AU2024201532B2

AU2024201532B2 - Selective leaching method for nickel-iron alloy and method for preparing high-purity nickel salt

Info

Publication number: AU2024201532B2
Application number: AU2024201532A
Authority: AU
Inventors: Jian Ding; Cheng Liu; Guo Liu; Yeda LU; Ninglei SUN; Kuiting WANG; Shuyan YIN
Original assignee: China Nonferrous Engineering Co Ltd; China ENFI Engineering Corp
Current assignee: China Nonferrous Engineering Co Ltd; China ENFI Engineering Corp
Priority date: 2023-07-14
Filing date: 2024-03-07
Publication date: 2025-04-17
Anticipated expiration: 2044-03-07
Also published as: CN116574923A; AU2024201532A1; CN116574923B

Abstract

The present application discloses a selective leaching method for a nickel-iron alloy and a method for preparing a high-purity nickel salt are disclosed, wherein the selective leaching method for a nickel-iron alloy comprises the following steps: using a nickel-iron alloy powder to prepare into a slurry, adding a combined reagent into the slurry to form a to-be-leached system, leaching the to-be-leached system at 30 °C or above and carrying out solid-liquid separation to obtain a leaching solution; wherein the combined reagent comprises an iron-containing solution, an oxidizing agent and an acidic reagent, or the combined reagent comprises an iron-containing solution, an oxidizing agent and a sulfur-containing reagent; the pH value of the to-be-leached system is 0.5-5.0, and the concentration of Fe ions is 2 g/L or more. According to the present application, through the mode of returning the leaching solution or adding the iron-containing solution, the dissolution of nickel is ensured, the dissolution of iron in the nickel-iron alloy powder can be avoided as much as possible, the leaching rate of iron is reduced, further the neutralization reagent required in the subsequent nickel-iron separation can be effectively reduced, and the production cost is greatly reduced under the condition of ensuring the yield of nickel. (FIG. 1) DRAWINGS Nickelion Combined Returninga Neutraization Oxidiiz ing agent reagent Leaching .v . Removing Removmg iron impurities Solid-liquid separation Solid-liquid separation evaporaion L Leac Iron removalPost-iron removal slag solution slag solution Nickel salt FIG.1 2

Description

DRAWINGS Nickelion Combined Returninga Neutraization Oxidiiz ing agent reagent

Leaching .v . Removing Removmg iron impurities

Solid-liquid separation Solid-liquid separation evaporaion

L Leac Iron removalPost-iron removal slag solution slag solution Nickel salt

FIG.1

SELECTIVE LEACHING METHOD FOR NICKEL-IRON ALLOYAND METHOD FOR PREPARING HIGH-PURITY NICKEL SALT FIELD OF THE INVENTION

The present application relates to the field of nickel extraction from nickel-iron ore,

and specifically relates to a selective leaching method for a nickel-iron alloy and a method

for preparing a high-purity nickel salt.

BACKGROUND OF THE INVENTION

Most of the nickel ore is converted into nickel-iron alloys by pyrometallurgical process,

and a small portion of the nickel ore is converted into nickel salt by hydrometallurgical

process. With the development of the new energy industry, the production of ternary lithium

batteries requires a large consumption of nickel sulfate, and the conversion of the nickel-iron

alloy into nickel sulfate produced by pyrometallurgical process can ensure the supply of

nickel sulfate.

However, in the process of converting the nickel-iron alloy into nickel sulfate, since the

nickel-iron alloy generally has certain corrosion resistance performance, the main impurity

in the nickel-iron alloy is iron, and iron will be leached out at the same time as nickel

leaching; therefore, the more critical issue in the process of converting nickel-iron into

nickel sulfate comprises not only dissolving the nickel-iron alloy to obtain a nickel-iron

leaching solution, but also treating the nickel-iron leaching solution to realize the separation

of iron and nickel; while the conventional methods for separating iron and nickel mainly

involve converting iron into iron phosphate or removing iron by neutralization and

precipitation method.

