Production of electrolytic nickel from crude nickel sulfate

I. Overview

A by-product of the purification process of crude nickel sulfate-based copper electrolysis waste liquid. China began experimenting with the production of electrolytic nickel from crude nickel sulphate in 1954. In 1955, it began to test the production of electrolytic nickel from crude nickel sulphate, which was put into production in 1955. The quality of electrolytic nickel produced by this process is in line with the international No. 3 nickel standard. The process includes preparing a nickel sulfate solution and electrolyzing nickel. The process flow is shown in Figure 1.

Figure 1 Process for producing electrolytic nickel from crude nickel sulfate

Second, raw materials

The anhydrous crude nickel sulfate is pale yellow and turns green in the air due to absorption of moisture. The composition of crude nickel sulfate is (%):

When the crude crude nickel sulfate is dissolved in water at 20-25 ° C, the insoluble matter is 54%; at 80-100 ° C, it is easily soluble in water, the insoluble matter is 1%, the insoluble residue is grayish white, and most of the compounds are antimony . It is mixed with copper, iron , arsenic , lead and a small amount of nickel.

Third, technical operating conditions

(1) Dissolving nickel sulphate

The crude nickel sulfate is dissolved in water in the dissolution tank, the liquid-solid ratio is 3:1, heated to 80-85 ° C with steam, and stirred for 2 to 3 hours. After the material is dissolved, the solution is dark blue with a density of 1.25 to 1.35 t/m ³ . The solution contains nickel 80-120g/L and impurities such as copper, iron, zinc , arsenic, antimony and tin and free sulfuric acid.

(2) Neutralization and removal of impurities

The crude nickel sulfate was dissolved and then neutralized once. One neutralization endpoint pH=4.2-4.5, temperature 85 °C, neutralizer is calcium carbonate emulsion. After neutralization, a part of copper, iron, tin, antimony and the like are hydrolyzed and precipitated into the slag. The primary neutralizing solution contains 80-90 g/L of nickel.

(3) Secondary neutralization and impurity removal

The neutralized filtered solution was neutralized twice in one time. The second neutralization end point pH = 6.65 ~ 6.75, temperature 85 ° C, the neutralizer is a calcium carbonate emulsion. After neutralization, most of the impurities such as copper, iron, and zinc are hydrolyzed and precipitated into the slag. The secondary neutralizing solution contains 50-60g/L of nickel and is used for power supply. The secondary neutralization slag contains about 7% nickel and returns to the dissolved ingredients.

(4) One neutralization slag treatment

The primary neutralization slag contains 1.5% to 2.5% of nickel and is dissolved in sulfuric acid, pH = 1.5 to 2.0, and the temperature is 80 °C. The solution contains nickel at 20 g/L or more and contains impurities such as copper, iron, and zinc, and the solution is returned to use.

And the pH value directly affects the rate of precipitation of the metal salt, and a pH = 4.2 ~ 4.5, the iron of about 90% into the slag, copper slag into the rate of about 70%, zinc of about 15% into the slag. The secondary neutralization pH=6.65～6.75, the iron and copper slag rate is 99%, the zinc slag rate is 98.5%, and the nickel slag rate is about 30%.

(5) Nickel electrowinning

Production of insoluble electrolytic nickel anode electrolysis, an anode of silver is 1% to 3% of Pb-Ag alloy plate, an aluminum plate as the cathode blank, the electrolyte is nickel sulfate solution. The electrolyte composition (g / L): 50 to 60 Ni, Fe ≦ 0.05, Cu ≤0.02, Zn ≦ 0.05, 0.04 Pb, 2-3 sulphate, boric acid 20 to 25, 50 to 100 over sodium sulfate. The electrolyte circulation mode is up and down.

1, the electrolyte contains nickel

The effect of the electrolyte containing nickel on the current efficiency is shown in Figure 2. High nickel content can suppress hydrogen ion discharge on the cathode and improve current efficiency. The amount of nickel in the electrolyte is preferably from 80 to 120 g/L.

Figure 2 Relationship between nickel content in electrolyte and current efficiency

2, the electrolyte contains acid

The acid content of the electrolyte, the effect on current efficiency is shown in Figure 3. When the acid content is high, the hydrogen ions are easily discharged on the cathode, and the cathode nickel sheet is easily broken, which is liable to cause a short circuit and lower the current efficiency. It is advisable to keep the electrolyte containing acid 3g/L during production.

Figure 3 Relationship between sulfuric acid and current efficiency in electrolyte

3, current density

The current density is generally selected according to factors such as production task, output size, power supply, and electricity price. The current density is high, the overvoltage of hydrogen is correspondingly increased, the hydrogen ion discharge can be suppressed, and the current efficiency is significantly improved. However, as the current density increases, the nickel sheet is easily broken, resulting in a short circuit and a decrease in current efficiency. . Tests have shown that increasing the current density to 350 A/m ³ , the physical form of the cathode nickel is still good, and the current efficiency is about 80%, but the current density is too high is uneconomical. The current density is generally 180 to 300 A/m ² . The relationship between current density and current efficiency is shown in Figure 4.

Figure 4 Relationship between current density and current efficiency

4, electrolyte temperature

The electrolyte temperature was maintained at 60 °C.

(6) Clean liquid (adjustment of electrolyte)

As the electrolysis process progresses, the concentration of nickel ions in the electrolyte continuously decreases, and the concentration of sulfuric acid continues to rise. A part of the electrolysis liquid is extracted and added to the nickel carbonate to remove the acid, and then a part of the new solution is added to the electrolysis system, and the remaining half is neutralized with sodium carbonate to prepare nickel carbonate, and the other half is concentrated and then combined with nickel carbonate to be electrolyzed. In the liquid.

Fourth, the product

Electrolytic nickel

Examples of the composition of electrolytic nickel are shown in Table 1.

Table 1 Electrolytic nickel composition, %

V. Technical and economic indicators

Nickel neutralization direct yield 50% to 70%

Nickel neutralization total yield 92% ~ 95%

Nickel electrolysis straight yield 45% to 55%

Total nickel electrolysis yield 98.5%~99.5%

System-wide recovery rate 90% to 93%

Current density 150～200A/m ²

Cell voltage 3.5~4.0V

Current efficiency 60% to 70%

Sulfuric acid consumption 2400kg/t nickel

Smoke coal consumption 2000 kg / t Ni

Calcium carbonate consumption 6500 kg / t nickel

Sodium carbonate consumption 450 kg/t nickel

Sixth, the main production equipment examples

(1) Electrolytic tanks, 10 pieces, with a specification of 1300×850×1000mm, the tank body is made of reinforced concrete and lined with 3mm thick lead skin.

(2) Purification tanks, 4 pieces, the specification is φ1600×3000mm, the tank body is made of reinforced concrete, lined with 3mm thick lead skin, and the tank is equipped with lead-shaped heating pipe and air duct.