Kinetic study of time-dependent fixation of UVI on biochar

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 timedependent fixation on biochar at 20 o 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 233 U VI confirmed the low, or time-dependent, lability of adsorbed 238 U 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.

Lead and uranium sorptive removal from aqueous solution using magnetic and nonmagnetic fast pyrolysis rice husk biochars

“…(2) Inner surface complexes were formed by interaction of U( vi ) and biochar, with complex surface coordination and precipitation being the main mechanisms governing the adsorption of U( vi ) over BC and MBC. Thus, the dissolution PO 4 3− and UO 2 2+ contributed to form coordination and oversaturate conditions; 40 (3) the ionic strength of NO 3 − and PO 4 3− influenced the activity coefficient of Pb( ii ) to a higher extent as compared to U( vi ), thereby limiting the transfer of Pb( ii ) on the biochar surface. The optimum anion strengths of NO 3 − and PO 4 3− were 0.01 mol L −1 for Pb( ii ) and 0.04 mol L −1 for U( vi ), respectively.…”

“…Additionally, the adsorption rate of Pb( ii ) on BC was higher than that on MBC, thereby revealing that Pb( ii ) was physically adsorbed on the biochar, while U( vi ) was preferably adsorbed via chemisorption processes on MBC owing to the higher number of functional groups of this material. 40 …”

“…Additionally, the adsorption rate of Pb(II) on BC was higher than that on MBC, thereby revealing that Pb(II) was physically adsorbed on the biochar, while U(VI) was preferably adsorbed via chemisorption processes on MBC owing to the higher number of functional groups of this material. 40 Adsorption isotherms and thermodynamic characteristics Fig. 6 shows the adsorption isotherms and the thermodynamic characteristics of the adsorption of Pb(II) and U(VI) on BC and MBC under three different temperatures (i.e., 298, 313, and 328 K).…”

Mechanisms of the Removal of U(VI) from Aqueous Solution Using Biochar: A Combined Spectroscopic and Modeling Approach

“…Recent studies have reported that biochar exhibits a strong affinity to adsorb U­(VI). − However, these studies only present bulk U­(VI) metal adsorption data, which do not provide molecular-scale insights into the coordination of aqueous uranyl species adsorbed to the biochar surface, − and, therefore, they cannot be used to calculate intrinsic stability constants of U­(VI)–biochar surface complexes. − Since U­(VI) has a complex aqueous speciation, especially in the presence of the common calcium (Ca 2+ ), carbonate (CO 3 2– ), and hydroxyl (OH – ) ions in natural waters, it is critical to consider changes in aqueous speciation when performing adsorption modeling. − …”

Enhancing adsorption of U(VI) onto EDTA modified L. cylindrica using epichlorohydrin and ethylenediamine as a bridge

“…Recovery of uranium from seawater has attracted great interest as a hot research topic recently, because of the heavy demand for uranium used in nuclear reactors1234. In seawater, the total amount of uranium is about 4.5 billion tons, one thousand times more than the amount found in mineral ores on land56.…”