Use of Eggshell as a Low-Cost Biomaterial for Coal Mine-Impacted Water (MIW) Remediation: Characterization and Statistical Determination of the Treatment Conditions

Abstract

Eggshells (ESs), a low-cost biosorbent rich in calcium carbonate (CaCO3), were used to sustainably reduce the acidity and remove the Fe(total), Al3+, and Mn(total) ions from coal mine-impacted water (MIW). The surface area and pore volume of ES biomaterial were 5.692 m2 g−1 and 0.0567 cm3 g−1, respectively. The remediation process was performed in two consecutive stages, with Fe(total) and Al3+ ions being removed in the first stage (treatment I) and the Mn(total) ions in the second one (treatment II). The best treatment conditions, statistically determined through a central composite rotatable design (CCRD), were 6.59 g L−1 ES and 95 rpm agitation rate for treatment I and 28 g L−1 ES and 280 rpm agitation rate for treatment II. However, the high ES dosage in treatment II, determined by extrapolation, led in practice to the formation of particle aggregates that decreased the treatment efficiency. Therefore, the best values experimentally determined for treatment II were 25 g L−1 ES and 250 rpm. In these conditions, the overall treatment provided complete MIW acidity neutralization, total removal of the Fe(total) and Al3+ ions, and 58% Mn(total) ion removal, providing treated fluvial water adequate for non-potable use based on the analyzed parameters.