Kinetics of Selenite Adsorption on Hydroxyaluminum‐ and Hydroxyaluminosilicate‐Montmorillonite Complexes

Abstract

A lack of understanding about the selenite adsorption behavior on hydroxyaluminum (HyA)‐ and hydroxyaluminosilicate (HAS)‐interlayered phyllosilicates led us to conduct the present study. The kinetics of selenite adsorption on montmorillonite (Mt), HyA(OH/Al = 2.0)‐Mt, HAS1(OH/Al = 2.0; Si/Al = 0.24)‐Mt, and HAS2(OH/Al = 2.0; Si/Al = 0.48)‐Mt were studied at pH 4.5, with an initial selenite concentration of 0.025 mM, a clay concentration of 0.5 g L−1, temperatures of 288, 298, 308, and 318 K, and background electrolyte concentration of 10−2 M NaNO3 Of the six different kinetic models tested, the second‐order rate equation best described the kinetic data obtained for the initial fast reaction (5–30 min) followed by a slow reaction (30–180 min) in the adsorption systems. Elevated temperatures brought about a substantial increase in the rate constants. Compared with Mt, different HyA/HAS‐Mts had 2 to 21 times higher rate constants for the fast reaction and up to five times higher rate constants for the slow reaction. Silication of HyA‐Mt to form HAS1‐Mt and HAS2‐Mt substantially lowered the rate constants for both the fast and slow reactions. For the fast reaction, Mt had the highest activation energy and HyA‐Mt had the lowest activation energy (around four times lower than Mt); silication increased the activation energy of selenite adsorption on the HAS‐Mts. The pre‐exponential factor, an index of the frequency of selenite collision with the clay surface, was remarkably lower for the HyA/HAS‐Mts in comparison with Mt. The data obtained in the present study are of fundamental significance in understanding the role of Al interlayering and coating and silication of Al polymers on expansible phyllosilicates in influencing the dynamics of Se in soil and related environments.

Effect of humic acid coating on arsenic adsorption on ferrihydrite-kaolinite mixed systems

“…This multi-phasic behaviour of arsenate adsorption has been observed in several studies on pure Al and Fe oxides Raven et al 1998;O'Reilly et al 2001;Arai and Sparks 2002) and soils (Livesey and Huang 1981;Zhang and Selim 2005). The multi-step rate processes have also been reported for the adsorption kinetics of different anions such as phosphate and selenite (Liu and Huang 2000;Saha et al 2004) and cations, such as Pb and Cd (Liu and Huang 2003;Yu et al 2006) and is generally attributed to the heterogeneity at the adsorption sites with different binding strength and different accessibility to the interior pores.…”

“…5. Similarly, phosphate adsorption on Fe oxides and selenite adsorption on hydroxy-Al-montmorillonite complexes were found to be properly described by the second-order rate equation (Liu and Huang 2000;Saha et al 2004).…”

“…Nevertheless, the parameters of the chosen model can provide some meaningful tools to compare the rates of the adsorption processes on different adsorbents (Liu and Huang 2000;Saha et al 2004) at least under the same experimental conditions. Comparing the fittings of the zero-, first-and secondorder rate equations to the kinetic data, the secondorder rate equation was found to better describe the adsorption data for both the 0.083Á1 h and the 1Á24 h steps of the adsorption kinetics at 288 and 318 K [Zeroorder: 0.907 Br 2 B0.668; 3.2 )10 (2 BP B1.2 )10 (3 ; 1.1 )10 (6 BSE B3.9 )10 (7 ; first-order: 0.923 Br 2 B 0.691; 2.4 )10 (2 BP B3.7 )10 (4 ; 1.2 )10 (6 BSE B 3.4 )10 (7 ; second-order: 0.963 Br 2 B0.711; 1.7 ) 10 (2 BP B8.9 )10 (5 ; 1.4 )10 (6 BSE B3.2 )10 (7 ].…”

Selenium fractions in selenate-fertilized field soils of Finland

“…The sorption of selenite onto mineral and oxide surfaces has been very extensively studied (e.g. Hingston et al 1974;Rājan and Watkinson 1976;Parfitt 1978;Rajan 1979;Balistrieri and Chao 1987;Saha et al 2004) and thought to explain the poor bioavailability of Se in soil. Overall, studies on the behaviour of Se in soil have emphasized the inorganic chemistry of Se.…”

Reduction of Nitrate and Ammonium Adsorption Using Microscale Iron Particles and Zeolitite

“…A change in the rate constant is not unusual in the case of surface reactions, such as the reactions of specific adsorption or desorption of anions and cations on/from the surfaces of iron or aluminum oxides (Liu and Huang, 2003), (Saha et al, 2004(Saha et al, , 2005, (Yu et al, 2006) and (Martin et al, 2009). …”