Utah Copper Leaching Plant, 1917-1921
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Ogden Standard, February 12, 1917
The following comes from Ogden Standard, February 12, 1917:
The leaching plant is located on the hillside about 1,200 feet in a southeasterly direction from the Magna plant, with the floor of the leaching tanks at an elevation of about seventy feet above the track on the Magna plant coarse bins. It will consist of a crushing plant, a series of leaching tanks, a pumping plant for handling the leaching solutions, a water service plant for furnishing the amount of water required, tanks for storage of sulphuric acid, a precipitation plant and a substation for distributing the power required.
The crushing plant, with grizzlies and feeders in the receiving bin, is designed along the same lines as the coarse crushing plants in operation at the Magna and Arthur mills, and the method of crushing and handling the ore through the crushers and rolls is practically the same as the one used at the two mills. After the ore, which contains copper in the form of carbonates, has been crushed to the one-half inch mesh it will be transported to the filling bridge at the leaching tanks by a belt conveyor. This conveyor is 700 feet long, forty-two inches wide and has a capacity of 500 tons per hour. At the filling bridge the conveyor belt passes over a detachable tripper and is carried out on the filling bridge conveyor. The filling bridge runs on top of the leaching vat wall and the belt conveyor on the bridge is provided with a self-propelling tripper, thereby making it possible, in combination with the movement of the bridge, to distribute the ore at any point in the leaching tanks. the arrangements are such that the filling bridge can be used to serve any future additions to the leaching tanks.
The discharging bridge will run on tracks that will be constructed alongside the leaching tanks for that purpose. It will be furnished with a gram bucket, suspended under a light trolley, and when the bucket, has been filled it will travel over to a hopper, into which it will discharge the tailings. The hopper will be provided with mechanism so that either one of two lines of care under same can be loaded. This bridge can also be used if the plant is ever extended to greater capacity. The discharging bridge will have a capacity of from 8,000 to 10,000 tons of tailings in two shifts per diem of eight hours each.
The first installation of leaching tanks will comprise twelve tanks, which will be built in two sections, each section to consist of six compartments, and each compartment will have a width of fifty feet, a length of 100 feet and a depth of eighteen feet. The foundations, the floors and the wells of the leaching tanks will be built of reinforced concrete, and the floors and walls will be lined on the inside with asphalt mastic to protect the concrete against the action of sulphuric acid in the leaching solution. Filter bottoms, consisting of lumber and cocoa matting, will be installed on the floors of these tanks. The capacity of each tank will be approximately 4,000 tons and about 290,000 gallons of solution will be required to fill the voids and cover the ore to a depth of six inches.
After the crushed carbonate ore is placed in the tanks it will be leached with a dilute solution of sulphuric acid, which will extract nearly all of the copper that occurs in the form of carbonates. The solution conduit system will consist of four rows of launders, running at the top of the leaching vats, and three pipe lines at the bottom of same. The launders are made or redwood, lead lined, and the pipes will be made of redwood, boiled in paraffins and machine banded with copper wire, and all fittings will be lead lined. The launders will carry the precipitation and wash solutions, and the pipe lines will be utilized for applying the upward percolation of the first leaching solution, the fresh water, as well as for draining the various compartments of the leaching vat. The pumping plant and the water service plant will have sufficient capacity to handle the solutions and the amount of fresh water required for the leaching plant when treating 4,000 tons of carbonate ore daily.
The precipitation plant will be located north of and below the leaching vats. The solutions will be drawn off from the vats and run into a storage tank having a capacity of twenty-four hours. From the storage tank the solution containing dissolved copper will be run through revolving drums charged with scrap iron, and it is expected that two of these drums will be sufficient to precipitate practically all of the copper. After leaving the drums the solution will carry the precipitated copper into a classifier, and from there the solution will run to a Dorr thickener and then overflow into a system of launders containing scrap iron, where the remainder of the copper will be removed. The precipitates will be loaded into cars and shipped to the smelter for treatment.
