DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH.

TIN AND TUNGSTEN RESEARCH BOARD,

ANNUAL REPORT FOR 1918-19,

    The tin mining industry of Cornwall has been worked over a long period of time with considerable energy and skill. Many ingenious mechanical appliances have been invented in that county in connection with mining operations and the extraction of the mineral from the matrix. Dressing appliances have been closely studied and gradually improved, but no consistent effort by combination among the producers was made to improve the percentage of extraction until 1916, when the Institution of Mining and Metallurgy, in co-operation with the Royal Cornwall Polytechnic Society, and with the approval and financial assistance of the Committee of the Privy Council for Scientific and Industrial Research, raised a small fund and initiated experimental research. A Tin and Tungsten Research Committee was formed, which had the assistance of the Cornish Research Sub-Committee and the Camborne Research Committee. Attention was particularly directed to ore dressing, with a view to improvement in appliances and their use. Professor Truscott did some valuable work,* to which reference was made in the Annual Report of the Committee of the Privy Council for Scientific and Industrial Research for 1916-17.† The funds available, however, were very limited in amount.

    Towards the end of 1917, the Department of the Ministry of Munitions for the Development of Mineral Resources took the matter up, and a successful meeting was held, with Sir Lionel Phillips, the Director of the Department, in the chair. The meeting was attended by Sir Frank Heath, Department of Scientific and Industrial Research, Mr. Edgar Taylor, President of the Institution of Mining and Metallurgy, and representatives of the Duchy of Cornwall, of the Royal Cornwall Polytechnic Society, of the Research Committee, and of a number of influential land owners and mining companies. As the outcome of this meeting the Research Board was constituted as follows: —

Sir Lionel Phillips, Bart. (Chairman).
Mr. John Gilbert (Cornish Chamber of Mines).
Sir Frank Heath, K.C.B. (Department of Scientific and Industrial Research).
Sir T. Kirke Rose (Chairman of the Research Committee).
Mr. Edgar Taylor (representing the Institution of Mining and Metallurgy).
Mr. R. Arthur Thomas (Cornish Chamber of Mines).
Sir Richard Threlfall, K.B.E. (Advisory Council for Scientific and Industrial Research),
with Mr. A. Richardson as Secretary.

After this meeting the Board had at its disposal a sum of about £5,000 per annum, half of which was promised for three years by those connected with the mining industry, the balance being provided by the Privy Council for Scientific and Industrial Research on the pound for pound principle. The duty of collecting the local contributions was undertaken by the Cornish Chamber of Mines. The Council of the Duchy of Cornwall took a lively interest in the work, which was shared by H.R.H. the Prince of Wales, who contributed £500, while other important contributors were: —

	£
Viscount Clifden	250
Dolcoath Mine, Ltd	250
East Pool and Agar, Ltd	250
South Crofty, Ltd	250
Cornish Tin Smelting Co., Ltd	250

    The total received from this source and credited to the Research Fund with the Imperial Trust for the encouragement of Scientific and Industrial Research amounted to £2,753 16s. The Institution of Mining and Metallurgy transferred the unexpended balance of the Research Fund, amounting to £494 7s. 9d. to the Department.

    The following statement shows the amounts received and expended, and balance remaining at the end of the year: —

Receipts.	£      s.    d.
Unexpended balance of the Tin and Tungsten Research Fund transferred by Institution of Mining and Metallurgy	494    7     9
Contributions from local Mineowners and Landlords collected by Cornish Chamber of Mines	2,753  16     0
From Investments	70    0     0
Contribution by Department of Scientific and Industrial Research, being one-half cost of Research	1,196    7     4
	——————
Total	£4,514  11    1

Expenditures.	£        s.    d.	£      s.    d.
Payments to investigators, travelling expenses, apparatus, materials, etc.	2,392    14     7
Special fee§ authorised by the Board to be borne entirely by the Fund	120      0     0
	——————	2,512    14     7
		——————
Balance held by the Imperial Trust at 31st March, 1919		£2,001    16     6

    The original Committees were re-appointed, and constituted as follows: —

Tin and Tungsten Research Committee.
Sir Thomas Kirke Rose (Chairman).
Professor William Frecheville.
Mr. Henry Jenner (President of the Royal Cornwall Polytechnic Society).
Mr. Josiah Paull.
Mr. H. K. Picard.
Mr. R. Arthur Thomas.
Mr. W. H. Trewartha-James.
Professor S. H. Truscott.
Mr William Thomas.
Sir Thomas Kirke Rose acts as Secretary of the Committee.

