Highly efficient U(VI) removal by chemically modified hydrochar and pyrochar derived from animal manure.

In recent decades, great attention has been given to developing methods for targeted modification of biochar with innovative properties to improve its remediation efficacy. This study investigated the sorption performance of animal manure-derived hydrochar and pyrochar modified with oxidizing agents (H 2 O 2) and alkaline (NaOH) solutions for U(VI). Characterization results showed that H 2 O 2 and NaOH modification provided more carboxyl and hydroxyl groups, respectively, on sample surface. NaOH treatment remarkably increased specific surface area by three to six times. H 2 O 2 and NaOH impressively improved the maximum adsorption capacity (Q max) of biochar for U(VI), and NaOH modification induced a higher enhancement. Among different biochar types, pyrochar produced at a medium-high temperature not only showed the highest Q max but also the strongest improvement. After NaOH modification, its Q max (221.4 mg/g) was roughly 5-fold higher than that of original sample, showing that with NaOH modification, the pyrochar produced from animal manure under a medium-high thermal temperature might be a promising candidate as a sorbent for U(VI) remediation. In addition, the obvious shift in the XPS spectrum and pore structure of sample after U(VI) loading, along with the semi-quantification of the contribution of surface complexation mechanism, demonstrated that additional carboxyl and hydroxyl groups and higher SSA jointly explained more efficient U(VI) adsorption. This study not only proposes a promising adsorbent for U(VI) in nuclear wastewater, but also provides a way for the efficient recycling of animal manure wastes. Image 1 • Animal manure-derived hydrochar and pyrochar were modified by H 2 O 2 and NaOH. • NaOH modification impressively increased the CO 2 -SSA by 3–4 times. • Each modification improved the Q max for U(VI), and NaOH caused a higher enhancement. • 450 °C pyrochar not only showed the highest Q max but also the strongest improvement. • More surface COOH/C–OH and higher SSA of modified biochar caused the higher Q max. [ABSTRACT FROM AUTHOR]