The capacity of the twelve compartments of the leaching tanks will be somewhere from 2,000 to 4,000 dry tons daily, depending upon the length of time required for one complete cycle of operation. However, it is hoped that the charging, leaching, washing and discharging can be done within a space of time that will give the twelve leaching plants a total capacity of 4,000 tons of carbonate ore daily. On the basis of amount of copper precipitated daily will be about 40,000 pounds. The site chosen for the plant will permit of at least doubling its capacity at some future time, if it seems desirable to do so. If the leaching capacity is doubled and if it should then prove more satisfactory to install an electrolytic precipitation plant, instead of doubling the iron precipitation plant, such a plant will be constructed. It is expected that this leaching plant will be ready for operation some time during the spring of 1917.
The year 1916 has been one of the greatest years in the history of the mine as to tonnage, copper produced and earnings. The company has handled 11,155,000 dry tons of ore, from which was extracted about 200,000,000 pounds of copper. For the year the company has paid a dividend of $12 per share on its 1,624,000 shares of outstanding stock, which amounted to $19,493,880. Total dividends paid to date are $52,216,777.50.
During the year the company sustained a severe loss in the death of Frank G. Janney, one of its most faithful officials. Mr. Janney had charge of all the milling operations of the company.
The officers of the company are: C. M. MacNeill, president; D. C. Jackling, first vice president and managing director; R. C. Gemmell, general manager; John M. Hayes, treasurer and assistant secretary, H. C. Goodrich, chief engineer; F. G. Janney, superintendent of mills; J. D. Shilling, superintendent of mines; C. F. Jennings, assistant purchasing agent; H. C. Smith and T. A. Janney, mill superintendents; R. H. Hawley, assistant mill superintendent, and J. D. Shillings, Jr., assistant superintendent of mines.
Utah Copper Enterprise, December 1918
The following comes from The Utah Copper Enterprise, published in 1919
THE LEACHING PLANT
The ore to be leached is the oxidized cap that is stripped from above the main mass of sulphide ore. It averages 0.65 per cent copper in the form of the carbonates (malachite and azurite) with a minute proportion of the silicate (chrysocolla), and contains an additional amount of copper, 0.1 to 0.2 per cent, in the form of chalcopyrite and chalcocite. The principle underlying the metallurgical process is borrowed from nature, for sulphuric acid, derived from the decomposition of sulphide mineral, is used to dissolve the copper, which is then precipitated upon scrap-iron. The plant has a capacity of 2000 tons of ore per day.
The railroad-cars, containing 64 dry tons each, are discharged over grizzlies made of I-beams covered with a mushroom top of manganese-steel. Pieces of ore too large for the openings, which are nine inches wide, are broken with sledge-hammers. The ore then falls on a second set of grizzly-bars, three inches apart, the oversize going to steel bins that discharge upon steel caterpillar-apron feeders delivering to 5-foot Stevens-Adamson pan-conveyors, by which it is discharged to screens, with one-inch openings, ahead of two gyrator crushers, No. 6 Gates, style K. From these crushers the ore passes to a belt-conveyor leading to a sizing-screen, inclined at 45 degrees, and made of 5/8-inch wire with 1-inch openings. The oversize from the screen goes to Garfield rolls, 72 by 20 inches, while the undersize passes direct to a hopper discharging upon the belt-conveyor that feeds the vats. The undersize from the 3-inch grizzly passes to another sizing-screen, similar to the one already described, from which the undersize falls upon the hopper discharging upon the belt-conveyor feeding the leaching-vats, while the oversize joins the crusher product on the conveyor ahead of the primary rolls. The product from these rolls is conveyed to a screen ahead of the secondary rolls, the oversize being returned by a conveyor after passing through the secondary rolls to the screen ahead of the primary rolls, while the undersize is delivered to the vats. The belt-conveyor carrying all the crushed ore discharges upon a 4-foot pan-conveyor provided with a transverse slot through which one part in 400 is removed as a head sample. This pan-conveyor delivers to a hopper that feeds a 42-inch rubber-belt conveyor discharging by means of a tripper traveling with a loading-bridge equipped with a Robins tripper-conveyor, discharging into and filling the leaching-vats. The product from the crushing department shows about 10 per cent coarser than half an inch, more than 40 per cent coarser than 3-mesh, and only 20 per cent finer than 20-mesh. About 39 per cent of the copper rests with the material between 1-inch size and 4-mesh. Evidently this is the critical point in the crushing; 58 per cent of the weight of the ore containing 48 per cent. of the copper in the ore has been separated at this stage.
