Separation of fine coal particles from centrifuge effluents: optimization of flocculation and comparative study of downstream separation techniques

Abstract

The main challenge in recovering fine coal particles from centrifuge effluents is due to the ultrafine size of these particles and their low specific gravity, which causes very slow settling in effluents with very low solids content. This study optimizes flocculation conditions to enhance fine coal recovery from Solid Bowl Decanter Centrifuge effluents at the Tabas Parvadeh Coal Washing Plant, Iran. Fine coal samples were characterized through particle size distribution analysis, zeta potential measurements, and ash analysis. Laboratory sedimentation tests examined key parameters (flocculant type and dosage, flocculant stock solution concentration, solids content, pH) influencing settling rate, total dissolved solids (TDS) of supernatant, mud line height, and floc size. Optimized conditions included a combined nonionic/anionic flocculant, a flocculant dosage of 200 g/t, a stock solution concentration of 500 mg/L, pH 10, and 2% solids content, which together produced stable flocs with improved settling rates and reduced TDS of supernatant. Industrial-scale tests assessed hydrocycloning, screening, and settling tank sedimentation for separating flocculated slurries. Settling tanks achieved 37.4% underflow solids, outperforming hydrocyclones and screens. The results demonstrate that optimized flocculation combined with settling tanks provides an efficient solution for fine coal recovery, enhancing product yield and water management in coal preparation plants.