Environmental conditions affecting the oxidation of thiosalts in treated mine milling effluent

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University of New Brunswick


The production of thiosalts (S203 2~, Sn06 2 \ etc.) in the milling of sulfide rich ore is inevitable with today's technologies. There is no economically feasible way of treating for thiosalts in milling effluent at the present time. They will pass through conventional lime treatment and eventually be released into effluent streams. Periodically the pH of the effluent streams will drop due to the oxidation of the thiosalts, leading to undesirable conditions for aquatic life. This only occurs a few times a year and although it is consistent with seasons, the time frame is relatively unpredictable. The key to this problem is to determine what conditions contribute to thiosalt oxidation in order to predict these pH depressions. From here, treatment times can be optimized to cut down on cost. This report indicates a number of conditions that contribute to pH depressions and thiosalt oxidation in a mine effluent stream in northeastern New Brunswick. A multivariate regression model has been formulated, using Minitabl2 statistical software, to help predict pH drops in stream receiving effluent from the mine. This model can be seen below. pHl 111/1112 = 5.66 +2.0E-06 (thiosalts)2 + 0.503(Rel Temp./thiosalts) - 7.53E-04(Rel.Temp)2 The model is able to predict pH depressions in range from 5.05 to 6.55 and predicts the time of these drops within ± 2 weeks of the measured drops. This is the first attempt at predicting the time frame for thiosalt treatment.