Using Calcined Waste Eggshells to Remove Sulfate in Nonpotable Concrete Mixing Water

The experimental and theoretical potential of using calcined waste eggshells (CWEs) to remove sulfate from sulfate-laden concrete mixing water was investigated in this work. Waste eggshells were first calcined at 800°C and batch-reacted with sodium sulfate solutions. Laboratory experiments elucidated the effect of initial sulfate concentration, temperature of reaction, and CWE particle size on total sulfate removal. Experimental results indicate a maximum sulfate removal of 29.5%±2.2% via calcium sulfate mineral precipitation in laboratory batch reactions. To quantify the maximum sulfate removal potential of CWEs, batch reactions were simulated using PHREEQC, a geochemical code. After validating the simulation approach with experimental data obtained herein, PHREEQC was used to investigate the maximum sulfate removed as a function of CWE addition (g/L). Results indicate that sulfate-laden waters (≤4,000 ppm) can be decreased to ≤3,000 ppm with CWE additions of ≥3 g/L in order to comply with the standard specification for maximum allowable sulfates in water intended for use in the production of hydraulic cement concrete.