Coal Preparation » Fine Coal
The Australian coal industry recognises the need to deal effectively with fine clays in coal flotation as they can negatively impact the recovery, ash content, and moisture of fine coal concentrates. Over the past decade, run-of-mine (ROM) coal has seen a steady increase in the clay mineral content especially with new resources have been encountered with higher clay content including the occurrence of more swelling clay types. Consequently, the industry is seeking solutions to deal effectively with clay particles in fine coal and thereby enhance the flotation performance. The ultimate goal is to increase the profits of the coal handling and preparation plants (CHPPs) without significant alteration to the plant facilities.
Dealing with clay issues becomes more challenging because the properties of coal flotation feed (involving the content and types of clay minerals, the chemistry of process water) vary greatly from one mine to another one. Most reports in the literature were derived from experiments based on tap water, which neglected the crucial interplay between clay minerals and ions in the process water. The process water in the industry contains high contents of ions which alter the nominal functions of clay depressants. Hence, resolving the clay issues in the real-world coal flotation must deal effectively with the interaction between clay minerals, coal and depressants (reagents) in the environment of saline water (process water).
This ACARP project (C35034), built on our prior experience of working with clay minerals, has succeed in (1) developing practical method based on customising XRD technique for quantitative analysis the clay types and contents of coal flotation feed for nine sites, providing a capable method that can be applied in the coal industry, (2) delivering quantitative analysis the chemistry of process water, ascertaining the need to consider the crucial roles of the process water chemistry when dealing with clay minerals in coal flotation, and (3) building effective collaborations with chemical manufacturers for systematic investigations into potential clay depressants. A huge amount of experimental work has been taken to quantify the mineralogical properties (in particular, the types and contents of swelling clays) and process water chemistry for coal flotation feed from nine sites, followed by identifying potential reagents and testing their clay-depressing effects on coal flotation using coal samples from three sites.
As the results, we found that clay minerals are abundant in coal flotation feeds and underpin the longstanding challenge in coal flotation. In particular, swelling clays are present in all sites, which present the most challenging issue in coal flotation. Likewise, process water showed a complex chemistry with the presence of various types on ions. For certain sites, the salinity of process water (expressed by the ionic strength) could be as high as one-third of that of sea water. The abundant presence of ions in process water plays a crucial role in the performance of flotation as well as the effectiveness of clay depressants.
We discovered the beneficial effects of SCIDEV ClariV 44 on laboratory flotation process using the samples from three sites. The application of SCIDEV ClariV 44 as a clay depressant at a dosage of 300 g/ton solid led to a significant reduction in the ash content of the coal concentrates for all three sites tested (i.e. ash content was decreased by 0.5 - 1 percent upon the application of this reagent) without compromising the flotation yield. We recommend further fundamental studies to explore and understand the working mechanism of this reagent toward developing cost-effective clay depressants for the coal flotation industry. Once the target cost-effective clay depressants have been developed and tested in laboratory flotation experiments, the next step would be site trials toward applications.