JPH09241768A - Method for refining platinum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of efficiently refining platinum from the reverse extraction liquid obtd. by executing solvent extraction using tributyl phosphate. SOLUTION: Platinum is refined by a precipitation and sepn. method from the soln. obtd. by reverse extraction of the platinum by using the tributyl phosphate or an org. solvent contg. the tributyl phosphate from an aq. acidic soln. of the hydrochloric acid of the platinum contg. impurities. At this time, the reverse extraction liquid is heated up and an oxidizing agent or alkali is added thereto. The impurities are then filtered as hydroxide and the platinum refining liquid is obtd. Further, ammonium chloride is added to the platinum refining liquid and the platinum is recovered as ammonium chloroplatinate. While the number of times of the refining by ammonium chloride is heretofore repeated 2 to 3 times, the number of these times is reduced to one times as the good platinum purity is obtd. The excellent effects, such as, for example, the reduction of the period for recovering the platinum, are thus admitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention purifies platinum from a solution obtained by back-extracting platinum from an acidic aqueous solution of platinum containing impurities with tributyl phosphate or an organic solvent containing tributyl phosphate by a precipitation separation method. It concerns the improvement of the method.

[0002]

2. Description of the Related Art A hydrochloric acid acidic aqueous solution of platinum containing impurities is
For example, it is generated in the silver electrolytic slime treatment step of the copper electrolytic slime treatment steps in copper refining. When silver electrolytic slime is decomposed with nitric acid, a silver extract and a residue are obtained, but when the precipitate obtained by neutralizing this silver extract is dissolved with hydrochloric acid, it contains gold, palladium, platinum, rhodium, and a base metal. A hydrochloric acid acidic aqueous solution is obtained. Further, by acid-treating the residue with hydrochloric acid and hydrogen peroxide, the same acidic hydrochloric acid solution as described above can be obtained.

Gold, palladium, platinum and rhodium contained in these hydrochloric acid acidic aqueous solutions have conventionally been collected by a chemical precipitation separation method. However, this method has a low separation efficiency in each step and is complicated and skilled. However, there was a problem that the actual yield was low.

Recently, various methods using solvent extraction have been proposed. For example, in the case of platinum, ferrous sulfate is added to an acidic aqueous hydrochloric acid solution to precipitate gold, and the filtrate obtained by separating the precipitate is brought into contact with an organic solvent using di-hexyl sulfide as an extraction solvent to form palladium. Is obtained as an aqueous phase after extraction into the organic phase.

The thus obtained impurity-containing platinum acid aqueous solution of hydrochloric acid has the following composition. That is, Pt: 2 to 10 g / l, Pd: 0.02
~ 0.1 g / l, Rh: 0.5-2.0 g / l, Cu,
Each of Pb, Bi, Te, and Fe is 0.1 g / l or less, and hydrochloric acid is about 1M solution.

As a method for purifying and recovering platinum from the aqueous solution, there is a solvent extraction method, for example, a solvent extraction method using tributyl phosphate. After the hydrochloric acid concentration in the aqueous phase is adjusted to about 3N, tributyl phosphate is used. Alternatively, an organic phase in which platinum is extracted by contacting with an organic solvent containing tributyl phosphate is obtained, and further, the organic phase is contacted with saline or hydrochloric acid of 0.5N or less to back-extract platinum, and the resulting reverse extraction is performed. A method is known in which the liquid is concentrated to a platinum concentration of about 30 to 50 g / l, and an ammonium chloride salt is added to this to purify platinum as ammonium chloroplatinate.

[0007]

However, the back extraction liquid obtained by carrying out the solvent extraction using tributyl phosphate in the above-mentioned aqueous solution contains a small amount of palladium, rhodium and base metal. For this reason, even if the back extract was concentrated and ammonium chloride was added to purify platinum as ammonium chloroplatinate, a single purification was not enough, and the obtained ammonium chloroplatinate was reduced with hydrazine or the like. It is necessary to repeat the operation of reducing platinum powder using an agent, dissolving platinum powder with hydrochloric acid and hydrogen peroxide, and adding ammonium chloride salt again to obtain ammonium chloroplatinate. For this reason, there are problems that the refining operation takes a long time and the cost of chemicals is high.

It is an object of the present invention to provide a method capable of efficiently purifying platinum from a back extract obtained by performing solvent extraction using tributyl phosphate.

[0009]

The inventors of the present invention have conducted various studies to solve the above problems and achieve the above objects, and as a result, removed impurities as hydroxides from the back extract by specific means. The inventors have found that the purpose can be achieved by adding an ammonium chloride salt, and have completed the present invention. That is, the present invention, the platinum hydrochloric acid aqueous solution containing impurities is contacted with an organic solvent containing tributyl phosphate or tributyl phosphate to recover platinum in the organic phase,
Next, in the method of purifying platinum from a solution in which platinum in the organic phase is back-extracted in an aqueous solution, the back-extract solution is heated, an oxidizing agent and an alkali are added, impurities are filtered out as hydroxides, and a platinum-purified solution is obtained. The method for purifying platinum is characterized by the steps of obtaining and recovering platinum as ammonium chloroplatinate salt by adding an ammonium chloride salt to the purified platinum solution.

