Effects of Humic Acid, Calcium and Bicarbonate on Arsenic(V) Removal from Groundwater by Zero-Valent Iron

摘要

The effects of humic acid (HA), Ca2+ and HCO3-on the arsenic(V) removal from groundwater by zero-valent iron (Fe0) were investigated using batch experiments. Arsenic was removed from groundwater, possibly by adsorption and co-precipitation, with the iron corrosion products. Ca2+ was observed to enhance significantly the removal of arsenic due to its aggregation with iron corrosion products. Higher Ca2+ concentration resulted in a faster removal rate of arsenic in the absence of HA. However, the presence of HA diminished the positive role of Ca2+ because of the formation of soluble Fe-humate complexes and the dispersion of colloidal iron corrosion products by HA in the groundwater. In the co-presence of Ca2+ and HCO3 -, the removal rate of arsenic increased with the higher concentrations of HCO3 -, which could result from the formation of CaCO3 and subsequently contribute to the aggregation of iron corrosion products. In the co-existence of HA, Ca2+ and HCO3 -, HA delayed the aggregation of iron corrosion products and thus inhibited the removal of arsenic. However, after the binding capacity of HA with dissolved iron was saturated, the presence of Ca2+ and HCO3-resulted in rapid aggregation of Fe-humate complexes and colloidal iron corrosion products and thus the removal of arsenic was significantly enhanced.