At present, the leaching method of nickel-iron is mainly acid leaching under oxidizing

conditions or using catalytic oxidation to remove iron for selective leaching. However, no

matter what kind of leaching method that has been disclosed in the prior art, when it ensures

that the leaching rate of Ni reaches 96% or more, the leaching rate of iron is also

significantly higher than 10%, which results in the need to use a large number of neutralization reagents to remove iron in subsequent separation of iron and nickel, and the cost is relatively high.

SUMMARY OF THE INVENTION Therefore, the main aspect seeking to be solved by the present application is that a large amount of iron is leached simultaneously when an existing nickel-iron alloy is subjected to nickel leaching, resulting in the problem of high iron leaching rate; thereby, the present application provides a selective leaching method for a nickel-iron alloy and a method for preparing a high-purity nickel salt which effectively reduce the iron leaching rate. A selective leaching method for a nickel-iron alloy comprises: using a nickel-iron alloy powder to prepare into a slurry, adding a combined reagent into the slurry to form a to-be-leached system, leaching the to-be-leached system at 30 °C or above and carrying out solid-liquid separation to obtain a leaching solution; wherein the combined reagent comprises an iron-containing solution, an oxidizing agent and an acidic reagent, or the combined reagent comprises an iron-containing solution, an oxidizing agent and a sulfur-containing reagent; the pH value of the to-be-leached system is in a range from 0.5 to 5.0, and the concentration of Fe ions is 2 g/L or more. The Fe ion concentration of the to-be-leached system may be 2 g/L, 4 g/L, 6 g/L, 8 g/L, 10 g/L, 12 g/L, 14 g/L, 16 g/L, 18 g/L, 20 g/L, and the like. The acidic reagent is at least one of sulfuric acid, nitric acid, and hydrochloric acid, preferably sulfuric acid; and/or, the oxidizing agent is oxygen; and/or, the iron-containing solution is a divalent iron solution or/and a leaching solution; and/or, the sulfur-containing reagent is sulfur dioxide, or/and a sulfur-containing substance that can decompose to produce sulfur dioxide under acidic or heating conditions; e.g., pyrosulfite, thiosulfate, sulfite, bisulfite, and the like. Preferably, the sulfur-containing substance is at least one of sodium sulfite, calcium sulfite, sodium bisulfite, sodium pyrosulfite, and calcium thiosulfate.

The oxygen is at least one of pure oxygen, compressed air and oxygen-enriched air;

and the oxygen is introduced in an amount of 0.2 to 100 L/min per 1 liter of the

to-be-leached system after converting.

When the to-be-leached system is subjected to leaching, a better leaching effect can be

achieved as long as the temperature reaches 30°C or above; preferably, the to-be-leached

system is subjected to leaching at a temperature ranging from 30°C to 100°C for a leaching

time ranging from lh to 24h;

and/or, the nickel-iron alloy powder has an average particle size of <100 mesh;

and/or, a solid-liquid ratio of the to-be-leached system is in a range from: 2 to 1:16;

and/or, a pH value of the to-be-leached system is in a range from 0.5 to 3.0, preferably

in a range from 2.0 to 3.0.

A method for preparing a high-purity nickel salt using a nickel-iron alloy comprises the

steps of:

leaching: obtaining a leaching solution by using the selective leaching method for a

nickel-iron alloy described above, wherein a part of the leaching solution is utilized as an

iron-containing solution;

removing iron: removing iron from the remaining part of the leaching solution to obtain

a post-iron removal solution and an iron removal slag; and

obtaining a nickel salt: obtaining a nickel salt after removing impurities from the

post-iron removal solution and evaporating.

In the step of removing iron, an oxidizing agent is used to oxidize divalent iron into

trivalent iron in the leaching solution, and a neutralization reagent is used to precipitate

trivalent iron.

