AU2017362828A1 - Method for removing manganese - Google Patents

Abstract

Provided is a method for removing manganese which can efficiently remove manganese contained in discharged water generated in an HPAL process, while effectively reducing the amount of a chemical agent such as a neutralizer used therein, without incurring a high cost or use of a large-scale facility. The method for removing manganese according to the present invention comprises adding a sulfiding agent to a leachate generated by acid leaching a nickel oxide ore containing at least nickel and manganese to obtain a nickel-containing sulfide and a post-sulfidation liquid, and thereafter, removing manganese from the post-sulfidation liquid from which the sulfide has been separated, wherein the post-sulfidation liquid is neutralized by adding an alkali thereto to generate neutralization precipitates and a post-neutralization liquid, and sludge that is generated in a pipe for discharging the post-neutralization liquid is added to and mixed with, through stirring, the post-neutralization liquid from which the neutralization precipitates have been separated.

Description

The present invention relates to a method for removing manganese, which is a method for efficiently removing manganese from discharged water (post-sulfidation liquid) generated in a hydrometallurgical process of a nickel oxide ore .

BACKGROUND ART

In a process (HPAL process) of extracting valuable components such as nickel by adding an acid such as sulfuric acid to a nickel oxide ore at a high temperature and a high pressure, then separating impurities from the leachate obtained, and recovering nickel, impurities such as iron, aluminum, manganese, magnesium, and calcium contained in the nickel oxide ore of a raw material are present in the discharged water obtained after nickel recovery. Among these impurities, iron (suspended particles containing iron oxide as a main component), aluminum, and manganese are generally mentioned as components which are required to be removed by discharged water treatment.

Among these, aluminum forms precipitates of hydroxide in a relatively low pH region and can be thus efficiently removed. In addition, iron can be completely settled and removed by settling the suspended particles in a thickener and the like and then releasing the supernatant obtained to the tailings dam and the like to pass therethrough.

However, manganese is present in a state of being dissolved in the discharged water and is thus required to be removed by adjusting the pH of the discharged water to 9 or higher by adding an alkali thereto or forming a precipitate in the form of manganese dioxide by adding an oxidizing agent to the discharged water.

Generally, in the wet treatment of nickel oxide ore, the amount of discharged water to be generated is great, and the treatment is performed in a reducing atmosphere. Hence, for example, upon the removal of manganese by oxidation, it is not realistic to oxidize the discharged water with an oxidizing agent such as sodium hypochlorite or ozone since high cost is required.

For this reason, in general, manganese is settled and removed in the form of manganese hydroxide by adjusting the pH of the discharged water to 9 or higher. However, in that case, magnesium contained in a large amount in the discharged water forms a hydroxide first and the alkali is consumed to form a hydroxide of magnesium when an alkali, which is a neutralizer, is added to raise the pH, and it is thus required to add the alkali in an amount to be more than the amount of manganese and this causes an increase in cost.

Hence, an attempt to be called an oxidation and neutralization method has been made in which oxidation is performed while maintaining the pH constant by positively oxidizing the discharged water containing manganese and removing the manganese at a lower pH. According to such a method, the amount of neutralizer can be decreased.

For example, Patent Document 1 discloses a method for preferentially removing manganese from a manganese acidic solution containing magnesium by an oxidation and neutralization method. Specifically, a method for preferentially precipitating and removing manganese by adjusting the manganese acidic solution containing magnesium with air, oxygen, ozone or a peroxide so that the redox potential (mV) of the solution becomes from 10 mV to 500 mV as well as setting the pH of the solution to from 8.2 to 8.8 is disclosed upon the removal of manganese as a precipitate from a manganese acidic solution containing magnesium.

However, in a case in which such an oxidation and neutralization method is applied to the treatment of discharged water generated through the HPAL process, the postsulfidation liquid to be the target of discharged water treatment exhibits a strong reducing atmosphere, and there is thus a problem that cost and labor increase by re-oxidation.

In addition, as a method for removing manganese, a method by bio-oxidation using manganese-oxidizing bacteria is also known. For example, Non-Patent Documents 1 to 5 disclose bacteria such as the genera Bacillus, Hyphomicrobium, Magnetospirillum, Pseudomonas, and Geobacter as the bacteria which oxidize manganese. However, it is difficult to identify and feed the bacteria which exert an effect in the oxidation removal of manganese.

