Recycling of hazardous solid waste material using high-temperature solar process heat. 1. Thermodynamic analysis

The thermochemical conversion and recycling of hazardous solid waste materials is investigated using high-temperature solar process heat. Two important sources of wastes contaminated with heavy metal oxides are considered: (1) electric are furnace dust (EAFD) and (2) automobile shredder residue (ASR). The chemical equilibrium composition of these complex materials and the energy required to process them, using carbon, methane, or pyre-coke as reducing agents, are computed for temperatures in the range 300-2000 K. Metals can be extracted from their oxides in reducing atmospheres at above 1300 K for both EAFD and ASR: Zn is obtained in the gas phase, while Fe, Pb, and Cu are obtained in the condensed phase. The thermal energy requirements for converting EAFD at 1500 K are 3008 kJ/ kg and 4143 kJ/kg using C(gr) and CH4 as reducing agents, respectively. For converting ASR at 1500 K, 2455 kJ/kg are required. The solar exergy conversion efficiency, i.e., the efficiency of converting solar energy into the chemical energy of the reaction products (given by the Gibbs free energy change of product oxidation), can be as high as 69% for the EAFD conversion and 87% for the ASR conversion. Major sources of irreversibilities are those associated with the reradiation losses of the solar reactor and the heat rejected during the quenching. The use of concentrated solar energy as the source of process heat avoids emissions of greenhouse gases and other pollutants derived from the combustion of fossil fuels and further offers the possibility of converting waste materials into valuable commodities for processes in closed and sustainable materials cycles.