A novel pre-treatment of calaverite by hydrothermal mineral replacement reactions

We report a new method for pre-treatment of refractory gold-bearing tellurides employing the hydrothermal mineral replacement reactions. The method is illustrated by the replacement of calaverite by metallic gold at 150-250 °C under vapor saturated pressures. The influences of temperature, pH, and additional salts (NaCl and Na₂SO₄) on the conversion rate were investigated using the orthogonal array design method. The results indicate that temperature is the most significant factor, followed by pH, and then additional salts. The optimal condition for fast and low cost conversion is 200 °C, pH 6.0, 0.01 M NaCl, and <38 μm particle size. Under this condition, the conversion can be completed within 15 h. These preliminary results indicate that the hydrothermal mineral replacement reaction is a promising pre-treating step for gold-bearing tellurides processing.