VAN METER AND BOSS.

James W. Van Meter and Martin P. Boss in 1902 invented an oil process, which was installed1 at the Santa Barbara mine and also by the Alpimina Mining Co., both in Peru. This process was similar to the Everson process and the old Elmore process in its main principles, but the apparatus was somewhat different. Though the published results were good, the process has disappeared from the field of concentration in consequence of further developments.

POTTER-DELPRAT.

Charles V. Potter in 1902 invented a process of mineral flotation wherein the flotation was accomplished in a I to 10% solution of acid. He added one ton of this solution to one ton of ore, agitated freely, and applied heat. As the temperature of the pulp increased, the heat caused the sulphides to rise to the surface, from which they were allowed to flow continuously or were skimmed off. Potter did not mention the use of any gas, but it is clear that he had in view a surface-tension process. In 1902 there had been rumours at Broken Hill 2 that a new process along radically new lines had been discovered at the Proprietary mine. This was especially interesting, as there were in the district several million tons of crushed material that had hitherto defied treatment. The rumour proved to be true, and later was announced as the Delprat or salt-cake process. The priority of patent, however, fell to Charles V. Potter, who had been working on similar lines to Guillaume D. Delprat. Potter used an acid liquor to effect flotation, while Delprat accomplished the same result in the same way with acid salt-cake solution. The effect of the acid or salt-cake is to generate bubbles of gas, which selectively adhere to the sulphides and float them. Potter and Delprat invented improvements from time to time subsequently, and their most recent patents indicate that the owners of these processes appreciate that a small quantity of oil is of decided advantage to flotation.

The Potter process received its chief application at the Block 14 mine at Broken Hill, in 1905 and 1906, where it had a measure of success on sharp sand, the attempt to treat slime being attended with many difficulties ; the plant is now dismantled. It was also tried at the Zinc Corporation's plant, where it was pronounced a failure. The Delprat process is installed at the Broken Hill Proprietary mine, where it is a decided success, and produces about 80,000 tons of zinc concentrate per year. This plant is the third largest flotation-concentration plant in the world, treating about 1,000 tons per day, and it is a pity that a policy of secrecy as to its later developments is thought necessary. The Potter and Delprat interests soon became involved in litigation, ending in a compromise, so that the process is now generally described as the Potter-Delprat.

FROMENT.

In 1901 Alcide Froment, of Traversella, Italy, discovered that when a sulphide ore is agitated in water in the presence of a small quantity of oil and sulphuric acid, the sulphide particles become oiled and attach themselves to and are floated by gas bubbles. He recommended adding a small amount of calcite to ores when needed. This discovery is of the greatest importance, as the successful development of oil-flotation processes has been based principally upon making use of the fact that oiled sulphide particles readily attach themselves to, and are floated by, gas bubbles. Minerals Separation Ltd. bought this patent in November, 1903.

MINERALS SEPARATION

In 1903 a company was organized by John Ballot, J. H. Curie, W. W. Webster, S. Gregory, H. L. Sulman, and H. F. K. Picard, all of whom had for many years been interested in ore-treatment problems. The original purpose of this company Minerals Separation, Ltd. was to acquire and operate the Cattermole patents. Soon after organizing, they purchased the Froment patents, and from time to time since then they have invented improvements and additions. Their present processes are based on surface-tension phenomena, accelerated by means of the addition to the pulp of very small quantities of oil and of air in a fine state of subdivision, the purpose of the oil being to coat the sulphides with a thin film of oil, and the purpose of the air being to adhere to the oiled mineral particles, and to raise them to the surface in the form of a froth.

