Highly efficient uranium (VI) capture from aqueous solution by means of a hydroxyapatite-biochar nanocomposite: Adsorption behavior and mechanism

Waqas Ahmed; Avelino Núñez-Delgado; Sajid Mehmood; Sehrish Ali; Muhammad Qaswar; Awais Shakoor; Di-Yun Chen

doi:10.1016/j.envres.2021.111518

Highly efficient uranium (VI) capture from aqueous solution by means of a hydroxyapatite-biochar nanocomposite: Adsorption behavior and mechanism

Environ Res. 2021 Oct:201:111518. doi: 10.1016/j.envres.2021.111518. Epub 2021 Jun 12.

Authors

Waqas Ahmed¹, Avelino Núñez-Delgado², Sajid Mehmood³, Sehrish Ali⁴, Muhammad Qaswar⁵, Awais Shakoor⁶, Di-Yun Chen⁷

Affiliations

¹ Guangdong Provincial Key Laboratory for Radionuclides Pollution Control and Resources, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, 510006, China; School of Civil Engineering, Guangzhou University, Guangzhou, 510006, PR China.
² Department of Soil Science and Agricultural Chemistry, Engineering Polytechnic School, Universidade de Santiago de Compostela, 27002, Lugo, Spain.
³ College of Ecology and Environment, Hainan University, Haikou City, 570100, PR China.
⁴ National Engineering Laboratory for Improving Quality of Arable Land, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
⁵ Key Laboratory of Industrial Ecology and Environmental Engineering, School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024, China.
⁶ Department of Environment and Soil Sciences, University of Lleida, 25198, Lleida, Spain.
⁷ Guangdong Provincial Key Laboratory for Radionuclides Pollution Control and Resources, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, 510006, China; School of Civil Engineering, Guangzhou University, Guangzhou, 510006, PR China. Electronic address: cdy@gzhu.edu.cn.

PMID: 34129867
DOI: 10.1016/j.envres.2021.111518

Abstract

The exploration and rational design of easily separable and highly efficient sorbents with the sufficient capability of retaining radioactive and toxic uranium U(VI) is paramount. In this study, a hydroxyapatite (HAP) biochar nanocomposite (BR/HAP) was successfully fabricated from rice straw biochar (BR), to be used as a new and efficient adsorbent for removing U(VI) from aqueous solution. Both BR and the BR/HAP composite were characterized via Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photo electron spectroscopy (XPS) techniques. Batch test results showed that BR/HAP exhibited remarkably higher adsorption capacity than the raw BR. A pseudo-second order kinetic model thoroughly explained the adsorption kinetics, providing the maximum U(VI) adsorption capacities (q_e) of 110.56 mg g^-1 (R² = 0.98) and 428.25 mg g^-1 (R² = 0.99), for BR and BR/HAP, respectively, which was indicative of the rate-limited sorption via diffusion or surface complexation after rapid initial adsorption steps. The Langmuir isotherm model fitted the experimental data to accurately simulate the adsorption of U(VI) onto BR and BR/HAP (R² = 0.97 and R² = 0.99). The thermodynamic results showed negative values for ΔG°, clearly indicating that the reaction was spontaneous, as well as positive values for ΔH° (11.04 kJ mol^-1 and 28.86 kJ mol^-1, respectively) and ΔS° (88.97 kJ mol^-1 K^-1, and 183.42 kJ mol^-1 K^-1), making clear the endothermic nature of U(VI) adsorption onto both sorbents, with an increase in randomness at a molecular level. FTIR spectroscopy and XPS spectrum further confirmed that the primary mechanisms were ion exchange with UO₂²⁺ and surface complexion by -OH and -COOH. In addition, BR/HAP showed an excellent reusability, making it a promising candidate as a new sorbent for U(VI) removal from wastewater. In view of that, it would be interesting to perform future research to explore practical implications of this sorbent material regarding protection from environmental and public health issues related to that pollutant.

Keywords: Adsorption; Biochar; Hydroxyapatite; Nanocomposite; Uranium; Wastewater treatment.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adsorption
Charcoal
Durapatite
Nanocomposites*
Uranium* / analysis

Substances

biochar
Charcoal
Uranium
Durapatite