IKE RARE EARTH MONAZITE

Otago Daily Times, Issue 17823, 3 January 1920, Page 8

IKE RARE EARTH MONAZITE

d|jr Edwabd Cahsn, A.R.C.Sc, F.1.C., a '-'<; In the World's Work.

. How many of us think when wo light tfrtf'tfncandescent gas at dusk of what the fragile mantle is made, or whence its material is derived? When the smoker germs' into a shop and asks for a new flint forbjs pocket-lighter does he imagine that hj^ja'buying a little bit of flint which is f&Wg : to give the spark against the steel and so ignite the spirit? It is not a Hjfttter of common knowledge that, these flints are made of the waste products of th» manufacture of the gas mantles, nor is it to he surprised at in an age' when e"very' man's'job is so highly specialised. Outside the ranks of the scientists there cannot be. many who have even heard the name "monazite," and yet monazite is in its way as much sought after as gold, and much harder to find in workable quantities than the precious metal. Monazite, as we know it in the European market to-day, is a beautiful, rich golden brown coloured sand, composed essentially of a phosphate bff'berium, one of the" so-called "Rare iSirths," a name which was given to a ■frhole series of rare mStals of which but little was known till quite recently. But monazite does not owe its importance to the cerium it contains, but to a yery small.proporion of another rare metal jjallfed thorium, which is much rarer than t&othera, and, consequently, more valuable;' Monazite is, in fact, sold on its thorium content—that is, the thorium in it is carefully analysed and estimated, and the price fixed according to the amount present. Furthermore, a sand containing as little as 6 per cent, is considered quite a rich find. The metal thorium was discovered as early as 1818 by the famous Swedish chemist, Berzelius in a mineral from Fahlttn, in Sweden, and was named by him' after the Scandinavian God of Thunder,

Thor. At:the.time of his discovery cerium had been known for some 15 years. It was not," however, till after Aucr von Welsbach patented his incandescent mantle in e 1885 that monazite and thorium atw£|j&a the importance they hold to-day. Until then thorium nitrate, which is the |a}ti v Mßed to impregnate- the mantles, was j| nfcere' chemical curiosity worth about £100 a pound. In 15 years the price had fjileh to £1. & Although monazite is very widely distributed throughout the world, and is even foußs,,,to a very small extent in Europe, it is only in.a very few localities that the sand-is found in a form which can be utilised commercially. The earliest source of supply .was' the alluvial deposits on the coast of Brazil. Here the sand was found w'etifcb in huge quantities in the States of- Espirito Santo, Rio de Janeiro, and Bahia; these coastal deposits go by the name of marinhas. Tii6 material is also found further inland in the beds of the rivers on private property, but the cost of production as a rule great to make it worth while exploiting'the material commercially. The sand, is derived from the disintegration of graaite and gneiss, and is concentrated by nature on the coast, the action of the tides Mljjng away the lighter ingredients and Igavfjagthe monazite, which has a specific g£as.ty considerably greater. It is owing to this cause that the sand varies so grlatly in its content of monazite. , It is almost needless to add the Germans were the first to exploit these deposits of valuable material which they found ready to hand, even concentrated by nature so that they only needed to ship the material to Hamburg as ballast, pretending that it had but little value, and consequently paying but little for it, and realising quite a big turnover at the other j_,|sjfWas some time before the Brazilian found out what was taking Siace. In 1903, however, the Brazilian SEeimment discovered the value of these faster deposits, and claimed them as their dfon"They invited bids for the working »f 'rjhe sand, and it was 'not long before <he l Germans acquired the righte and enf:ed the Government a handsome royalty •{Sheir property. In the early days there Sjwanother source of supply in North and South Carolina in the United States, but,the sand here was not so rich in thorium content as in Brazil, and the indjtistry had a hard time to compete against German "cut-throat" methods.

■B»*w : '_The German Monopoly.— The German Thorium Syndicate thus had practically a monopoly of the world's supply of' tnonazite, when in 1909 new Coastal deposits were discovered in Southern India at Travancore. A company was formed to work the find, and it was hoped tKat" it would be possible to break the German monopoly. Capital, however, was not forthcoming for the project, and again the Germans gained control, although the factV„was riot apparent on the surface. They found the money, but the sand had to go to Hamburg. The advent of the war in 1914 put an 'ejiil #0; this dominance, however, and left a British company in complete control, stitfcx provision for the future, whereby none but British-born subjects could have any interest in the concern. Since then the survey of the mineral resources of the Island of Ceylon, under the auspices of the Imperial Institute, has led to the discovery of a new source of monazite on the shore of the island. This will shortly be working. Furthermore, the monazite from India is much richer in thorium than the Brazilian variety, containing from 8 to 10 percent, as against but 6 per cent, of tne' Brazilian sand. The prospects for the future of the industry in the British Em{hre'*look particularly rosy at the moment. —Manufacture of Thorium Nitrate.— Though the Germans in the early days found that they* could export the sand flireetly as ballast, it soon became evident tftai s ihis could not go on for ever, and means of preparing the sands so as to: bring -them up to some sort of standard ] had" to be sought. These are three in number, and different methods are used in Paling with sands from different parts. 1 In Brazil the methods adopted are wet concentration followed by electro-magnetic separation. The former simply makes use of the difference in the gravity and washes away the lighter sands on .specially-con-structed tables of the Wifley ,type. The elecjjro-magnetic separators are very ingenious modern contrivances which depend for their effectiveness on the differences in-..magnetic permeability observed in the different minerals composing the sands. The latter is by far the most effective Separator on the market to-day, though in India a third method, concentration: by air, has been used with considerable success.

