JP7658359B2 - Control methods for high pressure sulfuric acid leaching of nickel oxide ores. - Google Patents

Description

The present invention relates to a method for controlling the high-pressure sulfuric acid leaching of nickel oxide ore, and more specifically, to a method for controlling the high-pressure sulfuric acid leaching of nickel oxide ore, which uses the ratio of the ore chromium grade to the ore magnesium grade as an indicator and determines the free sulfuric acid concentration to obtain a high nickel leaching rate.

One method for hydrometallurgy of nickel oxide ore is the high pressure acid leaching (HPAL) method using sulfuric acid. This method does not include dry processing steps such as drying and roasting, and instead consists of a continuous wet process, so it is advantageous in terms of energy and cost, and has the advantage of being able to obtain nickel-cobalt mixed sulfide with nickel content improved to about 50% by mass.

In the HPAL process, there is a need for a method that can leach valuable metals such as nickel at a high leaching rate while effectively reducing the amount of sulfuric acid used. It is known that the leaching process in the HPAL process leaches out unnecessary components contained in the ore, such as magnesium, aluminum, iron, and chromium, in addition to nickel. Magnesium in particular is an economically undesirable impurity, as most of it is leached out and consumes a large amount of sulfuric acid.

In response to such problems, for example, Patent Document 1 describes a leaching method in which sulfuric acid is added to a slurry (ore slurry) of nickel oxide ore containing magnesium to perform a leaching process, thereby obtaining a leaching slurry consisting of a leachate containing nickel and a leach residue, and the amount of sulfuric acid added is adjusted according to the magnesium concentration in the leach slurry obtained by the leaching process so that the free sulfuric acid concentration in the leach slurry becomes a predetermined concentration.

However, if the composition and properties of nickel oxide ore, or the form of nickel and magnesium, affect reactivity, there is a concern that the leaching rate of nickel and magnesium will change even with the same magnesium concentration, and the amount of sulfuric acid used will not be sufficiently reduced.

JP 2019-85620 A

The present invention has been made to solve this problem, and aims to provide a method for controlling the high-pressure sulfuric acid leaching of nickel oxide ore, which can effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate even when the ore type and its mixing ratio change.

The inventors discovered that the amount of sulfuric acid used in the leaching process of the hydrometallurgical smelting of nickel oxide ore can be effectively reduced by adjusting the amount of sulfuric acid added depending on the Cr/Mg ratio of the nickel oxide ore, and thus completed the present invention.

That is, one aspect of the present invention is a control method for high-pressure sulfuric acid leaching of nickel oxide ore, which includes a leaching step of adding sulfuric acid to an ore slurry containing nickel oxide ore and performing sulfuric acid leaching treatment under high-temperature and high-pressure conditions, and an ore composition measurement step of measuring the chromium and magnesium grades of the nickel oxide ore prior to the leaching step, in which the ratio Cr/Mg of the chromium grade Cr to the magnesium grade Mg in the ore composition measurement step is used as an index, and the amount of sulfuric acid added in the leaching step is adjusted based on the index, and the adjustment is performed by setting a value of 1.3 to 1.5 as a reference value, and when the index Cr/Mg is equal to or greater than the reference value, sulfuric acid is added so that the free acid concentration in the leaching solution becomes 42 to 46 g/L, and when the index Cr/Mg is less than the reference value, sulfuric acid is added so that the free acid concentration in the leaching solution becomes 48 to 52 g/L. (In this specification, "to" means a lower limit or more and an upper limit or less. The same applies hereinafter.)

According to one aspect of the present invention, by using the ratio of chromium grade Cr to magnesium grade Mg (Cr/Mg) as an indicator, it is possible to predict the magnesium leaching rate even when the ratio of ore types changes, and it is possible to effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate.

In one embodiment of the present invention, the magnesium content of the nickel oxide ore may be 1.0 to 4.0 mass%.

