Selective lanthanum recovery in the presence of sodium ions by N-(trimethoxysilypropyl)ethylenediamine triacetic acid (TMS-EDTriA)-modified silica

This study presents a novel approach investigating the silica particle modification using N-(trimethoxysilypropyl)ethylenediamine triacetic acid to enhance the recovery of lanthanum in three mixtures; 20 ppm La³⁺, 20 ppm La³⁺ with 20 ppm Na⁺, and 20 ppm La³⁺ with 100 ppm Na⁺. The influence of pH during modification was also tested. Characterization via Fourier Transform Infrared, Energy-dispersive X-ray Spectroscopy, and Thermogravimetric Analysis confirms the successful coating of propylene-(ethylenediamine)triacetic acid molecules on the silica surface, with modification under the basic conditions exhibiting the more accessible and stable coating. As a result, the La³⁺ adsorption capacity of the modification under the basic conditions has been increased, making it suitable for effective recovery. Particles modified with a few drops of acid (0.075 mL L⁻¹) recovered 95.27 % of La³⁺ in 20 ppm La³⁺ solution, while the unmodified particles recovered 82.62 %. The particles modified with 1.5 mL L⁻¹ of acid recovered only 11.18 %. In the mixed solutions, the performance of the basic-modified particles showed a selectivity of more than 98 %. The particles modified with 9 mL L⁻¹ of acid did not exhibit detectable La³⁺ recovery in all types of solutions. Kinetic experiments show that modified particles with a few drops of acid (0.075 mL L⁻¹) reach equilibrium for La sorption in less than 2 h, compared to 20 h for unmodified silica.