In addition, in the oxidation treatment using manganeseoxidizing bacteria, these bacteria are considered to complexly proliferate and form sludge in a mutually complementary relationship, it takes a greatly long treatment time and an excessive load to treat discharged water containing manganese at a high concentration only using manganese-oxidizing bacteria, the scale of facility required is also great, and this increases the cost.

Patent Document 1: Japanese Unexamined Patent Application, Publication No. H09-248576

Non-Patent Document 1: Enzymatic Manganese (11) Oxidation by Metabolically Dormant Spores of Diverse Bacillus Species ; Chris A. Francis and Bradley M. Tebo , Appl. Environ. Microbiol. February 2002, 68:2 874-880;

doi:10.1128/AEM.68.2.874-880.2002

Non-Patent Document 2: Enzymatic Manganese (11) Oxidation by a Marine α-Proteobacterium ; Chris A. Francis, Edgie-Mark Co, and Bradley M. Tebo , Appl. Environ. Microbiol. September 2001; 67:9 4024-4029; doi:10.1128/AEM.67.9.4024-4029.2001 Non-Patent Document 3: Reduced inorganic sulfur oxidation supports autotrophic and mixotrophic growth of Magnetospirillum strain J10 and Magnetospirillum gryphiswaldense ; Jeanine S. Geelhoedl,Robbert

Kleerebezeml, Dimitry Y. Sorokinl,Alfons J. M. Stams and Mark C. M. Van Loosdrecht , Environmental Microbiology Volume 12, Issue 4, pages 1031-1040, April 2010

Non-Patent Document 4: A Multicopper Oxidase Genes from

Diverse Μη(II)-Oxidizing and Non-Mn(II)-OxidizingPseudomonas Strains Chris A. Francis and Bradley M. Tebo Appl. Environ. Microbiol. September 2001 ; 67:9 4272-4278

Non-Patent Document 5: Going Wireless: Fe(III) Oxide Reduction without Pili by Geobacter sulfurreducens Strain JS-1 ; Jessica A. Smith, Pier-Luc Tremblay, Pravin Malla Shrestha, Oona L. Snoeyenbos-West, Ashley E. Franks, Kelly P. Nevin, and Derek R. Lovley ; Appl. Environ. Microbiol. July 2014; 80:14 4331-4340; Accepted manuscript posted online 9 May 2014

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The present invention has been proposed in view of the circumstances described above, and an object thereof is to provide a method for removing manganese, which can efficiently remove manganese contained in discharged water generated in an HPAL process while effectively decreasing the amount of a chemical agent such as a neutralizer used therein without incurring a high cost or use of a large-scale facility.

Means for Solving the Problems

The present inventors have conducted intensive investigations to solve the problem described above. As a result, it has been found out that it is possible to efficiently remove manganese by adding sludge generated in the pipe to be used to release the discharged water to the discharged water and stirring and mixing these together without increasing the amount of a chemical agent such as a neutralizer as in the prior art, whereby the present invention has been completed.

(1) A first aspect of the present invention is a method for removing manganese, the method including adding a sulfiding agent to a leachate generated by subjecting a nickel oxide ore containing at least nickel and manganese to acid leaching to obtain a nickel-containing sulfide and a postsulfidation liquid and then removing manganese from the postsulfidation liquid from which the sulfide has been separated, in which the post-sulfidation liquid is neutralized by adding an alkali to the post-sulfidation liquid to generate a neutralization precipitate and a post-neutralization liquid and sludge that is generated in a pipe for draining the postneutralization liquid is added to and mixed with, through stirring, the post-neutralization liquid from which the neutralization precipitate has been separated.

(2) A second aspect of the present invention is the method for removing manganese according to the first aspect, in which the pipe is a drainage channel pipe in which manganese-oxidizing bacteria exist and the sludge contains the manganese-oxidizing bacteria.

(3) A third aspect of the present invention is the method for removing manganese according to the first or second aspect, in which a pH is adjusted to a range of 8.0 or higher and lower than 9.0 by addition of the alkali in the neutralization treatment of the post-sulfidation liquid.

(4) A fourth aspect of the present invention is the method for removing manganese according to any one of the first to third aspects, in which the sludge is added to and brought into contact with the post-neutralization liguid for 4 hours or longer.

(5) The fifth aspect of the present invention is the method for removing manganese according to any one of the first to fourth aspects, in which an amount of the sludge added to the post-neutralization liguid is from 50 to 500 times an amount of manganese contained in the postneutralization liguid obtained after the neutralization treatment.

