Evaluation of inorganic adsorbents for the removal of problematic textile dyes and pesticides

Activated bauxite, Fullers earth and a synthetic hydrotalcite clay were compared with activated carbon for the removal of reactive dyes, pentachlorophenol and Propetamphos, which were contaminants of major concern in the U.K. textile industry. Thermogravimetric analyses indicated that bauxite and Fullers earth were best calcined at 700C before use and that the clay required no heat treatment. All the adsorbents were then chemically conditioned before their capacities were measured by batch adsorption tests. Residual dye was measured by spectrophotometry; the pesticides were analysed by high performance liquid chromatography. Synthetic clay removed reactive dyes most effectively at pH 5.5-8.5 and 20-40C; activated carbon performed comparably under neutral and alkaline conditions. Bauxite was as effective as activated carbon under acidic conditions, while Fullers earth was ineffective. Only activated carbon removed the pesticides to any degree.