In the hydrometallurgy of nickel oxide ore, it is preferable to prepare an ore slurry with the above magnesium grade.

In one aspect of the present invention, the ore slurry may also contain chromite.

Chromite is an ore that contains chromium (Cr), and the present invention can be effectively applied depending on the mixing ratio.

According to the present invention, it is possible to effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate even when the ore type and its mixing ratio change.

FIG. 1 is a process diagram showing a hydrometallurgical process for nickel oxide ore by high-pressure acid leaching. FIG. 1 is a diagram showing the relationship between the ratio of Cr content to Mg content (Cr/Mg) in an ore and the leaching rate of magnesium (Mg) in a leaching process.

The method for controlling high pressure sulfuric acid leaching of nickel oxide ore according to the present invention will be described below with reference to the drawings in the following order. Note that the present invention is not limited to the following examples, and can be modified as desired without departing from the gist of the present invention.
1. Hydrometallurgical method for nickel oxide ore 2. Control method for high-pressure sulfuric acid leaching of nickel oxide ore

<1. Hydrometallurgical method for nickel oxide ore>
First, prior to a specific description of the present invention, a hydrometallurgical method for nickel oxide ore to which a control method for high-pressure sulfuric acid leaching of nickel oxide ore according to the present invention is applied will be briefly described. This hydrometallurgical method for nickel oxide ore is a hydrometallurgical method for leaching and recovering nickel and cobalt from nickel oxide ore using a high-pressure acid leaching process (HPAL process). Figure 1 shows an example of a process diagram of a hydrometallurgical method for nickel oxide ore using a high-pressure acid leaching process.

In the slurry preparation process S1, nickel oxide ore is used as the raw ore. Several types of nickel oxide ore are mixed to achieve a specified Ni grade and impurity grade, and the ore is sieved to classify it at a specified classification point to remove oversized ore particles. After that, only the undersized ore is mixed with water to make a slurry.

In the leaching step S2, the nickel oxide ore slurry obtained in the slurry preparation step S1 is subjected to a leaching process using a high-pressure acid leaching method. Specifically, sulfuric acid is added to the ore slurry obtained by mixing the nickel oxide ore as the raw material, and nickel, cobalt, etc. are leached from the ore by pressurizing to 3 to 5 MPa under high temperature conditions of 220 to 280°C using, for example, a heat-resistant and pressure-resistant container (autoclave), and a leaching slurry consisting of a leachate and a leaching residue is formed. The control method for high-pressure sulfuric acid leaching of nickel oxide ore according to the present invention is applied in this leaching step S2. Details will be described later.

In the leaching step S2, excess sulfuric acid is added to improve the leaching rate. Therefore, the resulting leaching slurry contains excess sulfuric acid that was not involved in the leaching reaction, and its pH is very low.

For this reason, in the preliminary neutralization step S3, the pH of the leaching slurry obtained in the leaching step S2 is increased so that washing can be performed efficiently during the multi-stage washing in the next solid-liquid separation step S4. The pH can be adjusted to a predetermined range by adding a neutralizing agent such as limestone (calcium carbonate) slurry.

In the solid-liquid separation step S4, the leaching slurry whose pH has been adjusted in the preliminary neutralization step S3 is washed in multiple stages to obtain a leaching solution and leaching residue that contain nickel, cobalt, and zinc as an impurity element.

In the neutralization step S5, the pH of the leachate separated in the solid-liquid separation step S4 is adjusted, and the neutralized precipitate containing impurity elements is separated to obtain a neutralized end solution containing zinc as well as nickel and cobalt. The pH of the leachate is adjusted by adding a neutralizing agent such as limestone (calcium carbonate) slurry.

In the dezincing step S6, a sulfurizing agent such as hydrogen sulfide gas is added to the neutralization end liquid obtained in the neutralization step S5 to perform a sulfurization treatment to generate zinc sulfide, which is then separated and removed to obtain a mother liquor for nickel recovery (dezincing end liquid) containing nickel and cobalt.

