WO2015093363A1 - Method for suppressing elution of manganese - Google Patents

Abstract

The present invention suppresses elution of manganese from manganese sediment in slurry accumulated in a sedimentation tank. The present invention sets the pH of the slurry including manganese sediment accumulated in the sedimentation tank to 8.0-9.0 and suppresses the elution of manganese.

Description

Method for suppressing manganese elution

The present invention relates to a method for suppressing elution of manganese, which suppresses elution of manganese from manganese precipitates in a slurry containing manganese precipitates stored in a sedimentation basin. This application claims priority on the basis of Japanese Patent Application No. 2013-259175 filed on Dec. 16, 2013 in Japan. This application is incorporated herein by reference. Incorporated.

Recently, high-pressure acid leaching using sulfuric acid (High-Pressure-Acid-Leach) has attracted attention as a hydrometallurgical process for nickel oxide ore. Unlike the conventional dry smelting method, which is a conventional nickel oxide ore smelting method, this method does not include dry processes such as reduction and drying processes, and is a consistent wet process. Is advantageous. Further, this method has an advantage that a sulfide containing nickel and cobalt whose nickel quality is increased to about 50% by mass (hereinafter also referred to as “nickel / cobalt mixed sulfide”) can be obtained. .

The hydrometallurgical method of nickel oxide ore using this high-pressure acid leaching method is an ore treatment step in which nickel oxide ore is pulverized to a predetermined size to form a slurry, and sulfuric acid is added to the ore slurry under high temperature and high pressure. A leaching process (high pressure acid), a pre-neutralization process for performing a neutralization (hereinafter also referred to as “pre-neutralization”) treatment before the leaching slurry is washed in multiple stages, and a pre-neutralization process. A solid-liquid separation process (hereinafter also referred to as “CCD process”) in which the leaching slurry thus obtained is subjected to solid-liquid separation into a leaching residue and a leachate containing an impurity element together with nickel and cobalt while being washed in multiple stages. A neutralization step of adjusting the pH of the leachate to separate neutralized starch containing impurity elements and obtaining a neutralized final solution containing zinc together with nickel and cobalt, and zinc by adding a sulfurizing agent to the neutralized final solution Separation by forming sulfide A zinc removal step for obtaining a nickel recovery mother liquor, a nickel recovery step for forming a mixed sulfide containing nickel and cobalt by adding a sulfiding agent to the nickel recovery mother liquor, and a drainage (filtrate) in the nickel recovery step, And a final neutralization step in which the residue of the CCD step is mixed and neutralized (see, for example, Patent Document 1).

The high-pressure acid leaching method has been put to practical use as a method for recovering metal from low-grade nickel oxide ore. At the time of leaching, impurity components such as manganese and magnesium are leached in the leaching slurry, in addition to elements for recovery purposes such as nickel and cobalt. The leached manganese and the like are neutralized by adding an alkali after recovering nickel and cobalt. The sediment such as manganese is finally transferred as a slurry to a sedimentation basin called a tailing dam. In the sedimentation basin, the sediment is settled and the supernatant liquid is released into the sea.

In such neutralization treatment, in many cases, removal of manganese becomes a problem. This is because the content of manganese contained in the nickel oxide ore is large and difficult to precipitate. For such a problem, for example, Patent Document 2 describes a method for selectively and efficiently precipitating manganese.

However, after neutralization treatment, that is, after manganese is precipitated, there is no useful knowledge about the change in manganese concentration during solid-liquid separation in the sedimentation basin. Patent Document 3 describes a method of promoting aggregation and precipitation by adding a heavy metal inorganic compound during the neutralization treatment. However, Patent Document 3 does not mention the behavior of heavy metal concentration during solid-liquid separation after precipitation.

In the sedimentation basin, the manganese concentration is usually controlled to a concentration that does not affect the environment. However, in the sedimentation basin, the manganese concentration may fluctuate rapidly, especially the concentration may increase, and the cause is unknown. This makes it difficult to control the manganese concentration. Therefore, in the sedimentation basin, it is required to control the manganese concentration based on knowledge about the change in manganese concentration during solid-liquid separation.

