Yes we have wide experience in flotation for the past 25 years in VEDANTA HZL for minerals. Coal flotation is a very simple process. We can do lab testing and pilot plant testing. Kindly send us sample. We will let you know chemical usage after testing is done.

Can you please give us a little more information on why you are looking at 'modifiers' for the coal float? Is it oxidised or low rank or is there some other reason you are looking to improve its floatability? The 'modifiers' you require will be different for different problems.

In our case we are not able to fully recover the "low ash clean coals” from the raw coal fines. Our raw coal fines generally have ash content ranging from 23- 28 %. Targeted clean coal ash after beneficiation through mechanical flotation cells is 11-12%. These raw coals are not oxidized but contain some high proportion of fine clay & stone particles. In the cells we are using synthetic collector & organic frother. Can a modifier be suggested to improve the recovery? In general is using modifier is a standard practice- if the coal is normal and not oxidized. Using modifier is adding up cost in the process but if the recovery improves then it will be desirable.

You may be putting the cart before the horse. The first thing you need is a proper flotation response analysis for the coal. That would include determination of the particle size distribution, size-by-size ash analysis of feed and products, a release analysis (ultimate flotation response), and a kinetics test. We do these routinely at our lab in Erie, PA (USA), and scale-up from this information to commercial scale for our columns are quite well understood and reliable. A properly designed and operated flotation column can operate within the ultimate flotation response curve by preventing entrainment of clays, and providing adequate conditions to achieve the required recovery. If you don't have this information, I would strongly suggest getting these analyses done before worrying about additional reagents/modifiers. These tests will reliably predict the best possible performance you can achieve. Assuming you are talking about an existing preparation plant, it is common for these to be over-capacity when feed rates, flow rates, and fine-ness of the feed increase over time. Once you are over capacity, you will find you might be able to make grade, but never recovery. Capacity is a function of the particle size and the equipment size if you have already reached maximum carrying capacity, changing the chemistry cannot help you anyway.

Your views are very useful. Capacity wise our flotation cells are not fully utilised. You are right that the raw coals need to be fully tested from floatability point of views before going for a new collector. However, I am looking for a response to understand that whether on top of an existing collector using additional modifier is a conventional practice. What is the difference in chemistry between collectors & modifiers which helps in coal flotation additionally?

Understood! This is not my specialty, and I haven't run into any other modifiers in use that I can recall.

We have done extensive tests on West Bokaro Coals of Tata Steel, with Clariant'sMontanol 800 reagent in combination with Diesel Oil. Test result indicates that it is possible to achieve 5-6% recovery improvement at same level of ash.

Similarly coal is different in different areas and needs different treatments. We have HMS system Flotation is a very sensitive and vast subject. It cannot work if you have not done de slime. It works only for fine crystals and not on sub-micron particles. You need to optimization for all parameters:

•Size of liberation,

•Wt% Solids,

•Optimism equipment requirement-Cyclone,

• HMS,

•Jameson cell,

•Jigging,

•Trflo separator etc.

It is a job of mineral engineer. You can take guidance form a mineral engineer for all future works. 

But my original query was that using modifier for coal flotation is (on top of collector) a regular practice elsewhere.

Though I expected that different coal beneficiation plants would like to share experiences.

I think you have said it all here; these raw coals are not oxidized but contain some high proportion of fine clay & stone particles.

So if you clean/separate the Raw Coal from the "Clay & Stone" the flotation plant will be able to do its job. We have ultrasonic processors that can clean up to 135 tons of slurry per hour and if that is not enough you can run them in series or parallel for higher out puts. Ultrasonic separation or just cleaning is very efficient and will strip away the clay etc, leaving the coal fines ready for flotation.