Modelling and on-line estimation of zinc sulphide precipitation in a continuously stirred tank reactor

In this paper the ZnS precipitation in a continuously stirred tank reactor (CSTR) is modelled using mass balances. The dynamics analysis of the model reveals that the ZnS precipitation shows a two time-scales behaviour with inherent numerical stability problems, which therefore needs special attention during implementation. The mass balance model allows the design of an on-line estimator of the zinc concentration and precipitation rate, given only wet-chemical measurements of the sulphide concentration and of the pH in the reactor. The on-line estimation algorithm, also called observer or software sensor, is tested in a simulation experiment with a block disturbance showing numerically stable results. Furthermore, on the basis of real-world experimental data, the observer shows an appropriate performance. The estimation procedure offers good possibilities to be applied for other metal removal processes.