JP2010100524A - Method for producing scorodite and method for washing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably producing scorodite having low arsenic elution. <P>SOLUTION: The method for producing scorodite comprises a step of washing the synthesized and separated scorodite with water and separating the washed scorodite from the used washing water by solid-liquid separation. The step is carried out many times. After the n-th step (n≥1) is carried out, the concentration of a liquid component after reaction containing at least one selected from the group consisting of Cu, S and Fe contained in the used washing water and the concentration of the As ion contained therein are measured. The concentration of the liquid component after reaction to be targeted is decided according to the measured results and set. The step is repeated to the extent that the measured concentration of the liquid component after reaction in the washing water used for washing the synthesized and separated scorodite is reduced to the targeted value or lower. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing scorodite. In particular, the present invention relates to a method for producing scorodite from electrolytically precipitated copper produced in a copper smelting process. The present invention also relates to a cleaning method for reducing arsenic elution from scorodite.

Various impurities are mixed in the copper ore, and such impurities include arsenic (As). Arsenic (As) is volatilized and separated by high heat in a dry process of copper smelting, but a part of it is mixed with crude copper and brought into the copper electrolytic purification process.
As contained in the crude copper (copper anode) is partly eluted in the electrolytic solution, and the undissolved part is mixed in the anode slime that precipitates at the bottom of the electrolytic cell. Further, since the amount of copper eluted from the anode is generally larger than the amount of copper deposited on the cathode, the copper concentration in the electrolytic solution gradually increases. Therefore, a part of the electrolytic solution is extracted into another electrolytic cell to control the quality of the electrolytic solution. The extracted electrolytic solution is subjected to copper removal electrolysis, and impurities such as Cu and As are deposited on the cathode, and impurities such as Cu and As are separated and recovered by depositing them on the bottom of the electrolytic cell. In this field, those precipitated at the bottom of the electrolytic cell and those deposited at the cathode are collectively referred to as electrolytically precipitated copper.

  Electrolytically precipitated copper is usually repeated in the copper smelting process. For this purpose, it is preferable to separate impurities such as As from electrolytically precipitated copper. In addition, there is still a way to use As as a valuable resource. Therefore, a technique for separating and recovering As from electrolytically precipitated copper with high quality is desired. The separated and recovered arsenic is preferably immobilized as a stable compound so as not to cause environmental pollution.

In order to fix arsenic, it is known that it is effective to produce crystals of scorodite (FeAsO ₄ .2H ₂ O), which is an iron arsenic compound. Crystalline scorodite is chemically stable and suitable for long-term storage. On the other hand, amorphous scorodite lacks stability and is not suitable for long-term storage.

  For example, in Patent Document 1, in a method for removing and fixing arsenic from an arsenic-containing solution containing a non-ferrous metal component containing copper and / or zinc and arsenic, an iron (II) solution and / or iron is used as the arsenic-containing solution. (III) A scorodite containing a nonferrous metal component containing copper by solid-liquid separation from the arsenic-containing solution by generating a scorodite having stable crystallinity as an iron / arsenic compound by adding a solution and reacting at 120 ° C. or higher. The first step of recovering and re-pulping by adding water to the scorodite containing the nonferrous metal component containing copper obtained in the first step, and dissolving the nonferrous metal component containing copper contained in the scorodite into the liquid A method for removing and fixing arsenic from an arsenic-containing solution, characterized in that it comprises a second step of separating from scorodite. Thereby, it is possible to remove and fix arsenic as crystalline stable scorodite without losing valuable metals such as copper.

Japanese Patent No. 3756687

  Patent Document 1 describes a method for obtaining a highly stable scorodite: “Even if the Fe / As molar ratio is lower than 1.5 or higher than 2.0, the crystallinity of the produced iron arsenic compound is high. The description is remarkably lowered, and arsenic is easily eluted, and the description “if lower than 150 ° C., a crystalline iron arsenic compound is not formed, becomes amorphous and has poor stability, and arsenic is easily eluted.” There is.

And about the significance of the 2nd process performed after the 1st process which synthesizes scorodite, "copper, zinc, etc. are mixed in the form of a sulfate in scorodite. If copper is taken as an example, this amount will not be collected. In this state, arsenic is not eluted but copper, which is a valuable metal, is mixed into the precipitate. It separates from scorodite and collects copper etc. ".
That is, according to the teaching of Patent Document 1, the Fe / As molar ratio and temperature conditions in the reaction stage are important for the arsenic elution of scorodite.

  However, according to the experiment results of the present inventor, even if the reaction conditions of scorodite are optimized, arsenic may be eluted from the obtained scorodite exceeding the environmental standard, and the amount of elution is also variable. I understood that. It is not preferable that the scorodite quality varies. Therefore, an object of the present invention is to provide a method for stably producing scorodite having low arsenic elution.

  Until now, it was the presence of amorphous scorodite that was considered as a factor for arsenic to elute from scorodite. Amorphous scorodite has low stability, and if it is contained as an impurity in crystalline scorodite, it will cause arsenic to elute. For this reason, the low stability of the obtained scorodite was thought to be mainly due to the presence of amorphous scorodite. Thus, conventional techniques for improving the stability of scorodite have been focused on generating crystalline scorodite with high selectivity during synthesis.

