Precious metal main compounds and complexes (1)

(A) a platinum group metal oxide with an oxide multiple valence, such as _{PdO, Rh 2 O 3, Ir} 2 O 3, RuO 2, RhO 2, IrO, PtO 2, RuO 4, OsO 4 and the like. In addition to osmium, ruthenium oxide, oxides most unstable, pyrolysis of metal. In extractive metallurgy, many important properties of palladium , ruthenium, and osmium oxides directly affect their effective enrichment and separation. Palladium is easily oxidized to PdO when it is burned with a complex salt satin in the refining process. This oxide is insoluble in any acid and is insoluble in aqua regia, which makes the process of re-refining and re-refining difficult.
The metal powder of cerium and lanthanum can be oxidized by oxygen in the air at normal temperature. When a chlorine complex of ruthenium, osmate or ruthenium is present in an alkaline or acidic solution, various oxidants such as oxygen, chlorine, chlorate, hydrogen peroxide, and nitric acid can be oxidized to volatile high-valent oxides. . The octavalent oxides OsO ₄ and RuO ₄ are characteristic oxides, all of which have a caustic soda odor and are toxic. OsO ₄ is a colorless or light green transparent solid at normal temperature, and has a tetrahedral structure, but has a melting point of only 41 ° C and a boiling point of 141 ° C. It is easily vaporized and volatilized at a lower temperature, and gaseous OsO _{4 is} almost colorless. RuO ₄ is a yellow needle-like solid at room temperature, and also has a regular tetrahedral structure. The melting point is 25 ° C, the boiling point is 65 ° C, and it is easier to vaporize and volatilize than OsO ₄ . Gaseous RuO ₄ is orange and has poor thermal stability. When vaporized, sublimed or distilled, it will decompose spontaneously if it encounters a higher temperature (about 180 ° C). However, OsO ₄ has better thermal stability.
Both high-valent oxides are strong oxidants, which are decomposed or reduced to OsO ₂ , RuO ₄ and emit oxygen. RuO ₄ and OsO _{4 are} very soluble in many organic solvents and are relatively stable. For example, the solubility of OsO ₄ in CC1 ₄ is as high as 250%, which is one of the methods for extracting ruthenium and osmium from solution. Both octavalent oxides are acidic oxides and are soluble in water. The aqueous solution of OsO ₄ is colorless and up to 7.24% in 25 ° C water. The aqueous solution of RuO ₄ is golden yellow, which can reach 2.03% in 20 ° C water. They are all soluble in alkaline solution to form hydrazine and citrate, but they will re-evaporate at higher temperatures. OsO ₄ is less soluble in acidic solutions than RuO ₄ , which is reduced in hydrochloric acid solution and converted to stable low-cost chlorodecanoic acid. What kind of valence state is related to the concentration of hydrochloric acid and the time of standing. For example, in 6 mol/L HC1, all of them are in the state of Ru(IV) chloride acid, the acidity is reduced to 0.5 mol/L and the long time is converted into Ru. (VI). When the acidity is reduced to 0.1 mol/L, it is completely converted into a RuO ₄ black precipitate. In the extraction metallurgy, the octavalent oxide which is easily oxidized to be highly volatile by hydrazine and hydrazine is separated from other metals, and then separately absorbed by a cold dilute alkali solution and a dilute hydrochloric acid solution, and separated from each other.
(2) Hydrated oxides (hydroxides) [next]
The oxides of different valence states of the platinum group metals basically have their corresponding hydrated oxides, which are all prepared by neutralization and hydrolysis of a salt of each metal or an aqueous solution of the complex. When an oxidizing agent or a reducing agent is simultaneously added during hydrolysis, a hydrated oxide of a desired valence state can be controlled and prepared. If a protective gel is added to the solution, the corresponding colloidal solution is formed upon hydrolysis. The hydrated oxides often encountered in metallurgy extraction are mainly Au(OH) ₃ , Rh(OH) ₃ , Ir(OH) ₃ , Rh(OH) ₄ , Ir(OH) ₄ , Pt(OH) ₂ , Pt ( OH) ₄ , Pd(OH) ₂ , Ru(OH) ₃ , Ru(OH) _{4 ,} and the like. They have different colors, such as the newly precipitated tetravalent platinum hydrated oxide is white, boiled to brown, and turned black after drying. Rhodium, iridium oxide hydrate thereof depends on the color of the hydrolysis conditions, such as the alkaline precipitation with concentrated black prepared Rh (OH) ₃ (sparingly soluble inorganic acid) and Ir (OH) _3, and produced with dilute lye The precipitates were yellow Rh(OH) ₃ •H ₂ O and green Ir(OH) _{3 , respectively} .
All hydrated oxides have very low solubility and are easily redissolved in mineral acids. If heated completely dehydrated, they are converted to the corresponding oxides, which are poorly soluble or completely insoluble in the acid. The fresh precipitate is converted to the corresponding chlorine complex anion after dissolution with hydrochloric acid. Some hydrated oxides, such as PdO ₂ •xH ₂ O, RhO ₂ •xH ₂ O, are also soluble in organic acids (such as acetic acid) and also in caustic solutions to form the corresponding metal salts, such as NaRhO ₂ .
