Prior to implementing the Nalco program, the washery had ten float tanks in its two-stage processing program, run as five banks of two.

Washery management said they had wanted to convert to the more efficient single-stage processing system for some time but the existing collector medium, diesel, was unable to float the coarse coal in the single-stage format.

Director of the Qianjiaying washery Liu Taishun said the washery looked at various options for increasing the yield from the single-stage float circuit before deciding to trial the Nalco coal flotation program.

An analysis of the coking coal processed at the Qianjiaying washery revealed an ash content of 38-41% and feed to the fine coal float circuit running in the range of 18-30% ash.

The use of Nalflote 9836 Collector was recommended by Nalco, as it considered the coal hard to float.

Described as a “highly selective reagent”, Nalflote 9836 is a blend of active organic compounds and surface-active agents, which makes it appropriate for use over a wide particle size range and particularly effective for coarse coal.

The trial started in July 2005 and ran for five weeks with plant feed at 950 tonnes per hour, which allowed for a detailed analysis of the Nalco collector’s impact on the varying ash contents of the float circuit feed.

Various coal types were experienced throughout the trial, including a hard-to-float coal not previously experienced; however, even on this abnormal product, the collector still exhibited excellent selectivity and continued to control clean coal ash.

Along with an almost immediate and positive impact on yield, the trial also confirmed that the coal flotation program could successfully float the coarse, low-ash coal, was suitable for a range of coal types, and would lower the product ash when used with hard-to-float coal.

At the conclusion of the trial, flotation yield had increased by more than 9%, which meant an additional 7000 tonnes of clean, saleable coal per month.

The Qianjiaying mine and washery complex is about 200km east of Beijing and is regarded as one of China’s most efficient mining operations.