Method for recovering platinum from spent catalyst

Method for recovering platinum from spent catalyst

The catalyst in petroleum, chemical, environmental protection, mainly used as the carrier of the catalyst, which play a catalytic role and active ingredients for the platinum group metals, its content ranging from a few percent to the very few. Some of the active ingredients are single metals, and some are various metals. The materials used as catalyst supports are also various, usually oxides of base metals (such as Al ₂ O ₃ , Al ₂ O ₃ , -SiO ₂ , ZrO _{2 ,} etc.) or activated carbon, which provide a large surface area. The catalytically active component (platinum group metal or (and other metals)) is then supported on the surface of the support by impregnation, spraying or other means to form a highly dispersed catalytically active center. Some platinum group-containing metal catalysts using Al ₂ O ₃ as the main carrier are listed in Table 1.

Table 1 Catalysts containing platinum group metals

After long-term use of the supported catalyst, the catalyst is gradually deactivated due to various harmful impurities and is scrapped. Although the content of the platinum group metal in the catalyst is low, the platinum group metal is expensive and has a high recovery value.

First, the dissolution carrier method

Since the supported catalyst mainly aluminum oxide, aluminum is an amphoteric metal, a method of dissolving carriers are alkaline and acid method.

(1) Acid method

When the alumina in the carrier is in the form of γ-Al ₂ O ₃ crystal, it may be dissolved with hydrochloric acid or sulfuric acid. Sulfuric acid is often preferred because of its low price, low corrosiveness to equipment, and high boiling point.

In the dissolution of sulfuric acid, the effect of carbon deposition in the spent catalyst is large. If the spent catalyst does not burn off the carbon deposit before the sulfuric acid dissolves, it can inhibit the platinum group metal from entering the solution, and has a good promoting effect on the clarification of the dissolved material, which is favorable for solid-liquid separation. However, when carbon deposits and organic matter are present, it is easy to cause a trough. Therefore, the spent catalyst is generally subjected to charcoal treatment before the sulfuric acid is dissolved. When dissolved, a considerable part of the platinum group metal can enter the solution. In order to avoid the dissolution loss of the platinum group metal in the solution, a reducing agent (such as aluminum) may be added to the solution after dissolution, or sodium sulfide may be added to the solution to make the platinum group The metal precipitates as sulfide. For example, when treating a platinum-ruthenium spent catalyst, almost all of the ruthenium enters the solution, and the sulfide is added to precipitate it as a sulfide.

Studies have shown that when the concentration of sulfuric acid is less than 57%, platinum is not dissolved, and the concentration of sulfuric acid is further increased, platinum begins to enter the solution. In general, it is advantageous to appropriately increase the concentration of sulfuric acid for the dissolution of the carrier, and it has been proved that the concentration of sulfuric acid is suitably 20% to 50%.

The spent catalyst for ethylene hydrogenation reaction has a carrier of γ-Al ₂ O ₃ and a small amount of base metals such as Fe, Si, Ca, Mg, etc., containing Pd 0.031%, a shape of Φ 3 ~ 5 mm cylindrical, surface area carbon. The condition for dissolving the carrier with sulfuric acid is: boiling and dissolving with 40% sulfuric acid for 3 to 4 hours, the carrier dissolution rate is about 95%, most of the base metal is also dissolved and separated, and the insoluble slag contains Pd1%±, and the rest is mainly SiO _{2 .} And Al ₂ O ₃ .

If the carrier contains a large amount of α-Al ₂ O _{3 which} is difficult to dissolve, the sulfuric acid is incompletely dissolved, and the platinum group metal has a low enrichment ratio, and further enrichment by other methods is required.

(2) Alkali method

By utilizing the property that alkali can interact with SiO ₂ and Al ₂ O ₃ in the carrier, SiO ₂ and Al ₂ O _{3 are} dissolved to separate from the insoluble platinum group metal, and the usual base is sodium hydroxide.

