1172
ZND USTRIAL AND ENGINEERING CHEMISTRY
Vol. 21, No. 12
Sulfuric Acid Plant, Anaconda Reduction Works
Manufacture of High-Analysis Phosphates* E. L. Larison ANACONDA COPPERMINIBGCOMPANY, ANACONDA, MONT.
Occurrence and Mining of Phosphate Rock HOSPHATE rock in commercial grade and quantity is known to exist, though not in continuous beds, all the way from central Utah t,o the Canadian boundary and also into Canada. Utah, Idaho, Wyoming, and Montana are the four states containing the really extensive deposits. At Conda in southeastern Idaho, the Anaconda Company several years ago acquired claims in which lie extensive beds of phosphate rock. Conda is located about nine miles from Soda Springs, a station on the main line of the Oregon Short Line Railroad, and is served by a standard-gage connection with that point. Unlike the large deposits of phosphate rock in Florida and Tennessee, the western deposits resemble fissure veins. At Conda, for example, the rock exists as a vein from 6 to 9 feet thick extending through an eroded anticline, a hill several hundred feet higher than the surrounding country. The bed has been tilted to angles from about 50 to 90 degrees from the horizontal, and its outcrop can be followed for several miles. The bed has been attacked by driving adits substantially along its strike, entering the hill a t the base near the mill site. Raises from these adits are driven and from them sublevels. The rock is stoped and drawn down through chutes into pockets above the haulage way and from them into 10ton cars drawn by storage battery locomotives. The rock lies between a wall of limestone on one side and of shale and clay on the other. I n mining there is some slight admixture of the wall material. The rock proper contains up to 75 per cent B.P.L., but as actually delivered to the mill averages nearer 70 per cent. As the rock is rather soft and the region is one of considerable rain and snow fall, it contains from 4 t o 6 per cent moisture as it comes from the mine.
P
Crushing and Drying Phosphate Rock A mill is provided a t the mine for crushing and drying the rock. It includes a receiving bin for rock as mined, a gyra1 Presented by E. I ,. Larison and R. J. Caro before the Division of Fertilizer Chemistry at the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 to 13, 1929.
tory crusher, rolls, and a vibrating screen. This train reduces it to pass 3/4-in~hmesh. Drying is accomplished in a Ruggles Coles rotary drier with coal fire. This dries the rock to under 1 per cent moisture. From the drier the rock is elevated and distributed to storage bins of a total capacity of 4000 short tons. An analysis of the dried rock follows: P906 HzO CaO FezOs AlzOa Si01
F
P e r cent 32.00 1.0 44.20 0.53 1.20 5.60 1.10
cr
V Ignition loss
P e r cent 0.47 0.42 0.14 n -. 71 . 0.05 0.09 7.20
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It is interesting to note that for each ton of material mined about 0.90 to 0.94 ton of dry rock is produced. I n the southern deposits it is not unusual to mine from 10 to 15 tons of material for each ton of dry rock produced. Of course, the cost of mining by underground methods is much higher per ton of material mined than in the open pits of the south, so that the costs per ton of dry rock produced are not far apart in the two places. Rock from the storage bins is drawn to standard railroad cars for shipment. The rail haul from Conda, Idaho, to Anaconda, hlont., is about 300 miles. Flow Sheet of Manufacturing Plant Sulfuric acid is manufactured a t Anaconda from gases which are by-products of the ore-reduction processes. This acid is used t o render the PzOsin the rock soluble and available. The plant consists of the following apparatus: (1) rock-receiving bins and sulfuric acid storage, (2) rock-calcining furnaces, (3) ball mills for grinding rock, (4) electrically vibrated screens, ( 5 ) Pachuca agitating tanks, (6) continuous countercurrent decantation system, (7) continuous vacuum filters, (8) vacuum evaporators, (9) pan mixer for acidulating rock with phosphoric acid, (10) wet storage shed, (11).driers, (12) grinding machine with screens, and (13) dry storage and loading building. The quantities involved are about as follows per ton of rock charged to agitators:
INDUSTRIA I, A N D ENGINEERINC CHEMI8TRY
Ileceinber, 1929
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Rrrr rock i n
60- HE. sliifliiic &
