JP2017148726A - Neutralization processing method using boiler ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutralization processing method which can process effective neutralization by reducing consumption of neutralizer such as hydrated lime in a neutralization process to drain process fluid generated in a metal smelting process to outside of a system.SOLUTION: In a neutralization processing method neutralizing liquid exhausted from a metal smelting process by using boiler ash, the boiler ash contains blocking ash collected from a blast furnace bottom side of a fluid bed boiler in cinders generated in the fluid bed boiler, the cinders are generated by feeding coal, limestone and air in the fluid bed boiler and burning, and the supply of the limestone is more than a quantity necessary for desulfurization of exhaust gas generated from the fluid bed boiler.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a neutralization treatment method, and more particularly, to a neutralization treatment method that makes it possible to efficiently perform a final neutralization treatment on a process liquid discharged in a metal smelting process.

  The process liquid (process liquid) generated from the smelting process of metals such as nickel and copper contains a lot of heavy metals, and in order to discharge the process liquid into the environment (outside the system) It is necessary to perform drainage treatment (neutralization treatment) to remove and further adjust the pH to near neutrality.

  Specifically, in the neutralization treatment, the pH is raised by adding a neutralizing agent to the generated acidic process liquid, and the heavy metal contained in the liquid is solidified as a hydroxide, filtered, etc. To separate solid and liquid. The liquid out of the solid-liquid separation is discharged (drainage) or reused, while the solid containing the metal component is processed at the disposal site.

  Until now, in the neutralization treatment of the process liquid, a calcium-based neutralizing agent has been used, and limestone has been used to raise the pH to near neutrality, and slaked lime has been used to raise the pH from neutral to weakly alkaline. It was common to process. Although limestone is relatively inexpensive, slaked lime is more expensive than limestone, and the amount (necessary amount) of the neutralizing agent is to be increased as the amount of process liquid to be processed increases.

  As described above, the amount of the neutralizing agent used varies depending on the amount of the process liquid to be treated, and further on the acidity of the process liquid and the concentration of heavy metal contained therein. From the viewpoint of reduction, it is desired to reduce the use amount of the neutralizing agent, particularly to reduce the use amount of the neutralizing agent having a high unit price such as slaked lime.

In relation to the technology that uses boiler ash as a neutralizing agent, for example, Patent Document 1 discloses that a calcium-based desulfurizing agent is supplied to the empty part of a furnace or an incinerator of a combustion apparatus so that sulfur oxides in exhaust gas are reduced. A method of flue gas desulfurization to be removed is described.

  Further, Patent Document 2 discloses that the optimum limestone particles having a size that meets the sulfur content capturing conditions in the circulating fluidized bed combustion chamber are generated, and further, the sulfur content is obtained by dry scrubbing the hot gas flow from the old direct combustion boiler. Optimize the limestone particles to a particle size that can be used to capture limestone, or pack the limestone particles to a size suitable for continuous sulfur capture in the circulating fluidized bed combustion chamber, significantly reducing limestone loss A method and apparatus are described.

  In Patent Document 3, exhaust gas discharged from a boiler such as a thermal power plant is cooled by a cooling tower, and in an absorption tower, calcium sulfite is added from sulfur oxides contained in the exhaust gas cooled by the cooling tower in a limestone slurry. In order to remove sulfur oxides in the exhaust gas by generating calcium sulfate with gypsum slurry that becomes seed crystals from this calcium sulfite, the limestone slurry is supplied from the limestone slurry tank in the absorption tower circulation tank The method of supplying and applying the plaster slurry and the gypsum slurry from the centrifugal separator drain is described.

  However, Patent Documents 1 to 3 do not describe how to effectively use boiler ash generated by combustion by a boiler.

  Patent Document 4 is known as a technique using boiler ash as a neutralizing agent. Patent Document 4 describes the use of an ash-like boiler ash obtained after combustion of a fluidized bed boiler or a boiler ash slurry made into a slurry by adding water to the boiler ash as a neutralizing agent. .

  However, since such boiler ash has a smaller neutralization ability than slaked lime, a large amount is required to replace slaked lime. However, in coal boilers and fluidized bed boilers, since the amount of ash-like boiler ash generated is small, the amount of slaked lime used has not been reduced sufficiently. Patent Document 4 does not describe the type of ash suitable for neutralization or the amount of limestone added to the boiler.

