NATURALLY-OCCURRING CHROMIUM AND VANADIUM IN CHARLOTTE TERRANE ROCKS: A SOURCE OF TRACE ELEMENTS TO GROUNDWATER?
1 online resource (94 pages) : PDF
University of North Carolina at Charlotte
Vanadium (V) and chromium (Cr) contamination has become a rising concern in North Carolina due to a coal ash spill in February 2014. Coal ash is known to contain these trace elements, but V and Cr are also naturally occurring. Cr and V above health advisory guidelines has been identified in groundwater areas in the vicinity of coal ash sites, but the contamination source is still unknown. This coal ash spill occurred within the geologic region of the Charlotte Terrane rocks where the abundance of naturally occurring V and Cr is unknown. In this study, 46 samples were collected from five map scale units ranging from mafic to felsic rock compositions. Studies surrounding the behaviour of Cr and V have shown these elements tend to be associated with oxides, especially Fe and Mn. It was hypothesized that mafic Charlotte Terrane rocks would contain higher amounts of total Cr and V compared to intermediate/felsic rocks. A three-step sequential extraction was performed on each rock sample to quantify the amount of Cr and V that could potentially be released into groundwater. The third extraction, hydroxylamine hydrochloride, targeted oxides. It was hypothesized most Cr and V would be extracted in this step and more would be extracted from mafic rocks than intermediate/felsic rocks.After XRF analysis, it was determined that mafic rocks contain, on average, higher amounts of total Cr and V than intermediate/felsic rocks. For mafic rocks, the average total Cr was 356 μg/g and the average total V was 247 μg/g. For intermediate/felsic rocks, the average total Cr was 58 μg/g and the average total V was 85 μg/g. It should be noted that total Cr and V for intermediate/felsic rocks are semiquantitative because most of the XRF results for these rocks were near the detection limit. As for the hydroxylamine hydrochloride, the confirmed intermediate/felsic rocks, on average, had higher extraction concentrations of Cr (but not V) compared to the mafic rocks. On average, the hydroxylamine-extractable Cr was 23.1 μg/g in intermediate/felsic rocks and 13.2 μg/g for mafic rocks. When hydroxylamine-extractable Cr is compared to total Cr about 40.4% of total Cr was extracted from felsic/intermediate rocks and about 3.7% from mafic rocks. On average, the hydroxylamine-extractable V for intermediate/felsic rocks was 3 μg/g and 3.7 μg/g for mafic rocks. When hydroxylamine- extractable V is compared to total V about 3.5% of total V was extracted from felsic/intermediate rocks and about 1.5% was extracted from mafic rocks. Overall, rock type does seem to be a factor in Cr and V occurrence while leachability of Cr and V is less clear. A higher proportion of total Cr and V was leachable in felsic/intermediate which may imply that Cr and V in intermediate/felsic rocks are held in more leachable sites than in mafic rocks.In conclusion, total Cr and V can be associated with specific rock type. Mafic rocks have higher total Cr and V, but felsic/intermediate rock had higher hydroxylamine-extractable Cr compared to mafic rocks. A larger proportion of total Cr and V were extracted from the felsic rock than the mafic rocks. The results do not support mafic rocks as the main source of Cr and V into groundwater, but the results do support Charlotte Terrane rocks being a potential natural source of Cr and V to groundwater.
CHARLOTTE TERRANECHROMIUMGEOCHEMISTRYGEOLOGYVANADIUMWATER QUALITY
Diemer, JohnBobyarchick, Andy
Thesis (M.S.)--University of North Carolina at Charlotte, 2017.
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