The effect of adsorbed and non-adsorbed additives on the stability of coal-water suspensions

Modified coal-water suspensions were stabilized using two additives: an adsorbed non-ionic surfactant, dinonylphenol poly(oxyethylene) with 150 mol of ethylene oxide per dinonylphenol group (DNP 150), and a non-adsorbed water-soluble polymer, poly(oxyethylene) (POE). Settling rate, sediment concentration profile and compressional resistance and other properties were measured to assess these stabilized suspensions and to discriminate between the effects that these additives have on the strength of the flocculated networks formed in the coal suspension and their sediments. Improvement of the flocculated structure of the suspension resulted in sediments that had increased resistance to consolidation and were relatively non-settling. Yield stress measurements on the sediment allowed the strength of the flocculated network structure to be quantified and the mechanisms leading to particle interactions to be explored and related to the adsorption density of the additives on the coal surface. Full coverage of surfactant, together with soluble polymer, gave a suspension that resisted settling for 2 weeks. After this time the suspension exhibited minimal settling without large increases in suspension viscosity. There was a significant difference in ease of redispersion between suspensions flocculated with DNP 150, where 'bridging' network structures were formed, and those flocculated with 'free' POE.