Japanese Patent Laid-Open No. 06-205931 JP-A-10-026334 JP 2009-095698 A JP 2014-105367 A

  Therefore, the present invention has been made in view of the above situation, and in the neutralization treatment (final neutralization treatment) performed to discharge the process liquid generated in the metal smelting process out of the system, An object of the present invention is to provide a neutralization method that makes it possible to reduce the amount used and to perform an efficient neutralization treatment.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the massive sintered mass in the boiler ash generated in the fluidized bed boiler has a potential neutralizing ability. It was. The present inventors have intensively studied to utilize these, and by collecting and collecting incineration fly ash in the exhaust gas, the mixing and sticking of the incineration fly ash to the sintered ingot is suppressed, It was found that neutralization ability can be improved. Furthermore, the present inventors reduce the proportion of sand material used as solid particles for promoting the reaction at the bottom of the boiler by increasing the amount of limestone supplied to the boiler than the amount necessary for desulfurization of the exhaust gas, It has been found that the neutralization ability of the sintered mass can be improved.

  By using such a sintered lump as a neutralizing agent, it was found that the amount of neutralizing agent such as slaked lime used in the neutralization treatment of the process liquid can be effectively reduced, and the present invention was completed. It was.

  That is, one aspect of the present invention for achieving the above object is a neutralization method for neutralizing a liquid discharged in a metal smelting process using boiler ash, wherein the boiler ash is fluidized bed. Of the burning husk generated in the boiler, it contains massive ash collected from the bottom of the fluidized bed boiler. More than the amount necessary for desulfurization of the exhaust gas generated from the fluidized bed boiler.

  According to one aspect of the present invention, boiler ash containing bulk ash that has high Ca quality and can be easily recovered from the bottom of the boiler is used for neutralization treatment, so that boiler ash can be effectively used and a metal smelting process. Thus, the amount of slaked lime used can be reduced and efficient neutralization can be performed.

  At this time, in one embodiment of the present invention, neutralization may be performed using ash obtained by mixing boiler ash with recovered powdered ash suspended in exhaust gas.

  The powdered ash floating in the exhaust gas has a slightly lower Ca quality than the bulk ash, but can also be used effectively for neutralization by mixing with boiler ash.

  In one embodiment of the present invention, the amount of calcium contained in limestone is not less than 2.3 times and not more than 20 times the stoichiometric amount necessary to recover the sulfur content supplied to the fluidized bed boiler. There may be.

  By increasing the amount of limestone beyond the amount required for desulfurization of exhaust gas, the ratio of sand material used as solid particles for promoting the reaction at the bottom of the boiler can be reduced, and the neutralization ability of the sintered mass can be improved.

  In one embodiment of the present invention, boiler ash slurry using boiler ash as a slurry may be used as a neutralizing agent.

  By making the boiler ash into a slurry, the handling becomes easy when the neutralization treatment is performed.

  In one embodiment of the present invention, after-pulverized boiler ash obtained by pulverizing boiler ash, or boiler ash slurry obtained by pulverizing and slurrying boiler ash may be used as a neutralizing agent.

  By pulverizing the particles having a large particle size, the surface area of the boiler ash is increased and the neutralization ability can be improved.

  In one embodiment of the present invention, the boiler ash is classified into a large particle size side and a small particle size side, neutralized using the small particle size side, and the large particle size side is supplied to the fluidized bed boiler. It may be spread on the bottom.

  If it does in this way, the sand material used as solid particles (fluidized bed) for promoting reaction at the bottom of a boiler can be replaced, and Ca quality of the obtained sintered lump can be improved stably.

  In one embodiment of the present invention, the metal smelting process is a wet smelting process for recovering nickel and cobalt from nickel oxide ore, and is obtained through a leaching process, a solid-liquid separation process, a neutralization process, and a sulfurization process. Further, it may be used for neutralization treatment of the liquid after the sulfurization treatment.

  The neutralization process using boiler ash can be used suitably for the hydrometallurgical process of nickel oxide ore, for example.

  ADVANTAGE OF THE INVENTION According to this invention, in the neutralization process with respect to the process liquid generate | occur | produced in the metal smelting process, the usage-amount of a neutralizing agent can be reduced effectively and an efficient neutralization process can be performed.

It is process drawing of the hydrometallurgical process of nickel oxide ore. It is a flowchart which shows the flow which adds and neutralizes a fluidized bed boiler ash as a neutralizing agent in the final neutralization process with respect to the poor liquid generate | occur | produced in the hydrometallurgical process of nickel.

Hereinafter, specific embodiments of the neutralization treatment method according to the present invention (hereinafter referred to as “present embodiments”) will be described in detail in the following order. 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.
1. Outline 2. 2. fluidized bed boiler and its boiler ash 3. Neutralization treatment method 3-1. Method for hydrometallurgy of nickel oxide ore 3-2. Neutralization method

<1. Overview>
The neutralization treatment method according to the present embodiment is a neutralization treatment (hereinafter referred to as “final”) for discharging a process liquid (process liquid) discharged in a metal smelting process such as nickel or copper to the outside of the system. It is also referred to as “neutralization treatment”), which reduces the treatment cost and enables efficient neutralization treatment.