In the sulfurization step S7, the dezincification final liquor, which is the mother liquor for recovering nickel after the dezincification step S6, is used as the starting liquor for the sulfurization reaction, and hydrogen sulfide gas is blown into the starting liquor as a sulfurization agent to cause a sulfurization reaction, producing a mixed sulfide of nickel and cobalt with few impurities and a barren liquor in which the concentrations of nickel and cobalt are stabilized at low levels. In the sulfurization step S7, a larger amount of sulfurization agent such as hydrogen sulfide gas is added by applying pressure, etc., compared to the dezincification step S6.

The final neutralization step S8 neutralizes the leaching residue containing free sulfuric acid transferred from the solid-liquid separation step S4 described above, and the filtrate (poor liquid) containing impurities such as magnesium, aluminum, and iron transferred from the sulfidation step S7. The leaching residue and filtrate are adjusted to a predetermined pH range using a neutralizing agent, and become a waste slurry (tailings). The generated tailings are transferred to a tailings dam (waste storage area).

2. Control method for high-pressure sulfuric acid leaching of nickel oxide ore
Next, a method for controlling the high-pressure sulfuric acid leaching of nickel oxide ore according to the present invention will be described. As described above, in the leaching process (leaching step S2) in the HPAL method, other components contained in the ore, such as magnesium, aluminum, iron, and chromium, are also leached in addition to nickel. These reactions can be represented by the following reaction formulas (1) to (3), and the higher the free acid concentration, the faster and to a higher concentration the leaching reaction proceeds.
MO+ _H2SO4 = _MSO4 + _H2O ...Formula (1) ₍ M=Ni, Co, Cu, Mg, Zn)
H ₂ SO ₄ +H ₂ O=H ₃ O ⁺ +HSO ₄ ^-... Equation (2) Ka ₁ = 1.00×10 ³
HSO ₄ ⁻ +H ₂ O=H ₃ O ⁺ +SO _{4 2} ^−... Equation (3) Ka ₂ =1.99×10 ⁻²

Here, although an increase in the free acid concentration is favorable for the leaching rate, it means that the amount of sulfuric acid used increases. Therefore, for economic reasons, an excessively high free acid concentration is undesirable, and it is desirable to obtain a high nickel leaching rate at a lower free acid concentration. Furthermore, if it were possible to suppress the leaching of metal components other than the target recovery metals nickel and cobalt, it would be possible to suppress the amount of sulfuric acid used without changing the free acid concentration, so there is a demand for a means to efficiently leach only the target recovery metals nickel (and cobalt).

Not only nickel, but many other metal components are leached in an autoclave according to formula (1). Therefore, by increasing the sulfuric acid concentration, the reaction can be promoted to the right side, and the leaching rate can be improved. Next, when considering formulas (2) and (3) showing the dissociation of sulfuric acid, the equilibrium of formula (2) is sufficiently large on the right side, but the equilibrium of formula (3) is as large as the reaction to the left as the reaction to the right, so dissociation depends on the sulfate concentration in the leaching solution. Therefore, when the SO ₄ ^2- concentration in the leaching solution is high, that is, when a large amount of impurities are dissolved, the reaction of formula (3) is inhibited, and the leaching rate of nickel decreases even with the same amount of sulfuric acid added.

In addition, among the above formulas (1) to (3), formula (2) is a reaction process that constitutes formula (1), and the reaction rate of formula (2) is relatively fast, so the remaining reaction process (formula (1)-formula (2)=formula (4)) is the rate-limiting step.
MO+H ₃ O ⁺ +HSO ₄ ^- =M ²⁺ +SO ₄ ^2- +2H ₂ O...Formula (4) (M=Ni, Co, Cu, Mg, Zn)

