Removal of lead from waste material containing carbon

Abstract

During the process of catalytic pyrolysis in recycling of non-biodegradable plastic waste, black coloured carbon sludge is formed as by-product. Since this sludge emanates from lead bath, the sludge is expected to contain lead. Disposal of this sludge is environmentally hazardous. The objective of this investigation is to find a suitable process to separate lead from carbon sludge so as to recycle them into the same process. The average size of the carbon sludge was found to be 98µm and most of the micron and sub-micron carbon particles were found either adsorbed on larger size particles or strongly agglomerated. The x-ray diffraction indicated the presence of aluminium silicate/zeolite, pseudo alumino silicate, aluminium silicate hydride, calcium magnesium silicate and kaoline clay apart from carbon. The energy dispersive x-ray pattern showed the presence of 71.14% C, 13.58% Ca, 5.24% Si, 2.21% Al, 2.16% Fe, 1.09% Mg and 0.32% Pb. The physical separation methods such as heavy media separation and magnetic separation and physico-chemical separation like flotation were observed to be ineffective for the selective separation of lead from carbon waste. However, lead could be effectively separated to the extent of 98.6% (~ 0.005% Pb) by four stage leaching process using HNO3 as leachant. Thus the carbon sludge can then be safely disposed or utilized as adsorbent for the removal of toxic compound and metal ions. The dissolved lead can be removed by neutralization and precipitation or by other methods.