Characteristics of heavy metal absorption of river bed sludge components

This research work used quartz sands, kaolin, and humic acids to simulate the components of river bed sludge to study their absorption characteristics of Cu2+, Zn2+, Pb2+, and Cd2+, at different pH, individually and as a mixture. This work also measured the zeta potential of the sludge (Zp) before and after the absorption of heavy metals, attempting to seek the relationship between the changes of surface electrical charges on the fine particles (ΔZp) and per unit absorbent uptake of heavy metal ions (X/M). The results show that the capacity of metal ion absorption was, in a descending order, humic acidskaolin>quartz sands. The binding capacity of absorbants and metal ions was in the following order: Pb2+>Cu2+>Cd2+>Zn2+. However, at higher pH, Cd2+ and Zn2+ both exhibited an increased affinity for humic acids and kaolin. The straight line and logarithmic regression treatments of ΔZp and X/M data revealed the following relationships: kaolin exhibited an interaction relationship with Cu2+ and the mixed ions according to the expression, X/M = c(ΔZp)d, whereas Pb2+, Zn2+, and Cd2+ tended to conform to a relationship expressed by X/M = a(ΔZp)+b. As to humic acids, Cu2+ fitted best with X/M = c(ΔZp)d, and its R2 value was greater than 0.99. The remainder of the heavy metal ions had similar R2 values.