JP6093232B2 - Valuable metal recovery method - Google Patents

Description

  The present invention relates to a valuable metal recovery method.

  Many so-called valuable metals such as noble metals, rare earth elements, and other metals are industrially very useful materials and are used in a wide range of fields. For example, the electroplating method using gold and the electroless plating method are widely known, and as the plating solution, a cyan-based gold plating solution having excellent stability in the solution has been used as a gold supply source. Yes.

  However, the cyanide compound has strong toxicity, and the plating solution as described above generally has a medium to high concentration of the cyanide compound. Therefore, it is necessary to ensure the complete treatment of the waste solution after plating. On the other hand, valuable metals that are expensive materials are required to be recovered from the waste liquid after plating as much as possible and reused.

  Conventionally, for example, an in-furnace spray method is known as a treatment method for a waste liquid (medium to high concentration cyan waste liquid) containing a cyanide compound at a medium to high concentration. Here, the medium concentration means that the concentration of the cyanide compound in the waste liquid is, for example, 100 mg / L or more and less than 1000 mg / L. The high concentration means that the concentration of the cyanide compound in the waste liquid is, for example, 1000 mg / L or more.

  The in-furnace spraying method is a method of spraying the waste liquid into a high-temperature furnace exceeding 1000 ° C. to decompose the cyanide compound. However, this method is expensive, and inorganic carbonates, which are hot-melt salts, such as alkali metal carbonates or alkaline earth metal carbonates melt and adhere to the furnace and damage the furnace. There are problems such as being unable to collect.

  A method of treating a waste liquid containing a cyanide compound at a low concentration (low concentration cyan waste liquid) is also known. Here, the low concentration means that the concentration of the cyanide compound is less than 100 mg / L, for example.

  For example, Patent Document 1 discloses an alkali chlorine method in which sodium hydroxide is added to a low-concentration cyan waste liquid, sodium hypochlorite is added while adjusting the pH to 10 to 11, and the cyanide compound is decomposed to nitrogen. ing. However, when recovering valuable metals from medium to high-concentration cyanide waste liquor by the alkali chlorine method, a large amount of chemicals are required and the volume sum with the treatment waste liquor increases, accompanied by significant heat generation due to reaction heat, itself There are problems such as generation of harmful chlorine.

  Other known methods include thermal hydrolysis under high temperature and high pressure (see, for example, Patent Document 2), ozone oxidation method using the oxidizing power of ozone gas (see, for example, Patent Document 3), and the like. The former method has a problem that the cyan compound cannot be sufficiently decomposed, and the latter method is expensive.

Japanese Patent Laid-Open No. 50-118962 JP-A-1-194997 JP 2006-341229 A

  Accordingly, an object of the present invention is to treat, for example, medium to high-concentration cyan waste liquid at low cost and easily, and to treat so-called valuable metals such as precious metals, rare earth elements, and other metals remaining in the waste liquid in a furnace. An object of the present invention is to provide a metal recovery method that can be sufficiently recovered without causing corrosion.

  The present inventor is able to solve the above-mentioned problems by subjecting a concentrate of a waste liquid containing a cyanide compound, an inorganic carbonate and a valuable metal to a relatively low temperature and separating the waste liquid from cyan as a cyan gas. The headline and the present invention were completed.

That is, the present invention is as follows.
1. A waste solution concentrate containing a cyanide compound, an inorganic carbonate and a valuable metal is calcined at 400 to 650 ° C. and separated from the waste liquid concentrate using cyan as a cyan gas, and then a valuable metal is recovered from the calcined residue. Metal recovery method.
2. 2. The valuable metal recovery method according to 1 above, which comprises a step of recovering the valuable metal in a liquid phase.
3. 3. The valuable metal recovery method according to 1 or 2, wherein the inorganic carbonate is an alkali metal carbonate and / or an alkaline earth metal carbonate.
4). Any of the above 1-3, wherein the concentration of the cyanide compound and the carbonate ion equivalent concentration of the inorganic carbonate are 2 to 200 g / kg, 20 g / kg or more and less than 1000 g / kg in the concentrate of the waste liquid, respectively. The valuable metal recovery method according to item 1.

