Froth Flotation (Sulphide & Oxide)

Froth Flotation (Sulphide & Oxide)2017-04-04T06:57:31-04:00
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Floatation of ultrafine coal (1 reply)

3 years ago
cameron 3 years ago

The existing mechanical floatation cells treat fine coal particles(<500 micron).it recovers clean coal using air bubbles by utilising the difference in hydrophobicity of coal and ash. Uniform distribution of fine ash particles on the surface of coal particles makes its recovery difficult. How can we reduce this effect by changing the design of the existing floatation cells. ( Like microbubbles and increasing the residence time) or making of a customised reagent by blending different reagents

3 years ago
swadhinsaurabh 3 years ago
1 like by David

Hi Cameron,

People used to float -0.5mm coal in flotation cells in 1960s,70s and 80s, but now they have switched to -0.25mm flotation. It is recommended that maximum size particle that you try to float be 0.3mm. The reason is that 0.5mmx0.25mm flotation requires more residence time than 0.25mmx0 flotation. You can float both size fractions in one cell and can get the desired product, but it becomes difficult to maintain both the product yield and ash on a consistent basis in a real plant operation. If you float both size fractions in the same cell, the 0.25mmx0 will float quickly (requires less residence time) and 0.5mmx0.25mm will float slowly (requires more residence time). You will have 2 situations that can happen in flotation:

1. If you have high retention time in flotation cell, you may start obtaining 0.5x0.25mm flotation low ash product in the last cell, but by that time you will start floating 0.25mmx0 raw coal (because of more than required retention time of 0.25mmx0 size fractions). This will increase the desired flotation product ash and to maintain the overall product ash, you will cut at lower D50 in the DMC and lose more coarse clean coal to reject. Overall plant yield will be lower.

2. If you have low retention time (say 4-5 min) in the flotation cells, you will obtain low ash product for 0.25mmx0 size fractions but since the residence time is not enough to float 0.5mmx0.25mm, this coarse size fractions will not float and will report to the tailings. You will lose 0.5mmx0.25mm into tailings and the overall plant yield will be lower.

2 solution options:

1. Take the -0.5mm raw coal and classify that size fractions into 0.5mmx0.25mm and 0.25mmx0 size fractions and put both the fractions in separate flotation cells. The coarser size fractions will have high retention time and the finer will be low retention time. 

2. Most recommended option- Classify the -0.5mm size fractions into 0.5mmx0.25mm and 0.25mmx0 size fractions and put only the 0.25mmx0 into flotation with low residence time, and put the 0.5mmx0.25mm in a gravity based separation circuit such as Reflux Classifier or Teeter Bed Separator or Spiral Concentrator. Based on the washabilty characteristics, one of these three options will be selected. This will reduce your flotation reagent consumption tremendously. Using equal incremental ash method you can optimize the circuit by separating at lower SG50 in 0.5mmx0.25mm fraction and separating higher SG50 in DMC. The D50 cut points will be determined by simulation. This will not only reduce your operating cost, but also optimize the circuit by increasing the overall clean coal yield.

If you have any question, please let me know.

Swadhin Saurabh

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