Alkali dissolution is typically carried out in a higher temperature autoclave to reduce solution volatilization losses and enhance the dissolution process. However, some studies have suggested that the solution is boiled and dissolved in 40% NaOH solution. When the volume of the solution is reduced to half and the boiling point is raised from 120 ° C to 170 ° C, a certain amount of water is added and boiled for a while, and then diluted with a large amount of water, most of the platinum. Can be enriched in the slag.

In order to prevent the platinum group metal from being transferred into the solution to cause dispersion during alkali dissolution, a reducing agent may be added during the dissolution, for example, the catalyst is wet-milled into a slurry, mixed with an organic reducing agent, and then dissolved with an alkali. Reducing agents which can be used are hydrazine hydrate, formaldehyde, sodium borohydride, sodium tartrate, formic acid or glucose.

The alkali-dissolving method has a relatively complete dissolution of the carrier, and the platinum group metal has a high enrichment ratio, and can basically be quantitatively recovered. The sodium aluminate solution obtained after the dissolution is refined into a carrier required for the new catalyst according to the alumina production process, and comprehensive recovery of the spent catalyst can be achieved.

The alkali solution has a sodium hydroxide concentration of generally 200 to 300 g/L and a temperature of 140 to 200 °C.

However, the alkali solution method requires high-pressure equipment, and the sodium aluminate solution formed has a large viscosity, and solid-liquid separation is difficult, and practical application is not much.

(3) Calcination-dissolution method

When the carrier contains α-Al ₂ O _{3 which} is difficult to dissolve with an acid, the addition of a base can convert the insoluble α-Al ₂ O ₃ into a water-soluble sodium aluminate. The relevant reaction is:

Al ₂ O ₃ +2NaOH=2NaAlO ₂ +H ₂ O

In the ratio of sodium hydroxide: spent catalyst = 1 to 2:1, the furnace is heated to 700-800 ° C for 7-8 hours, and after boiling, it is boiled with 10 times of water for 30-40 minutes, Al ₂ O ₃ The dissolution rate can reach about 90%, the dissolution loss of the platinum group metal in the solution is very low, and the enrichment in the slag is about 10 times, and the repeated calcination three times can make the dissolution rate of Al ₂ O ₃ higher than 98%, and obtain the platinum group metal concentrate. The grade is about 20%, its solubility is very good, and it is oxidized and leached in the chlorination medium. The leaching rate of the platinum group metal can reach 99.8%, and the chlorinated slag can be returned to the roasting treatment.

Alkali calcination can also be used to treat alumina support waste catalysts containing platinum, palladium and rhodium. For example, for waste catalysts containing Pt 789g/t, Pd 331 g/t, Rh 62 g/t, alkali roasting-water immersion Once, the dissolution rate of Al ₂ O ₃ is about 84%, the concentration of Pt, Pd, and Rh in the solution is very low (less than 0.5 mg/L), and the grade of platinum group metal in the water leaching residue is about 0.7%, and the recovery rate is high. At 99.99%.

Second, direct leaching of platinum group metals

The platinum group metal in the spent catalyst can be dissolved into the solution by appropriate conditions, and then concentrated and separated, while the carrier is insoluble or rarely dissolved.

(1) Calcination-chlorination leaching method

For the spent catalyst in which the carrier is difficult to be dissolved by the acid, the treatment by this method is relatively simple. Since the platinum group on the surface of the catalyst is in a highly dispersed state due to the platinum group metal on the surface of the catalyst, its dissolution is much easier than the corresponding pure metal. Metals such as platinum and palladium generally do not need to be dissolved in aqua regia, and can be introduced into the solution with hydrochloric acid. The concentration of hydrochloric acid is 0.1 to 12 mol/L, usually 2 to 9 mol/L. Practice has proved that if it is difficult to obtain a satisfactory leaching effect with a single hydrochloric acid, it is often necessary to add a suitable oxidizing agent to the hydrochloric acid solution to promote the dissolution of the platinum group metal. Commonly used oxidants are nitric acid, chlorine, hydrogen peroxide, sodium chlorate, and the like.