  However, the present inventor has intensively studied the arsenic elution property of scorodite, and found that the elution amount and its variation greatly depend on the washing operation after scorodite synthesis. The washing operation is thought to be effective in that the post-reaction solution adhering to the scorodite is washed away to improve the quality of the scorodite. I was going. For example, the method that the present inventor has previously adopted as a method for cleaning scorodite is that the operation of adding water on the scorodite cake on the Buchner funnel for cleaning, no blue color of copper is recognized from the cleaning solution. Repeat until.

  According to conventional knowledge, the stability of scorodite was thought to be mainly due to the degree of crystallization during the synthesis of scorodite, so even if the washing operation of removing the post-reaction liquid adhering to scorodite was performed sufficiently, If the crystallinity of itself is low, elution of arsenic is inevitable. For this reason, arsenic that eluted after washing was thought to be due to the low crystallinity of scorodite.

  However, it has been found that surprisingly many arsenic elutions from scorodite are caused by insufficient cleaning. It was also found that if the post-reaction liquid component contained in the cleaning liquid decreases, the elution value of metal ions such as arsenic in the scorodite elution test also decreases. Therefore, the cleaning operation for separating the post-reaction liquid from scorodite has a desired elution amount by monitoring the post-reaction liquid components contained in the cleaning liquid, for example, the concentration of metal ions such as Cu and As, In addition, it has been found that scorodite with little variation in the elution amount can be easily obtained.

The present invention completed on the basis of the above knowledge, in one aspect,
Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
A method for producing scorodite, comprising:
The sulfuric acid leaching solution of electrolytically-precipitated copper is used as a raw material for the acidic aqueous solution in Step 1, and Step 3 is based on Cu, S, and Fe contained in the water washing solution after performing the n-th (n ≧ 1) Step 3. Measure the concentration and As ion concentration of at least one post-reaction liquid component selected from the group, set the concentration of the post-reaction liquid component to be targeted according to the measurement results, and wash the scorodite with water It is a method including repeating until the measured value of the concentration of the post-reaction liquid component contained in the washing solution used in the step is reduced to the target value or less.

In another aspect of the present invention,
Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
A method for producing scorodite, comprising:
The sulfuric acid leaching solution of electrolytically precipitated copper is used as a raw material for the acidic aqueous solution in step 1, and in step 3, the ratio of the amount of water used for washing and the dry weight of scorodite is set to a constant value, and then As is contained in the washing solution. The relationship between the measured concentration value and the measured concentration value of at least one post-reaction liquid component selected from the group consisting of Cu, S, and Fe is plotted. The remaining As concentration is estimated, and the process is repeated until the As ion concentration estimated from the measured concentration value of the post-reaction liquid component contained in the washing solution used for washing scorodite is lowered to 0.3 mg / L or less. It is a method including.

  In one embodiment of the method for producing scorodite according to the present invention, the concentration of the at least one post-reaction liquid component is a Cu ion concentration.

In another aspect of the present invention,
Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
A method for producing scorodite, comprising:
The sulfuric acid leaching solution of electrolytically precipitated copper is used as a raw material for the acidic aqueous solution in Step 1, the As ion concentration in the post-reaction solution is 0.1 to 3 g / L, the Cu ion concentration is 10 to 60 g / L, and Step 3 is 1 Washing is performed as a ratio of 100 to 300 g (dry weight) of scorodite per liter of water, and the Cu ion concentration contained in the washing solution used for scorodite washing is measured, and the measured Cu ion concentration is 10 mg / L. It is a method including repeating until it falls below.

  In yet another embodiment of the method for producing scorodite according to the present invention, the Cu ion concentration analysis contained in the rinsing liquid used for scorodite rinsing is performed by a colorimetric analysis method.

  In yet another embodiment of the method for producing scorodite according to the present invention, the water washing in step 3 is carried out by repulping and stirring after adding water to the scorodite.

  In yet another embodiment of the method for producing scorodite according to the present invention, step 2 is performed by natural filtration on a funnel, and step 3 is performed by pouring wash water on the scorodite installed on the funnel. While pouring, it is carried out by gravity or suction filtration including keeping the entire scorodite covered with washing water.

  In still another embodiment of the method for producing scorodite according to the present invention, step 3 is carried out by placing the scorodite in a vertical filter press and then pressing after washing water is supplied.

  In another aspect, the present invention is a scorodite washing method comprising an operation of washing scorodite with water and then separating the scorodite from the washing solution by solid-liquid separation, and is eluted from the scorodite contained in the washing solution used for washing Measuring the concentration of at least one component, and determining whether to repeat the above operation according to the measurement result.

  According to the present invention, it is possible to stably manufacture scorodite having low arsenic elution.

It is a figure which shows transition of the arsenic and copper density | concentration in the washing | cleaning liquid at the time of washing with water after carrying out preliminary water washing of the scorodite synthesized in Example 1. FIG.

One subject of the present invention is:
Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
The step 3 is a method that includes repeating until the concentration of the post-reaction liquid component contained in the washing liquid used for washing the scorodite falls below a preset value. is there.

Process 1
In step 1, scorodite is synthesized. The scorodite can be synthesized by heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite. As the scorodite synthesis conditions, any conditions known to those skilled in the art as being advantageous for the synthesis of crystalline scorodite may be adopted, and suitable conditions are exemplified below.

