Selective recovery of gold using some cross-linked polysaccharide gels

Abstract

Effective recovery of gold from aqueous acidic chloride media was achieved with different kinds of polysaccharides with different structures by treating with concentrated sulfuric acid. The gels were found to be highly selective for Au(III) over other precious and base metals at varying hydrochloric acid solution. The adsorption isotherms of Au(III) followed the Langmuir type of adsorption and the maximum adsorption capacities for Au(III) was evaluated as high as 7.57, 7.20, 5.64 and 4.80 mmol g⁻¹ for the gels of cellulose, dextran, alginic acid and pectic acid, respectively. Analysis of kinetic data shows that the uptake of gold(III) on celulose gel at the initial stage follows pseudo-first-order kinetics. Crystalline structure of the cellulose before and after the treatment with concentrated sulfuric acid was measured by XRD analysis. Furthermore, Au(III) was found to be reduced to elemental form by all types of polysaccharides gels, which was confirmed by the formation of clearly visible elemental gold particles and by means of the XRD-spectra of the adsorbents after adsorption. Infrared spectrum studies provided supporting evidence for the reduction of Au(III) to Au(0) with a suitable mechanism of Au(III) adsorption followed by reduction using various polysaccharide gels.