Predicting the Release and Migration of Potentially Harmful Elements (PHEs) during the Lightweight Ceramsite Preparation from Carbide Slag

Abstract

When preparing lightweight ceramsite using carbide slag, trace amounts of toxic elements are released into the atmosphere due to high-temperature calcination, posing a significant risk to the environment. The real-time monitoring of the released gases is challenging under laboratory conditions while preparing large quantities of ceramsite. Therefore, heating was simulated using experimental data and the FactSage 7.0 thermochemical database to study the release of harmful Al-, C-, H-, S-, and F-containing elements when using carbide slag to prepare lightweight ceramsite. The results indicated that no Al, C, H, S, or F elements were evident in the high-temperature liquid products obtained in a 50 °C to 1150 °C calcination temperature range. Al was present in a solid state with no gaseous products. When the temperature reached 450 °C, CO gas was released and its level increased as the temperature rose. H and S mainly combined into H2S gas, starting at 250 °C and reaching a peak at 1050 °C. H and F primarily combined into HF, starting at 400 °C. Other F-containing gases mainly included SiF4 and TiF3, which began to release at 800 °C and 900 °C, respectively. The release trends of HF, SiF4, and TiF3 were consistent with those of CO. This study aimed to conduct an environmental impact and management assessment for the preparation of lightweight ceramsite using carbide slag. The use of raw material carbide slag for the low-cost treatment of tail gas was proposed, which provides theoretical and up-to-date support for greening the application of the process.