Quantifying pyrite surface oxidation kinetics by contact angle measurements

Pyrite surface oxidation plays an important role in several mineral processing and hydrometallurgical systems. The initial oxidation takes place very quickly and affects the surface characteristics of pyrite greatly. Contact angles under different atmospheres were measured to quantify the oxidation kinetics of pyrites from various sources. The contact angle of water droplet on pyrite in air was found to decrease with time indicating that the surface was becoming less hydrophobic with time. Among the various pyrite samples, pyrite from coal sources oxidizes much faster than mineral pyrite. The oxidation rate was found to be dependent on solution pH. All pyrite samples studied exhibited a high oxidation rate in the acidic and alkaline pH range when compared to the neutral pH range. Under nitrogen atmosphere, the oxidation rate was much slower than air but a similar trend was observed. When contact angle measurements were done with samples immersed in n-alkanes such as hexane, the contact angle did not decrease with time since no oxidation took place. The above studies clearly demonstrate that oxidation of pyrite surfaces makes it less hydrophobic.