CATION-EXCHANGE BEHAVIOR OF BAUXITE REFINING RESIDUES FROM WESTERN-AUSTRALIA

Over 60 million tomes per year of bauxite refining residue (red mud) i s produced worldwide. Its high Na concentration inhibits plant growth and hence reclamation. The cation-exchange capacity (CEC) of red mud a nd the cation exchange equilibria between Na+ and several other cation s were measured to elucidate the mechanism of Na release from red mud. The CECs obtained by using K+ and NH4+ were significantly higher than those obtained using Ca2+ and Ba2+. This unusual cation exchange phen omenon can be attributed to the presence of zeolitic minerals in red m ud. Cation exchange equilibria show that Na+ originally present in red mud was preferentially adsorbed by the mud over other cations. At hig h cation fractions in red mud (>0.1), the mud selectively sorbed monov alent over divalent cations, with the following order of selectivity: K+ > Li+ > NH4+ > Ba2+ greater than or equal to Ca2+ > Mg2+. The excha nge of Na+ has been found to have significant negative correlations wi th the radius of hydration and Debye-Huckel parameter. Divalent cation s have little ability to exchange Na+ from zeolitic exchange sites. In cremental extraction of Na+ in red mud shows that K+ and NH4+ displace d 99 (63%) and 57 (44%) cmol(c) kg(-1) red mud whereas Ca2+ and Mg2+ c ould only displace 33 and 29 cmol(c) kg(-1) red mud, respectively, out of a total of 99 cmol(c) Na kg(-1) red mud, In a reverse process 95% of K+ adsorbed on red mud was readily replaced by Na+. The experimenta l evidence suggests that the release of Na+ from red mud is due to cat ion exchange.