JPH09263847A - Dissolving method of noble metal-containing slime - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the treatment time by introducing hydrogen peroxide to a slime containing Au, Pt and Pd in the presence of hydrochloric acid. SOLUTION: By this method, Au, Pt and Pd in a slime are oxidized by hydrogen peroxide and the oxides react with chlorine to produce a chloride complex which can be dissolved. In this method, hydrochloric acid and hydrogen peroxide are required to be present with the noble metals. It is preferable to add the hydrochloric acid in an amt. equal or larger than the required amt. (equiv.) to convent noble metals into chloride complex ion and smaller than twice of the required amt. It is preferable to add hydrogen peroxide in an amt. twice or more as the amt. required to oxidize Au into Au (III), Pt into Pt (IV) and Pd into Pd (IV) and less than four times of the required amt. Thereby, dissolution treatment can be done in several hours, which is shorter compared to a conventional treatment using aqua regia, and since the obtd. soln. is based on hydrochloric acid soln., it can be easily treated in the succeeding process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dissolving slime (hereinafter referred to as precious metal slime) containing a platinum group element of gold, platinum and paradium.

[0002]

2. Description of the Related Art Anode slime produced in the refining process of copper or nickel or the extraction residue produced in the refining process of nickel contains a considerable amount of gold, silver, platinum, palladium and other precious metal elements. The noble metal is recovered as crude silver by increasing the noble metal concentration through various steps of recovering copper-philic elements such as copper and selenium and tellurium.

As shown in FIG. 1, the recovered crude silver is subjected to electrolytic treatment to obtain deposited silver and anode slime (silver slime). Silver slime mainly contains silver and gold, and further contains a platinum group element. Silver slime is first treated with nitric acid. This causes metals other than gold to dissolve in the liquid. Gold is separated and collected by centrifugation or the like. Hydrochloric acid is added to the solution to remove most of silver as silver chloride. When a reducing agent such as hydrazine is added to the remaining solution, reduced slime in which metal components are deposited as fine particles is obtained. This reduced slime (precious metal slime) contains a small amount of gold and silver in addition to platinum and palladium.

Conventionally, this precious metal slime has been treated with aqua regia. PtCl ₆ ²⁻ , PdCl ₄ ²⁻ , AuCl ₄ ⁻ were added to platinum, palladium and gold by aqua regia treatment.
It becomes a chloride complex ion such as and dissolves. However, it takes half a day or about a day to dissolve the precious metal slime in aqua regia. In addition, since a large amount of nitric acid is contained in the solution, denitration must be performed by repeating evaporation to dryness and dissolution in hydrochloric acid, and this denitration step requires a processing time of about 2 days. However, there is a problem that it takes a long time to perform all the steps.

Therefore, a chlorine blowing method (Japanese Patent Publication No. 62-2014) has been proposed as an alternative method to the aqua regia dissolution. However, since chlorine gas is handled, ensuring work safety,
Special equipment was required to consider the surrounding environment, and it was difficult for conventional processing plants to handle this.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the conventional method for dissolving noble metal slime, has a short treatment time, does not require post-treatment such as denitration, and is toxic and highly corrosive. There is no need to use chlorine gas,
Provided is a method of safely and inexpensively and efficiently dissolving a precious metal slime.

[0007]

The present invention is a method for completely dissolving a precious metal containing gold, platinum and paradium in slime in about several hours by introducing hydrogen peroxide into the precious metal slime in the presence of hydrochloric acid. That is, the present invention provides (1)
A method for dissolving a noble metal-containing slime, characterized in that, by introducing hydrogen peroxide into a slime containing gold, platinum and palladium in the presence of hydrochloric acid, the contained noble metal is converted into a chloride complex and dissolved. .

The above-mentioned dissolution method is (2) the dissolution method according to (1) above, wherein the amount of hydrochloric acid is at least the minimum amount required to convert the contained noble metal in the slime into a chloride complex or at most twice the amount thereof, ( 3) The amount of hydrogen peroxide is at least twice the minimum amount required to oxidize the precious metal contained in slime or more to 4
Dissolution method according to (1) or (2) above, which is less than or equal to the double amount, (4) 6
The dissolution method according to any one of (1) to (3) above, wherein the dissolution is performed in a temperature range of 0 to 80 ° C.

