SYNTHESIS, SORPTION AND KINETIC CHARACTERISTICS OF SILICA-HEXACYANOFERRATE COMPOSITES

Selective Environmental Remediation of Strontium and Cesium Using Sulfonated Hyper-Cross-Linked Polymers (SHCPs)

Sulfonated hyper-cross-linked polymers based on 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP) were synthesized via metal-free (SHCP-1) and conventional Lewis acid-catalyzed (SHCP-2) Friedel-Crafts alkylation routes. The sulfonated polymers possessed BET surface areas in excess of 500 m²·g^-1. SHCP-1 was investigated for its ability to extract Sr and Cs ions from aqueous solutions via the ion-exchange reaction of the sulfonic acid moiety. Equilibrium uptake data could be accurately modeled by the Dubinin-Radushkevich isotherm, with maximum calculated loading values of 95.6 ± 2.8 mg·g^-1 (Sr) and 273 ± 37 mg·g^-1 (Cs). Uptake of both target ions was rapid, with pseudo second-order rate constants calculated as 7.71 ± 1.1 (×10^-2) for Sr and 0.113 ± 0.014 for Cs. Furthermore, the polymer was found to be highly selective toward the target ions over large excesses of naturally occurring competing metal ions Na, K, Mg, and Ca. We conclude that hyper-cross-linked polymers may offer intrinsic advantages over other adsorbents for the remediation of aqueous Sr and Cs contamination.

Pyrochlore Ta-doped antimony oxide as a novel adsorbent for efficient strontium removal

Incorporation of Ta⁵⁺ into the antimony oxide led to an expansion of the pyrochlore structure, and increases in the surface hydroxyl group content of the sorbent, consequently improving the Sr²⁺ adsorption capacity considerably.

Adsorption of cesium from aqueous solution using agricultural residue--walnut shell: equilibrium, kinetic and thermodynamic modeling studies

A novel biosorbent derived from agricultural residue - walnut shell (WS) is reported to remove cesium from aqueous solution. Nickel hexacyanoferrate (NiHCF) was incorporated into this biosorbent, serving as a high selectivity trap agent for cesium. Field emission scanning electron microscope (FE-SEM) and thermogravimetric and differential thermal analysis (TG-DTA) were utilized for the evaluation of the developed biosorbent. Determination of kinetic parameters for adsorption was carried out using pseudo first-order, pseudo second-order kinetic models and intra-particle diffusion models. Adsorption equilibrium was examined using Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. A satisfactory correlation coefficient and relatively low chi-square analysis parameter χ(2) between the experimental and predicted values of the Freundlich isotherm demonstrate that cesium adsorption by NiHCF-WS is a multilayer chemical adsorption. Thermodynamic studies were conducted under different reaction temperatures and results indicate that cesium adsorption by NiHCF-WS is an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

Preparation and characterization of La(III) encapsulated silica gel/chitosan composite and its metal uptake studies

Lanthanum loaded silica gel/chitosan composite (LaSiCS) was prepared by mixing silica gel, LaCl(3) · 7H(2)O and chitosan which was then cross-linked with glutaraldhyde. The LaSiCS composite was characterized using FT-IR, SEM-EDAX, XRD and BET. The adsorption of chromium(VI) ions onto LaSiCS composite has been investigated. The LaSiCS composite was found to have excellent chromium adsorption capacity than the silica gel/chitosan composite (SiCS), silica gel (Si) and chitosan (CS). The sorption experiments were carried out in batch mode to optimize various parameters viz., contact time, pH, initial chromium ion concentration, co-ions and temperature that influence the sorption. Langmuir and Freundlich adsorption models were applied to describe isotherm constants. Equilibrium data agreed very well with the Langmuir model. Thermodynamic studies revealed that the nature of chromium sorption was spontaneous and endothermic. The LaSiCS composite removes chromium by electrostatic adsorption coupled reduction/ion-exchange.