Siberian Federal University, Krasnoyarsk, Russia:

A. I. Ryumin, Associate Professor at the Department of Non-Ferrous Metallurgy
O. V. Belousov, Associate Professor at the Department of Non-Ferrous Metallurgy, e-mail: ov_bel@icct.ru
G. A. Sorkinova, Senior Lecturer at the Department of Non-Ferrous Metallurgy
D. Yu. Sirotina, Postgraduate Student

In palladium refining, the trans-dichlorodiaminepalladium salt serves as the basic compound for selective extraction of palladium from complex solutions. The final salt of trans-[Pd(NH₃)₂Cl₂], which is then used to produce refined metallic palladium, is subjected to hydrochloric acid deposition from ammonia solution containing non-ferrous metal impurities. Copper is the dominant impurity in refined palladium. This research aimed to understand the process of co-deposition of copper with dichlorodiaminepalladium. Copper (I) and (II) chlorides were introduced in the ammonia solution of palladium salt [Pd(NH₃)₄]Cl₂. Dichlorodiaminepalladium was then deposited from the solution, and the salt that formed was analysed for copper content. It is shown that due to the poorly soluble compound of CuCl being formed in acid media it is copper (I) that predominantly gets deposited with dichlorodiaminepalladium. Prior oxidation of the ammonia solution leads to a significantly reduced copper concentration in the deposited salt as CuCl₂ is highly soluble. It is demonstrated that as the concentration of copper in the solution goes down from 0.72 to 0.125 g/l, a reduction in the copper concentration in dichlorodiaminepalladium is observed (from 0.008 to 0.001%). Through a drastic change in the salt deposition conditions, it was clearly shown that both the absorption mechanism of copper co-deposition in trans-[Pd(NH₃)₂Cl₂] and occlusion are auxiliary. It was established that, in hydrochloric acid processing of ammonia solutions containing palladium and copper, once рН has reached 5–7 what precipitates first is copper in the form of poorly soluble hydroxide Cu(OH)₂ and maybe also hydroxochloride. рН ~ 5 launches large-scale deposition of dichlorodiaminepalladium. Cu(OH)₂ particles serve as salt nuclei helping [Pd(NH₃)₂Cl₂] nucleation. As a result, the Cu(OH)₂ microparticles find themselves in the cores of the dichlorodiam inepalladium cr ystals, so there are no conditions to enable the dissolution of copper hydroxides even at the final рН of 1.0. The salt deposition conditions were changed to prove that copper co-deposition with dichlorodiaminepalladium is mainly caused by the nonisomorphic inclusions of Cu(OH)₂ in the trans-[Pd(NH₃)₂Cl₂] crystals.

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