In the soluble anode electrolysis process of nickel , the anode current efficiency (about 86%) is lower than the cathode current efficiency (about 97%) due to the influence of anode impurities, and the electrolyte is entrained by the purification slag during the purification process. The loss causes the concentration of Ni 2+ in the electrolyte to continuously decrease. In order to prevent the electrolyte depleted of nickel, to ensure normal production, it is necessary to maintain a balance of metal ions. Nickel sulphide electrolysis requires about 0.2t of external length for each 1t of electrolytic nickel produced, the value of which depends on the amount of nickel recovered from the slag. Electrolytic rehydration is one of the effective methods to supplement nickel ions in electrolytes.
The cathodic process of electrolytic refining is different from the cathodic process of electrolytic production. In the production of finished electrolyzers, conditions are created to control the precipitation of hydrogen to ensure the preferential precipitation of nickel on the cathode. In the process of refining, the opposite is true. Hydrogen preferentially precipitates on the cathode, and nickel dissolves normally on the anode. As a result, the cathode current efficiency of nickel is much lower than that of the anode current, so that Ni 2+ in the electrolyte is enriched.
Table 1 Technical operating conditions for nickel sinter anodic electrorefining production | ||||||
project | unit | I factory | II factory | III factory | Thompson Smelter ((Plus) | |
yin | Ni | g/l | >70 | 60～65 | 60～70 | 75 |
pole | Cu | Mg/L | <3 | 0.3 | <0.3 | 　 |
liquid | Fe | Mg/L | <4 | 0.6 | <0.5 | 　 |
group | Co | Mg/L | <20 | 1.5 | <1 | 　 |
to make | Zn | Mg/L | <0.35 | 0.3 | <0.3 | 　 |
　 | Pb | Mg/L | <0.3 | 0.08 | <0.05 | 　 |
　 | Cl - | g/L | >70 | 70～90 | 120～130 | 45~50 |
　 | Na + | g/L | <40 | 45~60 | <50 | 65 |
　 | H 3 BO 3 | g/L | 4~6 | >5 | 8~15 | 20 |
　 | Organic matter | g/L | <0.7 | <1 | 1 | 　 |
　 | PH | 　 | 4.6~5.0 | 2 to 2.5 | 2 to 2.5 | 3.5 |
current intensity | kA | 13.5~13.8 | 4.1 | 5 | 10 | |
Current density | A/m2 | 250 | 180~210 | 170～200 | 240 | |
Electrolyte temperature | °C | 65 | 60～65 | 65 | 63 | |
Same pole center distance | Mm | 190 | 190 | 190~200 | 197 | |
Circulating amount | L/(Ah) | 0.065 | 0.08 | 0.085 | 0.08 | |
Anode cycle | d | 9 to 10 | 9 to 10 | 6 to 9 | twenty one | |
Cathode cycle | d | 4~5 | 3 | 6~7 | 10 | |
Yin and yang liquid surface difference | Mm | 30~50 | 30~50 | 50~60 | 20~25 | |
Groove cycle | month | 4~5 | 2 to 3 | 3 | 　 | |
The liquid-forming process is carried out in an electrolytic cell without a diaphragm. Purple copper sheet used as the cathode, making the process not only functions as a liquid supplement nickel ions, copper removal effect as well. Since the precipitation potential of copper ions is positive than that of nickel ions, copper ions in the electrolyte are precipitated together with hydrogen on the cathode to form sponge copper on the cathode.
The main reactions of the liquid-forming process are:
Cathodic reaction 2H + +2e=H 2 ↑
Cu 2+ +2e=Cu
Anode reaction Ni 3 S 2 -6e=3Ni 2+ +2S
Cu 2 S-4e=2Cu 2+ +S
The anode process of the liquid-forming process is identical to that of normal electrolysis, and the anode material includes a nickel sulfide anode, an alloy anode, or a relatively complete residue from the production tank. In order to increase the recovery rate of the precious metal, the anode plate is generally sheathed in a nylon bag to prevent the anode mud falling off from the anode from being mixed with the sponge copper deposited on the cathode.
In the liquid-forming process, a part of the anolyte is taken out, and the acidity thereof is adjusted to 50 to 55 g/L with a mixed acid of HCl and H 2 SO 4 as a liquid-forming electrolyte. In actual production, various solutions containing Ni 2+ and H + , such as copper slag leaching solution, iron slag slag filtrate, anode mud washing liquid and external liquid, are also introduced into the liquid forming process, and at the same time, the waste of the ceramic pipe is washed. The acid also enters the high-speed solution of the acid tank. Due to the high acidity of the electrolyte and the large amount of hydrogen evolved from the cathode, the acid mist in the workshop is large. In order to improve the working conditions and reduce the acid mist, foam formed by the commonly used saponin water is applied to cover the surface of the electrolyte.
The acidity in the electrolyte is lowered due to the precipitation of hydrogen gas on the liquid forming cathode. Based on this principle, in the Shicun nickel smelting plant in Japan, the neutralization electrolytic cell liquid-making method is used to supplement the nickel ions in the electrolyte, that is, in addition to hanging the nickel sulfide anode in several electrolytic cells, the metal nickel having a small surface area is also suspended. The rod (tube) acts as a cathode to reduce the cathode area and increase the cathode current density. When the anode current density is 120-160 A/m 2 , the anode can be dissolved smoothly, and the cathode current density is increased to 1500-3000 A/m 2 . At such a high current density, nickel is not precipitated, but only hydrogen. Precipitation at the cathode, so that the concentration of Ni 2+ in the electrolyte is increased, the concentration of H + is decreased, and the P value of the electrolyte is easily increased from 1.8 to 5.0, which not only reduces the consumption of soda ash in the purification process, but also avoids Na+ The danger caused by the introduction of electrolyte.
In the production practice, the acidic liquid-making electrolysis cell is often divided into two types: high acid liquid (18 to 22 g/L of acid in the solution 6) and low acid (4 to 7 g/L in the solution). . The number of acidic liquid-making electrolyzers is generally 25% of the total number of electrolytic cells and seed plate electrolyzers. The technical operating conditions are shown in Table 2.
Table 2 Technical conditions of acidic liquid-making electrolyzer | ||||
project | unit | I factory | II factory | III factory |
current intensity | kA | 8~10 | 4.1 | 5 |
Starting solution containing acid | g/L | 50~55 | 140～180 | 50~60 |
The final solution contains acid | g/L | 4~7 | 30~40 | 15~20 |
The final solution contains nickel | g/L | >80 | >100 | 70 |
Electrolyte temperature | °C | Normal temperature | 60～65 | 60～65 |
Same pole center distance | Mm | 210 | 190 | 180 |
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