According to the method of the present invention, the back extract obtained by solvent extraction is concentrated to a platinum concentration of 30 to 50 g / l and then heated to a boiling temperature of 90 ° C. or higher and an oxidizing agent. And alkali are added to adjust the pH of the solution to 7 to 8 and impurities are filtered off as hydroxide to obtain a purified platinum solution,
Next, it is preferable to add an ammonium chloride salt to the purified platinum solution to recover platinum as an ammonium chloroplatinate salt.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a back extract obtained by solvent extraction is heated to 90 ° C. or higher and a boiling temperature or lower,
Add an oxidizing agent and alkali to adjust the pH of the solution to 7
It is preferable to set to 8. This is because in the case of neutralizing with an alkali, when the temperature is high, impurities other than platinum are easily hydrolyzed into hydroxides, which becomes more remarkable as the temperature is higher. This is because the hydrolysis of rhodium is not sufficient at 90 ° C. or lower, and the boiling temperature is set to the boiling temperature or lower when the pH of the solution is controlled using a pH meter, the reliability becomes low, and the obtained hydroxide is This is because it is extremely fine, and if it is boiled too much, the flocculating effect of the precipitate deteriorates and the precipitate has poor filterability.

The reason why the oxidizing agent is added during neutralization is that platinum is less likely to precipitate in the presence of a strong oxidizing agent during neutralization. Examples of the oxidizing agent to be used include sodium bromate, sodium hypochlorite, chlorine gas and the like, but any of them can be added appropriately during neutralization to prevent platinum coprecipitation. At this time, the amount of the oxidizing agent added to prevent coprecipitation of platinum is at least 7 g-Cl ₂ as the effective chlorine amount.
/ L is necessary, and on the other hand, even if 9 g-Cl ₂ / l or more is added, the coprecipitation rate of Pt does not decrease but the amount of oxidizing agent increases, which is not preferable. That is, for example, when industrial sodium hypochlorite (effective chlorine amount: 12%) is used, it is possible to prevent coprecipitation of platinum considerably by adding about 60 g of the solution per liter. Around 60 to 80 g is suitable.

When the pH during neutralization is less than 7, Cu,
Although base metals such as Pb and Fe precipitate as hydroxides, the hydrolysis of noble metals such as Pd and Rh does not proceed sufficiently, and Rh is particularly unlikely to become hydroxide. So the pH
It is necessary to have a pH of 7 or higher, while the pH is set to a pH of 8 or lower because the precipitation rate of platinum also increases as the pH further rises. Therefore, the pH is preferably set to 7-8. After further neutralization, the generated hydroxide is removed by filtration, the filtrate is acidified with hydrochloric acid, and ammonium chloride is added according to a conventional method to recover ammonium chloroplatinate crystals. In this way, the number of times of purification can be reduced, and efficient purification can be achieved.

[0014]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

Example 1 A liquid having a liquid composition as shown in Table 1 below was dispensed into three 500 ml beakers, each having a temperature of 80 ° C. and a hot stirrer temperature of 9 ° C.
The temperature was adjusted to 0 ° C. and 100 ° C., the pH was set to 6.5, and 24% sodium hydroxide was added. When the set pH is reached, industrial sodium hypochlorite (effective chlorine amount: 12
%) Was added and stirred for 1 hour, cooled, filtered and the filtrate concentration was analyzed to determine the precipitation rate of each element. Table 2 shows the results.

[0016]

[Table 1] Composition of test solution (g / l)

[Table 2]

From the results shown in Table 1, it is understood that the higher the temperature is, the more the precipitation rate of platinum increases, but the impurities, especially Rh, can be removed as a precipitate.

Example 2 Using the liquid used in Example 1, 300 ml of the same solution was dispensed into four 500 ml beakers in the same manner, the temperature was adjusted to 90 ° C. with a hot stirrer, and the set pH was 6.0. , 6.5, 7.0, 8.0, 24% sodium hydroxide was added. Industrial sodium hypochlorite (effective chlorine amount 12
%) To each of which 7.5 ml was added and stirred for 1 hour,
After cooling, the solution was filtered and the filtrate concentration was analyzed to measure the precipitation rate of each element. The results are shown in Table 3.

[0019]

[Table 3]

From the results of Table 2, it can be seen that the higher the pH, the more the platinum precipitation rate increases as in Example 1, but the impurities are also removed as hydroxides. In particular, it can be seen that when the pH is 7 or more, Pd and Rh also become sufficient hydroxides and can be separated by precipitation.

