Characteristics and control of Cr pollution in electroplating wastewater.
Distribution characteristics of Cr in the electroplating wastewater and sediments were investigated in Caitang Town,Chaozhou City,Guangdong Province.FeSO4 was used to reduce Cr6+ and Cr3+ was precipitated and removed by controlled pH value in electroplating wastewater in the experiment.Results showed that Cr and Cr6+ concentrations in the electroplating wastewater were 57.3mg/L and 42.4mg/L,exceeding electroplating wastewater discharge standard by 37 and 83 times respectively,which resulted in Cr6+ in stream exceeding surface water standard.There were low pH value and high conductivity in the electroplating wastewater.Cr concentrations in the sediments in electroplating areas were much higher than background value.Concentrations of Cr in the sediments were dominated by residual fraction,followed by oxidizable fraction and reducible fraction.The sequential geochemical extraction test showed that the sediments had low mobility and bioavailability for Cr.Cr6+ could be reduced into Cr3+ by ferrous sulphate,and reduction efficiency was highest at 4 of the ratio of Fe2+ and Cr6+.Cr in the electroplating wastewater could be removed most effectively at pH value 9 after Cr6+ was reduced by ferrous sulphate.