Adsorption of Cu(II) and Cr(VI) ions by chitosan: kinetics and equilibrium studies

The ability of chitosan as an adsorbent for Cu (II) and Cr (VI) ions in aqueous solution was studied. The experiments were done as batch processes. Equilibrium studies were done on both cross-linked and non-cross-linked chitosan for both metals. Cr (VI) adsorption behaviour could be described using the Langmuir isotherm over the whole concentration range of 10 to 1000 mg·l-1 Cr. The maximum adsorption capacity for both types of chitosan was found to be 78 mg·g-1 for the non-cross-linked chitosan and 50 mg·g-1 for the cross-linked chitosan for the Cr (VI) removal. For the Cu (II) removal the Freundlich isotherm described the experimental data over the whole concentration range of 10 to 1000 mg·l-1 Cu (II). The maximum adsorption capacity for both types of chitosan can be estimated to be greater than 80 mg·g-1. Cr (VI) removal was the highest at pH 5 but pH did not have a large influence on Cu (II). From these results it is clear that the adsorption of heavy metals is possible with chitosan, but that with this method, end concentrations of below 1 mg·l-1 can hardly be obtained. WaterSA Vol.27(1) 2001: 1-

Tuneable ion-selective inorganic membranes

A new type of ion-selective ceramic membrane with electrically tuneable selectivity is reported. The membrane consists of a conventional supported γ-alumina membrane with porous gold electrodes sputtered on both sides. An electrical potential difference can be applied over the electrodes. The transport of Cu2+ ions was investigated as a function of the applied field strength over the membrane and the copper concentration in the feed solution. It is shown that the transport rate can be tuned efficiently by the magnitude and direction of the field. This technology may find application in micro-fluidic devices such as micro total analysis systems.\u

Synthesis and characterisation of dual-phase Y-TZP and RuO2 nanopowders: dense electrode precursors.

The synthesis and characterisation of nanopowders in the dual-phase system tetragonal-Y2O3-doped ZrO2 (Y-TZP) and RuO2 are described. Five powders were prepared from a co-precipitation (CP) method with stoichiometric variation in the RuO2 content (5–46 mol%) and two powders were prepared from solid-phase mechanical mixing of the above oxides prepared separately. In the CP method, an aqueous chlorometal solution containing appropriate precursor ions was co-precipitated in a concentrated aqueous ammonia (pH y14) solution. Following filtration, washing and drying (100 uC), the CP synthesis route yielded black coloured amorphous powders. Crystalline dual-phase powders were obtained after calcination in stagnant air at 600 uC for 2 h. The average Y-TZP and RuO2 crystallite sizes were, respectively, 10 and 20 nm, i.e. a nano/nano powder. The powders were characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM), backscatter Raman spectroscopy (ZrO2 phase determination) and quantitative X-ray fluorescence (XRF). Time-dependent calcination experiments for samples of similar composition revealed that under the synthesis conditions employed, a composite was formed where a fraction of the crystalline RuO2 phase was initially dissolved in the ZrO2 phase and which gradually transforms to a more stable, distinctly dual-phase system upon prolonged (¢20 h) calcination at 600 uC