Optimization of Flocculation/Coagulation Conditions of Coal Preparation Plant Tailings Using Chitosan and FeCl3 Through Experimental Design

Coal preparation plants generate large volumes of fine tailings containing negatively charged colloidal particles that remain stable in suspension and hinder efficient water recovery. In this study, the flocculation performance of coal tailings was statistically evaluated using inorganic and organic reagents, namely ferric chloride (FeCl₃) and chitosan. The effects of chitosan dosage, FeCl₃ dosage, pH, stirring speed, and pulp density on turbidity and water recovery were investigated through Response Surface Methodology (RSM). Zeta potential measurements revealed that the sample exhibited a negative surface charge over the entire pH range. In contrast, chitosan effectively shifted the surface charge toward positive values under acidic and near-neutral conditions, indicating charge neutralization and polymer bridging mechanisms. ANOVA results revealed that pH, chitosan dosage, and pulp density were the most significant parameters influencing turbidity and water recovery. Under optimized conditions, turbidity was reduced to 9.86 NTU with a water recovery of 76.92%. Using chitosan alone provided an effective and statistically validated strategy for dewatering samples by enhancing floc formation through combined charge neutralization and interparticle bridging mechanisms, resulting in minimal turbidity. Although chitosan alone was sufficient to achieve effective flocculation, its synergistic combination with FeCl₃ resulted in the highest water recovery values under optimized conditions.