Method for removing iron from ferronickel leachate and rapidly leaching laterite-nickel ore

Abstract

The invention discloses a method for removing iron from ferronickel leachate and rapidly leaching laterite-nickel ore, which comprises the following steps of: putting limonite type laterite-nickel ore into a high-pressure kettle, adding ferronickel leachate, water and nitrate into the high-pressure kettle, heating to 160 DEG C or above, introducing oxygen or oxygen-enriched air into the high-pressure kettle, and carrying out oxidation leaching reaction, carrying out liquid-solid separation on the reacted material, feeding the obtained liquid into a nickel-cobalt-magnesium recovery process, and preparing an iron product by using the obtained solid; wherein the ferronickel leachate is obtained by performing normal-pressure leaching on a ferronickel product obtained by a pyrogenic process of laterite-nickel ore by using inorganic acid; the addition amounts of the ferronickel leaching solution, the water and the nitrate are respectively that the acid-ore ratio in the high-pressure kettle is 230-280Kg / t, the ore pulp concentration is 10-40wt%, and the nitrate concentration is 0-35g / L. According to the method, iron removal of the ferronickel leaching liquid and leaching of the limonite type laterite-nickel ore containing the low-grade magnesium can be carried out synchronously, the leaching speed is high, and the effect is good.

Description

Technical Field

[0001] The invention relates to a nickel ore smelting method, and in particular to a method for removing iron from a nickel-iron leaching solution and coordinating the rapid leaching of laterite nickel ore. Background Art

[0002] As an important strategic metal, nickel is widely used in national defense, aerospace, transportation, petrochemical, energy and other fields due to its special physical and chemical properties. It is an important raw material for the production of stainless steel, nickel-based spray-plated materials, nuclear reactor components, etc.

[0003] Nickel resources are divided into two types: nickel sulfide ore and nickel oxide ore, depending on the nickel content of the ore. Nickel sulfide ore has a high nickel content and is the main source of nickel metal production. Most of the world's nickel production (about 70%) comes from this type of mineral, but its reserves account for only about one-third of the world's total nickel reserves. Nickel oxide ore is also called laterite nickel ore. The laterite nickel ore layer is usually divided into three layers, namely: ① The upper layer of limonite-type laterite nickel ore is characterized by low nickel, silicon and magnesium content, and high iron and cobalt content, of which the iron content is usually 35-50wt%. ② The lower layer of silicon-magnesium laterite nickel ore is characterized by high silicon and magnesium content, low iron and cobalt content, but high nickel content, of which the magnesium content is usually 10-25wt%. ③ The intermediate transition layer is characterized by the content of each major metal between the upper and lower layers.

[0004] In recent years, the application and development of fuel cells (such as nickel-cobalt-manganese ternary lithium-ion positive electrode battery materials), catalysts and electroplating industries with nickel as the main raw material have accelerated the consumption of nickel resources. As the sulfide nickel ore resources are gradually exhausted, the extraction of nickel resources from laterite nickel ore has received great attention. The processing technology of laterite nickel ore is mainly divided into three categories: pyrometallurgy, hydrometallurgy and pyrometallurgy-wet combined process. The siliceous-magnesium laterite nickel ore dominated by silicate minerals is suitable for pyrometallurgy, while the limonite type ore deposit is suitable for hydrometallurgy. Ores in the intermediate transition type can be treated by pyrometallurgy or hydrometallurgy. At present, the most widely used methods are rotary kiln drying pre-reduction-electric furnace smelting (RKEF) and sulfuric acid high pressure leaching process (HPAL). Among them, RKEF is mainly used to process siliceous-magnesia laterite-nickel ore containing high-grade magnesium, while HPAL is suitable for processing limonitic-type laterite-nickel ore containing low-grade magnesium. The advantage of this process is that the nickel recovery effect is good, and the recovery rate can be above 90%. Therefore, it is still the current and future mainstream route and development direction of the wet process.

[0005] In order to extract nickel from laterite nickel ore containing high-grade magnesium, it is necessary to first smelt it using a pyrometallurgical process, and then obtain a nickel-iron product (nickel-iron concentrate or nickel-iron powder) with a high nickel purity by a magnetic separation method. For example, in the invention patent with publication number CN101418388A, a desiccant is first added to the laterite nickel ore containing adsorbed water, and the mixture is stirred and mixed uniformly and then dehydrated and dried; then the mixture is crushed, a reducing agent and a nickel-iron aggregating agent are added, and after mixing uniformly, it is sent to a rotary kiln for reduction roasting; after reduction roasting, the material is subjected to water quenching, cooling, crushing, ball milling, and magnetic separation to obtain a high-grade nickel-iron concentrate.