The 12 leaching-vats are 100 feet long, 50 feet wide, and 171 feet deep. They are arranged in two contiguous groups of six each, so as to neutralize the expansion. They are made of concrete, heavily reinforced. The walls are lined with mastic.
The mastic is 11 inches thick and is reinforced with 2 by 2 by 0.162 inches diameter crimped wire. The floors of the vats are coated with mastic half an inch thick. Upon this floor come 6 by 6 inches stringers, spaced 10 inches apart, laid lengthwise of the vat. The stringers are 9 feet 6 inches long; their ends are beveled 3 inches, and they are 3 inches apart. Across them are placed wooden stringers 2 by 8 inches and 5/16-inch apart. On these is spread cocoa-matting 1/4-inch thick; then more 2 by 8 pieces, 5/16-inch apart, so that the two-by-eights lie across each other, separated by the mat.
Ample pumping-plant capacity has been provided for the transfer of the solution as required. The intention is to resort to a cyclic advance of solution. All the valves are of the disc-and-gate type, lined with lead, whereas the pipes are made of redwood staves that have been immersed in paraffins, wound with hard-drawn copper wire. When received from the Redwood Manufacturers Co. they are immersed in hot asphaltum paint. The cast-iron fittings and connections are lined with mastic.
When charging, the tripper-conveyor drops the ore at one side of the vat and continues to feed on the same side until the toe of the slope reaches the opposite side; then the filling re-commences from the opposite wall into the V-shaped space that has been left by the preceding operation. This is the method adopted at Chuquicamata.
METHOD OF FILLING THE TANKS
The idea is that the coarser particles of ore run to the bottom of the vat; if the filling were to advance continuously from one side, the coarse ore would extend up the opposite side, producing conditions unsuitable for the uniform percolation of the acid solution.
Fresh ore is fed into the vats in sequence, the freshest ore being subjected to the oldest solution, that is, the one containing the most copper and the least free acid. At the time of my visit, No. 5 vat was being emptied of its tailing, while No. 4 was being filled with fresh ore.
The solution is advanced at the rate of approximately 80 gallons per minute through the vats in series from 6 to 7-8-9-10-11-12-1-2-3. After all the solution in No. 6 has been advanced to No. 7, wash-water is added until the effluent from the tank contains from 0.08 to 0.15 per cent copper. The wash-water advancing in the cycle is gradually enriched with free acid and copper, the first addition of acid having been made to a selected number of the vats, No. 8, 9, and 10, in the cycle. From this point no more acid is added, the free acid being gradually neutralized by dissolving the copper, iron, aluminum, etc., content in the ore until the solution on the newest ore, or that last charged into the leaching-vats, contains 3.16 per cent copper, 0.37 per cent iron as ferrous, 0.95 per cent as ferric iron, and 0.24 per cent free sulphuric acid. The intention is not to add acid at any stage in such measure as to cause the proportion at the close to exceed 0.2 per cent. Thus, when the cycle of operations brings the solution to the fresh ore, the acidity is at its minimum and when the copper-bearing solution (the product of the leaching process) is drawn away from precipitation, it contains not more than 0.2 per cent free acid. To express the idea in another way, the acidity, or strength of the active solution, is brought to a peak in the middle of the series of operations, so that when it is applied to the new ore and likewise when it is withdrawn, enriched by 21 per cent copper, it contains not more than 0.2 per cent acid. The rich solution is drawn from the vat containing fresh ore, because, owing to the soluble components, it can neutralize the free acid quickest at this stage.
Ascending the stairway to the top level of the vats, I watched the solution (1.3 per cent. ferric, 0.3 per cent ferrous iron, with 2 per cent copper, and 2 per cent free acid) being circulated by an air-lift after withdrawal from the bottom of the same vat, to induce circulation. The yellowish green liquor was covered with a creamy foam, except where clear patches appeared indigo-blue, owing to the reflection of a perfect sky. As one proceeds to the end of the cycle, the solution circulating in each successive vat gradually changes in color from a greenish-straw to a greenish-blue color until finally the solution circulating on the freshest (or newest) ore is of a fairly clear blue color.