The neutralization reagent is at least one of calcium carbonate, calcium bicarbonate,

calcium oxide, calcium hydroxide, sodium hydroxide, sodium carbonate, sodium

bicarbonate, nickel hydroxide, nickel carbonate, cobalt hydroxide, nickel cobalt hydroxide,

cobalt carbonate, and cobalt oxide;

and/or, a reaction time of the step of removing iron is in a range from 0.5h to 16 h, and

the temperature of the reaction is 100 °C or below, and the pH is in a range from 3.0 to 5.5.

The oxidizing agent comprises oxygen; during the process of adding the oxidizing agent, a sulfur-containing reagent is also added; and preferably, the sulfur-containing reagent is added in an amount that the molar amount of sulfur element is 0 to 10% of the molar addition amount of oxygen after converting. In the step of removing impurities, a first extraction agent or/and a removing reagent is used for a first impurity removal, and then a second extraction agent is used for extraction. The first extraction agent is P204 and C272; and/or, the removing reagent is at least one of calcium carbonate, calcium oxide, calcium hydroxide, sodium hydroxide, sodium carbonate, nickel hydroxide, nickel carbonate, cobalt hydroxide, cobalt carbonate, and cobalt oxide; and/or, the second extraction agent is P507. The process of removing impurities is to separate Ca, Cu, Mn, Zn and other impurities by extracting with P204, and to separate Co by extracting with P507. The technical solution of the present application has the following advantages. 1. The present application provides a selective leaching method for a nickel-iron alloy, comprising the following steps: using a nickel-iron alloy powder to prepare into a slurry, adding a combined reagent into the slurry to form a to-be-leached system, leaching the to-be-leached system at 30 °C or above and carrying out solid-liquid separation to obtain a leaching solution; wherein the combined reagent comprises an iron-containing solution, an oxidizing agent and an acidic reagent, or the combined reagent comprises an iron-containing solution, an oxidizing agent and a sulfur-containing reagent; the pH value of the to-be-leached system is in a range from 0.5 to 5.0, and the concentration of Fe ions is 2 g/L or more. By controlling the Fe ion concentration in the to-be-leached system, through the cooperation of temperature and pH value, the technical solution of the present application can try to avoid the dissolution of iron in the nickel-iron alloy powder while ensuring the dissolution of nickel and reduce the iron leaching rate, and then can effectively reduce the neutralization reagent required in the subsequent nickel-iron separation, and greatly reduce the production cost under the circumstance of ensuring the nickel yield. 2. The present application provides a method for preparing a high-purity nickel salt using a nickel-iron alloy, which adopts a part of the leaching solution as an iron-containing solution to be returned to the leaching step to be utilized, which can reduce the leaching of iron from the nickel-iron alloy powder without adding other reagents, significantly reduce the iron leaching rate, significantly reduce the reagents required in the subsequent step of removing iron, and reduce the production cost.

3. The present application provides a method for preparing a high-purity nickel salt

using a nickel-iron alloy, which can effectively prepare a nickel salt with a yield higher than

90%, and in the case of achieving this yield, the nickel salt contains greater than 22% of

nickel, and has high purity and good quality.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the detailed description of

the present application or the prior art, the accompanying drawings need to be used in the

detailed description or the prior art will be briefly introduced below, and it will be obvious

that the accompanying drawings in the following description are some of the embodiments

of the present application, and for the person of ordinary skill in the art, other drawings can

be obtained based on these drawings without giving creative labor.

FIG. 1 is a process flow diagram of an example of the present application.

DETAILED DESCRIPTION OF THE INVENTION

The following examples are provided for a better and further understanding of the

present application, and are not limited to the best embodiments described, and do not

constitute a limitation on the content and scope of protection of the present application, and

any product identical or similar to the present application derived by any person under the

inspiration of the present application or by combining the features of the present application

with those of other prior art, falls within the scope of protection of the present application.

Where specific experimental steps or conditions are not indicated in the examples, the

operations or conditions of conventional experimental steps described in the literature in the

art can be performed. Where no manufacturer is indicated for the reagents or instruments

used, they are conventional reagent and products that can be obtained through commercially

available purchase.

