Analysis of a coal preparation plant. Part 1. Changes in water quality, coal seam, and plant performance

Coal preparation plants are under increasing pressure to reduce their consumption of fresh water leading to the use of recycle water. Recycled water generally contains a large quantity of dissolved inorganic electrolytes, which affect coal flotation. This paper reports the conductivity and pH measurements of water in the tailings stream of an industrial scale flotation cell covering a period of approximately two years. The different coal seams processed at the site were also compared and the influence the water quality on the overall yield of coal assessed. This study presents the large variation in inorganic content in recycled water observed for a wash plant and determines its possible effect on coal preparation. The maximum daily temperature was found to be an important factor controlling the amount of inorganic electrolytes in the water and, very significantly, the water management system implemented. The overall plant performance was somewhat affected by the use of water containing high concentrations of inorganic electrolytes. The effect of the quantity of ions in the water on the flotation process is explored in Part 2.