Modeling competitive adsorption of molybdate, sulfate, selenate, and selenite using a Freundlich-type multi-component isotherm.
This study examined the interactions of MoO4(2-) + SO4(2-), MoO4(2-) + SeO4(2-), and MoO4(2-) + SeO3(2-) systems on gamma-Al2O3 to better understand the competitive adsorption of these anions in the natural environment. The Freundlich isotherms of anionic adsorption onto gamma-Al2O3 in single and binary solutes were also investigated to estimate the competition between these anions. Experimental results indicate that a higher concentration of competitive solute yields a higher efficiency of the competitive solute's prevention of MoO4(2-) adsorption. The most significant result was found in the MoO4(2-) + SeO3(2-) system. The Freundlich isotherm constant (n) increases with the competitive solute concentration. The suitability of a Freundlich-type isotherm, the Sheindorf-Rebuhn-Sheintuch (SRS) equation, and the modified SRS equation in representing the competitive adsorption of MoO4(2-), SO4(2-), SeO4(2-), and SeO3(2-) on gamma-Al2O3 surface, was also examined. Each set of isotherm data was found to conform to linear SRS expressions, allowing competition coefficients to be derived on a concentration basis for each binary-solute system. The competition coefficient aij and relative affinity coefficients alphaij can be seen as a way to quantify competitive interactions. The proposed SRS and modified SRS equations are simple mathematical expressions accounting for competitive interactions of anions present in a mixture for the range of concentrations over which each individual component exhibits Freundlich behavior.
Wu
Chung-Hsin
CH
Department of Environmental Engineering and Health, Yuanpei Institute of Science and Health, Hsinchu City, Taiwan, ROC. chwu@pc.ymit.edu.tw
Kuo
Chao-Yin
CY
Lo
Shang-Lien
SL
Lin
Cheng-Fang
CF
D000327:Adsorption; D003102:Colloids / Q000737:chemistry; D008956:Models, Chemical; D008982:Molybdenum / Q000737:chemistry*; D064586:Selenic Acid; D018036:Selenium Compounds / Q000737:chemistry*; D018038:Sodium Selenite / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D013696:Temperature
D003102:Colloids; D018036:Selenium Compounds; D013431:Sulfates; C044659:molybdate; D008982:Molybdenum; D018038:Sodium Selenite; D064586:Selenic Acid