Preparation of chitosan mesoporous membrane/halloysite composite for efficiently selective adsorption of Al(III) from rare earth ions solution through constructing pore structure on substrate

Preparation of Zeolite A from Ion-Adsorbing Rare Earth Tailings for Selective Adsorption of Pb2+: An Innovative Approach to Waste Valorization

Ion-adsorbing rare earth tailings (IRETs) contain a large amount of clay minerals, which are a potential source of silicon and aluminum for the preparation of zeolite materials. The complexity of the tailings' composition and the impurity composition are the main difficulties in the controllable preparation of zeolite. Herein, IRETs were treated by classification activation technology for the preparation of IRET-ZEO, which was used for the removal of heavy metal Pb2+ in water. A new method of resource utilization of ion-type rare earth tailings is realized by "treating waste with waste". The results showed that the IRETs were classified and then thermally activated, and the optimal activation parameter was calcination at 850 °C for 1 h. The optimal NaOH concentration used in the crystallization process was 5 mol/L, with a crystallization time of 3 h and a crystallization temperature of 85 °C, and the crystallization product was zeolite A. The removal rate of the Pb2+ solution with an initial concentration of 100 mg/L was as high as 96.7% in an acidic solution with a pH value from 2 to 5.5. In particular, when the solution pH was higher than 4.2, the adsorption rate of Pb2+ was close to 100%. The IRET-ZEO showed a fast adsorption rate (5 min to reach adsorption equilibrium), a large adsorption capacity (378.35 mg/g), excellent acid resistance, and selectivity and regenerability for Pb2+. This work provides a new strategy for the green resource utilization of IRETs and the treatment of lead-containing wastewater.

Biochar/Delonix regia seed gum/chitosan composite as efficient adsorbent for the elimination of phenol from aqueous medium

In this study, biochar (BC) from Delonix regia pods peel and gum from Delonix regia seed (SG) were prepared, and also biochar/chitosan composite (BCS) and biochar/Delonix regia seed gum/chitosan composite (BCGS) were fabricated for the efficient adsorption of phenol. Various characterization tools such as SEM, TEM, ATR-FTIR, TGA, zeta potential, and textural investigation were studied to examine the features of the synthetized adsorbents, confirming their positive construction. It was fully studied how necessary factors, comprising pH, dose of adsorbent, contact shaking time, initial phenol concentration, and temperature influenced adsorption behavior. An obvious rise of the adsorption capacity from 60.16 to 165.20 mg/g was achieved by the modification of biochar with Delonix regia seed gum and chitosan under ideal circumstances of 2 h contact duration, pH 7, 15 °C, and a dose of 2.0 g/L. The phenol adsorption was well applied by Langmuir, Temkin, Dubinin-Radushkevich, and Sips isotherms, in addition to nonlinear pseudo-second-order kinetic model. Furthermore, the physisorption, endothermic, and spontaneous process was illustrated by thermodynamic investigation. Additionally, the fabricated adsorbents could be effectively used and regenerated without main losses of only 7.5, 4.6, and 4.0 % for BC, BCS, and BCGS, respectively in the removal percentage after seven cycles of application.

Ion-imprinted chitosan prepared without cross-linking agent for efficient selective adsorption of Al(III) from rare earth solution

In the aqueous phase, ion-imprinted materials exhibit excellent selective adsorption properties for specific ions, but their complicated preparation process and large amount of crosslinker consumption limit their application. In this study, ion-imprinted chitosan (IIP-CS) was prepared by a simple one-step hydrothermal method without a cross-linking agent for the efficient adsorption of trace amounts of Al(III) from a rare earth solution. The structures and morphology of IIP-CS were analyzed by FT-IR, SEM, and XRD. The Al(III) adsorption characteristics of IIP-CS were investigated under various preparation processes and adsorption conditions. It was found that the optimum mass ratio of IIP-CS is 3 : 1 and pH is 3 and the adsorption capacity reaches up to 40.36 mg g-1. In addition, three different isothermal models-Temkin, Freundlich, and Langmuir-were used to analyze the equilibrium adsorption of IIP-CS in aqueous solution. The results obtained are consistent with the Langmuir model. The adsorption process of Al(III) on IIP-CS follows a pseudo-secondary kinetic model, suggesting that electron sharing or exchange between IIP-CS and Al(III) is a key factor affecting its adsorption rate. IIP-CS shows high selectivity coefficients for Al(III) in mixtures of La(III), Y(III), and Gd(III), which are 792.50, 163.26, and 55.16, respectively. The mechanism of action is the formation of a complex via amidation between Al(III) and IIP-CS. IIP-CS is an adsorbent with excellent regeneration and selective adsorption performance in aqueous solution.