[0006] Ferronickel leachate is a ferronickel product obtained by pyrometallurgical process, which is leached by sulfuric acid at normal pressure, and contains a large amount of iron ions, sulfuric acid and a small amount of nickel sulfate. For extracting nickel in ferronickel leachate, a large amount of iron ions are not needed, so it is necessary to perform iron removal operation on it. On the other hand, nickel in limonite laterite nickel ore containing low-grade magnesium can be extracted by wet treatment process, that is, leached under certain strong acid, temperature and pressure conditions, and the leaching rate can reach more than 90%. Based on the above two aspects, the inventor team of the present application, after analysis and experiment, believes that it is feasible to carry out synchronous leaching of ferronickel leachate with iron removal and laterite nickel ore. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for removing iron from ferronickel leaching solution and leaching laterite nickel ore rapidly. The method can realize simultaneous removal of iron from ferronickel leaching solution and leaching of limonitic laterite nickel ore containing low-grade magnesium, and the leaching rate is fast and the effect is good.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A method for removing iron from ferronickel leaching solution and rapidly leaching laterite nickel ore comprises: taking a certain amount of limonitic laterite nickel ore and placing it in an autoclave, adding ferronickel leaching solution, water and nitrate into the autoclave in a certain proportion, heating the autoclave to above 160° C., introducing oxygen or oxygen-enriched air into the autoclave, maintaining the above temperature and pressure to carry out oxidation leaching reaction, discharging the material after the reaction is completed, carrying out liquid-solid separation, collecting liquid and solid respectively, sending the obtained liquid to a nickel-cobalt-magnesium recovery process, and using the obtained solid to prepare an iron product; wherein,

[0010] The nickel-iron leaching solution is obtained by leaching the nickel-iron product obtained from laterite nickel ore by pyrometallurgical process with inorganic acid at normal pressure;

[0011] The added amounts of the nickel-iron leaching solution, water and nitrate are respectively to control the acid-ore ratio in the autoclave to be 230-280 Kg / t, the slurry concentration to be 10-40 wt%, and the nitrate concentration to be 0-35 g / L.

[0012] In the above method, the temperature of the oxidation leaching reaction is preferably 170 to 240°C, and more preferably 210 to 230°C.

[0013] In the above method, during the oxidative leaching reaction, oxygen or oxygen-enriched air is introduced into the autoclave to maintain the oxygen partial pressure in the autoclave at 0.1-0.6 MPa, and more preferably at 0.3-0.4 MPa.

[0014] Under the conditions defined by the above method, when the reaction time of the oxidation leaching reaction is greater than or equal to 30 minutes, the limonitic laterite nickel ore can obtain a higher nickel leaching rate. Under other certain conditions, increasing the time of the oxidation leaching reaction can increase the leaching rate. The method of the present invention can achieve effective leaching of nickel in the limonitic laterite nickel ore within 60 minutes (leaching rate is above 95%). According to the test results of the applicant, the oxidation leaching reaction time is preferably controlled to be 35 to 60 minutes, and more preferably controlled to be 40 to 50 minutes.

[0015] The applicant found in the experiment that the addition of nitrate can accelerate the leaching rate of nickel metal from limonite laterite nickel ore. After analysis, the applicant believes that the reason is that the nitrate ions in the nitrate are further hydrolyzed into nitrite ions, which further accelerate the leaching of Fe 2+ Oxidized to Fe 3+ In the method of the present invention, the iron removal of the nickel-iron leaching solution and the leaching of the limonite-type laterite nickel ore are carried out simultaneously, and the main chemical reactions occurring in the reactor are as follows:

[0016] Reactions involving nitrates:

[0017] 4NO2+3H2O+2FeSO4=Fe2O3↓+2NO↑+2HNO3+2H2SO4

[0018] 2NO+O2=2NO2↑

[0019]

[0020]

[0021] 2HNO2=NO2↑+NO+H2O

[0022] Reaction of sulfuric acid with nickel leached from laterite nickel ore:

[0023] NiO+H2SO4=NiSO4+H2O

[0024] Iron removal reaction:

[0025] 2FeO·OH+3H2SO4=Fe2(SO4)3+4H2O

[0026] Fe2(SO4)3+H2O=Fe2O3↓+3H2SO4

[0027] Overall reaction formula: 2FeO·OH=Fe2O3↓+H2O

[0028] In the above method, the nitrate is one or a combination of two or more selected from sodium nitrate, potassium nitrate and calcium nitrate.

