Effects of Operating Variables of Sulphide Precipitation

Abstract

<p> The effects of engineering operating variables in the sulphide precipitation of Cu+2, Cd+2 and Zn+2 have been examined with a statistical experimental design. The independent (operating) variables studied were 1) the level of sulphide added, 2) the level of Fe+2 added as scavenger for excess HS- ion and 3) the pH level. The dependent variables were the concentrations of dissolved, suspended and total metals in the supernatant after treatment and the zone settling velocities of the suspensions.</p> <p> The major effect of the operating variables was to yield a precipitate which was either a stable colloid or a suspension which coagulated and settled. Stable colloid formation was associated with an excess of HS- ion. For those conditions which produced coagulant suspensions, 1) ten of the thirteen correlations between dependent and independent variables were not statistically significant at the 95% confidence level, 2) for practical purposes, variations in engineering operating variables did not alter the levels of dissolved and suspended Cu+2, Cd+2 and Zn+2 .</p> <p> When the precipitates coagulated and settled, concentrations of approximately 100 mg/l of each of Cu+2, Cd+2 and Zn+2 were reduced to mean values of 0.41, 0.33 and 0.62 mg/l total metals and 0.03, 0.01 and 0.37 mg/l dissolved metals respectively.</p>