Hexadecylpyridinium (HDPy) modified bentonite for efficient and selective removal of 99Tc from wastewater

Tc-99 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) = 2.13x10(5) y), high fission yield (similar to 6%), and high mobility in the environment. The development of highly-efficient, low-cost and easily available materials that can rapidly and selectively remove Tc-99 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 TcO4- as well as its surrogate ReO4-. 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 TcO4- from aqueous solution within 3 min. The distribution coefficient (K-d) of TcO4- in this material is up to 2.1x10(5) mL/g, which is significantly higher than most of the previously tested inorganic adsorbent materials. More importantly, HDPy-bent can selectively remove TcO4- in the presence of large excess (80,000 times) of competitive anions (NO3-, SO42-, CO32-, PO43- and Cl-). This work demonstrates that the HDPy-bentonite is a low cost, and effective adsorbent for removing Tc-99 from contaminated water.