[0029] In the above method, the nickel-iron leaching solution can be obtained by leaching the nickel-iron product obtained by reducing and roasting laterite nickel ore in a rotary kiln and then magnetically separating it with an inorganic acid at normal pressure. The inorganic acid can be a strong acid such as sulfuric acid or nitric acid, preferably sulfuric acid; the process parameters during normal pressure leaching are the same as those in the prior art.

[0030] In a preferred embodiment, the ferronickel leaching solution is obtained by leaching the ferronickel product obtained by magnetic separation after reduction roasting of laterite nickel ore containing high-grade magnesium in a rotary kiln with sulfuric acid at normal pressure. The effective sulfuric acid concentration in the ferronickel leaching solution can be determined as needed, such as 1.778 to 3.085 mol / L. Specifically, the ferronickel leaching solution can be obtained by the following method:

[0031] Take nickel iron powder (the particle size is preferably less than 100 meshes) and use concentrated sulfuric acid to leach nickel iron. During leaching, the temperature is controlled to be 80-90°C, the acid (sulfuric acid) material (nickel iron powder) ratio is controlled to be 180-220% by mass, the liquid-solid ratio is 5-7mL:1g, and the leaching time is usually 7-10h to obtain nickel iron leachate. The effective sulfuric acid concentration (the sum of ferrous sulfate concentration and sulfuric acid concentration) in the leachate obtained under the above leaching conditions is usually 1.778-3.085mol / L.

[0032] In the above method, the amount of nickel-iron leaching solution, water and nitrate added is preferably to control the acid-ore ratio in the autoclave to 250-260Kg / t, the slurry concentration to 25-35wt%, and the nitrate concentration to 8-35g / L, and further preferably to control the acid-ore ratio in the autoclave to 250-260Kg / t, the slurry concentration to 30-35wt%, and the nitrate concentration to 15-25g / L.

[0033] Compared with the prior art, the present invention is characterized in that:

[0034] 1. The nickel-iron leaching solution removes iron and generates sulfuric acid to react with the leaching of nickel in the laterite nickel ore in the same container, and the reaction is carried out in a coordinated manner, not only extracting nickel in the laterite nickel ore, but also improving the grade of iron in the leached residue; the liquid obtained after liquid-solid separation of the material after the oxidation leaching reaction according to the method of the present invention is a nickel-containing solution, which can be used for subsequent nickel extraction; the solid obtained is a hematite product, which can be further used for iron extraction.

[0035] 2. Further, the addition of nitrates accelerated the leaching reaction rate of nickel. The applicant believes that this is because the introduction of nitrates accelerated the speed at which oxygen entered the liquid surface and accelerated the Fe 2+ Oxidized to Fe 3+ speed. DETAILED DESCRIPTION

[0036] In order to better explain the technical solution of the present invention, the present invention is further described in detail below in conjunction with the embodiments, but the embodiments of the present invention are not limited thereto. If not specifically indicated, the technical features used in the embodiments can be replaced by other technical features known in the art that have equivalent or similar functions or effects without departing from the inventive concept.

[0037] The ferronickel leaching solution used in the following embodiments is a ferronickel powder (100 mesh sieve under material, the chemical composition quantitative analysis shows that the nickel content is 5.63%, the iron content is 69.29%) obtained by leaching at normal pressure with concentrated sulfuric acid according to the following process, after reduction roasting in a rotary kiln and then magnetic separation of laterite nickel ore:

[0038] Take nickel iron powder and use concentrated sulfuric acid to leach at normal pressure. During leaching, the temperature is controlled to be 85°C, the acid (sulfuric acid) material (nickel iron powder) ratio is controlled to be 200% by mass, the liquid (all liquids, including water and sulfuric acid) solid (nickel iron powder) ratio is 6mL:1g, and the leaching time is 8h to obtain nickel iron leaching solution. The effective sulfuric acid concentration in the leaching solution is 3.085mol / L, and the concentrations of iron, nickel, cobalt, and chromium ions are 61.316g / L, 4.938g / L, 0.147g / L, and 3.796g / L, respectively.

[0039] The components of the limonitic laterite nickel ore used for leaching nickel in the following examples are, by mass percentage, 0.83% Ni, 44.97% Fe, 0.07% Co, 1.02% Mg, 1.34% Si, 3.08% Al2O3, 0.06% Ca, and 0.69% Mn.

