THE INFLUENCE OF MICROBIAL COMMUNITIES AND SECONDARY OXIDES ON MANGANESE CARBONATE AND AMPHIBOLITE WEATHERING

The weathering of mine tailings from the Betts mine in western Massachusetts, a former Mn ore source, is of concern for Mn toxicity in Northern Hardwoods and animals present on and around mine tailings. A recent study on tree foliage showed Mn levels in the plants growing on the mine tailings were lower than level at control sites not directly exposed to mine tailings. The objective of this study was to weather mine tailings from the former Betts mine in order to determine the rate at which Mn is leaching into the soil from discarded ore and if microbial communities are enhancing the weathering rate. Two specific mineral assemblages were weathered: rhodochrosite (22.16% Mn) and kutnohorite (5.95% Mn), and the schist contained spessartine garnet (2.7% Mn). In order to reproduce weathering of the mine tailings and schist in the lab setting, a mine tailing and a schist were crushed into a powder and weathered for 10 days. The samples were rocked for two days at a time, centrifuged, put into a fresh solution of 0.005 M oxalic acid, 0.005 M citric acid, 0.005 M catechol and 0.01 M sodium chloride in de-ionized water at pH 3.5, 4.5, 5.5 and 6.5. Sodium azide was included in half of the solutions in order to remove microbes. The samples in solution quickly produced a black color on the rocker indicating the precipitation of a Mn oxide. However, comparing the samples before and after weathering using XRD showed no new crystalline Mn minerals had precipitated out of the samples. ICP OES analyses of the solutions decanted from the samples will show if the different pH and microbial treatments enhanced the weathering rates. These analyses will hopefully encourage further investigation into the weathering of Mn minerals into the soil and the uptake of Mn in plants at the former mine.