Remoção de cálcio de efluente de máquina de papel por precipitação/coprecipitação

• Autor(a) principal: Sousa, José Carlos Leandro de
• Data de Publicação: 2007
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2044
• topic: Cálcio; Efluente; Coprecipitação; Calcium; Effluent; Coprecipitation; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

In a integrated pulp and paper mill, 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), aluminum and manganese (IV) hydroxides, in the absence/presence of humic acid (extracted from humus) and phosphate-clay (extracted from per ferric latosol and modified with dibasic sodium phosphate), in addition to the precipitation in the presence of sodium oxalate. The results indicated that at low concentrations of ferric sulfate, aluminum sulfate and humic acid, the removal of calcium is low (5.9 to 12.7 %). In low concentrations of ferric and aluminum sulfate, but in the presence of humic acid 0.0025 % m/v, the removal percentages increased (17.2 to 18.8 %). 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 %), with the aluminum sulfate, the removal percentages were indifferent (close to 10.0 %). The use of manganese sulfate was not possible because it increased the concentration of calcium in the supernatant at pH 10. In this pH value, the presence of humic acid was unfavorable because the humic substances interact with the precipitated calcium carbonate, interfering with the crystal growth. The experimental procedure indicated that interactions occur between the used components and the calcium of the effluent. 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. The disadvantage is the residual oxalate, that can be removed in a biological treatment, for example, along with the organic matter present.