(III) Sulfides Sulfides are important compounds of precious metals. There are sulfide minerals with very stable properties in nature. Hydrogen sulfide gas is typically introduced into the body from an aqueous solution containing sodium sulfide or precious metals, can obtain their sulfide precipitation. It can also be directly prepared by reacting metal with sulfur under high temperature and vacuum conditions. The sulfides of different valence states frequently encountered in metallurgy extraction are Au ₂ S, Au ₂ S ₃ , Ag ₂ S, RuS ₂ , RuS ₃ , Rh ₂ S ₃ , Rh ₂ S ₅ , PdS, PdS ₂ , OsS ₂ , IrS, Ir ₂ S ₃ , IrS ₂ , IrS ₃ , PtS, PtS ₂ and the like. Since the hydrogen sulfide or sodium sulfide itself has a certain degree of reducibility and the resulting sulfide has an SS bond, the precipitated sulfide is actually in a low-cost state. If the concentration of the precious metal in the solution is very dilute, the sulfide formed is in a colloidal state and it is difficult to filter and separate. Some freshly precipitated sulfides, such as PtS ₂ and PdS, can also be slowly oxidized to sulfate in air.
All precious metal sulfides are darker (grey to black). When high-valent sulfides are heated, they can be degraded into low-priced sulfides step by step until they are decomposed into metals. All sulfides are insoluble in water, and the fresh sulfides prepared by precipitation are easily redissolved in mineral acids, and the presence of oxidants accelerates the dissolution process. However, the high-temperature synthesized sulfides are chemically stable, difficult to dissolve in inorganic acids, and even hard to dissolve in aqua regia. [next]
(4) Sulfate and Nitrate These two types of compounds are classified into two types according to the form of metal: one is a simple salt of a metal such as Ag ₂ SO ₄ , AgNO ₃ , Ru(SO ₄ ) ₂ , Rh ₂ ( SO ₄ ) ₃ , Ir ₂ (SO ₄ ) ₃ , Ir(SO ₄ ) ₂ , PdSO ₄ •H ₂ O, Pt(SO ₄ ) ₂ , Pd(NO ₃ ) _{2 ,} etc.; the other is a complex such as H[Rh(SO ₄ ) ₂ ], H[Pt(SO ₄ ) ₂ ], K ₂ [Pt(NO ₂ ) ₆ ], and the like. The corresponding simple sulfate is obtained by reacting an oxide or a hydrated oxide of silver , ruthenium, palladium or iridium with sulfuric acid under heating. Sulfate can be obtained by reacting metallic silver or palladium powder with hot concentrated sulfuric acid or with a mixed acid of nitric acid and sulfuric acid. The sulphide and bismuth sulfides are converted to the corresponding metal sulphates by oxidation with nitric acid. Metal platinum and concentrated sulfuric acid are heated to 380 ° C to form platinum sulfate. The metal ruthenium is converted to barium sulphate by calcination with KHSO ₄ or K ₂ S ₂ O ₇ . The sulphate of cerium (III) and cerium (III) is easy to form a double salt with alkali metal sulphate - hydrazine. The general formula of the phosphonium salt is M'M(SO ₄ )•12H ₂ O. In the formula, M' is an alkali metal cation such as lithium , sodium, potassium, rubidium or cesium .
The sulfate of the platinum group metal is soluble in water. Platinum and cerium sulfates are also soluble in ethanol and diethyl ether. The color of sulfate varies from yellowish red to reddish brown, depending on the amount of crystal water. For example, palladium sulfate with two crystal waters is reddish brown, one crystal water is olive green, and 15 crystal waters are grayish yellow. , reduced to 12 crystal waters to light yellow, reduced to 4 crystal waters turned red.
AgNO ₃ is the most important silver salt, colorless and transparent crystal, and easily soluble in water.
(5) Chloride The most important cyanides are AuCN, Au(CN) ₂ ^- , AgCN, Pd(CN) _2, etc., which are all soluble in alkaline cyanide solution and become an important method for extracting gold and silver.
(VI) Complexes Precious metals can form complexes with various valence states and very different properties. The differences in properties and different generation conditions of various complexes are important basis for many important and unique precious metal separation and refining methods.
The ligands in the gold and platinum group metal complexes are halogen (fluorine, chlorine, bromine , iodine ), nitro, nitroso, sulfur oxides or other compounds, cyanide, ammonia, water molecules, organic groups. There are many kinds of compounds, and the anion is complexed with the cations of many other elements. These complex salts have many structures such as tetrahedron, octahedron, cis, and trans. There are currently thousands of platinum-only complexes known. The most widely used metallurgy in precious metal extraction is halogen (especially chlorine), followed by ammonia, nitroso (NO ₂ ^- ), thiourea as ligands and complexes with alkali metal sodium, potassium and ammonium cations. With salt. The following are precious metal complexes that are used in the extraction of metallurgy. [next]
1. Chlorine complex chloride system (Aqua regia, chlorine, chlorate, etc.) has been the most important method for the dissolution of precious metals. The establishment and development of precious metal separation and refining methods are also based on the differences in the properties of their chlorine complexes. . This type of complex is the most important and well-studied system.
The solubility of AgCl in water is very low, but in the excess C1 ^- medium, the soluble complex AgCl ₂ ^{- is formed} .
Both gold and platinum group metals can form a chlorine complex of the formula mx'[M"Cly], wherein M' is a cation such as H ⁺ , Na ⁺ , K ⁺ , NH ₄ ⁺ , and M" is a noble metal cation, The M′′ valence state is different, x is usually 1-3, y is 4 or 6. In the crystalline state, it also contains different amounts of water of crystallization. The oxidation state of the central ion changes the stability of the complex and other chemical properties, It has an important influence on the selection and formulation of precipitation or extraction separation refining methods. The oxidation valence state of noble metals in chloride solution is: Ru(III IV II VI VIII V VII); Rh (III IV II I): Pd(II IV III); Os(IV VIII VI II III V); Ir(IV III VI II); Pt(IV II III V VI ); Au(III I).
The first two oxidation states of each metal are the most common, the first being the most stable oxidation state. The most common types and characteristics of chlorine anions are listed in the table below.

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