Monitoring polythionate bio-oxidation by conductivity measurement

• Conductivity measurement: an indirect method to determine polythionate concentration.
• Conductivity measurement reveals the evolution of polythionate concentration in real time.
• Conductivity helps to monitor polythionate bio-oxidation.
• Conductivity measurement is useful in the control of bioreactors.

Polythionates are formed by the incomplete oxidation of sulphide minerals in the grinding and flotation circuits, and particularly of those containing pyrite. Polythionate levels in the recycling water must be adjusted; otherwise, it can affect metal recoveries. The presence of different species, such as thiosulphate, trithionate, and tetrathionate in certain effluents can affect the environment. In this paper, an indirect method based on conductivity measurement for monitoring polythionate bio-oxidation is proposed. Firstly, the conductivity of acidic solutions containing polythionates is verified as the sum of the conductivities corresponding to acid and tetrathionate and, therefore, in synthetic solutions, polythionate concentrations can be estimated by simply measuring conductivity. In process water and cultures with background conductivity, polythionate concentrations are predicted from the linear relationship between polythionate concentration and the total conductivity of the system. Once the slope of the linear relationship is known, polythionate concentrations can be estimated, and therefore it is necessary to perform only chemical analysis at the beginning and at an intermediate point. The degradation of polythionates can be continuously recorded, and hence the kinetic study of a culture can be more easily and accurately performed.