Specifically, in the reaction of formula (4), the following reactions of formulas (4-1) to (4-5) proceed simultaneously in parallel.
NiO+H ₃ O ⁺ +HSO ₄ ^- =Ni ²⁺ +SO ₄ ^2- +2H ₂ O...Formula (4-1) Co ₂ O ₃ +3H ₃ O ⁺ +3HSO ₄ ^- =2Co ²⁺ +3SO ₄ ^2- +6H ₂ O...Formula (4-2) CuO+H ₃ O ⁺ +HSO ₄ ^- =Cu ²⁺ +SO ₄ ^2- +2H ₂ O...Formula (4-3) ZnO+H ₃ O ⁺ +HSO ₄ ^- =Zn ²⁺ +SO ₄ ^2- +2H ₂ O...Formula (4-4) MgO+H ₃ O ⁺ +HSO ₄ ^- =Mg ²⁺ +SO ₄ ^2- +2H ₂ O...Formula (4-5)

Of the formulas (4-1) to (4-5), the right-hand side of formula (4-5) is extremely stable, in other words, most of the magnesium in the ore generates SO ₄ ^2- . The SO ₄ ^2- generated in formula (4-5) causes the reverse reactions (leftward reactions) of formulas (4-1) to (4-4), preventing the leaching of nickel and cobalt.

For this reason, a method of adjusting the amount of sulfuric acid added according to the magnesium concentration in the leaching slurry has been proposed as described above (Patent Document 1, etc.). However, the applicant's internal knowledge has revealed that the leaching rate of magnesium from nickel oxide ore _is chromite (Fe, Mg) _Cr2O4 > talc ( _Mg3Si4O10 ( _OH ) ₂ ), and that the magnesium leaching of low-grade nickel oxide ore varies greatly depending on the ore type. For this reason, depending on the ore types contained in the ore slurry and their mixing ratios, there are _cases where the leaching rate cannot be adequately predicted by simply adjusting the magnesium concentration in the slurry as an index.

The present invention provides a control method for high-pressure sulfuric acid leaching of nickel oxide ore, which includes a leaching process in which sulfuric acid is added to an ore slurry containing nickel oxide ore and sulfuric acid leaching is performed under high-temperature and high-pressure conditions, and an ore composition measurement process in which the chromium and magnesium contents of the nickel oxide ore are measured prior to the leaching process. The ratio Cr/Mg of the chromium content Cr to the magnesium content Mg in the ore composition measurement process is used as an index, and the amount of sulfuric acid added in the leaching process is adjusted based on this index, and when the index falls below a preset reference value, the amount of sulfuric acid added is increased to increase the free acid concentration in the leaching solution.

Figure 2 shows the relationship between the ratio of Cr to Mg in the ore (Cr/Mg) and the leaching rate of magnesium (Mg) in the leaching process. The inventors discovered that when the Cr/Mg in the ore and the leaching rate of magnesium are plotted, there is a strong correlation as shown in Figure 2. Therefore, by monitoring the Cr/Mg of the ore to be treated, it is possible to predict the leaching rate of magnesium in advance, and it is possible to effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate even if the ore type and its mixing ratio change.

In the ore composition measurement process, the chromium and magnesium contents of the nickel oxide ore can be measured, for example, by ICP emission spectrometry or atomic absorption spectrometry. The nickel concentration may also be measured to calculate the nickel leaching rate. This measurement method is preferable because it allows the ore composition of the nickel oxide ore to be measured quickly. Furthermore, because the ore composition can be measured quickly in this way, even if the magnesium content of the nickel oxide ore fluctuates, the fluctuation can be detected quickly, and the free sulfuric acid concentration can be quickly adjusted according to the ratio of Cr content to Mg content in the ore (Cr/Mg).