Pentavalent As can be given in the form of arsenic acid (H ₃ AsO ₄ ), for example. Typically, pentavalent As is present in the form of arsenic acid (H ₃ AsO ₄ ) in the sulfuric acid leaching solution after the electrolytically precipitated copper is leached with sulfuric acid.
Trivalent Fe can be given in the form of iron oxide, iron sulfate, iron chloride, iron hydroxide, and the like. The trivalent Fe is preferably provided in the form of an acidic aqueous solution from the viewpoint of performing the reaction in an aqueous solution, and ferric sulfate from the viewpoint that it is most effective to return the liquid after deironing to the electrolytic solution of electrolysis. It is preferably provided in the form of an aqueous solution of (Fe ₂ (SO ₄ ) ₃ ). Moreover, the polyferric sulfate aqueous solution used by waste water treatment etc. can also be used.
The acidic aqueous solution can be given as an aqueous solution such as hydrochloric acid acidic, sulfuric acid acidic, nitric acid acidic or perchloric acid acidic. Typically, a sulfuric acid leaching solution after sulfuric acid leaching of electrolytically precipitated copper is used. The method of sulfuric acid leaching will be described later.

In order to increase the reaction rate of As contained in the acidic aqueous solution, it is preferable that the trivalent Fe is 1.0 equivalent or more with respect to the pentavalent As amount. More preferably, it is 5 equivalents.
The pH of the acidic aqueous solution is preferably 1.0 to 1.5 for producing crystalline scorodite.

  Crystalline scorodite can be produced by heating the acidic solution to 60 to 95 ° C., for example, under atmospheric pressure. For example, a sufficient amount of crystalline scorodite is produced by reacting for 8 to 72 hours. Since As is oxidized to pentavalent, crystalline scorodite is produced with trivalent iron and high reaction efficiency.

Process 2
In step 2, the synthesized scorodite is separated from the post-reaction solution by solid-liquid separation. The post-reaction solution contains ions of arsenic, copper and other metals. If these ions are attached to the scorodite, they will be eluted during storage, so it is necessary to remove them sufficiently. The solid-liquid separation method may be any known method and is not particularly limited, but filtration is common. Examples of the filtration include gravity (natural) filtration, suction filtration, pressure filtration, and centrifugal filtration. In general, gravity filtration has the lowest separation efficiency, and pressure filtration and centrifugal filtration have the highest efficiency. Suction filtration is intermediate.
However, in order to obtain the target separation efficiency according to the present invention, solid-liquid separation by any method is insufficient, and washing with water is necessary thereafter. In view of the subsequent washing efficiency, it is important to prevent cracks in the scorodite cake obtained by filtration at the stage of separating the scorodite from the post-reaction solution. If cracks occur in the cake, the subsequent water washing reduces the resistance of the water in the crack portion, so that water flows intensively through the portion, resulting in uneven cleaning.
In order to avoid cracks, it is better not to perform suction filtration, and it is preferable to perform gravity filtration (natural filtration). Although cracking may occur even under pressure filtration, the occurrence of cracks can be suppressed when a vertical filter press (the pressurizing direction of the cake is vertical) is used. This is because the vertical type can be a cake having a uniform thickness regardless of the amount. In horizontal filter press (cake pressurization direction is horizontal), slurry is filled from the bottom of the chamber, making it difficult to make a cake with uniform thickness like vertical filter press, and cracks enter the cake due to gravity. Cheap. Therefore, when the cake is washed with water, the water flows intensively in the thin portion of the cake or in the cracks, and it is difficult to uniformly wash the whole (even if washing is performed).

Process 3
Most of the post-reaction liquid adhering to the scorodite is removed by Step 2, but the arsenic elution at this stage often does not fall below the standard value for domestic disposal sites. The variation of the is also large. Therefore, in order to stably obtain a low-elution scorodite, it is important to further separate the post-reaction solution from the scorodite by further washing with water.

In step 3, the scorodite is washed with water and then separated from the washing solution by solid-liquid separation. Water-soluble components are washed away by water washing, and the arsenic elution property of scorodite gradually decreases as the number of times is increased. This is because most of the arsenic elution from scorodite is caused not by elution from scorodite itself but by adhesion of post-reaction solution.
Since amorphous scorodite that can be generated as a by-product during the synthesis of scorodite has high water solubility, it is considered that this thorough washing operation has been removed together with the post-reaction solution. Accordingly, the washing operation not only removes the post-reaction solution from the scorodite, but also serves to remove the by-produced amorphous scorodite.

  The washing method may be any known method and is not particularly limited, but the unit of washing operation is clarified, and the concentration of various post-reaction liquid components contained in the washing solution can be accurately measured after washing. Therefore, it is preferable to determine the amount of water to be used for one washing and to save all the washing liquid after being used for washing. If the water used for washing is drained and drained as it is, the unit of the washing operation becomes unclear, and even in a single washing operation, the components of the post-reaction liquid in the washing liquid at the start and end Therefore, the concentration of the cleaning liquid after cleaning the scorodite cannot be accurately grasped.