When the carrier is a γ-Al ₂ O ₃ which is easily dissolved by an acid, when the spent catalyst is treated by a method of adding an oxidizing agent with hydrochloric acid, the platinum group metal and the carrier may both enter the solution, and the phenomenon that the aluminum salt is hydrolyzed to release is extremely likely to occur. In order to dissolve only the platinum group metal in the spent catalyst without dissolving the alumina in the support, the spent catalyst must first be calcined to remove carbon deposits and convert the acid soluble γ-Al ₂ O ₃ to acid-insoluble α- Al ₂ O ₃ . The catalyst for petroleum reforming and xylene isomerization is a platinum-containing γ-Al ₂ O ₃ supported catalyst, and the spent catalyst contains Al ₂ O ₃ 96.5%, Fe 0.4%±, SiO ₂ 0.7%±, Pt 0.35%. ±. The metal platinum is adsorbed on the surface of the carrier or the voids of the carrier by fine particles (less than 500 mm, 70% to 80%). The spent catalyst adsorbs a large amount of organic compounds and surface carbon, first calcined at 1000-1100 ° C, eliminating carbon deposits and converting γ-Al ₂ O ₃ into inert α-Al ₂ O ₃ . Then, the spent catalyst was leached at 70 ° C with a 6 mol/L hydrochloric acid solution at a liquid-solid ratio of 6 and sodium chlorate as an oxidizing agent for 1 to 2 hours. The leachate contains (g/L): Pt 0.263, Al 1.2±, Fe 0.07±, HCl 1.9mol/L±, the composition of the solution is simple, and the platinum group metal can be enriched by displacement or extraction. If the catalyst contains ruthenium, it will be partially converted into a difficult-to-dip oxide state when calcined at a high temperature. The effective pretreatment method is to use a sodium borohydride alkaline solution for reduction to improve the leaching rate.

(2) Pressurized cyanidation

At normal pressure and normal temperature, the platinum group metal and cyanide solution have basically no effect. At the same time, when the platinum group metal mineral is treated by cyanidation, the nature of the platinum group metal minerals is large, and the difference is large; It is not easy to cyanide or consumes cyanide minerals, which causes difficulty in cyanidation of platinum group metals, large consumption of process reagents, unstable dissolution efficiency of precious metals, and complex solution components. In the spent catalyst containing platinum group metals, the composition of the carrier is relatively simple and has little effect on the cyanidation process. Pressurization can be used to increase the cyanide leaching rate of the platinum group metal in the spent catalyst, so that the platinum group metal which cannot be cyanated at normal temperature reacts, and the cyanidation process has high selectivity to the platinum group metal, and the extraction process is relatively It is shorter and less corrosive to equipment, and has certain application prospects.

For the cylindrical honeycomb automobile exhaust catalyst (the carrier is ceramic cordierite), the platinum group metal is platinum, palladium and rhodium. The content (g/t) is Pt 690～1050, Pd 350～1130, Rh 8.3～ 250, performing pressure cyanidation, the reaction is:

2Pt+8NaCN+O ₂ +2H ₂ O=2Na ₂ Pt(CN) ₄ +4NaOH

2Pd+8NaCN+O ₂ +2H ₂ O=2Na ₂ Pd(CN) ₄ +4NaOH

4Rh+24NaCN+4O ₂ +8H ₂ O=4Na ₂ Rh(CN) ₆ +16NaOH

After pretreatment, the spent catalyst was leached for 2 h at a NaCN concentration of 5%, a temperature of 160 ° C, a liquid-solid ratio of 4, and a Po ₂ of 1.0 Mpa. The leaching rate was (%): Pt 98%, Pd 99%, Rh 96 %.

Under high temperature and high pressure, cyanide can be decomposed to a certain extent:

2CN ^- +O ₂ +2H ₂ O+2OH ^- =2NH ₃ +2CO ₃ ^2-

The decomposition of NaCN at different temperatures is shown in Table 2.

Table 2 Decomposition of sodium cyanide at different temperatures

It can be seen from Table 2 that the amount of decomposition of cyanide increases as the temperature increases and the time increases. Therefore, the cyanidation time should not be too long during the pressure cyanidation process. In order to ensure that sufficient cyanide reacts with the platinum group metal, the required cyanide in the solution is much larger than the theoretical amount of the reaction.

