Highly Efficient Separation/Recycling Palladium(II) Ions from Aqueous Solutions by Silica Gel-Coated Graphene Oxide Modi
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INTRODUCTION
PALLADIUM is one of the most important platinum group metals, which is widely utilized in several fields, such as jewelry, electronic components, and chemical industry due to its promising physical and chemical properties.[1–3] Moreover, European Commission has included it in critical raw materials list owing to its economic importance and high supply risk.[4] However, it tends to maintain a high price due to its extremely low concentration in the earth’s crust, rising market demand, and hard to be replaced.[5,6] Therefore, the MIN LI, SI TANG, JIAN FENG, XIAOJING MENG, and SONGSHAN JIANG are with the Department of Chemical Engineering, Chongqing University of Science and Technology, Chongqing 401331, China. Contact e-mails: [email protected]; [email protected] KUN HUANG is with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China. FENG GAO is with the School of Resources, Environment and Materials, Guangxi University, Naning 530004, China. Manuscript submitted December 4, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
recycling of palladium from industrial waste and solutions is of great significance to ensure its steady supply and control the price. Several palladium recycling techniques, such as solvent extraction, ion-exchange, membranes separation, electrochemical reactions, and adsorption, have been proposed in the published literature to efficiently recover palladium from the secondary resources.[6–12] Among these methods, adsorption is considered as an effective strategy for palladium recovery due to its simplicity, high efficiency, and low cost.[13,14] Nevertheless, absorbent material used for Pd(II) ions capture need to maintain excellent chemical stability because the leaching solution containing Pd(II) ions is generally obtained by dissolving solid phase into hydrochloric acid in the presence of oxidants such as nitric acid or hydrogen peroxide.[15] Silica gel can be used as a matrix to prepare adsorbent for separation of Pd(II) ions due to its excellent chemical stability under acidic conditions and high chemical reactivity. For instance, Zhang et al.[16] have reported the adsorption of Pd(II) ions from aqueous solutions on nano-silica modified with imidazoline groups and the maximum adsorption capacity reached up to 69.6 mg g1. Ge et al.[17] and Dai et al.[10]
have also reported the adsorption of Pd(II) ions from 3 mol L1 of nitric acid and highly acid medium, respectively, on the silica-based adsorbent. Furthermore, our previous works have also demonstrated that silica gel can be used as a matrix to synthesize sorbents for removal of metallic ions from acidic media.[18,19] However, the adsorbents, obtained by directly modification of the silica gel surface with functional groups, have exhibited low adsorption capacity for Pd(II) ions.[10,16,20] Therefore, we aimed to prepare a sorbent with high adsorption capacity for Pd(II) ions, which can be employed to recover Pd(II) ions from the ac
