Pressure solution of electrically conductive minerals in shallow crust-galvanic processes: A case study from pyrite under differential stress

The pressure dissolution behaviour of pyrite was investigated via its polarisation curve and using electrochemical impedance spectroscopy (EIS) in a FeCl3 solution under differential stress. The results showed that the pyrite pressure dissolution process is a galvanic corrosion process and that there is a negative linear relationship between the pyrite potential difference and the stress action. The EIS experiments confirm that the pyrite was in a passive state in a 0.0010 mol L−1 FeCl3 solution and that a thin surface layer of Fe1−yS2 was present. In a 0.010 mol L−1 FeCl3 solution, the pyrite was in a trans-passive state, in which the aforementioned passive layer became porous. In a 0.10 mol L−1 FeCl3 solution, the pyrite was in an active state, the surface layer dissolved completely, and a lattice layer of S20 was created instead of a passive layer of S0. Under the present stress conditions, the stress action did not change the pyrite electrochemical dissolution mechanism; however, the conditions decreased the charge transfer resistance and passive resistance and increased the species diffusion capacitance.

► The pyrite pressure dissolution process is a galvanic corrosion process.
► There is a negative linear relationship between the pyrite potential difference and the stress action.
► Three different electrochemical dissolution mechanisms of pyrite are revealed.