Preparation of new alginate capsules enclosing diatomite and organic extractants to uptake lanthanum

Abstract

The present study conducted syntheses of Ca-alginate composite beads, which involved trioctyl-amine (TOA), tributyl phosphate (TBP), trioctylphosphine oxide (TOPO) organic extractants, and diatomite for separation of La(III) ions from dilute aqueous solutions. The surface morphology of the capsules was examined under Scanning Electron Microscopy, while their chemical structure was characterized using Fourier Transform Infrared Spectroscopy. Alginate composites were prepared by adding concentrations of TBP (1%–10%), TOPO (0.005 M–0.09 M) and TOA (1%–10%) organic extractants to the Na-alginate-diatomite mixture.The effects of various parameters on adsorption such as solution pH, contact time, metal ion concentration, and temperature, were individually tested using standard solutions of La(III). The maximum uptake capacity of the alginate composite adsorbent, consisting of TOA, diatomite, and alginate for La(III) ions, was examined at 25 °C. Adsorption data were analyzed using Langmuir, Freundlich, Dubinin–Radushkevich (D-R), Temkin, Flory-Huggins and Brunauer, and Emmett and Teller (BET) isotherm models. The biosorption isotherm parameters were estimated by both linear and nonlinear regression analyses. The results indicate that the Langmuir model provides a better fit than the other models for the adsorption equilibrium data.Thermodynamic parameters such as variations of enthalpy, entropy, and Gibbs free energy were calculated. The maximum uptake capacity of the alginate composite adsorbent, including TOA, diatomite, and alginate for La(III) ions from aqueous solutions was found to be 146.4 mg/g. The adsorption efficiency in dilute solutions was determined to be 97.2%.