Kinetic study of time-dependent fixation of UVI on biochar

A Ashry; E H Bailey; S R N Chenery; S D Young

doi:10.1016/j.jhazmat.2016.08.002

Kinetic study of time-dependent fixation of U^VI on biochar

J Hazard Mater. 2016 Dec 15:320:55-66. doi: 10.1016/j.jhazmat.2016.08.002. Epub 2016 Aug 2.

Authors

A Ashry¹, E H Bailey², S R N Chenery³, S D Young⁴

Affiliations

¹ Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, United Kingdom; Radiation Protection Department, Nuclear Research Centre, Egyptian Atomic Energy Authority, Cairo, Egypt.
² Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, United Kingdom. Electronic address: liz.bailey@nottingham.ac.uk.
³ British Geological Survey, Nicker Hill, Keyworth, Nottingham NG12 5GG, United Kingdom.
⁴ Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, United Kingdom.

PMID: 27513370
DOI: 10.1016/j.jhazmat.2016.08.002

Abstract

Biochar, a by-product from the production of biofuel and syngas by gasification, was tested as a material for adsorption and fixation of U^VI from aqueous solutions. A batch experiment was conducted to study the factors that influence the adsorption and time-dependent fixation on biochar at 20°C, including pH, initial concentration of U^VI and contact time. Uranium (U^VI) adsorption was highly dependent on pH but adsorption on biochar was high over a wide range of pH values, from 4.5 to 9.0, and adsorption strength was time-dependent over several days. The experimental data for pH>7 were most effectively modelled using a Freundlich adsorption isotherm coupled to a reversible first order kinetic equation to describe the time-dependent fixation of U^VI within the biochar structure. Desorption experiments showed that U^VI was only sparingly desorbable from the biochar with time and isotopic dilution with ²³³U^VI confirmed the low, or time-dependent, lability of adsorbed ²³⁸U^VI. Below pH 7 the adsorption isotherm trend suggested precipitation, rather than true adsorption, may occur. However, across all pH values (4.5-9) measured saturation indices suggested precipitation was possible: autunite below pH 6.5 and either swartzite, liebigite or bayleyite above pH 6.5.

Keywords: Adsorption; Biochar; Isotherm; Kinetics; Uranium; pH.