Phosphate adsorption on chemically modified sugarcane bagasse fibres

Integral sugarcane bagasse fibres of about 2 cm length that were pre-treated for removal of greases and sugars were carboxymethylated on their surface, retaining about 20% of impurities (as insoluble material and water). The fibres were doped with Fe2+ ion, by dipping in aqueous iron chloride solutions of different concentrations. This material was used to remove phosphate from water. Thermal analyses (differential scanning calorimetry – DSC) and infrared spectroscopy – FTIR show the occurrence of important changes on carboxymethylated fibres after incorporation of Fe2+ and PO43-. Non-carboxymethylated fibres, also treated with the iron solutions, also showed a good level of capture of phosphate from an aqueous solution. The chemical modification increases Fe2+ ion adsorption on the fibre surface, increasing the efficiency of phosphate adsorption. Apparently, the process of modification, without incorporation of Fe2+, also improves phosphate retention. When about 4% of iron is adsorbed on the fibres, 97% of phosphate is captured on the carboxymethylated material and 94% on the non-carboxymethylated material. The absorption data fit both the Langmuir and Freundlich isotherm. When quantified by measuring the monolayer adsorption in the Langmuir isotherm model, the presence of Fe2+ ions on the surface fibres increases the phosphate adsorption capacity by about 45%. Our results (Q max = 152 mg/g) are far superior or in the same order of magnitude, when compared with literature data, with the advantage be the raw material, waste of biomass, only somewhat changed chemically and even after the modifications compose materials harmless to the environment.

► Bagasse carboxymethylated or not, grafted with Fe2+, adsorbs phosphate from water.
► The higher quantity of Fe2+ on surface fibres results in higher phosphate adsorption.
► The adsorption of Fe2+ is higher on chemically modified fibres.
► The adsorption sites are the cellulose and lignin.
► 152 mg/g is phosphate maximum amount adsorbed on fibres modified and grafted with Fe.