The Nature of Passivation of Lead Sulfide during Anodic Dissolution in Hydrochloric Acid

Abstract

Effective electrowinning of lead directly from its sulfide ore requires a fundamental understanding of its electrodissolution process. Studies made on the anodic dissolution of normalPbS in hydrochloric acid have shown that there are obstructions to the electrodissolution due to some passivation. Detailed surface examination (SEM‐EDAX and x‐ray diffraction studies) is conducted to determine the nature of the passivation products at various potential regions. It has been shown that crystalline sulfur, lead chloride, and lead sulfate are responsible for the observed phenomena.

Physical and Chemical Analysis of Elemental Sulfur Formation during Galena Surface Oxidation

“…At þ258 mV, the initially high current is seen to decay, a behavior characteristic of the formation of a passivating sulfur layer. 3,5,7,23 The CA behavior is similar to that seen in the study of chalcopyrite oxidation by Biegler and Swift, 3 in which they suggest it is the result of a relatively uniform compact layer of amorphous plastic sulfur forming at the surface. As oxidation proceeds via reaction 1, a surface layer of sulfur is believed to form, which thickens over time.…”

“…2 The physicochemical surface properties of sulfide minerals are also important for hydrometallurgical operations such as leaching performed under acidic and oxidizing conditions. [3][4][5][6][7][8] In this case, the formation of oxidation products, such as elemental sulfur, will influence the rate of dissolution of metal ions into solution. The nucleation, growth, and overlap of oxidation products can result in a passivating layer, which obstructs the reacting sulfide mineral surface and hinders dissolution.…”

“…In terms of galena dissolution in oxidative and acidic conditions, the sulfur has been found to passivate the surface (seen as decreasing current over time at constant applied potential) at low anodic potentials. 5,7,8 The passivation is suggested to be due to the formation of an amorphous or plastic form of sulfur that covers ABSTRACT: The surface oxidation of sulfide minerals, such as galena (PbS), in aqueous solutions is of critical importance in a number of applications. A comprehensive understanding of the formation of oxidation species at the galena surface is still lacking.…”

“…Alternatively, if the oxidation products form in discrete areas or are loosely bound to on the surface, the electrochemical reaction is not hindered and dissolution of the sulfide mineral continues unabated. In terms of galena dissolution in oxidative and acidic conditions, the sulfur has been found to passivate the surface (seen as decreasing current over time at constant applied potential) at low anodic potentials. ,, The passivation is suggested to be due to the formation of an amorphous or plastic form of sulfur that covers the surface . At higher anodic potentials, the current reaches a minimum due to passivation and then increases due to the conversion of the amorphous sulfur to a crystalline form, which occurs through a nucleation and growth mechanism .…”

Electroanalytical chemistry for the analysis of solids: Characterization and classification (IUPAC Technical Report)

“…• Solid electrodes made of the material under investigation, e.g., for the analysis of minerals with semiconducting properties, typically magnetite [98][99][100] and galena [101][102][103]. Usually, the electrodes consisted of bars of the studied material housed in a Teflon shaft.…”