Eastaugh, F. A.

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• SUMMARY OF' "NOTES ON F'LOTAT10N. ,I By F. A. E ASl'AUGH, A.B..S.M. L ecture givell D ecember I71h, 19I2. Few modern advances in metallurgy and oredressing are of equal interest to the sudden development of methods of separating minerals by flotation. Nearly all older methods of separating metallic from earthy minerals depended on differences in specific gravity, flotation makes use of differences in surface propert ies such as affinities for oils or gases, and therefore may effect separa-tions previously impossible owing to similarity in specific gravity. Such has been the case 'at Broken Hill, the scene of the first great success of flotation, where fine Zinc Blende and Galena are separated from Rhodonite. That some minerals have " greasy " surfaces has been known for years, and also that under certain condit ions they float, for many devices have been used to catch float gold and tin. It was also known that acids sometimes made sulphides float, for Dr. Watson in his Chemical Essays, published many years ago, mentions the flotation of Galena when acted upon by nitric acid, and the sulphur set free during the solu-tion of a sulphide copper ore in nitric acid was early known to carry copper and suitable precautions taken. Many methods for ore treatment by flotation have been patented, the earliest being about 1860. The majority of these are unworkable, but that of Carrie J. Everson in 1885 makes a splendid separation of certain classes of ores and it is hard to understand why it was never work ed on a commercial scale. Separat ion by flotation may roughly be divided into the following c}asses:-1. Absorption of the metallic minerals in large volumes of thick oil, the chief example of which is the old Elmore Pro-cess. A mixture of ore and water was gently agitated with a large quantity of oil, the oil absorbed the metallic minerals and such quantities were used that the specific gravity of the loaded oil was less than that of water. Separation of the 54 oil and mineral from the gangue was effected by means of a spitz; the bulk of the oil was r emoved by a centrifugal and used again. 2. Flotation by gas generated in a mixture of ore and water. A good example of t his method is the P otter Process. The crushed ore was treated with hot dilute sulphuric acid which acted on the C'Etr boncit es present an d generated carbon deoxide. The bubbles of gas attached themselves to the mineral particles and carried them to the surface where they remained as a thick f r oth and were floated off. 3. Surface Float : De B MTay. The ore, after suitable treatment , such as washing with acid and chlorine, is made into a thin p ulp wit h water and a small quant ity of light oil, and allowed t o flow gently on to the surface of wat er. The mineral particles r emain on the surface an d are run off while the gangue sinks. 4. Air Emulsion Float. Minerals Separation Process. A thin pulp of finely-crushed ore is violently agitated with hot dilute sulphuric -acid. The acid is too weak to give a Potter flaat. A small quantity of some organic contamin-ating agent is added and the agitation continued. A thick froth of mixed metallic minerals and gas is obtained which is allowed to flow or is scraped off a spitz. This last process is one of the most interesting and seems destined to supersede all the others. It has recently been modified, givin g t he so-called differential pr ocess by which n ot only are sulphides separated from silicates, but one sulphide from another. That sulphides sh ould differ in their readiness to float was perhaps to be expected, but t hat gases should vary in their affinit ies for mineral surfaces seemed almost impossible. Yet ther e is evidence that carbon dioxide is a better float forming gas than ot hers, and 'analysis of the gas entw gled in float scums have shown it t o be the last t o be r emoved from the mineral par ticles by the air pump. St atements have been made that when oleic "acid is used as t he contaminating agent in the Minerals Separation Process it is impossible to det ermin e its distribution after flot ation, as t he amount found on the concent rates added to that on the t ailings always gives a result greater than the amount originally used. During the hearing of a lawsuit on the flotat ion patents "figures were given t ending to show that all the oleic acid used in the Minerals Separation P r ocess at tached itself to the sulphide particles. It was stated that the bulk was fOlmd in the concentrates and that the small amount in the tailings was exactly accounted for by the unfloated sulphides. The sUIll of these t wo wa;; about th e -amount of oleic acid added. These results wer e . so contrary to previous experience that the whole question was re-opened and remarkable :re-sults obtained. The oleic acid present in concent rates and tailings was determined by making et her extracts. The first results showed about 0.04 per cent. ether extract from both concen-trates and tailings, a .result much in excess of the oleic acid added. Yellow crystals were noticed in the extract, which proved it was not 'all oleic acid. These yellow crystals were examined, 'and found to be sulphur. Many more extractions were made on different samples, and the sulphur separated from the oleic acid. Different samples gave very dissimilar results ; the fol-lowing ar e fairly typical;-TOTAL ETHER EXTRACT. Concentrates .. .. .. .. Tailings .. . .. .. .. .. After Separation Concentrates; Sulphur . . Oleic Acid Tailings; Sulphur .. Oleic Acid . . .. No.1. 0.121% 0.062% of Sulphur. No.1. 0.090% 0.025% No.1. 0.028% 0.033 % No.2 0.147% 0.029% No.2 0.048% 0.096% No.2 0.013% 0.015 % The amount of pleic acid found aft er separating the sul-phur is still more than that added, so the mill tailings being fed to the flotation plant were treated with ether. The following result was obtained;-Sulphur . . . . . . . . . . . . .. 0.0006% Oil . . . . . . . . . . . . . . . . . .. 0.0052% It was calculated that to supply this amount of oil, two tons would be required per week, while the whole plant was using less than one t on. Finally a piece of ore was taken from the centre of a big uncracked block, carefully kept from contact with anything greasy, and an ether extract made. The surprising result was obtained of 0.0037% oily matter in clean Broken Hill sul-phide ore. Samples of ore were ·also taken from Cobar and Cloncurry, and both found to give an oily residue after extracting with ether. 56 Mention should be made of the fact that all the ether used had been distilled t hree times and found to give no residue. It was hoped to obtain enough extract from perfectlJ clean ore to invesigate its nature, but so far this has been im possi.ble. During the lawsuit already referrred to, attempt~ were made to show that small pieces of pl-atinum foil were not raised to the surface of liquids by carbon dioxide bubbles if they were p erfectly clean. Slightly greased particles of platinum were readily buoyed to the surface of soda water on warming, while pieces that had been cleaned by treatment with strong nit ric acid -did not attach themselves to bubbles, but following the nitric aCId treat · ment by heating to redness, made the platinum ali ost as ready to float as the oiled pieces. . A final outcome of the investigation of flotation is the pos-sible use of the principles involved for deoiling boiler.- water. This has not yet been t ested on a l'arge scale, but smalleexperi-ments show that water which is opalescent owing to . il con-tamination, becomes perfectly clear after filtration throug1: finely crushed galena. 'I t. P.N. RuSSELL SCHOOL OF ENGINEERING T. H. HOUGHTON LIBRARY .>J' 

Summary of "Notes on flotation"

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Summary of "Notes on flotation"

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