Among other things, the composition of the nickel-iron alloy powder used in the following examples is shown in Table 1 below:

Table 1 Element Ni Co Fe Cr Mn Content,% 19.19 10.21 182.771 1.25 10.018

The mass ratio of the part with a particle size of less than 200 mesh (less than 0.74

microns) of the nickel-iron alloy powder used in this example is 49.32%.

Example 1

A method for preparing a high-purity nickel salt using a nickel-iron alloy, as shown in

FIG. 1, comprised the steps of leaching, removing iron and obtaining a nickel salt.

Leaching: a nickel-iron alloy powder and water were added at a rate of 120 kg/h and

432 kg/h, respectively, in a vessel with an effective volume of 4 m 3 , and the returned

leaching solution was also introduced into the vessel at a rate of 648 kg/h, with an overall

liquid-solid ratio of 9:1 (mass ratio). Air was introduced into the vessel at a rate of 480 m3/h

(after converting, 2 L of air per minute per liter of ore slurry), and S02 was introduced into

the vessel intermittently at a rate of 4.8 m 3/h (after converting, 20 mL of S02 per minute per

liter of ore slurry) to control the pH value of the system to be 2.5. The reaction temperature

was controlled to 60 °C and the slurry retention time was about 4 hours. The leaching

system was subjected to a liquid-solid separation, obtaining a leaching solution of

approximately 1,080 kg/h. 60% of the leaching solution was returned (648 kg/h) as an

iron-containing solution. After the system reached equilibrium, the leaching solution was

tested, and the test results showed that the leaching solution contains 24.51 g/L of Ni, 0.41

g/L of Co, and 11.20 g/L of Fe, which corresponds to a leaching rate of Ni of 96% and a

leaching rate of Fe of 5% after converting.

Removing iron: 0.5 L/(min-L) of oxygen and 20 mL/(min-L) of S02 were continuously

introduced into the leaching solution from the previous step, and the neutralization reagent

CaCO3 was added to control the pH value to be 3.5, and a post-iron removal solution and an

iron removal slag were obtained after the reaction for 2 h. At the same time, the post-iron

removal solution was detected, and it was found that the post-iron removal solution

contained 24.40 g/L of Ni, 0.39 g/L of Co, and 0.1 g/L of Fe.

Obtaining a nickel salt: the post-iron removal solution was extracted with P204 to

separate impurities such as Ca, Cu, Mn, and Zn, and Co was separated with P507. The solution after separation was evaporated to obtain nickel sulfate. The prepared nickel sulfate complied with the standard of battery grade nickel sulfate, with 22.3% of Ni, and the impurities such as Na, Ca, Cu, and Mg therein did not exceed the standard.

Example 2

A method for preparing a high-purity nickel salt using a nickel-iron alloy, comprised

the steps of leaching, removing iron and obtaining a nickel salt.

432 kg/h into a vessel with an effective volume of 4 m3 , concentrated sulfuric acid was

added at a rate of 43.2 kg/h, and the returned leaching solution was also introduced into the

vessel at a rate of 648 kg/h, with an overall liquid-to-solid ratio of 9:1 and a pH value of 1.0.

Air was introduced into the vessel at a rate of 480 m3 /h (after converting, 2 L of air per

minute per liter of ore slurry). The reaction temperature was controlled to be 60 °C and the

slurry retention time was about 4 hours. The leaching system was subjected to a liquid-solid

separation, obtaining a leaching solution of approximately 1,080 kg/h. 60% of the leaching

solution was returned (648 kg/h) as an iron-containing solution. After the system reached

equilibrium, the leaching solution was tested, and it was found that the leaching solution

contains 24.35 g/L of Ni, 0.48 g/L of Co, and 29.29 g/L of Fe, which corresponds to a

leaching rate of Ni of 95.4% and a leaching rate of Fe of 12.7% after converting.

