Studies on removal of boron from aqueous solution by fly ash agglomerates

The objective of the present study is to assess the efficiency of fly ash agglomerates (particle size 1.0–1.6 mm) with respect to boron removal from aqueous solution. The experiments have been carried out by using fly ash from brown coal and biomass burning power plant Zgierz (Poland). The effects of pH, temperature, adsorbent dosage, initial boron concentration and contact time on the adsorption were investigated. Removal of boron from aqueous solution by fly ash agglomerates is slightly affected over the investigated pH range (5–11); minimum of adsorption was found around pH 8.5. Natural pH imposed by fly ash agglomerates, i.e. about 10.5, is favorable to boron adsorption by coprecipitation with calcium and aluminum oxides. The maximum adsorption capacity achieved for fly ash agglomerates is 6.9 mg/g for 0.0025 (g/mL) adsorbent-to-solute ratio. For 100 mg/L boron solution the maximum removal was about 90% for 0.75 adsorbent-to-solute ratio. The adsorption kinetics experimental data were fitted well with the pseudo-second-order model. An intraparticle diffusion model was examined and the pore diffusion control of adsorption rate in the initial stage of the process was found. The Freundlich isotherm model is more adequate than the Langmuir one while simulating the adsorption of boron onto fly ash agglomerates at 25, 35 and 45°C. Results also revealed that the adsorption of boron increased with increasing temperature. Thermodynamic parameters revealed an endothermic nature of boron adsorption on such adsorbents. Column studies' data were evaluated by using Thomas and Yoon–Nelson models. Fly ash agglomerates can be effective, low-cost, and handy adsorbent for the removal of boron from aqueous solutions both in batch and column processes.

► Removal of boron from aqueous solution was investigated, using fly ash agglomerates.
► The adsorption kinetics obeys pseudo-second order model.
► The experimental data were fitted using the Freundlich isotherm.
► Thermodynamic parameters revealed an endothermic nature of boron adsorption.