  In the present invention, the waste compound concentrate containing cyanide, inorganic carbonate and valuable metal is baked at a relatively low temperature of 400 to 650 ° C. to separate the cyanide as cyan gas, Certain inorganic carbonates do not melt in the furnace and do not corrode the furnace. Moreover, generation | occurrence | production of an alkali fume is also prevented and safety | security increases. Furthermore, low cost is achieved by the low firing temperature. The fired residue from which the cyanide compound has been separated has low toxicity and facilitates subsequent metal recovery. Further, according to the form in which the separated cyan gas is further burned, the cyan gas can be decomposed into water, carbon dioxide and nitrogen, and further processing of the exhaust gas becomes easy.

It is process drawing for demonstrating the preferable form of this invention.

  Hereinafter, the present invention will be described in more detail.

  The waste liquid used in the present invention contains a cyanide compound, an inorganic carbonate and a valuable metal, and the waste liquid contains noble metals such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd ), Rhodium (Rh), iridium (Ir) and ruthenium (Ru), rare earth metals scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd) , Promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) And lutetium (Lu), other metals such as tin (Sn), lead (Pb), zinc (Zn), copper (Cu), ni Examples include waste liquids containing valuable metals such as Kell (Ni), cobalt (Co), thallium (TI), indium (In), gallium (Ga), especially waste liquids containing noble metals, and optimally waste liquids containing gold. It is.

  Examples thereof include those derived from a plating solution in an electrolytic plating method or an electroless plating method using a noble metal. For example, there are known plating solutions such as Au—Ni, Pd—Ni, and Au—Pd—Ni.

  The waste liquid in the present invention is not limited to this form, and examples include cyan waste liquid generated by precious metal recovery industry, surface treatment industry, electrical / electronic parts manufacturing industry, pharmaceutical / agrochemical manufacturing industry, etc. Will be described with reference to an example of a waste solution of gold-containing plating solution (hereinafter referred to as gold plating waste solution).

  The concentration of cyanide compounds in the gold plating waste liquid is generally medium to high. As described above, if the gold plating waste liquid is treated by using the conventional in-furnace spray method, high temperature heating is required, resulting in high cost. There are problems such as damage to the furnace due to adhesion of molten inorganic carbonate (heat-meltable salt), and inability to recover gold.

  The inorganic carbonate in the gold plating waste solution is derived from an additive that is appropriately added to the plating solution; a part of CN is anodized and decomposed into carbonate ions during the electroplating operation; For example, carbon is absorbed and carbonate ions build up; and the concentration thereof is, for example, 1 to 100 g / L as carbonate ions.

  Therefore, in the present invention, the above-mentioned problem is achieved by a step of baking a concentrate of a waste liquid containing a cyanide compound, an inorganic carbonate and a valuable metal at a relatively low temperature of 400 to 650 ° C. and separating the cyanide compound as cyan gas. It has been solved.

  First, in the present invention, a waste liquid concentrate containing a cyanide compound, an inorganic carbonate and a valuable metal is prepared. Examples of the method for concentrating the waste liquid include a method of evaporating and drying at 100 to 110 ° C., a method of heating in an evaporating dish, and a method of natural air drying. It is preferable to concentrate the waste liquid to a solid such as a powder or a lump by these various means because subsequent processing operations are facilitated.

  In the present invention, even when the concentration of the cyanide compound in the waste liquid concentrate is 2 g / kg or more, it is possible to efficiently separate the cyanide compound as cyan gas, preferably 2 to 200 g / kg, more preferably 5 It can be carried out at ˜200 g / kg.

  In addition, the inorganic carbonate can be preferably implemented with a waste liquid concentrate containing an alkali carbonate carbonate and / or an alkaline earth carbonate carbonate, more preferably a waste concentrate containing an alkali carbonate carbonate having a melting point of 700 to 1000 ° C. Will be implemented.

  The inorganic carbonate in the waste liquid concentrate can efficiently separate the cyanide compound as cyan gas even if the concentration in terms of carbonate ion is as high as 20 g / kg or more, and is 20 g / kg or more. Preferably in the range of less than 1000 g / kg.

  Even if the concentration of valuable metals in the waste liquid concentrate is 1000 mg / kg or less, the cyanide compound can be efficiently separated as cyan gas and valuable metals can be efficiently recovered. 10 mg / kg This can be preferably implemented.

