An integrated approach for coal tailings management

A detailed study on an integrated process featuring three distinct mechanis ms (i.e., hydrophobic extraction, coagulation and flocculation) is presente d. In this process, fine coals in the tailings stream are extracted into a mineral oil by hydrophobic extraction, while coagulant and flocculant are u sed to aid effluent clarification by coagulation/flocculation. With a singl e stage process, a coal-in-oil mixture is produced as a potential fuel, whi le clarifying the water for recycling. The hydrophobicity of coal is found to be a key parameter in coal extraction. The addition of mineral oil prior to flocculant and coagulant, especially in the presence of fine clays, is beneficial for recovering weakly hydrophobic fine coals. Fine clays are fou nd to stabilize coal-rich oil droplets, reducing coal recovery. The presenc e of hydrophobic coal enhances droplet coalescence and improves process per formance. In a case study using a tailings stream from OBED coal preparatio n plant, it was found that re-grinding of original tailings is necessary to expose fresh hydrophobic surfaces. Applying this single stage unit operati on to a tailings containing 52% ash, a combustible recovery greater than 85 % in the form of coal-in-oil mixture at product ash content less than 14 wt % was achieved.