Characterization of Precipitates Associated with Bituminous Coal Mine Drainage, Northern Appalachian Region, USA

Changes in precipitate mineralogy, morphology, and major and trace elemental concentrations and associations throughout five coal mine drainage remediation systems in Pennsylvania and Maryland that treat discharges of varying chemistries were investigated. The precipitates are dominantly (>70%) goethite with minor amounts of other iron and/or manganese oxides and quartz. Crystallinity varies throughout an individual system and is a function of the treatment system and how rapidly ferrous iron oxidizes, precipitates, and settles. Precipitates formed earlier in the systems have the highest crystallinity; less crystalline precipitates are associated with enhanced sorption of trace metals. High surface area and vacancies within the goethite structure enable incorporation of metals from mine drainage polluted waters. Sorption affinities follow the order Al>Zn>Co=Ni>Mn. As pH increases in the individual treatment systems toward the pHpzc, arsenic sorption decreases and aluminum and transition metal sorption increases. Sulfate, sodium and ferrous iron potentially influence the sorption of trace metals.A sequential extraction procedure was developed to determine how trace elements are associated with the precipitates. Arsenic, cobalt, manganese, nickel and zinc are not released until the iron hydroxide phase is dissolved, indicating these metals are either tightly sorbed to the surface or incorporated into the hydroxide structure. Cobalt and nickel preferentially partition into a manganese oxide/hydroxide phase (if present), over the iron hydroxide phase. The stability of the precipitate controls the long-term mobility of trace metals. Associated trace metals will remain unavailable to the environment as long as the precipitate is not altered.Additionally, spatial and temporal variations between precipitates formed from a net-alkaline coal mine discharge were examined. The precipitates are all moderately crystalline goethite with minor variations in morphology and composition. They contain 20 - 30% more iron than the natural mined iron oxides examined in this study, and concentrations of manganese, nickel and zinc are up to three orders of magnitude lower than the natural iron oxides. Geochemical analysis indicates that mine drainage precipitates formed from net-alkaline waters are of a higher purity than natural iron oxides. Results of this study have implications for disposal, resource recovery, and the optimization of mine drainage passive remediation systems

Characterization of Wetland Soils Receiving Drainage from an Abandoned Mine in Southwestern Montana

The Bismark Mine in Montana was mined for copper, lead, and small amounts of silver and gold between 1913 and 1963. The geology of the area consists mainly of Precambrian Pony Series (quartzofeldspathic gneiss) and the Tobacco Root Batholith (quartz-monzonite granite), which intrudes the Pony Series. Mineralization occurs within fissures near the contact between the granite and gneiss. Pyrite, chalcopyrite, and molybdenite are found in addition to the primary ore minerals (Ag, Au, Cu, and Pb) in these veins. Bismark Mine is situated near several of these fissures. During mining, pyrite (an iron sulfide mineral) is also extracted and discarded with the waste rock (tailings). The tailings were deposited downslope from the main (lowermost) adit, and once the mine closed, a wetland developed over the tailings due to water flowing from the main adit and springs on the surrounding slope. Pyrite oxidation typically leads to the formation of acidic waters. However, water tested from the adits and seeps have a pH value between 6.78 and 8.05. One possible explanation is that the flow bypasses the mined area and any remaining zones of pyrite through fractures in the rock. The chemistry of the main adit includes: 15 µg/L of zinc, 14.8 µg/L of lead, 43 µg/L copper, 11.7 µg/L of chromium. The purpose of this research was to evaluate the concentration of trace metals in the soils formed in the wetland area receiving drainage from the abandoned Bismark Mine and to evaluate potential mobility of these metals. Twelve grab samples of the soils were collected from two separate soil pits in the wetland area by students enrolled in Indiana University’s field camp in the summer of 2015. Samples were placed in labeled, Ziploc® bags and were transported to Winona State University (WSU) for analysis. In the laboratory, pH, loss on ignition (LOI; used as a proxy for soil organic matter), moisture content and easily mobilized elements were determined. Splits of the samples were sent to Activation Laboratories in Ancaster, Ontario, Canada, for total metal analysis using acid digestion followed by analysis on ICP-OES. The pH of the samples varied from 2.91 to 6.44. Soil organic matter ranged from 0.0014 g/g to 0.6382 g/g, with most of the values falling between 0.0192 g/g to 0.3193 g/g. Results from total metal analysis and extracted metal from both pits will be presented

Metal Retention in a Peat Wetland in Northeastern Minnesota

This research project consisted of two separate parts. For the first part, existing data sets were compiled to evaluate the effectiveness of a constructed wetland treating mine drainage in northern Minnesota. The second part involved determining metal accumulation in peat samples from a natural wetland in northern Minnesota that receives mine drainage from a nearby seep originating from a mineralized zone related to the Duluth Complex. Metal concentrations in and metal availability from the peat samples were determined by total digestion and sequential extraction techniques. Data from the first part of the project was added to an existing database maintined by the faculty advisor and will be used for an upcoming publication. Results from the second part of the project are summarized in the attached poster, which was presented by Elaine at the WSU research celebration in April 2013

Preliminary Assessment of Metals Partitioning in Soil and Vegetation in a Subalpine Wetland

The Bismark Mine is located near the headwaters of the South Boulder River in Madison County, Montana (Figure 1). The bedrock of the area is predominantly metamorphic rock of the Archean Pony series, intruded by a tongue of the Cretaceous quartz monzonitic Tobacco Root batholith. The gneiss and the granite are both weakly fissured and mineralized near the contact. The mine is located on several of these fissure veins near the granite-gneiss contact. Additionally, numerous small veins of pyrite, chalcopyrite, and molybdenite with quartz are present. During its operation, over 58,000 lbs. of copper, more than 7,000 lbs. of lead, and almost 1,200 oz. of silver and smaller amounts of gold were removed. The mine was abandoned by 1963. During the mining process mine tailings were discarded downslope from the mine adits. A wetland naturally developed on top of the tailings due to diffuse seepage of seasonal snowmelt from the surrounding area and discharge from the lower adit of the mine. Multiple unmapped seeps contribute flow to the wetland. The water emerging from the adit and seeps has a pH between 6.78 and 8.05 and contains measurable concentrations of major and trace elements, including Fe (up to 1.47 mg/L), Pb (up to 17.4 µg/L), Zn (15 – 36 µg/L), Cu (up to 116.7 µg/L), and As (up to 3.66 µg/L). The purpose of this study, which is part of a more extensive wetland characterization, was to investigate metal retention and accumulation within the wetland soils and vegetation and to evaluate potential for metal release from the soils