The equipment selection for a fine coal tailings dewatering application is filled with numerous challenges and complications. There are known technologies operating in the Australian coal industry such as belt press filters and, recently, solid bowl centrifuges. This paper looks at three known technologies, namely belt press filters, plate and frame filters, and solid bowl centrifuges to dewater thickened fine coal tailings. A comparison of recovery, moisture, reagent addition, solids and volumetric throughput is presented. Some pros and cons of each application will also be provided. Specialised technical information on each application including the major factors that have the greatest dewatering impact on the technologies will be highlighted. Information from an installation from South Africa is shared. The paper assists with the selection process and explains important information that must be brought to light when considering a change from wet disposal to dry disposal. Elements of this paper were previously published in Meiring (2021).
?Chile produces large amounts of tailings daily which must be safely disposed on the earths surface. There are a series of strategies that have been successfully used in our country to store tailings, among them are thickened and paste tailings. Paste tailings are an advantageous technique that allows for greater recovery of water while improving physical stability of the structure. Although challenges are faced worldwide when large production rates are tried to be thickened, the technique seems promising for countries like Chile where there is an ongoing water crisis. The stability of paste tailings facilities is highly influenced by water content or saturation. As consolidation occurs the tailings loses water. However, as the evaporation front takes place, the material goes from a saturated to a non-saturated state. Unsaturated paste has shown improved resistance, e.g. liquefaction resistance almost double when saturation drops below 90%. A well planned facility operation should consider the monitoring of the water content of the paste. However, this is sometimes difficult, due to the large areas that must be controlled and the danger associated with manual moisture measurements in the field. In this context, we proposed the use of hyperspectral cameras to obtain a relationship between the paste moisture content and light reflectance. This would allow to generate moisture surface map and to the use of this data to monitor for instance evaporation rates or water balance in tailings storage facilities. This article summarizes laboratory main findings and proposes a series of procedures to implement the technique in the field.
?Tailings filtration is growing in interest with increased pressure on water resources and Tailings storage facility legislation. In greenfield projects limited sample is available to evaluate filtration performance and often composite samples to represent mineral recovery are utilised. The mineral resource over the life of the mine can be variable and small changes in clay or other material can have significant effects on the filterability. This paper looks at methods to predict filterability of a tailings stream with changes in mineralogy. Based on initial testwork and historical database information, mineralogy and particle size data can be analysed in HSC SIM to predict the rate and achievable moisture. Together with plant model information, alternative dewatering strategies can be evaluated to determine the capital and operating costs.
?Tailings Storage Facilities (TSF) are characterized by high moisture contents of their materials even after thickening processes. After deposition the tailings undergoes to a series of phenomena such consolidation, seepage, desiccation, etc., which results in the desaturation of the pore space. The occurrence of these phenomena is influenced by several factors, such as evaporation, contraction and surface cracking. Particularly, it has been found that the surface cracking affects evaporation rates while influencing the stability of the facility due to the desaturation of deeper soil layers. Nowadays, the assessment of water content in the field is a complex and sometimes not viable activity due to risk of personnel when moisture content is controlled manually. Knowing the moisture content can be advantageous if the stability of the facility needs to be evaluated or the water balance of the structure analyzed. So, one question that arises is: can the water content of the facility being indirectly monitored through the observations of cracks? The latter is explored in this article by conducting desiccation tests in paste tailings under temperature and field conditions of northern Chile. The slurry is desiccated until the shrinkage limit is exceeded while RGB images captured periodically and rated of evaporation monitored. The images are then processed utilizing segmentation, linear filtering, and thresholding techniques. The processed images of the laboratory samples are then compared with images captured by unmanned aerial vehicle (UAV) in a paste storage facility. Finally an index that correlates cracking and moisture content is proposed. In addition to this, a new approach to estimate shrinkage limit is proposed.