Equilibrium and Kinetics of Silver Uptake by Multinuclear Alginate Microcapsules Comprising an Ion Exchanger Matrix and Cyanex 302 Organophosphinic Acid Extractant

Abstract

Uptake characteristics of alginate microcapsules containing bis(2,4,4-trimethylpentyl)monothiophosphinic acid for adsorption of Ag(I) ions were examined using batch methods. Under a definite initial Ag+ concentration (C b), at equilibrium, all the Ag(I) ions are adsorbed by extractant, while above C b, ion exchange by the alginate matrix becomes the dominating mechanism. The kinetic mechanism varies depending on the presence of coexisting ions (CI). If the concentration of CI is low, the kinetics is controlled by a combination of slow adsorption of Ag(I) ions by Cyanex 302 (HA) microdroplets and shielding of inner microdroplets by the outer reacting ones (physical−chemical shielding mechanism). At higher concentrations of CI, intrapore diffusion controls the kinetics. Different types of the shrinking core model remarkably fitted the kinetics experiments. The microcapsules were able to selectively adsorbed 90% of the Ag(I) ions from a 10 ppm Ag(I) + 3 mol·dm-3 Na+ solution. In addition, the uptake percentage was constantly high in wide range of pH values and Ag+ concentrations.

Functionalization of microcapsules for the removal of heavy metal ions

“…The choice of the shell material for the microencapsulation of extractants, as well as the diluent, plays an important role in improving the structure, permeability of the ions and chemical and mechanical stability of the microcapsules. Several polymers have been employed as shell materials and these include styrene‐divinylbenzene,2, 3, 36 styrene,4, 35 divinylbenzene,5, 29, 37 polyurea,32 polyamide33 and even sodium alginate 12, 34. Styrene‐ethylene glycol dimethacrylate was found to have sufficient hydrophobicity to retain the extractant under investigation here (i.e.…”

“…Polymeric adsorbents and clays impregnated with liquid ligands,6–9 extractants in supported liquid membranes10, 11 and polymeric microcapsules containing extractants5, 12, 13 are three methods and processes for separating and concentrating metal ions to overcome the aforementioned limitations of conventional ion exchangers. However, some disadvantages have been documented and these include the loss of extractant and steric hindrance for solvent‐impregnated resins,3, 12, 14 and slow kinetics and low stability for liquid membranes 15, 16…”

Encapsulation of Cyanex 302 with Alginate for Palladium Recovery

“…This study focuses on the encapsulation of Cyanex 302 (bis(2,2,4‐trimethylpentyl) monothiophosphinic acid) in mononuclear (N) calcium alginate gel beads. The conventional process (matrix‐type encapsulation, M) consists of the mixing of the extractant with alginate solution making an emulsion before dropping the mixture into an ionotropic gelation solution (i.e., CaCl 2 , for example) . Various shapes of microcapsules such as granules, fibers and films have been prepared .…”

“…The conventional process (matrix-type encapsulation, M) consists of the mixing of the extractant with alginate solution making an emulsion before dropping the mixture into an ionotropic gelation solution (i.e., CaCl 2 , for example). [15,[19][20][21][22] Various shapes of microcapsules such as granules, fibers and films have been prepared. [23] Moreover, alginate microcapsules were prepared by coating of fresh alginate microcapsules with chitosan or polyethyleneimine (PEI).…”

Extractant Immobilization in Alginate Capsules (Matrix- and Mononuclear-Type): Application to Pb(II) Sorption from HCl Solutions

“…However, new processes have been recently developed for the immobilization of extractants and ionic liquids. The extractant is encapsulated in a polymer or a biopolymer matrix [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. In this case, the extractant is generally immobilized in the matrix of the polymer by emulsification and subsequent polymerization or jellification (for example, ionotropic gelation of alginate in the presence of calcium ions), the so-called matrix-type encapsulation process (M).…”