TIDBITS OF INFO-PLATINUM

rehab · TIDBITS OF INFO-PLATINUM

for MARCH 30, 1929

History and Metallurgy of Platinum
By C. A. ACKERMAN, San Francisco, California. Recent reports of the
discovery of platinum have created a greater interest in the history,
mineralogy and metallurgy of the metal.

Recent reports of the discovery of platinum in various Pacific Coast states makes some observations on that metal peculiarly timely. Platinum seems to have been observed by Sealiger, for in his book entitled “Exercitationes Exoterio De Subtilitate,” published A. D. 1558, he disagrees with the views of Gardanus “that all metals are fusible,” for he adds that in the mines of Mexico and Darian a metal is found which it is not possible to bring to a liquid state. Inasmuch as platinum has been found in the districts referred to in this book it appears probable that this is the metallic substance meant.

It was not until two centuries later that platinum attracted attention again and many chemists occupied themselves with the subject. In 1748 a publication entitled “Relación de Yiage a Ia America Merídional,” by Antonio De Ullóa, there is described “an unworkable metal, which makes gold’ useless if it occurs mixed with it in large quantities.”

William Watson seems to be the first to describe platinum as a compact metal, for in his “Philosophical Transactions,” published in London in 1750, he states that he obtained a metal from Charles Wood, who brought it to England from Granada by way of Jamaica. This metal was, later most carefully examined by Schéffer, who describes it in us “Menmoirs,” Stockholm Academy, 1752, under the heading of “white gold, or the Seventh metal,” “Platina del Pinto” (or the small silver from Pinto), and so the metal became known as platina and later as platinum.

Scheffer stated that the metal was insoluble in nitric acid, but could be dissolved in aqua regía and precipitated by mercury; infusible at the strongest heat of the wind furnace but could be fused by the aid of arsenic and be alloyed with all other metals.

In 1757, Marcgraf in his communications to the Berlin Academy made observations which have proven to be of great service to chemists—that platinum solution produces with the salts of all alkalis, except mineral alkali soda, orange yellow precipitate. In the following year, 1758, Maguer and Bame, in “Memoirs’ Academy Paris,” reported that they had succeeded in fusing platinum with a powerful burning glass. They further stated that platinum had heretofore been a rare substance because the Spanish government had forbidden the export of the metal on the ground that—as gold could be alloyed with a considerable quantity of it without the color being sensibly changed, it would give an opportunity for fraud.

Count von Sickingen was the first to prepare platinum foil and wire and to show that the metal could be dissolved in nitric acid when alloyed with silver. All of this research had been done with metal from South America, and it was not until platinum had been discovered in the auriferous sands of the Ural mountains that work was taken up diligently and cause furnished for the explorations of Humboldt, Rose and Ehrenberg in 1829. Humboldt may be considered to be the first to occupy himself with the mineralogy of the metal.
Platinum occurs only in the native state, but native platinum is seldom pure. There is herewith given a typical analytical report of ore samples from various sections of the world.
Analysis of the ore shows that osmiridium occurs as an alloy of osmium and, iridium ‘and was’ found to be insoluble in aqua regia. The sand, chiefly quartz, contained chromium, spinelle, and titanium.

Geologically, little is known of the conditions of existence, as it is almost entirely found in alluvial formations. In at least one instance, however, in the exploration of Mount Solovieff, in Siberia, and at the head of the platiniferous gravels of the Ural mountains, a piece of rock over one foot in diameter was encountered, consisting of chrome iron and serpentine in alternate bands, associated with a small quantity of dolomite and some disseminated fragments of country rock, and in which grains of platinum could be distinguished by means of a lens. Even the rock in which no platinum was visible with a lens showed 0.0107 per cent upon analysis.

The richest platinum deposits are found on serpentine, and, in California, the placers containing platinum are always found in close proximity to a serpentine formation. In some of the Canadian mines it is found associated with nickeliferous pyrhotite as well as the greenstone group of diorites and diabase. Most platiniferous alluvials consist largely of diorites containing chrome iron resulting from the erosion of diorite. In some localities it occurs largely in situ in ferruginous felsite and granite and in gravels largely composed of serpentine.

