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• An efficient and economic HDPy-bent material was synthesized and applied for removing 99Tc from contaminated water. 99Tc is one of the critical fission products in the treatment of wastewater and the nuclear waste repository due to its long half-life (t 1/2 = 2.13 × 105 y), high fission yield (~6%), and high mobility in the environment. The development of highly-efficient, low-cost and easily available materials that can rapidly and selectively remove 99Tc is of great significance, but remains a challenge. In this work, bentonite-based materials (HDPy-bent) were obtained through modifying bentonite with hexadecylpyridinium (HDPy) and applied for the remove of TcO 4 − as well as its surrogate ReO 4 −. The structure of HDPy-bent (e.g., the values of d 001) was evaluated and the maximum loading amount of HDPy on bentonite was found to be 200% CEC. The loaded HDPy+ might replace exchangeable cations in the inter-layer space of bentonite. Batch experiment results show that HDPy-bent could quantitatively remove TcO 4 − from aqueous solution within 3 min. The distribution coefficient (K d) of TcO 4 − in this material is up to 2.1 × 105 mL/g, which is significantly higher than most of the previously tested inorganic adsorbent materials. More importantly, HDPy-bent can selectively remove TcO 4 − in the presence of large excess (80,000 times) of competitive anions (NO 3 –, SO 4 2−, CO 3 2−, PO 4 3− and Cl−). This work demonstrates that the HDPy-bentonite is a low cost, and effective adsorbent for removing 99Tc from contaminated water. [ABSTRACT FROM AUTHOR]