Surface chemistry of oxidised pyrite during grinding: EDTA extraction analysis

Abstract

This paper investigates the surface chemistry of oxidised pyrite under two different grinding conditions (forged steel grinding media and 30% chrome steel grinding media with nitrogen gas flow) using the ethylene diamine-tetra acetic acid (EDTA) extraction technique. The measurement of EDTA extractable iron and dissolved total sulfur (DTS) in the solid and aqueous phase of the grinding slurry enables us to decouple the relative intensity of the pyrite oxidation and galvanic interactions in the mill. It is found that the galvanic interaction predominates in the mill when pyrite samples are ground with forged steel media in the presence of sufficient dissolved oxygen. While the oxidation of pyrite becomes the predominant reaction when the concentration of dissolved oxygen is low in the mill. However, the oxidation of pyrite predominates in the mill when pyrite samples are ground with 30% chrome steel media regardless of the concentration of dissolved oxygen. Reducing the level of dissolved oxygen in the mill (e.g., purging the system with nitrogen gas) or applying less electrochemically active grinding media (e.g., high chrome steel) can reduce the hydrophilic species on the pyrite surface during grinding (e.g., iron hydroxides/oxyhydroxides). Hence, it would be expected to consequently increase the floatability of pyrite.