Examples of efficient cleaning methods include the following methods.
When washing and filtration are carried out continuously using a funnel, a washing method is preferred so that cracks do not occur in the scorodite cake. This is because cracks adversely affect cleaning efficiency. Filtration using a funnel does not generate cracks while water is present on the cake, i.e., when the cake is completely immersed in water, but if the water breaks and the cake is exposed on the surface of the water, the volume of the cake will increase. It shrinks and cracks occur. Therefore, it is desirable to perform filtration so that water is supplied without interruption and the entire cake is covered with washing water (eg, a state where the cake is completely immersed).
It is also effective to perform solid-liquid separation after adding scorodite into a washing tank and stirring or repulping. What is necessary is just to measure the density | concentration of the post-reaction liquid component contained in a water washing liquid with respect to the water washing liquid after solid-liquid separation. In this case, any of the methods described above in Step 2 may be used as the solid-liquid separation method, and the generation of cracks need not be concerned.
Another preferred method is to prepare a scorodite cake with a filter press, and supply the washing water in the filter press and then squeeze to wash and filter the cake directly (for example, a vertical type manufactured by Lalox) Cleaning with a filter press). It is preferable to store all of the used washing water in a suitable container so that it can be analyzed later. According to this method, the washing and filtering operation can be performed more simply than repulping. If it is a vertical filter press, cracks are less likely to occur.

  By the way, the concentration of As ions adhering to the scorodite immediately after synthesis varies from lot to lot, and the water content of the scorodite cake after solid-liquid separation also varies depending on the particle size of the scorodite. The number of washings and the amount of washing water required to obtain scorodite having elution characteristics vary from lot to lot. For this reason, the method of performing the cleaning simply by determining the number of times of cleaning and the amount of cleaning water may result in variations in the quality of the scorodite due to inadequate or excessive water cleaning. In addition, since the scorodite dissolution test requires shaking for 6 hours, if the scorodite dissolution test was performed for each cleaning to determine the end point of the cleaning, it was too laborious and lacked practicality.

  Therefore, in the present invention, if the concentration of post-reaction liquid components contained in the cleaning liquid decreases, the elution value of metal ions such as arsenic in the scorodite elution test also decreases, and the cleaning liquid after cleaning scorodite The elution characteristics of scorodite are controlled by monitoring the concentration of at least one selected from the following reaction components, such as As, Cu, Fe and S.

  While the concentration of the post-reaction liquid component contained in the washing liquid is high, the correlation with the elution value of As by the scorodite elution test is small, but as the concentration of the post-reaction liquid component decreases, the scorodite elution test (Ministry of the Environment notification) The correlation with the As elution value according to No. 13) becomes stronger, and the predictability of the As elution value by the scorodite elution test is increased from the concentration of the post-reaction liquid component contained in the cleaning liquid. For example, when one washing is performed at a ratio of 100 to 300 g of scorodite per liter of water, more typically 150 to 250 g (dry weight), when the As ion concentration in the washing liquid is reduced to about 1 mg / L, The As elution value by the scorodite elution test is approximately 1/10 to 10 times the concentration. When the As ion concentration in the washing solution decreases to 0.1 mg / L or less, the dissolution value of As in the scorodite dissolution test is approximately 1/3 to 3 times, typically 1/2 to 2 times the concentration. Become.

  Therefore, the elution value can be estimated by analyzing the arsenic concentration in the water washing solution without the need to perform a scorodite elution test. Since the washing operation takes about 10 minutes per time including solid-liquid separation, the elution characteristics of scorodite can be grasped in a short time. Since the current standard value for dissolution of As at domestic disposal sites is 0.3 mg / L or less, if this is the target for the dissolution value of As in the scorodite dissolution test, the target value of As ion concentration in the cleaning solution should be If it is set to 0.1 mg / L or less, preferably 0.05 mg / L, a scorodite that satisfies the elution standard can be obtained with a high probability.

  It is also possible to predict the elution value of As by the scorodite elution test from the concentration transition of other components contained in the post-reaction solution. If the ratio between the amount of water used for washing and the dry weight of scorodite is set to a constant value and the relationship between the concentration of As contained in the washing solution and the concentration of any post-reaction liquid component other than As is plotted, the reaction The As concentration remaining in the cleaning liquid can be estimated from the transition of the concentration of the post-liquid component. If the As concentration remaining in the cleaning liquid can be predicted, the elution value of As in the scorodite elution test can also be predicted as described above. In this way, it is possible to set a target concentration for any post-reaction liquid component remaining in the cleaning liquid.

  Since the As ion concentration in the washing solution generally changes at a low concentration of 1 to 0.01 mg / L, an advanced analytical instrument such as ICP is required for the analysis of arsenic. In addition, arsenic has low sensitivity and has a difficulty in low concentration analysis with low emission intensity. Therefore, by monitoring the post-reaction liquid component contained in the cleaning liquid at a higher concentration, the concentration analysis can be easily performed.

  For example, since a scorodite post-reaction solution using a sulfuric acid leaching solution of electrolytically precipitated copper as a raw material for an acidic aqueous solution contains Cu ions at a high concentration, it can be monitored. The Cu ion concentration in the washing solution generally changes in the range of 100 to 1 mg / L, and is higher than arsenic. Furthermore, with ICP, copper is more sensitive than arsenic. Therefore, analysis of copper is easier than analysis of arsenic.

