JP2017186611A - Removing method of scale of heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a removing method of scale of a heat exchanger capable of removing scale stuck to a heat exchanger without putting in a lot of labor and time.SOLUTION: A removing method of scale of a heat exchanger comprises cooling an iron-free solution obtained in an iron-removing step for depositing iron (III) hydroxide from a nickel chloride aqueous solution containing iron and subjecting the obtained slurry of the nickel chloride aqueous solution containing the iron (III) hydroxide to solid-liquid separation. The heat exchanger is equipped with a heat transfer surface made of pure titanium or an anticorrosive titanium alloy for cooling the iron-free solution. Scale stuck to the iron-free solution flow channel side of the heat transfer surface is removed by introducing a hydrochloric acid aqueous solution of a concentration of 5-10 wt.% into the heat exchanger.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for removing scale adhered to a heat exchanger. More specifically, the present invention relates to a method for removing scale attached to a heat exchanger used for cooling a deiron-free final solution obtained from a deironing step of removing iron from a nickel chloride aqueous solution containing iron.

  In nickel smelting, a dry smelting method in which nickel ore or nickel concentrate is melted in a dry furnace such as a blast furnace or electric furnace, and nickel in the ore or nickel concentrate is leached into an aqueous solution to remove impurities. After that, there is a hydrometallurgical method for recovering nickel, and an optimum method is industrialized according to the purpose and application.

  Among them, in the hydrometallurgical method, as described in Patent Document 1, for example, nickel mat and mixed sulfide are leached using the oxidizing action of chlorine gas, and the leached nickel ions and cobalt ions are removed. Chlorine leaching processes have been put into practical use that are commercialized as electrolytic nickel and electrolytic cobalt by electrowinning.

  In the chlorine leaching process of the chlorine leaching process, the mixed sulfide and cementation residue described later are repulped into an aqueous chloride solution, and then nickel and cobalt are leached into the aqueous chloride solution by blowing chlorine gas into the slurry. .

Next, in the cementation process, a nickel matte mainly composed of pulverized Ni ₃ S ₂ and metallic nickel is added to a chlorine leaching solution containing divalent copper chloro complex ions as an oxidizing agent obtained in the chlorine leaching process. By carrying out a substitution reaction between copper and nickel by contact, nickel in the nickel mat is substituted and leached into the liquid, and the copper ions become a solid (cementation residue) in the form of Cu ₂ S or Cu ⁰ (metallic copper). Part).

The cementation residue comprising the cementation final solution, the substitution leaching residue of nickel matte, and the solid precipitated in the form of Cu ₂ S or Cu ⁰ (metal copper) is solid-liquid separated, and then cemented. The final liquid is sent to the next cleaning process, and the solid cementation residue is sent to the chlorine leaching process.

Here, the cementation final solution contains impurities such as copper, iron, lead, zinc, etc. in addition to nickel and cobalt, which are the metals to be collected, so cobalt is separated and recovered to remove the impurities. In order to obtain a high-purity nickel chloride aqueous solution suitable for electrowinning, a liquid purification process is configured. The cementation final solution is processed through a deironing process, a cobalt separation process, a deleading process, and a dezincing process to remove impurities, and is supplied to the electrowinning process.

In the iron removal step, for example, an oxidation neutralization method using chlorine gas as an oxidizing agent and carbonate as a neutralizing agent is used. The oxidation neutralization method utilizes the property that some heavy metals, such as iron, tend to be hydroxides even in a low pH region when they become ions in a higher oxidation state. This method is widely used for wastewater treatment including heavy metals.

In the cobalt separation step, for example, a solvent extraction method is used. In the chloride bath, a solvent extraction method using an amine-based extractant is generally carried out. This is because cobalt forms chloro complex ions when the chloride ion concentration in the aqueous solution is sufficiently high. Nickel utilizes the fact that it does not form chloro complex ions. The cobalt separated from the nickel chloride aqueous solution containing cobalt in the solvent extraction process becomes a cobalt chloride aqueous solution by back extraction operation, and after impurities are removed in the cobalt chloride liquid purification process, Cobalt.

For the deleading step and the dezincing step, known methods are appropriately selected as necessary.