(6) The sixth aspect of the present invention is the method for removing manganese according to any one of the first to fifth aspects, in which the post-neutralization liguid and the sludge are stirred and mixed at a temperature of 35°C or higher and 60°C or lower.

Effects of the Invention

According to the present invention, manganese contained in discharged water generated through an HPAL process can be efficiently removed while effectively decreasing the amount of a chemical agent such as a neutralizer used therein.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a graph which shows the transition of a concentration of manganese in a post-neutralization liguid with respect to the time passed after sludge containing manganese-oxidizing bacteria has been added to the post8 neutralization liquid.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, specific embodiments of the present invention (hereinafter, referred to as the present embodiments) will be described in detail. It should be noted that the present invention is not limited to the following embodiments and various modifications can be made without changing the gist of the present invention.

The method for removing manganese according to the present embodiment is a method for removing manganese from discharged water containing manganese. The discharged water is a post-sulfidation liquid to be drained after the separation and recovery of nickel by a sulfidation treatment in a hydrometallurgical process (hereinafter also referred to as the HPAL process) in which an acid such as sulfuric acid is added to a nickel oxide ore containing at least nickel and manganese and a leaching treatment is performed at a high temperature and a high pressure to recover nickel.

Specifically, the method for removing manganese according to the present embodiment is a method for removing manganese in which manganese is removed from the post-sulfidation liquid after separation of nickel in the HPAL process as described above and includes a step (pH adjustment step) of neutralizing the post-sulfidation liquid by adding an alkali to the postsulfidation liquid to generate a neutralization precipitate and a post-neutralization liquid and a step (sludge mixing step) of adding and stirring sludge that is generated in a pipe for draining the post-neutralization liquid to the postneutralization liquid from which the neutralization precipitate has been separated.

Here, in the HPAL process of a nickel oxide ore, nickel is recovered as a sulfide by subjecting a slurry of nickel oxide ore containing at least nickel and manganese to a leaching treatment to generate a leachate and then adding a sulfiding agent such as hydrogen sulfide gas to the leachate to perform a sulfidation treatment. Incidentally, the leachate can be appropriately subjected to a neutralization treatment (first neutralization treatment) to separate and remove impurities and the post-neutralization liquid obtained can be subjected to a sulfidation treatment.

Meanwhile, the post-sulfidation liquid obtained after the separation and recovery of a sulfide of nickel contains manganese and impurities such as magnesium and aluminum, and a neutralization treatment is performed to remove the impurity components when draining the water. Incidentally, the neutralization treatment of this post-sulfidation liquid is a so-called discharged water treatment and is the final neutralization treatment before drainage and thus is also called a final neutralization treatment.

The post-sulfidation liquid is a solution obtained by adding a sulfiding agent to the leachate and subjecting the leachate to a sulfidation treatment and is thus a relatively strongly reducing solution. Hence, in the case of conventionally adding an oxidizing agent to the postsulfidation liquid to separate and remove manganese as a precipitate in the form of manganese dioxide as in the prior art, the amount of oxidizing agent used for the oxidation is great and the treatment cost is thus great. In addition, the post-sulfidation liquid often contains magnesium together with manganese, thus the alkali is preferentially used for the formation of a hydroxide of magnesium, and a large amount of neutralizer is required to finally separate and remove the entire amount of manganese only by the neutralization treatment in which the pH is adjusted using a neutralizer such as an alkali.

On the other hand, in the method for removing manganese according to the present embodiment, an alkali is added to the post-sulfidation liquid of the target of treatment, a neutralization treatment of the post-sulfidation liquid is performed, manganese which can be separated only by pH adjustment based on the neutralization treatment is removed to roughly decrease the manganese content to a certain extent, then a specific sludge is added to the post-sulfidation liquid, and the mixture is subjected to a stirring treatment. According to such a method, manganese can be efficiently separated and removed from the post-sulfidation liquid which is discharged water while effectively suppressing the amount of a chemical agent such as a neutralizer used therein.

[pH adjustment step]

In the method for removing manganese according to the present embodiment, a treatment of neutralizing the postsulfidation liquid of the target of treatment by adding an alkali to the post-sulfidation liquid and adjusting the pH of the solution to generate a neutralization precipitate and a post-neutralization liquid is performed. Incidentally, this step is called a pH adjustment step.