Mineralogically, platinum is nearly always alloyed with iridium, osmium, palladium, rhodium or ruthenium in metallic form, but a notable exception is its occurrence as an arsenide-sperrylite which has been found to contain 52.50 per cent platinum, 41 per cent arsenic, 4.50 per cent tin oxide, 0.75 per cent rhodium or ruthenium, 0.50 per cent antimony and 7 per cent iron in the nickeliferous pyrrhotite of Canada.

Russia virtually supplies the world market. There the metal occurs in grains and sometimes in nuggets. One has been reported from the Nijni-Taglisk District weighing 22 pounds. Russian sands and gravels from the Avrorinsco district contain from a quarter ounce to nine ounces per ton.

The total production from California in the year 1887 was 40.475 ounces, mostly from the auriferous sands and gravels of Humboldt county. California production has been lessening, but small quantities have been coming from Oregon. Reports of finds of platinum in California and Oregon indicate a greater interest in the metal, and it is reported as probable that the United States production may increase.

Metallurgy of Platinum
Platinum, if chemically pure, has a light steel-gray color, is very lustrous, moderately hard and very difficult to fuse- 1,800 to 2,000 degrees- depending upon the exactness in regulation of the oxygen. It is easily fused if in contact with another metal, especially phosphorus or arsenic, and it can be alloyed with all metals but zinc. If pure, it is as malleable as gold, but with a small content of iridium or titanium it is brittle. It does not oxidize upon ignition in the air and is insoluble in nitric, hydrochloric, or sulphuric acid, but dissolves when heated in aqua regia. The solution contains hydrochloroplatinic acid and is the source of chemically pure platinum obtained by the “wet method.’
In the preparation of pure platinum, England and Germany have a monopoly. There seems to be no real reason for such a monopoly for, while the recovery is at times difficult, it is not beyond average intelligence, and the cost is small as compared to the value of the product.

The method used by the metal refiners in Europe is as follows: The crude platinum ore is mixed with an equal amount of low-grade galena ore and treated in a reverberatory furnace. When the metal contained in the ore has formed an alloy with the lead, ground glass and borax are added as fluxes and the mass maintained in a molten state for quite some time. During this period the osmiridium, not alloying with the lead, sinks to the bottom by reason of its higher specific gravity. The sulphur content is then oxidized by the addition of litharge, the slag skimmed off and the metal run into ingots.

By cupellation, the lead is disposed of and platinum is obtained containing a small amount of iridium and rhodium. The use of this method is most successful when the furnace charge is not in excess of 200 pounds. The metal as obtained in this manner is an impure platinum and well adapted for ordinary use. If greater purity is desired, the platinum is melted with six times its weight of chemically pure lead, the product then granulated by dropping from a tower into cold water and the granulated product dissolved in eight parts of water and one part nitric acid, which removes most of the lead, iron, copper, palladium and rhodium, leaving a black amorphous powder containing all the platinum and minute particles of other metals.

The iridium that is in the residue shows as brilliant crystals which are insoluble in nitric acid. This residue is treated with dilute aqua regia, which dissolves all of the platinum and lead but not the iridium crystals. The solution is now evaporated to about one-third its original bulk and sulphuric acid added to precipitate the remaining lead. The solution is then filtered and ammonium and sodium chlorides added, precipitating the platinum as potassium platinum chloride (K2PtC1S), a yellow crystals. The solution is then heated to 1760 F. and left to stand for two days.

When the precipitate has completely settled, the solution which still contains the rhodium as a double salt, is poured off and the precipitate washed with a weak solution of ammonium chloride and then water. As some rhodium may still be present, the platinum chloride, after drying, is mixed with potassium bisulphate containing a small amount of ammonium sulphate and heated in a platinum crucible until the platinum is completely reduced. The rhodium, if present, remains as rhodium bisulphate, which may be removed by washing with water.

