Recycling of hazardous and industrial solid waste as raw materials for preparing novel high-temperature-resistant sulfoaluminate-magnesia aluminum spinel cement

Abstract

Secondary aluminum dross from aluminum smelter plants is a hazardous waste with no effective method for realizing its disposal and utilization safely. This research evaluated the potential of preparing novel high-temperature-resistant sulfoaluminate-magnesia aluminum spinel (SAC-MA) cement using secondary aluminum dross, carbide slag, magnesite tailings and desulfurization gypsum as the raw materials for the replacement of natural resources. Furthermore, the leaching toxicity of unroasted and preroasted secondary aluminum dross was analyzed. The mineral phase and microstructure of clinkers and hydration products were also considered and their effect on the mechanical properties and microstructure of the high-temperature-resistant SAC-MA samples was researched. The experimental results showed that roasting detoxification was effective in realizing the safe disposal of secondary aluminum dross and magnesia aluminum spinel, dicalcium silicate and Fe→Al substitutional ye'elimite formed in the SAC-MA clinker after the sintering using hazardous and industrial solid waste. Improved high temperature resistance of SAC was also observed. High temperature induced the decomposition of ettringite and led to its structural relaxation. Surprisingly, the existence of magnesia aluminum spinel made the structure of ettringite smaller and decreased the decomposition degree of ettringite, as well as improving the high temperature resistance of SAC. Changes in the main skeletal structures of ettringite and AH3 gel were not noticeable, which still had good stability at 200 °C for the SAC-MA sample. However, ettringite gradually became amorphous at 200 °C for the SAC sample. These results strongly indicated that using hazardous waste, including secondary aluminum dross, as raw materials for preparing SAC-MA was far superior to SAC with regards to high temperature resistance. This study contributed a novel example of converting hazardous and industrial solid waste into high value-added materials and may open a new approach for synthesizing high temperature-resistant SAC-MA cement from low-cost feedstocks.