Coal Preparation » General
Flotation of oxidized coals is a challenge confronting the Australian coal industry. The conventional flotation collector, diesel, used for floating non-oxidized coals is not suitable for floating oxidized coals, leading to a significant loss of valuable coals to the tailings. In the previous project C23039, several techniques were developed to quantify the degree of coal oxidation, and a relationship between the degree of coal oxidation and the flotation performance was identified. In addition, a new reagent system was developed to float the oxidized coals. Following the previous project, this project was developed to transfer these technologies to the full scale plant operation. This includes the implementation of the oxidation monitoring tools in the plant, the correlation of plant flotation performance with the degree of coal oxidation, and the trial of the new reagent system in the plant to improve the oxidized coal flotation.
In this project, two oxidation measurement tools, UV/Vis measurement and Dissolved oxygen (DO) demand test, were implemented in two plants processing oxidized coals. It was found that the UV/Vis measurement was accurate for all different types of coals, while the DO demand method was less accurate especially when measuring high-ash coals. As a result, the UV/Vis measurement was selected to monitor the coal oxidation during the plant trial.
Plant surveys were conducted to measure the degree of coal oxidation on a large number of different feed samples, and the degree of coal oxidation was well correlated with plant flotation performance. The results show a general trend that combustible recovery decreases sharply with the increase of the degree of coal oxidation, and a critical oxidation degree occurs, below which the flotation recovery became nearly zero. These results will help the plants predict their plant coal flotation performance based on the degree of coal oxidation and then better manage their plant operation.
A polar collector identified in the previous project was trialled at a full scale plant in Central Queensland, where the degree of coal oxidation of the flotation feed was monitored throughout the trial. In addition, the froth properties were monitored online by installing a froth camera on top of a flotation cell, which significantly improved the efficiency of the plant trial and the accuracy of data analysis. Statistical design and analysis using paired t-test were adopted and more than 100 tests were conducted to obtain statistically confident results. The polar collector dosages from 40 g/t to 160 g/t were trialled. It was found that 80 g/t provided the best overall improvement. The average combustible recovery increased from 35.2% to 44.0% with a 99.9% confidence level.