A Study On Removal Of Mercury And Lead Ions From Wastewater By Sulfide Precipitation-Flotation

Abstract:In this paper, Hg2+and Pb2+in the wastewater were removed by sulfide precipitate flotation. The influence of initial pH value of wastewater, reaction time, sodium sulfide concentration, stirring intensity and heavy metal ion concentrations on sulphide precipitation and of pH value of flotation, dosage of collectorr, flotation time on flotation behavior have been investigated. Based on the tests, the related mechanism problems are analyzed and investigated.The precipitation test results show that:sulfide precipitation is suitable for different concentrations of Hg2+and Pb2+wastewater treatment and precipitation rate is less affected by the pH value of wastewater. When sulfide/mercury molar ratio is1.1, the precipitation effect of Hg2+is still very good and the residual Hg2+was0.03mg/L even under strongly acidic conditions. When pH value is from3to10and sulfide/lead molar ratio is1.5, the residual Pb2+was less than0.50mg/LThe flotation test results show that butyl xanthate, diethyl dithiocarbamate and butyl ammonium aerofloat can be used as a collectorr of mercury, lead sulfide deposits. They have good collectivity for deposits when pH value is from5to10, but only butyl ammonium aerofloat has good collectivity and consumes a small amount of agent under the strong acid condition. Treated the Hg2+and Pb mixed wastewater by coprecipitation flotation, Hg2+and Pb2+are less than0.03mg/L and0.30mg/L respectively in the treated wastewater. By fractional precipitation flotation to recovery mercury and lead one by one, the recovery of mercury is99.80%and grade is32.42%in the scum of the first stage flotation. The recovery of lead is99.50%and grade is up to83.25%in the scum of second stage flotation, the residual Hg2+is less than0.03mg/L and residual Pb2+is less than0.30mg/L in treated wastewater.Thermodynamic analysis results show that fractional sulfide precipitation Hg2+and Pb2+step is feasible by controlling the pH value of the solution and the dosage of sodium sulphide.The analysis of FT-IR indicate that butyl xanthate, diethyldithiocarbamate and butyl ammonium aerofloat have chemical adsorption on the surface of lead deposit and mercury deposit.