Cyanidation kinetics of argentian jarosite in alkaline media

The cyanidation of argentian potassium jarosite in alkaline media is charac terized by an induction period, followed by a conversion period, as was obs erved in other synthetic jarosites. The induction period shows an apparent order of 0.7 (NaOH) and 0.2 [Ca(OH)(2)] with respect to the [OH-], and an a pparent activation energy of 86 kJ mol(-1) (NaOH) and 36 kJ mol(-1) [Ca(OH) (2)]. The conversion period is characterized by the presence of a reaction front with an unreacted jarosite core. The decomposition products are amorp hous. The process is chemically controlled in both media. In NaOH-CN-, the order of reaction is 0.6 with respect to the [OH-] and the activation energ y is 43 kJ mol(-1). in Ca(OH)(2)-CN-, the order of reaction with respect to [OH-] is 0.5 and the activation energy is 80 kJ mol(-1). The order of reac tion with respect to the [CN-] concentration is zero in both media. The pro cess is faster than that observed in natural arsenical potassium jarosite f rom gossan ores (Rio Tinto, Spain). The addition of potassium chloride to t he reaction system increases the reaction rate; the order of reaction with respect to the [Cl-] was 0.13. (C) 2000 Elsevier Science B.V. All rights re served.