RU2328061C1 - Method of cleaning off iron from nickel sulphate solution - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used for cleaning off iron impurities from a solution of nickel sulphate NiSO₄ during recycled production of nickelous hydroxide Ni(OH)₂ from used alkaline accumulators. During precipitation of iron from the nickel sulphate solution with calcined soda at pH=3.0-3.3, the ratio of the quantity of iron to the insoluble nickel in the precipitate from the process is about 8-10 g of iron to 1g nickel. After the first iron precipitation stage, the second precipitation stage is carried out at pH of 6.3-6.8. The deposit of the ferrous cake obtained from the first cleaning stage is extracted from the process, and the deposit of the ferrous cake obtained from the second cleaning stage is returned into the process at the initial stage and then again transferred to the solution.

EFFECT: lower nickel losses during cleaning off iron from nickel sulphate solution; higher degree of purity of the nickel sulphate solution; reduction of iron content requirements for the raw materials and a cheaper method.

Description

The invention relates to the electrical industry and can be used to purify a solution of nickel sulfate NiSO ₄ from iron impurities in the recycling manufacture of nickel nitrous oxide hydrate Ni (OH) ₂ from spent alkaline batteries.

The initial nickel-containing material — the anode mass extracted from the electrodes — contains a certain amount of iron, both metallic and in the form of oxides (Fe ₂ O ₃ , FeO). Iron is removed by one chemical method or another after dissolving the nickel contained in the anode mass in sulfuric acid, and the accompanying metal impurities also pass into the solution.

A known method [1] of purifying a solution of nickel sulfate from iron by recycling the production of nickel oxide hydrate from spent alkaline batteries by successive conversion of Fe ^{2+ ions} to Fe ^{3+ with} trivalent nickel and precipitation of iron with an alkali solution of 1.45 g / l density at pH = 3 -5 in accordance with the following reactions:

The iron content in the final product with this cleaning method should not exceed 0.07 wt.% With respect to nickel.

Closest to the claimed method is [2], in which the conversion of ferrous iron ^ions Fe ²⁺ to Fe ³⁺ ions is carried out with atmospheric oxygen with the addition of hydrogen peroxide and precipitation of iron with a solution of soda ash at pH = 5.0-5.5 in accordance with following reactions:

The iron content in the final product with this cleaning method should not exceed 0.2 wt.% With respect to nickel.

In both cases, a nickel coprecipitation proceeds as a side reaction:

The purified solution at the end of the reaction is filtered to remove the glandular cake, after which it is transferred to a further redistribution, and the glandular cake containing a certain amount of nickel, previously dried, is sent to obtain ferronickel.

It should be noted some significant drawbacks characteristic of these methods of purifying a solution of nickel sulfate from iron:

1. At the indicated pH = 3.0-5.5 Reaction (5) and (6) occur only in the presence in the solution of ions Fe ^3+, wherein the amount of coprecipitated nickel directly proportional to the amount of deposited iron. Since it is economically feasible to minimize the amount of nickel removed from the solution, it is necessary to limit the content of iron impurities in the starting material. According to [1], the amount of iron relative to nickel before leaching should not exceed 3 wt.%, Otherwise the material is subjected to additional mechanical cleaning (magnetic separation), which leads to increased costs and losses of nickel in additional operations.

2. A limitation on the quantitative content of iron in the starting nickel-containing material with these methods is also necessary to achieve the indicated result of the ratio of iron to nickel in the final product (not more than 0.2 wt.% According to the requirements of TU48-3-63-90). For example, if the ratio of iron to nickel in the starting material is 3-5 wt.%, The residual iron in the purified solution will increase to 0.1-0.3 wt.% To nickel, due to the instability of Fe ³⁺ ions in the solution with the specified interval pH and reverse reaction of Fe ³⁺ in Fe ²⁺ . Since the transition of iron ions from trivalent to bivalent is a rather lengthy process, it is necessary to regulate the time from the end of Fe ²⁺ oxidation to the end of iron deposition. Nevertheless, the process of stabilization of the pH value with alkali (i.e., the direct conduct of the precipitation reaction) is time-consuming, which accounts for the transition of some part of iron to Fe ²⁺ and, as a result, the iron content in the solution after cleaning is directly proportional to the iron content in stock solution.

3. The amount of coprecipitated Nickel during the deposition of iron when changing the pH from 3 to 5 by the method [1] varies from 0.1 g of Nickel per 1 g of iron at pH = 3 to 2-2.5 g of Nickel per 1 g of iron at pH = 5, i.e. Nickel losses can be up to 7.5 wt.% when the iron content in the starting material is 3 wt.% and the process is carried out at pH = 5. When carrying out the process according to the method [2], nickel losses at pH = 5.0-5.5 are up to 3.5 g per 1 g of iron removed from the solution, i.e. up to 10-11 wt.% of the initial nickel content.

The proposed method of purification of a solution of Nickel sulfate from iron impurities eliminates these disadvantages.

