An Investigation of Gold Adsorption from Binary Mixture Using Selective Mesoporous Silica Adsorbents

Koon Fung Lam
Hong Kong University of Science and Technology

King Lun Yeung
Hong Kong University of Science and Technology

Gordon McKay
Hong Kong University of Science and Technology

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     Last modified: January 25, 2006

Abstract
Besides health and environmental problems of heavy metal pollution, there is a strong economic motivation for the removal and recovery of expensive, heavy metals from process water for recycle and reuse. Gold-selective adsorbents were prepared from MCM-41 by grafting organic amine groups (i.e., RNH2, R2NH and R3N; R = propyl). NH2-MCM-41, NRH-MCM-41 and NR2-MCM-41 displayed strong affinity for gold and at 1 mmole/g loading adsorbed 0.40, 0.33 and 0.20 mmol/g of gold. Copper and nickel were not adsorbed on these adsorbents. A series of binary adsorption equilibrium studies using NH2-MCM-41 containing 2.2 mmole RNH2/g shows that NH2-MCM-41 adsorbs only gold from solutions containing copper and nickel with adsorption capacity of 0.6 moles Au/mole RNH2 (1.1 mmole Au/g NH2-MCM-41). Copper and nickel was not adsorbed by NH2-MCM-41 regardless of the solution concentration, composition and pH (i.e., 2 to 4) in the presence of gold. LeVan and Vermeulen adsorption model, based on single component Freundlich isotherm, accurately predicted the binary adsorptions. The adsorbed gold was completely recovered by a simple acid wash and the recovered gold solution is ninety nine percent pure. The regenerated NH2-MCM-41 remained 100% selective for gold removal and exhibited the same adsorption capacity even after several reuses.