JP-A-2005-350766 JP-A-9-248576 JP 2012-250226 A

This invention is proposed in view of such a situation, and it aims at providing the elution suppression method of manganese which suppresses that manganese elutes from a manganese deposit in a sedimentation basin.

The manganese elution suppression method according to the present invention is a manganese elution suppression method for suppressing manganese elution from the manganese precipitate in the slurry containing manganese precipitate stored in the sedimentation basin. The pH of the slurry is 8.0 to 9.0.

In the present invention, by setting the pH of the slurry containing manganese precipitates stored in the sedimentation basin to 8.0 to 9.0, it is possible to suppress manganese elution from the manganese precipitates, and to precipitate the manganese precipitates. The manganese concentration of the obtained supernatant can be lowered.

FIG. 1 is a diagram showing the relationship between changes in manganese concentration and pH of slurry stored in a sedimentation basin. FIG. 2 is a graph showing the relationship between the manganese concentration and the pH of the slurry from which the solid content has been removed from the sedimentation basin.

Hereinafter, the method for suppressing elution of manganese according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

The manganese elution suppression method is a method for suppressing elution of manganese from the manganese precipitate by setting the pH of the slurry containing the manganese precipitate stored in the sedimentation basin to 8.0 to 9.0.

The slurry stored in the settling basin is, for example, limestone in the leaching residue after the nickel and cobalt are recovered from the leach residue and leachate produced when high pressure acid leaching of nickel and cobalt from nickel oxide ore It is a slurry containing a precipitate produced by neutralization with powder and slaked lime powder. That is, in order to prevent the manganese concentration in the wastewater stored in the settling basin after the neutralization treatment of the wastewater containing leaching residue and filtrate produced by, for example, nickel oxide ore hydrometallurgy, It can be applied to suppress elution of manganese.

Nickel oxide ore contains manganese and aluminum as impurities in addition to nickel and cobalt. For this reason, when leaching residue and filtrate are neutralized with limestone powder or slaked lime powder, precipitates such as manganese and aluminum are generated.

In the neutralization treatment, the pH of the waste water containing the leach residue and filtrate is preferably 8.0 to 10.0. If the pH of the wastewater is too low, poor manganese precipitation occurs. If the pH is too high, the amount of neutralizing agent used is increased, which is not preferable.

Slurry containing precipitates such as manganese and aluminum is once stored in a sedimentation basin before being discharged into the sea or river. Here, the sedimentation basin includes a dam. In the sedimentation basin, a slurry containing manganese precipitates is stored for a while to deposit sediments such as manganese precipitates. Then, after the sediment is settled, the detoxified supernatant is pumped up and discharged to the outside such as the sea or river.

In sedimentation basins, it is necessary to discharge the detoxified supernatant to the sea, rivers, etc. in order to reduce the environmental load. In the sedimentation basin, for example, manganese is preferably precipitated as a precipitate and not dissolved in the supernatant, but the manganese concentration in the supernatant is increased.

The increase in manganese concentration is related to the pH of the slurry. The manganese concentration increases as the pH of the slurry decreases. The pH of the slurry is considered to decrease as carbon dioxide in the air dissolves and generates protons.

Manganese elutes from the precipitate when the pH of the slurry decreases. The relationship between the pH of the slurry and the manganese concentration can also be seen from the measurement results of the pH and manganese concentration shown in FIG.

FIG. 1 shows the results of measuring the pH and manganese concentration of the slurry in the sedimentation basin for about 70 days. The ultimate pH due to the dissolution of carbon dioxide is about 7.7. As shown in FIG. 1, manganese elution starts when the pH of the slurry falls below 8.5, and the manganese concentration exceeds 1 mg / L when the pH falls below 8.0. This 1 mg / L is a specified value defined by, for example, the National Pollution Control Committee (NPCC) in the Philippines. Therefore, it is necessary to suppress the manganese concentration in the slurry to less than 1 mg / L.

Further, from the results shown in FIG. 1, the time for the slurry pH to reach 8.5 is about 20 days, and after 20 days, elution of manganese due to the decrease in pH starts abruptly, and on the 30th day, manganese elution It can be seen that the concentration of 1 mg / L.

