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Platinum is "little silver" (platina) evolved into Platinum comes, America Indian people already know, the first Spaniard de Ulloa • A (DADeulloa) to South America know "little silver." In 1741 Wood (C. Wood) brought "Little Silver" to Europe. In 1803, the British (War Wollaston) determined the La Platinum process. At the same time, two new elements, palladium and rhodium , were separated from the aqueous solution of platinum .
Platinum properties
Platinum, silver-white metal. It has excellent corrosion resistance to common acids and chemicals. Platinum does not interact with common acids, but dissolves slowly in aqua regia to form chloroplatinic acid. Platinum has excellent oxidation resistance and can maintain gloss in the air for a long time. At high temperatures, platinum reacts with oxygen to form volatile oxides, increasing its rate of evaporation. Platinum has a strong adsorption capacity for gases. When the particle size is very fine (such as platinum black, palladium black) or colloidal (such as colloidal platinum), the adsorption capacity is stronger, so it has excellent catalytic properties. Platinum transition metal, with multiple valences, the most stable valence is as follows: 钌 is +3; 铑 is +3; palladium is +2, +4; 锇 is +3, +4; 铱 is +3, +4; platinum It is +2, +4. They have a strong tendency to form complexes, the most common being complexes that produce a coordination number of 4 or 6. It has a strong tendency to form complexes, the most common being the complex with a coordination number of 4. In short, its chemical nature is very complicated. Pure platinum has good ductility, and the cold plastic deformation without intermediate annealing can reach more than 90%, and can be processed into micron-sized filaments and foils.
Platinum resources
At present, more than 80 kinds of platinum group minerals and platinum group-containing minerals have been discovered, and there are 200 varieties of variants and unnamed minerals. In nature, the natural form of the platinum group metal elements of the main countries, natural minerals alone alloy, antimony, sulfides, sulfur, arsenic and bismuth compounds tellurides exist, some were present in the isomorphism sulfides, such as brass ore, Nickel pyrite, purple sulfur nickel (Fe) in the ore.
Platinum preparation
1. Extraction of platinum group metals: Platinum ore or platinum-bearing metal gold ore is re-selected by re-election method to obtain concentrate. The content of platinum or rhodium and ruthenium can reach 70-90%, which can be directly refined. Since the 1950s, platinum group metals have been mainly extracted from copper-nickel sulfide symbiotic ores, and a small part has been extracted from copper smelting by-products. The ice nickel with high platinum group content is now leached by sulfuric acid under oxygen pressure, or chlorinated metallurgical separation of other metals to obtain platinum group concentrate. The platinum group concentrate is directly dissolved, separated, purified, or the ruthenium and osmium are first oxidized and evaporated, and then the other platinum group metals are separated and purified. 2. Platinum group metal regeneration: Platinum group metals are rare and expensive, and have always paid attention to recycling. The platinum group metal can be recovered from waste catalysts, waste electrical components, platinum-containing broken vessels, waste plating solutions, and wastes from jewelry and jewelry factories. 3. Separation and purification of platinum group metals: The extraction and purification processes of platinum group metals vary depending on the composition and content of the raw materials. The platinum group metal concentrate or the anode mud containing the platinum group metal is dissolved in aqua regia, and palladium, platinum, and gold are all introduced into the solution. Treatment with hydrochloric acid to destroy the nitrosyl compound, followed by precipitation of gold by the addition of ferrous sulfate. Ammonium chloride is added, platinum is precipitated as ammonium chloroplatinate, and calcined ammonium chloroplatinate can obtain sponge platinum containing more than 99.5% of platinum. After separating the platinum filtrate, an excessive amount of ammonium hydroxide is added, and then acidified with hydrochloric acid to precipitate palladium in the form of dichlorodiamine palladium, and then calcined in hydrogen to obtain a sponge palladium having a purity of 99.7% or more. Following the above treatment after Wang insolubles sodium carbonate, borax, litharge and coke eutectic, Degui lead. Most of the lead is removed by ash blowing, and then silver is dissolved with nitric acid, and the remaining lead, bismuth, bismuth, bismuth, and antimony are concentrated in the residue. The residue is melted with sodium hydrogen sulfate, converted into a soluble sulfate, leached with water, added with sodium hydroxide to precipitate barium hydroxide, and then dissolved with hydrochloric acid to obtain chlorodecanoic acid. After the solution is purified, ammonium chloride is added, and the ammonium chloroantimonate is crystallized and concentrated. Calcination in hydrogen gives a sponge. When sodium hydrogen sulfate is melted, lanthanum, cerium and lanthanum do not react and remain in the water leaching residue. The residue is melted together with sodium peroxide and caustic soda, and leached with water; chlorine gas is introduced into the leachate and distilled, and hydrazine and hydrazine are distilled off as an oxide. After absorption with an ethanol-hydrochloric acid solution, the absorption liquid is heated and distilled again, and sodium citrate is obtained by absorption with an alkali solution. When ammonium chloride is added to the absorption liquid, the antimony is precipitated as an ammonium salt and calcined in hydrogen to obtain a crucible powder. Ammonium chloride is added to the residual liquid of the steamed mash to obtain an ammonium salt of cerium, which is then calcined in hydrogen to obtain cerium powder. The residue after leaching ruthenium and ruthenium is mainly ruthenium oxide, dissolved in aqua regia, and ammonium chloride is precipitated by adding ammonium chloride. After purification, it is calcined in hydrogen to obtain bismuth powder. The metal ingot can be obtained by powder metallurgy or by high-frequency induction furnace melting. 4. Preparation of high-purity platinum group metal: After the metal is dissolved, after repeated purification, the purification method includes carrier oxidative hydrolysis, ion exchange, solvent extraction and repeated precipitation, etc., and then precipitated with ammonium salt, and calcined to obtain corresponding High purity metal.
Use of platinum
Platinum group metals and alloys have many important industrial uses. In the past, the distillation tank was mainly used to produce dilute sulfuric acid by the concentrated lead chamber method. The standard meter and weight were also made of platinum-rhodium alloy. In the middle of the 19th century, Russia had made platinum-ruthenium alloy coins circulating in the market. Currently, the main use of platinum group metals and their alloys is in the manufacture of catalysts. Platinum-rhodium alloys are particularly resistant to molten glass and can be used to make enamels for the production of glass fibers. Platinum rhodium, platinum rhodium, and platinum-palladium alloys have high arc-resistance and are used as electrical contact alloys, which is one of the main uses of platinum. Due to the stable chemical nature of platinum, experimental vessels such as tantalum, electrodes, and resistance wires made of pure platinum, platinum-rhodium alloy or platinum-rhodium alloy are essential for chemical laboratories. Platinum cobalt alloy is a hard magnetic material with high magnetic energy. Platinum and platinum alloys are widely used in the manufacture of rings, cases and pins for a variety of jewellery, especially diamonds. Alloys of platinum or palladium can also be used as dental materials. Platinum, palladium and rhodium can be used as electroplated layers and are commonly used in the electronics industry and in jewelry processing. In recent years, the titanium anode coated with bismuth and platinum replaced the graphite anode in the electrolytic cell, which improved the electrolysis efficiency and prolonged the electrode life. It is an important technical improvement in the chlor-alkali industry and opens up new avenues for industrial use. . Niobium alloy can be used to make nibs and styluses. Palladium alloys are also used in the manufacture of hydrogen purification materials and high temperature brazing solders. Platinum equipment is also used in the chemical industry.