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Color removal from kraft mill effluents by a coagulation-flotation process Wood, Arnaldo Hugo

Abstract

The technique of coagulation-flotation has been evaluated for the removal of color bodies from kraft mill effluents. The process was based upon coagulation of the colloidal chromophores using a cationic surfactant (didodecyldimethylammoniurn bromide) as a coagulant and flotation agent. Several sets of batch experiments were designed and carried out in a flotation cell. The effects of pH over the range 3.6-5.6 and of surfactant concentrations from 100-200 ppm were investigated. An interaction was shown to exist between these two factors. The best results were obtained at pH 3.6 and 100 ppm of surfactant. Since the percentage of color removed was proven not to be reliable in expressing the process result, another approach had to be developed. Other studies embraced: a) the floatability of the surfactant in aqueous solution at different pHs and initial concentrations; b) the behaviour of the kraft mill waste during several acidification-alkalization sequences; c) the effect of storage on the color and solids content of the effluent. Variables such as premixing time, stirrer speed, air flow rate, sparger size, introduction of the surfactant and temperature were briefly inspected. Laboratory scale continuous equipment was assembled and run at the optimum batch conditions. The presence of a premixing stage turned out to be essential for the process. The results were comparable to those previously obtained in batch and hence the possibility of developing a continuous coagulation-flotation process was established.

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