introduced into the leaching solution from the previous step, and CaCO3 was added to

control the pH value to be 3.5, and a post-iron removal solution and an iron removal slag

were obtained after reacting for 2h at 60 °C. At the same time, the post-iron removal

solution was detected, and it was found that the post-iron removal solution contained 24.17

g/L of Ni , 0.43 g/L of Co , and 0.1 g/L of Fe.

separate impurities such as Ca, Cu, Mn, and Zn, and Co was separated with P507, and nickel

sulfate was obtained after evaporation, which complied with the standard of battery-grade

nickel sulfate, with 22.3% of Ni, and the impurities such as Na, Ca, Cu, Mg, etc. therein did

not exceed the standard.

Example 3

A method for preparing a high-purity nickel salt using a nickel-iron alloy comprised the

steps of leaching, removing iron and obtaining a nickel salt.

648 kg/h into a vessel with an effective volume of 4 m3 , and the returned leaching solution

was also introduced into the vessel at a rate of 432 kg/h, with an overall liquid-solid ratio of

9:1. Air was introduced into the vessel at a rate of 480 m3 /h (after converting, 2 L of air per

minute per liter of ore slurry), and S02 was introduced into the vessel intermittently at a rate

of 7.2 m3 /h (after converting, 30 mL of S02 per minute per liter of ore slurry) to control the

pH value of the system to be 2.5. The reaction temperature was controlled to be 60 °C. The

separation, obtaining a leaching solution of approximately 1,080 kg/h. 40% of the leaching

solution was returned (432 kg/h) as an iron-containing solution. After the system reached

contained 16.34 g/L of Ni, 0.27 g/L of Co, and 15.33 g/L of Fe, which corresponds to a

leaching rate of Ni of 96% and a leaching rate of Fe of 10% after converting.

Removing iron: 2 L/(min-L) of air and 30mL/(min-L) of S02 were continuously

introduced into the remaining part of the leaching solution, and NiCO 3 was added to control

the pH value to be 3.5, and a post-iron removal solution and an iron removal slag were

obtained after reacting for 2 h at 30 °C. At the same time, the post-iron removal solution was

detected, and it was found that the post-iron removal solution contained 16.21 g/L of Ni,

0.25 g/L of Co, and 0.1 g/L of Fe.

nickel sulfate, with 22.1% of Ni, and the impurities such as Na, Ca, Cu, Mg, etc. therein did

not exceed the standard.

Example 4

steps of leaching, removing iron and obtaining a nickel salt.

Leaching: nickel-iron and water were added at a rate of 120 kg/h and 432 kg/h into a vessel with an effective volume of 4 m3 , and an iron-containing solution was also introduced into the vessel at a rate of 648 kg/h to give a ferrous iron content of 7 g/L in the to-be-leached system, with an overall liquid-solid ratio of 9:1. Oxygen was introduced into the vessel at a rate of 120 m3 /h (after converting, 0.5 L of pure oxygen per minute per liter of ore slurry), and S02 was introduced into the vessel intermittently at a rate of 4.8 m3 /h (after converting, 20 mL of S02 per minute per liter of ore slurry) to control the pH value of the system to be 2.9. The reaction temperature was controlled to be 60 °C and the slurry retention time was about 4 hours. The leaching system was subjected to liquid-solid separation. The leaching solution was tested, and it was found that the leaching solution contained 9.70 g/L of Ni, 0.19 g/L of Co, and 12.52 g/L of Fe, which corresponds to a leaching rate of Ni of 95% and a leaching rate of Fe of 6% after converting.

Removing iron: 2 L/(min-L) of air and 20 mL/(min-L) of S02 were continuously

introduced into the leaching solution, and nickel cobalt hydroxide (MHP) was added to

were obtained after reactining for 2h at 60 °C. At the same time, the post-iron removal

solution was detected, and it was found that the post-iron removal solution contained 11.43

g/L of Ni, 0.44 g/L of Co, and 0.1 g/L of Fe.

nickel sulfate, with 22.2% of Ni, and the impurities such as Na, Ca, Cu, Mg, etc. therein did

not exceed the standard.

