Temporal Changes of Pyrite Oxidation Rate in Bolivian Sulphidic Mining Wastes

Since the 70's, when huge sulphidic open pits were developed, the acidic rock drainage (ARD) become the leader problem of the sulphidic mining industry. Although the recycling is an essential technology, it cannot cover the demand alone, thus mining activity needs to continue. Acidity in mine drainage commonly requires most of the attention, but the main problem is the caused elevated level of metal mobility and leaching, which are generated by the increased rates of sulphide weathering under acidic conditions. The Itos mine is a polymetallic vein deposit in Bolivia, had been mined for silver and tin until 1990, leaving behind much and huge tailings and mine waste heaps, where quite often the pyrite content exceeds 10 %. Serious ARD effects take place in the mine waste heaps. These processes can be well characterized with the pH 1 or 2 of the seepage water, which forms serious alteration in the waste itself and the neighbouring rocks. In three consecutive years, the pyrite oxidation rate was investigated on the same 7 samples by humidity cell test. 5-6 months pauses were left between the humidity cell test periods, which mimics the alternation of wet and dry periods, typical for the place. The results give much more information, than the oxidation rate in the individual test periods, showing the changes by time. This applied method gave good result to characterize the behaviour of the waste in long-term. The column test was complemented with mineralogical analyses, such as electron probe micro analysis. The mineralogical and column test analyses show, that the changes of the pyrite oxidation rate split the samples into three different groups, one where the oxidation rate decreases, second where it increases with time and the third where oxidation rate is maximal and stays stable for several years.

Prediction of drainage water chemistry by experimental data (on the example of the Nakhodka porphyry copper prospect, Western Chukotka, Russia)

Prediction of drainage water chemistry is a critical part of mine planning; particularly water and mine waste management. This study investigates a potential composition of drainage water for various storage times of sulphide-bearing geological materials by experimental data. The paper presents the results of Short-Term Leach tests and Humidity Cell tests for geological materials of the Nakhodka porphyry copper ore field, the Baimka ore trend (Western Chukotka, Russia). The results obtained can be used to forecast of wastewater composition as well at the initial stage of storage of sulphide-bearing geological materials as over the long-term.

Cytotoxicity of Three Light-Cured Orthodontic Adhesives

Objective: The aim of this study was to evaluate the cytotoxic effects of three commercial light-cured orthodontic adhesives.Materials and methods: The potential cytotoxic effects of three types of orthodontic adhesives, Grengloo, Green Glue, and Transbond XT, were tested on L929 cell culture. The cell line was grown in 96-well tissue culture plates (1x105 cells/mm3). Thin resin discs weighing 0.4, 0.6, 0.8, 0.8, and 0.8 gram of each material were prepared and aged for 1, 3, 6, 8, and 10 days, respectively, in Minimum Essential Medium (MEM) at 37°C with 5% CO2 at 100% humidity. Cell viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay according to ISO 10993-5: 2009 (E). The differences among the groups was statically analyzed by independent paired t-test (α = 0.05).Results: After 1 day of storage, all adhesive systems showed cytotoxic effects. However, ageing tended to considerably reduce the cytotoxicity of Green Glue. Grengloo was essentially non-cytotoxic day 3 onwards, while Green Glue and Transbond XT exhibited potential cytotoxicity at all times of the experiment. Conclusion: All tested light-cured orthodontic adhesives had cytotoxic potential during the first day. Grengloo had the highest cell viability, whereas, Green Glue had the lowest.