Partially calcined CaCO3 for remediating multi-heavy metals-contaminated groundwater

Abstract

Calcium-based materials, known for their ease of handling and cost-effectiveness, are commonly used for removing heavy metals from groundwater. Unfortunately, among the calcium-based materials, calcium carbonate (CaCO3) is not a viable means of removing heavy metals due to its low solubility. Calcium oxide (CaO) with high solubility, obtained through the calcination of CaCO3, does effectively remove most heavy metals by raising the pH to alkaline condition. However, the dissolution of CaO increases the system temperature rapidly due to the heat associated with hydration, and excessive alkalinity is released due to rapid dissolution and pores become clogged due to hardening. To overcome these problems, this study proposed partially calcined CaCO3 (PCC) as a potential remediator of groundwater contaminated with multi-heavy metals. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) analysis confirmed the co-existence of CaCO3 and CaO phases in one material. In the partially calcined CaCO3 samples, the amount of CaO present increased with calcination temperature and residence time. More CaO was observed to result in greater removal of heavy metals. Compared to a binary mixture of CaO and CaCO3, PCC showed a slower dissolution rate of CaO, indicating control over CaO dissolution kinetics. It was determined that 1 kg of PCC was capable of purifying approximately 154.6 L of contaminated groundwater with an 18.2 wt.% CaO content, twice as much as the binary mixture of CaO and CaCO3. Based on the results, partially calcined CaCO3 is a potential reactive medium to remediate groundwater contaminated with heavy metals.