Using absorbance as a measure of turbidity in highly caustic solutions

This note shows that the dissolution of kaolin and its subsequent re-crystallization as DSP can be monitored using a simple UV–vis method that measures the turbidity of the system. The method is shown to be accurate, reproducible and sensitive. The dissolution of kaolin can be accurately determined by way of a solids calibration curve and this is supported by simultaneous measurements of the dissolved silicate by an inductively coupled plasma (ICP) technique. Additionally, turbidity is often used to measure induction times of nucleation thus the method can monitor dissolution and nucleation simultaneously. It must be remembered, however, that turbidity will show different behaviour to ICP when phenomena such as settling and aggregation occur thus these processes must be considered when interpreting data. Finally, the size limit of the turbidimetric technique must be determined as this, too, can influence the interpretation of data.

Graphical abstractTurbidity can be used to monitor dissolution and precipitation of DSP in Bayer liquors at 90 °CFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The turbidimetric method can follow dissolution in synthetic Bayer liquors at ≤ 90 °C. ► The method is accurate and precise when compared to ICP data. ► Changes in turbidity don't always reflect concentration effects (e.g. sedimentation). ► The method also detected DSP formation in synthetic Bayer liquors. ► This method can be applied more generally to different systems.