After the pH adjustment, the aqueous nickel chloride solution that has undergone the liquid purification process is sent to the electrowinning process, and becomes electronickel in the electrowinning process.

In this chlorine leaching process, the reaction is operated at a high temperature in order to increase the reaction efficiency in the cementation step. Therefore, the cementation final liquid processed at the deironing process of the following process is high temperature, and the deironing final liquid after iron removal also becomes high temperature.

However, in the next solvent extraction step, it is necessary to operate at a certain temperature or lower in view of evaporation of the organic solvent, decomposition of the organic solvent, heat resistance of the apparatus material, etc. To be cooled.

However, since the iron removal final solution is a high concentration nickel chloride aqueous solution, the heat removal surface of the heat exchanger used for cooling the iron removal final solution contains calcium on the side of the iron removal final solution flow path. Scale gradually precipitates and grows. This scale causes a decrease in the flow rate and makes it difficult to continue the operation. Therefore, the scale that adheres to the heat transfer surface periodically stops the flow of the deironed final solution to the heat exchanger. It was necessary to perform the removal work.

However, the removal of the scale requires a lot of labor and time. Normally, multiple heat exchangers are arranged in parallel, so that the remaining heat exchanger can be operated even during scale removal work and the removal of the final iron removal liquid can be continued. If the removal work time of the iron is prolonged, there is a possibility that the production of electronickel may be reduced due to a decrease in the flow rate of the iron removal final solution.

Patent Document 2 discloses a method for preventing scaling of piping. However, since the conditions such as the liquid composition and pH are different, the method is not applicable to the deironation final liquid of the chlorine leaching process in nickel smelting.

JP 2012-026027 A JP-A-10-202213

  Therefore, the present invention has been devised in view of the above-described problems of the prior art, and is used to cool a deiron-free final solution obtained from a deironing step of removing iron from an aqueous nickel chloride solution containing iron. In a heat exchanger, the scale removal method of the heat exchanger which can remove the scale adhering to the said heat exchanger without requiring a lot of time and effort is provided.

In order to achieve the above-mentioned object, the present inventor, in particular, as a result of intensive studies on the method for dissolving the scale, removes the scale by passing an aqueous hydrochloric acid solution having a concentration of 5 to 10% by weight through the heat exchanger. The present inventors have found that the present invention can be accomplished and have completed the present invention.

That is, in the heat exchanger descaling method of the first aspect of the present invention, an iron (III) hydroxide precipitate is produced from an aqueous nickel chloride solution containing iron, and the nickel chloride containing the iron (III) hydroxide is produced. A scale removal method for a heat exchanger for cooling a deiron removal liquid obtained from a deironation step for solid-liquid separation of an aqueous slurry, and passing an aqueous hydrochloric acid solution having a concentration of 5 to 10% by weight through the heat exchanger. By removing the scale adhering to the deiron final liquid flow channel side of the heat transfer surface made of pure titanium or corrosion resistant titanium alloy for cooling the deiron final liquid with which the heat exchanger is provided. Features.

  The scale removal method for a heat exchanger according to the second aspect of the present invention is characterized in that, in the first aspect of the present invention, the aqueous hydrochloric acid solution is circulated.

The scale removal method for a heat exchanger according to a third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the concentration of the aqueous hydrochloric acid solution is 5 to 6% by weight.

According to a fourth aspect of the present invention, there is provided a heat exchanger scale removing method according to any one of the first to third aspects of the present invention, wherein the heat exchanger is a plate heat exchanger. To do.

According to the scale removal method of the heat exchanger of the present invention, in the heat exchanger of the iron removal process for removing iron from the nickel chloride aqueous solution containing iron, the heat exchanger adheres to the heat exchanger without much effort and time. The scale can be removed, and there is no possibility of a reduction in the production of electronickel due to a decrease in the flow rate.

It is a schematic flowchart of the iron removal process which concerns on this invention. It is the figure which showed the weight change of the titanium test piece in an Example and a comparative example.

