Selective Flocculation for Coal De Mineralization

Selective flocculation has long been suggested as a method for the treatment of ultra-fine particles typical of which are those produced in a de-sliming process ahead of flotation. In this paper the results of the coal de-mineralization, using synthetic polyacrylamide polymers, are presented. A prescreening test on the suitability of the polymers using Run-Of-Mine (R.O.M.) coal and artificial mixtures of Shirebrook coal and shale the floe settling rates and supernatant clarity of the suspension was carried out and three polymers. Floe Aid ۲۰۲ (medium anionic). Floe Aid ۲۰۴ (high anionic) and Polyethylene oxide (P.E.O.) (non- ionic) were employed in subsequent experimental work. The effectiveness of the polymers was established by carrying out settling rate tests using polymers dosages between ۰.۰۰۰۲۵ to ۰.۰۰۷۵ g/۲۵g feed and at various suspension pH values. P.E.O. showed significant differences in the flocculation of coal and shale. The results concerning polymers FA ۲۰۲ and FA ۲۰۴ are not discussed. Slurry pH, dispersant concentration and polymer dosages were examined and are discussed. Shale entrapment was believed to be due to three reasons. Firstly the mineral particles not fully liberated from the coal structure. This could be infered from the S.E.M. micrographs. Secondly, once coal floes have been formed, they become larger in size, and on settling collect the much smaller mineral particles, beneath themselves, to the bottom of the container. And thirdly polymers may possess a weak affinity for the shale surface. 

Keywords:

Selective Flocculation , De , Sliming , Polymers , Settling Rate