Journal of Hazardous Materials 174 (2010) 556–562 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Synthesis of a novel dithiooxamide–formaldehyde resin and its application to the adsorption and separation of silver ions Zeliyha C ¸ elik, Mustafa Gülfen ∗ , Ali Osman Aydın Department of Chemistry, Faculty of Arts & Sciences, Sakarya University, TR-54187 Sakarya, Turkey article info Article history: Received 5 August 2009 Received in revised form 14 September 2009 Accepted 15 September 2009 Available online 23 September 2009 Keywords: Dithiooxamide acid–formaldehyde resin Thiourea–formaldehyde resin Silver ions Adsorption Separation Chelating resin abstract In this study, a new chelating resin of dithiooxamide (rubeanic acid)–formaldehyde (DTOF) has been synthesized by the reaction of dithiooxamide and formaldehyde. Also a well-known chelating resin of thiourea (thiooxamide)–formaldehyde (TUF) has been prepared by the reaction of thiourea and formalde- hyde. DTOF and TUF chelating resins were used in the adsorption, separation and concentration of silver ions by batch and column techniques. These resins were characterized using FTIR and elemental analysis. It was found that DTOF resin has silver adsorption capacity of 3333.3 mg g -1 or 30.86 mmolg g -1 and TUF resin has the capacity of 1428.6 mg g -1 or 13.22 mmol g -1 . DTOF resin showed more affinity to silver ions according to Cu(II), Zn(II), Ni(II) and Co(II) base metal ions than TUF resin. It was also demonstrated that DTOF resin can be used in the separation and concentration of silver ions. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Silver is generally found together with copper and lead min- eralization in nature. Silver metal is used in jewelry, silverware, food and beverage-processing, and metal alloy industries. Silver compounds are used in mirroring, photographic, electroplating, catalyst, antimicrobial materials, batteries and ink-formulation industries. In case of a solution including silver ions in a hydromet- allurgical, recycling or wastewater process, preliminary separation of silver ions from the solutions containing alkaline, earth alka- line or base metal ions may be more profitable than other metal ions. The chelating resins can be used in the concentration and selective separation of silver ions. Also, the ion exchange resins can be used for silver ions, but the chelating resins are preferred instead of the ion exchange resins because of their selectivity [1–8]. The chelating resins have different functional groups and matrix or support. Functional groups in these resins may include N, O, S and P donor atoms. Chelating resins are used widely in the separation, concentration or analytical pre-concentration of metal ions [9,10]. For silver ions, N and/or S atoms in functional groups are preferred due to the Hard-Soft Acid Base (HSAB) theory by ∗ Corresponding author. Tel.: +90 264 2956051; fax: +90 264 2955950. E-mail address: mgulfen@sakarya.edu.tr (M. Gülfen). Pearson [11]. Silver ion is known as a soft Lewis acid and it has smaller effective ionic radii (2.5 Å) in aqueous solution (O donor atom media) than a lot of metal ions [12]. On the other hand, N and S atoms are softer ligand than oxygen atom. Silver ion shows affinity to N atom and especially S atom in a functional group. Chelating resins containing N and/or S atoms as donor atoms have great attention due to their selectivity towards silver(I) ions [6,7,13–17]. Many researchers have studied the adsorption, separation or concentration of silver ions using chelating resins with different functional groups including N and/or S atoms. Some examples of these functional groups in chelating resins studied for the adsorption, separation or concentration of silver ions are thiourea [6,7,18–20], dithiocarbamate [1,20–23], bisthiourea [24], thiol and amine [1,3,4], thiosemicarbazide [25], polythiazaalkane [26], 2- mercaptobenzothiazole [27], thiophene [28] and amberlite XAD-16 resin [29]. Thiourea functional group has been widely used in chelat- ing resins for the adsorption of silver ions and other precious metal ions. Rubeanic acid (dithiooxamide) has similar molec- ular structure to thiourea (thiooxamide) molecule and it includes more S donor atoms. A few examples of the poly- mers or chelating resins functionalized with dithiooxamide are 2,4-dihydroxyacetophenone–dithiooxamide–formaldehyde ter- polymer for Fe(III) Cu(II) Ni(II) Co(II) and Zn(II) ions adsorption by Rahangdale et al. [30], polystyrene–divinylbenzene functionalized 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.09.087