Siberian Federal University, Krasnoyarsk, Russia:

D. Yu. Sirotina, Postgraduate Student
V. I. Bragin, Professor, Head of the Department of Mineral Beneficiation
N. V. Belousova, Professor, Head of the Department of Non-Ferrous Metallurgy, e-mail: netmamba@mail.ru

Krastsvetmet, Krasnoyarsk, Russia:

E. I. Pavlova, Lead Researcher

In the platinum group metal refining process, palladium is deposited in the form of trans-dichlorodiaminepalladium [Pd(NH₃)₂]Cl₂, which is then subjected to high-temperature thermolysis to produce refined metal. Decomposition process is characterized with a considerable precious metals dust entrainment and vaporization of hydrogen and ammonium chlorides. It is a power consuming process which uses containers made of expensive material, i.e. palladium, to roast and reduce partially forming palladium oxides. This research aims to investigate the process of paraformaldehyde reduction as an alternative way to obtain palladium powder. The following parameters were selected to be variables: paraformaldehyde-to-palladium molecular ratio, slurry pH, process temperature and time, liquid-to-solid ratio of the slurry. It is shown that the relationships between the above parameters and the reduction degree can be consistently described with exponential functions. The palladium reduction degree of over 99% can be reached in the following conditions: PFA:Pd >1.5; slurry рН >9; process temperature over 60 ^oC; L:S >2; time over 1 h. Regression analysis showed that the statistically significant factors governing the bulk density of palladium powders only include temperature and liquid-to-solid ratio. Higher temperatures and lower concentrations of solids in the slurry would result in coarser powders. The established regression relationship can be used to predict the bulk density based on the above specified parameters with a standard error of 0.18 g/cm³. The resultant palladium black contains no crystalline impurities detectable by X-ray. The shape of the highs on the radiographs indicates the presence of fine and coarse crystals. The findings indicate that the proposed method of producing refined palladium powder by paraformaldehyde reduction from dichlorodiaminepalladium helps reduce the loss of palladium without affecting the powder performance.

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