APPLICATION OF THE PROCESS
A large number of trials, both on a small scale and with a full-sized apparatus, have been conducted on a great variety of ores, but it is not claimed that the process and plant are applicable to all ores, although its scope of application is wide.
The process has been applied with success to the concentration of ores which, because of their peculiar characteristics, are quite impossible of concentration by usual methods. For instance, chalcopyrite is readily separated from magnetite and spathic iron gangue ; galena and zinc blende from a gangue of barite ; and copper sulphides from oxide of tin, leaving the tin in the tailing to be subsequently separated by the usual methods. Zinc, copper; and lead minerals may be separated from garnet and similar heavy gangue ; and such minerals as antimony or molybdenum sulphides which, because of their friable nature, suffer prohibitive losses in water concentration, are found amenable to treatment by the Elmore process. Cinnabar and iron pyrite carrying gold are readily concentrated, yielding high-grade products with practically clean tailing. The native metals, gold, silver, and copper, when in a fine state of division, are said to concentrate readily and with very small loss.
Continuous working has shown that the plant is eminently practical ; no delicate adjustments are required, wear and tear is to all intents a negligible quantity, and the excellent mechanical design and substantial construction of the apparatus have made breakages almost unknown.
DOLCOATH, CORNWALL.* In certain parts of this mine the ordinary tin ore of Cornwall is found impregnated with varying proportions of sulphides, principally of copper. This ore is crushed in an Edgar Allen ball-mill, and passed direct to one Elmore vacuum unit. By this operation almost the whole of the sulphides are recovered as a high-grade copper concentrate, which is saleable as such. This concentrate contains a remarkably small proportion of tin, on the average probably not exceeding 2 to 3 Ib. of tin per ton of concentrate. Substantially, the whole of the tin oxide is left in the tailing from the vacuum unit. The tailing is subsequently treated by Frue vanners, etc., in the ordinary way for the recovery of the tin oxide. The oil and acid used in no way injuriously affect the subsequent recovery of the tin. This plant was supplied to the Dolcoath company in March, 1907, and yielded highly satisfactory results for some time, giving an extraction of over 90% of the copper contents, but the plant is not now in use.
RAMSLEY MINE, DEVONSHIRE. Here the ore consists of a mixture of chalcopyrite and bornite with some chalcocite in a slaty micaceous gangue. The average grade of the crude ore is about 2|% copper. It is crushed in stone-breakers, high-speed rolls, and a Huntington mill in the usual way, the pulp being sent direct to one unit of Elmore plant. On the average the concentrate produced assays about 12% copper.
DOLGELLY MINE, NORTH WALES. The ore consists of chalcopyrite with varying proportions of iron pyrite in a schistose gangue. The grade of the ore is usually about 1.2% copper, o.oSoz. gold, and o.8oz. silver per ton. The ore is crushed by a reciprocating stone-breaker, followed by a 20-head Californian stampbattery (i,o5olb.), through 6-mesh screens. The pulp from the battery is sized on a i6-mesh screen, and the oversize re-crushed in a grinding pan. The pulp is then sent direct to 3 Elmore units, and yields a concentrate of about 12% copper, o.7oz. gold, and 7oz. silver per ton, the tailing assaying about 0.25% copper, with very small amounts of gold and silver. Prior to the installation of the vacuum plant, much money had been spent at this mine on various forms of water-concentration machines ; but, owing to the extreme softness of the copper mineral and the unusually tough character of the rock, the loss of fine material was always prohibitive.
ZINC CORPORATION.* The material treated here was a zinc tailing from the lead-concentration plants. The gangue consists largely of quartz, garnet, and rhodonite, being of practically the same specific gravity as the blende with which it is associated ; hence no separation by ordinary water- concentration was possible. Much of the tailing on the dump was already fine enough for direct treatment in the Elmore plant ; that portion that was too coarse was crushed in 12 grinding pans, sized on improved revolving screens, the oversize being re-crushed in six additional grinding pans. The average assay of the material treated in this plant was about 19% zinc, 5% lead, and 8oz. silver per ton. This yielded a concentrate assaying on the average about 43% zinc, 11% lead, and lyoz. silver per ton. It was found that, if this concentrate was dried and subjected to a sufficiently high temperature to expel the small quantity of oil which it contained, the de-oiled concentrate could then be mixed with water and passed over Wilfley tables, yielding a zinc product assaying 46% zinc, 6.1% lead, and I3oz. silver per ton, and a lead concentrate assaying about 57% lead, 16% zinc, and 37oz. silver per ton. The assay of the final residue depended, to a great extent, upon the more or less oxidized condition of the mineral, much of the material on these dumps having been exposed to atmospheric oxidation for many years ; but the following may be taken as fairly representative : Zinc, 5.90% ; lead, 2.5% ; and silver, 4oz. per ton.
Fig. 33 gives a condensed flow-sheet of the arrangement of this mill, including crushing, sizing, flotation, and re-treatment on Wilfley tables. The plant contained 16 units, and was installed only after exhaustive trials had been conducted with one unit. The mill was in continuous operation for two years, and gave a higher capacity, better grade of concentrate, and greater percentage of extraction than was indicated by the trials with the one-unit plant.
