Agricultural waste biomass converted to activated carbon as a material for gold processing
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ORIGINAL ARTICLE
Agricultural waste biomass converted to activated carbon as a material for gold processing William K. Buah • Paul T. Williams
Received: 11 January 2012 / Accepted: 28 August 2012 / Published online: 27 September 2012 Ó Springer 2012
Abstract Waste biomass in the form of coconut shells was pyrolyzed and activated with steam to produce activated carbons, which were then assessed for their potential for use in the processing of gold. Activated carbons with different amounts of carbon burn-off were prepared by steam activation of carbonized coconut shells. Carbonization of the shells was performed at a pyrolysis temperature of 600 °C and the resulting chars were activated in steam at a gasification temperature of 900 °C and various durations of activation time. Textural characteristics of the derived activated carbons were determined and their effects on gold adsorption from an acidified gold chloride solution were studied. The surface area and porosity of the activated carbons increased with activation time up to 59 wt % carbon burn-off. A further increase in the burn-off resulted in the loss of structural walls between pores and consequently, a decline in the surface area and porosity of the activated carbons. The gold adsorption capacity and rate of gold adsorption from the gold chloride solution onto the activated carbons were found to increase significantly with the total pore and micropore volumes of the activated carbons. Keywords Activated carbon Gold processing Coconut Surface area Porosity
Introduction Agricultural waste biomass residues include organic material by-products from the harvesting and processing of W. K. Buah P. T. Williams (&) Energy Research Institute, The University of Leeds, Leeds LS2 9JT, UK e-mail: [email protected]
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agricultural crops. Agricultural residues include harvesting wastes generated in the field, such as rice straw and maize stalks, whereas agricultural wastes produced during the processing of the crop include rice husks, coconut shells and coconut coir. The world’s total coconut production was an estimated 55.5 billion nuts in 2006 [1], with production dominated by Indonesia (16 billion nuts), India (13 billion nuts), Philippines (13 billion nuts) and Brazil (3.5 billion nuts). The average weight of a coconut is 1.2 kg and the shell comprises about 15 % of the weight; consequently, approximately 10 million tonnes of post-processing coconut shell waste material is generated per year [1]. The shell is a waste material, but has the potential to be processed to produce activated carbon. Currently, it is estimated that only 0.13 million tonnes of activated carbon are generated from coconut shells, annually [1]. Therefore, there is great potential for coconut shell waste to be more widely recycled and processed into a useful and valuable product. Activated carbons have a highly developed porous structure and a large internal surface area, and are used extensively in a range of industrial applications. In general, activated carbons with higher s
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