The pure platinum sponge which has now been obtained is put into a limestone furnace, consisting of two pieces of quick lime, cylindrical in shape, the top one hollowed out dome-shaped with a conical opening in the center to receive the fuel pipe, with a vent of proportionate size to the outer edge to permit of the elimination of fumes. The lower stone is shaped with a flat and level bottom with the sides curved so as to meet the top arch above. In order to secure a perfect fusion of the charge, it must be of such a size so that the molten metal will run in a layer from 8 to 4 mm. thick. The vent in the lower stone is shaped to permit of use as a lip and tap hole. The two stones are neatly fitted and held securely together by an iron band while operating.

The fuel may be illuminating gas and oxygen, which is the most economical, or it may be oxy-hydrogen, and the oxygen must be kept slightly in excess of actual requirements. In. this type of furnace, platinum is not only melted but refined as all iron or silicon present is absorbed and osmium volatilized as oxide. The application of the oxy-hydrogen blowpipe was first used by Hare to fuse 1arge masses of platinum sponge and later the method was considerably improved by Deville and Debrey1 two French chemists, to whom metallurgists are greatly indebted for their painstaking work on platinum and the platinum group of metals.

The German government works, Heraus at Hanau, for many years have employed the following process for the extraction of platinum: The raw ore is treated in a glass retort under a pressure of 12 inches of water with a mixture of one part aq1ua regia and two parts of water. The solution is evaporated to dryness and the dried mass heated to 125 degrees, at which temperature the palladium and rhodium salts are reduced to lower chlorides. The clear aqueous solution, acidified by hydrochloric acid, is precipitated by ammonium chloride; the pure double chloride of platinum and ammonium being thrown down, while the corresponding iridium salt is obtained by evaporating the mother liquor.

The solution, after removing the platinum salt, is treated with scrap iron, which throws down the other metals, and the precipitate from which the excess of iron has been dissolved by hydrochloric acid is again treated with aqua regia. From this solution, a new portion of platinum and iridium is thrown down and the mother liquors as well as the residue left on dissolving the ore in aqua regia, contain the palladium, rhodium, ruthenium, osmium and iridium.

The double chloride is broken up, pressed into molds and ignited and the spongy platinum thus obtained is melted in a limestone furnace as described above with an excess of oxygen, the resulting metal being commercial platinum, which contains about 2 per cent iridium or Osmiridium, with traces of rhodium and ruthenium.

In order to obtain chemically pure platinum, the following process is perhaps the best: the metal is re-dissolved in aqua regia by a gentle heat. After adding a little ammonium chloride, the solution is evaporated to dryness and well washed in 80 per cent alcohol, then washed in diluted C. P. sulphuric acid, then in a 5 per cent solution of ammonium chloride. Now a solution of ammonium oxalate is added and gently warmed and electrolyzed by the use of one Bunsen cell, or its equivalent. The metal is rapidly deposited on the cathode.

The deposited metal cannot be distinguished from hammered platinum and it is easy to deposit from one-half to one gram in 5 hours from a solution containing 0.6 grams per 200 cc., by the use of one cell only. If the metal is now fused in the lime furnace and the flame suddenly stopped so as to cause the metal to solidify from the outside in and preventing the formation of bubbles, it has a tin white color, is as soft as copper and as malleable as gold and has a specific gravity of 21.5. It can be melted at a white heat and an extremely fine wire can be melted in the flame of a Bunsen burner, but in bulk it will not flow at a less temperature than 2,0000 C.

The red-hot metal has the power of absorbing hydrogen, taking up 8.8 volumes of this gas, which it will give up on heating in a vacuum, the surface of the metal becoming covered with bubbles. Oxygen is not absorbed by platinum, but the metal possesses the unusual power of condensing this gas on its surface, which is the cause of its “spitting” and is regarded as a means of identification.

