THE EFFECT OF CONCENTRATION AND SIZE OF THE SOLID PHASE ON THE EFFICIENCY OF FLOCCULATION AND SEDIMENTATION OF FINELY DISPERSED SUSPENDED PARTICLES IN COAL SLUDGE

Abstract

The results of studies on the influence of solid phase concentration and the presence of coarse-grained fraction on the efficiency of flocculation and sedimentation of finely dispersed suspended particles in coal sludge from coal preparation plants are presented. Real samples of liquid waste with a solid phase concentration of 13–48 g/l were used, where the proportion of finely dispersed particles (<20 μm) is 77–79%. The granulometric analysis was carried out by wet sieving, and the sedimentation kinetics were studied in 500 ml measuring cylinders at 19°C. It was found that at low concentrations (~13 g/l), free sedimentation prevails with an initial rate of up to 0.14 mm/s without a clear phase boundary. At concentrations above 48 g/l, a clear boundary is immediately formed, and the process transitions to hindered sedimentation at a rate of 0.01–0.013 mm/s. The maximum sedimentation rate is achieved at 40–80 g/l. The effect of adding coarse-grained fraction (>0.1 mm) on flocculation using anionic (A-19), non-ionic (TFN) and cationic (Zetag 8185) flocculants was investigated. The introduction of 6–30 g/l of coarse particles increases the sedimentation rate of flocs from 3.2 to 18 mm/s and the strength of aggregates (speed after destruction — from 0.04 to 3.8 mm/s). The coarse-dispersed phase promotes the formation of larger and heavier flocs, which reduces flocculant consumption and increases resistance to hydrodynamic influences. The results obtained indicate the advisability of preparing sludge prior to flocculation by adjusting the concentration of the solid phase (dilution or mixing of flows) and introducing a coarse fraction. This makes it possible to optimise wastewater treatment processes in settling tanks, reduce reagent consumption, improve water clarification and intensify sludge dewatering. The proposed approaches can be implemented at industrial enterprises to improve the environmental and economic efficiency of water-sludge coal preparation schemes.