4 r#* has .already been mentioned, the thorium is but a small proportion of the whole sand, and it is a matter of considerable difficulty to get this out compfetflly. and economically. The methods adopted are more or less shrouded in mystery, _ and even the larger treatises on qhemifltry are strangely silent on this subtest, though the barest outlines of the industry are known. The finely-ground sand is treated in castiron ror acid-proof stone-ware pans with Bulghuric acid, whereby the sulphates of thorium and the rare earths in general are Obtained. These are dissolved in water, nvwjhich they are very soluble. The solution' is allowed to settle, and the clear Ijauid-ia syphoned off. 1 The thorium is precipitated from this clear liquid by partial neutralisation with alkali. The preparation of the nitrate from thiri impure phosphate thus obtained ig a trade secret. Thorium nitrate is now

manufactured on a large scale in Germany, the United States, and in England and Franco. It.is difficult to give any idea KE-thiS relative quantities manufactured in m[cli country, because tho figures vary from year to year pending on circumetanfces.

The incandescent, gas mantle, liko so many so-called German inventions, was known many years before Auer von Welsbach took out his patent. Many attempts had. already been made to utilise the observation made by Berzelius as early as 182!r that the oxides of thorium and the other rare earths emitted a bright light tftien heated in the Bunsen flame. In 1839 Cruikshank produced the first incari-. descent mantle, and about 1883 Fahnehjelm patented a process in Stockholm. —Mesothoriirm.—

But it was not till 1880 that Welsbach started his experiments, and only after five years'; patient study and experiment was he able to take out his patent. His early mantles were made of loosely wren matembof vegetable origin, impregnated with a solution of rare earth salt*. The organic fabric was burnt off, leaving a ekeleton of

rare earth oxides, which emitted a bright light when heated in a non-luminous flame. It took him another six years of patient work to discover the exact proportion of cerium oxide to mix with the thorium oxide to produce the brightest possible light. It is this proportion which is used to this day—namely, but 1 per cent, of the cerium"to 99 per cent, of the thorium compound. The fabric now used in the manufacture of the mantles is either cotton, ramie fibre, or artificial silk. ■Special machines weave the material into the required cylindrical shape, they are. then steeped in a solution of thorium and cerium nitrates in the proper proportion. This solution varies in strength from 25 to 50 per cent, according to the idiosyncracies of various manufacturers. Each mantle should take about a gram of thorium nitrate to impregnate it, though some of the cheaper German mantles, no doubt, did not contain as much. After the mantle has been impregnated and dried the maker's name -is ofteiv printed on 't. For this purpose a rubber stamp is utilised with a solution of another rare earth salt, didyminm, which is also obtained from monazite. This salt, when burnt, leaves a pinkish brown residue which shows up against the white background of the mantle. The next process is called "burningoff," and consists in burning away the fabric leaving a fragile skeleton of oxides, much too fragile in fact to allow of the mantles being sent into the market without disastrous results. The mantles are therefore immersed in a solution of collodion and dried. Every manufacturer no doubt has his little secrets, but in a popular article of this kind the simplestoutline of the process is all that is I required. All industry depends for its success on the use it can make of its by-products, and the monazite, or thorium, industry presents no exception to this rule. Here we are dealing with a mass of material from .which but a small proportion is used for the actual manufacture of the mantles. In addition the actual process of manufacture of the thorium nitrate gives rise to a very important by-product apart from those obtained from the manufacture of the thorium nitrate from the sand. All thorium minerals exhibit the same peculiar properties as the minerals of uranium—namely, radio-activity, which >s popularly supposed to be a peculiar property alone possessed bv radium. This is another popular fallacy. It has been' estimated that one ton of monazite containing 5 per cent, of thorium oxide yields about two and a-half milligrams of the radio-active substance associated with the thorium and called mesothorinm. The latter is worth about £9 to £12 a milligram. Mesathorium has ' been used, especially during the war, as a substitute for radium in the manufacture of the luminous dials of various instruments for use in aeroplanes at night. Not, only is it considerably cheaper than the latter but Its use enabled the very limited supplies of radium to be conserved for medical use. Mesothorium has one disadvantage in that its life is considerably more limited than that of radium.

