JPS609890A - Method for electrolytically refining copper - Google Patents

Abstract

PURPOSE:To inhibit the generation of gaseous cyanogen when copper is electrolytically refined in an electrolytic soln. contg. thiocyanate ions, by adding a substance whose oxidation-reduction potential is equal to or lower than that of thiocyanate ions to the electrolytic soln. CONSTITUTION:When copper is electrolytically refined in an electrolytic soln. contg. thiocyanate ions, a substance whose oxidation-reduction potential is equal to or lower than that of thiocyanate ions is added to the electrolytic soln. The substance added to the electrolytic soln. is preferentially oxidized on the surface of an anode during decoppering electrolysis, so the oxidation reaction of thiocyanate ions is inhibited. Fe<2+>, Sb<2+>, H2O2 or the like is preferably used as the substance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a copper electrolytic refining method for the purpose of preventing the generation of toxic cyanide gas that may occur when copper is electrolytically refined by adding thiocyanate ions to an electrolytic solution. It is related to.

Electrolytic refining of copper is generally carried out at a liquid temperature of lIO~70°C, copper content) 10
~55 guat, free sulfuric acid 100~250 r/sulfuric acid, acidic copper sulfate solution as the electrolyte, blister copper with a purity of about 99 as the anode, a pure copper thin plate as the cathode, current density 1~
The stain was vapor decomposed using a direct current of 5 A/c1mF,
This is done by depositing 9999% pure electrolytic copper on the cathode.

The types and amounts of impurities contained in Japanese copper vary depending on the ore that is the raw material for blister copper, but among these impurities, metals baser than copper, such as nickel, cobalt, iron, manganese, and zinc, can be removed by electrolysis. Since these impurities are eluted into the electrolyte solution, these impurities gradually accumulate in the electrolyte solution as the process of refining the rice cake progresses.

Metals more harmful than copper, such as gold, silver, platinum, and palladium, do not dissolve into the electrolytic solution and accumulate at the bottom of the electrolytic cell as anode slime.

On the other hand, the copper itself in the blister copper undergoes a dissolution reaction due to dissolved oxygen in the electrolytic solution, and an amount ranging from 0.5 to 1.0% of the precipitated steel is eluted into the electrolytic solution, and the copper concentration in the electrolytic solution increases.

Therefore, in the electrolytic refining of copper, in order to keep the electrolytic conditions constant, an insoluble anode such as lead is always placed in a part of the electrolytic tank, and electrolytic winning of the copper (de-bonding electrolysis) is performed.
After adjusting the concentration and extracting a part of the copper, electrolytically winning copper or concentrating it to crystallize tanban (Cu5Ot.580), the copper-removal electrolysis is performed to remove copper and remove arsenic from the liquid. Nickel sulfate (NIS○, 6
H20) is recovered and sulfuric acid produced as a by-product is returned to the electrolytic solution in a so-called liquid purification process.

In addition to the main components of sulfuric acid and copper sulfate, various additives are added to the copper electrolyte for various purposes, but a small amount of precious metal impurities in the blister copper is eluted into the electrolyte. Thiocyanate ions, which are added to the electrolytic solution in an amount of about 1 to 20 ppm for the purpose of preventing copper removal, pose a problem during copper removal electrolysis.

In other words, there is no problem with thiocyanate ions when the anode is blister copper, but when the anode is an insoluble anode such as lead, it is oxidized and rodan is inevitably produced as shown in equation (1). However, as shown in equation (2), this decomposes heterogeneously to produce HON, and acid decomposition generates highly poisonous cyan gas, which is extremely hazardous to the working environment.

2SCN--2e: (SCN) t Redox potential Eo=0.77 V ・(1)5 (SON) z+1
IH20-) 58CN" + sot1HCN +
7H''・Old and Old・' (2) The present invention was made in view of the above-mentioned circumstances, and is the development of a copper electrolytic refining method that suppresses the generation of cyan gas during copper removal electrolysis. The same electrolytic refining method in which thioanate ions are added to the electrolytic solution is characterized by adding to the electrolytic solution a substance having an oxidation-reduction potential that is the same as or lower than that of the thiocyanate ions.

Due to the presence of such a substance in the electrolyte, it is preferentially oxidized on the anode surface during copper removal electrolysis, thereby preventing the oxidation reaction of thiocyanate ions.

Although there are many such substances, desirable substances are those that do not adversely affect the quality of the electrolytic copper deposited on the cathode.
-e→Fa""-oxidation-reduction potential E. -0.77V input s
b3+(sb ” −e −> sb ′−1Ea =
0.6g2 V), H20t(H202e→2H'-
+Ot EO=0.6E! 2V), etc. The desired addition amount for these is 01 to 2 for Fe"+
7/l, 01~ly/lX for H2O2, OF/l, and OF/l for H2O2, but the reason is that both are 0.
If the value is less than 1 f/, the effect is not sufficient.
/l, H2O2 exceeding 10 f/l will dissolve the precipitated electrolytic copper, leading to a decrease in current efficiency, and it is difficult to dissolve Sb leaves in the electrolytic solution in excess of 1t7t. Because there is.

Since H2O2 self-decomposes in the electrolyte, it must be added continuously, but Fe! Since + and sb''+ are oxidized on the anode and simultaneously reduced on the cathode, they do not need to be added continuously, and are therefore more preferable substances for the purpose of the present invention.

The present invention will be explained below with reference to Examples.

Example: 1.57 in a 5t desiccator with a sealable lid.
Synthetic copper electrolyte (Cut+ 409/l, H2SO41
F! Of/l.

C6-Oppm, KSCN 1f/L) was added and maintained at 50°C.

Insert the Cu plate and Pb alloy plate of 5crnr:′ here.Cu
Using the plate as a cathode and the Pb alloy plate as an anode, various substances shown in Table 1 were added and electrolysis was performed at a current density of 2.5 A/d- for 2 hours. Gas was collected from the desiccator and the concentration of cyan gas was measured. did. The results are shown in Table 1.

tDip≠; → Since it is not yet possible to compare, electrolysis was carried out in the same manner in the case where the substance according to the present invention was not added, and the hydrogen cyanide concentration was also measured, and the results are also listed in Table 1.

Table 1 As is clear from Table 1, it can be seen that cyan gas generation during copper removal electrolysis 1 is significantly suppressed by the present invention.

As described above, the present invention solves the problems in the working environment that occur during the electrolytic refining of planes, and has a significant industrial effect.

511-

Claims (1)

[Claims] A copper electrolytic refining method in which thiocyanate ions are added to an electrolytic solution, characterized by adding to the electrolytic solution a substance having a redox potential that is the same as or more base than that of thiocyanate ions. Electrolytic refining method of copper.