  Specifically, the neutralization treatment method according to the present embodiment is a boiler ash obtained after combustion of a fluidized bed boiler as a neutralizing agent, and the sulfur content derived from coal as fuel is added to limestone. It is characterized by performing neutralization treatment using boiler ash obtained by burning while desulfurizing.

  As will be described in detail later, in a fluidized bed boiler, limestone for desulfurization treatment for removing sulfur content of coal is introduced and burned together with coal as boiler fuel. Therefore, Ca derived from limestone charged for the desulfurization treatment remains in the fluidized bed boiler ash. Therefore, by using this fluidized bed boiler ash for the neutralization treatment, the process liquid can be neutralized with Ca contained in the boiler ash.

  According to such a neutralization treatment method, it is possible to effectively reduce the amount of a neutralizing agent such as slaked lime added and added in the neutralization treatment of the process liquid generated in the metal smelting process. It is possible to perform an efficient neutralization treatment.

  In addition, fluidized bed boiler ash has generally been discarded as industrial waste. At the time of disposal, since unreacted alkali remains in the boiler ash, it is necessary to perform a special treatment for neutralizing the alkali. However, as in this embodiment, by using the fluidized bed boiler ash as a neutralizing agent for the neutralization treatment for the process liquid, the amount of waste from the boiler can be reduced, and the alkali content in the boiler ash can be reduced. Can be effectively utilized, so that the processing cost required for the disposal process can be effectively reduced.

  In the husk generated in a fluidized bed boiler, the massive sintered mass in the boiler ash has a potential neutralizing ability. In the fluidized bed boiler, the main sintered mass and incineration fly ash are generated, but the incineration fly ash has a high surface area, but it has a lower Ca quality than the sintered mass and absorbs a large amount of acid gas to neutralize it. There is not much left. On the other hand, since the massive sintered ingot has a relatively high Ca quality and can be kept at the bottom of the boiler, an unreacted part may remain as a result.

  This unreacted portion can be recovered by suspending the incinerated fly ash in the exhaust gas, thereby suppressing the mixing and sticking of the incinerated fly ash to the sintered ingot and improving the neutralization ability of the sintered ingot. Furthermore, by increasing the amount of limestone supplied to the boiler, more than that required for exhaust gas desulfurization, the proportion of sand material used as solid particles to promote the reaction at the bottom of the boiler is reduced, and the sintered mass is neutralized. Ability can be improved.

  By using such a sintered lump as a neutralizing agent, the amount of neutralizing agent such as slaked lime used in the neutralization treatment of the process liquid can be effectively reduced.

<2. Fluidized bed boiler and its boiler ash>
Here, the boiler ash generated by the combustion of the fluidized bed boiler will be described in more detail. The boiler ash in the present invention refers to massive ash recovered mainly from the furnace bottom side of the fluidized bed boiler among the burning husks generated in the fluidized bed boiler, but floats in the exhaust gas of the fluidized bed boiler. Such powdery ash may be mixed. Moreover, you may use what mixed the block ash and powdered ash which were collect | recovered separately as a neutralizing agent.

  In general, boiler combustion methods using coal include, for example, a fixed bed method, a spouted bed method, and a fluidized bed method. Specifically, in the fixed bed system, the massive coal that has been charged reacts with air in a stationary state and is burned or gasified. However, this fixed bed system requires a large amount of excess air for combustion, has a limit on the scale of the apparatus because it has low boiler efficiency and is difficult to increase in size. The spouted bed method is a method in which finely pulverized coal charged into a boiler is jetted together with air and burned. This spouted bed system has good combustibility and requires less excess air, but has the limitation that pulverized coal must be used.

  On the other hand, the fluidized bed system is a system in which granular coal is injected into a fluidized bed such as silica sand that is suspended and fluidized by an air stream and burned. In this fluidized bed method, the heat transfer in the fluidized bed is good, so the boiler can be downsized, and combustion at a low temperature of about 1000 ° C. or less is possible, so it is combusted compared to the fixed bed method. There is an advantage that the NOx concentration in the gas is low and low grade coal can be used.

  In this fluidized bed type boiler (fluidized bed boiler), a Ca source is charged and mixed with coal as boiler fuel in the furnace. This Ca source is used to remove (desulfurization treatment) sulfur derived from coal, and in the furnace, coal is burned while performing desulfurization treatment, and boiler ash is generated. In addition, as a technique regarding a fluidized bed boiler, there exist some which are disclosed by patent documents 1-4, for example.