The following table gives the total tonnage treated from the beginning of February, 1908, to the end of July, 1911, inclusive, with the results :
The Elmore process has now been discarded for reasons before given, and the Minerals Separation process installed in its place.
EDMUNDIAN COPPER MINE. The ore at this mine in South Africa consists of chalcopyrite finely disseminated through a felspathic gangue. It is crushed by stone-breakers and Holman pneumatic stamps, and passes direct to a two-unit Elmore plant. The ore assays on the average about 2.5%, and yields a concentrate assaying about 22.5%, with a recovery of 85%.
GARPENSBERG MINE, SWEDEN. The ore consists of a quartzitic gangue with some magnetite carrying chalcopyrite and iron pyrite. The ore, although fairly heavily mineralized with iron pyrite, is of low grade, assaying on the average about i% copper. The crushing plant consists of a stone-breaker, followed by rolls, the product going to jigs and tables in the ordinary way. The fine tailing, together with the jig tailing after re-crushing in wet ball-mills, is treated in the vacuum machines. One unit of plant was tried first ; later two more were installed, but the plant is now closed.
TRAAG MINE, NORWAY. The ore carries both zinc and lead associated with a heavy gangue. After crushing in stone-breakers and in an Allis-Chalmers Anaconda-type Huntington mill, the pulp is treated on Wilfley tables for the production of a lead concentrate. The tailing from the Wilfley table is passed to a one-unit Elmore plant, which yields a concentrate assaying on the average 58% zinc. The zinc sulphide in the ore is present in the form of a very friable resin blende, and, in consequence of excessive sliming, coupled with heavy gangue, could not be collected by any ordinary water concentration appliances. This plant has now ceased working.
HADELAND MINE, NORWAY. The ore consists of blende associated with a large proportion of magnetite and some spathic iron. Trials with various water-concentration appliances had all proved unsatisfactory. The ore is crushed in Krupp ball-mills, and sent direct to the Elmore plant. It yields a high-grade concentrate with a satisfactory extraction. The company, after having operated the one-unit plant for about six months, has ordered additional units.
TELEMARKEN MINE, NORWAY. The ore consists of chalcopyrite and bornite in a gangue composed of hornblende, micaceous schist, and hard quartz. The crude ore from the mine is handsorted with a view to rejecting some of the waste. The ore thus enriched assays on the average about 4.5% copper. It is crushed in a No. 5 Gates crusher, followed by Ferraris wet ball-mills. The pulp is sent direct to a three-unit Elmore plant, from which a concentrate assaying about 26% copper is obtained, the final tailing containing only 0.20%, thus giving a recovery of about 95% of the total content. Fig. 34 shows a section of the vacuum plant, and Fig. 35 a flow-sheet of the plant at this mine.
SULITELMA MINE, NORWAY. The ore carries copper in the form of chalcopyrite associated with a large proportion of iron pyrite, the gangue being micaceous schist. As the ore comes from the mine it is crushed in large stone-breakers, and carefully hand-sorted with a view to selecting clean lump pyrite, which is sold to sulphuric acid works for its sulphur content, the burnt ore being subsequently treated for its copper content. The lowgrade ore left after hand-sorting is crushed in rolls and passed to jigs, tables, and vanners. This water-concentration plant is of first-class design, operated with good labour and under excellent technical supervision and control. Nevertheless, the loss of copper in the tailing is heavy owing to the friable nature of the copper pyrite. The residue from this water-concentration plant varies in grade from i to ij% copper, with a quite considerable proportion of iron pyrite and some magnetite. The concentration mill handles about 800 to 900 tons a day, and produces about 500 to 600 tons a day of tailing. This tailing is in the form of an unusually dilute pulp, the proportion of water to solid being probably 100 to i. At the present time about 400 tons of solid per day with the above proportion of water is sent to the 12-unit Elmore plant for the recovery of the copper mineral. Arrangements are being made which will enable the whole of the 500 to 600 tons of tailing from the water-concentration plant to be sent to the Elmore plant. The small part of the tailing, which is too coarse for treatment direct in the Elmore process, is re-crushed by Heberle ball-mills. The pulp, which, as before stated, is associated with an immense amount of water, is run into large settling-tanks with a view to getting rid of the excess of water before treatment in the Elmore plant. Concentrate varying from 6% up to n% of copper (the grade depending upon the proportion of iron pyrite) is produced. The final tailing assays on the average 0.2% copper. The great bulk of the material handled by the vacuum machines consists of absolute slime. An average of about 250 tons of concentrate per week is produced from waste material which had previously been discharged direct to the tailing dump. Six additional machines have been delivered to this firm, and will shortly be erected at one of their other mines.
SAXBERGET MINE, SWEDEN. The ore here is a mixed zinc-leadsilver material, which, after crushing in stone-breakers and wet Grondal ball-mills, is treated on tables for the recovery of the lead. The lead recovery, however, is not good, and consequently the tailing from the tables contain notable proportions of lead and silver in addition to the zinc. Various attempts had been made previously to treat the tailing without success. The Elmore plant produced a mixed lead-zinc-silver concentrate, which was subsequently smelted in an electrical furnace. Its use has been discontinued and a Minerals Separation plant of 125 tons per day capacity is at present in operation. Other Elmore plants have been installed in several places, but data as to results are not available.
