Neutralization and co-precipitation of heavy metals by lime addition to effluent from acid plant in a copper smelter

The effluents from acid plants generated in copper pyrometallurgy contain high concentrations of sulphates and heavy metals that difficult further reuse of contained water. In this study, the neutralization of an effluent was studied by progressive addition of lime as a pH-modifying agent. Batch and continuous tests were conducted to evaluate the neutralization potential between pH 1 and 11 on an effluent containing As, Cu, Fe, Zn, Ni, Pb, Cd, Hg, Sb, Mn, Mo, Al and SO42−. In batch process neutralization, an efficiency of about 99.5% was attained except for Sb 98% and Pb 97%. Similar values were obtained for the continuous mode. The production of gypsum with commercial value was also evaluated based on the Chilean standard for hazardous solid waste measured by the TCLP (Toxicity characteristic leaching procedure) test. Best results were obtained between pH 1 and 2, after a minimum of four washes. The rheology of the residual solids was characterized using filtration tests and the sedimentation rate determined with different flocculants. The final liquid effluent was evaluated by the ASTM corrosion test and showed a non-corrosive nature, with a corrosion rate of 0.07 mm/year, well below the value allowed by established standard of 6.35 mm/year.