Method for removing hexavalent chromium in high-pressure acid leaching process of laterite nickel ore

Abstract

This invention provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The method includes the following steps: washing, screening, classifying, beneficiating, and grinding the laterite nickel ore to obtain leaching raw material; separating chromite during beneficiation; mixing high-grade nickel matte slag with the leaching raw material to obtain a compound leaching material; and subjecting the compound leaching material to high-pressure acid leaching to remove hexavalent chromium. This invention provides a method for removing hexavalent chromium from laterite nickel ore during high-pressure acid leaching by separating a portion of chromite through physical beneficiation and then removing Cr(VI) through Fe(II) dissolved in the high-grade nickel matte slag, achieving highly efficient removal of Cr(VI) during the high-pressure leaching reaction.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology and relates to a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. Background Technology

[0002] High-pressure acid leaching is the mainstream process for extracting nickel and cobalt from limonite-type laterite nickel ore. During the leaching process, valuable metals Ni, Co, and Mn dissolve into the liquid phase, but impurities such as Fe, Al, Mg, and Cr also enter the liquid phase. At the same time, Cr(III) in chromium minerals is easily oxidized to Cr(VI) by high-valence minerals. Cr(VI) is highly toxic, and its entry into MHP will reduce the quality of the product and increase the cost of wastewater treatment.

[0003] The common method for removing Cr(VI) in existing technologies is the redox method, which involves adding a reducing agent to reduce Cr(VI) to Cr(III), and then adjusting the pH to remove Cr(VI) as Cr(OH)3 precipitate. Currently, commonly used reducing agents include sulfur, pyrite, pulverized coal, ferrous sulfate, sodium sulfite, sodium sulfide, and sulfur dioxide. Sulfur, pyrite, and pulverized coal are added before high-pressure acid leaching, and Cr(VI) is removed during the autoclave reaction. However, the sublimation of sulfur and pyrite can cause blockages in pipes, valves, and instruments during use, while pulverized coal is expensive and has high production costs. Reducing agents such as ferrous sulfate, sodium sulfite, sodium sulfide, and sulfur dioxide are added to the leachate, but these can easily generate toxic gases during use, causing environmental problems; furthermore, these reducing agents are expensive and used in large quantities, resulting in high production costs.

[0004] Based on the above research, there is a need to provide a low-cost, environmentally friendly method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The method separates a portion of chromite through physical beneficiation and then removes Cr(VI) by dissolving Fe(II) in high-grade nickel matte slag, thus achieving efficient removal of Cr(VI) during the high-pressure leaching reaction.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] This invention provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, the method comprising the following steps:

[0008] (1) The laterite nickel ore is washed, screened, classified, beneficiated and ground to obtain leaching raw material;

[0009] Chromite is separated during the mineral processing;

[0010] (2) Mix the high-grade nickel matte slag and the leaching material described in step (1) to obtain a compound leaching material;

[0011] (3) The compound leaching material described in step (2) is subjected to high-pressure acid leaching to remove hexavalent chromium.

[0012] To address the issues of high reducing agent usage, high cost, and environmental concerns associated with the removal of hexavalent chromium (Cr), this invention first washes laterite nickel ore to fully disperse the cohesive minerals in water, while simultaneously screening to remove large pieces of low-nickel ore, thus improving the processing capacity of the raw ore. Then, it classifies the ore, separating and recovering a portion of the chromium minerals to reduce the Cr(VI) content at the source. High-grade nickel matte slag is then used as a reducing agent. The ferrous iron generated by the acid dissolution of the high-grade nickel matte slag provides a reducing atmosphere for the high-pressure acid leaching process of laterite nickel ore, inhibiting the generation of Cr(VI) during the reaction or the reduction removal of Cr(VI). Since high-grade nickel matte slag is widely available and easily obtained, and its comprehensive utilization rate is improved, it has high socio-economic benefits. Therefore, this invention combines physical and chemical methods to achieve highly efficient Cr(VI) removal during the leaching process of laterite nickel ore.

