Carbon dioxide-hardened sodium silicate-bonded sand regeneration using calcium carbide slag: The design and feasibility study

Abstract

Wet regeneration of sodium silicate sand (SBS) can yield a high regeneration rate. However, its large-scale implementation is limited by high cost of reagents and required alkaline wastewater treatment. Therefore, excessive SBS is extensively piled-up or buried, causing a huge waste of resources and environmental pollution. This study aimed to mitigate this problem by regenerating CO2-hardened SBS using a cheap regeneration reagent, namely calcium carbide slag (CCS), which is an easily available industrial waste, and considering the alkaline substance recovery. The regeneration mechanism was explored by macro-tests and micro-analysis. The results proved that CCS causticized the regenerated wastewater, forming a strong alkaline environment and speeding up the sodium silicate film peeling-off. In 20 min, a 92% regeneration rate was reached. The compressive strength of the sand core prepared by regenerated sand (RS) exceeded that of the new sand nearly twice if the same binder is used. At the same time, the regenerated wastewater flocculated after adding CCS, and there was no need to add other reagents. After natural precipitation, an alkaline solution with NaOH purity of 84% was obtained, which could be reused in chemical industry. This method has the advantages of low regeneration energy consumption, small secondary pollution, and excellent regeneration effect, making lucrative implying its large-scale implementation. It also substantiates the further SBS application in construction and chemical industry.