Production practice of purifying iron by nickel electrolyte

Nickel Electrolyte Purification and Iron Removal Practice Nickel electrolysis plants usually use oxygen in the air to oxidize Fe ²⁺ in the anolyte to Fe ³⁺ and then hydrolyze and precipitate. The iron removal reaction process is controlled by the Fe ²⁺ oxidation reaction rate, and when a small amount of copper ions are present in the solution, it catalyzes the oxidation of Fe ²⁺ . Therefore, the iron removal process is usually arranged before copper removal.

The nickel-containing iron slag obtained by hydrolyzing and precipitating the nickel electrolysis anolyte is acid-dissolved and oxidized with sodium chlorate, and then iron is removed by the yellow-sodium iron samarium method.

First, the anolyte purification and iron removal

The iron removal operation has two modes of operation: continuous and intermittent. Large nickel electrolysis plants use continuous operations; small plants use intermittent operations. The continuous purification method has stable quality and large equipment production capacity, which is the direction of this process development.

The iron removal process includes ferrous ion oxidation and ferric hydrolysis precipitation:

In the iron removal process, H ^{+ is} generated, and a neutralizing agent must be added at the same time as the blast. In order to avoid excessive sodium ions entering the production system, NiCO ₃ is often used as a neutralizing agent for iron removal:

4H ⁺ +2NiCO ₃ =2Ni ²⁺ +2CO ₂ ↑+2H ₂ O

Increasing the reaction P can accelerate the iron removal reaction, but if the pH is too high, the nickel content of the slag will increase.

The presence of copper ions in the solution accelerates the oxidation of Fe ²⁺ . This is because copper ions act as electrons in the oxidation of Fe ²⁺ :

Cu ⁺ -e=Cu ²⁺

Cu ²⁺ +Fe ²⁺ =Cu ⁺ +Fe ³⁺

Purifying the hydrolyzed iron slag also removes 1/3 to 2/5 of the copper in the solution, reducing the burden of copper removal.

In the process of iron removal, the solution potential formed by using air as the oxidant is not enough to oxidize Ni ²⁺ and Co ²⁺ to a high valence state, but part of Ni ²⁺ is hydrolyzed and precipitated as a basic salt:

3NiSO ₄ +4NiCO ₃ +4H ₂ O=3NiSO ₄ .4Ni(OH) ₂ ↓+4CO ₂ ↑

Fe(OH) ₃ has strong adsorption. During the process of removing iron, a certain amount of zinc can be coprecipitated with Fe(OH) ₃ to be removed, and some copper will also hydrolyze and precipitate:

3CuSO ₄ +2NiCO ₃ +2H ₂ O=CuSo ₄ .2Cu(OH) ₂ ↓+2NiSO ₄ +2CO ₂ ↑

In the de-ironing process of a factory, the anolyte is heated to 65-75 °C through a titanium tube heat exchanger, and then continuously passed through five 75 m ³ Paqika-type air agitation tanks. Air is blown into the tank, both as an oxidant and for agitation. At the inlet of the first agitation tank, nickel carbonate is added to neutralize the acid precipitated by the iron removal reaction, so that the iron removal reaction control pH is in the range of 3.5 to 4. After continuous iron precipitation in 5 tanks, the iron removal liquid is pumped into the tubular filter for liquid-solid separation to obtain iron slag containing ～10% Fe and -20% Ni and Fe<0.01g/L. Remove the iron after the liquid. [next]

2. Purification and removal of iron by hydrolyzed iron slag acid leaching solution

In the process of nickel electrolysis anolyte with NiCO ₃ and hydrolyzed iron, according to theoretical calculation, ferric ions are hydrolyzed and precipitated at pH ≤ 3.5, which can completely remove iron without losing nickel, but actually neutralize the precipitate. The control pH is high, so some Ni ²⁺ is double precipitated with iron, so the iron slag produced in industrial production contains high nickel. In order to reduce the nickel content of the iron slag, a plant dissolves the iron slag and then removes the iron by the yellow sodium iron slag method to recover the nickel in the acid immersion liquid. The process flow is shown in FIG. After the iron slag is slurried, it is dissolved in industrial acid sulfuric acid in an acid-soluble tank to obtain an acid-soluble liquid. The acid-soluble solution is heated to 90 ° C in the iron-sodium ferrite removal tank, and sodium chlorate is used as an oxidant to oxidize the ferrous ions in the solution to ferric ions, leaving a small amount of yellow sodium iron slag in the tank. Seed crystal, chlorine can not be sodium oxidant, the ferrous ion in the solution is oxidized to ferric ion, the acid formed by the reaction of a small amount of yellow sodium iron in the tank, can be recovered through the process of crystallization of yellow sodium iron strontium Purify 90% to 95% of nickel in iron slag.

The process flow and technical operating conditions for the treatment of electrolyte slag by acid-soluble yellow-sodium iron slag removal in a plant are shown in Table 1.