  Furthermore, it is known that a colorimetric analysis (semi-quantitative) by visual observation using a copper ammonia complex is possible if the copper concentration is in the above range. Colorimetric analysis is a method in which when ammonia water is added to a dilute copper solution, a strong blue color is developed, and the intensity of the color development is compared with a standard sample to determine the copper concentration (semi-). By using this method, the end point of scorodite cleaning can be easily determined without using an advanced analytical instrument such as ICP.

  If the Cu ion concentration and As ion concentration contained in the cleaning liquid are known at a certain point in time, the As concentration also decreases by n digits (in the range of n−1 digits to n + 1 digits) when the Cu ion concentration is reduced by n digits. If the As ion concentration in the cleaning liquid at a certain time is 1 mg / L and the Cu ion concentration is 200 mg / L, the As ion concentration is 0.1 to 0.01 mg / L if the Cu ion concentration is reduced to 2 mg / L. Decreases to about L. When one washing is performed at a ratio of 100 to 300 g of scorodite per liter of water, more typically 150 to 250 g (dry weight), as described above, the As ion concentration in the washing solution is 0.1 mg / When it falls to L or less, it can be predicted that the dissolution value of As in the scorodite dissolution test is approximately 1/3 to 3 times, typically 1/2 to 2 times the concentration. Therefore, in this case, since the Cu ion concentration in the cleaning liquid has decreased to 2 mg / L, it can be predicted that the elution value of As in the scorodite elution test will be 0.3 mg / L or less.

  Therefore, when electrolytically precipitated copper sulfuric acid leachate is used as the acidic aqueous solution that is the raw material for scorodite, the transition of As ion concentration in the washing solution is grasped from the change in Cu ion concentration in the washing solution by the following general method. can do. That is, Cu ion concentration and As ion concentration contained in the water washing solution after performing step 3 n times (n ≧ 1), typically once, are measured, and targets are set according to the measurement results. After the Cu ion concentration to be set is set, the process is repeated until the Cu ion concentration contained in the washing solution used for washing the scorodite is lowered below the target value.

  When scorodite is produced under the suitable reaction conditions as described above, the As ion concentration in the post-reaction solution is 0.1 to 3 g / L, more typically 0.3 to 1 g / L, The Cu ion concentration is 10 to 60 g / L, more typically 20 to 40 g / L. Under such conditions, when one washing is performed at a ratio of 100 to 300 g of scorodite per liter of water, more typically 150 to 250 g (dry weight), the amount of arsenic eluted from scorodite is 0.3 mg / It has been empirically known that the copper concentration in the cleaning solution may be 10 mg / L or less, preferably 5 mg / L or less in order to make L or less. If the ratio of arsenic and copper in the solution after the reaction is significantly different, the target value of the Cu ion concentration may be reviewed.

  If copper is not included as a main component in the washing solution after scorodite washing, the end point of scorodite washing is similarly determined from the transition of the concentration of other main components such as iron and sulfur (contained as sulfate radicals) in the washing solution. Can also be determined.

In summary, the point of step 3 is that the concentration of the post-reaction liquid component contained in the washing solution used for washing scorodite and the arsenic elution characteristics of scorodite are related. By monitoring the concentration of post-reaction liquid components dissolved in the water washing solution, the arsenic elution characteristics of scorodite can be grasped indirectly, and the end point of washing can be easily determined. Specifically, the cleaning of the scorodite can be terminated when the concentration of at least one post-reaction liquid component contained in the water washing liquid falls below a preset value.
When sulfuric acid leaching solution of electrolytically precipitated copper is used as the acidic aqueous solution in Step 1, it is preferable to monitor Cu, S, Fe and As ions to be monitored as post-reaction liquid components contained in the washing solution, Preferred is Cu ion.

Electrolytically precipitated copper sulfuric acid leaching solution An electrolytically precipitated copper sulfuric acid leaching solution suitable as a raw material for scorodite can be obtained, for example, as follows.
First, a water washing treatment is optionally performed on the electrolytically precipitated copper. The washing process involves repulping the electrolytically precipitated copper with water, stirring for 0.5 to 6 hours, and including in the electrolytic solution (including copper sulfate, Ni, Fe, etc.) attached during the production of the electrolytically precipitated copper and the electrolytically precipitated copper After dissolving a minute amount of Ni, Fe and the like, the slurry is filtered and solid-liquid separation can be performed. In this step, most of Fe and Ni can be separated from the electrolytically precipitated copper.
However, this operation is necessary for the sulfuric acid leaching of the electrolytically precipitated copper in the next step by clarifying the amount of zero-valent (not dissolved in water) copper excluded from the copper amount in the electrolytically precipitated copper. The main purpose of this operation is to obtain a more accurate amount of sulfuric acid. This step is not necessary when trace elements such as Ni and Fe are not particularly concerned, or when the content of copper sulfate is known or the electrolytic solution is not brought into the electrolytically precipitated copper.

  After optionally washing with water, while introducing an oxygen-containing gas into the electrolytically precipitated copper in sulfuric acid acid, at a liquid temperature and time sufficient to oxidize the As component contained in the electrolytically precipitated copper to pentavalent The solution is stirred and subjected to sulfuric acid leaching, and then solid-liquid separation into a leaching residue containing an Sb component and a Bi component and a sulfuric acid leaching solution containing a pentavalent As component.

