Leaching Behavior and Stabilization Mechanisms of Nickel and Copper in Ceramic Matrix

Abstract

For soils and waste materials contaminated by hazardous metals, stabilization and solidification, such as cementation and thermal treatment, may provide an opportunity to significantly reduce the release of metals from the stabilized products. However, due to the compositional complexity of most environmental materials, the mechanism of such stabilization effect was often not clearly identified, not even mentioning to be quantitatively evaluated. As many waste-to-resource strategies are employed for more sustainably treating and beneficially using the waste materials in a wide variety of applications, scientific investigations and quantitative evaluation of the stabilization effects of hazardous metals in the products are crucial to safeguard the human health and prevent further environmental pollution. In addition, the understanding of the metal incorporation efficiencies achieved by different metal stabilization mechanisms is also important to facilitate the design of reliable treatment schemes. Our current findings on the incorporation mechanisms between kaolinite and hazardous metals (nickel and copper) under different thermal conditions are reported in this study. The results show the important role of forming aluminates and ferrites to significantly reduce the metal leachability from the treated products. Quantitative X-ray diffraction (XRD) technique and prolonged leach tests were applied to report the metal incorporation efficiencies and the durability of thermally treated products. In addition to the product leachability, the leaching of metals on different water-mineral interfaces were also analyzed for their congruent and incongruent leaching behavior, together with the assist of examining the chemical composition of leached surface via the surface-sensitive X-ray photoelectron spectroscopy (XPS) technique. With the reported information, this study has identified the key mechanisms of stabilizing the hazardous nickel and copper metals in ceramic matrix and also demonstrates the importance of quantitative understanding in the development of safer waste-to-resource strategies.