Therefore, the discharge from the sedimentation basin is performed before the pH of the stored slurry falls below 8.0, preferably 8.25. That is, if the slurry pH is maintained within the range of 8.0 to 9.0, preferably within the range of 8.25 to 8.75, elution of manganese is suppressed, and the manganese concentration is 1 mg / L. It can be discharged in a state where the specified value of NPCC is satisfied.

In the sedimentation basin, the slurry is stored for 30 days or less, preferably 20 days or less, as a method for making the pH of the slurry less than 8.0, preferably less than 8.25. When the storage time is 30 days or less, the elution of manganese is suppressed, and the manganese concentration can satisfy less than 1 mg / L.

Here, the relationship between the decrease in pH and carbon dioxide was separately investigated by measuring the pH in the absence of solids (precipitate). The result is shown in FIG. Although the precipitate was removed from the slurry, not all could be removed, and a trace amount of manganese was detected.

From the results shown in FIG. 2, it can be seen that even when the solid content (precipitate) is removed from the slurry and kept in the air, the pH drops to 7.7 as in the case of containing the solid content described above. That is, it can be seen that the pH drops to about 7.7 when the slurry is kept in the air regardless of the presence or absence of solids. The decrease in pH is accelerated because there is nothing to elute if there is no solid content. Therefore, it can be seen that the decrease in pH is caused by the dissolution of the acidic gas contained in the air into the carbon dioxide slurry as described above.

In the manganese elution suppression method, the pH of the slurry is preferably 8.0 to 10.0 when the slurry is discharged to the sedimentation basin. In the manganese elution suppression method, by setting the pH of the slurry to 8.0 to 10.0, manganese is not eluted and the slurry can be discharged to the sedimentation basin in a very low concentration of manganese. .

From the above, the manganese elution suppression method can suppress an increase in manganese concentration even if the slurry before being discharged into the sea or river is stored in a sedimentation basin that comes into contact with the outside air. Thereby, the method for suppressing elution of manganese can suppress the influence on the environment, and its effect is very large.

An embodiment to which the present invention is applied will be described. In addition, this invention is not limited to the following Example at all.

<Example>
In the examples, first, limestone powder and slaked lime powder are added to wastewater containing manganese produced by high pressure acid leaching for leaching nickel and cobalt from nickel oxide ore to perform neutralization treatment, and slurry containing manganese precipitates is obtained. Obtained.

Next, in the examples, the slurry was discharged into a sedimentation basin. The pH of the slurry when the slurry was discharged into the sedimentation basin was 9.10, and the manganese concentration was 0.3 mg / L.

Next, in the examples, the slurry was allowed to stand for 15 days in a sedimentation basin in an air atmosphere. Thereafter, the supernatant was pumped up to the sea. The pH of the slurry at this time was 8.5, and the manganese concentration was 0.1 mg / L.

Therefore, elution of manganese is suppressed in the examples.

<Comparative example>
In the comparative example, the waste water containing manganese produced by the high pressure acid leaching method was neutralized as in the example. Next, in the comparative example, the slurry was discharged into the settling basin with the slurry having a pH of 9.15.

Next, in the comparative example, the slurry was allowed to stand for 40 days in a sedimentation basin in an air atmosphere. The manganese concentration of the slurry was 2.5 mg / L.

Claims (6)

A method for suppressing elution of manganese, which suppresses elution of manganese from the manganese precipitate in a slurry containing manganese precipitate stored in a sedimentation basin,
A method for suppressing elution of manganese, wherein the pH of the slurry in the sedimentation basin is 8.0 to 9.0. The method for suppressing manganese elution according to claim 1, wherein the slurry is stored in the sedimentation basin for 30 days or less. 2. The manganese elution suppression method according to claim 1, wherein the slurry is drainage generated by a high pressure acid leaching method in which nickel and cobalt are leached from nickel oxide ore. 4. The manganese elution suppression method according to claim 3, wherein the waste water contains the manganese precipitate produced by limestone and slaked lime as precipitants. 2. The manganese elution suppression method according to claim 1, wherein the supernatant is pumped up from the sedimentation basin and discharged to the outside. 2. The manganese elution suppression method according to claim 1, wherein the pH of the slurry is 8.0 to 10.0 when the slurry is discharged into the sedimentation basin.

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