Leaching characteristic and environmental implication of rejection rocks from Huainan Coalfield, Anhui Province, China

• The mineralogical characterizations of rejection rocks were studied.
• The rejection rocks could be utilized as landfill materials under management.
• The trace element in rejection rocks may lead to environmental impacts.

Rejection rocks including intra-seam parting, boundary roof and floor intimately associated with coal seams, are commonly produced along with bulk coal. In general, these non-combustible rocks are rejected during coal processing activities, accumulated on the surface, and subjected to natural weathering and leaching. The degree that the rejection rocks threaten the surrounding ecosystems is determined by total concentrations, modes of occurrence of hazardous elements and minerals therein. Three hundred and ninety-four samples of coal seam parting (30), roof (182) and floor (182) in the Huainan coalfield were collected to investigate the geochemical characteristics and environmental risks of rejection rocks. The morphological analysis revealed that rejection rocks are composed of lithic fragments with organic and inorganic layering, clay minerals, quartz, pyrite and chlorite. Correlation analysis between elements and ash yield suggested that most of the environmentally sensitive elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, Sn V and Zn) are associated with inorganic matter, but boron is mainly associated with organic matter. In-house sequential leaching experiments conducted on selected rejection rocks showed that the rejection rocks from Huainan Coalfield could be suitable for landfill under high regularization and management. However, in the currently unconfined deposits, trace elements (such as Cu, Ni, Pb, Sb, Sn and Zn possibly) may pose a medium risk to the ecosystem.