[0013] The high-grade nickel matte slag of this invention can be obtained by the following method: laterite nickel ore is dried, reduced and sulfided and smelted to produce low-grade nickel matte and smelting slag; low-grade nickel matte is smelted in a converter to produce high-grade nickel matte and smelting slag, i.e., high-grade nickel matte slag. The main component of high-grade nickel matte slag is fir olivine, and the content of divalent iron is above 42%.

[0014] Preferably, in step (1), the grading process yields coarse particles and fine particles. The coarse particles are then beneficiated and ground. The fine particles are mixed with the ground particles to obtain leaching raw materials.

[0015] Preferably, the particle size of the coarse particles is ≥0.074mm, which means that the minimum particle size is greater than 0.074mm. For example, it can be 0.074mm, 0.08mm, 0.085mm, 0.09mm, 0.1mm or 0.2mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the particle size of the fine particles is <0.074mm, which means that the maximum particle size is <0.074mm. For example, it can be 0.073mm, 0.070mm, 0.065mm, 0.06mm or 0.05mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the sieve aperture size in step (1) is 1.0mm-3mm, for example, it can be 1.0mm, 1.25mm, 1.5mm, 1.75mm, 2.0mm, 2.5mm or 3.0mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, in step (1), the sieving process yields undersize and oversize materials, and the undersize is subjected to the grading, beneficiation and grinding processes.

[0019] Preferably, the mineral processing in step (1) includes a spiral chute, a first shaking table, a second shaking table, and magnetic separation.

[0020] Preferably, the grinding to particle size < 0.074 mm in step (1) means grinding to a maximum particle size < 0.074 mm, for example, it can be 0.073 mm, 0.070 mm, 0.065 mm, 0.06 mm or 0.05 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the high-nickel matte slag described in step (2) is crushed and ground before use.

[0022] Preferably, the proportion of particles ground to a size <0.074mm is 70wt%~95wt%, for example, it can be 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or 95wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the amount of high-grade nickel matte slag added in step (2) is 1wt%-10wt% of the dry mass of the leaching raw material in step (1), for example, it can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] The amount of high-grade nickel matte slag added according to this invention will affect the removal effect of hexavalent chromium. If the amount of high-grade nickel matte slag added is too small, the removal effect of hexavalent chromium will decrease; if the amount of high-grade nickel matte slag added is too large, the content of divalent iron in the leachate will be too high, which will increase the cost of subsequent iron removal.

[0025] Preferably, the compound leaching material described in step (2) is prepared into a slurry with a mass fraction of 35%-40%, for example, 35%, 36%, 37%, 38%, 39% or 40%, and the high-pressure acid leaching is carried out according to an acid-to-ore ratio of (0.30-0.36):1, for example, 0.30:1, 0.32:1, 0.34:1 or 0.36:1, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the high-pressure acid leaching temperature in step (3) is 240℃-255℃, for example, it can be 240℃, 245℃, 250℃ or 255℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the high-pressure acid leaching time in step (3) is 45min-90min, for example, it can be 45min, 55min, 65min, 75min, 85min or 90min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, after the high-pressure acid leaching in step (3), solid-liquid separation is also performed.