Cornish Research Sub-Committee.
Mr. R. Arthur Thomas (Chairman)
Mr. F. C. Cann.
Mr. S. Furze.
Mr. Henry Jenner.
Mr. T. Knowles.
Mr. Josiah Paull.
Mr. Arthur Richards.
Mr. M. T. Taylor.
Mr. Ernest Terrell.
Captain Willie Thomas.
Mr. William Thomas.

Camborne Research Committee.
Mr. T. Knowles (Chairman)
Mr. H. R. Beringer
Mr. E. H. Davison.
Mr. H. W. Hutchin.
Mr. F. H. Michell.
Mr. Josiah Paull.
Mr. J. W. Partington
Mr. T. Knowles is Secretary of both these Cornish Committees.

    The larger resources rendered it possible to extend experimental research. Not only were laboratory experiments multiplied, but attention was given to proving upon a more practical scale results that appeared promising. The initial calls upon the Research Fund have not been very heavy because the operations are still in the earlier stages. When, however, it becomes necessary to demonstrate upon a working scale any process that may appear promising in the laboratory, the charge upon the Board's resources will become very much greater.

    During the period under review the Board met on twelve occasions, having held their first meeting in February, 1918. One of the meetings was held in Camborne, in order that members might have an opportunity of inspecting the research work in progress there, besides familiarising themselves with Cornish ore dressing practice, and the difficulties that militate against a higher recovery of the mineral contents of the ore. The Board gathered much useful information from this visit, and they believe it was helpful to the Committees in Cornwall.

    Owing to the war, considerable difficulties have been experienced during the year in securing the services of suitable research workers and materials for their operations, so that, had normal conditions prevailed, the progress would no doubt have been more rapid.

    Appended hereto are notes by Sir Thomas K. Rose, giving a description of the research work that has been done, with results so far obtained, and an account of discussions entered into for the furtherance of research.

    It has been thought desirable in the national interest to publish some of the results obtained in the form of papers read before the Institution of Mining and Metallurgy and printed in their Transactions. The papers read during the period were as follows: —

        The Wet Assay of Low Grade Tin Ores, H. W. Hutchin.

        The Uses of Cinchonine in the Assay of Tungsten Minerals, H. W. Hutchin.

        Recovery and Losses of Tin at Giew Mill, the Cornish Sub-Committee.

        Giew Mill Test-Elutriation of the Crushed Products, S. J. Truscott.

        Effect of Heating and Quenching Cornish Tin Ores before Crushing, Arthur Yates.

        Slime Treatment on Cornish Frames—Supplements, S. J. Truscott.

    As the outcome of an advertisement in the technical press inviting firms and others associated with metallurgical chemistry to undertake research work with a view to the introduction of improved processes for the extraction of tin and tungsten from Cornish ores, negotiations have been entered into with various competent persons, who have been invited to make preliminary tests with a view to submitting to the Board any schemes of research they may devise.

    The Board venture to think that the progress already made augurs well for securing a higher extraction from Cornish ores.

    The Board desire to express their thanks to the Research Committee and to the Committees in Cornwall for their valuable assistance; to the Governors of the Imperial College of Science and Technology and to the Board of Governors of the School of Metalliferous Mining (Cornwall) for granting the use of their laboratories; to the Institution of Mining and Metallurgy for printing papers in their Transactions; to those investigators who have given their services gratuitously; and to the mine managements in Cornwall who kindly supplied samples of ore, and afforded facilities for practical tests on their dressing floors.

LIONEL PHILLIPS,                
Chairman.    

Alex Richardson,
                Secretary,
    25th April, 1919.

* See Bulletin No. 158. The Institution of Mining and Metallurgy, Nov 1917.

† Cd 8718 p39.

§ The Department could not contribute to the fee, as it was for an officer whose whole salary, considerably exceeding the amount of the fee, had been contributed by the Government.

    The examination of the physical condition of cassiterite in Cornish lodes has been continued by Mr. E. H. Davison throughout the year. He has examined large number of sections of lode material with the aid of the microscope and finds that most of these contain fine cassiterite particles so minute in size as to be difficult to save in dressing operations. Certain clearly marked types of veinstone were recognised, readily distinguishable from one another. Mr. Davison's investigation is not yet complete, but his report will probably be ready for publication in a few months. Mr. H. W. Hutchin, assisted by Mr. L. J. Meade, has begun a parallel examination with the microscope of the grains of cassiterite in certain mill products.
    Professor S. J. Truscott, assisted by Messrs. J. H. Goodchild, K. S. Low and H. L. Burnie, has continued and completed his research on Slime Treatment on Cornish Frames, working partly in the laboratory and partly at Dolcoath. His results have enabled him to draw the following conclusions, which are reproduced from Professor Truscott's paper, published in Bulletin No. 175 of the Institution of Mining and Metallurgy :—

    It is considered that the following points concerning the factors governing frame working have been established:

    The plane surface, and particularly that of wood, does better work than the fluted surface on ordinary slime. The finely fluted surface is the better of the two on reground material.

