Dissolution of noble metals and copper in the DMSO-HBraq system

Abstract

The processes occurring in the DMSO-HBr aq system at different ratios of the components were studied by electronic and IR spectroscopy. The interaction of the components in the system results in the accumulation and consumption as oxidants of bromine containing (Me 2 S(OH)Br, Me 2 S•Br 2 ) and oxygen containing compounds (H 2 O 2 , HBrO). It was shown by the pH metric method that the equilibrium concentration of species that are accumulated in the system and oxidize the metal is achieved on the fifth day after mixing of the components. The dependence of the dissolution rate of platinum (Pt 0 ) on the ratio of components (DMSO : HBr) has three maxima, whose positions are determined by the nature of intermediate species formed in the system and the state of the metal surface containing the oxide film.Key words: donor acceptor electron transport system, dimethyl sulfoxide, hydrobromic acid, oxidative dissolution, noble metals, metal surface, oxide film, IR spectroscopy, pH metry.Studies of donor acceptor organic and aqueous organic systems that oxidize transition metals are still important for both an understanding of processes occurring in the liquid phase and on the metal surface and the solution of prac tical problems on extraction of precious metals from indus trial waste and various types of mineral raw materials. 1 Similarly to aqua regia, the aqueous organic donor ac ceptor electron transport DMSO-HBr aq system («cher nogolovskaya vodka») studied in this work dissolves tran sition metals, including noble metals (Au 0 , Ag 0 , Pd 0 , Pt 0 , Rh 0 , and others). 2 A distinctive feature of metal disso lution in the DMSO-HBr aq system is the presence of several maxima in the plot of the metal dissolution rate vs DMSO : HBr ratio. This possibly indicates the forma tion in the system (due to the interaction of the compo nents) of several reactive species that oxidize the metal. 3,4The DMSO-HBr aq system was studied by electronic and IR spectroscopy and the dynamics of the change in time of its state was examined by pH metry in order to reveal the processes occurring in the system upon a change in the ratio of the components in the liquid phase and to determine the nature of species oxidizing the metal.The dependence of the dissolution rate of platinum (Pt 0 ) on the DMSO : HBr ratio was studied and the posi tions of maxima in the curves of the dependence of the dissolution rate of metals (Pt 0 , Au 0 , Ag 0 , Pd 0 , Cu 0 ) on the ratio of the components of the system were examined in comparison.

Solution-Processed Cesium Hexabromopalladate(IV), Cs2PdBr6, for Optoelectronic Applications

“…This shift of absorbance peak to a lower energy indicates that the bond order of SO bond in DMSO changes due to the formation of DMSO-HBr adduct. HBr:DMSO is known to function as the oxidizing agent in organic synthesis, as well as oxidization of metals. , Here, HBr:DMSO oxidizes Pd 2+ to Pd 4+ and the available bromide ions in HBr:DMSO leads to the formation of [PdBr 6 ] 2− , which is then the building block to form the compound with Cs + as the counterion. The oxidation of Pd­(II) and formation of a new complex are often associated with a change in the absorbance spectrum.…”

Oxidative Dissolution of Metals in Organic Solvents

“…A distinctive feature of metal dissolution in the DMSO-HBr aq system is the presence of two or three maxima in the plot of the metal dissolution rate as a function of the molar fraction of HBr, indicating that several species that can oxidize metals are formed upon the interaction of DMSO and HBr. Besides bromine-containing compounds, oxygen-containing compounds (H 2 O 2 , HXO) are formed as well, due to the interaction between DMSO and HX in aqueous solutions . DMSO-HX aq dissolves both transition metals (Cu) and noble metals (Au, Ag, and Pt), whereas gold is insoluble in the nonaqueous system DMSO–HCl solv .…”

“…Besides bromine-containing compounds, oxygen-containing compounds (H 2 O 2 , HXO) are formed as well, due to the interaction between DMSO and HX in aqueous solutions. 72 DMSO-HX aq dissolves both transition metals (Cu) and noble metals (Au, Ag, and Pt), whereas gold is insoluble in the nonaqueous system DMSO–HCl solv . Therefore, the latter system can be used for selective dissolution of copper in the presence of gold.…”

“…The DMSO–halide acids (HX, X = Cl, Br, I) in both aqueous and organic systems have been studied for oxidative dissolution of metals such as copper, silver, gold, palladium, and platinum. − The final products of the reaction between DMSO and HX are mainly dimethyl sulfide (Me 2 S), dihalogens, and water, together with some byproducts such as CO and CS 2 . The intermediate products Me 2 S­(OH)­X, Me 2 S·X 2 , and X 2 are most likely responsible for the oxidation of metals.…”