Abstract
Underwater disposal of mine tailings in lakes and seas has been considered favorable due to the geochemical stability obtained during long-term storage in anoxic sediments. Sulfides are stable in the ore; however, oxidation and transformation of some substances into more soluble forms may impact bioavailability processes and enhance the risk of toxic effects in the aquatic environment. The goal of this work was to construct a model for simulating the nickel (Ni) cycle in the water column and upper sediments and apply it to the mine tailing sea deposit in the Jøssingfjord, SouthWest Norway. A one-dimensional (1D) benthic–pelagic coupled biogeochemical model, BROM, supplemented with a Ni module specifically developed for the study was used. The model was optimized using field data collected from the fjord. The model predicted that the current high Ni concentrations in the sediment can be a potential source of Ni leaching to the water column until about 2040. The top 10 cm of sediments were classified as being of “poor” environmental state according to the Norwegian Quality Standards. A numerical experiment predicted that with complete cessation of the discharges there would be an improvement in the environmental state of sediment to “good” in about 20 years. On the other hand, doubling of discharge would lead to an increase in the Ni content in the sediment, approaching the boundary of the “very poor” environmental state. The model results demonstrated that Ni leaching from the sea deposits may be increased due to sediment reworking by bioturbation at the sediment–water interface. The model can be an instrument for analysis of different scenarios for mine tailing activities from point of view of reduction of environmental impact as a component of the best available technology.
Highlights
Tailings from the mining industry are fine-grained rock materials left over from the process of separating the valuable fraction from the uneconomic fraction of an ore
The model can be an instrument for analysis of different scenarios for mine tailing activities from point of view of reduction of environmental impact as a component of the best available technology
During the period of natural conditions, the model reproduced the seasonal changes in burying velocity within the limits of 0.5–4.4 cm/year with a maximum following the period of synthesis of organic matter in the productive periods of the year
Summary
Tailings from the mining industry are fine-grained rock materials left over from the process of separating the valuable fraction from the uneconomic fraction of an ore. In addition to fragmented rock material, tailings may contain potentially harmful substances such as trace metals and remnants of production chemicals [1]. The production, along with the problem of waste disposal, is rising exponentially with increasing demand for metals and other mineral products [4]. Metal sulfides are stable in the ore, but bioavailability and risk of toxic effects may increase in the water environment due to oxidation and transformation into more soluble forms [8]. The leaching of metals such as Cu, Ni, Co, As, Cd, Zn, Pb, and Hg is a major issue in the disposal of tailings and mineral products from these mines [7,9,10,11]. Oxidation and dissolution may be prolonged in lake or sea deposits due to sediment reworking by bioturbation at the sediment–water interface [12,13,14]
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