Metal ion interaction with the hydrous oxides of aluminium |
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| Authors: | J Slavek W F Pickering |
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| Institution: | 1. Department of Chemistry, University of Newcastle, 2308, N.S.W., Australia
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| Abstract: | Suspensions of Al(OH)3 gel, gibbsite or alumina were loaded with varying amounts of Cu, Cd, Zn, or Pb ions by varying the system pH. A complex relationship between metal uptake and equilibrium pH was noted (due to substrate buffering) but total loss of metal ion from solution was observed at pH > 6.5. The pre-loaded particles were back-extracted with fifteen different chemical solutions and the percentage of sorbed ion retrieved generally varied along the sequence NaCl, CaCl2 < MgCl2, NH4NO3 < CH3OOONH4, Na citrate, Na4P2O7, EDTA, DTPA ≈ CH3OOOH, H2C2O4, HCI, HN03. The recovery value varied with initial surface loading and an observed minimum around 1 gruel M2+ per 20 mg solid is considered to reflect changes in metal species nature (e.g., bonded M2+, MOH+, precipitated M(OH)2) and substrate surface charge. In the ‘minima’ region less than 10% of metal ion was displaced by many reagents. With different loadings up to 40% was displaceable by salts (i.e., weakly sorbed) while acids or complex formers at times released over 90 % of the pre-sorbed metal species. It was concluded that the degree of metal ion interaction varied with the initial system pH, with retention being due to a combination of weak adsorption, occlusion in gels, chemi-sorption and precipitation of M(OH)2. |
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