Third, the treatment of waste catalyst with carbon as carrier

Pd-C, Pt-C, Ru-C and other catalysts are often used in petrochemicals. The common feature of these catalysts is the use of activated carbon as a carrier. The activated carbon as a carrier is usually coconut shell charcoal, and is impregnated and adsorbed by a salt of a platinum group metal, and the noble metal is distributed in the surface of the carbon particles and in the pores in a state of fine metal. After the catalyst is scrapped, a large amount of organic matter is adsorbed, and in addition to the platinum group metal, a small amount of impurities such as Al, Cu, Zn, Fe, and Si are contained.

Since the platinum group metal penetrates into the interior of the carbon particles, the carbon density is small, floating on the surface of the solution during leaching, the carbon itself has reducing and adsorbing properties, and the method of directly leaching the platinum group metal from the carbon without pretreatment is effective. Good, that is, using Wangshui to boil and leaching, the leaching effect is also very poor.

The effective treatment method is incineration. After ignition, the scrapped platinum group metal activated carbon can be self-ignited and completely ashed, and the ash burning rate is very low. The grade of the platinum group metal in the ash is increased by several tens of times compared with the spent catalyst. Times. The incineration process is the key to affecting the recovery rate of platinum group metals. The incinerator cannot force the blast to prevent flying loss. For Pd-C, it is necessary to prevent the temperature from being too high to produce chemically inert PdO; due to the low incineration temperature and the reduction of carbon, the palladium in the burnt ash remains in an easily leached metal state, and if palladium is converted into a immersible PdO state, Hydrogen reduction can be carried out prior to leaching. For the spent catalysts of Pd-C and Pt-C, after incineration, the platinum group metal is recovered by chlorination leaching, and a small amount of oxidant is used in the solution of hydrochloric acid (about 6 mol/L) to make the leaching rate of the platinum group metal More than 99%, after purification, the leachate can produce pure metal with a purity greater than 99.95%. For the Ru-C spent catalyst, after incineration, it may be pretreated by an alkali dissolution method and purified by distillation.

(A) the platinum group metals osmium, ruthenium and other separation

The most economical and effective method for separating ruthenium and osmium from platinum group metal materials is oxidative distillation, because ruthenium and osmium are easily oxidized to OsO ₄ and RuO _{4 to} volatilize. The melting point of OsO ₄ is 40.6 ° C, the boiling point is 131.2 ° C, and the melting point of RuO ₄ is 25.4 ° C and the boiling point is 40 ° C. When cesium and strontium have high recovery value, they should be separated preferentially. Oxidation distillation is mainly carried out in an aqueous solution, and it can also be oxidized at a high temperature when the grade of ruthenium is high.

1 and 2 are an Os-H ₂ O-based potential-pH diagram and a Ru-H ₂ O-system potential-pH diagram, respectively.

Figure 1 Os-H2O system potential-pH diagram

1 OsO ₄ (hydrated) +4H+ ⁺ 4e=Os+2H ₂ O, φ=0.687-0.0591pH; 2 OsO ₄ ^2- +8H+ ⁺ 6e=Os+4H ₂ O, φ=0.994-0.0788pH+0.0098 lga _oso4 ^2- ; 3 HOSO ₅ ^- +H ⁺ =OsO ₄ +H ₂ O, pH=10.55+lga _{oso5 ^-} ; 4 OsO ₄ +4H ⁺ +4e=OsO ₂ (hydrated)+2H ₂ O, φ=1.005-0.0591pH; 5 OsO ₄ +2e=OsO ₄ ^2- , Φ=0.402-0.0295 lga _oso4 ²

Figure 2 R u -H ₂ O system potential - pH map

From Figures 1 and 2 can be stable region OsO _4, RuO ₄ is larger than that generated easier than OsO ₄ also generates RuO _4. In a relatively wide pH range, ruthenium can be oxidized to OsO _{4 by} oxidizing agents such as Cl ₂ , HNO ₃ , and H ₂ O ₂ ; while ruthenium cannot be oxidized to RuO ₄ by nitric acid. When oxidized with chlorine gas, it is only after pH>2. May be oxidized to RuO ₄ . Therefore, it is possible to selectively separate ruthenium and osmium with a suitable oxidizing agent. However, in the distillation of ruthenium and osmium, the simultaneous oxidation and evaporation method is usually used, and the separation is carried out while absorbing OsO ₄ and RuO ₄ .

