Abstract
To investigate the influence of residence time on molybdenum [Mo(VI)] adsorption behavior in soil environments, kinetic batch experiments coupled with X-ray near-edge structure (XANES) spectroscopy were performed for a neutral-pH soil (Webster loam) and two acidic soils (Mahan sand and Windsor sand) at different time scales (1 day–1 year). Batch-type experiments indicated that retention of Mo(VI) was rate limited and typical biphasic for soils. Initial rapid retention was followed by a continued slow retention with increasing aging time for Mahan and Windsor soils. In contrast, the reaction for Webster soil was nearly complete after 8 h, reflecting difference in soil properties. XANES analysis for Webster soil confirmed that most of Mo was bound to montmorillonite during long-term reaction time, whereas kaolinite constitutes a very important host phase for Mahan and Windsor soils. Sequential extraction results indicated that the percentages of Fe/Al oxide and residual fractions increased at the advanced time periods for Mahan and Windsor soils. The goodness-of-fit of numerical modeling results indicated that a simple version of multi-reaction model (MRM) with equilibrium and kinetic sorption sites was capable of describing Mo(VI) retention data for Webster loam. However, for Windsor and Mahan soils, an additional irreversible sorption site was required to simulate Mo(VI) retention over time. Although each site from MRM model cannot be unequivocally clarified from each other by either XANES analysis or sequential extraction results, their finding provided evidence of surface irreversible reactions at long residence times.
Highlights
Molybdenum (Mo) is in the second row of the transition metal elements with atomic number 42 and atomic weight of 95.94 g/mol
Sequential extraction results indicated that the percentages of Fe/Al oxide and residual fractions increased at the advanced time periods for Mahan and Windsor soils
The reactivity of Mo in soil environments is strongly dependent on binding affinity between Mo solution and soil reactive surfaces, such as clay minerals, soil organic matter (SOM), and metal oxides [2,3,4,5,6,7,8]
Summary
Molybdenum (Mo) is in the second row of the transition metal elements with atomic number 42 and atomic weight of 95.94 g/mol. Mo sorption mechanisms for long-term retention time (up to 1 year) has not been investigated by using XANES analysis. WHAM 7 coupling with XAS analysis was successfully utilized to simulate kinetics of Zn release from soils [15] Such kinetic geochemical models were less successful over long-term reaction time since they failed to account for slow metal adsorption processes. Mo(VI) on soils having different properties; (ii) to evaluate the capability of MRM model to simulate the long-term Mo(VI) sorption process on soils; (iii) to investigate the influence of residence time (1 day to 1 year) on Mo(VI) sorption mechanism using XANES analysis and sequential extractions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