The reference value set in advance for the indicator Cr/Mg is preferably 1.3 to 1.5, more preferably 1.4. When the indicator Cr/Mg is below the reference value, the magnesium leaching rate is high, and the reactions of the above formulas (4-1) to (4-4) do not proceed easily, and therefore the formula (1) also does not proceed easily for elements other than magnesium. Therefore, unless the sulfuric acid concentration is increased, the nickel leaching reaction does not proceed easily. On the other hand, when the indicator Cr/Mg exceeds the reference value, the magnesium leaching rate is low, and the reactions of the above formulas (4-1) to (4-4) proceed easily, and therefore the formula (1) also proceeds easily for elements other than magnesium. Therefore, even if the sulfuric acid concentration is reduced, the nickel leaching reaction is close to equilibrium, and the nickel leaching rate can be maintained high even if the free acid concentration is reduced. The specific numerical value of the set reference value can be appropriately set based on the progress of the nickel leaching rate and the correlation between the free acid concentration and the nickel leaching rate plotted when the indicator Cr/Mg is changed. Since the gram equivalent of chromium is 17.3g and the gram equivalent of magnesium is 12.2g, the magnesium in the ore can be considered to be equivalent to 17.3÷12.2=1.4 times the mass of chromium. Setting the standard value at 1.4 is equivalent to treating ores with Cr/Mg>1.4 as having more chromium and ores with Cr/Mg<1.4 as having more magnesium.

The amount of sulfuric acid added in the leaching process is such that sulfuric acid remains as a free acid, for example, about 300 kg to 400 kg per ton of ore. If the magnesium grade of the nickel oxide ore is high, this magnesium consumes a lot of sulfuric acid to cause the leaching reaction. Therefore, in order to maintain a high nickel leaching rate, it is necessary to increase the amount of sulfuric acid added in the leaching process. On the other hand, if the magnesium grade of the nickel oxide ore is low, it is desirable to maintain a high nickel leaching rate while suppressing the amount of sulfuric acid added in the leaching process.

As an example, when the indicator Cr/Mg is equal to or greater than the standard value, sulfuric acid may be added so that the free acid concentration in the leachate is 42-46 g/L, and when the indicator Cr/Mg is below the standard value, sulfuric acid may be added so that the free acid concentration in the leachate is 48-52 g/L. When the indicator Cr/Mg is below the standard value, the magnesium grade is high and it is necessary to increase the amount of sulfuric acid added, but when the indicator Cr/Mg is equal to or greater than the standard value, there is no need to increase the amount of sulfuric acid added more than necessary, and it is possible to effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate.

The magnesium content of nickel oxide ore is not particularly limited, but it is generally easy to obtain nickel oxide ore with a magnesium content of 1.0 to 4.0 mass%. In the hydrometallurgical smelting of nickel oxide ore using the HPAL method, the magnesium content of nickel oxide ore is often in the above numerical range.

In addition, the ore slurry preferably contains chromite (Fe, Mg)Cr ₂ O _4. Chromite is an ore containing chromium (Cr) and is unlikely to cause the magnesium leaching reaction (4-5), so the present invention can be effectively applied depending on the mixing ratio.

As described above, the control method for high-pressure sulfuric acid leaching of nickel oxide ore according to the present invention makes it possible to effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate even when the ore type and its mixing ratio change.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

Example 1
The raw ore was separated and the entire amount was dissolved, and the chromium (Cr), magnesium (Mg) and nickel (Ni) contents were analyzed by ICP emission spectroscopy. The remaining raw ore was then placed in a beaker together with a small amount of water, and an amount of sulfuric acid was added so that the free acid concentration was a predetermined value between approximately 41 and 55 g/L based on the analysis value of the raw ore. After a certain period of time, the Ni concentration in the solution was measured, and the nickel (Ni) leaching rate was calculated. This operation was performed multiple times for multiple samples. Table 1 shows a summary of the Ni leaching rates (%) for each range of free acid concentrations (g/L). The values in parentheses in Table 1 include estimated values.

As shown in Table 1, when the Cr/Mg ratio in the ore is used as an indicator and the values are classified as being greater than or less than 1.4, it was found that there is a large difference.

