[Characteristics of Cu2+ adsorption by sawdust]

Sawdust was used to remove the copper ion from water as an absorbent. The result showed that adsorption of Cu2+ on the sawdust was a very rapid process and arrived at equilibrium about 1 h. The pseudo-second order kinetic equation gave better fitting result (R2 > 0.99). The main mechanism of adsorption of Cu2+ on the sawdust was ion exchange, and the adsorption capacity increased as pH increased. Ion strength had some effects on adsorption capacity: one part of Cu2+ was held in an inner-sphere complex and the other part of Cu2+ was held in an outer-sphere complex. Adsorption capacity of treated sawdust by acid and base increased compared to original sawdust. Isotherm of treated sawdust was fitted well by Langmuir-Freundlich model; original sawdust was fitted well by Langmuir model. Thermodynamics analysis showed that the adsorption process was spontaneous, exothermic and the entropy increased.