As the Ca source used for the desulfurization treatment, alkali components such as slaked lime (Ca (OH) ₂ ), quick lime (CaO), limestone (CaCO ₃ ) can be used. In order to collect the total amount of sulfur trioxide in the exhaust gas, a stoichiometric amount that converts the total amount of sulfur supplied to the boiler into gypsum (CaSO ₄ ) is necessary. For example, if CaO and Ca (OH) ₂ are used for the elemental sulfur contained in the coal, it is necessary to supply one or more times as much calcium. When supplying calcium as limestone (CaCO ₃ ), since CaCO ₃ is a neutralized salt of carbon dioxide (carbonic acid), its neutralizing ability is low, and more than 2.3 times the stoichiometric amount (molar basis). It is preferable to supply, more preferably 2.6 times or more. Calcium supplied in excess of the stoichiometric amount can be recovered as a sintered mass.

CaCO ₃ heated in the boiler is decomposed to produce CaO having a high neutralization capacity. Since the raw material for this reaction is only CaCO ₃ , if the CO ₂ partial pressure in the boiler (that is, the reverse reaction rate) is constant, more CaO can be obtained as the input amount of limestone is increased. However, in order to ensure the reaction efficiency, it is desirable to secure the reaction time (residence time) from when limestone is charged until the sintered mass is recovered and to heat the limestone to the reaction temperature. It is safe to set the amount to 20 times or less, more preferably 11.5 times or less the stoichiometric amount (molar basis) necessary for recovering the sulfur content.

  In the present embodiment, fluidized bed boiler ash is used as a neutralizing agent for a neutralization treatment (final neutralization treatment) for a process liquid generated in a metal smelting process such as nickel or copper. Thereby, Ca content in boiler ash can be effectively utilized in the neutralization process, and it becomes possible to effectively reduce the amount of neutralizer such as slaked lime to be used for the neutralization process.

The sintered ingot contains a large amount of CaO and CaCO ₃ but is baked and hardened to increase the particle size. Therefore, it is desirable to pulverize to a size suitable for the neutralizing agent to obtain a boiler ash after pulverization. For the pulverization, a known pulverization method such as a ball mill can be used. For pulverization, the maximum particle size of the boiler ash after pulverization is preferably 75 μm or less. If it is 75 micrometers or less, a neutralization reaction can be performed rapidly. The minimum particle size after pulverization is preferably 1 μm or more. If it is 1 micrometer or more, grinding | pulverization can be completed with little energy and little processing time. Even if the pulverization is performed to less than 1 μm, the time for the neutralization step is not so much reduced although the pulverization time is long. In addition, the average particle diameter as used in the field of the present invention is specifically the median diameter (D50) based on the mass by the laser diffraction method (Microtrack (registered trademark) method) or the median diameter based on the mass by the sieving method ( D50).

Classification with a cyclone or sieve separates into a small particle size side with an average particle size of 75 μm or less and a large particle size side with an average particle size of 75 μm or more, and the small particle size side is used for neutralization. A part or all of the radial side may be supplied to the boiler and spread on the bottom. By doing this, the sand material used as solid particles (fluidized bed) for promoting the reaction at the bottom of the boiler can be replaced, and the CaO quality and CaCO ₃ quality of the obtained sintered mass can be stably increased. It can be used effectively in the neutralization step. The classification may be performed before pulverization, may be performed after pulverization, or may be performed both before and after pulverization.

<3. Neutralization method>
Hereinafter, the neutralization processing method according to the present embodiment will be described more specifically. Here, the case where the neutralization treatment method according to the present embodiment is applied to the neutralization treatment for the poor liquid which is a process liquid generated in the hydrometallurgical process of nickel oxide ore will be described as an example.

<3-1. Method of hydrometallizing nickel oxide ore>
First, the outline of the hydrometallurgical process (method) of nickel oxide ore will be described. Here, a wet smelting method using a high-temperature pressure acid leaching method (HPAL method) will be described as a specific example.

  FIG. 1 is a process diagram of a hydrometallurgical smelting method by high-temperature pressure acid leaching of nickel oxide ore. As shown in FIG. 1, the nickel oxide ore hydrometallurgical method is a liquefaction process S11 in which nickel and cobalt are leached from nickel oxide ore of low nickel grade, and the leaching slurry and the leaching residue obtained from the obtained leaching slurry are solid-liquid. Solid-liquid separation step S12 for separation, neutralization step S13 for neutralizing the leachate and separating it into a mother liquor and neutralized starch slurry for nickel and cobalt recovery, and sulfurization by blowing hydrogen sulfide gas into the sulfuric acid solution as the mother liquor And a sulfiding step S14 for obtaining a mixed sulfide containing nickel and cobalt and a poor solution by performing the treatment.

(1) Leaching step In the leaching step S11, sulfuric acid is added to the nickel oxide ore slurry, and the mixture is stirred at a temperature of 220 to 280 ° C. to form a leaching slurry composed of a leaching solution and a leaching residue. In the leaching step S11, for example, a high-temperature pressurized container (autoclave) is used.