The leaching reaction occurring at this time generally follows the following equation: Cu is oxidized to Cu ²⁺ and As is oxidized to As ⁵⁺ .
Cu + H ₂ SO ₄ + 1 / 2O ₂ → CuSO ₄ + H ₂ O (1)
2As + 5 / 2O ₂ + 3H ₂ O → 2H ₃ AsO ₄ (2)
The amount of sulfuric acid used is preferably 1.0 to 1.2 equivalents relative to the amount of Cu. When it is less than 1.0 equivalent, the leaching solution becomes weakly acidic, precipitates such as Cu ₃ AsO ₄ are generated, and the leaching rate of Cu and As decreases. When it exceeds 1.2 equivalents, the leaching rate of Cu and As is not affected, but the amount of sulfuric acid used is increased. The concentration of Cu and As in the sulfuric acid solution is not particularly limited. However, if the solubility is exceeded, the leaching rate of Cu and As decreases, so that it is preferably not more than the solubility of Cu ²⁺ and As ⁵⁺ .
Further, the pH suitable for the production of the crystalline scorodite synthesized thereafter is 1.0 to 1.5, but if the sulfuric acid concentration is low, the efficiency of sulfuric acid leaching, that is, the recovery efficiency of copper and arsenic tends to decrease. Therefore, it is preferable that the concentration of sulfuric acid used at the time of sulfuric acid leaching is such that the pH is less than 1. Even if the sulfuric acid leachate has a pH of 1 or more, the trivalent iron added when synthesizing scorodite is preferably provided in the form of an acidic aqueous solution. For example, ferric sulfate aqueous solution or polysulfate The pH of the ferric aqueous solution is about 0.6.

In sulfuric acid leaching, in order to oxidize As to pentavalent, for example, it may be stirred at 70 to 95 ° C. for 4.5 to 11 hours, preferably at 80 to 95 ° C. for 7 to 11 hours. Since sulfuric acid leaching is an exothermic reaction, it can be performed without heating from the outside. The stirring time may be longer, and may be determined as appropriate in consideration of economy and effect.
In order to increase the oxidation efficiency of As, it is preferable to supply a sufficient amount of oxygen-containing gas bubbles to be introduced (for example, 10 equivalents of oxygen to copper for 7 hours). Therefore, it is preferable to vigorously perform stirring, and for example, introduction of oxygen-containing gas and / or stirring is conveniently performed by jet injection. This value is the case of jet injection (trade name of “Jet Agitator”), and in the case of a stirrer using a normal turbine blade, the reaction efficiency is lowered and the amount of oxygen-containing gas is introduced 3.5 times or more. However, a reaction time of 2 times or more is required. By performing As valence control at this stage, subsequent scorodite generation is facilitated. Cu ²⁺ also has the effect of promoting As oxidation.

  The oxygen-containing gas is not particularly limited as long as it does not have a significant adverse effect on the above reaction. For example, pure oxygen or a mixture of oxygen and an inert gas can be used. Air is preferable from the viewpoint of handling and cost.

An acidic aqueous solution containing pentavalent As and trivalent Fe is obtained by adding trivalent iron to the sulfuric acid leaching solution of the electrolytically precipitated copper thus obtained. In this case, examples of the trivalent iron include iron oxide, iron sulfate, iron chloride, and iron hydroxide. The trivalent iron is provided in the form of an acidic aqueous solution from the viewpoint of performing the reaction in the aqueous solution. It is preferable to provide it in the form of an aqueous solution of ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) from the viewpoint that it is most effective to return the solution after deironing to the electrolytic solution for electrolysis. Moreover, the polyferric sulfate aqueous solution used by waste water treatment etc. can also be used.
The amount of trivalent iron used is required to be 1.0 equivalent or more with respect to the amount of As from the viewpoint of removing As, and is preferably 1.1 to 1.5 equivalents from an economical viewpoint.

  Hereinafter, examples for better understanding of the present invention and its advantages will be described, but the present invention is not limited thereto.

Example 1
<Production of sulfuric acid leaching solution of electrolytically precipitated copper>
259 g of 98% concentrated sulfuric acid (1 equivalent to the copper contained in the electrolytically precipitated copper) was added to 418 g (dry weight) of the electrolytically precipitated copper, water was further added, and the amount of slurry was 1.85 L (slurry concentration 256 g / L). The mixture was stirred and leached for 7 hours while introducing air at 4 L / min. In order to increase the reaction efficiency, it is effective to make fine bubbles of air to be introduced. Therefore, a jet agitator (JET AJITER manufactured by SHIMAZAKI) was used for air introduction and stirring. The liquid temperature was controlled at 80 ° C. with a water bath. The copper concentration at the end of leaching was about 90 g / L, exceeding the solubility at room temperature of about 50 g / L. In order not to precipitate copper sulfate pentahydrate, it was diluted with water to 3.5 L. Then, the liquid after sulfuric acid leaching filtration (sulfuric acid leaching liquid) and the sulfuric acid leaching residue were separated into solid and liquid by suction filtration using a Buchner funnel. Table 1 shows the amounts of the obtained sulfuric acid leaching solution and sulfuric acid leaching residue.
The above operation was performed for two batches, and the resulting solution after sulfuric acid leaching filtration was mixed. It was used for the synthesis of the next scorodite crystal.

