AU2017362828B2 - 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

METHOD FOR REMOVING MANGANESE TECHNICAL FIELD

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 post

sulfidation 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 manganese

oxidizing 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(II) 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(II) Oxidation by a

Marine a-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 Mn(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 aim 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 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,

wherein sludge that contains manganese-oxidizing bacteria and

that is generated in a pipe which is for draining the post

neutralization liquid and in which the manganese-oxidizing

bacteria exist is added to and mixed with, through stirring,

the post-neutralization liquid from which the neutralization

precipitate has been separated, and wherein the sludge is

brought into contact with the post-neutralization liquid for 4

to 6 hours.

(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,

6A

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 liquid 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 liquid is from 50 to 500

times an amount of manganese contained in the post

neutralization liquid 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

liquid and the sludge are stirred and mixed at a temperature

of 350C or higher and 600C 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 liquid

with respect to the time passed after sludge containing

manganese-oxidizing bacteria has been added to the post- 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 post

sulfidation 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 post neutralization 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 post sulfidation 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 post sulfidation 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 post

sulfidation 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 post

sulfidation 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 post

neutralization 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 manganese

oxidizing bacteria existing on the surface thereof. Manganese

oxidizing 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 post

sulfidation 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 manganese

oxidizing 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 post

neutralization 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 post

neutralization 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

g/L to 500 g/L, for example, in cases in which the

concentration of manganese contained in the post

neutralization 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 post

neutralization 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 post

neutralization 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 post

neutralization 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 post

neutralization 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 liquid after a predetermined amount of sludge is added to and brought into contact with the post-neutralization liquid 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 liquid

(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 post

neutralization liquid 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 liquid temperature (water temperature)

when the sludge is added to the post-neutralization liquid and

the sludge and the post-neutralization liquid are stirred and

mixed together may be room temperature (normal temperature)

around 250C, but the reaction rate is slow at this temperature, and it is thus preferable to perform the treatment at a temperature condition of 350C or higher and 600C 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 400C or higher and 550C or lower is more preferably set.

As described above, the sludge contains manganese

oxidizing 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 600C. Consequently,

the liquid temperature upon the reaction is set to preferably

600C or lower and more preferably 550C 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 post

neutralization 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 manganese

oxidizing 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 post

sulfidation 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 post

neutralization 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 post

neutralization 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 post

neutralization liquid decreased to approximately 6 mg/L by the

4 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 post

neutralization 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

times the amount of manganese contained in the post

sulfidation 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 manganese

oxidizing bacteria, the discharged water thus obtained was

charged into a vessel as it was, sludge containing manganese

oxidizing 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

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 400C.

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

500C.

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

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 31

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

200C.

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.

The reference in this specification to any prior

publication (or information derived from it), or to any matter

which is known, is not, and should not be taken as, an

acknowledgement or admission or any form of suggestion that

prior publication (or information derived from it) or known

matter forms part of the common general knowledge in the field

of endeavour to which this specification relates.

Throughout this specification and the claims which follow,

unless the context requires otherwise, the word "comprise",

and variations such as "comprises" or "comprising", will be

understood to imply the inclusion of a stated integer or step

or group of integers or steps but not the exclusion of any

other integer or step or group of integers or steps.

Claims (9)

The claims defining the invention are as follows:

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,

wherein sludge that contains manganese-oxidizing bacteria

and that is generated in a drainage channel pipe which is for

draining the post-neutralization liquid and in which the

manganese-oxidizing bacteria exist is added to and mixed with,

through stirring, the post-neutralization liquid from which

the neutralization precipitate has been separated, and

wherein the sludge is brought into contact with the post

neutralization liquid for 4 to 6 hours.

2. The method for removing manganese according to claim 1,

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.

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

2, 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.

4. The method for removing manganese according to any one of

claims 1 to 3, wherein the post-neutralization liquid and the

sludge are stirred and mixed at a temperature of 350C or

higher and 600C or lower.

FIG. 1 10 OF MANGANESE (mg/L)

9 CONCENTRATION

8

7

6

5 0 2 4 6 8 10 12 TIME (h)

1/1