A Novel Fiber-Coated Strong Base-Type Anion Exchanger with Superfast Kinetics. Removal and Recovery of Silver Thiosulfate from Aqueous Solutions Manas Chanda, S. Arumugom Pillay, Amitava Sarkar, Jayant M. Modak Department of Chemical Engineering, Indian Institute of Science, Bangalore 560012, India Received 25 February 2005; accepted 23 August 2005 DOI 10.1002/app.23617 Published online 2 February 2006 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A commercial acrylic fiber with 92% (w/w) acrylonitrile content was partially hydrolyzed converting a fraction of the nitrile (OCN) groups to carboxylic acid (OCOOH) groups, to coat the fiber with polyethylenimine (PEI) resin, which was then crosslinked with glutaraldehyde and further quaternized with ethyl chloroacetate to produce a novel strong-base anionic exchanger in the form of fiber. Designated as PAN(QPEI.XG)(Cl - ), the fibrous sorbent was compared with a commercial bead-form resin Amberlite IRA-458(Cl - ) in respect of sorption capacity, selectivity, and kinetics for removal of silver thiosulfate complexes from aque- ous solutions. Though the saturation level of [Ag(S 2 O 3 ) 2 ] 3- on PAN(QPEI.XG)(Cl - ) is considerably less than that on IRA- 458(Cl - ), the gel-coated fibrous sorbent exhibits, as com- pared to the bead-form sorbent, a significantly higher sorp- tion selectivity for the silver thiosulfate complex in the pres- ence of excess of other anions such as S 2 O 3 2- , SO 4 2- , and Cl - , and a remarkably faster rate of both sorption and stripping. The initial uptake of the sorbate by the fibrous sorbent is nearly instantaneous, reaching up to 80% of the saturation capacity within 10 s, as compared to only 12% on the bead-form sorbent. The high initial rate of uptake fits a shell-core kinetic model for sorption on fiber of cylindrical geometry. With 4M HCl, the stripping of the sorbed silver complex from the fibrous sorbent is clean and nearly instan- taneous, while, in contrast, a much slower rate of stripping on the bead-form sorbent leads to its fouling due to a slow decomposition of the silver thiosulfate complex in the acidic medium. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2604 –2613, 2006 Key words: acrylic fiber; anionic exchanger; adsorption; sor- bent fabric; silver thiosulfate complex; silver removal and recovery INTRODUCTION The discharge of heavy metals with aqueous effluents is both a loss of valuable resources and a source of environmental pollution. The main treatment pro- cesses for the removal of metal ions include chemical precipitation, membrane separation, and sorption/ion exchange. Ion exchange sorption is often preferred as it offers the advantages of possible recovery of metal values, minimum space requirement, and recovery of water of sufficient purity for reuse. The subject of metal ion sorption is of major interest at present, as evident from a number of major reviews. 1,2 Commercial ion-exchange sorbents, commonly sup- plied in the form of granules or beads, have the draw- back that the attainable sorption capacity is often much less than the theoretical capacity due to the inaccessibility of many sorption sites remaining bur- ied inside the bead and this difference becomes greater as the bead/particle size increases. The rela- tive inaccessibility of sorption sites inside the beads also results in relatively slow rates of sorption. The slow kinetics, in addition to relatively high cost of ion-exchange sorbents, is an important factor prevent- ing large scale and widespread applications of the ion-exchange method of separation. Considerable re- search was therefore directed in recent years at devel- oping ion exchange/chelating sorbents of significantly faster kinetics. Shell functionalization was a common approach adopted by several workers to achieve faster kinetics. In one approach, 3,4 shell-functionalization was achieved by using a reagent system and a partic- ulate resin in which the functionalization rate was faster than the rate of diffusion of the reagent and stopping the reaction when the most readily accessible sites were functionalized. A simple process of shell-functionalization was de- veloped by Chanda and Rempel 5–10 in which ion- exchange or chelating resins were gel-coated as a thin layer on a solid support, such as silica or polystyrene, using Cu(II) ions as a transient host. The process em- ployed Cu(II) host ions preloaded on a solid substrate, such as silica 5–8 or polystyrene 9 to build a surface Correspondence to: M. Chanda (chanda@chemeng.iisc. ernet.in). Contract grant sponsor: Council of Scientific and Indus- trial Research, New Delhi; contract grant number: 21/0529/ 02/EMR-II.s Journal of Applied Polymer Science, Vol. 100, 2604 –2613 (2006) © 2006 Wiley Periodicals, Inc.