[0029] Preferably, the concentration of hexavalent chromium in the filtrate obtained from the solid-liquid separation is ≤1 mg / L, for example, it can be 1 mg / L, 0.5 mg / L or 0.1 mg / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention provides a method for removing hexavalent chromium (CrVI) during high-pressure acid leaching of laterite nickel ore. To address the issues of high reducing agent usage, high cost, and environmental concerns associated with CrVI removal, the method first washes the laterite nickel ore to fully disperse the bonded minerals in water, while simultaneously screening to remove large pieces of low-nickel ore, thus improving the processing capacity of the raw ore. Then, it classifies the ore, separating and recovering a portion of the chromium minerals, thereby reducing the Cr(VI) content at the source. High-grade nickel matte slag is then used as a reducing agent. The ferrous iron generated by the acid dissolution of the high-grade nickel matte slag provides a reducing atmosphere for the high-pressure acid leaching process of laterite nickel ore, inhibiting the generation of Cr(VI) during the reaction or the reduction and removal of Cr(VI). Since high-grade nickel matte slag is widely available and easily obtained, and its comprehensive utilization rate is improved, it has high socio-economic benefits. Therefore, this invention combines physical and chemical methods to achieve highly efficient Cr(VI) removal during the leaching process of laterite nickel ore. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method described in Embodiment 1 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0034] The composition of the laterite nickel ore used in the following examples and comparative examples is shown in Table 1:

[0035] Table 1

[0036]

[0037] The high-grade nickel matte slag used in the following examples and comparative examples was obtained by the following method: laterite nickel ore was dried, reduced and sulfided and smelted to produce low-grade nickel matte and smelting slag; low-grade nickel matte was smelted in a converter to produce high-grade nickel matte and smelting slag, which is the high-grade nickel matte slag, and its main component is fir olivine.

[0038] Example 1

[0039] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The flowchart of the method is as follows: Figure 1 As shown, the specific steps include the following:

[0040] Water is added to laterite nickel ore and stirred to fully disperse it. The mineral is separated into coarse and fine particle sizes using a 1.5mm sieve. The coarse particles are discarded directly. The fine particles are further classified into coarse particles of +0.074mm (particle size > 0.074mm) and fine particles of -0.074mm (particle size < 0.074mm). The coarse particles of +0.074mm are separated into some chromite using a combined beneficiation process of spiral chute-shaking table-shaking table-magnetic separation. The tailings are then ground into particles of -0.074mm using a ball mill. The ground particles are then mixed with the fine particles of -0.074mm as leaching raw material.

[0041] The high-grade nickel matte slag was crushed and ball-milled to a particle size of -0.074 mm, accounting for 80 wt%. It was then mixed with leaching raw materials at 1 wt% of the dry ore mass to prepare a slurry with a mass fraction of 35%. The slurry was reacted in a high-pressure reactor at 250°C for 60 min at an acid-to-ore ratio of 0.30:1. After the reaction, it was filtered to obtain the filtrate.

[0042] Example 2

[0043] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, the method comprising the following steps:

[0044] Water is added to laterite nickel ore and stirred to fully disperse it. The mineral is separated into coarse and fine particle sizes using a 1.5mm sieve. The coarse particles are discarded directly. The fine particles are further classified into coarse particles of +0.074mm (particle size > 0.074mm) and fine particles of -0.074mm (particle size < 0.074mm). The coarse particles of +0.074mm are separated into some chromite using a combined beneficiation process of spiral chute-shaking table-shaking table-magnetic separation. The tailings are then ground into particles of -0.074mm using a ball mill. The ground particles are then mixed with the fine particles of -0.074mm as leaching raw material.

[0045] The high-grade nickel matte slag was crushed and ball-milled to a particle size of -0.074 mm, accounting for 95 wt%. It was then mixed with leaching raw materials at 3 wt% of the dry ore mass to prepare a slurry with a mass fraction of 35%. The slurry was reacted in a high-pressure reactor at 255°C for 60 minutes at an acid-to-ore ratio of 0.30:1. After the reaction, the mixture was filtered to obtain the filtrate.

[0046] Example 3

[0047] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, the method comprising the following steps:

[0048] Water is added to laterite nickel ore and stirred to fully disperse it. The mineral is separated into coarse and fine particle sizes using a 1.5mm sieve. The coarse particles are discarded directly. The fine particles are further classified into coarse particles of +0.074mm (particle size > 0.074mm) and fine particles of -0.074mm (particle size < 0.074mm). The coarse particles of +0.074mm are separated into some chromite using a combined beneficiation process of spiral chute-shaking table-shaking table-magnetic separation. The tailings are then ground into particles of -0.074mm using a ball mill. The ground particles are then mixed with the fine particles of -0.074mm as leaching raw material.

