Ion Exchange Capacity of Synthetic Zeolite L: A Promising Way for Cerium Recovery

Abstract Due to the increasing demand for Rare Earth Elements (REE) and the current political scenario, it is essential to recover these elements from industrial or mining waste. Zeolites are microporous materials little investigated for REEs recycle. Here, we propose the use of NH4+-exchanged synthetic zeolite L for cerium recovery from a solution mimicking the Ce3+ concentration of the liquors deriving from the recovery of spent catalysts (0.002 M). A NH4+-exchanged sample was used since the presence of only ammonium as exchangeable cation in the zeolite porosities greatly simplifies the Ce recovery once the exchange is accomplished. The aim of this work is twofold, in fact we want to investigate the exploitability of zeolite L as cation exchanger in the Ce recovery and determine the best working conditions. The investigated process consists of a coupled cation exchange: 1) Ce3+(solution)+3NH4++(zeolite) ↔ Ce3+(zeolite)+3NH4++(solution). In the first exchange the NH4+ cations - present in the zeolite porosities- are exchanged with the Ce3+ of the solution and in the second experiment the Ce3+ trapped into the zeolite is recovered through a further exchange with the NH4+ of a rich solution. The best working conditions for Ce3+ exchange of NH4-L are: batch system, liquid/solid ratio equal to 90 mL/g and 180 mL/g, 24 h of contact at 25 °C. The resulting cerium adsorption capacity (qt) is equal to ~25 mg/g and ~39 mg/g and the removal efficiency 100 % and 77 % for the two tested liquid/solid ratios, respectively. The kinetics was proved to be fast and consistent with industrial timing, no energy cost for temperature setting is required and the acid pH (~4) of the solutions does not affect the zeolite structure stability and its exchange performance. At these conditions, cerium of the solution was first incorporated into the zeolite porosities and then completely recovered. It has been demonstrated that the zeolite framework is not affected by the exchange so that the same absorbent can be employed many times.