Improving the dewatering efficiency of clay–rich tailings in saline water

Tailings water balance and management

Di Liu

Sustainable Minerals Institute, UQ

The presence of clay minerals slows down the settling rate and mitigates compact consolidation efficiency in tailing dewatering. The increasing use of saline water in many plants affects the dewatering performance and makes the situation even more complicated. Efficient tailing dewatering becomes a great challenge due to the lack of understanding of tailing compositions, especially clay minerology, clay content, and water chemistry. In this study, the dewatering behaviours of three types of commonly observed clay minerals in tailings such as kaolinite, bentonite, and illite were investigated in saline water with different water salinity. Additionally, different polymeric flocculants such as Polyethylene oxide (PEO) and anionic polyacrylamide (PAM) were tested to improve the dewatering efficiency of clay minerals in saline water.

The settling rates of clay minerals were found to be affected by water salinity, clay type, clay content and polymer dosage levels. High salinity water hinders the settling of kaolinite but assists the settling of bentonite and illite. Anionic PAM works better than PEO to increase the settling rate of all clay minerals due to the creation of compact floc structures in saline water. It is evident that PAM takes a more condensed conformation due to the suppressed intramolecular electrostatic repulsion, leading to an enhanced adsorption density and a strong bridging effect on kaolinite particles in saline water.  Cryo-SEM, which snap-freezes water samples to allow their properties to be examined, proved to be a useful tool for understanding polymer-flocculated clay aggregation structures in saline water and can be used in combination with dewatering results to guide tailing management. This study identified new research directions leading to emerging strategies to improve the dewatering of clay-rich tailings in saline water.

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