  Examples of the nickel oxide ore used in the leaching step S11 mainly include so-called laterite ores such as limonite ore and saprolite ore. The nickel content of the laterite ore is usually 0.8 to 2.5% by weight, and is contained as a hydroxide or a siliceous clay (magnesium silicate) mineral. Further, the iron content is 10 to 50% by weight and is mainly in the form of trivalent hydroxide (goethite), but partly divalent iron is contained in the siliceous clay.

Specifically, in the leaching step S11, a leaching reaction and a high-temperature thermal hydrolysis reaction represented by the following formulas (1) to (5) occurred, and leaching as sulfates such as nickel and cobalt was leached. Immobilization of iron sulfate as hematite is performed. However, since the immobilization of iron ions does not proceed completely, the leaching slurry obtained usually contains divalent and trivalent iron ions in addition to nickel, cobalt and the like.

・ Leaching reaction MO + H ₂ SO ₄ ⇒ MSO ₄ + H ₂ O (1)
(In the formula, M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn, etc.)
2Fe (OH) ₃ + 3H ₂ SO ₄ ⇒ Fe ₂ (SO ₄ ) ₃ + 6H ₂ O (2)
FeO + H ₂ SO ₄ ⇒ FeSO ₄ + H ₂ O (3)
・ High temperature thermal hydrolysis reaction 2FeSO ₄ + H ₂ SO ₄ + 1 / 2O ₂ ⇒ Fe ₂ (SO ₄ ) ₃ + H ₂ O (4)
Fe ₂ (SO ₄ ) ₃ + 3H ₂ O => Fe ₂ O ₃ + 3H ₂ SO ₄ (5)

(2) Solid-liquid separation step In the solid-liquid separation step S12, the leaching slurry formed in the leaching step S11 is washed in multiple stages,
A leachate containing nickel and cobalt and a leach residue are obtained.

The multi-stage washing method in the solid-liquid separation step S12 is not particularly limited,
It is preferable to use a continuous countercurrent cleaning method (CCD method: Counter Current Detection) in which a countercurrent is brought into contact with a cleaning solution not containing nickel. As a result, the cleaning liquid newly introduced into the system can be reduced, and the recovery rate of nickel and cobalt can be 95% or more.

(3) Neutralization step In the neutralization step S13, calcium oxide or the like is used so that the pH of the leachate becomes 4.0 or less, preferably 3.2 to 3.8, while suppressing the oxidation of the separated leachate. A neutralizer is added to form a mother liquor for nickel and cobalt recovery and a neutralized starch slurry containing trivalent iron. In the neutralization step S13, the neutralization treatment of the leachate is performed in this way, so that the excess acid used in the leaching step S11 by high-temperature pressure acid leaching is neutralized, and the trivalent remaining in the solution Impurity components such as iron ions and aluminum ions are removed. When the pH of the leachate exceeds 4.0, the generation of nickel hydroxide increases.

(4) Sulfurization step In the sulfidation step S14, hydrogen sulfide gas is blown into the sulfuric acid solution, which is the mother liquor for nickel and cobalt recovery obtained in the neutralization step S13, to cause a sulfidation reaction, and a mixture containing nickel and cobalt A sulfide (nickel / cobalt mixed sulfide) and a post-sulfurized liquid (poor liquid) are produced. In addition, when zinc is contained in the mother liquor, a process of selectively separating zinc as a sulfide can be performed prior to forming a mixed sulfide of nickel and cobalt by a sulfidation reaction.

  The mother liquor is an aqueous sulfuric acid solution containing nickel and cobalt obtained by neutralizing the leachate as described above. Specifically, for example, the pH is 3.2 to 4.0, the nickel concentration is 2 to 5 g / L, the cobalt concentration is 0.1 to 1.0 g / L, and as impurity components, for example, iron, A sulfuric acid solution containing an impurity metal element containing at least one of magnesium and manganese can be used. Impurity metal components vary greatly depending on the redox potential of leaching, the operating conditions of the autoclave, and the ore quality, but generally contain about several g / L of iron, magnesium, manganese, and other impurity metal elements. Yes.

Here, the alkaline metal such as iron, manganese, alkali metal, and magnesium, which are impurity metal components contained in the sulfuric acid aqueous solution, is present in a relatively large amount with respect to the recovered nickel and cobalt. The stability as the sulfide formed is low. Therefore, these metal impurities are not contained in the formed sulfide, but are contained in a poor liquid obtained by removing the formed sulfide. The poor solution has a pH of about 1.0 to 3.0.

  Thus, in the sulfidation step S14, a mixed sulfide of nickel and cobalt with a small content of impurities and a poor liquid whose nickel concentration is stabilized at a low level are generated and recovered. As a recovery method, the sulfide slurry obtained by the sulfidation reaction can be separated by settling using a settling separator such as a thickener, and the precipitate sulfide is separated from the bottom of the thickener. It is recovered and the aqueous solution component overflows and is recovered as a poor solution.