[0040] Example 1

[0041] The method of the present invention is as follows: in a 1-liter autoclave, 200 g of limonite laterite nickel ore is added, then nickel-iron leaching solution and sodium nitrate are added, and finally, an acid-ore ratio of 260 kg / t, a pulp concentration of 30.3%, an effective sulfuric acid concentration of 0.87 mol / L, and a sodium nitrate concentration of 0 to 35.0 g / L are added in a municipal tap water control system. The temperature in the kettle is raised to 170 to 240 ° C, and the temperature is kept constant when the set temperature is reached. Oxygen is introduced into the kettle to make the oxygen partial pressure in the kettle reach 0.3 to 0.5 MPa, and oxygen is continuously introduced for 1 hour under heat preservation and pressure maintenance. After the reaction is completed, the material is discharged, filtered, and the filtrate and leached residue are collected respectively. The leached residue is washed and dried to detect the nickel ion content. In the leaching process, nickel, cobalt and magnesium in the laterite nickel ore enter the solution (a small amount of aluminum also enters the solution), and iron is left in the leached residue. The obtained filtrate can be sent to the subsequent nickel and cobalt recovery process, and the obtained leaching residue can be used as an iron ore concentrate product or further used to produce iron products after desulfurization.

[0042] The method for detecting the nickel ion concentration in the leaching residue is as follows: take 2.0g of the filter residue into a conical flask, pour in aqua regia, keep heating until the leaching residue is completely melted (about 4 to 5 hours), cool and filter, collect the filtrate and place it in a volumetric flask and make up the volume, and the concentration and content of the metallic nickel in the solution can be obtained by ICP detection.

[0043] According to the above method, the concentration of metallic nickel in the raw limonitic laterite nickel ore was detected to be 116.874 mg / L. The leaching rate of metallic nickel in the limonitic laterite nickel ore was calculated based on this data.

[0044] Specific Example 1-1

[0045] The leaching conditions were as follows: temperature of 170°C, slurry concentration of 30.3%, oxygen partial pressure of 0.4 MPa, sodium nitrate concentration of 33.33 g / L, and continuous oxygenation for 1 hour. Samples were taken through the sampling tube at oxygenation times of 0 min, 15 min, 30 min, 45 min, and 60 min, respectively. The samples were separated into solid and liquid, and the obtained solids were washed and dried and then tested according to the above-mentioned method for detecting the nickel ion concentration in the leached residue. The results showed that the nickel ion concentrations in the samples taken when the oxygen flow time was 0 min, 15 min, 30 min, 45 min, and 60 min were 91.418 mg / L, 75.501 mg / L, 61.032 mg / L, 45.709 mg / L, and 42.016 mg / L, respectively. Finally, it was calculated that the leaching rates of metallic nickel in the limonitic laterite nickel ore at the above-mentioned oxygen flow times were 21.78%, 35.40%, 47.78%, 60.89%, and 64.05%, respectively.

[0046] Specific Examples 1-2

[0047] The leaching conditions were as follows: temperature of 190°C, slurry concentration of 30.3%, oxygen partial pressure of 0.4 MPa, sodium nitrate concentration of 33.33 g / L, and continuous oxygenation for 1 hour. Samples were taken through the sampling tube at oxygenation times of 0 min, 15 min, 30 min, 45 min, and 60 min, respectively. The samples were separated into solid and liquid, and the obtained solids were washed and dried and then tested according to the above-mentioned method for detecting the nickel ion concentration in the leached residue. The results showed that the nickel ion concentrations in the samples taken when the oxygen flow time was 0 min, 15 min, 30 min, 45 min, and 60 min were 69.341 mg / L, 55.749 mg / L, 41.420 mg / L, 27.407 mg / L, and 21.645 mg / L, respectively. Finally, it was calculated that the leaching rates of metallic nickel in the limonitic laterite nickel ore at the above-mentioned oxygen flow times were 40.67%, 52.30%, 64.56%, 76.55%, and 81.48%, respectively.

