Comparison of Adsorption Properties of Activated Carbons with Different Crops Residues as Precursors for Gold Cyanide Recovery: An Iranian Gold Industry Guide

Document Type: Research Article

Authors

1 1. Department of Chemical Engineering, Faculty of Engineering, Arak University, Arak 38156-8-8349, Iran.

2 Department of Chemical Engineering, Faculty of Engineering, Arak University, Arak 38156-8-8349, Iran.

Abstract

Adsorption of gold cyanide onto three types of activated carbons (ACs) has been investigated in batch and column adsorption conditions. Applied ACs have been derived from different crops precursors i.e., coconut shell (CAC), peach stone (PAC) and walnut shell (WAC). As peach stone and walnut shell are abundant agricultural residues in Iran, the activated carbons produced from these precursors are economically preferable for the gold recovery process. The ACs were characterized using FTIR, SEM, BET, and Wet-Bed Compaction Hardness analyses. Batch equilibrium adsorption data was analyzed using the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. Freundlich isotherm was in better agreement with the equilibrium data and the maximum adsorption capacity (40.8 mg/g) was tabulated for CAC. Adsorption kinetics was also modeled using pseudo-first order, pseudo-second order, and intraparticle diffusion models. The PAC recorded the highest removal rate in the light of better agreement of the pseudo second order model. Fixed-bed column experiments were carried out at different initial gold concentrations (30, 50 mg/l) to determine the characteristics of the breakthrough curves. The maximum bed capacity (37.55 mg/g) was obtained for CAC. Three column adsorption models including, Thomas, Yoon–Nelson, and Adam–Bohart, were applied to describe the breakthrough curves. Both Thomas and Yoon–Nelson models were in appropriate agreement with the experimental column adsorption results. This research introduces peach stone as a promising precursor considering availability, technical, and economical aspects for the production of AC for gold recovery from cyanide leach solutions. Results are also conductive for gold mining industries to select the appropriate activated carbon.

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