  The present invention relates to a deironation process obtained from a deironation step in which an iron (III) hydroxide precipitate is produced from a nickel chloride aqueous solution containing iron and the nickel chloride aqueous solution slurry containing the iron (III) hydroxide is solid-liquid separated. A method for removing scale from a heat exchanger for cooling a final liquid, wherein the final heat removal liquid is provided in the heat exchanger by passing an aqueous hydrochloric acid solution having a concentration of 5 to 10% by weight through the heat exchanger. The scale adhering to the de-iron final liquid flow channel side of the heat transfer surface made of pure titanium or corrosion-resistant titanium alloy for cooling the steel is removed.

Therefore, here, as one embodiment of the present invention, nickel matte and mixed sulfides are leached using the oxidizing action of chlorine gas, which is a hydrometallurgical method for recovering nickel, and leached nickel ions and cobalt are leached. In the chlorine leaching process in which ions are commercialized as electrolytic nickel and electrolytic cobalt by electrowinning, the following description will be given by taking as an example an application to a heat exchanger used to cool the final iron removal liquid obtained from the iron removal process. .

1. Chlorine Leaching Process In the chlorine leaching process, the nickel matte used as raw material refers to nickel sulfide produced from dry smelting, and mixed sulfide refers to nickel / cobalt produced from low-grade laterite ore by sulfuric acid leaching. Refers to mixed sulfides. In the chlorine leaching process of the chlorine leaching process, the mixed sulfide and cementation residue described later are repulped into an aqueous chloride solution, and then nickel and cobalt are leached into the aqueous chloride solution by blowing chlorine gas into the slurry. .

Next, in the cementation process, a nickel matte mainly composed of pulverized Ni ₃ S ₂ and metallic nickel is added to a chlorine leaching solution containing divalent copper chloro complex ions as an oxidizing agent obtained in the chlorine leaching process. By carrying out a substitution reaction between copper and nickel by contact, nickel in the nickel mat is substituted and leached into the liquid, and the copper ions become a solid (cementation residue) in the form of Cu ₂ S or Cu ⁰ (metallic copper). Part).

The cementation residue comprising the cementation final solution, the substitution leaching residue of nickel matte, and the solid precipitated in the form of Cu ₂ S or Cu ⁰ (metal copper) is solid-liquid separated, and then cemented. The final liquid is sent to the next cleaning process, and the solid cementation residue is sent to the chlorine leaching process.

Here, the cementation final solution contains impurities such as copper, iron, lead, zinc, etc. in addition to nickel and cobalt, which are the metals to be collected, so cobalt is separated and recovered to remove the impurities. In order to obtain a high-purity nickel chloride aqueous solution suitable for electrowinning, a liquid purification process is configured.

The cementation final solution is processed through a deironing process, a cobalt separation process, a deleading process, and a dezincing process to remove impurities, and is supplied to the electrowinning process.

2. Overview of Deironing Process FIG. 1 is a schematic flow diagram of a deironing process according to the present invention. In the iron removal step, chlorine gas was blown into the final cementation solution to adjust the oxidation-reduction potential (Ag / AgCl electrode standard) to 900 to 1000 mV, and nickel carbonate was added to adjust the pH to 1.5 to 3.0. By adjusting to produce an iron (III) hydroxide precipitate, and solid-liquid separation of the aqueous nickel chloride slurry containing the iron (III) hydroxide, a deiron-free final solution and a deironized starch are obtained. is there.

The temperature of the cementation final solution treated in the deironing step is as high as about 70 ° C., and the deironing final solution after deironing is also 65 to 70 ° C.

In the cobalt separation process, which is the next process of the iron removal process, when the high-temperature iron removal final solution is fed, the amount of organic solvent evaporated increases and the amount of retained organic solvent decreases. Due to the decrease in the amount of organic solvent retained, process problems such as an increase in the amount of nickel mixed in the organic solvent from which cobalt was extracted due to deterioration in oil-water separation, and cost problems such as an increase in the replenishment amount of the organic solvent occurred. To do. Furthermore, when the amount of evaporation of the organic solvent increases, safety and security problems such as odor generation also occur. Moreover, since decomposition | disassembly of an organic solvent will be accelerated | stimulated when a high temperature deiron removal final solution is sent, there also exists a possibility of the COD load increase of the waste_water | drain by mixing a decomposition product into a back extract. In addition, since resin materials such as polyvinyl chloride and FRP are frequently used in the solvent extraction equipment, problems such as softening and deformation due to high temperatures and liquid leakage due to the softening and deformation occur.