[0049] The high-grade nickel matte slag was crushed and ball-milled to a particle size of -0.074 mm, accounting for 95 wt%. It was then mixed with leaching raw materials at 4 wt% of the dry ore mass to prepare a slurry with a mass fraction of 35%. The slurry was reacted in a high-pressure reactor at 255°C for 60 minutes at an acid-to-ore ratio of 0.30:1. After the reaction, the mixture was filtered to obtain the filtrate.

[0050] Example 4

[0051] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, the method comprising the following steps:

[0052] Water is added to laterite nickel ore and stirred to fully disperse it. The mineral is separated into coarse and fine particle sizes using a 1.5mm sieve. The coarse particles are discarded directly. The fine particles are further classified into coarse particles of +0.074mm (particle size > 0.074mm) and fine particles of -0.074mm (particle size < 0.074mm). The coarse particles of +0.074mm are separated into some chromite using a combined beneficiation process of spiral chute-shaking table-shaking table-magnetic separation. The tailings are then ground into particles of -0.074mm using a ball mill. The ground particles are then mixed with the fine particles of -0.074mm as leaching raw material.

[0053] The high-grade nickel matte slag was crushed and ball-milled to a particle size of -0.074 mm, accounting for 95 wt%. It was then mixed with leaching raw materials at 5 wt% of the dry ore mass to prepare a slurry with a mass fraction of 35%. The slurry was reacted in a high-pressure reactor at 255°C for 60 min at an acid-to-ore ratio of 0.30:1. After the reaction, it was filtered to obtain the filtrate.

[0054] Example 5

[0055] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, the method comprising the following steps:

[0056] Water is added to laterite nickel ore and stirred to fully disperse it. The mineral is separated into coarse and fine particle sizes using a 1.0 mm sieve. The coarse particles are discarded directly. The fine particles are further classified into coarse particles of +0.074 mm (particle size > 0.074 mm) and fine particles of -0.074 mm (particle size < 0.074 mm). The coarse particles of +0.074 mm are separated into some chromite using a combined beneficiation process of spiral chute-shaking table-shaking table-magnetic separation. The tailings are then ground into particles of -0.074 mm using a ball mill. The ground particles are then mixed with the fine particles of -0.074 mm as leaching feedstock.

[0057] The high-grade nickel matte slag was crushed and ball-milled to a particle size of -0.074 mm, accounting for 75 wt%. It was then mixed with leaching raw materials at 8 wt% of the dry ore mass to prepare a slurry with a mass fraction of 38%. The slurry was reacted in a high-pressure reactor at 240℃ for 90 minutes at an acid-to-ore ratio of 0.36:1. After the reaction, it was filtered to obtain the filtrate.

[0058] Example 6

[0059] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, the method comprising the following steps:

[0060] Water is added to laterite nickel ore and stirred to fully disperse it. The mineral is separated into coarse and fine particle sizes using a 2mm sieve. The coarse particles are discarded directly. The fine particles are further classified into coarse particles of +0.074mm (particle size > 0.074mm) and fine particles of -0.074mm (particle size < 0.074mm). The coarse particles of +0.074mm are separated into some chromite using a combined beneficiation process of spiral chute-shaking table-shaking table-magnetic separation. The tailings are then ground into particles of -0.074mm using a ball mill. The ground particles are then mixed with the fine particles of -0.074mm as leaching raw material.

[0061] The high-grade nickel matte slag was crushed and ball-milled to a particle size of -0.074 mm, accounting for 70 wt%. It was then mixed with leaching raw materials at a dry ore mass of 10 wt% to prepare a slurry with a mass fraction of 40%. The slurry was reacted in a high-pressure reactor at a temperature of 255℃ for 45 minutes at an acid-to-ore ratio of 0.33:1. After the reaction was completed, the mixture was filtered to obtain the filtrate.

