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Hexavalent chromium removal from wastewater using sheep wool was investigated at several equilibration periods. The influence of contact time, pH, adsorbent dosage and initial concentration was investigated. Adsorption isotherms for long and short periods were fitted to the Langmuir and Freundlich isotherms. For short contact times, the Langmuir adsorption isotherm was obeyed with no detectable change in the oxidation state but removal percentages did not exceed 90%. Long contact times resulted in more than 99% removal of Cr(VI). A 2-step mechanism for the removal is proposed. Free wool and wool loaded with Cr(VI) were characterized by FTIR and SEM.

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Alizarin red S (ARS) removal from wastewater using sheep wool as adsorbent was investigated. The influence of contact time, pH, adsorbent dosage, initial ARS concentration and temperature was studied. Optimum values were: pH = 2.0, contact time = 90 min, adsorbent dosage = 8.0 g/L. Removal of ARS under these conditions was 93.2%. Adsorption data at 25.0 °C and 90 min contact time were fitted to the Freundlich and Langmuir isotherms. R2 values were 0.9943 and 0.9662, respectively. Raising the temperature to 50.0 °C had no effect on ARS removal. Free wool and wool loaded with ARS were characterized by Fourier Transform Infrared Spectroscopy (FTIR). ARS loaded wool was used as adsorbent for removal of Cr(VI) from industrial wastewater. ARS adsorbed on wool underwent oxidation, accompanied by a simultaneous reduction of Cr(VI) to Cr(III). The results hold promise for wool as adsorbent of organic pollutants from wastewater, in addition to substantial self-regeneration through reduction of toxic Cr(VI) to Cr(III). Sequential batch reactor studies involving three cycles showed no significant decline in removal efficiencies of both chromium and ARS.

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a b s t r a c tCr(VI) removal from wastewater streams using sheep wool in sequential batch contactors (SBC) mode was investigated. The influence of the number of contactors on removal efficiency was also studied. SBC was carried out in tanks containing 100 and 1000 mL solutions. Four SBC runs ensured complete removal of Cr(VI) whereas three runs reduced its concentration from 100 to 0.06 mg/L. Experiments in both tanks gave similar results, thus permitting scalability to a pilot plant and eventual industrial scale utilization. Regeneration studies were carried out using KCl. The optimum parameters in terms of time, concentration and temperature were 25 min, 0.10 m and 50.0°C. Simultaneous adsorption-desorption cycles showed that sheep wool can be regenerated several times with no discernible change in removal efficiency.

Apparent thermodynamic parameters for the hydroxy proton ionisation of Bordeaux‐R were obtained in micellar solutions using the thermochromic method. The effect of addition of the surfactants CTAB, TX‐100 and SDS was investigated in buffered solutions in the pH range of 6–13. Ionisation constants in water and in the presence of surfactants were determined spectrophotometrically and the pK′ of Bordeaux‐R in water was found to be 10.90 in the absence of surfactant. However, at concentrations above critical micelle concentration, pK′ dropped to 10.14 with CTAB, increased to 11.29 with TX‐100 but was insensitive to SDS addition. Standard enthalpies and entropies of ionisation were obtained using the thermochromic method. This method, in conjunction with pK and spectral measurements and comparison with different azo dyes, has been shown to provide detailed information on the mechanism of dye–surfactant interaction.