Microstructure of clay fabric in electrokinetic dewatering of phosphatic clay dispersions

Abstract

Abstract Electrokinetic dewatering is considered a promising method for separation of water from clay dispersions in the mining industry. Numerous studies over the past few decades have been conducted on electrokinetic dewatering process in order to identify potential performance improvements. However, little is known about the impact of process on clay microstructure that determines its water content. Here, for the first time, scanning electron microscopy (SEM) was utilized to study the impact of electrokinetic dewatering process on clay fabric microstructure. The studies were conducted on three experimental platforms including 1) a gravity settling experiment to determine the clay structure in the absence of an electric field, 2) a cylindrical tank in which a static electrokinetic separation process was conducted under an electric field applied along the tank height and 3) a continuous dewatering system in which electrokinetic separation took place in two stages along a conveyer belt. The studies suggested that formation of honeycomb microstructures was responsible for poor settling and an acidic environment promoted a more voluminous honeycomb with a higher water content. Under an electric field, a less-ordered structure than a honeycomb was formed during the electrophoresis separation process near the region where the pH was above the point of zero charge. The less-ordered structure was later compressed (i.e. the structure partially collapses) in the 2nd stage of the continuous system in which an already formed clay cake was dewatered through the electro-osmotic process. The insight provided in this study can help improve the performance of electrokinetic separation process.