title: Column-mode fluoride removal from aqueous solution by magnesia-loaded fly ash cenospheres.
abstract: Column experiments in a fixed bed reactor packed with a certain amount of magnesia-loaded fly ash cenospheres (MLC) were conducted to examine the effects of adsorbent mass, flow velocities, influent concentrations and coexisting anions on fluoride removal. The breakthrough time increased with an increase in adsorbent mass, but decreased with increasing influent fluoride concentration. The exhaustion time decreased with the increase in the influent fluoride concentration. The capacity at the breakthrough point increased with an increase in adsorbent mass, flow velocity and the influent fluoride concentration. The capacity at the exhaustion point increased with an increase in flow velocity, but showed no specific trend with an increase in the initial fluoride concentration. The bed volumes at breakthrough point increased with an increase in adsorbent mass, flow velocity and the influent fluoride concentration. The empty bed contact time decreased with an increase in flow velocity. The coexisting anions reduced the adsorption capacity of the fixed bed reactor in the order: mixture of all three anions > dihydric phosphate > nitrate > sulfate. The adsorbent exhaustion rate decreased with the increase in flow velocity and adsorbent mass, whereas it increased with increasing influent fluoride concentration. Columns with large amounts of MLC are preferable in order to obtain optimal results during the adsorption process, and the higher the flow velocity, the better the column performance. The Bohart and Adams model and the Thomas model were applied to the experimental results. Column adsorption was reversible and the regeneration operation was accomplished by pumping 0.2 M NaOH through the loaded MLC column.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210046, China.
authors.forename: Xiaotian
authors.initials: X
authors.lastname: Xu
authors.forename: Qin
authors.initials: Q
authors.lastname: Li
authors.forename: Hao
authors.initials: H
authors.lastname: Cui
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Pang
authors.forename: Hao
authors.initials: H
authors.lastname: An
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Jianping
authors.initials: J
authors.lastname: Zhai
mesh_terms: D000327:Adsorption; D000838:Anions / Q000737:chemistry; D019149:Bioreactors; D060729:Coal Ash / Q000737:chemistry; D005459:Fluorides / Q000302:isolation & purification*; D018508:Water Purification
chemical_list: D000838:Anions; D060729:Coal Ash; D005459:Fluorides