Example 3: Using the solution used in Example 1, the same 300 ml each was divided into five 500 ml beakers, the temperature was raised to 90 ° C. with a hot stirrer, and the set pH was 6.5. , 24% sodium hydroxide was added. When the pH reaches the set level, industrial sodium hypochlorite (effective chlorine amount: 12%) is added to each of 1.3%, 2.5%, 5.0% and 6.3% of the used liquid to obtain 1 After stirring for a period of time, cooling, and filtration, the filtrate concentration was analyzed to measure the precipitation rate of each element. The results are shown in Table 4.

[0022]

[Table 4]

From the results shown in Table 3, it can be seen that the larger the amount of the oxidizing agent added, the more the precipitation rate of impurities can be suppressed as it is.

Example 4 A silver extract obtained by decomposing silver electrolytic slime with nitric acid was neutralized to obtain a precipitate, which was then dissolved in hydrochloric acid to prepare an acidic aqueous hydrochloric acid solution containing gold, platinum, palladium and rhodium base metal. Obtained.

Ferrous sulfate was added to this acidic aqueous hydrochloric acid solution to precipitate gold, and the filtrate obtained by separating the precipitate was brought into contact with an organic solvent using di-hexyl sulfide as an extraction solvent to remove palladium. The quality of the aqueous phase after extraction into the organic phase is P
t: 8.14 g / l, Pd: 0.051 g / l, Rh:
1.11 g / l, Cu, Pb, Te, Fe are all 0.
It was 1 g / l or less and hydrochloric acid was about 1M.

Hydrochloric acid was added to this solution so that the concentration of hydrochloric acid was 4N, and tributyl phosphate was added as an extraction solvent to 8%.
Contact with an organic solvent containing 0% at a phase ratio (O / A) of AC of 3 steps = 1 to move platinum contained in the solution into the organic solvent, and then with 2% concentration of saline and AC of 3 steps. It was back-extracted into sodium chloride at a phase ratio of 1. The back extract was concentrated to a concentration of about 3 times to obtain a liquid having the composition shown in Table 5 below.

[0027]

[Table 5]

This solution was heated to 90 ° C. in a 200 l FRP tank and 25.5% of 48% sodium hydroxide was added.
1 was added and the pH of the solution was adjusted to 7. Next, 11.2 l of industrial sodium hypochlorite (effective chlorine amount: 12%)
Add and hold for 1 hour. Then, the temperature was lowered to 60 ° C., filtration was carried out, the obtained filtrate was analyzed, and the analysis values are shown in Table 6.

[0029]

[Table 6]

Subsequently, hydrochloric acid was added to the filtrate, and 3.64 kg of ammonium chloride salt was added to obtain ammonium chloroplatinate, which was washed with an aqueous solution of 1% ammonium chloride salt and then reduced with hydrazine to give a sponge state. Platinum was obtained as platinum and analyzed. The platinum purity was 99.99%, which was sufficiently marketable.

Comparative Example 1: The same treatment as in Example 1 was carried out and Table 7 was obtained.
The concentrated liquid shown in was obtained.

[0032]

[Table 7]

Ammonium chloride was added to this solution in an amount 1.5 times the theoretical amount of platinum to obtain ammonium chloroplatinate. It was washed with an aqueous solution of ammonium chloride salt in the same manner as in Example 1 and reduced to analyze the purity of platinum. Platinum purity is 9
9.95%, Pd of 120 p as an impurity
It contained 60 ppm of pm and Rh. It was necessary to repeat the purification with ammonium chloride again.

[0034]

Industrial Applicability According to the present invention, the platinum back-extract solution is once neutralized to remove impurities as hydroxides, and ammonium chloride salt is added. What was conventionally repeated 2 to 3 times has a good platinum purity and can be shortened to 1 time, and excellent effects such as shortening the platinum recovery period are recognized.

Claims (5)

[Claims] 1. A platinum-acidic aqueous solution of platinum containing impurities is brought into contact with tributyl phosphate or an organic solvent containing tributyl phosphate to recover platinum in the organic phase, and then platinum in the organic phase is added back to the aqueous solution. In the method for purifying platinum from an extracted solution, the step of heating the back extract, adding an oxidizing agent and an alkali, and filtering out impurities as hydroxide to obtain a platinum purified solution; and ammonium chloride in the platinum purified solution. A method of purifying platinum, comprising the step of adding a salt to recover platinum as an ammonium chloroplatinate salt. 2. The method for purifying platinum according to claim 1, wherein the temperature rise of the back extract is 90 ° C. or higher and the boiling temperature or lower. 3. The method for purifying platinum according to claim 1, wherein the pH after neutralization is adjusted to 7 to 8. 4. The method for purifying platinum according to claim 1, wherein sodium bromate, sodium hypochlorite or chlorine gas is used as the oxidizing agent. 5. The amount of the oxidizer is 7 g as an effective chlorine amount.
The method for purifying platinum according to claim 1, wherein -Cl ₂ / l or more is added.