Suppression of pyritic sulphur during flotation tests using the bacterium Thiobacillus ferrooxidans

Abstract

Environmental concern about sulphur dioxide emissions has led to the examination of the possibility of removing pyritic sulphur from coal prior to combustion during froth flotation, a routine method for coal cleaning at the pit-head. The bacterium Thiobacillus ferrooxidans was effective in leaching 80% and 63% -53 mum pyrite at 2% and 6% pulp density in shake flasks in 240 and 340 h, respectively.The natural floatability of pyrite was significantly reduced in the Hallimond tube following 2.5 min of conditioning in membrane-filtered bacterial liquor prior to flotation. The suppression effect was greatly enhanced in the presence of Thiobacillus ferrooxidans. A bacterial suspension in pH 2.0 distilled water showed 85% suppression, whereas in spent growth liquor this value was 95%. The optimum bacterial density was 3.25 x 10(10) cells/g pyrite in 230-ml distilled water (2% pulp density) in the Hallimond tube. The degree of suppression by the cells was related to particle size but not to pH or temperature. The sulphur content of a synthetic coal/pyrite mixture was reduced from 10.9 to 2.1% by flotation after bacterial preconditioning. It is postulated that pyrite removal in coals which are cleaned by froth flotation could be significantly reduced using a bacterial preconditioning stage with a short residence time of 2.5 min.

Mechanism of microbial flotation using Thiobacillus ferrooxidans for pyrite suppression

“…'.~' In this work filtrate without bacteria had the ability to suppress pyrite floatability, in agreement with reports. 20 The suppressive effect of the filtrate suggests that cell components such as protein or lipid from broken cells during cultivation and/or ferrous iron in filtrate may depress pyrite floatability. From Figure 3, it is suggested that the reduction of pyrite floatability by the bacterium occurred within a few seconds after which the bacterium no longer suppressed pyrite floatability.…”

Reducing sulfur and ash from coal using Bacillus subtilis and Paenibacillus polymyxa

“…In the last two decades, bioflotation became one of the essential methods for beneficiation of different ores in general and for desulfurization of coal in particular [6][7][8]. In bioflotation process, bacteria replace the conventional chemical reagents or work synergistically with them to produce high-grade concentrates with a reasonable recovery [9][10][11].…”

“…As a depressant, Thiobacillus ferrooxidans was used to reduce pyritic sulfur, in coal-pyrite synthetic mixture, to about 2% from about 11% in the flotation feed using Hallimond tube tests [16]. A. ferrooxidans can selectively depress the pyrite from complex pyritic coal [8,17]. Another example is the study of the thermophilic Sulfolobus acidocaldarious for removal of pyritic sulfur from coal [18].…”

A Rapid Method for Determination of Growth ofThiobacillus Ferrooxidansby Series Piezoelectric Quartz Crystal

“…Its commercial potential in the treatment of arsenic refractory gold ores 6 " 9 , desulfurization of coals and oils 10 , environmental control 11 and in the benefication of difficult -to -dress minerals 12 is ever increasing. It is an obligate chemolithoautotroph feeding ferrous iron as main energy source, as represented by reaction (1).…”