[0062] Example 7

[0063] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The method is the same as in Example 1, except that the high-grade nickel matte slag is mixed with the leaching raw material at 0.5 wt% of the dry ore mass.

[0064] Example 8

[0065] This embodiment provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The method is the same as in Example 1, except that the high-grade nickel matte slag is mixed with the leaching raw material at 12 wt% of the dry ore mass.

[0066] Comparative Example 1

[0067] This comparative example provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The method is the same as in Example 1 except that high-grade nickel matte slag is not added.

[0068] Comparative Example 2

[0069] This comparative example provides a method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore. The method is the same as in Example 1, except that the coarse particles were not sorted and some chromite was not separated.

[0070] The composition of the filtrate obtained after high-pressure acid leaching and filtration in the above embodiments and comparative examples is shown in Table 2:

[0071] Table 2

[0072]

[0073] As can be seen from Table 2 above:

[0074] As can be seen from Example 1 and Comparative Example 1, the addition of high-grade nickel matte slag during high-pressure acid leaching in this invention can increase the Fe content in the leaching solution. 2+ Concentration, reduced Cr 6+ The concentration indicates that the high-grade nickel matte slag can remove Cr(VI) produced by the high-pressure acid leaching reaction; as shown in Example 1 and Comparative Example 2, the present invention can reduce the Cr(VI) content from the source through physical mineral processing; as shown in Example 1 and Examples 7-8, the amount of high-grade nickel matte slag added in the present invention will affect the removal effect of hexavalent chromium, and it is preferred to add it within a specific range.

[0075] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore, characterized in that, The method for removing hexavalent chromium during the high-pressure acid leaching process of laterite nickel ore includes the following steps: (1) The laterite nickel ore is washed, screened, classified, beneficiated and ground to obtain leaching raw material; Chromite is separated during the mineral processing; (2) Mix the high-grade nickel matte slag and the leaching material described in step (1) to obtain a compound leaching material; (3) The compound leaching material described in step (2) is subjected to high-pressure acid leaching to remove hexavalent chromium.

2. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1, characterized in that, In step (1), the grading process yields coarse particles and fine particles. The coarse particles are then beneficiated and ground. The fine particles are mixed with the ground particles to obtain the leaching raw material. Preferably, the coarse particles have a particle size ≥ 0.074 mm; Preferably, the particle size of the fine particles is <0.074 mm.

3. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, The sieve aperture size in step (1) is 1.0mm-3mm; Preferably, in step (1), the sieving process yields undersize and oversize materials, and the undersize is subjected to the grading, beneficiation and grinding processes.

4. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, The mineral processing in step (1) includes a spiral sluice, a first shaking table, a second shaking table, and magnetic separation; Preferably, the particle size of the grinding particles in step (1) is <0.074 mm.

5. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, The high-nickel matte slag described in step (2) must be crushed and ground before use; Preferably, the proportion of particles ground to a size <0.074mm is 70wt%-95wt%.

6. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, The amount of high-grade nickel matte slag added in step (2) is 1wt%-10wt% of the dry mass of the leaching raw material in step (1).

7. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, The compound leaching material described in step (2) is prepared into a slurry with a mass fraction of 35%-40%, and high-pressure acid leaching is carried out at an acid-to-ore ratio of (0.30-0.36):

1.

8. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, The high-pressure acid leaching temperature in step (3) is 240℃-255℃; Preferably, the high-pressure acid leaching time in step (3) is 45 min to 90 min.

9. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 1 or 2, characterized in that, After the high-pressure acid leaching in step (3), solid-liquid separation was also performed.

10. The method for removing hexavalent chromium during high-pressure acid leaching of laterite nickel ore according to claim 9, characterized in that, The concentration of hexavalent chromium in the filtrate obtained from the solid-liquid separation is ≤1 mg / L.

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