  Next, the concentrate is fired at 400 to 650 ° C. Firing can be performed under sealed conditions, under atmospheric pressure, under pressure, or under reduced pressure (for example, under −60 to −10 Pa). The rate of temperature increase is, for example, 1 to 10 ° C./min, and preferably 1 to 5 ° C./min. The high temperature holding time for firing is, for example, 30 to 120 minutes.

  By this firing, the organic matter contained in the waste liquid burns to generate carbon dioxide and water. The cyanide compound reacts with the carbon dioxide and water and is separated as cyan gas by the following reaction formula (1), for example. When a complex of valuable metal such as gold and cyan is formed, part or all of the complex is decomposed and separated into valuable metal and cyan gas by thermal decomposition.

  When a valuable metal such as gold forms a complex with cyan, it is difficult to decompose at a low temperature. Therefore, at a temperature lower than 400 ° C., the complex between the valuable metal such as gold and cyan does not decompose and is separated as cyan gas. Is difficult. When the temperature exceeds 650 ° C., there are problems that the alkali metal carbonate melts and adheres to the furnace and damages the furnace, and valuable metals cannot be recovered.

The separation of the cyan gas in the present invention, including the separation due to the release of the waste concentrate cyanide gas produced by decomposition of above cyanide.

2NaCN + CO ₂ + H ₂ O → Na ₂ CO ₃ + 2HCN ↑ (1)

  Generally, the decomposition of cyanide is started at about 600 to 850 ° C., but in the present invention, the concentrate is calcined at a relatively low temperature to generate cyan gas and to remove the cyanide compound from the concentrate. it can.

In the reaction formula (1), NaCN or KCN usually contained in the gold plating waste liquid easily reacts with light, heat, moisture, and CO ₂ to generate HCN. In the above-mentioned calcination temperature range, these reactions are promoted and the production of HCN is increased.

  Subsequently, in the present invention, after separating the waste liquid concentrate using cyan as cyan gas, the inorganic carbonate is not hard sintered by heat melting, but the valuable metal is recovered in a liquid phase from a soft and porous firing residue. At this time, since the inorganic carbonate is in a fine powder state without sintering due to heat melting, the firing residue is highly soluble in water and excellent in liquid permeability, and the inorganic carbonate is washed with water. Suitable for liquid phase recovery of valuable metals from residues after removal. Examples of the liquid phase recovery method of valuable metals include a method of dissolving aqua regia and reducing with a reducing agent.

  The cyan gas in the separated exhaust gas 106 can be collected by alkali and burned at a known oxidative decomposition method such as alkali chlorine method, ozone, electrolysis method, or high temperature of 800 ° C. or higher. In the present invention, it is preferable to further include a step of burning at a high temperature of 800 ° C. or higher in order to completely burn cyan gas after the step of baking at 400 to 650 ° C.

  The combustion temperature is preferably 800 to 950 ° C., for example. The rate of temperature rise is, for example, preferably 1 ° C./min to 10 ° C./min, more preferably 1 ° C./min to 5 ° C./min. The combustion time is, for example, preferably 30 to 120 minutes after reaching the specified temperature. By this step, cyan gas is decomposed into water, carbon dioxide and nitrogen by the following reaction formula (2), for example, and further processing of the exhaust gas becomes easy.

4HCN + 5O ₂ → 2H ₂ O + 4CO ₂ + 2N ₂ (2)

  FIG. 1 is a process diagram for explaining a preferred embodiment of the present invention. In FIG. 1, the gold plating waste liquid 100 is evaporated and dried to obtain a concentrate 101. The obtained concentrate 101 is baked at 400 to 650 ° C. and separated into a baking residue 102 and a cyan gas 103.

  The firing residue 102 is washed with water and separated into a water washing residue and a waste alkali 105. The washing with water at this time is performed by a method such as putting water, preferably warm water, about 5 to 10 times by mass of the baking residue 102 into a washing bath and stirring both.

  As for the obtained water washing residue 104, gold | metal | money is collect | recovered by the method which was illustrated above after baking at 500-800 degreeC for 1-4 hours as needed. Since the waste alkali 105 has a low cyanide concentration, it can be rendered harmless by a conventional alkali chlorine method, for example.

