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Journal of Environmental Quality Abstract -

Cation Exchange Behavior of Bauxite Refining Residues from Western Australia


This article in JEQ

  1. Vol. 24 No. 3, p. 461-466
    Received: Jan 11, 1994

    * Corresponding author(s): jwcwong@ctsc.hkbc.hk
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  1. J. W. C. Wong * and
  2. G. E. Ho
  1. Dep. of Biology, Hong Kong Baptist Univ., 224 Waterloo Rd., Kowloon, Hong Kong;
    School of Biology and Environmental Sciences, Murdoch Univ., Murdoch, WA 6150, Australia.



Over 60 million tonnes per year of bauxite refining residue (red mud) is produced worldwide. Its high Na concentration inhibits plant growth and hence reclamation. The cation-exchange capacity (CEC) of red mud and the cation exchange equilibria between Na+ and several other cations were measured to elucidate the mechanism of Na release from red mud. The CECs obtained by using K+ and NH+4 were significantly higher than those obtained using Ca2+ and Ba2+. This unusual cation exchange phenomenon can be attributed to the presence of zeolitic minerals in red mud. Cation exchange equilibria show that Na+ originally present in red mud was preferentially adsorbed by the mud over other cations. At high cation fractions in red mud (>0.1), the mud selectively sorbed monovalent over divalent cations, with the following order of selectivity: K+ > Li+ > NH+4 > Ba2+ ≥ Ca2+ > Mg2+. The exchange of Na+ has been found to have significant negative correlations with the radius of hydration and Debye-Huckei parameter. Divalent cations have little ability to exchange Na+ from zeolitic exchange sites. Incremental extraction of Na+ in red mud shows that K+ and NH+4 displaced 99 (63%) and 57 (44%) cmolc kg−1 red mud whereas Ca2+ and Mg2+ could only displace 33 and 29 cmolc kg−1 red mud, respectively, out of a total of 99 cmolc Na kg−1 red mud. In a reverse process 95% of K+ adsorbed on red mud was readily replaced by Na+. The experimental evidence suggests that the release of Na+ from red mud is due to cation exchange.

This research was supported by funds from the Alcoa of Australia Pty. Ltd.

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