PRECIOUS METALS

B. M. of high purity is obtained by refining. The loss of gold in this case (including melting) does not exceed 0.06%, the gold content in the refined metal is usually not lower than 999.9 samples; the loss of platinum metals is not less than 0.1%. Work is underway to intensify the cyanide process (cyanidation under pressure or oxygen purging), non-toxic solvents are being sought for the extraction of B. M., combined methods (e.g., flotation-hydrometallurgical) are being developed, organic methods are being used. reagents, etc. Deposition of B. M. from cyanide solutions and pulps, it is effectively carried out with the help of ion-exchange resins. B. M. are successfully extracted from deposits with the help of bacteria (see Bacterial leaching).

While preserving the functions of currency metals, gold (see Money), B. M. at the same time have been widely used in technology.

Methods of hydrometallurgy, often combined with enrichment, are widely used for the extraction of BM. Gravitational enrichment of B. M. makes it possible to isolate large metal particles. It is complemented by cyanidation and amalgamation, the first is theoretical. the rationale for k-roy is given by sov. scientist I. N. Plaksin in 1927. Silver chloride is most favorable for cyanidation; sulfide silver ores are often cyanized after pre-chlorinating firing. Gold and silver from cyanide solutions are usually precipitated with metallic zinc, less often with coal and resins (ionites). Gold and silver are extracted from ores by selective flotation. About 80% of silver is obtained mainly by pyrometallurgy, the rest by amalgamation and cyanidation.

According to the efficiency of extraction of B. M. from placers, the best is the draining method (see Draining development), scraper-bulldozer and hydraulic are less economical.Underground placer mining is almost 1.5 times more expensive than the draining method; in the USSR it is used on deep placers in the valleys of pp. Lena and Kolyma. Silver is extracted mainly from ore deposits. It is found mainly in lead-zinc deposits, which annually produce about 50% of all mined silver; 15% are obtained from copper ores, 10% from gold; about 25% of silver production falls on silver vein deposits. This means that some of the platinum metals are extracted from copper-nickel ores. Platinum and metals of its group are smelted together with copper and nickel, and when the latter are purified by electrolysis, they remain in the sludge.

In 1887-88 in England, J. S. MacArthur and br. R. and W. Forrest received patents for methods of extracting gold from ores by treating them with dilute alkaline cyanide solutions and depositing gold from these solutions with zinc chips. In 1893 gold was deposited by electrolysis, in 1894 - by zinc dust. In the USSR, gold is extracted mainly from placers; abroad, about 90% of gold is from ore deposits.

In addition to amalgamation, in 1886, for the first time in Russia, gold was extracted from ores by chlorination (Kochkar mine in the Urals). In 1896, the first cyanide gold extraction plant in Russia was launched at the same mine [the first such plant was built in Johannesburg (South Africa) in 1890]. Soon the cyanide process was used to extract silver from ores.

The purification and processing of platinum was hampered by its high melting rate (1773.5°C). In the 1st half of the 19th century, A. A. Musin-Pushkin received malleable platinum by calcining its amalgam. In 1827, Russian scientists P. G. Sobolevsky and V. V. Lyubarsky proposed a new method of purification of crude platinum, which marked the beginning of powder metallurgy. During the year , this method was cleaned for the first time in the world approx. 800 kg of platinum, i.e. platinum processing has been carried out on a large scale. In 1859, French scientists A. E. St. Clair Deville and A. Debre for the first time melted platinum in a furnace in an oxygen-hydrogen flame. The first works on the electrolysis of gold date back to 1863, in production this method was introduced in the 80s of the 19th century.

Starting from the 2nd half of the 19th century. deep placers in Russia are developed underground, and in the 90s of the 19th century. excavators and scrapers are introduced.

In 1767 F. Bakunin in Russia for the first time applied the melting of silver ores using slags as fluxes. The works of the Swedish chemist K. V. Scheele (1772) contained an indication of the transition of gold into solution under the action of cyanide compounds. In 1843, the Russian scientist P. R. Bagration published a work on the dissolution of gold and silver in aqueous solutions of cyanide salts in the presence of oxygen and oxidants, laying the foundations of hydrometallurgy of gold (see Hydrometallurgy).

To extract B. M. from placer deposits in the 19th century, numerous designs of gold mines were created. cars (e.g., bootpar, cradle). Since the 1st half of the 19th century, butor mining has been widely used in the Ural mines. In the 30s of the 19th century. in the mines, water for the erosion of placer rocks was supplied under pressure. Further improvement of this method led to the creation of hydromonitor prototypes. In 1867 A. P. Chausov near the lake. Baikal for the first time carried out a hydraulic lift. development of placers; later (1888) this method was applied by E. A. Cherkasov in the valley of the Chebalsuk River in the Abakan taiga. In the beginning . 19th century . dredgers were used to extract gold and platinum from watered placers, and in 1870 a dredge was used in New Zealand for this purpose.