<3-2. Neutralization method>
As described above, the poor solution obtained through the sulfiding step S14 of the nickel oxide ore hydrometallurgical process contains impurities metal ions containing at least one of iron, magnesium, and manganese. Therefore, in discharging the poor liquid, which is the process liquid (process liquid) discharged by this nickel smelting method, to neutralize the acid in the poor liquid, and the residual metal in the poor liquid It is necessary to carry out a neutralization treatment (final neutralization treatment) for removing ions. Further, even when this poor solution is repeatedly used in the above-described hydrometallurgical process, it is preferable to carry out a neutralization treatment in order to reduce the impurity component as much as possible.

  Conventionally, the neutralization treatment for the poor liquid has been performed using a highly alkaline neutralizing agent such as limestone or slaked lime in order to achieve the pH necessary for neutralization. However, such a highly alkaline neutralizing agent requires complicated pretreatment and pretreatment facilities when the amount of poor liquid generated from the sulfurization step S14 increases and the amount of use increases. Moreover, even if it is a neutralizing agent such as slaked lime, which is relatively advantageous in terms of cost compared to other neutralizing agents, if the amount of the poor liquid to be processed increases, There is a problem that the degree of influence is large.

  Therefore, in the present embodiment, the boiler ash obtained after the combustion of the fluidized bed boiler is used as a neutralizing agent in the neutralization treatment for the poor liquid that is the process liquid generated in this smelting process, Boiler ash obtained by burning sulfur derived from a coal while adding limestone while desulfurizing, that is, boiler ash after desulfurization in the furnace is used.

  FIG. 2 shows the final result using the boiler ash after desulfurization in the furnace generated from the fluidized bed boiler as a neutralizing agent for the poor liquid (process liquid) which is the post-sulfurization liquid obtained in the nickel hydrometallurgical process. It is a flowchart which shows the flow which performs a neutralization process.

  As shown in FIG. 2, the poor liquid recovered after the sulfidation treatment is transferred to the neutralization treatment tank for the final neutralization treatment. On the other hand, slaked lime or limestone is added to the neutralization treatment tank as a neutralizing agent for the neutralization treatment. At this time, as the neutralizing agent, boiler ash after desulfurization in the furnace generated from the fluidized bed boiler is added and added together with slaked lime and limestone as part of the neutralizing agent.

  In-furnace desulfurized boiler ash used as part of the neutralizing agent is obtained by burning limestone used for desulfurization of coal with coal as boiler fuel into the furnace of a fluidized bed boiler. Boiler ash. As described above, since the Ca component derived from the limestone used for the desulfurization treatment remains in the boiler ash after the in-furnace desulfurization, the boiler ash is converted into a poor liquid based on the residual Ca. It can be effectively used as a neutralizing agent for neutralization treatment. In particular, since the massive ash as boiler ash contains a large amount of unreacted Ca due to excessive addition of limestone, an efficient neutralization treatment can be performed.

  Here, the amount of boiler ash used as a neutralizing agent is not particularly limited, and is appropriately determined depending on the amount of process liquid to be treated, the acid concentration in the process liquid, the content of impurity components, and the like. Can be determined. Moreover, it does not specifically limit about the upper limit of the addition amount, The usage-amount of neutralizing agents, such as slaked lime added simultaneously, can be reduced more effectively as the addition amount of boiler ash is increased.

  In addition, the boiler ash can be used by adding a predetermined amount to the neutralization tank even in the ash state. preferable. It is desirable that the boiler ash is pulverized to have the same particle size at the same time as the addition of moisture, before the addition of moisture, or after the addition of moisture. Thus, using boiler ash slurry as a neutralizing agent and adding it to the neutralization tank before neutralizing the process liquid or during the neutralization reaction facilitates handling, and boiler ash after desulfurization in the furnace The unreacted Ca content therein can be used efficiently. Moreover, by using a slurry state, for example, automatic supply using a liquid feed pump or the like can be efficiently performed.

  The slurry concentration of the boiler ash slurry is not particularly limited, but is preferably 20.0% by weight or less. When the slurry concentration of the boiler ash slurry exceeds 20.0% by weight, the viscosity of the post-neutralization slurry containing the neutralized product after the addition of the boiler ash slurry is increased, and the post-neutralization slurry is post-processed. There is a possibility of affecting the pumping liquid for transfer to the dispensing process and the specific gravity separation process. If the slurry concentration is too low, the amount of liquid in the neutralization tank may increase and a load may be imposed on the solid-liquid separation operation, and power consumption associated with pump operation may increase. Therefore, the lower limit value of the slurry concentration is preferably adjusted as appropriate from the viewpoint of operation management in consideration of the load amount of the solid-liquid separation operation described above, the power consumption of the pump, and the like.