In the pH adjustment step, pH adjustment is performed by adding an alkali to the post-sulfidation liquid containing manganese to roughly separate and remove manganese which can be separated only by the pH adjustment and thus to decrease the manganese content in the post-sulfidation liquid as described above. In addition, it is possible to separate and remove the impurity components such as magnesium contained in the post-sulfidation liquid together with manganese by the treatment in this pH adjustment step.

Specifically, in the pH adjustment step, the pH of the solution is preferably adjusted to a range of 8.0 or higher and lower than 9.0 by adding an alkali to the post-sulfidation liquid. In this pH adjustment step, the solution is not neutralized up to a pH range of higher than 9.2 in which manganese contained in the post-sulfidation liquid can be practically completely separated but the pH of the postsulfidation liquid is rather preferably adjusted and controlled to a range of about 8.0 or higher and lower than 9.0 in which a small amount of manganese remains in the discharged water. In such a pH range, the pH of the postsulfidation liquid can be easily controlled by addition of a small amount of neutralizer and manganese can also be removed to a proper extent.

Here, when the pH of the post-sulfidation liquid is adjusted to 9.0 or higher, manganese is completely separated and removed, but a significantly large amount of alkali (neutralizer) is required as in the prior art, and it is impossible to perform an efficient manganese removal treatment. On the other hand, when the pH of the post-sulfidation liquid is adjusted to lower than 8.0, the amount of neutralizer required decreases, but the residual amount of manganese contained in the post-sulfidation liquid after being subjected to the pH adjustment increases, and there is the possibility that a sufficient amount of manganese cannot be removed when removing manganese by a mixing treatment with sludge to be described later.

The alkali (neutralizer) to be added in the pH adjustment is not particularly limited but slurries of slaked lime, limestone and the like can be used. In the present embodiment, as the range of pH adjusted is set to preferably a range of 8.0 or higher and lower than 9.0, it is possible to effectively decrease the amount of neutralizer used than in the prior art and to perform an efficient treatment.

[Sludge mixing step]

Next, in the method for removing manganese according to the present embodiment, a specific sludge is added to and mixed with the post-neutralization liquid obtained by the neutralization treatment and the stirring treatment of the mixture is performed. Incidentally, the post-neutralization liquid to which sludge is to be added is a solution obtained after separation and removal of the neutralization precipitate generated by the neutralization treatment. In addition, this step is called a sludge mixing step.

(Specific treatment)

Specifically, in the sludge mixing step, sludge generated in a pipe for draining the post-neutralization liquid obtained after the discharged water treatment is added to the postneutralization liquid accommodated in a predetermined reaction vessel and the mixture is stirred and mixed by a batch operation .

Here, the pipe for draining the post-neutralization liquid is a drainage channel pipe for releasing water after the discharged water treatment and is, for example, a pipe which having a length of 3 km or longer and manganeseoxidizing bacteria existing on the surface thereof. Manganeseoxidizing bacteria exist as a water channel deposit on the surface of the drainage channel pipe for releasing the treated solution after the discharged water treatment of the postsulfidation liquid obtained through the HPLA process.

Hence, the sludge generated in the pipe for draining the post-neutralization liquid refers to sludge containing manganese-oxidizing bacteria. Moreover, in the present embodiment, the sludge containing such manganese-oxidizing bacteria is added to the post-neutralization liquid obtained after the neutralization treatment described above, and the manganese remaining in the post-neutralization liquid is separated and removed by being precipitated by the oxidation action of manganese-oxidizing bacteria.

Manganese-oxidizing bacteria are a general term for microorganisms having the ability to oxidize manganese. Specifically, the manganese-oxidizing bacteria are not particularly limited, and examples thereof may include the genera Hyphomicrobium, Magnetospirillum, Geobacter, Bacillus, and Pseudomonas. Discharged water such as the post-sulfidation liquid drained through the HPAL process contains various salts, and the interior of the drainage channel pipe is in an environment in which manganese-oxidizing bacteria can favorably proliferate as such discharged water passes through the drainage channel pipe.

It is preferable that such a drainage channel pipe further contains essential nutrient salts and the like for the manganese-oxidizing bacteria so that the manganese-oxidizing bacteria can efficiently proliferate. In addition, the existence proportion (concentration) of the manganeseoxidizing bacteria in the drainage channel pipe is preferably a high concentration of, for example, about from 100 mg/L to 1000 mg/L.

