Study of sorption of platinum and palladium cyanometallate complexes as the key to understanding the mechanism of binding the [Au(CN)2]− anion with carbon adsorbents

Abstract

Goldcarb WSC-207C GR activated carbons with platinum and palladium complexes adsorbed from aqueous solutions of K 2 [Pt(CN) 4 ], K 2 [Pt(CN) 6 ], and K 2 [Pd(CN) 4 ] were studied by the methods of X-ray photoelectron spectroscopy and IR spectroscopy with Fourier transformation, and also by MALDI massspectrometry. Platinum and palladium cyanide complexes are not reduced onto surface of active charcoal while adsorption. A certain part of the [Pd(CN) 4 ] 2-and [Pt(CN) 4 ] 2-anions directly bound to active centers on the activated carbon is oxidized more deeply and functions as particles-anchors, forming oligomers resembling Krogmann salt. A correspondence between the structure of the complex cyanometallate ion and a mode of its binding with active carbon is found. The adsorption of complex species with a linear structure or a square planar structure is defined by a possibility of the formation of donor-acceptor and metallophilic bonds. The mode of the anion [Au(CN) 2 ] -binding with the surface of active carbon was considered.In last 30 years a stable interest arose to the application of activated carbons in hydrometallurgical processes. First of all, it is connected with industrial usage of coals as main adsorbents for extraction of gold(I) from cyanide solutions and pulps. In spite of it the reason of a selective sorption of gold(I) cyanide complex on carbon adsorbents is not yet elucidated at present. Unlike the corresponding complexes of gold, adsorption of platinum and palladium cyanide complexes is by no means studied though the knowledge of specificity of their behavior in relation to carbon adsorbents can present both theoretical and practical interest. This interest is connected, firstly, with the study of mechanisms of binding complexes of noble metals with active carbons and also with the search for methods improving kinetic and capacity properties of carbon adsorbents and increasing their selectivity. Results of such studies promote the improvement of the process of mining and refining platinum metals and gold.Depending on the nature of a central atom and its ligand environment, and also on the composition of a solution and conditions, in which transition metal complexes contact carbon adsorbents, partial or complete reduction of a metal center and (or) chemisorption, which is accompanied by a change in its oxidation state, can occur at the adsorption. To predict a possible result of the interaction between activated carbon and complexes of noble metals, it was suggested to use a comparison of working and stationary potentials of coal in a solution with appropriate redox potentials of complex compounds [1]. The nature of adsorbate at the adsorption of transition metal complex compounds on activated carbons depends on several factors. The composition

Deposition of Gold (III) from Hydrochloric Acid Solutions on Carbon Nanotubes under Hydrothermal Conditions

“…Процессы осаждения золота на различных углеродных материалах представляют интерес, с одной стороны, в области создания новых функциональных композитных материалов [1][2][3], а с другой -в технологиях извлечения и аффинажа золота [4][5][6], а также понимания геохимических процессов миграции и осаждения золота на углистых веществах в гидротермальных условиях [7].…”

Use of ion-exchange resins to deal with the effect of preg-robbing of gold in the course of cyanide leaching

“…In MINIX anion exchangers, the dicyanoaurate(I) anion is sorbed due to the ion exchange with OHanions neutralizing the positive charge of quaternized tributylammonium cations fi xed on the polymeric matrix of the resin. In contrast to MINIX anion exchanger, activated carbons bind [Au(CN) 2 ]anions simultaneously in several independent ways [11,12]. Depending on the sorption conditions, [Au(CN) 2 ]anions may change in the course of sorption the method of binding with the matrix of activated carbon.…”

“…Second, [Au(CN) 2 ]anions are sorbed on defects in crystal lattice layers and edges of graphite microparticles [33][34][35], just where carbenelike carbon atoms are predominantly situated. In all probability, metallic gold, platinum, and palladium are originally reduced and released on the same centers when activated carbons are in contact with aqueous solutions containing [Au(CN) 2 ] -, [PtCl 6 ] 2-, and [PdCl 4 ] 2anions [11,36]. At the same time, [Au(CN) 2 ]ions are not adsorbed on C 60 fullerene particles having the ideal defect-free structure [37].…”

“…However, a back transition of [Au(CN) 2 ]ions from strongly basic centers of the anion exchanger both to weakly basic centers of activated carbon and to adsorbed [Au(CN) 2 ]ions in neutral and, especially, alkaline solutions is substantially less probable. This circumstance is presumably a reason why thermodynamically stable cyanide complexes of transition metals whose central atoms are in a tetrahedral or octahedral environment sterically hindered for interaction with carbene-like centers are hardly adsorbed on the surface of activated carbons [11,42]. At the same time, [Fe(CN) 6 ] 3anions are adsorbed on activated carbons from acid solutions [42], and [Pt(CN) 6 ] 2-, from neutral solutions [11].…”

“…This may lead to a certain transfer of linear [Au(CN) 2 ]anions that are in equilibrium with the saturated resin across the aqueous phase to activated carbon because the donor-acceptor binding mechanism is operative. Analysis of published data [11,43] shows that thermodynamically stable cyanide complexes of those metals whose central atoms are in a linear or planar ligand environment are fi rmly sorbed on activated carbons in alkaline solutions.…”