title: Equilibrium analysis for heavy metal cation removal using cement kiln dust.
abstract: Ion exchange, reverse osmosis, and chemical precipitation have been investigated extensively for heavy metal uptake. However, they are deemed too expensive to meet stringent effluent characteristics. In this study, cement kiln dust (CKD) was examined for the removal of target heavy metals. Adsorption studies in completely mixed batch reactors were used to generate equilibrium pH adsorption edges. Studies showed the ability of CKD to remove the target heavy metals in a pH range below that of precipitation after an equilibrium reaction time of 24 h. A surface titration experiment indicated negative surface charge of the CKD at pH below 10, meaning that electrostatic attraction of the divalent metals can occur below the pH required for precipitation. However, surface complexation was also important due to the substantive metal removal. Accordingly, a surface complexation model approach that utilizes an electrostatic term in the double-layer description was used to estimate equilibrium constants for the protolysis interactions of the CKD surface as well as equilibria between background ions and the sorbent surface. It was concluded that the removal strength of adsorption is in the order: Pb > Cu > Cd. The experiments were also supported by Fourier transform infrared spectroscopy (FTIR).
authors.affiliation: (ASCE/EWRI), Environmental Engineering PhD Program, American University in Cairo, P.O. Box 74, New Cairo 11835, Egypt E-mail: m_elzyat@aucegypt.edu.
authors.forename: Mohamed
authors.initials: M
authors.lastname: El Zayat
authors.affiliation: Egypt Solid Waste Management Center of Excellence, Ain Shams University, 1 El-Sarayat St., Abassia, Cairo 11517, Egypt.
authors.forename: Sherien
authors.initials: S
authors.lastname: Elagroudy
authors.affiliation: Department of Mechanical Engineering, American University in Cairo, P.O. Box 74, New Cairo 11835, Egypt.
authors.forename: Salah
authors.initials: S
authors.lastname: El Haggar
mesh_terms: D000327:Adsorption; D002412:Cations; D003252:Construction Materials / Q000032:analysis*; D004391:Dust / Q000032:analysis*; D007220:Industrial Waste / Q000032:analysis*; D007474:Ion Exchange; D019216:Metals, Heavy / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014874:Water Pollutants, Chemical
chemical_list: D002412:Cations; D004391:Dust; D007220:Industrial Waste; D019216:Metals, Heavy; D014874:Water Pollutants, Chemical