Effect of chopped light on the dissolution and leaching of chalcopyrite

• Published in: Minerals engineering Vol. 160; p. 106703
• Main Authors: Crundwell, F.K., Bryson, L.J., van Aswegen, A., Knights, B.D.H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-2021
• Subjects: Chalcopyrite; Dissolution; Leaching; Light; Passivating layer; Semiconductor; Passivating layer; Semiconductor; Chalcopyrite; Leaching; Dissolution; Light
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2020.106703

•Photo-response to chopped light is observed without increase in temperature.•Photo-response is dependent on potential.•Photo-response due to semiconducting properties, not thermal effects.
The interaction of light with a solid, such as chalcopyrite, can increase the current by inducing a photocurrent (exciting an electron from the valence band to the conduction band) or by thermal heating of the surface that increases the rate of reaction. A study was undertaken to determine if the effect of light on a natural chalcopyrite electrode is due to thermal heating of the electrode surface or due to its semiconducting properties. Experiments were conducted in which a thermistor was attached to the face of the chalcopyrite electrode to measure the effect of light on the temperature of the electrode. Three different types of tests were conducted (i) a light chopper was used to shine short bursts of light on the electrode, (ii) potential step tests, and (iii) mixed potential tests. It is concluded that the response is due to the semiconducting properties of chalcopyrite for four reasons: (1) the photocurrent is a function of applied voltage across the interface, which is not anticipated by thermal heating; (2) a photocurrent is observed when chopped light of a frequency of about 1.4 Hz shone at the electrode, but there is no corresponding response in the surface temperature; (3) the current decreased faster than expected by the activation energy of the reaction after the electrode was illuminated for 100 s, which results in activation energies that are between 2 and 4 times higher than the reaction activation energy; (4) with light on the chalcopyrite electrode (with no applied potential) in an acidic ferric sulphate solution, it was the redox potential that changed significantly more than the mixed potential, suggesting faster dissolution of chalcopyrite in the presence of light. An explanation for the effect of light on the electrode is proposed, and rate equations are derived for transient and steady-state conditions.