Nickel electrolyte purification and iron removal method

In the electrolytic production of nickel, iron-containing anolyte is generally 100 ~ 500mg / L, the solution was purified in claim reduced iron content 0.5 ~ 4mg / L, usually iron hydrolysis precipitation.

(A) hydrolysis hydrometallurgical common iron precipitation method

Hydrolytic precipitation and iron removal methods commonly used in industrial production include neutralization hydrolysis, yellow sodium (potassium) iron sputum method, goethite method and hematite method.

1) Neutralization hydrolysis

The so-called neutralization hydrolysis method is to adjust the pH value of the solution with a base. When the main metal ion to be extracted is not hydrolyzed and precipitated, the impurity metal ions are precipitated in the form of hydroxide M(OH) _n , so it is also called hydrogen. Oxide precipitation method.

Metal ions do not work as follows:

M ⁿ⁺ +nOH ^- =M(OH)n↓

The OH ^- ion is derived from the dissociation reaction of water. If [M ⁿ⁺ ] is the concentration at which the metal ions in the solution reach equilibrium when the hydrolysis reaction reaches equilibrium, the relationship of [M ⁿ⁺ ] to PH can be illustrated by FIG. 2 . When the metal ion concentration is constant, the pH at which Mn ⁺ is hydrolyzed and precipitated is shown in Table 1.

Table 1 Balance of pH of Mn ⁺ (25 ° C) when hydroxide precipitates

M n+		Ca 2+	Mg 2+	Ni 2+	Fe 2+	Pb 2+	Zn 2+	Co 2+	Cu 2+	Fe 3+	Co 3+
balance	[M n+ ]=lmol/L	11.37	8.37	7.1	6.35	6.22	5.65	5.1	4.37	1.53	-0.2
PH value	[M n+ ]=10-6mol/L	14.7	11.37	10.1	9.35	9.22	8.65	8.1	7.37	3.53	1.8

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From Figure 2 and Table 1, the following conclusions can be drawn:

(1) In the case where the ion concentration is the same, the equilibrium of the various ions on the left side of the figure is P敊, so they can precipitate in a small P眄, or their salts are easily hydrolyzed, and the salts of alkaline earth metals are difficult to be hydrolysis.

(2) According to the hydrolysis equilibrium line of Fe ²⁺ —Fe ³⁺ and Co ²⁺ —CO ³⁺ , it is known that for a valence metal, a high valent ion of the same metal is easily hydrolyzed than a low valent ion. Therefore, in the purification of the nickel electrolyte, in order to preferentially hydrolyze and precipitate Fe ²⁺ in the solution, air is blown in to oxidize Fe ²⁺ to Fe ³⁺ , and further precipitates as Fe(OH) ₃ . By the same token, Co ^{2+ is} oxidized to Co ³⁺ with chlorine gas and precipitated with Co(OH) ₃ .

The hydroxide precipitation method is the most widely used iron removal method in extracting metallurgy, but the main disadvantage of this method is that Fe(OH) ₃ has colloidal properties, which is not only slow in precipitation, but also difficult to clarify and filter, and makes metals and other valuables. The metal is adsorbed and lost. Therefore, when the concentration of Fe ³⁺ is large, it is difficult to separate Fe(OH) ₃ from the solution. Production practices have shown that this method is only suitable for purifying solutions with low concentrations (eg, iron ion concentrations around /L).

2) Yellow sodium (potassium) iron sputum method, goethite and hematite method

How to remove F ³⁺ (or Fe ²⁺ ) from a solution with a higher concentration of iron ions, the conventional hydrolysis precipitation method is difficult to obtain liquid-solid separation in the iron-plating process due to the formation of a large amount of Fe(OH) ₃ colloidal precipitate. After long-term research and practice, in the 1960s, three new methods of removing iron from the yellow potassium (sodium) iron sputum method, goethite method and hematite method were promoted and applied in hydrometallurgy. The common feature of the three methods is to control certain iron-iron conditions, so that the iron ions in the solution are precipitated as artificial minerals (such as iron shovel, goethite and hematite). These artificial mineral deposits are crystalline and easy to settle. , filtration and washing.

(1) Yellow sodium (potassium) iron sputum iron method

Some minerals in nature have similar composition, the same structure and the same crystalline form. This is what geochemically called the isomorphism. The so-called 矾 is a general term for a series of isomorphous minerals, and monovalent metal ions (such as K ⁺ , Na ⁺ , Ag ⁺ , NH ^{4 +} , etc.) and trivalent metal ions (such as Al ³⁺ , Fe ³⁺ , Cr The sulfates of ^3+, etc. are most likely to form hydrazine together.

The ferrite of the jarosite, such as potassium iron, sodium iron, ammonium iron, etc., has a chemical formula of MFe ₃ (SO ₄ ) ₂ (OH) ₆ . M may be a monovalent metal ion such as K ⁺ , Na ⁺ , NH ⁴⁺ or the like, and its color is yellow. In hydrometallurgy, considering the economic cost of the reagents (wherein the K ⁺ containing base or salt is expensive), soda ash or liquid ammonia is often used as a ferrous iron reagent to provide the monovalent metal ions required to form the samarium. [next]

When the nickel electrolysis anolyte is neutralized and the water is used to remove the high nickel iron slag produced by the iron, the sodium sulphate is dissolved in the sulphuric acid to remove the iron by the sulphate method. The immersion iron process is to form a yellow-sodium samarium precipitate at a high temperature (90-95 ° C) and control the appropriate P (5-1.8) when there is enough Na ⁺ and SO ₄ ^2- in the solution.

3Fe ₂ (SO ₄ ) ₃ +Na ₂ SO ₄ +12H ₂ O=Na ₂ Fe ₆ (SO ₄ ) ₄ (OH) ₁₂ ↓+6H ₂ SO ₄

The iron-bismuth complex salt is yellow or light yellow orthorhombic crystal, the composition is stable, the solubility in the acidic solution is small, the sedimentation, filtration and washing performance are good, and the liquid-solid separation is easy to carry out, so the iron removal effect is good.

(2) goethite iron method

The goethite iron method is also called air oxidation and iron removal. It is in a high temperature (~90 ° C) and low acid concentration of sulphate solution, the dispersion of air into the solution to oxidize Fe ²⁺ into Fe ^{3 +} , and is expressed with natural goethite (such as fibrite, The chemical formula is γ-FeOOH) precipitation of a compound similar in crystal form and chemical composition:

The goethite formed by this reaction is a-FeOOH, which is a brown needle crystal. An important condition for iron removal by goethite method is that the concentration of Fe ^{3+ in the} solution should be less than 1g/L, so it is necessary to increase a reduction process to reduce Fe ³⁺ to Fe ²⁺ .

(3) Hematite iron method

Hematite is a raw material for iron making. It has been found that under high temperature and high pressure conditions, when the concentration of sulfuric acid is not high, the hydrolysis reaction of Fe3+ in the solution will occur, resulting in a-Fe ₂ O ₃ precipitation:

It can be seen from the chemical composition represented by the chemical formula that the content of iron (-60% Fe) in the hematite precipitated slag is higher than that in the yellow sodium (potassium) iron slag method and the iron slag method, so the iron slag of the method less, the raw material can be used for iron, but the need for expensive autoclave equipment Shentie, like module in advance to restore Fe ³⁺ Fe _^2+, a large investment in the construction method. At present, the only method also abroad wet zinc smelting plant has a production application.

See Table 2 for a comparison of the methods for removing iron from oxidized water in hydrometallurgy.