Adsorption and competitive adsorption of Pb~(2+),Cu~(2+),Cd~(2+) to humic acid

The given paper is aimed at presenting our research results on the adsorptive behavior of Cu2+,Pb2+ and Cd2+ onto humic acid which is extracted as a result of deposition of alkali-dissolving acid. As is known,the power of adsorption of Cu2+ by humic acid is stronger than that of Pb2+ and Cd2+ under the same initial concentration. Actually,the adsorption power of the three can be ordered as follows:Cu2+Pb2+Cd2+. In addition,significant relationship to the adsorption of Pb2+ and Cd2+ can be found in the equilibrium data of Langmuir,Freundlich and Temkin isotherms with the Freundlich isotherm fit best for (Pb2+:R2=0.994 9,Cd2+:R2=0.973 6). while Langmuir isotherm should be fit better for Cu2+(R2=0.998 4) than Freundlich isotherm. But the Temkin isotherm proves not to fit very well. Though pH value is the main factor that may influence the adsorption of Cu2+ and Cd2+,the influence of Pb2+ proves less significant. However,on the whole,it can be said that at low pH value humic acid tends to go against the adsorption of Cu2+,Pb2+and Cd2+. But with the increase of pH (pH=2-8),both the adsorption and adsorption rate would also rise in turn. Seen from the infrared spectrum of response,our research results have shown that the linking point among the humic acid and Pb2+ and Cd2+ lies mainly in between phenolic hydroxyl group and carboxyl of aromatic ring. Thus,it can be concluded that humic acid and Cu+ in addition to their relation with the phenolic hydroxyl group and carboxyl group,more link can be found between carboxyl and carboxyl of the aromatic ring.