.3.3. EIS measurements
Impedance measurements were conducted to give an in-situ detection of possible modification of pyrite surface exposed to cyanide solutions. The impedance (Z) consists of real (Zr) and imaginary (Zi) parts that can be calculated by the means of phase angle. As shown in Fig. 12, the impedance spectra are commonly represented as either a Bode plot (with log frequency on the X-axis and both the absolute value of impedance and the phase-shift on the Y-axis) or a Nyquist plot which consists of the imaginary part of impedance (Y-axis) and the real part of impedance (X-axis). At higher frequency region (100–10,000 Hz), the Z values are low and relatively constant, while the phase angle values decrease towards zero. This is a typical response of a resistor to an AC with high frequency, corresponding to solution resistance. In the intermediate frequency region (0.1–100 Hz), the relationship between Z and frequency becomes linear with a slope of −1 and the phase angle reaches maximum within this region. This part corresponds to capacitive behaviour caused by the electrical double layer at the mineral/solution interface and/or the possible surface layer.