Optimization of Arsenic Adsorption by Mill Scale–Derived Magnetite Particles Using Response Surface Methodology

This study focuses on the optimization and application of mill scale–derived magnetite particles for the adsorptive removal of arsenic (As) from groundwater. The reverse coprecipitation method is applied to synthesize the magnetite from the mill scale, a byproduct of the iron and steel industry. The independent variables (initial As concentration, pH, contact time, and adsorbent size) affecting the adsorption process were optimized by central composite design of the response surface methodology (RSM). The analysis of variance (ANOVA) results showed that all the independent variables significantly influenced the adsorption capacity. ANOVA analysis exhibited a good fit between the experimental values and the quadratic model predictions, thus resulting in R2 of 0.986. The P-value (<0.0001) displayed the significance of the model at 99% level. The P-values for pH, As(V) concentration, particle size, and contact time are determined as <0.0001, <0.0001, 0.0002, and 0.0009, respectively. The experimental optimization of batch adsorption parameters revealed 100% As(V) removal efficiency with pH 7, particle size 75 µm, 120 min contact time, and 550 µg/l initial concentration. At the maximum initial concentration (1,000 µg/l), the arsenic removal efficiency was 78% when the pH, particle size, and the contact time were 5, 45 µm, and 120 min, respectively. The reproducibility of adsorption experiments at higher concentration (1,000 µg/l) under optimal conditions confirmed the adsorption capacity 8.13 ± 0.08 mg/g.