When the post-sulfidation liquid (discharged water) begins to pass through the drainage channel pipe so that the manganese-oxidizing bacteria have not sufficiently proliferated in the drainage channel pipe, the manganese load in the discharged water is increased, and the like, it is preferable to increase the concentration of manganese in the discharged water to be supplied to the drainage channel pipe by approximately 1 mg/L per month and to gradually apply the manganese load to the manganese-oxidizing bacteria existing in the drain by gradually decreasing the set pH value of the discharged water to pass through the drainage channel pipe from lower than 9.0. This makes it possible to efficiently propagate the manganese-oxidizing bacteria in the drain and to generate a film of manganese-oxidizing bacteria which perform manganese oxidation, a so-called biofilm, on the inner wall surface of the drainage channel pipe.

Incidentally, in specific Examples of the present invention, manganese-oxidizing bacteria sampled from the drainage channel pipe of a discharged water treatment facility of a smelter operated in Palawan island, Philippines are cultured and subjected to the test as to be described later, but the manganese-oxidizing bacteria which can be used are not limited to manganese-oxidizing bacteria sampled from such a specific production site.

(Mixing treatment of post-neutralization liquid with sludge)

In the present embodiment, the sludge generated in a pipe for draining the post-neutralization liquid, namely the sludge containing manganese-oxidizing bacteria is added to the postneutralization liquid accommodated in a predetermined reaction vessel, and these are stirred and mixed together as described above .

The method for adding sludge to the post-neutralization liquid is not particularly limited, but for example, a certain amount of post-neutralization liquid is charged into a predetermined reaction vessel and then a slurry of sludge having a predetermined concentration is charged and added thereto as described above.

The amount of sludge added is determined depending on the concentration of manganese remaining in the postneutralization liquid, but roughly the sludge is added preferably in an amount to be from 50 times to 500 times, more preferably in an amount to be from 80 times to 200 times, and particularly preferably in an amount to be 100 times the amount of manganese contained in the post-neutralization liquid before being subjected to the addition of sludge. Incidentally, the amount to be from 50 times to 500 times the amount of manganese in the post-neutralization liquid herein means to add a slurry of sludge having a concentration of from 50 g/L to 500 g/L, for example, in cases in which the concentration of manganese contained in the postneutralization liquid is 1 g/L.

It is not preferable that the amount of sludge added is more than 500 times the amount of manganese from the viewpoint of cost and efficiency such as securing of sludge and labor for handling the sludge since a large amount of sludge added is required although the effect of removing manganese is not further improved. On the other hand, when the amount of sludge added is less than 50 times the amount of manganese, there is a case in which the amount of manganese removed by the sludge is significantly small and there is the possibility that manganese is not sufficiently removed.

As one of the specific treatment methods, stirring and mixing are performed by a batch operation as described above. At this time, the concentration of manganese in the postneutralization liquid containing manganese gradually decreases by the stirring and mixing with the sludge, but the rate at which the concentration of manganese decreases generally decreases with the passage of treatment time. As the contact time between the post-neutralization liquid and the sludge is extended, the concentration of manganese in the postneutralization liquid decreases, that is, the amount of manganese removed increases, but the effect becomes constrictive when the contact time exceeds 10 hours or longer. Hence, the upper limit value of the treatment time is preferably 10 hours or shorter.

Here, Fig. 1 is a graph which shows the transition of the concentration of manganese in the post-neutralization liquid with respect to the time passed after the sludge containing manganese-oxidizing bacteria has been added to the postneutralization liquid, namely, the treatment time. Incidentally, the test conditions and the like will be described in Example 1. As shown in this Fig. 1, it can be seen that the concentration of manganese in the postneutralization liquid rapidly decreases at the initial stage at which the addition and mixing of sludge is started but the rate of a decrease in the concentration of manganese gradually becomes slower along with the passage of treatment time. For such a reason, in order to efficiently remove manganese, it is preferable to terminate the treatment by the sludge and to add fresh sludge to the post-neutralization liguid after a predetermined amount of sludge is added to and brought into contact with the post-neutralization liguid for a certain time, and this makes it possible to perform a more efficient treatment.

As shown in Fig. 1, a further effect is not obtained even if the reaction is continuously performed for longer than 10 hours. On the other hand, when the reaction time is too short, there is the possibility that the effect by sludge mixing is minor and manganese is not sufficiently removed. The concentration of manganese in the post-neutralization liguid (discharged water) intended before release is, for example, 6 mg/L or less, thus the time (reaction time) for which the sludge is added to and brought into contact with the postneutralization liguid is preferably set to 4 hours or longer, and this makes it possible to perform an efficient treatment having a reaction rate of 80% or more. Incidentally, the contact time is particularly preferably set to from 4 hours to 6 hours .

