Migration and removal of toxic trace elements during coal washing

Coal washing,which has been widely applied,is an economical and effective way to reduce the emission of pollutants caused by coal combustion. In this study,the onsite sampling and analysis of raw coals and related products from three large-scale coal washing plants were conducted. By measuring the contents of trace elements in raw coals and coal washing products,the migration and removal of some toxic trace elements during coal washing were studied, which included As,Be,Cd,Co,Cr,Hg,Mn,Ni,Pb,Sb and Se. The results show that the conventional physical coal washing technology could effectively remove the inorganic mineral components in coal. The toxic trace elements in the cleaned coal can be partially removed with the decrease of ash yield and sulfur content. The removal ratios of all trace elements were above 20% except Se (13. 3% ). This is mainly due to the removal of trace elements with the associat- ed minerals. Be,Cd,Co,Cr,Hg,Mn and Ni removed during coal washing would mainly be enriched in gangue while Se mainly went into middling coal. The distribution of As,Pb and Sb in the products of coal washing was complicated.