The problem, however, was to find some use for the huge mass of apparently ■ waste material after the thorium had been extracted. This consisted for the most part of rare earths of which but little was known at the time, and it was again due to the researches of Auer von Welsbach that these waste materials found a use.

It was about the year 1907 that he observed that an alloy of iron with the rare earth metals, and, especially cerium, gave off a shower of bright sparks when struck with steel. Furthermore, these were quite hot enough to ignite the yapour of alcohol, oy, any other volatile spirit, such as benzine or petrol. The new alloy was named Auermetal after the inventor, and soon many other names were given to it such as mizchmetal, or mixmetal, lanthan, cer or erdmetal, all of them referring to its constituents. The alloys were made in Austria, at Treibach, and soon found their way on to the open market in the form of various kinds of cigarette-lighters, or other simple devices for lighting, the domestic gas supply, where no mantle was employed, such as the gas stove. They could not be used in the case of burners furnished -with mantles because the spark needs to be produced in the flame itself, and this could not be done in the case of the incandescent burners without disastrous results to the latter.

• Though the war put a stop to the export of these devices for a short time it was not long before the Americans took advantage of the opportunity to put similar alloys on the market. A Philadelphia company has several of these alloys which it advertises largely. The alloy is now sold under many names which no longer betray its country of origin, such as Ferrocerium, Pyrophoric alloy, sparking metal, ignition stone, flint, and firestone. Of these perhaps flint is best known to the ordinary smoker, who more than likely has no idea what he i 3 getting when he purchases a new flint j for his automatic lighter. ' I The flints are quite small, and it has been estimated that as many as 18C0 to 2800 can be manufactured from one pound of material. The price of a pound of material is now roughly £6, but as is the case with all materials obtained from the rarer metals it is difficult to give any figures which are not subject to alteration from day to day. In addition to the use of these alloys in pocket lighters during the war they found a very special application for defining the path of shells at night. A small portion of alloy affixed to a shell will burst into flame soon after leaving the gun, thus tracing the course of the projectile in the darkness of the night. Thev have also been employed for lighting certain types of acetylene miners' lamps. It appears that it is only the exterior of the alloy which gives off the sparks, which are actually minute particles of the alloy itself raised to incandescence. It is for this reason that it is necessary to renew the flints from time to time. One flint will give as many as from 2000 to 6000 ignitions. Another use has of late years been found for the wasta cerium metals, which utilises about 300 tons annually. It has been found that arc lamp carbons saturated with a solution of these mixed metal salts burn with a much steadier flame and give a more brilliant light in addition. Prom what has been said of the monazite and thorium industry in the above very brief outline it will be seen that there is plenty of scope for reconstruction work in this small field alone. At present the waste products of the incandescent mantle factory are greater than the demand for them in industry, but there is no reason why other uses should not be found for them.

In the very unlikely case of some use being found for cerium and allied "metals which would absorb more than the supplies accruing from the mantle industry there are many other minerals containing cerium in large amount which could be obtained commercially from America. Among these mention might bo made of allanite, which exists in considerable quantities in Texas.

— The latest claimant to tho title of Lord Lennox of Dumbarton, which is reputed to carry a rent roll of £36.000 and an acreage of 10 square miles, is Thomas Walter Lewis Gordon Lennox, of Pendleton, Manchester. Mr Lennox, who is a Wigtownshire man, is an automobile engineer, and has business connections both in Manchester and in Birmingham. Ho is a grandson of the late Mr Lennox, Newmihis and Low Gotland, Wigtown. Tho new claimant is confident that ho :'s descended from Damley and Mary Queen of S»x>ts. Mr T«nnox, who is unmarried, points out that the other claimante are 'by the female side, whereas ho is by th* male aide, and ho has every confidence that ho will soon bo recognised as Lord Lennox of Dumbarton. — Sir Oliver Lodge has selected Humpstead Gardon suburb as a congenial spot to settlo in after rolinguishing his post at Birmingham University. Sir Oliver is oneof the greatest thinkers of the day—and incidentally one of tho most picturesque,— but he does not possess that absent-minded-ness which is usually associated with professors whose thought© aro bound up in ethics and otfear. He is, as a matter of fact, a keen observer of all that happem, and is as quick at rcpeiteo as a playwright. Ho has no patience with fools who pose, and he onco brought a flush to the oheek of a boasting student who observed in his hearing: "I have rathor a oontempt for PJato!" "A oontempt," observed Sir Oliver acidly, "not born, I'm afraid, of familiarity 1"