In addition, the liguid temperature (water temperature) when the sludge is added to the post-neutralization liguid and the sludge and the post-neutralization liguid are stirred and mixed together may be room temperature (normal temperature) around 25°C, but the reaction rate is slow at this temperature, and it is thus preferable to perform the treatment at a temperature condition of 35°C or higher and 60°C or lower. By performing stirring and mixing under such a condition of liquid temperature, the reaction efficiency can be increased and the manganese removal efficiency in a short time is increased. In addition, a temperature condition of 40°C or higher and 55°C or lower is more preferably set.

As described above, the sludge contains manganeseoxidizing bacteria. Manganese-oxidizing bacteria are one of general kinds of bacteria, and thus there is the possibility that the proteins constituting the bacteria are altered and the proliferation and reaction efficiency are suppressed, for example, when the reaction is performed under a temperature condition of a high temperature exceeding 60°C. Consequently, the liquid temperature upon the reaction is set to preferably 60°C or lower and more preferably 55°C or lower.

As a method for adjusting the liquid temperature of the post-neutralization liquid, for example, it is possible to utilize various methods such as a method in which heating is performed using fossil fuel and a heat exchanger, a method in which heating is performed by operating a heat exchanger by electric power and other powers, a method in which solar heat is utilized, a method in which geothermal heat and other plant heat sources are utilized, and a method in which heat sources by biological fermentation are utilized. As described above, the method for adjusting the liquid temperature is not particularly limited as long as a heat source for raising the temperature or maintaining the temperature can be secured.

However, when the industrial scale is considered, generally the amount of post-neutralization liquid to be drained as discharged water is extremely large, and a large amount of heat energy is required to keep the water temperature high. For this reason, it is not advisable to raise the temperature to an excessively high temperature and to consume a large amount of heat energy.

[Release treatment]

As described above, after the sludge has been added to the post-neutralization liquid in the reaction vessel to separate and remove manganese, the post-neutralization liquid after being subjected to the treatment is allowed to pass through the drainage channel pipe and drained (released). Specifically, after the treatment in which the concentration of manganese in the post-neutralization liquid is decreased to 6 mg/L or less by bringing the post-neutralization liquid into contact with the sludge has been performed, the postneutralization liquid after being subjected to the treatment is released via the drainage channel pipe.

At this time, the post-neutralization liquid to pass through the drainage channel pipe passes through the pipe and flows toward the outfall through which the liquid is released to the sea area and the like, but a biofilm of manganeseoxidizing bacteria is formed on the inner wall surface of the drainage channel pipe as described above, and thus manganese is finally completely removed to a concentration of 1 mg/L or less than 1 mg/L as the liquid passes through the drainage channel pipe.

The retention time of the post-neutralization liquid when passing through the drainage channel pipe corresponds to the reaction time in the treatment in the pipe, thus the retention time in the drainage channel pipe may be determined from the required reaction time, and the length and inner diameter of the pipe satisfying this time may be determined. For example, the length of drainage channel pipe is preferably 3 km or longer, and it is preferable to perform the discharged water treatment so that the post-neutralization liquid passes through the drainage channel pipe having such a length for a retention time of 1 hour or longer.

EXAMPLES

Hereinafter, the present invention will be more specifically described with reference to Examples, but the present invention is not limited to the following Examples at all.

<1. Verification of method for removing manganese>

[Example 1]

A hydrometallurgical process was performed to recover valuable metals such as nickel from a leachate obtained by subjecting a slurry of nickel oxide ore containing at least nickel and manganese to acid leaching using sulfuric acid at a high temperature and a high pressure by adding a sulfiding agent to the leachate. Thereafter, the post-sulfidation liquid obtained by the sulfidation treatment was used as a drainage source liquid, and an operation was performed to remove manganese contained in the drainage source liquid.

Incidentally, in the present Example, manganese-oxidizing bacteria sampled from the inner wall of the drainage channel pipe of the discharged water treatment facility in the hydrometallurgical plant for nickel oxide ore of Coral Bay Nickel Corporation located in Rio Tuba, Bataraza, Palawan 5306, Philippines were used.

