Removal of arsenic and sulphate from the copper smelting industrial effluent

Effluent from the processing of arsenic-bearing ores may contain varying amounts of As(III) and As(V), oxyanion, arsenite and arsenate. The industries are adopting the ferric arsenate precipitation; the problems aroused in this method are the formation of large amount of sludge. The effective pH range for the precipitation of ferric arsenate is 4–8. But pH of the effluent is about 0.6 only and the sulphate concentration is more in the effluent. Therefore it is required to raise the pH for precipitation of ferric arsenate by the addition of an alkali. Due this reason the alkali consumption is more. The addition of chemicals may elevate the total dissolved solids (TDS) level. This investigation aims at the removal of arsenic (incoming contaminants levels are in the range of 1000–2000 mg/L containing other heavy metals) from the metallurgical effluent either by electrodialysis (ED) or electrochemical ion-exchange (EIX) technique, followed by electrocoagulation (EC). Using ED, at the current density of 2 A/dm2, arsenic can be removed up to 91.4% and sulphate up to 37.1%. Using EIX, at the current density of 3 A/dm2, arsenic can be removed up to 58.2% and sulphate up to 72.7%. Using EC, at the current density of 1.5 A/dm^2, arsenic can be removed up to below detectable limit by atomic absorption spectrometer. By combining both the EIX and EC processes the consumption of alkali needed to raise the pH can be effectively minimized.