Characteristics and Affecting Factors of Humic Acid Adsorbing Heavy Metals Cu~(2+)Pb~(2+)Cd~(2+)

The adsorptive behavior of Cu2+, Pb2+, Cd2+ onto humic acid which extracted by alkali dissolution-acid deposition was investigated. Adsorption capacity of Cu2+ by humic acid was higher than Pb2+ and Cd2+ at the same initial concentration. The order of adsorption capacity was as follows: Cu2+Pb2+Cd2+. Equilibrium data of Langmuir, Freundlich and Temkin isotherms showed significant relationship to the adsorption of Pb2+、Cd2+, and the Freundlich isotherm fitted best(Pb2+:R2=0.994 9, Cd2+:R2=0.973 6). Langmuir isotherm was best for Cu2+(R2=0.998 4), then Freundlich isotherm, but Temkin isotherm did not fit very well. pH value was the main factor affecting adsorption of Cu2+ and Cd2+, but less effect of Pb2+. As a whole, at low pH value humic acid went against the adsorption of Cu2+, Pb2+, Cd2+. Along with the increase in pH(pH=2~8), both adsorption and adsorption rate were all rise. Characterization through the infrared spectrum of responses, the results showed that the link point of humic acid and Pb2+, Cd2+ mainly in between phenolic hydroxyl group and carboxyl of aromatic ring. Humic acid and Cu2+ in addition to combination between phenolic hydroxyl group and carboxyl, more link between carboxyl and carboxyl of aromatic ring.