(pH adjustment step)

First, a slurry of slaked lime was added to the postsulfidation liquid, a neutralization treatment to adjust the pH of the solution to 8.0 was performed, and a neutralization precipitate containing magnesium, a trace amount of manganese and the like and a post-neutralization liquid were thus generated. Thereafter, the neutralization precipitate was separated from the post-neutralization liquid by solid-liquid separation. At this time, the concentration of manganese contained in the post-neutralization liquid obtained was 10 mg/L .

(Sludge mixing step)

Next, the sludge which was attached to and generated on the inner wall of the drainage channel pipe for draining the post-neutralization liquid to the outfall was stripped off and collected, and the sludge was prepared as sludge for addition. Incidentally, it has been confirmed that manganese-oxidizing bacteria exist in this sludge.

Specifically, DNA analysis was performed using a test sample of the inner wall of the drainage channel pipe, and as a result, it has been confirmed that among 3,776 known base sequences thus detected, the number of base sequences of bacteria likely to be manganese-oxidizing bacteria is 975, the number of base sequences of other bacteria is 2,801, at least one-fourth of the identified DNA is manganese-oxidizing bacteria, and manganese-oxidizing bacteria exist on the inner wall of the pipe. As manganese-oxidizing bacteria, the presence of bacteria of the genera Hyphomicrobium, Magnetospirillum, Geobacter, Bacillus, and Pseudomonas has been confirmed. Incidentally, the known base sequences refer to the base sequences of bacteria registered in the database upon the DNA analysis.

Thereafter, the post-neutralization liquid obtained in the pH adjustment step was charged into a reaction vessel, the sludge for addition prepared was added to the postneutralization liquid as a slurry having a slurry concentration of 1 g/L (corresponding to an amount to be 100 times the amount of manganese contained in the postneutralization liquid), and these were stirred and mixed together at normal temperature for 4 hours.

Fig. 1 is a graph which shows the transition of the concentration of manganese in the post-neutralization liquid with respect to the treatment time (contact time with sludge) in Example 1, and the concentration of manganese in the postneutralization liquid decreased to approximately 6 mg/L by the hours of stirring treatment after the addition and mixing. In addition, the concentration of manganese decreased to 5.5 mg/L when the stirring was further continuously performed for 6 hours .

(Release treatment)

The post-neutralization liquid, in which the concentration of manganese decreased to 6 mg/L by the treatment described above, was allowed to flow through the drainage channel pipe having a length of 10 km to the outfall. As a result, the concentration of manganese was decreased to less than 1 mg/L when the concentration of manganese in the post-neutralization liquid in the vicinity of the outfall was measured.

[Example 2]

In the same manner as in Example 1, the post-sulfidation liquid was subjected to the treatment in the pH adjustment step and then a slurry of sludge having a concentration of 1 g/L was added to the post-neutralization liquid obtained.

The concentration of manganese at the time point at which stirring and mixing were performed for 3 minutes and the time point at which stirring and mixing were performed for 0.5 hour was measured while performing stirring at normal temperature, and as a result, the concentration of manganese was 9.7 mg/L and 8.0 mg/L, respectively. Thereafter, the stirring and mixing time was further extended to 2 hours. As a result, the concentration of manganese in the post-neutralization liquid was 7.3 mg/L.

From the results in Example 2, it has been found that it is possible to perform an efficient treatment so as to decrease the amount of neutralizer used. However, based on the results in Example 1, it has been found that the contact time (reaction time in stirring and mixing) of the postneutralization liquid and the sludge is preferably 4 hours or longer .

[Example 3]

After the post-sulfidation liquid was subjected to the treatment in the pH adjustment step, a slurry of sludge having a concentration of 0.1 g/L (corresponding to an amount to be 10 times the amount of manganese contained in the postsulfidation liquid) was added to the post-neutralization liquid obtained in Example 3.

These were stirred and mixed together at normal temperature for 4 hours. As a result, the concentration of manganese in the post-neutralization liquid was 9.7 mg/L.

From the results in Example 3, it has been found that it is possible to separate and remove manganese by an efficient treatment to decrease the amount of neutralizer used. However, the effect of decreasing manganese was less as compared with the results in Example 1.

[Comparative Example 1]

In the same manner as in Example 1, the post-sulfidation liquid obtained by the hydrometallurgical treatment of nickel oxide ore was subjected to the pH adjustment step, a slaked lime slurry was additionally and continuously added to the post-neutralization liquid obtained, and the treatment was thus performed to raise the pH from 8.0 to 8.6.