The Cattermole invention was a process of ore concentration in which use was made of the idea of oil selection. He added to a freely flowing pulp from 4 to 6% of oil in proportion to the sulphide contents and also to the pulp, 2% of soap, the amount depending on the metallic contents of the ore, the object being to produce granules of sulphides of a definite size, or in other words, coagulation of the sulphides. For slimy ores he added a portion of coarser sulphide particles to serve as nuclei for the formation of granules, and effected the separation by an upcast current of water, taking the gangue off the top and the granules at the bottom. Another of this company's inventions was by Sulman & Picard in 1903, a process of 011 concentration in which they introduced bubbles of air or other gas, and also oil in the form of a spray, into the freely flowing acidulated pulp. This invention follows Froment and Cattermole in its main lines, but is novel in the methods of introducing the oil, and in the method of the introduction of air into the slightly oiled pulp. The best development of this series was the introduction, in 1905, of a method which I am informed by their solicitor has recently been denominated by the Minerals Separation, Ltd., as the agitation-froth process,' a method of flotation in which an extremely small amount of oil, less than 0.1%, was added to a freely flowing pulp, followed by violent agitation for from i to io minutes. Innumerable small bubbles of air were thus mechanically included in the pulp, which joined the oil-coated mineral particles by means of the surface tension of bubbles, and floated them in the form of a froth, which was separated in a spitzkasten. The tailing from the spitzkasten was then exposed to the air as it flowed over an inclined surface, and any oiled mineral that had escaped coming in contact with air-bubbles there took up its proper air-film and floated as a film on a second spitzkasten. Other improvements in this company's method and apparatus have been made from time to time, the most important of which was the Hoover apparatus.

The first plant using this process was erected in Australia, on the Central mine at Broken Hill, to treat an accumulation of zinkiferous tailing from the Sulphide Corporation's lead-concentrating mill. It had a capacity of 400 tons per day. This plant ran two years with an average of 72 per cent, recovery of the zinc in the form of a high-grade concentrate. The Sulphide Corporation then built a second plant, as part of a new concentrating mill, to take the current tailing from the lead concentrators, and thus has a complete mill, turning out lead concentrate by ordinary tables, and zinc concentrate by the Minerals Separation process in one continuous operation. This plant has a capacity of 900 tons per day. The Minerals Separation, Ltd., purchased the remainder of the Central mine's accumulated zinkiferous milltailing, and erected a third plant for the treatment of this material by their own process. This plant had a capacity of 900 tons per day. When the two last-mentioned plants were in successful operation the first plant was abandoned, being antiquated by virtue of later improvements. A fourth plant for the use of this process on an accumulation of zinkiferous and plumbiferous slime from the Block 10 and Central mines was then erected. Nearly all this material was fine enough to pass a loo-mesh screen. No difficulty was encountered in producing a pure mixed lead and zinc sulphide from this material, but the smelting of the concentrate presented such difficulty that the operation of the plant was discontinued. Recent developments in both the art of smelting zinkiferous concentrate and also in the methods of flotation-concentration warrant the belief that this slime-plant can now operate at a profit.

This process was, among others, tried by the Zinc Corporation in its early struggles, but for some reason it was impossible to get the results that were being obtained on the Central mine. Thereupon the process was discarded in 1907 in favour of the Elmore vacuum process, which was in use profitably for two years. Then in 1910, owing to the exhaustion of the material treatable by this process and to decided improvements in the apparatus for the Minerals Separation process, the Elmore process was discarded and the Minerals Separation process installed.

This process was tried in South Russia, at the Caucasus Copper mine, on a small scale, but although the trials were favourable, the company did not see fit to give it an extended application.

A unit having a capacity of 250 tons per day was installed at the Great Fitzroy mine, Queensland, and after extended trials and being several times re-modelled, now seems in a fair way toward commercial success.

On the Orijarvi mine, in Finland, a small unit of this process was installed, but is not now in use.

A small plant was also built at the Emu Works, Swansea, for a trial of the San Francisco del Oro ore, but the attempt was not a commercial success, because of the excessive acid consumption. Recent developments indicate that possibly this ore can be treated by the use of sodium bisulphate and other reagents.

The Junction North mine, at Broken Hill, is installing a plant designed to treat slime mixed with crushed crude ore from the mine.

A large plant has recently been erected on the Braden copper mine for the treatment of a copper ore which had hitherto given considerable trouble. The plant is a large one and the results are excellent.