In 1824 on the east. a rich placer of platinum and gold was found on the slope of the Ural Mountains and the first platinum mine in Russia and Europe was laid. Later K. P. Gollyakhovsky et al . The Issov system of gold-platinum placers, which has gained worldwide fame, has been discovered. In 1828, the Russian scientist V. V. Lyubarsky published works on the world's first indigenous platinum deposit discovered near the Main Ural Ridge, 95% of platinum until 1915 was mainly extracted from placers, the rest was obtained by electrolytic. refining of copper and gold.

Mining of B.M. in Russia began in the 17th century in Transbaikalia with the development of silver ores, which was carried out underground. The first written mention of gold mining from placers in the Urals dates back to 1669 (the chronicle of the Dolmatovsky monastery). One of the first gold deposits in Russia was discovered in Karelia in 1737; its development dates back to 1745. The beginning of gold mining in the Urals is considered to be 1745, when E. Markov discovered the Berezovsky ore deposit. In 1819, a "new Siberian metal" (platinum) was discovered in placer gold deposits in the Urals.

In 1803, scientist W. H. Wollaston discovered palladium and rhodium, and in 1804, scientist S. Tennant discovered iridium and osmium. In 1808, the Russian scientist A. Sniditsky, examining platinum ore brought from South America, extracted a new chemical element, which he named vestium. In 1844 , Prof. K. K. Klaus of Kazan University comprehensively studied this element and named it ruthenium in honor of Russia. Platinum group metals are found in nature most often in polymetallic compounds. (copper-nickel) ores, as well as in gold and platinum deposits.

In the 1st half of the 16th century, the Spanish colonialists drew attention to the non-melting heavy white metal found along with gold in placers of N. Granada. According to the external similarity with silver (Spanish plate), they gave it a diminutive name. "platinum" (platina). Platinum was known in ancient times, nuggets of this metal were found together with gold and called them "white gold" (Egypt, Spain, Abyssinia), "frog gold" (Borneo Island), etc. Initially, the Spaniards considered it a harmful impurity, so a decree was issued by the government, prescribing to throw platinum into the sea. The first scientific. the description of platinum was made by Watson in 1741 in connection with the beginning of its mining in prom. scale in Colombia (1735).

In the 11th-6th centuries BC, gold was mined in Spain in the valleys of the Tagus, Duero, Minho and Guadjaro rivers. In the 6th-4th centuries BC, the development of indigenous and placer gold deposits began in Transylvania and Zap. The Carpathians. In the Middle Ages (up to the 18th century), preim was mined. silver, gold production has declined. Since the 16th century, the Spaniards have been developing B.M. on the territory of South America: since 1532 - in Peru and Chile, and since 1537 - in N. Granada (modern Colombia). In Bolivia, in 1545, the development of the "silver mountain" of Potosi began. In 1577, gold-bearing placers were discovered in Brazil. To ser. 16 in . In America, gold and silver were mined 5 times more than in Europe before the discovery of the New World.

B. M. was extracted from placers by washing sands on shields, animal skins with trimmed wool were laid on top of them (to catch grains of gold), as well as using primitive troughs, trays and ladles. B. M. from ores was extracted by heating the rock to cracking, followed by crushing the blocks in stone mortars, grinding with millstones and washing. The separation by size was carried out on sieves. From the technique of that time, the method of separating gold and silver alloys by acids, the separation of gold and silver from a lead alloy by cupellation (etc. Egypt), extraction of gold by amalgamation with mercury or using a fatty surface (Dr. Greece). The cupellation was carried out in clay crucibles, where lead, salt, tin and bran were added.

Gold and silver have been known to mankind for many years. millennia; this is evidenced by the products found in ancient graves, and primitive mine workings that have survived to the present day. The main centers of mining of B. M. in ancient times were the Upper. Egypt, Nubia, Spain, Colchis (Caucasus); there is information about the extraction of B. M. on the Amer. continent (Center, and South. America) and in Asia (India, Altai, Kazakhstan, China). On the territory of Russia, gold was mined already in the 2-3 th millennium BC (the so-called Chudsky works).

PRECIOUS METALS, gold, silver, platinum and platinum group metals (iridium, osmium, palladium, rhodium, ruthenium), which received their name mainly due to high chemical properties. durability and beautiful appearance in products. In addition, gold, silver and platinum have high plasticity, and platinum group metals are refractory. These advantages of the B. M. department are combined in their alloys, which are widely used in engineering.