SURFACE-CHARGE DENSITY AND POTENTIAL OF COAL-LIQUID MIXTURES AND CONTROL OF THEIR STABILITY AND FLUIDITY

The preparation conditions of concentrated (> 70%) aqueous suspensions of coal were optimized, as were the surface charge density and the su rface potential of the coal-water suspensions. The theoretical study s howed that (1-3) or (2-3) electrolytes such as Na2SO4 or Na5P3O10, gre atly increase the surface charge density and the surface potential of the coal particles in water. This study has led to the interesting res ult that thinners and stabilizing agents of concentrated clay suspensi ons, such as lignosulphonates, tripolyphosphates, polynaphtalene sulph onates, etc., must also be good thinners and stabilizing agents for gr ound coal-water suspensions. Two parameters were controlled: the stabi lity and the fluidity of the suspensions. A penetrometry technique rev ealed the importance of the resistance coefficient, C-r that can be us ed as a criterion for the evaluation of coal-water mixture stability a nd fluidity. Concentrated coal suspensions (about 75% of solid by weig ht) were prepared in water by using different additives, for instance sodium tripolyphosphate (NaTPP) and surfactants like lignosulphonates (by coupling of the dispersion and stabilizing effects) with the optim um concentration ratio of these two products equal to 1.9. The stabili ty of the suspensions was then greater than 2 months and the viscosity was 1900 cP.