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

Abstract

This paper discusses the sorption characteristics of Pb(II) and U(VI) on magnetic and nonmagnetic rice husk biochars. The porosity, specific surface area, hydrophobility, and reusability of biochar were effectively improved (1–2 times) after magnetic modification. The optimum adsorption conditions were as follows: biochar loading was 0.4 g L⁻¹, pH value was 7.0, and anion strength of NO₃⁻ and PO₄³⁻ were 0.01 mol L⁻¹ for Pb(II) and 0.04 mol L⁻¹ for U(VI) respectively. Compared with U(VI), Pb(II) had the faster adsorption rate and higher adsorption capacity on magnetic biochar (MBC). The adsorption experimental data were well fitted by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of Pb(II) and U(VI) on MBC was 129 and 118 mg g⁻¹ at 328 K respectively, which was significantly higher than that of other sources biochars. Pb(II) was mainly bonded to biochar by physisorption but the adsorption of U(VI) on biochar was mostly chemisorption. Fe oxides in MBC noticeably improved the ion exchange and complexation action between biochar and metal ion especially for U(VI). The experimental results confirmed MBC material can be used as a cost-effective adsorbent for the removal of Pb(II) and U(VI) and can be separated easily from aqueous solution when application.