Thermodynamic study of the acid-induced decontamination of waste green sand generated in a brass foundry
2020
Sawai, Hikaru | Rahman, Ismail M. M. | Jii, Naoyuki | Egawa, Yuji | Mizutani, Satoshi | Hasegawa, Hiroshi
Waste foundry sand (WFS) from the brass and bronze casting and molding process include various potentially toxic elements (PTEs), such as copper, zinc, tin, and lead. Hence, the utilization of WFS in construction and geotechnical applications evokes environmental concerns due to the rain-induced leaching of PTEs into the groundwater system. The present study investigated the extractive decontamination of WFS using mineral acids, e.g., HCl, H₂SO₄, or HNO₃. Favorable extraction efficiency was achieved with HCl as compared to the other mineral acids, which was further enhanced at high temperatures and increased acid concentrations. The thermodynamic analysis indicated that ≥ 4 mol L⁻¹ of HCl and ≤ 100 °C temperature ensured maximum extraction of PTEs due to the endothermic interactions between the HCl and PTEs. The HCl-treated WFS needed to be rinsed with water to restrict the after treatment elution of PTEs. The hazardous environmental impact of acid-treated WFS was evaluated following the standard leaching test and comparison with legislative recommendations for PTEs, which showed the water-assisted leaching rate of all the PTEs are within the regulatory limits.
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