The interstitial location of selenium and arsenic in rocks associated with coal mining using ultrasound extractions and principal component analysis (PCA).

The release of selenium and arsenic from coal mine wastes into main waterways is an environmental cause for concern in the mining industry due to a myriad of subsequent ecotoxicological problems associated with the two metalloids. In a 2002 USEPA study undertaken in a mountaintop removal/valley fill (MTR/VF) mining area in southern West Virginia, measured Se concentrations were higher than the stipulated 5 ng/mL in 66 out of the 213 water samples collected. We studied the chemical composition of forty seven randomly selected pulverized core rock samples collected from depths of 25 ft to 881 ft from MTR/VF sites to determine the amounts of bioaccessible (ultrasound leachable) As and Se concentrations and their tentative locations within the rock matrix. The application of principal component analysis (PCA) to the chemical data, suggested that ultrasound leachable selenium concentrations were associated with 14 Å d-spacing phyllosilicate clays (chlorite, montmorillonite and vermiculite all 2:1 layered clays) whilst ultrasound leachable arsenic concentrations were closely related to the concentration of illite, another 2:1 phyllosilicate clay. Negative correlations between leachable arsenic and selenium with kaolinite a 1:1 layered clay, were also observed. We used the observed negative correlations to rule out the presence of selenium or arsenic in 1:1 kaolinite. Hence mining waste from MTR/VF sites containing substantial amounts of illite and 14 Å d-spacing clays may require to be placed in priority landfills or valley fills.