[0048] Specific Examples 1-3

[0049] The leaching conditions were as follows: temperature 210°C, slurry concentration 30.3%, oxygen partial pressure 0.4 MPa, sodium nitrate concentration 33.33 g / L, and continuous oxygen flow for 1 hour. Samples were taken through the sampling tube at oxygen flow times of 0 min, 15 min, 30 min, 45 min, and 60 min, respectively. The samples were separated into solid and liquid, and the obtained solids were washed and dried and then tested according to the above-mentioned method for detecting the nickel ion concentration in the leached residue. The results showed that the nickel ion concentrations in the samples taken when the oxygen flow time was 0 min, 15 min, 30 min, 45 min, and 60 min were 63.404 mg / L, 37.517 mg / L, 22.475 mg / L, 8.356 mg / L, and 7.889 mg / L, respectively. Finally, it was calculated that the leaching rates of metallic nickel in the limonitic laterite nickel ore at the above-mentioned oxygen flow times were 45.75%, 67.90%, 80.77%, 92.85%, and 93.25%, respectively.

[0050] Specific Examples 1-4

[0051] The leaching conditions were as follows: temperature 230°C, slurry concentration 30.3%, oxygen partial pressure 0.4 MPa, sodium nitrate concentration 33.33 g / L, and continuous oxygen flow for 1 hour. Samples were taken through the sampling tube at oxygen flow times of 0 min, 15 min, 30 min, 45 min, and 60 min, respectively. The samples were separated into solid and liquid, and the obtained solids were washed and dried and then tested according to the above-mentioned method for detecting the nickel ion concentration in the leached residue. The results showed that the nickel ion concentrations in the samples taken when the oxygen flow time was 0 min, 15 min, 30 min, 45 min, and 60 min were 56.661 mg / L, 13.441 mg / L, 6.031 mg / L, 2.069 mg / L, and 2.688 mg / L, respectively. Finally, it was calculated that the leaching rates of metallic nickel in the limonitic laterite nickel ore at the above-mentioned oxygen flow times were 51.52%, 88.50%, 94.84%, 98.23%, and 97.70%, respectively.

[0052] Specific Examples 1-5

[0053] The leaching conditions were as follows: temperature 240°C, slurry concentration 30.3%, oxygen partial pressure 0.4 MPa, sodium nitrate concentration 33.33 g / L, and continuous oxygen flow for 1 hour. Samples were taken through the sampling tube at oxygen flow times of 0 min, 15 min, 30 min, 45 min, and 60 min, respectively. The samples were separated into solid and liquid, and the obtained solids were washed and dried and then tested according to the above-mentioned method for detecting the nickel ion concentration in the leached residue. The results showed that the nickel ion concentrations in the samples taken when the oxygen flow time was 0 min, 15 min, 30 min, 45 min, and 60 min were 58.250 mg / L, 10.752 mg / L, 5.552 mg / L, 3.389 mg / L, and 3.740 mg / L, respectively. Finally, it was calculated that the leaching rates of metallic nickel in the limonitic laterite nickel ore at the above-mentioned oxygen flow times were 50.16%, 90.80%, 95.25%, 97.10%, and 96.80%, respectively.

[0054] Specific Examples 1-6

[0055] The leaching conditions are temperature 230°C, slurry concentration 30.3%, oxygen partial pressure 0.4MPa, sodium nitrate concentration 0mg / L, and continuous oxygen flow for 45min. After the reaction is completed, the nickel ion concentration in the leached residue is 4.532mg / L, and the leaching rate of metallic nickel in the limonitic laterite nickel ore is finally calculated to be 96.13%.

[0056] Specific Examples 1-7

[0057] The leaching conditions are temperature 230℃, pulp concentration 30.3%, oxygen partial pressure 0.4MPa, sodium nitrate concentration 8.33g / L, and continuous oxygen flow for 45min. After the reaction is completed, the nickel ion concentration in the leached residue is 3.740mg / L, and the leaching rate of metallic nickel in the limonitic laterite nickel ore is finally calculated to be 96.80%.

[0058] Specific Examples 1-8

[0059] The leaching conditions are temperature 230°C, slurry concentration 30.3%, oxygen partial pressure 0.4MPa, sodium nitrate concentration 16.67g / L, and continuous oxygen flow for 45min. After the reaction is completed, the nickel ion concentration in the leached residue is 3.121mg / L, and the leaching rate of metallic nickel in the limonitic laterite nickel ore is finally calculated to be 97.33%.

[0060] Specific Examples 1-9

[0061] The leaching conditions are temperature 230°C, slurry concentration 30.3%, oxygen partial pressure 0.4MPa, sodium nitrate concentration 25.00g / L, and continuous oxygen flow for 45min. After the reaction is completed, the nickel ion concentration in the leached residue is 3.495mg / L, and the leaching rate of metallic nickel in the limonitic laterite nickel ore is finally calculated to be 97.01%.