RuO ₄ was absorbed by adding 3% ethanol and a concentration of 4 mol/L HCl solution, and converted into H ₂ RuCl _{6 which} can be stably present in the solution:

2RuO ₄ +22HCl=2H ₃ RuCl ₆ +8H ₂ O+5Cl ₂

OsO ₄ is absorbed by a solution of 20% sodium hydroxide and 4% ethanol. The chemical reaction occurring during the absorption process is:

OsO ₄ +4 NaOH = 2Na ₂ OsO ₄ + 2H ₂ O + O ₂

The oxidized volatilized RuO ₄ -containing OsO is first cooled by cooling, and the high-boiling substance and water vapor are condensed and refluxed to the distillation apparatus, and the remaining gases are sequentially passed through the helium absorption system and the hungry absorption system. The entire absorption system consists of 3 to 4 é’Œ absorbing liquids and 3 to 4 锇 absorbing liquids. The enthalpy absorption system temperature is maintained at 25 to 35 ° C, and the final stage maintains a slight negative pressure. When the OsO ₄ gas passes through the hydrochloric acid absorption liquid of RuO ₄ , it is also partially converted into H ₂ OsCl ₆ . Therefore, when the absorption liquid of the antimony is treated after the absorption, a small amount of nitric acid or double oxidation boiled and oxidized during the concentration process should be added, and the new solution will be obtained. The oxidation is OsO ₄ volatilization, and is absorbed by the alkaline absorption liquid of the crucible.

The four oxides of sputum and sputum are toxic, especially for the eyes, and the tears and the light are afraid of light, which may lead to temporary blindness. Therefore, the distillation device should be strictly sealed, and the site should be well ventilated. In order to prevent the damage caused by the four oxides of bismuth and antimony, eye masks and anti-virus masks should be worn during operation.

(2) Alkaline medium chlorine distillation

The material treated by this method is a pre-treated active platinum group metal concentrate or a cerium-containing or cerium-containing material after being melted by sodium oxide.

After the chlorine gas is introduced into the alkali solution (NaOH), a strong oxidizing agent sodium hypochlorite can be formed:

Cl ₂ +2NaOH=NaClO+NaCl+H ₂ O

Sodium hypochlorite can oxidize lanthanum and cerium to volatilize tetraoxide. When treating a platinum group metal active powder, the reaction is:

Os+4NaClO=OsO ₄ ↑+4NaCl

Ru+4NaClO=RuO ₄ ↑+4NaCl

When the ruthenium and osmium-containing materials after the sodium oxide melt treatment are treated, the ruthenium and osmium in the alkaline solution are in the form of Na ₂ OsO ₄ and Na ₂ RuO ₄ respectively, and the chemical reaction occurs as follows:

Na ₂ OsO ₄ +Cl ₂ =OsO ₄ ↑+2NaCl

Na ₂ RuO ₄ +Cl ₂ =RuO ₄ ↑+2NaCl

Na ₂ OsO ₄ +NaClO+H ₂ O=OsO ₄ ↑+NaCl+2NaOH

Na ₂ RuO ₄ +NaClO+H ₂ O=RuO ₄ ↑+NaCl+2NaOH

Distillation can be carried out in a mechanically stirred enamel reactor. The material is slurried in water and placed in a kettle. The mixture is heated to 80-95 ° C. Depending on the pH of the solution, sodium hydroxide is added and chlorine gas is continuously introduced to maintain the solution. The pH is not lower than 6-8.