[0009]

[Detailed Description] The noble metal slime to which the present invention is applied is a slime containing gold, platinum and palladium, and a typical one thereof is, as described above, produced in the step of refining copper or nickel. Nitrogen treatment of the extraction residue generated in the anode slime or nickel refining process recovers gold, and further hydrochloric acid treatment recovers silver to reduce the residual precious metal by adding a reducing agent such as hydrazine to the residual liquid. It's a slime. This reduced slime is washed with water as necessary, nitric acid and the like are removed, and then subjected to the treatment of the present invention.

The method of the present invention includes two steps: (a) hydrochloric acid addition step and (b) hydrogen peroxide addition step. Gold, platinum, and palladium are oxidized by hydrogen peroxide, and chlorine reacts with them to dissolve them by forming a chloride complex. That is, these precious metals M (M: Pt, Pd, Au) are hydrogen peroxide H ₂ O ₂
Noble metal ion M ^x- becomes by the reaction with and this and chlorine C
The reaction with l ⁻ produces MCln ^{(xn) −} and the base metal M dissolves in the liquid. Hydrochloric acid and hydrogen peroxide may be present together with the above noble metal. Introducing hydrogen peroxide prior to hydrochloric acid is not preferred because hydrogen peroxide is consumed before chloride complexes are formed.

(1) Hydrochloric Acid Addition Step The amount of hydrochloric acid added is at least the minimum amount (equivalent amount) necessary to convert gold, platinum and palladium contained in slime into chloride complex ions, but not more than twice that amount. preferable. If the amount of addition is less than the equivalent, naturally, these noble metals cannot be sufficiently dissolved. Further, if the addition amount exceeds twice the equivalent amount, the cost becomes high, and when silver is contained in the slime, this silver becomes a chloride complex ion and dissolves, and palladium or This causes problems such as mixing when platinum is separated. The hydrochloric acid concentration is preferably about 8 to 12 mol / l. If it is less than 8 mol / l, the amount of liquid becomes excessive, and there is a problem that post-treatment is costly. It is difficult to obtain a product having a concentration higher than the above range as a commercial product, and it is not suitable for practical use.

(2) Hydrogen Peroxide Adding Step The amount of hydrogen peroxide added is such that palladium (Pd), platinum (Pt) and gold (Au) contained in slime are Pd (IV), Pt (IV),
The amount is preferably 2 times or more and 4 times or less the amount necessary to oxidize up to Au (III). If the added amount is less than 2 equivalents, these noble metals cannot be sufficiently oxidized. On the other hand, if the added amount exceeds four times the equivalent, the cost increases. The concentration of hydrogen peroxide is preferably about 8 to 11 mol / l. Concentration is 8 mol
If it is less than / l, the amount of liquid becomes excessive, which causes problems such as high cost for post-treatment. A product having a concentration higher than the above range is difficult to obtain as a commercial product and is not suitable for practical use.

[0013] The addition of hydrogen peroxide is preferably carried out at 60 to 80 ° C. If the temperature is lower than 60 ° C., oxidative dissolution does not proceed, and the efficiency decreases. If the temperature exceeds 80 ° C, the added hydrogen peroxide decomposes without contributing to the dissolution of slime, and the efficiency also decreases. It is preferable that the required amount of hydrogen peroxide is gradually added. If the required amount of hydrogen peroxide is present from the beginning, the decomposition reaction will proceed rapidly, resulting in intense heat generation. This heat promotes the decomposition of hydrogen peroxide, lowers the reaction efficiency, and generates oxygen by the decomposition of hydrogen peroxide, which is dangerous because the liquid volume is rapidly increased by so-called forming. The speed of addition depends on the amount of slime and the concentrations of hydrochloric acid and hydrogen peroxide, but typically the total amount of addition determined above is added on average over a period of about 100 to 120 minutes. Preferably.