    On ordinary slime a bed 3 ft. in length does twice as good work as one of 6 ft. The longer bed requires a greater rush to get rid of the gangue in the time allowed. On reground material even a shorter length of say 2 ft. could be used with advantage.

    The inclination should be such that during feed about 80 per cent. of the gangue is removed.

    Washing to remove some of the little remaining gangue is effective, raising the value of the concentrate at an insignificant sacrifice of recovery. It is, on the other hand, of diminished service when a large proportion of the material has settled during feed.

    With ordinary slime the best rate of feed appears to be about 4 tons per day for an 18 ft. concave round frame and 15 cwt. per day for a 6 ft. flat frame. At a rate much greater than this too great a drop in recovery would occur, while at a lower rate there would be an unnecessary drop in capacity.
    With reground material the above-mentioned rate may be increased substantially and perhaps doubled.

    The liquid-solid ratio of the feed is kept about 10:1. No greater ratio is required for effective concentration, while, within limits, a smaller ratio has the advantage of permitting a heavier rate of feed without causing a rush.

    The duration of feed, that is, the time taken to load the frame is best kept about 4 min.; the flat frame should accordingly be flushed at that interval, while a round frame should make a revolution in about 4½ min. A shorter duration would not give the gangue particles time to travel down the bed.

    To the above factors must be added the need for regularity in feed. Such regularity can only be given by pyramidal or conical settlers with pointed bottom discharge.

    As a result of the whole series of tests, modifications of two fundamental factors in policy, namely, the rate of enrichment and the amount of regrinding, have suggested themselves.

    Employing the working conditions just specified, the first frame concentrate from a slime feed assaying 10 lb. or more would be of such increased value and reduced bulk that its further dressing could be justifiably and advantageously undertaken in buddles. Buddles possess in their mineral surface the best possible surface for catching both fine and granular tin, while at the same time the products are sized so that the next buddling is of sized as well as graded material. Moreover, they are worked in a closed circuit from which only top water flows away, the solid products remaining in a comparatively dry state. The loss of tin in buddle treatment is accordingly small.
    With reground material the first frame concentrate from a feed assaying even lower than 10 lb. could go at once to the buddles or even to the calciner since from such material a higher rate of enrichment is obtainable.
    On such lines the ratio of enrichment in the primary slime treatment would be generally 6:10 in the place of 2:4 as at present, and the policy would be that of rapid enrichment in the place of the present practice of gradual enrichment.
    It is considered the tests indicate that by this policy the present recovery could be obtained with one-half the present frame area, and that the area thus set free, applied to the retreatment of the tailings, would improve the slime recovery 25 per cent, and the total recovery, say, 3-5 per cent.
    Beyond this, if the preset frame area is as much as the mines can reasonably accommodate, it might not be convenient for them to go. On account of the diminished value of the material any further recovery would require much additional frame area. Such work, rightly or wrongly, is largely left to the streamers, who from the large bulk at their disposal are repaid with a low percentage recovery. Extending the principle of rapid enrichment to their working the total recovery of tin in Cornwall would be improved, say, 5 per cent.
    With the passage of time it has been the experience that the tin in the available rock has become finer and finer, and it seems more than likely that in the future slime tin will bulk larger than it does now. Any endeavour to improve slime recovery is accordingly doubly justified.