The volatilized gas containing RuO ₄ and OsO ₄ is introduced into the absorption system of ruthenium and osmium by micro-negative pressure, and an inspection port is set at an appropriate position in the absorption line, and the test paper (or cotton ball) impregnated with the thiourea acidic solution is distilled out. Gas and exhaust. If the gas contains a trace amount of ruthenium, the test paper turns blue. If there is a trace amount of ruthenium in the gas, the test paper turns red; when the cesium concentration in the gas is high, the test paper turns black.

The advantage of this method is that it uses inexpensive chlorine as an oxidant and is relatively easy to handle. The disadvantage is that the ruthenium metal and some platinum group metals form hydroxides in the lye to deposit on the surface of the solid material, thereby reducing the distillation efficiency of ruthenium and osmium. In addition, other precious metals are substantially insoluble during the distillation process and need to be dissolved separately for separation.

(III) Sulphuric acid medium sodium chlorate distillation

The material treated by the sulfuric acid medium sodium chlorate distillation method is an active platinum group metal concentrate. The concentrate is firstly pulverized with 1.5 mol/L H2SO4 solution, the liquid-solid ratio is controlled to be 5, the boiling is near boiling, sodium chlorate solution or solid is added, and the amount of sodium chlorate is 1 to 1.5 times of the concentrate. In the sulfuric acid solution, sodium chlorate decomposes to produce a new ecological chlorine [Cl], which can oxidize various precious metals in the concentrate and form a complex to dissolve:

Os+2HCl+4[Cl]=H ₂ OsCl ₆

Ru+2HCl+4[Cl]=H ₂ RuCl ₆

Pt+2HCl+4[Cl]=H ₂ PtCl ₆

Pd+2HCl+2[Cl]=H ₂ PdCl ₄

Au+HCl+3[Cl]=HauCl ₄

Rh+3HCl+3[Cl]=H ₂ RhCl ₆

Ir+2HCl+4[Cl]=H ₂ IrCl ₆

The resulting H ₂ OsCl ₆ and H ₂ RuCl _{6 are} easily further oxidized to form OsO ₄ and RuO ₄ :

H ₂ OsCl ₆ +4[Cl]+4H ₂ O=OsO ₄ +10HCl

H ₂ RuCl ₆ +4[Cl]+4H ₂ O=RuO ₄ +10HCl

The distillation temperature is controlled at about 100 ° C. OsO4 and RuO4 are continuously vaporized. After the distillation is completed, the absorption system is disconnected, and then chlorine gas is introduced to dissolve other platinum group metals and gold. During the distillation process, hydrazine is usually first volatilized. In the later stage of distillation, the concentration of HCl in the solution is increased, and the formed H ₂ RuCl ₆ is very stable in the HCl solution, so the distillation efficiency of hydrazine is low.

If the ruthenium or osmium in the material cannot be directly separated by this method, it may be first treated with sodium peroxide and then oxidized and distilled in a sulfuric acid medium with sodium chlorate.

(4) Sulphuric acid medium sodium bromate distillation

This method is mainly used for the distillation of ruthenium and osmium which have entered the solution, and is mainly divided into two cases. First, the solution is first neutralized and hydrolyzed to form a hydroxide of ruthenium and osmium, and then distilled by adding sulfuric acid and sodium bromate; the second is to evaporate and concentrate the chlorine complex solution containing the platinum group metal to a small volume, and then add Sodium bromate is distilled. Hydrolytic distillation can ensure high recovery rate and stable effect, but the operation process is tedious, and the filtration and washing of the hydrolyzate are difficult. The concentrated distillation operation is simple, but the distillation effect is not stable enough. In the hydrolyzed distillation, the hydrolyzate is slurried with water and placed in a reactor. At the same time, a sodium bromate solution is added, the temperature is raised to 40 to 45 ° C, sulfuric acid is added, and the temperature is raised to 95 to 100 ° C. Volatile. During concentrated distillation, the concentrated solution was transferred to a reactor, an equal volume of 12 mol/L sulfuric acid was added, and the temperature was raised to 95 to 100 ° C to drive off the chloride ions, followed by continuous addition of sodium bromate to dilute the sputum and sputum.

After the ruthenium and osmium in the solid material are melted by sodium oxide, it can also be acidified with sulfuric acid and then distilled with bromine.

