Evaluation of Residual Frother Minimisation Strategies

This project was undertaken to quantify the effectiveness of a number of approaches recommended for minimising unwanted frothing caused in part by residual frother in process streams in coal preparation plants.  In order to be able to make these assessments, a rapid, portable frother sensor able to detect the low residual frother concentrations was needed.  In the first part of the study, a reliable analytical sensor system and measurement technique were developed capable of determining low concentrations of frother as encountered in CHPP process streams. This instrument has been used to determine frother concentrations in aqueous solutions and slurry samples collected in laboratory, pilot-scale and CHPP process streams.

It examined frother concentration distribution in process streams and frother removal kinetics in flotation systems. The frother removal kinetics in two and three-phase batch flotation tests was found to be well described by the first order chemical reaction kinetics model. The role of frother adsorption onto coal particle surfaces in frother partition in three-phase flotation was also examined. It was found that surprisingly high proportion of initial frother added was adsorbed onto the coal water interface during the condition stage and the degree of adsorption was rank dependent. The higher the rank the greater the amount of frother adsorbed.

Frother removal in air stripping packed column system showed that it is effective in removing frother from aqueous solutions but at very high air/liquid ratios. Up to 80% of frother was removed in a pilot scale unit when operated at an air to liquid ratio of 680. Solids content of the liquid containing frother needed to be very low to prevent fouling and blockage of the channels in the packed bed. This is likely to make it difficult to apply it in the coal preparation environment.

The plant audit data showed that the actual frother dosage to primary flotation cells was lower than what was measured using the frother detector. This is an indication that the coal thickener was functioning to contain the frother associated with the concentrate within the ultrafines circuit and thus minimising the residual frother to other circuits where frothing is not required. It also showed that the frother partitioning to the product in the secondary flotation circuit was relatively small.