In other words, when Cr/Mg<1.4, the magnesium leaching rate is high, so when the amount of sulfuric acid added is such that the free acid concentration is 41-45 g/L, the nickel leaching rate is less than 90%. Therefore, when Cr/Mg<1.4, it is necessary to increase the free acid concentration to about 50 g/L (increase the amount of sulfuric acid added) in order to maintain a high nickel leaching rate.

On the other hand, when Cr/Mg>1.4, the magnesium leaching rate is low, so even if the free acid concentration is reduced to about 44 g/L, the nickel leaching rate does not decrease. From the above, when Cr/Mg>1.4, the nickel leaching rate can be maintained high even if the free acid concentration is reduced, and it is possible to reduce the amount of sulfuric acid used.

In this way, by using the ratio of chromium grade Cr to magnesium grade Mg (Cr/Mg) as an indicator, it is possible to predict the magnesium leaching rate even when the mixing ratio of ore types changes, and it has been demonstrated that it is possible to effectively reduce the amount of sulfuric acid used while maintaining a high nickel leaching rate.

Example 2
The raw ore was separated and the entire amount was dissolved, and the chromium (Cr), magnesium (Mg) and nickel (Ni) contents were analyzed by ICP emission spectroscopy. The remaining raw ore was then placed in a beaker together with a small amount of water, and the magnesium content in the ore was adjusted to 1.0 to 4.0 mass% based on the analysis value of the raw ore, and sulfuric acid was added in an amount such that the free acid concentration was approximately 43 g/L. While periodically analyzing the Ni concentration, sulfuric acid was added to the beaker until the Ni leaching rate reached 92% or more. The sulfuric acid concentration (=free acid concentration) remaining in the beaker at the time when the Ni leaching rate reached 92% or more was determined by titration with an aqueous sodium hydroxide solution. The results are shown in Table 2.

As shown in Table 2, when Cr/Mg>1.4, the free acid concentration must be increased (the amount of sulfuric acid added must be increased), whereas when Cr/Mg<1.4, the free acid concentration can remain low (the amount of sulfuric acid added can be small). Furthermore, these characteristics were confirmed regardless of the magnesium (Mg) content in the ore, regardless of the content by mass of 1.0 to 4.0%.

Although one embodiment of the present invention and each example have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible that do not substantially deviate from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

For example, a term that is described at least once in the specification or drawings together with a different term having a broader or synonymous meaning may be replaced with that different term anywhere in the specification or drawings. In addition, the configuration of the control method for high-pressure sulfuric acid leaching of nickel oxide ore is not limited to that described in one embodiment of the present invention and each example, and various modifications are possible.

Claims (3)

A method for controlling high pressure sulfuric acid leaching of nickel oxide ore, comprising the steps of:
a leaching step of adding sulfuric acid to the ore slurry containing the nickel oxide ore and performing a sulfuric acid leaching treatment under high temperature and high pressure conditions;
and an ore composition measuring step for measuring a chromium content and a magnesium content of the nickel oxide ore prior to the leaching step,
adjusting the amount of sulfuric acid added in the leaching step based on a ratio of a chromium grade (Cr) to a magnesium grade (Mg) in the ore composition measurement step as an index;
The adjustment is performed by setting a value of 1.3 or more and 1.5 or less as a reference value,
a control method for high-pressure sulfuric acid leaching of nickel oxide ore, the method comprising the steps of: adding sulfuric acid so that a free acid concentration in the leaching solution becomes 42 to 46 g/L when the indicator Cr/Mg is equal to or greater than the reference value; and adding sulfuric acid so that a free acid concentration in the leaching solution becomes 48 to 52 g/L when the indicator Cr/Mg is less than the reference value. 2. The method for controlling high-pressure sulfuric acid leaching of nickel oxide ore according to claim 1 , wherein the magnesium content of the nickel oxide ore is 1.0 to 4.0 mass%. The method for controlling high-pressure sulfuric acid leaching of nickel oxide ore according to claim 1 or 2, characterized in that the ore slurry contains chromite.