An electrometallurgical procedure, which must have close attention if it is to be successful, involving the purification of the carbon plates, is to immerse the plates in sulphuric acid, diluted with a to 4 times its volume of pure water for 6 to S hours; next in sulphuric acid with 10 volumes of water for the same length of time. With crystals of platinum chloride added, the plates should now be straw color and are to be connected to a suitable battery. The carbon becomes ‘platinized’ which is shown by the rising of hydrogen from the surface. More platinum chloride dissolved in a saturated solution of ammonium oxalate is added and kept at a temperature of IOO F.; the depositing of the metal continuing until the solution is exhausted.

Palladium is best treated in the same manner, the solution consisting of three pints of pure water, 10 grams palladium chloride, 100 grams ammonium phosphate, 500 grams sodium phosphate and 5 grams benzoic acid. From this solution, metallic palladium is deposited on all metals but zinc.

Editor’s Note.—The author of this article, C. A. Ackerman, 565 Bryant Street, San Francisco, California, states that he will be pleased to answer by mail all questions relative to platinum or the platinum group of metals. (rehab notes: the process now used is described by C W Ammen’s book, RECOVERY & REFINING OF PRECIOUS METALS.)

rehab · CONTROL OF PLATINUM MARKET TOUGH EMJ 8 25 1928

Control of Platinum Market Desirable, Yet Difficult of Achievement

UP TO MARCH, 1927, the marketing of platinum was largely controlled by a syndicate consisting of Johnson & Matthey (London), Baker (New York), Marret, Bonnin (Paris), and Heraus (Hanau), according to a review which will appear in the forthcoming issue of “Mineral Industry” (McGraw-Hill Book Company), by Dr. 0. F. Kunz, who, in addition to presenting complete statistics and other important and pertinent comment, adds:
“This syndicate had agreed to take from the Soviet government 60,000 to 70,000 oz. a year, on the condition that no Russian platinum be sold directly. But with the Russian production in 1925 and 1926 materially exceeding this amount, the Soviet representatives desired a larger allotment of the supply, while the syndicate on its part, due to increased production elsewhere, desired to reduce the Russian quota. As a result, the agreement was not renewed, and the Soviet output was put on the market directly in competition with the syndicate. In May, 1927, the Soviet government organized the Rusplatina to handle the distribution, and by the end of the year had sold an amount considerably exceeding the quota that had been previously allotted to Russia by the syndicate.
“Although no specific figures are available on the cost of production of Russian platinum, estimates place this at $40 to $50 per ounce. In view of this fact, and of the rapidly increasing production in Russia, the opinion has been freely expressed that the heavy decline in the price of platinum in the first half of 1927 was the result of Soviet manipulation of the market, in order to discommode other producers, practically all of whom have higher production costs, and particularly the new fields in South Africa. With prices still low, and a large proportion of the possible profits thereby forfeited, production is probably somewhat restricted below what it otherwise would be, but nevertheless the industry is still going forward. Although it is not likely that it will soon, if ever, reach the predominating position so enthusiastically predicted for it two or three years ago, this failure would seem to be attributable fully as much to the metallurgical difficulties encountered in handling the South African ores as to the price situation.
“Another view of the matter is that the price was forced down with the idea that the lower prices would lead to proportionately increased demand. With such a large percentage of the metal going into jewelry, where low prices are not necessarily the ruling factor, this may not be realized.
“While never controlled in the way or to the extent that the diamond market is, the price of platinum has for many years been more or less artificially inflated, but the present situation seems to promise a return to the rule of the law of supply and demand. If this be the case, a heavy overproduction would result disastrously for all concerned. The only other alternative would seem to be a rigid control, such as is maintained with diamonds. This has been repeatedly discussed and advocated for platinum, but the manifest difficulties in establishing a régime of this kind have thus far prevented any definite arrangement, and the breach between Russia and the previous syndicate would seem to make the possibility of the establishment of such a control more remote than ever.

August 25, 1928— Engineering and Mining Journal

TIDBITS OF INFO-PLATINUM

CONTROL OF PLATINUM MARKET TOUGH EMJ 8 25 1928