    Repeatedly in the tests the little difficulty experienced in catching the tin resulting from fine grinding was remarked.
    This fact was particularly expressed in the treatment of reground sand residue from South Crofty, when, at a rate of feed equivalent to 10 tons per day on a standard round frame and from material assaying as low as 5 lb., a recovery approaching 60 per cent. was obtained in a concentrate assaying 100 lb.
    The sand residues in Cornwall will generally assay about 5 lb., from which by framing followed by buddling it could be expected to recover 2.0 lb. per ton in the form of marketable concentrate. Such an amount would leave a profit with tin as low as £150 per ton. Assuming the sand to amount to 60 per cent. of the whole pulp, and the present recovery in Cornwall to be about 20 lb. of tin per ton, that recovery would be increased about 6 per cent. On these lines the whole of the ore would, first or last, receive a frame treatment. For the reground material, shaking tables would not be so efficient and are more expensive.
As the accompanying flow-sheets* indicate, the amount of regrinding at present done in Cornwall is, generally speaking, limited to the middling products. It is suggested that this regrinding should be extended to embrace all the sandy material and that it should be ground to pass 120 mesh.
    The losses in the past have not been due to excessive comminution; they have rather been due to the natural state of fine division of some of the cassiterite. On the other hand, the loss due to tin passing away imprisoned in the sand has not been fully appreciated. Witness the grading analysis of the Giew Mill tailing, which showed that 50 per cent. of the tin was lost in the granular material. The fact that the sand was equally responsible for the tin lost has been obscured by the notoriously low percentage recovery from the slime. Moreover, this sand as it goes away invariably carries with it granular slime tin which has escaped the tables and been discharged from the sand pits or separators. This and the bulk of the imprisoned tin would be recovered if all the sands were ground and framed as slime.
    Where the ore contains little or no wolfram or arsenic, it is possible that complete fine grinding might, with advantage, take place without previous removal of the coarse tin, leaving that, as well as the fine tin, to be recovered by frames. The obvious advantages of such a course would be the greater simplicity and lower cost of the plant; a disadvantage would be the finer condition of the concentrate. With respect to recovery, the tests made in the laboratory and recorded in Supplement I.† indicate that an improved recovery would be obtained from such a treatment.
    In addition to the above-mentioned laboratory tests, complete fine grinding finds support in the scale at which regrinding is being used in the recovery of tin from old tailings at the milling plant of the Cornwall Tailings Co. Any further tests would unavoidably have to be done on a large scale.

These conclusions and the evidence in support of them, already published, will no doubt receive the careful consideration of the industry, and it may be hoped that it will be found advantageous to adopt the two principles of rapid enrichment of slime and of expended fine grinding. It is to be noted that Professor Truscott claims that in this way an increase of 11 per cent, of the present recovery of tin would be gained. The extra cost of rapid enrichment appears to be trifling, while that of fine grinding is left to the industry for determination.
    A series of tests were made by Mr. A. Yates to see if the addition of a deflocculator would break up aggregates of mill pulp containing cassiterite and render the material more amenable to concentration. The results as a whole were negative. It did not appear that the condition of the mill pulp would be improved in that way. Experiments in flotation by Messrs. Low and Burnie are in progress, but it is too soon to make any statements as to the results to be expected.
    The treatment of complex low grade refractory materials (e.g., "tinny iron" or "black iron") by fusion with nitre cake has been investigated by Mr. H. R. Beringer, Captain A. M. Drummond and Mr. F. H. Michell. They found in the laboratory that by fusion at a red heat and treatment of the melt with water, the iron and tungsten passed in great part into solution and the cassiterite remained in the residue in a suitable condition for recovery on the dressing floors. An experimental reverberatory furnace with a flat cast-iron bed was built at the King Edward Mine and about a ton of refractory material from East Pool treated, with promising results. A furnace of larger capacity but different design is now in course of erection by the management of the South Crofty Mine with the object of utilizing the process. There seems reason to expect that the remaining difficulties will be overcome and that the nitre cake process will be available for treating such complex refractory low grade concentrates, which at present realise little or nothing, involving a loss of many thousand pounds a year in the county.
The same investigators have also been engaged in endeavours to find a chemical method of removing and recovering the tungsten from concentrates as they leave the calciner and from certain ores containing wolfram, and have had most success with a modification of the Oxland process. It does not appear at present, however, that the method can be applied industrially.
    Dr. O. J. Stannard has also succeeded in separating tungstic acid in a remarkably pure form by a new process from concentrates and from wolfram ores. Further work is required before his method is ready for tests on a larger scale. Details will be forthcoming as soon as protection has been secured.
    Mr. H. W. Hutchin, assisted by Mr. L. J. Meade, made experiments on the recovery of tungsten from concentrates by digestion with solutions of caustic soda, and found that dilute solutions were ineffective (a point confirmed by independent work by Mr. Beringer). Strong solutions, however, acting on uncalcined material effected what was apparently complete extraction of WO₃, the extraction from, calcined material being incomplete. Further prosecution of this enquiry has been suspended as economic success appears to be unlikely.
A process devised by Mr. Janson and Mr. Annable for the recovery of tin has been carefully examined, the tests being watched by Mr. J. H. Goodchild. The method is promising, and extracts the tin from finely divided cassiterite more readily than from coarse particles which can be easily saved by ordinary ore-dressing methods. It is proposed to make further efforts to develop the process, and to examine certain modifications of it which present themselves.

T. K. ROSE.

    20th March, 1919.

* The flow-sheets are omitted in this Report.

† Omitted in this Report.

Published for the Department of Scientific and Industrial Research by His Majesty's Stationery Office, 1919.