Chars from 20 lignite samples were prepared from two types of original lignites by multistage removal of inherent metallic species and subsequent pyrolysis and then were gasified with CO2. A kinetic model, which assumed the progress of noncatalytic and catalytic gasification in parallel, quantitatively described the time-dependent changes in char conversion up to 0.999 for all the chars by employing multicatalytic species having different initial activities and deactivation kinetics. A single piecewise linear function, which followed a nucleation–growth mechanism of the catalysts, showed the relationship between the total concentration of Na, K, Ca, and Fe and the initial total catalytic activity (ICA-2) for the chars. The overall rate of catalyst deactivation (ICD-2) was given by a single linear function of ICA-2 and a factor for the composition of metallic species. This function was also applicable to previously reported ICA-2/ICD-2 relationships for chars from lignite and biomass, showing fast deactivation of Fe catalyst and an important role of Mg in the promotion of catalyst deactivation.

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In an attempt to investigate the use of bacteria and their metabolites as bioflotation reagents for environmentally friendly mineral processing, laboratory cell flotation tests were carried out using copper sulfide ores bearing a high content of pyrite, which were mixed with a biosurfactant-producing mixotrophic bacterium as bioflotation reagents. The interaction of bacterial cells and their metabolic products with the sulfide ores resulted in the alteration of the surface chemistry of both ores and bacterial cells as evidenced by FTIR and SEM-EDS observations as well as surface tension and contact angle measurements. The change in the surface properties of the sulfide ores in turn enabled the bacterium to function as flotation bioregeants in the flotation of copper sulfide ores as a function of bacterial cell concentration, conditioning time, flotation time and pH. Overall, the bacterium and its metabolites as bioreagents yielded flotation recoveries which might be attributed to the multi-function of the bacterium as depressant, collector and frother. Thus, the bacteria tested in this study could potentially be used as flotation bioreagents, providing an alternative to conventional flotation reagents.

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