Pilot Plant Beneficiation Studies On a Low Grade Mixed Apatite Sample From Singhbhum District, Bihar

Abstract

Four samples of low grade apatite , each weighing about 20 tonnes and drawn from different localities of Singhbhum District, Bihar were received from the Bihar Government for beneficiation studies in National Metallurgical Laboratory and recommendation of a flowsheet for production of a concentrate suitable for manufacture of superphosphate. A composite sample, prepared by mixing four samples in the proportions specified by the Bihar Government, assayed 17.34% P2O5 with 25% total oxides. Microscopic examination revealed that the mixed sample contained about 40% apatite, 12% magnetite, the rest comprising quartz, feldspar, chlorite, biotite and other ferromagnesium minerals. The average grain size of apatite is relatively coarse as compared to the other minerals and is liberated at about 65 mesh. Batch tests indicated that-(1) the optimum grind for floatation is 63% -200 mesh,(2) 0.69 Kg/tonne of sodium silicate and 0.5 Kg/tonne sodium silicate are required to get a clean concentrate with good recovery of appetite.(3)conditioning and floatation times are 11 minutes and 4 ½ minutes respectively.(4) magnetic separation followed by flotation of the non-magnetic fraction produced better grade of concentrate than that obtained by straight floatation. Two continuous tests on a pilot scale were run. Test I employed magnetic separation of the classifier overflow followed by floatation whereas Test II employed straight floatation of the classifier overall. The former produced a final concentrate constituting 28.7% by weight of feed and assaying 41.6% P2O5 with less than 4% total oxides and with a recovery of 79.6% P2O5 .This meets the specifications laid down by the Bihar Government. The recovery of phosphate could be appreciably improved to 90-97 % if a final concentrate assaying about 5% total oxides is acceptable to the manufacturers of Superphosphate. Side by side with the production of an apatite concentrate, a magnetic concentrate constituting 8% by weight of the mill feed and assaying about 63% Fe could also be produced as a by-product after one cleaning. This can perhaps find a ready market in the coal washers employing heavy media. Straight flotation did not produce the desired grade of concentrate even after one cleaning. From the Pilot Plant test results, it could be concluded that the low grade apatite sample of Singhbhum District, Bihar, can easily be upgrade to produce an apatite concentrate suitable for manufacture of superphosphate and a magnetic concentrate, having a market value of Rs. 30/- per tonne, required by coal washeries employing heavy media. A flowsheet is recommended for upgrading this sample and a list of machinery for upgrading 150 tonnes per day of the apatite ore is included in the Report.