Example 5

A method for preparing a high-purity nickel salt using a nickel-iron alloy, distinguished

from Example 1 in that the content of the nickel-iron alloy powder was adjusted so that the

solid-liquid ratio of the leaching system was 1:2.

The leaching solution prepared in this example contained 107.98 g/L of Ni, 1.84 g/L of

Co, and 54.73 g/L of Fe, which corresponds to a leaching rate of Ni of 94.0% and a leaching

rate of Fe of 5.3% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 6

from Example 1 in that the solid-liquid ratio of the leaching system was 1:5.

The leaching solution prepared in this example contained 43.88g/L of Ni, 0.84 g/L of

Co, and 28.97 g/L of Fe, which corresponds to a leaching rate of Ni of 95.5% and a leaching

rate of Fe of 7.0% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 7

from Example 2 in that sulfuric acid was used to adjust the pH value of the to-be-leached

system to be 2.0, and other conditions were the same as those in Example 2.

The leaching solution prepared in this example contained 24.76 g/L of Ni, 0.41 g/L of

Co, and 21.85 g/L of Fe, which corresponds to a leaching rate of Ni of 97.0% and a leaching

rate of Fe of 9.5% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 8

from Example 1 in that calcium thiosulfate was used to adjust the pH value of the

to-be-leached system to be 2.5, and other conditions were the same as those in Example 1.

The leaching solution prepared in this example contained 24.51 g/L of Ni, 0.41 g/L of

Co, and 9.20 g/L of Fe, which corresponds to a leaching rate of Ni of 96.0% and a leaching

rate of Fe of 4.0% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 9

from Example 1 in that the pH value of the leaching system was controlled to be 1.0, and

other conditions were the same as those in Example 1.

The leaching solution prepared in this example contained 24.76 g/L of Ni, 0.43 g/L of

Co, and 22.99 g/L of Fe, which corresponds to a leaching rate of Ni of 97.0% and a leaching

rate of Fe of 10.0% after converting; and the nickel salt prepared has a Ni content which is greater than 22%.

Example 10

from Example 1 in that the pH value of the leaching system was controlled to be 0.5, and

other conditions were the same as those in Example 1.

The leaching solution prepared in this example contained 24.89 g/L of Ni, 0.41 g/L of

Co, and 24.14 g/L of Fe, which corresponds to a leaching rate of Ni of 97.5% and a leaching

rate of Fe of 10.5% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 11

from Example 1 in that the pH value of the leaching system was controlled to be 3.5, and

other conditions were the same as those in Example 1.

The leaching solution prepared in this example contained 24.25 g/L of Ni, 0.36 g/L of

Co, and 4.60 g/L of Fe, which corresponds to a leaching rate of Ni of 95.0% and a leaching

rate of Fe of 2.0% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 12

from Example 1 in that the pH value of the leaching system was controlled to be 4.5, and

other conditions were the same as those in Example 1.

The leaching solution prepared in this example contained 24.20 g/L of Ni, 0.39 g/L of

Co, and 0.46 g/L of Fe, which corresponds to a leaching rate of Ni of 94.8% and a leaching

rate of Fe of 0.2% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Example 13

from Example 4 in that the concentration of iron ions in the iron-containing solution was

adjusted so that the iron ions in the to-be-leached system after addition iron ions were about

20 g/L, and other conditions were the same as those in Example 4.

The leaching solution prepared in this example contained 9.70 g/L of Ni, 0.18 g/L of

Co, and 24.18 g/L of Fe, which corresponds to a leaching rate of Ni of 95.0% and a leaching

rate of Fe of 4.5% after converting; and the nickel salt prepared has a Ni content which is

greater than 22%.

Comparative Example 1

steps of leaching, removing iron and obtaining a nickel salt.

