The objective of this study was to identify a practical solution to mitigating over-stable froth problems in fine coal flotation in saline water. The effect of coal particle size, water quality and chemical reagents which can be manipulated in flotation plants, on the froth stability and coal flotation performance was investigated. It was found that froth stability was dependent on the coal particle size, the proportion of process water mixed with de-ionised water and the dosage of the collector or frother. Mixing coarse coal particles with fine coal, diluting process water, and reducing collector or frother dosage all significantly decreased the froth stability. However, only the reduction of reagent usage was recommended as a sound strategy since it did not negatively impact the coal flotation performance while eliminating the over-stable froth problems.

The previous study indicates that both reagent usage and the variation of water conductivity affect froth stability and therefore coal flotation behavior. In this study, Central Composite Rotatable Design (CCRD) was conducted to investigate the interaction 1 of saline water with collector (diesel) and frother (MIBC) in controlling froth stability which was indicated by air recovery. The results show that a significant interaction 1 existed between flotation reagents and water conductivity, which affected froth stability, combustible mater recovery and the mineral matter content of flotation concentrate. Frother and salt ions had a joint action in producing a more stable froth. On the other hand, collector and salt ions had a joint action in reducing the combustible matter content of flotation concentrate and the combustible matter recovery. A 1 A term in statistics meaning that the effect of two or more variables is not simply additive.

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