Comparison of static and mineralogical ARD prediction methods in the Nordic environment.

Acid rock drainage (ARD) is a major problem related to the management of mining wastes, especially concerning deposits containing sulphide minerals. Commonly used tests for ARD prediction include acid-base accounting (ABA) tests and the net acid generation (NAG) test. Since drainage quality largely depends on the ratio and quality of acid-producing and neutralising minerals, mineralogical calculations could also be used for ARD prediction. In this study, several Finnish waste rock sites were investigated and the performance of different static ARD test methods was evaluated and compared. At the target mine sites, pyrrhotite was the main mineral contributing to acid production (AP). Silicate minerals were the main contributors to the neutralisation potential (NP) at 60% of the investigated mine sites. Since silicate minerals appear to have a significant role in ARD generation at Finnish mine waste sites, the behaviour of these minerals should be more thoroughly investigated, especially in relation to the acid produced by pyrrhotite oxidation. In general, the NP of silicate minerals appears to be underestimated by laboratory measurements. For example, in the NAG test, the slower-reacting NP-contributing minerals might require a longer time to react than is specified in the currently used method. The results suggest that ARD prediction based on SEM mineralogical calculations is at least as accurate as the commonly used static laboratory methods.

Arsenic, antimony, and nickel leaching from northern peatlands treating mining influenced water in cold climate.

Increased metal mining in the Arctic region has caused elevated loads of arsenic (As), antimony (Sb), nickel (Ni), and sulfate (SO42-) to recipient surface or groundwater systems. The need for cost-effective active and passive mine water treatment methods has also increased. Natural peatlands are commonly used as a final step for treatment of mining influenced water. However, their permanent retention of harmful substances is affected by influent concentrations and environmental conditions. The effects of dilution, pH, temperature, oxygen availability, and contaminant accumulation on retention and leaching of As, Sb, Ni, and sulfate from mine process water and drainage water obtained from treatment peatlands in Finnish Lapland were studied in batch sorption experiments, and discussed in context of field data and environmental impacts. The results, while demonstrating effectiveness of peat to remove the target contaminants from mine water, revealed the risk of leaching of As, Sb, and SO42- from treatment peatlands when diluted mine water was introduced. Sb was more readily leached compared to As while leaching of both was supported by higher pH of 9. No straightforward effect of temperature and oxygen availability in controlling removal and leaching was evident from the results. The results also showed that contaminant accumulation in treatment peatlands after long-term use can lead to decreased removal and escalated leaching of contaminants, with the effect being more pronounced for As and Ni.

Extractability of metals and ecotoxicity of soils from two old wood impregnation sites in Finland.

Four metal-contaminated soil samples were classified using physical methods, extracted by selective extraction procedures and analyzed for chemical concentrations. De-ionized water, 0.01 mol/l barium chloride, 1 mol/l ammonium acetate and concentrated nitric acid were used as extraction solutions. Ecotoxicity of water extracts and soil samples was analyzed in order to describe the bioavailability of the contaminants. Samples from old wood impregnation plants contained high amounts of As, Cu, Cr and Zn, which originated from chromated copper arsenate, ammoniacal copper-zinc arsenate, and ammoniacal copper quaternary compound. Total As concentrations of the heavily contaminated samples varied from 752 to 4340 mg/kg, Cu concentrations from 339 to 2330 mg/kg, Cr concentrations from 367 to 2,140 mg/kg and Zn concentrations from 79 to 966 mg/kg. The extractabilities of metals differed according to soil type, extractant and element. Cu and Zn were proposed to cause the highest toxicity in the water extracts of the soils. Ecotoxicity tests displayed rather high differences in sensitivity both for water extracts and for solid soil samples. Reproduction of Enchytraeus sp. was the most sensitive and seed germination of Lactuca sativa the least sensitive and the other tests were in decreasing order of sensitivity: Folsomia candida>reverse electron transport>MetPLATE>Toxichromotest>Allium cepa root growth>Lemna sp. growth. As a conclusion, polluted soils rich in sand retain heavy metals with less firm bindings, particularly in the case of Cu and Zn, than soils rich in clay, indicating that chemical methods for measuring the bioavailability of metals need to be optimized taking into account the soil type, acidity, redox state and the individual contaminants.