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 (Z(p)) before and after the absorption of heavy metals, attempting to seek the relationship between the changes of surface electrical charges on the fine particles (ΔZ(p)) 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 acids >> kaolin > 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 ΔZ(p) 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(ΔZ(p))(d), whereas Pb²⁺, Zn²⁺, and Cd²⁺ tended to conform to a relationship expressed by X/M = a(ΔZ(p))+ b. As to humic acids, Cu²⁺ fitted best with X/M = c(ΔZ(p))(d), and its R² value was greater than 0.99. The remainder of the heavy metal ions had similar R² values.