As a result, the concentration of manganese in the solution obtained after the treatment was decreased to 6 mg/L or less. However, the treatment cost increased by the amount of slaked lime of a neutralizer added, and it was impossible to perform an efficient treatment.

<2. Verification of temperature condition upon manganese removal/ [Example 4]

A nickel oxide ore was treated by the HPAL process in the same manner as in Example 1, and a post-sulfidation liquid (discharged water) having a concentration of manganese of 100 mg/L was obtained. In order to verify the temperature condition upon the reaction with sludge containing manganeseoxidizing bacteria, the discharged water thus obtained was charged into a vessel as it was, sludge containing manganeseoxidizing bacteria was added to this vessel, and the mixture was allowed to react. Incidentally, the sludge added was sludge which was attached to and generated on the inner wall of the drainage channel pipe for draining the discharged water to the outfall in the same manner as in Example 1, and this sludge was added as a slurry having a slurry concentration of 10 g/L (concentration corresponding to 100 g/L per 1 g/L of concentration of manganese contained in the discharged water).

At this time, stirring and mixing were performed for 4 hours while adjusting and maintaining the liquid temperature of the discharged water at 40°C.

As a result, the concentration of manganese in the aqueous solution decreased to 40 mg/L.

[Example 5]

In the same manner as in Example 4, the sludge was added to the discharged water having a concentration of manganese of 100 mg/L as a slurry having a slurry concentration of 10 g/L, and the mixture was allowed to react. At this time, stirring and mixing were performed for 4 hours while adjusting and maintaining the liquid temperature of the discharged water at 50°C.

As a result, the concentration of manganese in the aqueous solution decreased to 20 mg/L.

[Comparative Example 2]

In the same manner as in Example 4, the sludge was added to the discharged water having a concentration of manganese of 100 mg/L as a slurry having a slurry concentration of 10 g/L, and the mixture was allowed to react. At this time, stirring and mixing were performed for 4 hours while adjusting and maintaining the liquid temperature of the discharged water at 5°C.

As a result, the concentration of manganese in the aqueous solution merely dropped to about 55 mg/L and the reaction efficiency was thus decreased as compared with those in Examples 4 and 5 in which the discharged water was brought into contact with the sludge under relatively high temperature conditions .

[Comparative Example 3]

In the same manner as in Example 4, the sludge was added to the discharged water having a concentration of manganese of 100 mg/L as a slurry having a slurry concentration of 10 g/L, and the mixture was allowed to react. At this time, stirring and mixing were performed for 4 hours while adjusting and maintaining the liquid temperature of the discharged water at 20°C.

As a result, the concentration of manganese in the aqueous solution merely dropped to about 50 mg/L and the reaction efficiency was thus decreased as compared with those in Examples 4 and 5 in which the discharged water was brought into contact with the sludge under relatively high temperature conditions .

Claims (6)

1. A method for removing manganese, the method comprising adding a sulfiding agent to a leachate generated by subjecting a nickel oxide ore containing at least nickel and manganese to acid leaching to obtain a nickel-containing sulfide and a post-sulfidation liquid and then removing manganese from the post-sulfidation liquid from which the sulfide has been separated, wherein the post-sulfidation liquid is neutralized by adding an alkali to the post-sulfidation liquid to generate a neutralization precipitate and a post-neutralization liquid, and sludge that is generated in a pipe for draining the postneutralization liquid is added to and mixed with, through stirring, the post-neutralization liquid from which the neutralization precipitate has been separated.

2. The method for removing manganese according to claim 1, wherein the pipe is a drainage channel pipe in which manganese-oxidizing bacteria exist, and the sludge contains the manganese-oxidizing bacteria.

3. The method for removing manganese according to claim 1 or

2, wherein a pH is adjusted to a range of 8.0 or higher and lower than 9.0 by addition of the alkali in the neutralization treatment of the post-sulfidation liquid.

4. The method for removing manganese according to any one of claims 1 to 3, wherein the sludge is added to and brought into contact with the post-neutralization liquid for 4 hours or longer .

5. The method for removing manganese according to any one of claims 1 to 4, wherein an amount of the sludge added to the post-neutralization liquid is from 50 to 500 times an amount of manganese contained in the post-neutralization liquid obtained after the neutralization treatment.

6. The method for removing manganese according to any one of claims 1 to 5, wherein the post-neutralization liquid and the sludge are stirred and mixed at a temperature of 35°C or higher and 60°C or lower.