Effect of pH, ionic strength, foreign ions and humic substances on Th(IV) sorption to GMZ bentonite studied by batch experiments

Ultra-effective modified clinoptilolite adsorbent for selective thorium removal from radioactive residue

This study investigated the efficacy of using phosphate-modified zeolite (PZ) as an adsorbent for removing thorium from aqueous solutions. The effects of various factors such as contact time, adsorbent mass, initial thorium concentration, and pH value of the solution on the removal efficiency were analyzed using the batch technique to obtain optimum adsorption condition. The results revealed that the optimal conditions for thorium adsorption were a contact time of 24 h, 0.03 g of PZ adsorbent, pH 3, and a temperature of 25 °C. Isotherm and kinetics parameters of the thorium adsorption on PZ were also determined, with equilibrium studies showing that the experimental data followed the Langmuir isotherm model. The maximum adsorption capacity (Q_o) for thorium was found to be 17.3 mg/g with the Langmuir isotherm coefficient of 0.09 L/mg. Using phosphate anions to modify natural zeolite increased its adsorption capacity. Furthermore, adsorption kinetics studies demonstrated that the adsorption of thorium onto PZ adsorbent fitted well with the pseudo-second-order model. The applicability of the PZ adsorbent in removing thorium from real radioactive waste was also investigated, and nearly complete thorium removal was achieved (> 99%) from the leached solution obtained from cracking and leaching processes of rare earth industrial residue under optimized conditions. This study elucidates the potential of PZ adsorbent for efficient removal of thorium from rare earth residue via adsorption, leading to a reduction in waste volume for ultimate disposition.

Surface complexation modeling of U(VI) sorption on GMZ bentonite in the presence of fulvic acid

In this work, experiments and modeling for the interactions between uranyl ion and GMZ bentonite in the presence of fulvic acid are presented. The results demonstrated that FA is strongly bound to GMZ bentonite, and these molecules have a very large effect on the U(VI) sorption. The results also demonstrated that U(VI) sorption to GMZ bentonite in the presence and absence of sorbed FA can be well predicted by combining SHM and DLM. According to the model calculations, the nature of the interactions between FA with U(VI) at GMZ bentonite surface is mainly surface complex. The first attempt to simulate clay interaction with humus by the SHM model.

Adsorption and desorption of uranium (VI) in aerated zone soil

In this paper, the adsorption and desorption behavior of uranium (VI) in aerated zone soil (from Southwest China) was systematically investigated using a static experimental method in order to provide useful information for safety assessment of the disposal of (ultra-)low uraniferous radioactive waste, as well as a potential remediation method for uranium-contaminated soils. The adsorption behavior of uranium (VI) was firstly studied by batch experiments as functions of contact time, pH, liquid/solid ratio, temperature, colloids, minerals and coexistent ions. The results indicated that the adsorption of uranium (VI) by natural soil was efficient at an initial concentration of 10 mg/L uranium (VI) nitrate solution with 100 mg natural soil at room temperature when pH is about 7.0. The adsorption was strongly influenced by the solution pH, contact time, initial concentration and colloids. The adsorption equilibrium for uranium (VI) in soil was obtained within 24 h and the process could be described by the Langmuir adsorption equation. For uranium (VI) desorption, EDTA, citric acid and HNO(3) were evaluated under different conditions of temperature, concentration and proportion of liquid to solid. The adsorbed uranium (VI) on natural soil could be easily extracted by all these agents, especially by HNO(3), implying that the uranium-contaminated soils can be remedied by these reagents.