  In addition, the boiler ash added as a neutralizing agent precipitates with the neutralized starch produced by a neutralization process. Therefore, even when this boiler ash is used as a neutralizing agent, there is no effect on the clarity of the supernatant liquid after the neutralization treatment, and there is no adverse effect on the solid-liquid separation treatment after the neutralization treatment.

  As described above in detail, in the neutralization treatment method according to the present embodiment, in the final neutralization treatment for the process liquid generated in the metal smelting process, the boiler ash obtained after combustion of the fluidized bed boiler is Then, neutralization treatment is performed using boiler ash obtained by burning the sulfur content derived from coal, which is fuel, while adding limestone and desulfurizing it.

  According to such a neutralization treatment method, the amount of neutralizing agent such as slaked lime or limestone can be effectively reduced, and the neutralization treatment cost can be reduced and efficient treatment can be performed. Moreover, since the solid content in the used boiler ash comes to be contained in the neutralized starch, the amount of processing waste generated from the fluidized bed boiler can be reduced by discarding together with the neutralized starch. Furthermore, since the unreacted alkali content in the boiler ash is consumed by using the boiler ash as a neutralizing agent in this way, even when the boiler ash is separately disposed of, the alkali content is neutralized. For this reason, it is possible to significantly reduce the processing cost.

  In addition, in the final neutralization process which showed the flowchart in FIG. 2, the neutralization process of the 1st step using limestone as a neutralizing agent, and the neutralization process of the 2nd step using slaked lime as a neutralizing agent, It is known that an efficient final neutralization treatment can be performed by performing a stepwise neutralization treatment consisting of Even in such a case, in each of the neutralization treatments in the first stage and the second stage, the above-described boiler ash is added as a part of the neutralizing agent, thereby effectively using each amount of limestone and slaked lime. To reduce the total amount of neutralizing agent used in the final neutralization treatment.

  In the above-described embodiment, the neutralization treatment for the poor liquid that is a process liquid generated in the nickel smelting process is taken as an example, but the neutralization treatment method according to the present embodiment may be applied. The process liquid that can be used is not limited to this, and any acidic solution can be suitably used. Further, the types of heavy metals and acids contained in the process liquid are not particularly limited, and various acidic solutions can be used as treatment targets.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Examination of use as neutralizer of fluidized bed boiler ash>
[Example 1]
In Example 1, with a fluidized bed boiler, CaCO ₃ (limestone) having a molar ratio of 7.8 corresponding to three times the conventional addition amount was added to coal having a sulfur grade of 0.68% by weight and desulfurized in the furnace. The powdered ash floating in the exhaust gas was removed by an electric dust collector and a bag filter. In this process, the boiler ash separated at the bottom of the furnace was recovered, and the boiler ash was slurried by adding water to obtain a boiler ash slurry having a slurry concentration of 20% by weight.

  On the other hand, in the hydrometallurgical method of nickel oxide ore (nickel hydrometallurgical process), nickel, cobalt, iron, magnesium, manganese, etc. recovered through the leaching process, solid-liquid separation process, and neutralization process After performing a sulfiding step to form a mixed sulfide containing nickel and cobalt by blowing hydrogen sulfide gas into a mother liquor composed of an aqueous sulfuric acid solution containing impurity metals, the poor solution discharged from the sulfiding step (process Slurry) was recovered.

  In the final neutralization treatment when discharging the recovered process slurry out of the system, the prepared boiler ash slurry is used as a neutralizing agent, and the neutralization treatment is performed to remove impurity metals in the process slurry while adjusting the pH of the liquid. Went. Specifically, the process slurry is accommodated in the neutralization treatment tank in the final neutralization step, and the boiler ash slurry as a neutralizing agent is added at an addition amount of 1.97 t / hr in terms of boiler ash powder, Slaked lime was added at the same time for neutralization.

As a result, the amount of slaked lime required to increase the pH of the process slurry of 800 m ³ / hr from 5.0 to 9.0 was 11.06 t / hr, and the conventional method using only slaked lime as a neutralizing agent (described later) The amount of slaked lime used can be reduced by 1.37 t / hr per unit time as compared with the amount of 12.43 t / hr added in the neutralization treatment of Comparative Example).

  In this way, the amount of slaked lime required for neutralization of the process slurry can be greatly reduced by adding the boiler ash after in-furnace desulfurization to the process slurry as part of the neutralizing agent and performing the neutralization treatment. I understood.

  In addition, the heavy metal density | concentration of the neutralization final solution after boiler ash addition was not different compared with the case where boiler ash is not added. From this, by using boiler ash as a neutralizing agent, the neutralizing treatment can be efficiently and effectively performed by reducing the amount of neutralizing agent used without adversely affecting the neutralizing treatment. I understood.