The explanation of this variation in coloring is that the percentage of ferric phosphate present gradually decreases, owing to its precipitation in the ore, as the free sulphuric acid present is neutralized in the cyclic advance. The ore contains 0.2 per cent, phosphorus, which evidently first goes into solution, and is then precipitated, the greater portion being eventually discharged in the tailing. Until the presence of phosphorus was noticed, it was thought the precipitate of cement copper was contaminated with basic ferric sulphate by reason of atmospheric oxidation occurring in the scrap-iron precipitation launders. Apparently this contamination is due to the presence of basic ferric phosphate instead.
From No. 5 vat the residue (tailing), after leaching had been completed, was being removed by a Mead-Morrison excavator, which has a 10-ton grab-bucket, enabling 4000 tons to be removed in an eight-hour shift The grab takes the tailing from the floor cleanly, planing any boards that rise above the general level. This excavator discharges into a hopper having a motor-controlled gate that empties into 45-ton Clark air-dump cars. The tailing shows only a trace of soluble copper, the greater loss being in undissolved sulphide. It would not be fair to quote the exact assay, because operations are still in the experimental stage.
Acid is obtained from the Garfield Chemical Co., five miles distant and adjoining the Garfield Smelting Co.'s (A. S. & R. Co.) plant. Fresh acid is added in the middle of the leaching advance. Very little (0.06 to 0.09 per cent) ferric sulphate passes from the precipitation vats. All of this solution is wasted.
The copper-bearing solution flows through wooden-stave pipes of 10 inches diameter to the precipitation vats. The first series consists of four rows of four mastic-lined vats, each 9-1/2 by 62-1/2 feet and 6 feet deep, made of reinforced concrete, the walls being 6 to 10 inches thick, with a suitable batter. The flow of the solution continues up and down the total length of 1000 feet. In the second series likewise, the flow is continuous through 27 wooden vats, 9 by 64 feet each, and 3 feet 7 inches deep, a total length of 1728 feet.
In the first vat (62-1/2 by 9-1/2 feet) of the first series are five barrels, 7 feet 4 inches diam. and 8 feet long, which are turned at the rate of two revolutions per minute. One of these is made of maple and four are made of fir. The wooden staves (4 by 8 in.) of the barrels are perforated with 5/8-inch holes placed 8 inches apart, permitting the solution to enter. The barrels are loaded with tin-cans and other small scrap-iron, which, as it becomes corroded by the solution and replaced by the copper, disintegrates. When small enough, the particles of iron, with the cement copper, escape from the barrel through the perforations into the vat. These products of the process are discharged by pulling a wooden plug in the bottom of the vat, from which the thin mud of cement copper and iron runs over a screen of 1-inch openings by which the coarser particles of undissolved iron are held. The same screen is used to clean up the residue from the other vats, and it serves to catch any leaf or plate copper that might interfere with the accurate sampling of the "cement", or copper mud. All the vats, except the first, are filled with scrap, the heavier pieces being placed in the concrete vats and the lighter ones in the wooden vats. When cleaning up, the solution is withdrawn through a hole in the bottom, and a hose is played on the scrap so that the water removes the cement, which runs into one of the four settling-vats covered with a screen. The wash-water is decanted and the copper precipitate is removed by a clam-shell excavator into cars that transport it to the drying-vats. The decanted water flows into another vat, 75 feet diameter and 12 feet deep, where any remaining particles of copper settle. To this vat comes the waste solution from the entire series of vats, in order to arrest any copper that otherwise would be lost.
At the south end of the leaching-vats are three shallow wooden vats, 65 by 70 feet, full of red clay apparently. That is the cement copper undergoing atmospheric drying, or evaporation of its excess water. The method seems ill-adapted to winter or to the rainy season. The yellowish green slime of basic ferric phosphate discolors the copper. The solution coming to the precipitation vats from the leaching-vats is vividly bluish-green, the color of copper sulphate mixed with ferrous and ferric sulphates.
The precipitation plant looks like a junk-store in chemical liquidation. One regrets that the scrap cannot be macerated or otherwise reduced to small and nearly uniform particles so as to expose a large surface to corrosion and precipitation. Sponge-iron is being tried for this purpose at Ajo successfully, but the use of it depends upon the cost of production.