FIELD OF THE INVENTION
The present invention relates to a method of improvement of yield of flotation by using innovative grinding method. More particularly, the invention relates to a shear-crushing based process for effective separation of inferior coal from mineral materials.
BACKGROUND OF THE INVENTION
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing. In the coal beneficiation circuit the fine particles (less than 0.5 mm) are sent to flotation circuit. Fine coal beneficiation is important in deciding the overall clean coal yield in any coal washery. Of different methods flotation is the most versatile process capable of treating the entire size range of fines.. In froth flotation the coal becomes hydrophobic (due to addition of different collector) and is separated from the mineral matter using air bubbles. A chemically stable froth is produced owing to the addition of a frother. For improved efficiency of flotation process the surface properties of coal particles are very important.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose a process for improving the efficiency of flotation of inferior coal.
Another object of this invention is to propose a shear-crushing based process for effective separation of inferior coal from mineral materials.

SUMMARY OF THE INVENTION
This invention is to improvement of efficiency of flotation of middling from captive mines of Tata Steel. To achieve this, a specific crushing method based on shear has been developed. This investigation revealed that when the middling is crushed by shear method and then subjected to flotation the efficiency of the process get improved in terms of yield and ash.
The present invention introduces new concept of crushing by shear. In this method the inferior coal is crushed by shearing instead of conventional impact method. Shear crushing enable more reactivity on the surface hence make it convenient for beneficiation compared to the conventional method.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIGURE 1 Shows a schematic of flotation study of the yields of the process of present invention vis-à-vis the yield of prior art process.
Figure 2 Shows a result of the column floatation of the prior art yield as well as the yield of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Materials: Middling coal sample has been taken from one of the captive mine. The properties of the sample presented in Table 1.
Crushing and Grinding: From 100 kg as received middling 10-20 kg was taken by coning quadrating method. It is divided in two parts. One part is crushed in conventional ball mill. Another part is crushed in shear crusher. In both the cases, the sample is crushed in such a way that 100% should pass through 0.5 mm sieve. Ball mill follows an impact crushing where the middlings break randomly. A portion of – 0.5mm screened iron ore crushed

under shear. In this crushing, the middling is kept inside two plates in which one is fixed and another is rotating at a desired rpm (50-70 rpm). The arrangement is horizontal. Once the middling is crushed by the rotation of the plate it is taken out. In both cases, characterization of product conducted. The products are then subjected to flotation study. The whole scheme of experiment is presented in figure 1.
Characterization of the samples: Products from two different crushing scheme has been characterized for the ash and VM.
Ash determination: Ash is determined by following ASTM standard D 3174-11. 1 gm of 250 mm size sample is taken to a weighed capsule. Then the sample is placed in a cold muffle furnace and heated gradually at such a rate that the temperature reached 4500C to 5000C by 1 hr. At the end of the 2 hr it will reach 9500C. After cooling the weight of the sample then measured and ash is calculated by weight difference.
VM determination: Ash is determined by following ASTM standard D 3175-11. In this test 1 gm of 250 mm size sample is taken in a covered platinum crucible and heated in a furnace of 9500C for 7 min. The VM is calculated by weight difference.
Crucible swelling number: Crucible swelling number test has been done by following ASTM D720-91 (2010). In which 1 gm of sample (-0.212 mm size) is taken in a translucent squat shaped silica crucible and the sample is leveled by tapping the crucible 12 times. The crucible is covered with a lid and heated under standard conditions, either by a special type of gas burner or muffle furnace. After the test the shape of coke button is compared with a standard chart and accordingly, the crucible swelling number (0 to 9) is assigned to the coal sample.

Petrography of coal: This is done by following ASTM standard D2797M-11a, D2798-11 a and D 2799-1. For microscopic studies 5 kg coke sample is crushed to minus 3 mm size and by using coning and quartering method, 100 gm sample is prepared and mounted on carnauba wax. The mounted sample is polished using silicon carbide coated grinding papers of 320, 400, 600 grids respectively, followed by buffing on a blazer cloth using alumina polishing compounds (1.0 and 0.3 mm). The polished specimen is dried using an air dryer prior to microscopic studies. The microscopic studies were done by Leica DMS 4000 microscope along with QW in software.
Flotation study: Flotation study is done in a lab flotation cell of 2.5 lit capacity. 250 gm sample (10% solid capacity) is taken for 1 batch. Synthetic collector and frother used for this study. The dosage of the frother and collector are 15 gm/t and 150 gm/t respectively. Air velocity is maintained at 4 lpm.
Results:
Table 1 presents the properties of original middling sample, sample crushed in ball mill and shear crusher respectively.
Table-1:


From Table 1 , it is evident that when the middling sample crushed by shear crushing, the reactive maceral percentage increases. During shearing, the major breakage of coal macerals and minerals place by attrition. Due to the attrition the liberation of reactive macerals are better. These two products are then subjected to the flotation study. The few terms related to flotation is described below:

The results of column flotation is presented in the figure 2. It is evident from the result that the sample which crushed by the shear method is giving better yield and ash, and hence the separation efficiency get improved.

WE CLAIM :
1. A shear-crushing based process for effective separation of inferior coal from mineral materials wherein the coal is crushed below 0.5 mm size in a horizontal crushing device having at least one fixed plate and a rotary plate rotating at a desired speed, and wherein the coal is interposed between the plates.
2. A process as claimed in claim 1, wherein the efficiency of flotation of the crushed coal is improved.
3. The process as claimed in claim 1 or claim 2, wherein the yield of the flotation product of coal is improved.
4. The process as claimed in claim 1 wherein the original coal sample contain around 33% of ash.
5. The process as claimed in claim 1 wherein the ash percentage of flotation product of the crushed coal is improved.

6. The process as claimed in claim 1 wherein after shear crushing of the coal there is enhancement in reactive macerals compared to conventional crushing method.
7. The process as claimed in claim 1 wherein a flotation study is conducted in a flotation cell.