Enrichment of heavy metals in coal gangue by puff balls and mechanism research

Coal gangue with/without wild puff balls growing on or covering up were analyzed by means of inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic fluorescence spectrometry (AFS) to detect the contents of heavy metal elements in the plants. Seven heavy metals were chosen to do the experiments, which showed that the puff balls have strong enrichment capacity for heavy metals (As, Pb, Mn and Ni). The highest enrichment level was Mn, 220.3 mg/kg (dry weight) for puffball fruiting bodies, and the highest As, Cr and Pb enrichment levels for puffball mycelium were 111, 265.3 and 86 mg/kg, respectively. Cd, Mn and Ni could transfer from puffball mycelium to its fruiting bodies, while As, Cr, Pb and Co mainly accumulated in the mycelium. The contents of five organic acids (tartaric acid, glycolic acid, lactic acid, citric acid and malic acid) in puffballs were determined with high performance liquid chromatography. With water, ethanol and ethyl acetate as solvents, the puffball extracts performed dissolution reactions with coal gangue, in which the water extract (containing a large amount of organic acids) was most effective in releasing heavy metals, especially As, Pb, Cr, Mn, Co and Ni from coal gangue. As a pioneer species, puff balls absorbed the hazardous trace elements in coal gangue matrix to reduce its eco-toxicity, on the other hand, it raised the pH value of coal gangue, improving the vegetation growing conditions for coal gangue matrix to a certain extent and laying the foundation for ecological restoration of coal gangue dumps.