<Synthesis of scorodite crystals>
To 6.95 L of the sulfuric acid leachate (pH 0.86) of the electrolytically precipitated copper obtained above, 1.112 L of polyferric ferric sulfate (hereinafter referred to as polyiron) manufactured by Nittetsu Mining Co., Ltd. was added. The pH was 0.59. Then, while adjusting the liquid volume to 8.1 L during heating, it was heated to 95 ° C., and scorodite was synthesized for 24 hours. During heating, water was appropriately added and maintained at 8.1 L so as not to reduce the liquid volume too much due to evaporation. After the completion of the scorodite synthesis, the scorodite crystals were naturally filtered with a Buchner funnel, and solid-liquid separation was performed with care not to generate cracks. Table 2 shows the quantities of the obtained scorodite crystals and the post-crystal filtration liquid (post-reaction liquid).
In addition, in order to see the elution value of arsenic from scorodite when scorodite was separated from the reaction solution, scorodite was separately produced under the same conditions as described above. As a result of the arsenic elution test (test according to Ministry of the Environment Notification No. 13) for the scorodite, the arsenic elution was 7 mg / L and the copper elution was 1200 mg / L (see Table 3).

<Cleaning scorodite>
Subsequently, it was washed 6 times (3 L in total) with 500 mL of water on a scorodite cake (756.5 g wet weight, equivalent to 605 g dry weight) on a Buchner funnel. Filtration should be natural filtration (gravity filtration), and the washing water should be poured without interruption to maintain the condition that the scorodite crystals are immersed in the washing water so as not to crack the cake and cause uneven washing as described above. We paid close attention to prevent the cleaning effect from decreasing. Finally, it was confirmed that the blue color of copper ions disappeared from the washing solution and was colorless and transparent (previously, this was considered sufficient for washing). When a part of the scorodite was used to conduct an arsenic elution test (test in accordance with Ministry of the Environment Notification No. 13), the arsenic elution was 0.21 mg / L and the copper elution was 170 mg / L. (See Table 3). Thereafter, 338.4 g of scorodite on the Buchner funnel was collected, put into a 3 L beaker, 2 L of water was added, and repulped and stirred for 10 minutes. Thereafter, this was subjected to suction filtration and solid-liquid separation was performed.
This operation of repulping, stirring, and solid-liquid separation was repeated 10 times, and the residual concentrations of arsenic and copper in each filtrate (cleaning solution) were analyzed by ICP. The analysis values are shown in Table 4 and FIG. Further, when the scorodite after the 10 operations were subjected to an arsenic elution test (Ministry of the Environment Notification No. 13), the arsenic elution was 0.05 mg / L and the copper elution was 6.6 mg. / L (see Table 3).

Example 2
<Production of sulfuric acid leaching solution of electrolytically precipitated copper>
To 742 g (dry weight) of electrolytically precipitated copper, 702 g of 98% concentrated sulfuric acid (1.1 equivalents with respect to the copper contained in the electrolytically precipitated copper) was added, water was further added, and the slurry amount was 2.7 L (pulp concentration). 274 g / L). While introducing air at 5 L / min, the mixture was stirred and leached for 13.5 hours. In order to increase the reaction efficiency, it is effective to make fine bubbles of air to be introduced. Therefore, a jet agitator (JET AJITER manufactured by SHIMAZAKI) was used for air introduction and stirring. The liquid temperature was controlled at 80 ° C. with a water bath. The copper concentration at the end of leaching was about 150 g / L, exceeding the solubility at room temperature of about 50 g / L. In order not to precipitate copper sulfate pentahydrate, it was diluted with water to 8 L. Then, the liquid after sulfuric acid leaching filtration (sulfuric acid leaching liquid) and the sulfuric acid leaching residue were separated into solid and liquid by filtration. Table 5 shows the amounts of the obtained sulfuric acid leaching solution and sulfuric acid leaching residue. The obtained solution after filtration with sulfuric acid leaching was used for the synthesis of the following scorodite crystals.

<Synthesis and washing of scorodite crystals>
1.15 L of polyferric sulfate (hereinafter referred to as polyiron) manufactured by Nittetsu Mining Co., Ltd. was added to 8.08 L of the sulfuric acid leachate (pH 1.02) of the electrolytically precipitated copper obtained above. The pH was 0.74. Then, while adjusting the liquid volume to 9.3 L during heating, it was heated to 95 ° C., and scorodite was synthesized for 24 hours. During heating, water was appropriately added and maintained at 9.3 L so that the amount of liquid was not reduced excessively by evaporation. Immediately after mixing the sulfuric acid leachate and the ferric sulfate solution at room temperature, the reaction did not proceed, but the formation of scorodite was observed at 85 ° C. with heating. After the completion of the scorodite synthesis, the scorodite crystals were suction-filtered with a Buchner funnel and separated into solid and liquid. Table 6 shows the quantity of the obtained scorodite crystals and the liquid after crystal filtration.

