Arsenic in the Wisniowka acid mine drainage area (south-central Poland) Mineralogy, hydrogeochemistry, remediation

This paper summarizes different aspects of arsenic mineralogy and geochemistry in the Wisniowka acid mine drainage (AMD) area, south-central Poland. The basic source of this metalloid in AMD water bodies is micro-grained pyrite that forms two different mineralized zones within the Upper Cambrian rock formation. Due to specific textural and geochemical characteristics, this mineral undergoes rapid oxidation on exposed quarry walls and unvegetated tailings piles, thus contributing to elevated arsenic concentrations in acid pit lakes and ponds, and locally intermittent pools. The latter were highlighted by the highest As levels reaching even 370 mg/L. Of the three AMD large reservoirs, the Podwisniowka (eastern) lake revealed distinctly raised As concentrations varying from 7.02 to 22.2 mg/L. Another interesting water body is the Marczakowe Doly acid pond showing diverse seasonal As concentration patterns in colloids and a water column. Results of geochemical modeling showed that the saturation indices (SI) of hematite and goethite exhibited the highest values (range of 6.96 to 12.84 and 2.47 to 5.39, respectively) tending to precipitate in all the water bodies examined. In addition, the positive SI values of nanosized epsilon-Fe2O3 (1.64 to 4.13) and schwertmannite (0.90 to 2.10) were found only in the Wisniowka Duza and Marczakowe Doly acid waters. Laboratory experiments revealed that the best chemical and cost-effective method (out of the limited number of options) of arsenic removal from the AMD waters examined was the use of high-grade powdered limestone (fraction 0.0-0.09 mm) or more effective although more expensive limewater (calcium hydroxide). The positive SI values of hematite, goethite, epsilon-Fe2O3 and schwertmannite of neutralized solutions suggest that these minerals should precipitate. Due to diverse concentrations in the examined rock series, arsenic has been used for fingerprinting hot places within the mining and neighboring areas, as well as for predicting the directions and effects of strip mining for quartzites. The As signature can also be applied to monitor a detrimental AMD impact on local surface and underground waters.