JPH04276032A - Method for recovering high purity sponge cadmium - Google Patents

Abstract

PURPOSE:To decompose tellurium at a low cost from a sulfuric acid soln. containing tellurium and cadmium and to recover high purity sponge cadmium. CONSTITUTION:The aq. soln. above described is adjusted to pH 0.5-3.0, to which 1-3eq. reducing agent to the tellurium is added to cause precipitation. Then a reducing agent is added by 0.8-1.2eq. to the cadmium in the soln. from which the precipitate is separated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering high-purity sponge cadmium with a low tellurium content from an acidic sulfuric acid aqueous solution containing tellurium and cadmium.

0002

BACKGROUND OF THE INVENTION The conventional method for recovering high-purity sponge cadmium from an acidic cadmium sulfate aqueous solution is to pass the aqueous solution through an ion exchange column to remove impurities such as arsenic, and then add sodium carbonate to pH 9.0-9. 5 to precipitate cadmium as cadmium carbonate,
Next, after separating and recovering the precipitate by filtration, etc., the precipitate is dissolved with sulfuric acid, filtered, and after removing lead etc., zinc powder is added to the solution, and the precipitated sponge cadmium is recovered. There is.

However, in the sponge cadmium recovery method, if the aqueous solution contains a large amount of tellurium,
Because tellurium behaves in the same way as cadmium, separation of tellurium becomes insufficient, and only sponge cadmium with a high tellurium content is obtained.As a result, the sponge cadmium is dissolved with sulfuric acid and cadmium is electrolytically extracted. Alternatively, even if this sponge cadmium is alkali-fused using sodium hydroxide to form cadmium metal and then purified by dry distillation, tellurium cannot be separated.

Furthermore, since tellurium reduces the particle size of cadmium sponge, there is a drawback that when cadmium sponge is melted, cadmium is easily oxidized and losses are large.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for separating tellurium and recovering high-purity sponge cadmium at low cost without making any major changes to the conventional sponge cadmium recovery process.

[0006]

[Means for Solving the Problems] The method of the present invention for achieving this object is a sulfuric acid acidic aqueous solution containing tellurium and cadmium, which is generated as an intermediate product when recovering cadmium from zinc ore or smoke ash. , pH 0.5~
After adjusting to 3.0, add a reducing agent to the solution at a ratio of 1 to tellurium.
~3 equivalents of reducing agent are added to the solution from which the resulting precipitate is separated, and the amount of reducing agent is 0.8 equivalent to cadmium contained in the solution.
The feature is that ~1.2 equivalents are added.

[0007]

[Operation] In the present invention, the pH of the target aqueous solution is adjusted to 0.5~
The reason for adjusting the pH to 3.0 and adding a reducing agent is that if the pH is less than 0.5, cadmium that co-precipitates with tellurium will be easily redissolved, making it difficult for tellurium to precipitate. If it exceeds the limit, not only will the cadmium co-precipitated with tellurium become fine and difficult to precipitate, but also, for example, when using zinc dust as a reducing agent, the reduction reaction will be slow, and undissolved zinc dust will become an impurity in the sponge cadmium. It is from.

[0008] Furthermore, the reason why the reducing agent is added in an amount of 1 to 3 equivalents to the tellurium contained in the target aqueous solution is that if the reducing agent is less than 1, tellurium is difficult to precipitate and the effect of separating tellurium is hardly obtained. , 3, not only does the tellurium precipitation effect not increase, but also the amount of cadmium precipitated increases and the recovery rate of high-purity cadmium deteriorates.

[0009] Furthermore, in order to obtain sponge cadmium,
The reason why the reducing agent is added in an amount of 0.8 to 1.2 equivalents to the cadmium contained in the liquid is that if the amount is less than 0.8, cadmium will not be completely precipitated, and if it exceeds 1.2, for example, reduction This is because when zinc powder is used as the agent, unreacted zinc is encapsulated in the sponge cadmium, lowering the purity of the sponge cadmium.

In the present invention, zinc or zinc-cadmium alloy powder is used as the reducing agent because of its economic efficiency and ease of handling. Further, the reducing agent used for tellurium and the reducing agent used for cadmium may be different in type.

[0011]

[Example] Example 1 Put 1 liter of sulfuric acid acidic aqueous solution containing 96.9 g/l cadmium and 1.9 g/l tellurium into a 2 liter beaker, and while stirring at 500 rpm with a propeller type stirrer, dilute sulfuric acid solution After adjusting the pH of the aqueous solution to 1.0, 2.0% of the tellurium contained in the aqueous solution was added.
2.4 g of zinc powder was added to give a weight of 5 equivalents and held for 3 hours. After separating the precipitate by filtration and adding dilute sulfuric acid to the solution after separating the precipitate and readjusting the pH to 1.0, 0.9 equivalent of cadmium contained in the solution was added. 50g of zinc powder was added and held for 3 hours. After filtering the precipitated sponge cadmium and drying the obtained sponge cadmium at 105°C for 3 hours, the tellurium content in the sponge cadmium was measured and the result was 0.0.
It was 0.4% by weight. In addition, after drying the precipitate obtained in the reduction reaction in the first stage after adding zinc powder at 105°C for 3 hours, the weight was measured to be 4.5 g, and the weight of the precipitate was 4.5 g.
The results of quality analysis were 29.9% and 42.1% by weight, respectively.
% by weight.

Examples 2 to 4 The pH of the aqueous solution was set to 1.0 or 2.5, and the equivalent amount of zinc added to Te contained in the aqueous solution was set to 1.0 or 2.5. It was carried out in the same manner as in Example 1. These results are shown in Table 1.

Comparative Examples 1 to 5 Comparative examples 1 to 5 were carried out in the same manner as in Example 1, except that the combinations of the pH of the aqueous solution and the equivalent amount of zinc added to Te contained in the aqueous solution were changed as shown in Table 1. These results are shown in Table 1.
Shown below.

[0014]

[Table 1]

From Table 1, a reducing agent such as zinc powder is added to a sulfuric acid acidic aqueous solution containing Te and Cd whose pH is adjusted to 0.5 to 3.0, at a pH of 1 to 3.0 with respect to Te contained in the aqueous solution.
It can be seen that when 3 equivalents are added, the Te content in the obtained sponge Cd becomes 0.01% by weight or less.

[0016] In Comparative Examples 1 and 5, the tellurium quality in the sponge cadmium was sufficiently low, but in Comparative Example 1, the recovery rate of cadmium was poor, and in Comparative Example 5, zinc was mixed in the sponge cadmium. This reduces purity.

[0017]

According to the present invention, tellurium can be separated at low cost and high purity sponge cadmium can be easily recovered.

Claims (1)

[Claims] Claim 1: After adjusting a sulfuric acid acidic aqueous solution containing tellurium and cadmium to pH 0.5 to 3.0, a reducing agent is added to the solution in an amount of 1 to 3 equivalents based on tellurium, and then the resulting precipitate is A method for recovering high-purity sponge cadmium, characterized by adding a reducing agent in an amount of 0.8 to 1.2 equivalents to the cadmium contained in the solution into a solution from which a substance has been separated.