(5) Sodium bromate distillation method for adjusting pH

This method is suitable for distilling the hydrazine which has entered the solution. Before the distillation, the solution is concentrated and acidified, and then diluted with water (reducing the concentration of chloride ions in the solution) to make the pH value 0.5 to 1, and transferred to the reactor, and heated to near Boiling, then adding sodium bromate solution and sodium hydroxide solution to raise the pH. When a large amount of osmium tetroxide is volatilized, the addition of the alkali solution is stopped, and the sodium bromate solution is continuously added until the hydrazine is distilled, and the distillation efficiency of hydrazine is almost reached. 100%. However, the distillation effect on hydrazine is very poor and is only suitable for the treatment of cerium-containing solutions.

(6) Sodium peroxide melting-water leaching separation method

After the material containing cerium and lanthanum is melted by sodium oxide, the molten material is leached with water, and cerium and lanthanum are respectively introduced into the solution with Na ₂ OsO ₄ and Na ₂ RuO ₄ . Filtration, washing the slag with a solution containing sodium hypochlorite to obtain a black red solution containing Na ₂ OsO ₄ , Na ₂ RuO ₄ and water-insoluble insoluble slag to achieve separation of ruthenium, osmium and other platinum group metals. The alkaline solution containing cerium and lanthanum can be directly separated by distillation; however, in order to remove a large amount of sodium ions in the cerium and lanthanum solution, ethanol can be added and neutralized with sulfuric acid to reduce Na ₂ OsO ₄ and Na ₂ RuO ₄ to insoluble. Os(OH) ₄ and Ru(OH) ₄ .

Na ₂ OsO ₄ +CH ₃ CH ₂ OH+H ₂ SO ₄ =Os(OH) ₄ +Na ₂ SO ₄ +CH ₃ CHO

Na ₂ RuO ₄ +CH ₃ CH ₂ OH+H ₂ SO ₄ =Ru(OH) ₄ +Na ₂ SO ₄ +CH ₃ CHO

The precipitate containing Os(OH) ₄ and Ru(OH) ₄ is obtained by filtration, and then separated by distillation of hydrazine or hydrazine; or the precipitate is dissolved in a HCl solution, and the hydrochloric acid solution containing hydrazine and hydrazine is selectively distilled by an oxidizing agent. hungry.

Filtration of the sodium peroxide melt-water immersion method is very difficult, and since the alkali (NaOH) concentration of the water immersion liquid is high, it can only be filtered by a sand core funnel. The ruthenium and osmium in the material cannot be completely converted into Na ₂ OsO ₄ or Na ₂ RuO ₄ , and it is necessary to repeatedly melt the sodium peroxide. The operation is difficult and the reagent consumption is high.

(7) Fire distillation

It is easily oxidized to OsO ₄ volatilization at high temperatures and in the presence of oxygen:

Os+2O ₂ =OsO ₄

Distillation is carried out in a tube furnace at a temperature of 700 to 900 ° C. Oxygen in the air can be used as an oxidant, or pure oxygen can be used as an oxidant. Under these conditions, ruthenium can only be oxidized to weakly volatile RuO ₂ .

The advantage of pyrometallurgy is that the volatilization process does not consume reagents and can selectively separate from hungry. However, it is only suitable for the treatment of materials with high content of hungry, and can only be carried out on a small scale. After the fire treatment, the other platinum group metals ( 铱 , 铑, 钌) are converted into insoluble state, which can be dissolved after alkali fusion treatment. .

Fourth, the refinement of 钌

As with the separation and purification of hydrazine, the most effective method for the separation and purification of hydrazine is the oxidative distillation-hydrochloric acid solution absorption method. When the ruthenium-containing material is subjected to oxidative distillation, the volatilized RuO ₄ is absorbed into H ₂ RuCl ₆ with a hydrochloric acid solution:

2RuO ₄ +20HCl=2H ₂ RuCl ₆ +8H ₂ O+4Cl ₂

Therefore, the refining of hydrazine is mostly based on the absorption of hydrazine hydrochloride, which is mainly to effectively separate the hunger.

