The Use of Mineral Matter Dispersants and Depressants During the Flotation of Bituminous Coals

Abstract

While much data from the froth flotation of bituminous coals indicate that liberated mineral matter enters the clean coal froth by way of water carry-over, other results show that discrete sulfur-bearing and ash-forming minerals can be collected by entrapment into the froth mass, by attachment to coal surfaces as slime coatings, by specific flotation, or by the mutual flocculation and flotation of dissimilar fine particles. In several of these cases, the use of mineral matter dispersant and depressant systems during flotation can enhance the selective separation of fine coal and refuse materials. To ascertain the relative effectiveness of adding dispersants and depressants during coal froth flotation, laboratory flotation tests were completed on several minus 0.15-mm (100 mesh) raw coal samples. Candidate reagents were selected using a simple laboratory observation technique that allowed macroscopic evaluation of mineral matter dispersion behavior. For the coals tested, the use of dispersants during froth flotation often improved the rejection of sulfur-bearing mineral matter from the froth product. Judicious addition of these reagents was required, however, in order to attain maximum pyrite and mineral matter rejection while preventing coal depression. The use of joint dispersant-depressant systems also decreased the total sulfur and ash content of some of the clean coal froths more than did the use of dispersants alone. This indicates that mineral matter contamination in these coal froths is sometimes caused by accidental flotation of free pyrite or locked coal-pyrite particles or by entrapment of mineral matter into a froth mass that has poor drainage capabilities.