Redução das perdas de zinco associadas aos processos de purificação do licor por cementação e de tratamento dos resíduos gerados da Votorantim Metais

Abstract

The present work aims at reducing the losses of zinc associated to the processes of "purification of the zinc sulfate solution by cementation" and "treatment of the cementation residues", in the Três Marias plant of the Votorantim Metals Zinc, MG. The generation of the residues,approximately 300t/month imply in a reduction of the overall zinc recovery of the plant in 0,50-0,60%. In addition to these losses, the generation of the ementationresidues results in important environmental liabilities, and in significant disposal costs. The present work involved two stages of investigation. The first one focused on the reduction zinc consumption in the "purification of the zinc sulfate solution by cementation". The second one aimed the optimization of the current "treatment of the cementation residues ",using the methodology Six Sigma. The kinetic studies showed that is possible to reach the required level of impurities within a residence time of 90 minutes with the adjustment of the particle size of zinc dust used in the stage of purification. These conditions allow theelimination of the "2nd stage of purification of the liquor", with a potential reduction of 23t Zn/mês, which is equivalent to 8.4% of the total zinc dust consumption in the plant. The results obtained in the analyses of the solid residues point to further possibilities of improvements of the purification process to decrease the consumption of metallic Znthrough parallel reactions and to favor the cementation of copper. The optimization of the process of "treatment of the cementation residues" was reached by the application of the methodology Six Sigma, through rigorous controls identified in the statistical planning of experiments. It was possible to reduce significantly the variability of the process as well as the associated losses of contained zinc (with respect to the zinc fed in the plant) from 0,48% to 0,102 ± 0,026%. In the sigma scale, the process reached a world-class level,increasing from 0,24 to 7 sigma. The zinc recovery from the residues was of 68t Zn/month,contributing with an increase of 0.37% in the overall yield of the plant and a 62% reductionof the amount of the residues. The reduction of 91t Zn/month, in the two stages of this investigation, is equivalent to an economy of 496,000 US$/year with Zn dust and a potential savings of 781,000 US$/year, with the associated reduction in the consumption of imported concentrate.