Adsorption of selected herbicides from water using activated carbon and polymeric adsorbents
A range of adsorbents have been evaluated for the adsorption of selected herbicide compounds from aqueous solution. The adsorption performance of LF -1, a carbonised polymer produced in the laboratory, Amberlite XAD-4, a commercially available polymeric adsorbent produced by Rohm and Haas and MN-200, a HypersolMacronet polymer produced by Purolite, were compared with a commercial activated carbon, Chemviron F -400. The pore size distributions of the adsorbents have been investigated using nitrogen adsorption. F-400, LF-1 and MN-200 were found to contain similar microporous structures. The carbons also possess a significant degree of mesoporous structure, which may enhance the diffusion of organic species into the micropores. The pore size distribution for XAD-4 shows an almost exclusive meso/macroporosity with very little microporous structure. Spectroscopic analysis and titration of the adsorbents indicated a number of different oxygen functional groups. XPS and elemental analysis suggested higher oxygen concentrations than those obtained using direct titration, which was attributed to bound oxygen within the structure of the adsorbents. The adsorption capacity of phenol was assessed as a characterisation technique. The capacity of the carbons was much greater than the polymeric adsorbents. Analytical techniques were developed and validated for the determination of trace levels (0.1 parts per billion) of five herbicides; atrazine, benazolin, bentazone, imazapyr and tric1opyr. Single and multi-component adsorption isotherms are presented for trace concentrations of the herbicides in aqueous solution. The effect of pH and fulvic acid upon the adsorption was also investigated. Mini-column experiments were performed using multi-component mixtures. In all cases, the uptake of herbicides on F -400 is greater than on the other adsorbents. Regeneration of F-400 and MN-200 was investigated usmg solvent stripping techniques. Significant regeneration efficiencies were observed using ethanol at pH 12 and 50°C to make the technique a viable option.