Coal Preparation

Ultimate Froth Flotation Performance Test

Coal Preparation » Fine Coal

Published: March 08Project Number: C14068

Get ReportAuthor: Michael Campbell, Noel Lambert | ACIRL, TUNRA Clean Coal

This report describes the development of a new reliable method for determining the ultimate flotation response for 0 to 500 µm higher rank coals.  The method evolved from continuous development of laboratory flotation tests that were then compared to the “Standard” methods. By continuous evaluation of results and observation, the method evolved to the 16th and final method. This was found to be robust and to equal or outperform all “Standard” methods on all coal types tested.

The “Standard” methods were the current Australian Standard froth flotation AS 4156.2.21998, the International Standard for hard coal froth flotation testing ISO 88583 and another new froth flotation method developed in ACARP project C10044.

Four coal samples of different types and from various regions of Australia were tested. The 1st a high coal ash, high slimes contaminated sample from the Hunter Valley (identified as HV) with a feed ash of 72(%, d). The 2nd a low coal ash, high slimes contamination sample from the Bowen basin region (identified as BB) with a feed ash of 37(%, d). The 3rd , an intermediate coal ash, intermediate slimes contamination sample from the NewcastleLake Macquarie area (identified as NLM) with a feed ash of 35 (%, d) The 4th, a low ash, low slimes contaminated sample from the Illawarra region (identified as I) with a feed ash of 15 (%, d).

The Australian standard method for froth flotation AS 4156.2.21998 uses a series of refloats to remove the slimes contamination from the concentrates. This method performed poorly on the high ash feed samples due to large amounts of slimes contamination of the products, but it did perform well on the Illawarra region (I) sample. The current AS 4156.2.21998 gives little operator guidance. This results in the possibility of numerous and highly variable methods all of which may comply with the published procedure. The C14068 UFT froth flotation test method is a very precise method with very limited operator interpretation.

The International Standard ISO 88583 for froth flotation testing of hard coal was only trialled on the Hunter Valley (HV) sample and the results were extremely poor when compared to the other methods. Due to this poor performance, no further tests using ISO 88583 were conducted.

The method developed in ACARP Project C10044 gave good ultimate flotation response curves for the high slimes contaminated coal samples, but performed poorly on the low slimes contamination sample. The best results using this method however were achieved when the sample was initially sized at 106µm and the coarse and fine fractions floated separately.

The new C14068 UFT method uses a laboratory sizing at 106 micron to perform a perfect desliming step so that at least the portion of material larger than 106 micron is known to be completely free of slimes. This is analogous to the C10044 method where washwater is used for desliming. The advantage of a sizing step in conjunction with the flotation separation is that it guarantees the removal of slimes from the coarse concentrate material allowing these fractions to now be considered completely free of contamination. An ultimate flotation response, as the name suggests, requires the perfect separation of all components. Washwater is an imperfect desliming step.

The C14068 UFT method has tight controls over reagent dose rates and types, apparatus setup, air rates, desliming / sizing procedures and uses a transparent flotation cell. These tight controls and a step by step methodology ensure that the flotation procedure is more likely to be robust and repeatable.

Further statistical validation of the method however would be required before it can gain industry wide acceptance and possible documented Australian Standard status.


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