Competitiveness in removing copper, zinc and chromium trivalent in plating industrial effluent by using hydroxide precipitation versus sulphide precipitation

Plating industry wastewater is one of the processes that may contain various types of heavy metals. The most common heavy metals that mostly found are copper, nickel, cadmium, chromium, silver, zinc, and lead. In this study, three types of metals which are copper, zinc and chromium trivalent were removed using hydroxide precipitation and sulphide precipitation. Both performances of the method were observed and compared. A jar test was used to determine the optimum pH, coagulant dosage and precipitant dosage. The coagulant and precipitant used in this experiment was ferric chloride (FeCl₃), poly aluminium chloride (PAC), sodium hydroxide (hydroxide precipitant) and sodium sulphide (sulphide precipitation) respectively. In order to remove chromium trivalent, sodium metabisulfite was used to reduce chromium hexavalent to chromium trivalent. Based on the result, hydroxide precipitation can remove 86.61% of copper, 99.81% of zinc and 99.99% of chromium trivalent. While, for sulphide precipitation, 93.91% of copper, 99.37% of zinc and 99.99% of chromium trivalent were removed. Therefore, sulphide precipitation can remove better mixed heavy metals, thus it also produces less total suspended solid compared to hydroxide precipitation.