Adsorption Mechanism of Copper and Cadmium onto Defatted Waste Biomass

In this study, the amount of copper or cadmium adsorbed using waste biomass (i.e., coffee grounds (CG) and rice bran (RB)) was investigated. The amount of crude protein in defatted CG (D-CG) or RB (D-RB) was greater than that in CG or RB, respectively. The amount of copper or cadmium adsorbed using CG was greater than that using RB. Additionally, the amount of copper or cadmium adsorbed was not affected by the presence of fat in CG. Adsorption data was fitted to the Freundlich equation, and the correlation coefficients were in the range of 0.794-0.991. The main adsorption mechanism was thought to be monolayer adsorption onto the surface of the waste biomass. The adsorption rate data was fitted to the pseudo-second-order model, and the correlation coefficient average was in the range of 0.891-0.945. This result showed that the rate-limiting step may be chemisorption. Moreover, the amount of copper or cadmium desorbed from CG or RB using 0.01 mol/L or 1.00 mol/L HNO(3) was investigated. Desorption with 0.01 mol/L HNO(3) resulted in the recovery of 86-97% of the copper and cadmium, indicating that copper or cadmium that was adsorbed using waste biomass was recoverable.