Effect of Chemicals on Stabilising Tailings Disposals of Coarse and Fine Coal Rejects

The risk of potential catastrophic liquefaction failure and costs associated with tailings storage facilities  is reduced substantially by co-disposal strategies, i.e. disposing of a dried mixture of coarse and fine coal tailings rejects. This process involves dewatering of fine rejects from high rate thickeners using mechanical dewatering devices such as belt press or centrifuge filters. When a large amount of clay is present, it is difficult to capture fine particles and achieve necessary (low) moisture and cake structure by mechanical dewatering devices for effective disposal. The degree of difficulty associated with fine tailings dewatering differs from mine to mine as the surface properties of tailings particles can change significantly, so suitable chemical aids are necessary. This project aimed to investigate the effect of chemicals on the handleability and disposal stability of fine and co-disposed rejects, then develop a simple but effective tool for on-site measurement to assess the rheological properties of co-disposal rejects.

A new technique was developed to screen suitable chemicals for coal-tailings disposal. This technique determined the handleability of dewatered fine coal tailings by measuring the sample's stickiness, which is a combination of tack (cohesive/adhesive) energy and bonding strength (peak force).  Researchers proposed a cylindrical bucket rheometer and its testing procedure which can be used by on-site operators to access the stability of the co-disposed rejects. A co-disposed reject is simply loaded into a suitable cylindrical bucket, which is then lifted to let the reject slumping by itself. The slump height was measured and used to calculate the shear yield stress using a mathematic correlation. Bucket rheometer results were confirmed by two standard methods including the vane shear method for fine particles (<1 mm) and the shear box method for large particles (>1 mm). The difference between the prediction and experimental results is less than 10 % for fine rejects and from 8 to 15 % for mixtures of coarse and fine rejects. It was shown that the geometry of the bucket rheometer and its testability is dependent on the maximum particle size and moisture content of co-disposed rejects.

These results are significant and applicable to coal tailings co-disposal strategies. The benefits to the coal industry include new and efficient approaches and reliable test results for coal tailings disposal using effective reagents.