William K. Buah

Activated carbons prepared from refuse derived fuel and their gold adsorption characteristics

Activated carbons produced from refuse derived fuel (RDF), which had been prepared from municipal solid waste have been characterized and evaluated for their potential for gold adsorption from gold chloride solution. Pyrolysis of the RDF produced a char, which was then activated via steam gasification to produce activated carbons. Steam gasification of the char at 900°C for 3 h yielded 73 wt% activated carbon. The derived activated carbon had a surface area of 500 m2 g−1 and a total pore volume of 0.19 cm3 g−1. The gold adsorption capacity of the activated carbon was 32.1 mg Au g−1 of carbon when contacted with an acidified gold chloride solution. The gold adsorption capacity was comparable to that of a commercial activated carbon tested under the same conditions and was well in the range of values of activated carbons used in the gold industry. Demineralization of the RDF activated carbon in a 5 M HCl solution resulted in enhancement of its textural properties but a reduction in the gold adsorption rate, indicating that the metal content of the RDF activated carbon influenced its gold adsorption rate.

Granular activated carbons from palm nut shells for gold di-cyanide adsorption

Granular activated carbons were produced from palm nut shells by physical activation with steam. The proximate analysis of palm nut shells was investigated by thermogravimetric analysis, and the adsorption capacity of the activated carbons, produced as a result of shell pyrolysis at 600°C followed by steam activation at 900°C in varying activation times, was evaluated using nitrogen adsorption at 77 K. Applicability of the activated carbons for gold dicyanide adsorption was also investigated. Increasing the activation hold time with the attendant increase in the degree of carbon burn-off results in a progressive increase in the surface area of the activated carbons, reaching a value of 903.1 m2/g after activation for 6 h. The volumes of total pores, micropores, and mesopores in the activated carbons also increase progressively with the increasing degree of carbon burn-off, resulting from increasing the activation hold time. The gold di-cyanide adsorption of the activated carbons increases with the rise of pore volume of the activated carbons. The gold di-cyanide adsorption of palm nut shell activated carbon obtained after 6-h activation at 900°C is superior to that of a commercial activated carbon used for gold di-cyanide adsorption.

Combustible gaseous products from pyrolysis of combustible fractions of municipal solid waste

Municipal Solid Waste (MSW) sample was pyrolysed under inert atmosphere of nitrogen in a static bed pyrolysis reactor, heated at a controlled rate of 10°C min-1 to a final temperature of 700°C to recover combustible gaseous product. The yield of the combustible gaseous product was 23.01 wt%. Other pyrolysis products were 32.00 wt% char and 44.99 wt% oil. The combustible gaseous product evolved, analysed off line by gas chromatography to contain mainly CO2, CO, H2, CH4, C2H6 and C3H8 has relatively high calorific value of 18.0 MJ m-3, making the gas suitable for use as a fuel. The significance of this research is that the pyrolysis recovered combustible gas can now be stored conveniently and easily transported for various applications. This research, in addition to providing energy needs if implemented, has the capacity to stimulate regular collection of MSW to feed a pyrolysis plant thereby reducing accumulation of the waste in communities, especially in developing countries.

Recovery of Gold from Waste Jute Material - A Case Study

Recovery of gold from aurocyanide complex solutions by zinc precipitation requires a relatively clear solution for effective precipitation of the gold. Goldfields Ghana Limited (GGL), one of the companies in Ghana, which used zinc precipitation in its former treatment plant to recover gold from solution, clarified the gold pregnant solution by passing it through sand vats, which were lined with jute materials. The jute liners in the sand vats, intended to remove suspended solids from solution, were found to have adsorbed gold in the order of 2.27 g/t. These liners have been accumulated over the years as waste. This paper investigates the feasibility of extracting the gold locked up in the waste jute material. Samples of the waste jute material were collected at uniform intervals from the surface of the waste dump, thermally oxidized to produce ash and leached with cyanide. Gold recovery from the jute ash into solution after 20 hours cyanidation was 97.92%. It was also established that favourable gold recovery was obtainable by leaching the jute ash mixed with the ore being treated at the plant. At GGL, where it is estimated that about 500 tonnes of the waste jute material has been accumulated over 118 years of operation of the zinc precipitation plant, about 1.1343 kg of gold can be leached into solution and recovered to increase the total gold recovered by the company. The implication is that in processing plants where this technology is applied, the waste jute accumulating over a period of time could be occasionally treated to recover its gold content as an additional income. Ghana Mining Journal Vol. 9 2007: pp. 50-53