Therefore, the iron removal final solution needs to be cooled to about 55 ° C. by a heat exchanger. The heat exchange method is not particularly limited as long as it can cool the deiron-free final solution, such as a shell-and-tube heat exchanger. Among them, a plate heat exchanger is preferable. Therefore, as one embodiment of the present invention, cooling is performed using water as a refrigerant by a plate cooler. As for the refrigerant, water that is close and has high cooling efficiency is optimal, but there is no particular limitation even if, for example, cold air or a special refrigerant such as ethylene glycol is used.

3. As described above, when the cooling of the deironing final liquid is continued by the plate cooler using water or the like as a refrigerant, calcium is contained in the deironing final liquid flow path side of the heat transfer surface of the plate cooler. The scale gradually precipitates and grows. This scale causes a decrease in the flow rate of the final iron removal liquid and makes it difficult to continue the operation.Therefore, periodically stop the liquid flow to the heat exchanger and remove the adhered scale. There was a need to do.

For this purpose, normally, multiple heat exchangers are arranged in parallel, so that the remaining heat exchanger can be operated even during scale removal work, and the flow of the final iron removal liquid can be continued. If the removal work time of the iron is prolonged, there is a possibility that the production of electronickel may be reduced due to a decrease in the flow rate of the iron removal final solution. In FIG. 1, two plate coolers are arranged in parallel, and at the time of removing the scale, only one iron that has not undergone the removing work of the scale is made to pass the final iron removal solution.

In the conventional removal work of the scale, since the plate cooler is disassembled and each plate is carefully cleaned, it requires a lot of labor and time and also requires advanced maintenance techniques. Further, in order to disassemble the plate cooler, it is necessary to renew the gasket that seals between the plates every time it is disassembled, and the maintenance cost is high. Furthermore, since the work for disassembling the plate cooler involves reassembling the disassembled plate cooler, there is always a risk of liquid leakage at the start of liquid flow.

By the way, as a result of investigation, it was found that the main component of this scale is gypsum (CaSO ₄ .2H ₂ O). Therefore, in the present invention, the scale is dissolved using hydrochloric acid.

In the descaling operation of the present invention, the deironation final solution and cooling water flow are stopped, and a 5 to 10% by weight hydrochloric acid aqueous solution is passed through the deiron final solution flow path side. At this time, the aqueous hydrochloric acid solution is preferably recycled. Necessary facilities include a hydrochloric acid tank, a pump for feeding hydrochloric acid to the plate cooler, and a return and return pipe and a switching valve. The hydrochloric acid concentration of the aqueous hydrochloric acid solution passed through the hydrochloric acid tank is adjusted, and when the hydrochloric acid concentration decreases, readjustment may be performed.

Dissolution of the scale with hydrochloric acid follows the reaction shown in (Formula 1).
CaSO ₄ .2H ₂ O + 2HCl → CaCl ₂ + H ₂ SO ₄ + 2H ₂ O (Formula 1)

Since the plate that forms the heat transfer surface of the plate cooler is pure titanium, when high-concentration hydrochloric acid is used, wear due to corrosion of the plate occurs. The plate is made extremely thin, which guarantees a high heat transfer coefficient. However, if a hole is made in the plate, nickel chloride aqueous solution leaks to the cooling water side, causing environmental problems. Also occurs.

  Then, the density | concentration of the hydrochloric acid aqueous solution which permeate | transmits the iron removal final liquid flow path side of a plate cooler heat-transfer surface shall be 5-10 weight%. If it is less than 5% by weight, the effect of removing the scale is lowered, and if it exceeds 10% by weight, the titanium material may be corroded. Furthermore, the concentration of the aqueous hydrochloric acid solution is more preferably 5 to 6% by weight.

According to the scale removal method of the heat exchanger of the present invention, since it is not necessary to disassemble and clean the heat exchanger, it is possible to remove the scale attached to the heat exchanger without much effort and time. In addition, there is no possibility that the production of electronickel will be reduced due to a decrease in the flow rate of the final iron removal solution. In addition, since there is no need to reassemble the disassembled heat exchanger, there is no risk of liquid leakage at the start of the passing of the final iron removal liquid. Furthermore, in the case of a plate heat exchanger, since there is no work of disassembly and reassembly, there is no need to replace the gasket, and there is no cost.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, the range of this invention is not specifically limited by description of a present Example and a comparative example.