The invention consists in the fact that the process of deposition of iron from a solution of Nickel sulfate is carried out in two stages:

- transfer of Fe ³⁺ ions to the precipitate at pH = 3.0-3.3;

- transfer of Fe ^{2+ ions} to the precipitate at pH = 6.3-6.8.

In this process, obtaining a solution of Nickel sulfate, purified from iron impurities, consists of the following stages:

1. Leaching of Nickel from the starting material with sulfuric acid.

2. Precipitation of iron with a solution of soda ash at pH = 3.0-3.3.

3. The first filtering of the solution (obtaining the first glandular cake).

4. Precipitation of iron with a solution of soda ash at pH = 6.3-6.8.

5. Second filtering of the solution (obtaining a second glandular cake).

6. The use of the second glandular cake as an additive to the nickel-containing material sent to leach nickel (the first stage of the process).

Obtained by leaching (1 stage), a solution of nickel sulfate contains a certain amount of Fe ^{2+ ions} ; Fe ³⁺ . The solution is purified from Fe ³⁺ iron ions (stage 2 of the process) in accordance with the following reactions:

Reactions are carried out at a solution temperature of t = 70-75 ° C, with mechanical stirring and bubbling of the solution with air to convert Fe ^{2+ ions} to Fe ³⁺ . For the same purpose, before the first filtration, hydrogen peroxide (H ₂ O ₂ ) is added to the solution at the rate of 1 l of 25% H ₂ O ₂ per 1000 l of nickel sulfate solution at a density of 1.22 g / l. The density of the soda solution is 1.14 g / l.

The average amount of iron removed from a solution during these reactions is 85-95%, as well as during processes using technologies [1], [2]. In the process under consideration, the amount of residual iron in the solution is not of fundamental importance, which is a limitation in the quantitative ratio of iron to nickel in the starting material, since the resulting solution is sent to the subsequent purification of iron. The main indicator of this stage is that in the ferrous cake removed from the process, the ratio of the amount of iron to insoluble nickel in the precipitate is 8-10 g of Fe per 1 g of Ni. Moreover, the ratio of iron to nickel can be increased to a value of 30 g Fe per 1 g Ni during subsequent washing of the gland cake in the filter press with a hot weakly acidic solution of sulfuric acid at a pH of the wash solution of 3.0 and water.

The transition of Fe ^{2+ ions} to Fe ³⁺ according to reaction (3) occurs at acidic pH values of the solution in the presence of a free sulfate ion. At pH values close to neutral and alkaline in an aqueous solution of nickel sulfate in the presence of oxygen and soda, the mechanism of transition of the valence of iron from Fe (II) to Fe (III) changes and can be described by the reaction, according to which the second purification operation iron (stage 4 of the process):

This transition occurs more fully at higher pH values. A limitation of pH to 6.8 is a significant increase in the amount of nickel that reacts (6). However, in the indicated pH range, the amount of precipitated from the iron solution by the reaction (7) is directly proportional to the duration of the process. Therefore, the time of the process can be adjusted at the time of the reaction, for example, according to the results of a rapid analysis on the quantitative content of iron ions in the solution and, as a rule, the reaction time does not exceed 4-5 hours when the iron content in the starting material is 7 wt. % with respect to nickel.

The ratio of the amount of iron to insoluble nickel in the precipitate during this stage of the process is 1 g of Fe per 4-8 g of Ni. This precipitate is sent to the first stage of the process for joint dissolution in sulfuric acid with the original Nickel-containing material.

The total loss of Nickel during the process is 0.1-1%. The return to leaching of the second ferruginous cake does not lead to a general accumulation of iron in the production line, since iron with valency III, which is then removed from the process during the first precipitation, is involved in the turnover. The resulting solution of Nickel sulfate contains 0.01-0.1 wt.% Iron in relation to Nickel, with the iron content in the source material sent for leaching, up to 7 wt.% In relation to Nickel.

The technical result of the invention is:

- the use of a relatively inexpensive component (soda ash) for converting iron to precipitate;

- reduction of nickel losses during the purification of a solution of nickel sulfate from iron;

- increase the degree of purification of a solution of Nickel sulfate;

- reduction of requirements for the source material for the quantitative content of iron.

References taken into account:

1. Patent No. 2178931, Cl. 7 H01M 4/26, H01M 4/52, 2000

2. Nickel recovery from spent alkaline batteries, Report NI-724, USSR Ministry of Color, Gipronickel Research Institute, Leningrad, 1966

Claims (1)

A method of purifying a solution of nickel sulfate from iron with a solution of soda ash, characterized in that the precipitation of iron is carried out in two stages, at pH values of the solution in the first precipitation stage 3.0-3.3 and in the second precipitation stage 6.3-6.8, wherein the precipitate of ferruginous cake obtained in the first stage of purification is removed from the process, and the precipitate of ferruginous cake obtained in the second stage of purification is returned to the process to the initial stage and again transferred to the solution.