title: Effective removal and fixation of Cr(VI) from aqueous solution with Friedel's salt.
abstract: Friedel's salt (3CaO x Al2O3 x CaCl2 x 10 H2O or Ca4Al2(OH)12Cl2(H2O)4) is a calcium aluminate hydrate formed by hydrating cement or concrete in seawater at a low cost. In the current study, we carefully examined the adsorption behaviors of Friedel's salt for Cr(VI) from aqueous solution at different concentrations and various initial pHs. The adsorption kinetic data are well fitted with the pseudo-first-order Lageren equation at the initial Cr(VI) concentration from 0.10 to 8.00 mM. Both the experimental and modeled data indicate that Friedel's salt can adsorb a large amount of Cr(VI) (up to 1.4 mmol Cr(VI)/g) very quickly (t1/2 = 2-3 min) with a very high efficiency (>99% Cr(VI) removal at [Cr] < 4.00 mM with 4.00 g/L of adsorbent) in the pH range of 4-10. In particular, the competitive adsorption tests show that the Cr(VI) removal efficiency is only slightly affected by the co-existence of Cl(-) and HCO3(-). The Cr(VI)-fixation stability tests show that only less than 0.2% adsorbed Cr(VI) is leaching out in water at pH 4-10 for 24 h because the adsorption/exchange of Cr(VI) with Friedel's salt leads to the formation of a new stable phase (3CaO x Al2O3 x CaCrO4 x 10 H2O). This research thus suggests that Friedel's salt is a potential cost-effective adsorbent for Cr(VI) removal in wastewater treatment.
authors.affiliation: School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200072, PR China.
authors.forename: Yingchun
authors.initials: Y
authors.lastname: Dai
authors.forename: Guangren
authors.initials: G
authors.lastname: Qian
authors.forename: Yali
authors.initials: Y
authors.lastname: Cao
authors.forename: Ying
authors.initials: Y
authors.lastname: Chi
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Xu
authors.forename: Jizhi
authors.initials: J
authors.lastname: Zhou
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
authors.forename: Zhi Ping
authors.initials: ZP
authors.lastname: Xu
authors.forename: Shizhang
authors.initials: S
authors.lastname: Qiao
mesh_terms: D000327:Adsorption; D000465:Algorithms; D002840:Chromates / Q000737:chemistry / Q000302:isolation & purification; D002857:Chromium / Q000302:isolation & purification*; D003252:Construction Materials; D006863:Hydrogen-Ion Concentration; D007475:Ion Exchange Resins / Q000737:chemistry*; D007700:Kinetics; D012623:Seawater; D012996:Solutions; D013816:Thermodynamics; D014867:Water
chemical_list: D002840:Chromates; D007475:Ion Exchange Resins; D012996:Solutions; D014867:Water; D002857:Chromium