  On the other hand, the cyan gas 103 is introduced into the combustion furnace, burned as described above, and becomes the exhaust gas 106. The exhaust gas 106 is detoxified by a method such as cooling with a saturated water vapor quenching tower or a complete evaporation quenching tower using caustic alkaline water, and collecting with an electric dust collector, etc., and is discharged into the atmosphere.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrict | limited to the following example.

[Example 1]
A gold plating waste solution having the following composition was prepared. Table 1 below shows the measurement results of the composition in the gold plating waste liquid.

  The gold plating waste liquid was treated by the process shown in FIG. First, the gold plating waste liquid 100 was evaporated and dried at 110 ° C. using a rotary disk evaporation concentrator as an apparatus to obtain a concentrate 101. The concentrate 101 was quantitatively analyzed. The results are shown in Table 2 below.

  Subsequently, 10 kg of the concentrate 101 was put into a rectangular baking container with a thickness of 10 cm, introduced into a baking furnace, and baked at 500 ° C. Firing was performed under reduced pressure, the rate of temperature increase was 3 ° C./min, and the firing time was 30 minutes after reaching 500 ° C. The obtained baked residue 102 was quantitatively analyzed. The results are shown in Table 3 below.

  Next, 200 g was collected from the obtained baked residue 102, placed in a water-washing bath with 1 liter of water, and washed with water by stirring both. The water washing residue 104 obtained as an insoluble matter was calcined at 600 ° C. under reduced pressure (−10 Pa) at a high temperature holding time of 1 hour, and then quantitative analysis was performed. The results are shown in Table 4 below.

  Subsequently, 9 mg of gold was recovered in a liquid phase by a method in which the obtained water washing residue 104 was dissolved in aqua regia and reduced with a reducing agent. In addition, other valuable metals other than gold can be recovered by a conventional method as necessary.

  Further, the waste alkali 105 was also quantitatively analyzed. The results are shown in Table 5 below. In Table 5 below, T-CN represents the total CN amount of the complex cyanide compound and free cyanide compound in the waste alkali 105.

[Example 2]
Except for the firing conditions, the same procedure as in Example 1 was performed until washing with water. Firing was carried out under reduced pressure at 400 ° C., the rate of temperature increase was 3 ° C./min, and the firing time was 120 minutes after reaching 400 ° C. The obtained baked residue 102 was quantitatively analyzed. The results are shown in Table 3.

[Example 3]
Except for the firing conditions, the same procedure as in Example 1 was performed until washing with water. Firing was performed under reduced pressure at 650 ° C., the rate of temperature increase was 3 ° C./min, and the firing time was 60 minutes after reaching 650 ° C. The obtained baked residue 102 was quantitatively analyzed. The results are shown in Table 3.

[Comparative example]
The gold plating waste liquid concentrate 101 used in Example 1 was introduced into a firing furnace and fired at 800 ° C. Firing was performed under reduced pressure, the rate of temperature increase was 3 ° C./min, and the firing time was 30 minutes after reaching 800 ° C.

  As a result, it was confirmed that the alkali metal carbonate melts and adheres to the wall surface of the furnace in a glassy state and corrodes the furnace.

  In addition, although the said Example demonstrated the collection | recovery method of gold | metal | money, of course, what is called valuable metals, such as other noble metals and rare earth elements, can also be collect | recovered.

Claims (4)

A waste liquid concentrate containing a cyanide compound, an inorganic carbonate and a valuable metal is calcined at 400 to 650 ° C. and separated from the waste liquid concentrate using cyan as a cyan gas without burning and decomposing the cyan gas from the calcined residue. A method for recovering valuable metals, including a step of recovering valuable metals.   The valuable metal recovery method according to claim 1, comprising a step of recovering the valuable metal in a liquid phase.   The valuable metal recovery method according to claim 1 or 2, wherein the inorganic carbonate is an alkali metal carbonate and / or an alkaline earth metal carbonate.   The density | concentration of the said cyanide compound and the carbonate ion conversion density | concentration of inorganic carbonate are 2-200 g / kg, 20 g / kg or more and less than 1000 g / kg in the concentrate of the said waste liquid, respectively. The valuable metal recovery method according to claim 1.

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