Adsorption of palladium, platinum, and gold chloride complexes by carbon fibers with various structures

Abstract

Data are given characterizing the effects of the porous structures in activated carbon fibers (ACF) and the amounts of oxidized carbon forms on the extent and rate of adsorption for various chloride complexes of the platinum metals and gold. The adsorption mechanisms on ACF are considered for these metal chloride complexes. The practical significance of the research is considered.Beginning in the mid-1980s, research has been done on the sorption and complexing of platinum-group metals and gold on fibrous-structure ionites [1][2][3][4][5]. In that period, various papers have appeared on the sorption of precious metals and metals of the platinum group on activated coals [6][7][8]. Activated coals and activated carbon fibers either usual or modified (for example, with coordinating compounds [9]) are capable of quantitatively and selectively absorbing trace amounts of the platinum metals from solution, which is used in isolating those metals and in making catalytically active materials [6,[10][11][12][13][14]. Carbon granulated and powder sorbents are used to extract the platinum metals from spent industrial solutions [7,14,15] and in the making of metal-carbon catalysts [16,17]. When one makes materials with catalytic activity, very often the metalbearing precursors are chloride complexes of palladium and platinum. Platinum and palladium amino complexes have also been used for these purposes [18].The sorption of palladium(II) chloride complexes on activated coals is accompanied by reduction of the palladium to the metal [6,10,11]. This is a transient process in which the rate-limiting stage is internal diffusion. The view is taken that when the platinum-metal complexes come in contact with carbon materials, there may be simultaneous physical adsorption, ion exchange, redox reactions, and complexing involving the participation of the carbon matrix π systems [7,14]. There is a discussion [19] of the formation of Pd 0 particles of size 6-100 nm and π complexes of PdCl 2 with >C=C< parts of graphite-similar materials. In that paper it is noted that most of the H 2 PdCl 4 is reduced at the outer surface of the coal granules, and the coal is thereby oxidized. Research has been done on the effects of the degree of oxidation in graphitized fibers and of the degree of activation on the adsorption of Ag + , Au 3+ , Pd 2+ , Pt 4+ [20], which showed that electrochemically oxidized fibers are capable of sorbing up to 12.6 mol/g of Ag + and up to 4.0 mol/g of Au 3+ . High-resolution X-ray photoelectron spectroscopy has shown that the carbon sorbent phase contains palladium in two forms: (Pd 0 , Pd 2+ ), and platinum in three degrees of oxidation (Pt 0 , Pt 2+ , Pt 4+ ).Research has been done [21] on the adsorption of Pt(IV) chloride complexes from hydrochloric acid solution on granulated synthetic coal. The platinum sorption falls as the temperature is raised. Sorption equilibrium is established slowly (in 24 h at 20°C). There are discussions [22,23] on the effects of temperature and pH of solutions containing Pt(IV) ions. At hig...

Kinetic modeling of the adsorption process of Pd(II) complex ions onto activated carbon

“…There are two main application areas. The first one, related to recycling of metals [1][2][3][4][5][6][7][8][9][10][11] and the second one, related to the environmental protection [12][13][14][15][16][17]. Our work refers to the first area mentioned above.…”

“…In the case of acidic solutions containing chloride ions, palladium forms chloride complexes. There are several reports which indicate that during the adsorption process on activated carbon, palladium(II) is reduced to the metallic form [5,6,9,11].…”

Facile Synthesis of Nanoporous Hydroquinone/Catechol Formaldehyde Resins and their Highly Selective, Efficient and Regenerate Reactive Adsorption for Gold Ions

“…In addition to the acid-base interaction, the oxidationreduction (O-R) interaction between absorbents and metal ions has been found for several absorbents, such as poly- (1,8-diaminonaphthalene) microparticles, [13,14] sulfanyl absorbents, [7,15,16] tannin gel, [17] crosslinked lignophenol gel, [18,19] and active carbon. [20][21][22] The O-R interaction usually leads to very-high selectivity for precious-metal ions with strong oxidizing ability, such as gold(III) ions. [18,19] However, adsorbents based on the O-R interaction are generally not reusable [13,14,[17][18][19][20][21][22] except for a few examples.…”

Kinetic studies of the sorption process of Pd(II) chloride complex ions from diluted aqua solutions using commercially available activated carbon

“…Especially, cyanide leaching and cyanide complexes adsorption using activated carbon is one of the most often applied method for its preconcentration [1][2][3][4]. In the case of platinum, adsorption processes can be also applied [5][6][7][8].…”