Evaluation of the multiple-ion competition in the adsorption of As(V) onto reclaimed iron-oxide coated sands by fractional factorial design.
This study describes the competitive effects of selected ions and natural organic matter on As(V) removal using reclaimed iron-oxide coated sands (RIOCS) in the single- and multi-ion systems. A 2(7-3) factional factorial experimental design (FFD) was employed for screening main competitive factors in this adsorption process. As a result, the inhibitive competition effects of the anions on As(V) removal in the single ion system were in the following sequence: PO(4)(3-)>SiO(3)(2-)>HCO(3)(-)>humic acid (HA)>SO(4)(2-)>Cl(-), whereas the cation Ca(2+) was observed to enhance the As(V) removal. In addition, the optimum initial pH for As(V) removal in single-ion system was 5. Based on the estimates of major effects and interactions from the FFD, PO(4)(3-), SiO(3)(2-), Ca(2+) and HA were important factors on As(V) removal in the multi-ion system. The promoters for the As(V) removal were found to be Ca(2+) and, to a lesser extent, SO(4)(2-). The competitive effects of these ions on As(V) removal were in the order of PO(4)(3-), SiO(3)(2-), HA, HCO(3)(-), and Cl(-). In the single ion system, the efficiencies of As(V) removal range from 75% to 96%, much higher than those in the multi-ion system (44%) at the initial pH 5. Clearly, there were some complex anion interactions in the multi-ion system. To promote the removal of As(V) by RIOCS, it is proposed to lower the pH in the single-ion system, while in the multi-ion system, the increase of the Ca(2+) concentration, or decreases of PO(4)(3-), SiO(3)(2-) and HA concentrations is suggested.
Hsu
Jia-Chin
JC
Institute of Engineering Science and Technology, Department of Safety Health and Environmental Engineering, Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan.
Lin
Chien-Jung
CJ
Liao
Chih-Hsiang
CH
Chen
Shyi-Tien
ST
D000042:Absorption; D001151:Arsenic / Q000737:chemistry* / Q000302:isolation & purification*; D001639:Bicarbonates / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D006812:Humic Substances; D010710:Phosphates / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000302:isolation & purification*
D001639:Bicarbonates; D002712:Chlorides; D005290:Ferric Compounds; D006812:Humic Substances; D010710:Phosphates; D017640:Silicates; D013431:Sulfates; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D012822:Silicon Dioxide; D001151:Arsenic; D002118:Calcium