This study investigated adsorption of Lead (Pb 2+ ), Copper (Cu 2+ ) and Cadmium (Cd 2+ ) from minerals processing wastewater using activated carbons prepared from waste corn cobs. The activated carbons were prepared by carbonisation of the waste at 900°C to obtain carbonised corn cobs. Samples of the carbonised material were activated at 900°C for various durations using steam as an activating agent. The derived activated carbons were contacted with the wastewater containing heavy metals to assess their heavy metal removal abilities. From the results, up to 99.9%, 99.8 and 99.7% adsorption were attained for Pb 2+ , Cu 2+ and Cd 2+ respectively. This reduced the concentrations of Pb 2+ , Cu 2+ and Cd 2+ from 1.56 mg/L, 1.87 mg/L and 0.69 mg/L, respectively, to <0.002 mg/L for each metal ion. The results demonstrate that the derived activated carbons have the capacity to significantly reduce heavy metal concentrations to levels below the World Health Organisation (WHO) standards for safe drinking water.
The Gray acid mine drainage index (AMDI) was developed to detect, quantify, and categorise mine water and to monitor recovery of contaminated sites. A modified index (MAMDI) is proposed, incorporating the concentration of the dissolved metals that are present (at significant levels) and analysed at a site, and adjusting the weighting to reflect, in part, the maximum contaminant levels permitted by the U.S. EPA and WHO. In 98% of 206 analytical results applied to MAMDI, one or more of the four metals (Al, Zn, Cu, or Cd) used in AMDI were replaced by Mn, Ni, As, Pb, Tl, CN, and Be, while 63% had two or more replaced. A scatter diagram shows that in general, MAMDI is lower than AMDI when the total score is less than 50 and greater when the score is more than 50.
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 degrees 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.
Globally, major avenues available for dealing with waste Poly-Urethane (PU) are disposal at landfill sites and incineration. However, PU contains high levels of carbon and hydrogen that can be recovered for use as reductant in metal extraction processes. In this work the use of post-consumer PU as reductant for the production of metallic iron from iron oxide was investigated in a horizontal tube furnace through the composite pellet approach. Composite pellets were formed from mixtures of iron oxide and post-consumer PU. The iron oxide-PU composites were heated from room temperature to 1200 °C and then between 1200-1600 °C in a continuous stream of pure argon and the off gas was analysed continuously using an infrared (IR) gas analyser. Elemental analyses of samples of the reduced metal were performed chemically for its oxygen content using a LECO oxygen/nitrogen analyser. The extent of reduction was then determined at two temperatures 1200 °C and 1550 °C. Gas emission studies revealed the emission of large volumes of the reductant gas CO along with CO2. It is further demonstrated that post-consumer PU is effective at reducing iron oxide to produce metallic iron with complete reduction achieved in less than 4 min at 1550 °C. Keywords: Polyurethane, Composite Pellets, Infrared gas Analyser, LECO Carbon/Sulphur Analyser
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