Example 1
Collect the scale attached to the plate cooler for the final iron removal cooling in the deironing process in actual operation, put 10 g of scale into 200 mL of hydrochloric acid aqueous solution adjusted to 5% by weight of hydrochloric acid, and soak at room temperature for 20 hours. The calcium concentration in the aqueous hydrochloric acid solution was measured.

(Example 2)
10 g of the same scale as in Example 1 was put into 200 mL of an aqueous hydrochloric acid solution adjusted to a hydrochloric acid concentration of 10% by weight, and the calcium concentration in the aqueous hydrochloric acid solution when immersed for 20 hours at room temperature was measured.

(Comparative Example 1)
10 g of the same scale as in Example 1 was put into 200 mL of an aqueous hydrochloric acid solution adjusted to a hydrochloric acid concentration of 18% by weight, and the calcium concentration in the aqueous hydrochloric acid solution when immersed for 20 hours at room temperature was measured.

In Example 1, Example 2, and Comparative Example 1, the calcium concentration was measured using an ICP emission spectroscopic analyzer. The results of Example 1, Example 2, and Comparative Example 1 are shown in Table 1.

  From Example 1, Example 2, and Comparative Example 1, approximately 4 g of scale could be dissolved with 5 wt% hydrochloric acid and 10 wt% hydrochloric acid by dipping for 20 hours at room temperature. On the other hand, with 18 wt% hydrochloric acid, the dissolution amount of the scale decreased. At 18% by weight hydrochloric acid, there may be a reverse reaction due to sulfuric acid produced by the dissolution of gypsum.

(Example 3)
About 21.8 g of a pure titanium test piece was immersed in an aqueous hydrochloric acid solution adjusted to a hydrochloric acid concentration of 5% by weight and left at room temperature for 60 days to examine the change in weight.

Example 4
About 21.8 g of a pure titanium test piece was immersed in an aqueous hydrochloric acid solution adjusted to a hydrochloric acid concentration of 10% by weight and allowed to stand at room temperature for 60 days to examine the change in weight.

(Comparative Example 2)
About 21.7 g of a pure titanium test piece was immersed in an aqueous hydrochloric acid solution adjusted to a hydrochloric acid concentration of 35% by weight and left at room temperature for 60 days to examine the change in weight. The results of Example 3, Example 4, and Comparative Example 2 are shown in FIG.

  From FIG. 2, 5 wt% hydrochloric acid and 10 wt% hydrochloric acid did not change significantly even when immersed for 60 days, but 35 wt% hydrochloric acid decreased by about 1 g.

As a result, when removing the scale adhering to the deironation final liquid flow channel side of the heat transfer surface made of pure titanium, it was confirmed that there was no corrosion of the titanium material if a hydrochloric acid aqueous solution having a concentration of 5 to 10% by weight was used. It was.

Claims (4)

An iron (III) hydroxide precipitate is produced from an iron-containing nickel chloride aqueous solution, and the final iron-free solution obtained from the deironing step of solid-liquid separation of the nickel chloride aqueous solution slurry containing the iron (III) hydroxide is cooled. A heat exchanger descaling method that comprises:
By passing an aqueous hydrochloric acid solution having a concentration of 5 to 10% by weight through the heat exchanger, pure titanium or a corrosion-resistant titanium alloy for cooling the deiron-free final solution provided in the heat exchanger is provided. Remove the scale adhering to the hot iron desulfurization final flow path side,
The scale removal method of the heat exchanger characterized by the above-mentioned. The scale removal method for a heat exchanger according to claim 1, wherein the hydrochloric acid aqueous solution is circulated. The method for removing a scale from a heat exchanger according to claim 1 or 2, wherein the concentration of the hydrochloric acid aqueous solution is 5 to 6% by weight. The scale removal method for a heat exchanger according to any one of claims 1 to 3, wherein the heat exchanger is a plate heat exchanger.

Images