MANAGEMENT AND CONTROL OF SILICA IN THE BAYER PROCESS

Management of reactive silica is a major focus of effort for most alumina producers. However, like many aspects within the Bayer process, the treatment of silica has both detrimental and advantageous aspects. Controlled formation and precipitation of sodium aluminosilicates - often referred to as desilication product or DSP - can substantially reduce the amount of silica in solution and so prevent or reduce the potential for silica contamination in alumina product. Additionally, removal of DSP from the circuit (for example in a desilication step) can also be used as a sink for other problem contaminants such as sulfate or chloride. On the other hand, DSP formation as scale in heat exchangers can substantially limit energy transfer and restrict flow capacity. A range of new technologies have recently been developed to address the differing aspects of silica control with the aim of enhancing the advantageous properties of DSP precipitation, while minimizing the detrimental aspects. A review of recent developments in improving control of silica in Bayer process liquor is presented, outlining new options for process operators to improve management of silica and gain better control in this process area.