[0062] Example 2

[0063] The method of the present invention is as follows: 200g of limonite laterite nickel ore is added to a high-pressure reactor with a capacity of 1 liter, and then nickel-iron leaching solution, sodium nitrate and municipal tap water are added to form a slurry, and the acid-ore ratio in the control system is 250Kg / t, the slurry concentration is 25%, and the sodium nitrate concentration is 20g / L. The temperature in the reactor is raised to 230°C, and the temperature is kept constant when the set temperature is reached. Oxygen is introduced into the reactor to make the oxygen partial pressure in the reactor reach 0.3MPa, and oxygen is continuously introduced for 45min under heat and pressure. After the reaction is completed, the material is discharged, filtered, and the leached residue is collected, and the leached residue is washed and dried. The leaching rate of nickel is measured and calculated using the same method as in Example 1.

[0064] The nickel ion concentration in the collected leaching residue was 4.535 mg / L, and the leaching rate of metallic nickel in the limonitic laterite nickel ore was finally calculated to be 96.12%.

[0065] Example 3

[0066] The method of the present invention is as follows: 200g of limonite laterite nickel ore is added to a high-pressure reactor with a capacity of 1 liter, and then nickel-iron leaching solution and municipal tap water are added to form a pulp, and the acid-ore ratio in the control system is 230Kg / t and the pulp concentration is 35%. The temperature in the reactor is raised to 220°C, and the temperature is kept constant when the set temperature is reached. Oxygen is introduced into the reactor to make the oxygen partial pressure in the reactor reach 0.6MPa, and oxygen is continuously introduced for 40 minutes under heat and pressure. After the reaction is completed, the material is discharged, filtered, and the leached residue is collected, and the leached residue is washed and dried. The leaching rate of nickel is measured and calculated using the same method as in Example 1.

[0067] The nickel ion concentration in the collected leaching residue was 16.865 mg / L, and the leaching rate of metallic nickel in the limonitic laterite nickel ore was finally calculated to be 85.57%.

Claims

1. A method for removing iron from ferronickel leaching solution and rapidly leaching laterite nickel ore, characterized in that: A certain amount of limonitic laterite nickel ore is placed in an autoclave, and nickel-iron leaching solution, water and nitrate are added to the autoclave in a certain proportion, the temperature is raised to above 160°C, oxygen or oxygen-enriched air is introduced into the autoclave, and the above temperature and pressure are maintained for oxidation leaching reaction. After the reaction is completed, the material is discharged, and liquid-solid separation is performed to collect the liquid and solid respectively, and the obtained liquid is sent to the nickel-cobalt-magnesium recovery process, and the obtained solid is used to prepare iron products; wherein, The nickel-iron leaching solution is obtained by leaching the nickel-iron product obtained from laterite nickel ore by pyrometallurgical process with inorganic acid at normal pressure; The added amounts of the nickel-iron leaching solution, water and nitrate are respectively to control the acid-ore ratio in the autoclave to be 230-280 Kg / t, the slurry concentration to be 10-40 wt%, and the nitrate concentration to be 0-35 g / L.

2. The method according to claim 1, characterized in that: The reaction temperature is 170-240°C.

3. The method according to claim 1, characterized in that: During the reaction, the oxygen partial pressure in the autoclave was 0.1 to 0.6 MPa.

4. The method according to claim 1, characterized in that: The reaction time is greater than or equal to 30 minutes.

5. The method according to claim 1, characterized in that: The reaction time is 35 to 60 minutes.

6. The method according to any one of claims 1 to 5, characterized in that: The nitrate is one or a combination of two or more selected from sodium nitrate, potassium nitrate and calcium nitrate.

7. The method according to any one of claims 1 to 5, characterized in that: The nickel-iron leaching solution is obtained by leaching the nickel-iron product obtained by reduction roasting of laterite nickel ore in a rotary kiln and then magnetic separation with inorganic acid at normal pressure.

8. The method according to claim 7, characterized in that: The nickel-iron leaching solution is obtained by leaching the nickel-iron product obtained by reduction roasting high-grade magnesium-containing laterite nickel ore in a rotary kiln and then magnetic separation with sulfuric acid at normal pressure.

9. The method according to any one of claims 1 to 5, characterized in that: The amount of the nickel-iron leaching solution added is to control the acid-ore ratio in the autoclave to be 250-260 Kg / t.

10. The method according to any one of claims 1 to 5, characterized in that: The amount of nitrate added is to control the nitrate concentration in the autoclave to be 8-35 g / L.

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