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In situ neutralisation of uncarbonated bauxite residue mud by cross layer leaching with carbonated bauxite residue mud
► Leaching uncarbonated bauxite residue mud with carbonated bauxite residue mud leachate lowers the pH of uncarbonated bauxite residue leachate. ► Dual layer systems maintained lower leachate pH than uncarbonated bauxite residue only systems over 400 pore volumes leached. ► Carbonated residue porewa...
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Published in: | Journal of hazardous materials 2011-10, Vol.194, p.119-127 |
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Main Authors: | , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | ► Leaching uncarbonated bauxite residue mud with carbonated bauxite residue mud leachate lowers the pH of uncarbonated bauxite residue leachate. ► Dual layer systems maintained lower leachate pH than uncarbonated bauxite residue only systems over 400 pore volumes leached. ► Carbonated residue porewater as well as dawsonite and calcite dissolution were identified as sources of (bi-)carbonate which buffered pH. ► Leachate concentrations of As, Cr, Cu, Ga and La were immediately reduced in dual layer treatments compared with uncarbonated only. ► Deposition of carbonated bauxite residue over existing uncarbonated residue may be useful for
in situ neutralisation of uncarbonated residue.
Unameliorated residue mud from the Bayer process generates highly alkaline leachates (pH ca. 13) after deposition in storage areas. Pre-deposition treatment of bauxite residue mud (BRM) with CO
2 gas (carbonation) lowers leachate pH to ca. 10.5. Laboratory scale leaching columns were used to investigate the potential for
in situ pH reduction in existing uncarbonated BRM deposits through exposure to carbonated mud leachate. Leachates from uncarbonated and carbonated residues in single and dual-layer column configurations were analysed for pH, electrical conductivity, carbonate and bicarbonate content, and element concentrations. Air-dried solids were analysed by X-ray diffraction before and after leaching.
Cross layer leaching lowers leachate pH from uncarbonated BRM. Leachate pH was significantly lower in dual layer and carbonated residue than in uncarbonated residue between one and 400 pore volumes leached. Carbonated residue porewater as well as dawsonite and calcite dissolution were identified as sources of (bi-)carbonate. Leachate concentrations of As, Cr, Cu, Ga and La were immediately reduced in dual layer treatments compared with uncarbonated residue. No element analysed exhibited a significantly higher leachate concentration in dual layer treatments than the highest observed concentration in single layer treatments. The implementation of dual layer leaching in the field therefore presents an opportunity to improve leachate quality from existing uncarbonated residue deposits and justifies further testing at field scale. |
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ISSN: | 0304-3894 1873-3336 |
DOI: | 10.1016/j.jhazmat.2011.07.090 |