<Long-term operation of neutralization using fluidized bed boiler ash>
[Example 2]
Next, in Example 2, the poor solution (process slurry) after the sulfidation step in the nickel hydrometallurgical process was charged into a neutralization treatment tank at a flow rate of 800 m ³ / hr, and boiler ash was added to the process slurry. Neutralization treatment as a neutralizer was carried out for 30 days. In addition, the boiler ash slurry similar to Example 1 was added and added to the neutralization processing tank by the addition amount of 1.97 t / hr in conversion of boiler ash powder, and slaked lime was also used as a neutralizing agent with the boiler ash slurry.

  As a result, the amount of slaked lime used was 7,970.2 t in total for 30 days. Since the amount of slaked lime used when the neutralization treatment using only conventional slaked lime was carried out for 30 days was 8,948.9 t, boiler ash slurry was used as a part of the neutralizing agent for a long period of time. By carrying out the neutralization treatment, 978.7 t of slaked lime could be reduced.

<Examination of the amount of limestone added to the fluidized bed boiler>
[Examples 3 and 4]
Next, the effect of reducing the amount of slaked lime used in the neutralization tank when the amount of limestone CaCO ₃ added to the fluidized bed boiler was increased was examined.

  Specifically, using the same coal as in Example 1, as Example 3, when adding 1.13 t / hr (Ca / S molar ratio of 2.6) of limestone, and as Example 4, the amount three times this amount. This was compared with the case where 3.39 t / hr (Ca / S molar ratio of 7.8) was added. In each case, the boiler ash slurry having the slurry concentration of 20.0% by weight was added to the total amount of boiler ash generated at the furnace bottom of the fluidized bed boiler to form a slurry concentration of 20.0% by weight. The same amount was added, and slaked lime was added at the same time for neutralization.

As a result, the amount of slaked lime required to increase the pH of the process slurry of 800 m ³ / hr from 5.0 to 9.0 is 11.98 t / hr in Example 3, which is a comparative example described later. 0.45 t / hr of slaked lime could be saved compared to the case. In the case of Example 4, it was 11.06 t / hr, and 1.37 t / hr of slaked lime could be saved as compared with the case of the comparative example described later. That is, the use of boiler ash produced by adding three times the amount of limestone CaCO ₃ to a fluidized bed boiler as a neutralizing agent further reduces slaked lime by 0.92 t / hr compared to the case where limestone is added. It was possible.

[Reference example]
Neutralization was performed in the same manner as in Example 3 except that the limestone added to the fluidized bed boiler was 0.87 t / hr (Ca / S molar ratio 2.0). As a result, the amount of slaked lime required to raise the pH of the process slurry of 800 m ³ / hr from 5.0 to 9.0 was 12.25 t / hr, and 0.18 t / hr of slaked lime was saved. .

[Comparative example]
Neutralization was performed in the same manner as in Example 3 except that the limestone added to the fluidized bed boiler was 0.43 t / hr (Ca / S molar ratio 1.0). As a result, the amount of slaked lime required to raise the pH of the 800 m ³ / hr process slurry from 5.0 to 9.0 was 12.43 t / hr.

Claims (7)

A neutralization treatment method for neutralizing a liquid discharged from a metal smelting process using boiler ash,
The boiler ash includes massive ash recovered from the furnace bottom side of the fluidized bed boiler among the burning husks generated in the fluidized bed boiler,
The burning husk is produced by supplying coal, limestone and air to the fluidized bed boiler and burning them,
The neutralization method according to claim 1, wherein a supply amount of the limestone is larger than an amount necessary for desulfurization of exhaust gas generated from the fluidized bed boiler.   The neutralization processing method of Claim 1 which performs the said neutralization using the ash which mixed the thing which collect | recovered the powdery ash which floats in the said waste gas into the said boiler ash.   The amount of calcium contained in the limestone is not less than 2.3 times and not more than 20 times the stoichiometric amount necessary for recovering the sulfur content supplied to the fluidized bed boiler. The neutralization processing method of Claim 1 or Claim 2.   The neutralization method according to claim 1, wherein a boiler ash slurry using the boiler ash as a slurry is used as a neutralizing agent.   2. The neutralization method according to claim 1, wherein the boiler ash after pulverizing the boiler ash, or the boiler ash slurry obtained by pulverizing and slurrying the boiler ash, is used as a neutralizing agent.   The boiler ash is classified into a large particle size side and a small particle size side, the neutralization is performed using the small particle size side, and the large particle size side is supplied to the fluidized bed boiler and spread on the bottom. The neutralization processing method according to any one of claims 1 to 5.   The metal smelting process is a hydrometallurgical process for recovering nickel and cobalt from nickel oxide ore, and is a medium for the liquid after sulfidation obtained through the leaching process, solid-liquid separation process, neutralization process, and sulfidation process. The neutralization treatment method according to claim 1, wherein the neutralization treatment method is used for sum treatment.

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