Leaching: nickel-iron and water were added at a rate of 120 kg/h and 1080 kg/h into a

vessel with an effective volume of 4 m3 , with a liquid-solid ratio of 9:1. Oxygen was

introduced into the vessel at a rate of 120 m3/h (after converting, 0.5 L of pure oxygen per

minute per liter of ore slurry), and SO2 was introduced into the vessel intermittently at a rate

of 4.8 m3 /h (after converting, 20 mL of S02 per minute per liter of ore slurry) to control the

pH value of the system to be 2.5. The reaction temperature was controlled at 60°C, and the

liquid-solid separation was carried out after a slurry retention time of about 4 h. The

leaching solution was tested, and it was found that the leaching solution contained 9.80 g/L

of Ni, 0.16 g/L of Co, and 11.04 g/L of Fe, which corresponds to a leaching rate of Ni of

96% and a leaching rate of Fe of 12% after converting.

Removing iron: 0.5 L/(min-L) of oxygen and 20 mL/(min-L) of SO2 were continuously

introduced into the remaining part of the leaching solution, and NiCO3 was added to control

obtained after reacting for 2 h. At the same time, the post-iron removal solution was detected,

and it was found that the post-iron removal solution contained 9.76 g/L of Ni, 0.15g/L of Co,

and 0.1 g/L of Fe.

not exceed the standard.

Comparative Example 2

A method for preparing a high-purity nickel salt using a nickel-iron alloy comprised the steps of leaching, removing iron and obtaining a nickel salt.

1080 kg/h into a vessel with an effective volume of 4 m3 , and concentrated sulfuric acid was

added, with an overall liquid-solid ratio of 9:1 and a pH value of 1.0. The reaction

temperature was controlled to be 60 °C and the slurry retention time was about 4 hours. The

leaching system was subjected to a liquid-solid separation, and about 1080 kg of leaching

solution was obtained per hour, and the leaching solution contained 9.75 g/L of Ni, 0.19 g/L

of Co, and 21.34 g/L of Fe, which corresponds to a leaching rate of Ni of 95.5% and a

leaching rate of Fe of 23.2% after converting.

solution was detected, and it was found that the post-iron removal solution contained 9.70

g/L of Ni, 0.18 g/L of Co, and 0.1 g/L of Fe.

not exceed the standard.

As can be seen from the comparison of Example 1 and Comparative Example 1, as

well as the comparison of Example 2 and Comparative Example 2, respectively, when the Fe

ion concentration in the to-be-leached system is controlled to be 2 g/L or more, it can avoid

the dissolution of iron in the nickel-iron alloy powder as much as possible without

decreasing the leaching rate of Ni, significantly reduce the leaching rate of Fe, effectively

reduce the neutralization reagent required in the subsequent separation of nickel and iron,

and greatly reduce the production cost under the circumstance of ensuring the nickel yield.

As can be seen from Example 1 and Examples 9-12, the leaching rate of Ni and the

leaching rate of Fe both increase gradually with the decrease of the pH value, and the

leaching rate of Ni thereof all are higher than 95% within the range of pH value of 0.5 to 3.0, and the leaching rate of Fe can be ensured to be lower than 10% within the range of pH value of 2.0 to 3.0.

Obviously, the above examples are merely examples for the purpose of clear

illustration, and are not a limitation of the embodiments. For a person of ordinary skill in the

art, other variations or changes in different forms may be made on the basis of the above

description. It is neither necessary nor possible to exhaust all of the embodiments herein.

The obvious variations or changes derived therefrom remain within the scope of protection

of the present application.

Throughout this specification and the claims which follow, unless the context requires

otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be

understood to imply the inclusion of a stated integer or step or group of integers or steps but

not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from

it), or to any matter which is known, is not, and should not be taken as, an acknowledgement

or admission or any form of suggestion that that prior publication (or information derived

from it) or known matter forms part of the common general knowledge in the field of

endeavour to which this specification relates.

