Amino-Functionalized Urea-Formaldehyde Framework Mesoporous Silica for U(VI) Adsorption in Wastewater Treatment

A mesoporous silica prototype (MSP) was produced by attaching SiO2 colloid to urea formaldehyde resin. Treatment of the MSP using different grafting methods yielded three different amino-functionalized mesoporous silica samples. The materials were characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, C-13 nuclear magnetic resonance, zeta potential measurements, and isothermal N-2 sorption/desorption. For a 1:2000 solid-to-liquid ratio, all adsorbents could almost completely remove uranyl from sulfate and carbonate solutions of 3.6 mg L-1 U(VI) at pH 3.5 to 5.5 and pH 6.5 to 9.5, respectively. The adsorption equilibrium time was less than 30 min. The adsorption equilibrium curve showed that the maximum sorption capacity was 117 mg L-1 at pH 4.0. Through the experimental adsorption, it was found that the most effective sample could reduce the U(VI) concentration from 3.6 mg L-1 to 0.79 mu g L-1 with 99.98% removed. In desorption experiments, 0.1 mol L-1 nitric acid could desorb U(VI) almost completely from the adsorbent. However, this kind of adsorbent is unsuitable for use in high acid or alkaline environments.