[0014]

Embodiments of the present invention and comparative examples will be described below. In addition, these are illustrations and do not limit the scope of the invention. The noble metal slime of the sample was obtained by removing the precipitated gold from the nitric acid solution of silver slime, reducing it with hydrazine, and washing it.
The one containing 5 wt% Pd, 2 wt% Au and 0.3 wt% Ag was used.

Example 1 50 g of noble metal slime reduced with hydrazine was placed in a 200 ml reaction vessel equipped with a temperature control device and a stirrer, and 70 ml of 36% concentration hydrochloric acid (1.4 times the equivalent amount) was added thereto.
While maintaining the liquid temperature at about 65 ° C., 30 ml of 31% hydrogen peroxide solution (3 times the equivalent amount) was added at a rate of 0.3 ml / min while stirring. When the stirring was continued while maintaining the above temperature after the addition was completed, the slime was completely dissolved in 4 hours. After the reaction was completed, the liquid was filtered, but almost no residue was observed. The filtrate is I
Analysis by PC analysis confirmed that 95% or more of Pt and Pd in slime were leached into the solution. The filtrate also contained Ag and Au, but Ag was precipitated as silver chloride by diluting it with twice the amount of water, and metallic Au could be recovered and removed by adding oxalic acid. It was

Example 2 The slime treatment was carried out in the same manner as in Example 1 except that the addition amount of hydrochloric acid was reduced to 60 ml (1.2 times the equivalent amount) and the leaching temperature was changed to 70 to 80 ° C. The total amount of slime was dissolved in 4 hours. IPC analysis of the filtrate revealed that P in slime
It was confirmed that 95% or more of t and Pd were dissolved in the solution.

Comparative Example 1 Slime was treated in the same manner as in Example 2 except that the amount of hydrochloric acid added was reduced to 40 ml (0.8 times the equivalent amount). When this treatment liquid was filtered, a small amount of black slag was observed. The Pd leaching rate of the treatment liquid was 95% or more, but the Pt leaching rate was 61.2%.

Comparative Example 2 A slime was prepared in the same manner as in Example 2 except that the amount of hydrochloric acid added was 200 ml (4 times the equivalent amount) and the amount of hydrogen peroxide solution was reduced to 15 ml (1.5 times the equivalent amount). Was processed. When the liquid was filtered, a small amount of black slag was observed, the Pd leaching rate was 79.2%, and the Pt leaching rate was as low as 29.3%.

Comparative Example 3 Hydrochloric acid was added in an amount of 50 ml (one equivalent) and the liquid temperature was 45 ° C.
The slime treatment was performed in the same manner as in Example 1 except for the above. When the treatment liquid was filtered, a small amount of black slag was observed. The Pd leaching rate was 74.9% or more, but the Pt leaching rate remained at 56.6%.

[0020]

According to the conventional method for treating platinum group slime, it takes about half a day to about one day to dissolve aqua regia, and denitrification treatment is required for more than 2 days to remove nitric acid. According to the above method, slime can be dissolved in a time of about several hours as a whole. Further, since the obtained solution is a hydrochloric acid solution, the post-process treatment is easy. further,
The dissolution rate of precious metals contained in slime is also high. Further, since the process of the present invention can directly use the facility used in the conventional aqua regia dissolution method, the process can be improved with almost no additional capital investment.

[Brief description of drawings]

FIG. 1 is a process diagram of a conventional precious metal-containing slime.

Claims (4)

[Claims] 1. A noble metal-containing slime, characterized in that, by introducing hydrogen peroxide into a slime containing gold, platinum and palladium in the presence of hydrochloric acid, the contained noble metal is converted into a chloride complex and dissolved. Dissolution method. 2. The method according to claim 1, wherein the amount of hydrochloric acid is at least the minimum amount required to convert the precious metal contained in the slime into a chloride complex or at most twice the amount thereof. 3. The method according to claim 1, wherein the amount of hydrogen peroxide is at least twice the minimum amount required to oxidize the precious metal contained in the slime and at most four times the minimum amount. 4. The melting method according to claim 1, wherein the melting is performed in a temperature range of 60 to 80 ° C.