Sorption of copper (II) ions from acqueous solutions by regenerated spent bleaching earth
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Date
2011-08-23
Authors
Enos, Wamalwa Wambu
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Abstract
Copper pollution of water systems has increased greatly in the recent years in many parts of the world because of increased industrial demand for copper, its heavy use in agrochemicals and inefficiency of conventional water filtration techniques. The present study was designed to investigate the efficacy of Spent Bleaching Earth (SBE) as a low cost adsorbent for the removal of copper from aqueous solutions. The SBE, a clay waste generated by edible oil refineries, was washed in excess methyl-ethyl ketone and subjected to heat and/or acid treatments at various conditions. The resultant regenerated spent bleaching earth (RSBE) was then used in a series of experiments to assess its ability to sorb Cu (II) ions from aqueous solutions. The time of contact, adsorbate concentration, adsorbent dosage and the effects of change in adsorbate pH were studied among other parameters. The study showed that copper (II) ions could be removed from aqueous solutions by adsorptive method using RSBE. Methyl-ethyl ketone residual oil extraction followed by heat treatment of the material at 350-370 °C was most effective SBE regeneration procedure for copper adsorption. The materials obtained in this way were characterized by high Cation Exchange Capacity (CEC) of up to 6000 mg/g of Na ions equivalents. They had Point of Zero Net Charge (PZNC) at pH 5.5. The pH, sorbent dosage and initial adsorbate concentrations were key parameters affecting adsorption characteristics of Cu (II) ions onto RSBE. Over 94% Cu (II) removal was recorded at pH 5.5 using 272 mg/l of initial Cu (II) concentration at 0.1 mass (grams) to volume (milliliters) of adsorbent dosage. Based on analysis of changes in solution pH during the adsorption process, it was suggested that that hydrolysis species were more favorably adsorbed onto the RSBE soil particles. The highest distribution coefficient, KD, of 590.76 was recorded for 370 °C regenerated materials and the standard Gibbs free energy (G0) (which ranged from -11.9611 kJmol-1 to5.8042) indicated that the adsorption process was spontaneous and mainly based on physical ion-exchange type interactions between the metal ions and cations at the RSBE surfaces. Analysis of the adsorption kinetics indicated that Cu (11) adsorption on RSBE is a rapid phenomenon reaching its initial equilibrium in less than six hours. The sorption process fitted Lagergren pseudo-second order mechanism in the initial stages although the MorisWeber intra-particle diffusion mechanism was more favored at prolonged periods of equilibration. The adsorption data was better described by the Langmuir isotherm than the Freundlich Isotherm was. And desorption experiments illustrated that pH adjustments were more effective in recovery of sorbed copper ions from RSBE than competitive cationic desorbing agents. Over 80% removal of sorbed copper was realized showing that the sorbed metal can substantially be recovered from the materials before their final disposal
Description
The QD 181.C9 W3
Keywords
Copper ions//Copper--absorption and adoption--Kenya