respectively, which indicated inflection points for the carbonate, bicarbonate and kaolin, components capable of interaction with the soluble calcium. The methods for calcium removal consisted of coprecipitation/adsorption with iron (III) and aluminum hydroxides, and precipitation in the presence of sodium oxalate. The results indicated that at low concentrations of ferric sulfate and aluminum sulfate, the removal of calcium is low. In the adsorption assays in the presence of Fe(OH)3 and Al(OH)3, the increased of the ferric sulfate concentration enabled a slight increase in the calcium removal (16.5 to 31.0 %), reaching 65.0% in the adsorption more precipitation process in pH 10.0. In case of aluminum sulfate, the removal percentages were indifferent (close to 10.0%). In the precipitation of Ca2+ in the oxalate presence, the possibility of satisfactory percentages of removal was observed (75 to 87%), keeping the effluent with the conductivity and pH unchanged, it’s very important, because the increase of effluent conductivity to reuse cause break of paper made. The calcium oxalate recuperated can be heated excessively and changed and calcium carbonate and to be reused. Tests in the highest scale have to be realized to approve the reuse of water and calcium of paper machine.