In coal mining,the extracted coal usually contains some impurities.Firstly,they are separated according to the difference in gravity between coal and impurities in the medium of water.The coal is suspended on top,and the impurities sink to the bottom of the water.In further processing,the separation efficiency of coal and impurities can  be improved by adding flotation agents.Clean coal floats out and tailings settle.Then,the clean coal in the first coal  is sent back and forth through sedimentation,filtration,or centrifugation.Polyacrylamide is applied in the settling    process to promote solid-liquid separation.Then it is sent to the thickener,and the clean water is recovered and recycled by the overflow of the thickener.Powdered clean coal is filtered and centrifuged for recovery.During the filtration and centrifugation process,the addition of polyoxometalamide enhances separation efficiency.