TESTING AND ANALYSES OF CHAT AND ASPHALT-CONTAINING CHAT

摘要

Granular mine waste are generated from the extraction and beneficiation of lead/zinc minerals. The fine gravel waste, commonly known as chat, contains elevated levels of lead, zinc and cadmium which can result in potentially serious human health and ecological concerns. With the use of chat in a variety of applications such as road construction, there is an increased environmental concern due to the potential teachability of lead (Pb), cadmium (Cd) and zinc (Zn) at high concentrations. In this study, we examine the release of these three metals from raw chat and its reuse products, mainly cold-mix asphalt (CMA) and hot-mix asphalt (HMA), to determine the environmental stability of the materials under different environmental conditions. The teachability of metals was evaluated using extraction tests including the toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and deionized water extraction procedure (DWEP). In addition, the relative bioaccessability of the metals was determined by the relative bioaccessability leaching procedure (RBLP) tests. Based on the conducted leaching tests, it was observed that all the three samples failed the TCLP test. The Cd and Pb concentrations in the TCLP extracts were higher than the mandated TCLP limits for leaching from wastes. The TCLP extracts of CMA and HMA samples were found to be less than the limit for Cd, but higher for Pb. The experimental data also showed that the concentrations of Cd and Pb in the SPLP extracts were less than the National Drinking Water Primary Standards of 0.005 mg/L and 0.015 mg/L, respectively. This indicated the suitability of the mine tailing and its reuse products for beneficial applications. The percent bioaccessible metal followed the order: raw chat < HMA < CMA, probably due to its smaller particle size (< 250 mu m), compared to the particle sizes of CMA and HMA tested (< 2 mm). The data indicated that while the use of chat in asphalt is environmentally safe, care should be taken as metals could leach in significant concentrations when placed in moist environments for longer duration.