Multi Response Statistical Optimization of the Flocculation Parameters for Enhancing the Settling Performance of Coal Fine Tailings

Coal preparation plants generate huge quantity of fine tailings that pose significant challenges in solid–liquid separation, water recovery, and tailings management due to their fine particle size and colloidal nature. Therefore, flocculation technology is essential to enhance settling performance and improve supernatant clarity. In this study settling behaviour of coal fine tailings using a high molecular weight cationic polyacrylamide (CPAM) flocculant was systematically investigated and optimized. Unlike previous studies that primarily focus on settling rate alone, this work simultaneously evaluates settling rate, turbidity, and density of settled slurry to provide a more comprehensive assessment of flocculation performance relevant to thickener operation. Settling tests were conducted on coal fine tailings (− 0.5 mm) collected from a coal preparation plant in the Jharia coalfield, Dhanbad, India. The effects of pH, flocculant dosage, and pulp density were examined using a Box–Behnken design coupled with response surface methodology. Quadratic regression models were developed and statistically validated through analysis of variance, demonstrating excellent agreement between experimental and predicted responses. The results indicate that pulp density exerts the most significant influence on settling rate and density of settled slurry, while flocculant dosage predominantly governs turbidity reduction. Multi objective optimization identified optimal operating conditions at a pH of 8.5, flocculant dosage of 14.6 g/t, and pulp density of 7.2% solids, yielding a high settling rate of 174.3 mm/min, low turbidity of 22.4 NTU, and a density of settled slurry of 40.6% solids, with an overall desirability of 81.6%. The findings provide practical insight into CPAM assisted flocculation and demonstrate an effective optimization framework for improving settling efficiency, water clarity, and tailings handling in coal preparation plants.