Water treatment technologies for removal of acid, sulphate and metals
Geldenhuys, Andries Johannes
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A great deal of research effort has been undertaken to find an effective solution to the problem of acid mine drainage. Indeed, South African legislation requires mining companies to respect environmental regulations by minimising water intake from local municipalities and providing a rehabilitation plan. In order for the South African mining industry to remain competitive, the proposed solutions have to be not only efficient but also economic. This is the reason for the use of a waste material being attractive for water treatment and an integrated treatment technology being developed to treat water to different quality levels. The main objectives of this study were to develop more cost-effective treatment processes specific to the needs of the mining industry in southern Africa and to investigate the technical and environmental feasibility of utilising an alkaline waste product from the local paper industry as stabilising agent for acid mine residues. All the research and development work was carried out on laboratory and pilot scale plants. Five papers, with the present author as principal contributor, will form the basis of this thesis, of which one has been published and four are being peer reviewed, presented at international conferences (locally and overseas) and published in the proceedings of the various conferences. Another five papers, with the author as co-author, have also been presented at international conferences and are being published in the proceedings of these conferences, and are included in this thesis. The results of the laboratory and pilot scale studies have been incorporated into the design and implementation of the following full-scale plants: • A limestone handling and dosing system to supply slurried limestone of constant density to the neutralisation plant was constructed and commissioned during 2001 at Navigation Section of Landau Colliery, Witbank • A limestone handling and dosing system, including a fluidised-bed limestone neutralisation plant, was constructed and commissioned during 2001, at Ticor, Empangeni • An iron(II)-oxidation and fluidised-bed limestone neutralisation plant was constructed and commissioned during 2002 at BCL, Selebi-Phikwe, Botswana • A limestone handling and dosing system, to supply slurried limestone of constant density to the neutralisation plant, was constructed and commissioned during 2003, at Kromdraai Colliery, Witbank • An iron(II)-oxidation and fluidised-bed limestone neutralisation plant was constructed and commissioned during 2004, at the Navigation Section of Landau Colliery, Witbank. These plants consist of specific units (stages) of the completely integrated process, developed by the CS1R:Environmentek over the past four years. These stages are: • Heating unit: Production of CaO (quick lime) and C02-gas from burned coal and precipitated CaC03 (limestone) • Limestone neutralisation and partial sulphate removal to a level of 1 900 mg/l • Ca(OH)2 (hydrated lime) stage: CaO contacted with the acid water to produce Ca(OH)2 • Lime treatment stage: Partial sulphate removal as CaS04 (gypsum) to below 1 200 mg/l, and full removal of magnesium and other metals • pH adjustment stage: C02 from the heating unit applied to reduce the pH to 8.6 while CaC03 precipitates • Barium sulphide treatment or biological sulphate removal treatment: Removal of sulphate to below 200 mg/l • Production (regeneration) of barium sulphide: Heating barium sulphate from the above stage • Stripping of H2S either from the barium sulphide or the biological sulphate removal processes. H2S is contacted with Fe(lll)-rich water for elemental sulphur production.
- Engineering