Abstract

JOHNSTONE, A.C.. Are pit lakes an environmentally sustainable closure option for opencast coal mines?. J. S. Afr. Inst. Min. Metall. [online]. 2021, vol.121, n.10, pp.531-536. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/1551/2021.

The aim of the study is to determine if pit lakes are a sustainable coal mine closure option in South African. The water balance, chemistry, limnology, and bacterial population of three selected pit lakes were investigated. The lakes are in the three major coal basins of South Africa and are associated with different lithologies and mining methods. The major factors driving the water balance of the pit lakes are direct rainfall, runoff, inflow from old mine workings, and groundwater infiltration, with the major losses being evaporation or discharge onto surface. The study indicated that pit lakes can be designed as 'terminal sinks' to provide a sustainable mine closure option. The pit lakes sampled have an alkaline pH, and mostly a sodium/calcium sulphate water with total dissolved solids content of less than 3000 mg/l. The phytoplankton and microbiological data indicates that the pit lakes support aquatic life. The study shows that correctly designed pit lakes can be an environmentally sustainable closure option for South Africa's coal mines. A suggested design manual has been developed to assist mine owners and regulators in developing sustainable coal mine pit lakes as a closure option.

Keywords : coal mine; pit lakes; water quality; water balance; mine closure.

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