Analysis of the composition and morphology of products of the anodic dissolution of Cu2S

The anodic dissolution of copper (I) sulphide in an electrolyte with a comp osition similar to that of refining electrolyte leads after a sometime to a potential jump. Any of the following may bring about the occurrence of the potential jump: crystallisation of CuSO4 within anode pores, the appearanc e of copper hydroxides, the appearance of an extremely slowly dissolving Cu S layer on the surface of the sulphide, or the presence of elemental sulphu r which blocks the anodic reactions. The composition and morphology of the products of the electrolysis of powde r and solid anodes dissolved by applying a current with an anodic density r anging between 100 and 500 A/m(2) has been investigated. The phase composit ion of the surface layers of powder granules was examined by means of X-ray analysis, mass spectroscopy, and linear micro-X-ray analysis. The topograp hy of Cu2S granule surface before and after dissolution was observed in pol arised light and also by using a scanning microscope or an atomic force mic roscope (AFM). Changes were observed in the chemical and phase composition of the surface layers of powder granules. Instrumental methods were applied in order to de termine the presence of copper (II) sulphide and elemental sulphur. Copper (II) sulphide (CuS) constitutes the dominant phase. Elemental sulphur is pr esent in small quantities, difficult to detect. No traces of hydrated CuSO4 or copper hydroxides were detected. Changes in phase composition are accom panied by changes in surface topography, i.e. the surface undergoes distinc t development. Fractures along the boundaries of sulphide crystals appear, and they make it possible for the electrolyte to penetrate within the mater ial.