Oxidation of metal sulphides and their mobility within Brunswick mines tailings
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Date
1993
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University of New Brunswick
Abstract
The oxidation of tailings and its relation to grain size has been investigated at the Brunswick Number 12 Mine. The most recent tailings typically show higher metal contents than do 'stratigraphically' lower, older tailings, despite current extraction processes being more efficient. The tailings comprise sulphide grains, usually exceeding 90% volume at < 37 μm. These sulphide grains coagulate into "clumps" up to 1 mm diameter in polished sections during their preparation. Smaller sulphide grains liberated from these clumps show a greater tendency to oxidize than do the larger grains. This is attributed to an increased surface area of the smaller grains. When oxidized, sulphur-bearing minerals produce sulphuric acid. The acid may dissolve metals and transport them in solution to the perimeter seepage collection ditch as surface run- off (Welch, 1990). There is also evidence of material being transported to the underlying glacial till. This allows metals to enter the environment untreated. Acids are the primary cause of remobilization of metals. Other factors, such as density contrasts and grain size variations that affect porosity and water content, are also important. The oxidation reaction of metals produces sulphur dioxide which, if allowed to enter the environment, can contribute to acid rain and other pollutants. Control of grain size by an induced electrostatic charge, causing a net neutralizing effect, may coagulate particles, decrease surface area and depress overall acid generation from future tailings