Authors: Fisseha, B; Bryan, R; Simms, P

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Fisseha, B, Bryan, R & Simms, P 2009, 'Evaporation, Unsaturated Flow and Oxidation in Multilayer Deposits of Gold Paste Tailings', in R Jewell, AB Fourie, S Barrera & J Wiertz (eds), Paste 2009: Proceedings of the Twelfth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 251-260,

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The behaviour of surface deposited paste mine tailings is strongly influenced by the evaporation and saturated-unsaturated flow through the tailings, which not only controls desiccation, but also governs salt accumulation and oxidation. Select data is presented from a series of drying tests on multilayer deposition of a gold paste tailings. During drying, rewetting after precipitation, and interlayer flow after placement of fresh layer, including small scale tests (0.15 m diameter column tests) and large scale tests (1.7 x 1.7 m in plan) were undertaken to study unsaturated flow and evaporation from two-layer deposits of two gold paste tailings. It is shown that the interlayer flow after addition of the second layer can be reasonably modelled using unsaturated flow codes. Though significant cracking occurred during drying of the paste tailings, its effect on the rate of evaporation was minimal. In some of the tests, the accumulation of salt at the surface substantially suppressed the rate of evaporation. The accumulation of salts could be tracked by sampling the surface of the tailings and measuring the electrical conductivity of the pore-water. Mass transport could be qualitatively modelled by one-dimensional contaminant transport theory. Profiles of sulphide oxidation with depth and time are also presented. The degree of oxidation is shown to be small but significant, and can be reasonably approximated by oxygen diffusion modelling coupled to the unsaturated flow codes.

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