Copper Biosorption by Spent Coffee Ground: Equilibrium, Kinetics, and Mechanism

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Abstract

The potential use of spent coffee ground (SCG) for the removal of copper has been investigated as a low-cost adsorbent for the biosorption of heavy metals. Adsorption batch experiments were conducted to determine isotherms and kinetics. The biosorption equilibrium data were found to fit well the Freundlich model and an experimental maximum biosorption capacity of copper ions 0.214 mmol/g was achieved. The biosorption kinetics of SCG was studied at different adsorbate concentrations (0.1–1.0 mM) and stirring speeds (100–400/min). The results showed an increase in the copper ion uptake with raising the initial metal concentration and the kinetic data followed the pseudo-second order rate expression. The effect of stirring speed was a significant factor for the external mass transfer resistance at 100/min and coefficients were estimated by the Mathews and Weber model. Biosorption of copper ions onto SCG was observed to be related mainly with the release of calcium and hydrogen ions suggesting that biosorption performance by SCG can be attributed to ion-exchange mechanism with calcium and hydrogen ions neutralizing the carboxyl and hydroxyl groups of the biomass.

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