Claims

CLAIMS The claims defining the invention are as follows:

1. A selective leaching method for a nickel-iron alloy, comprising: using a nickel-iron alloy

powder to prepare into a slurry, adding a combined reagent into the slurry to form a

to-be-leached system, leaching the to-be-leached system at a temperature ranging from

30 °C to 100 °C and carrying out solid-liquid separation to obtain a leaching solution;

wherein the combined reagent comprises an iron-containing solution, an oxidizing

agent and an acidic reagent, or the combined reagent comprises an iron-containing solution,

an oxidizing agent and a sulfur-containing reagent; a pH value of the to-be-leached system

is in a range from 0.5 to 5.0, and the concentration of Fe ions is 2 g/L or more;

wherein the iron-containing solution is a divalent iron solution;

wherein the acidic reagent is sulfuric acid; and

wherein the sulfur-containing reagent is sulfur dioxide, and/or a sulfur-containing

substance that can decompose under acidic or heating conditions to produce sulfur dioxide.

2. The selective leaching method for a nickel-iron alloy of claim 1, wherein the oxidizing

agent is oxygen.

3. The selective leaching method for a nickel-iron alloy of claim 2, wherein,

the oxygen is at least one of pure oxygen, compressed air, and oxygen-enriched air;

and/or,

the oxygen is introduced in an amount of 0.2 to 100 L/min per 1 liter of the

to-be-leached system after converting; and

the sulfur-containing substance is at least one of pyrosulfite, thiosulfate, sulfite, and

bisulfite.

4. The selective leaching method for a nickel-iron alloy of claim 2, wherein the

sulfur-containing substance is at least one of sodium sulfite, calcium sulfite, sodium

bisulfite, sodium pyrosulfite, and calcium thiosulfate.

5. The selective leaching method for a nickel-iron alloy of any one of claims 1-4, wherein,

the to-be-leached system is subjected to leaching for a time period ranging from lh to

24h; and/or,

the nickel-iron alloy powder has an average particle size of equal to or less than 100

mesh; and/or,

a solid-liquid ratio of the to-be-leached system is in a range from 1: 2 to 1:16; and/or,

the pH value of the to-be-leached system is in a range from 0.5 to 3.0.

6. The selective leaching method for a nickel-iron alloy of claim 5, wherein the pH value of

the to-be-leached system is in a range from 2.0 to 3.0.

7. A method for preparing a high-purity nickel salt using a nickel-iron alloy, comprising the

steps of leaching, removing iron and obtaining a nickel salt,

wherein the step of leaching comprises: obtaining a leaching solution by using the

selective leaching method for a nickel-iron alloy of any one of claims 1-6, wherein a part of

the leaching solution is utilized as an iron-containing solution;

wherein the step of removing iron comprises: removing iron from the remaining part

of the leaching solution to obtain a post-iron removal solution and an iron removal slag; and

wherein the step of obtaining a nickel salt comprises: obtaining a nickel salt after

removing impurities from the post-iron removal solution and evaporating.

8. The method of claim 7, wherein,

trivalent iron; and/or,

in the process of removing impurities, a first extraction agent and/or a removing

reagent is used for a first impurity removal, and then a second extraction agent is used for

extraction.

9. The method of claim 8, wherein,

calcium oxide, calcium hydroxide, sodium hydroxide, sodium carbonate, sodium

cobalt carbonate, and cobalt oxide; and/or,

in the step of removing iron, a reaction time is in a range from 0.5h to 16h, a

temperature of the reaction is 100 °C or below, and a pH value is in a range from 3.0 to 5.5;

and/or,

during the process of adding the oxidizing agent, a sulfur-containing reagent is also

added in an amount that the molar amount of sulfur element is 0 to 10% of the molar

addition amount of oxygen after converting.

10. The method of claim 8, wherein the first extraction agent is P204 and C272; and/or,

the removing reagent is at least one of calcium carbonate, calcium oxide, calcium

hydroxide, sodium hydroxide, sodium carbonate, nickel hydroxide, nickel carbonate, cobalt

hydroxide, cobalt carbonate, and cobalt oxide; and/or,

the second extraction agent is P507.