Coal Preparation » Fine Coal
The major objectives of this project were to develop a technique for measurement of residual frother in plant streams and to determine the mechanisms by which residual frother is adsorbed and transported through the plant circuits.
The current trend in coal flotation is towards installation of the newer, high intensity, column-style flotation cells, typified by the Microcel and Jameson Cell, for the combined treatment of the full fines fraction. Considerable test work and plant experience to date has shown that, in order to maximise efficiency with these deeper froths, the Microcels and Jameson Cells require higher levels of frother than the conventional flotation circuits (ACARP Project C5050). Since the plant water circuits are fully integrated, the residual frother levels compromise the performance of other parts of the circuit, in particular the dense medium circuit and density gauges, sumps, pumps, and the thickener and clarifier.
The operating philosophies (with respect to frother dosing) for the Jameson Cells at BHP Coal Goonyella and Riverside preparation plants, where test work for a previous ACARP Project C5050 was conducted, are discussed. These show how the plants are constrained by excess or residual frother depending on how their various circuits are integrated.
A simple, standard test that is suitable for use in the plant environment was developed to estimate the concentration of frother in plant water and slurry streams. The technique is based on the measurement of the height of froth formed in the slurry, which is related to the amount of residual frother that it contains. Initial attempts to use a household blender as the test vessel failed due to the lack of reproducibility. The use of a Denver laboratory flotation machine was more successful, as it allowed greater control over the aeration and agitation of the slurry. Test work at Riverside clearly showed that the froth test was able to identify realistic MIBC concentrations in plant streams with changes in both feed type and frother addition. The results indicated a 1 to 2 hour plant response to changing the frother dosage, which correlated with the estimated residence times of the plant circuits.
Early test work indicated that there was significant adsorption of MIBC by fine coal solids. Laboratory trials were conducted jointly with the flotation group from the CSIRO Division of Energy Technology to measure the adsorption rate of MIBC. This work indicated that up to 80% of the MIBC is adsorbed onto the coal (removed from the liquid phase) within 10-15 minutes in a stirred environment. The adsorption rate was observed to be much slower without agitation. When the solids from the adsorption study were removed (by centrifugation) from the slurries and re-mixed with fresh water, analysis of the resultant solutions indicated that no desorption of MIBC from the coal occurred.
A program was undertaken jointly with the flotation group from the CSIRO Division of Energy Technology to better understand the partitioning of frother in a pilot scale Jameson Cell at their Catherine Hill Bay pilot plant facility. The detection of less MIBC in the concentrate and tailings streams together was evidence that a significant amount of frother is removed from the liquid phase via adsorption by the coal solids.