(1) Concentration rushing - ammonium chloride precipitation

The hydrazine hydrochloride absorption liquid was charged into a distiller, and the exhaust pipe was connected to a helium absorption system containing 20% ​​NaOH and 3% ethanol solution, and was connected to a vacuum system. The absorbing liquid of the hydrazine is heated to boiling, and the OsO ₄ in the hydrazine absorbing liquid is volatilized and absorbed by the alkaline absorbing liquid, and the escaping gas is inspected by using a test paper or a cotton ball impregnated with the thiourea acidic solution, and when it is not discolored, it is added. The oxidizing agent (H ₂ O ₂ , Cl ₂ or HNO ₃ ) completely evaporates OsO ₄ . The solution after removing the ruthenium is further concentrated, so that the concentration of ruthenium in the solution is about 30 g/L, and solid ammonium chloride is added in a hot state to produce the following reaction:

H ₂ RuCl ₆ +2NH ₄ Cl=(NH ₄ ) ₂ RuCl ₆ ↓+2HCl

Note that the ruthenium in the solution is kept as Ru(IV), otherwise it is difficult to precipitate safely. After the precipitation was completed, it was cooled, filtered, washed with absolute ethanol until the washing liquid was colorless, and the precipitated (NH ₄ ) ₂ RuCl ₆ was brown or black, dried and then subjected to calcination-hydrogen reduction.

(2) 钌 absorption liquid heavy distillation - concentration - ammonium chloride precipitation

If the absorbing liquid of cerium contains high impurities, it can be purified by double distillation. There are two methods.

(1) The hydrazine-containing hydrochloric acid solution is concentrated to near dryness, dissolved in water, adjusted to a pH of about 1 with a dilute alkali solution, transferred to a distiller, connected to a hydrazine hydrochloric acid absorption system, and 20% oxidized by adding to the distiller. The sodium solution is used to raise the pH, and a 20% NaBrO ₃ or NaClO ₃ solution is added dropwise, and the RuO _{4 is} oxidized and volatilized by heating. When a large amount of RuO ₄ escaped, the addition of the sodium hydroxide solution was stopped, and only the NaBrO ₃ or NaClO ₃ solution was continuously added until the escaped gas was checked to be free of hydrazine. The resulting chlorinic acid solution was further smashed, concentrated, and finally purified by ammonium chloride to precipitate pure ammonium chloroantimonate.

(2) The hydrazine-containing hydrochloric acid solution is neutralized with sodium hydroxide to precipitate Ru(OH) ₃ . After filtration, the precipitate is slurried with pure water and transferred to a distiller, and the hydrazine hydrochloride absorption system is connected to the distiller. Sulfuric acid was added while adding a 20% NaBrO ₃ a or NaClO ₃ solution, and after concentration, ammonium chloroformate was precipitated with ammonium chloride.

When re-distillation of raw material and high-grade ruthenium, RuO ₄ should be controlled by the addition of the speed control evaporation rate of the oxidizing agent, RuO ₄ volatilization should not be too fast. Because RuO _{4 has} poor thermal stability, RuO ₄ decomposes into RuO ₂ and O ₂ even when the concentration of RuO _{4 in the} gas phase is too high, the temperature is too high, or when it encounters a reducing agent, even causing an explosion.

Third, product production

In air, the volatility of ruthenium is much worse than that of ruthenium. The purified ammonium chlorate can be calcined first and then reduced with hydrogen. The purified and dried ammonium chloroantimonate is placed in a special covered porcelain crucible, sent to a muffle furnace and slowly heated to 300 to 400 ° C, and calcined for 1 to 2 hours. The calcined product is reduced with hydrogen in a tube furnace at a temperature of 750 to 850 ° C for a period of 2 to 4 hours. After the restoration is completed, the power is turned off and the temperature is lowered. When the furnace temperature was lowered to 400 ° C, argon or nitrogen was turned on and cooling was continued to room temperature to obtain a sponge powder. The sponge is boiled once with a 6 mol/L hydrochloric acid solution, and then washed with distilled water until neutral, and the dried powder is the finished powder.