Water was added to the scorodite crystals, repulped to a pulp concentration of about 200 to 250 g / L, stirred for 10 minutes, filtered, and separated into scorodite and washing solution. This operation was repeated 4 times. The filtration was gravity filtration so that cracks would not occur in the cake as in Example 1. Each washing solution was measured by a colorimetric method using a copper ammonia complex. The colorimetric analysis was performed according to the following procedure. About 90 mL of water washing solution after scorodite was washed with water was collected in a 100 mL transparent glass bottle with a lid, about 10 mL of 25% aqueous ammonia (reagent) was added, and the mixture was stirred to produce a copper ammonia complex for coloring. For copper standard solutions with known copper concentrations (for example, 50, 20, 10, 5, 1, 0 mg / L), a copper ammonia complex is generated and colored in the same manner. The concentration was quantified (semi).
In the first washing solution, since a blue color was observed in copper ions, it was determined that it greatly exceeded 50 mg / L and was not measured. The second time was 30 mg / L, the third time was 7 mg / L, and the fourth time was 7 mg / L. After the above washing, an arsenic elution test from scorodite was performed three times. The elution values were 0.09, 0.08, and 0.04 mg / L, and the elution was small and stable.

  Under the same conditions, a series of operations of electrolytic leaching copper leaching-scorodite synthesis-scorodite washing was performed a total of 8 times. It was judged that the cleaning was finished (by the copper ammonia complex) that the copper concentration in the washing solution was 10 mg / L or less. The number of washings until the copper concentration in the washing solution became 10 mg / L or less varied between batches and was 4 to 7 times. The respective elution values are shown in Table 7 (right side). The elution value of arsenic is stable with an average of 0.05 mg / L and a standard deviation of 0.03 mg / L.

Example 3
3.14 kg of scorodite synthesized in the same manner as in Example 2 (wet amount, dry weight conversion: 2.59 kg) was filtered with a vertical filter press (model: filtration test apparatus PF 0.1 type) manufactured by Lalox, and then pressed. The solid liquid was separated into a scorodite cake. Subsequently, 8 L of water was poured into the cake in the chamber of the filter press for washing and pressing. This operation was repeated 4 times. Each washing solution was quantified by colorimetric analysis of copper concentration in the same manner as in Example 2. The first washing was not measured. The second, third, and fourth washings were 50, 10, and 1 mg / L, respectively. After the above washing, the elution value of arsenic was 0.06 mg / L. As a result, it was proved that the method for determining the end point of cleaning with copper is effective even with a filter press.

Comparative Example 1
<Sulfuric acid leaching of electrolytically precipitated copper>
A sulfuric acid leachate was obtained from electrolytically precipitated copper by the same method as in Example 1, and used as a raw material for the next scorodite crystal synthesis.

<Synthesis method and cleaning of scorodite crystal>
To 1.24 L of electrolytically precipitated copper sulfuric acid leaching solution (pH 1.03), 0.265 L of polyferric sulfate (hereinafter referred to as polyiron) manufactured by Nippon Steel Mining Co., Ltd. was added. The pH was 0.61. Then, it heated to 95 degreeC, adjusting the liquid quantity to 1.5L during heating, and scorodite was synthesize | combined for 24 hours. During heating, water was appropriately added and maintained at 1.5 L so as not to reduce the liquid volume too much by evaporation. After the completion of the scorodite synthesis, the scorodite crystals were naturally filtered with a Buchner funnel, and solid-liquid separation was performed with care not to generate cracks. Table 8 shows the quantity of the obtained scorodite crystals and the liquid after crystal filtration.

Subsequently, it was washed 5 times (total 0.8 L) with 160 mL of water on a scorodite cake (220.9 g wet weight, equivalent to 163 g dry weight) on a Buchner funnel. The filtration was gravity filtration so that cracks would not occur in the cake as in Example 1. After the completion of the scorodite synthesis, it was finally confirmed that the blue color of the copper ions disappeared from the washing solution and was colorless and transparent. Using the scorodite, the arsenic elution test (test in accordance with Ministry of the Environment Notification No. 13) was conducted twice. As a result, the arsenic elution was 0.2 and 0.5 mg / L.
Under the same conditions, a series of operations of electrolytic leaching copper leaching-scorodite synthesis-scorodite washing was performed 13 times in total. Finally, it was confirmed that the blue color of copper ions disappeared from the washing solution and was colorless and transparent. The respective elution values are shown in Table 7 (left side). The average 0.4 mg / L, standard deviation 0.4 mg / L, and the elution value and variation are large.

Claims (8)

Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
A method for producing scorodite, comprising:
The sulfuric acid leaching solution of electrolytically-precipitated copper is used as a raw material for the acidic aqueous solution in Step 1, and Step 3 is based on Cu, S, and Fe contained in the water washing solution after performing the n-th (n ≧ 1) Step 3. Measure the concentration and As ion concentration of at least one post-reaction liquid component selected from the group, set the concentration of the post-reaction liquid component to be targeted according to the measurement results, and wash the scorodite with water The method comprising repeating the steps until the measured concentration value of the post-reaction liquid component contained in the washing solution used in step 1 falls below the target value. Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
A method for producing scorodite, comprising:
The sulfuric acid leaching solution of electrolytically precipitated copper is used as a raw material for the acidic aqueous solution in step 1, and in step 3, the ratio of the amount of water used for washing and the dry weight of scorodite is set to a constant value, and then As is contained in the washing solution. The relationship between the measured concentration value and the measured concentration value of at least one post-reaction liquid component selected from the group consisting of Cu, S, and Fe is plotted. The remaining As concentration is estimated, and the process is repeated until the As ion concentration estimated from the measured concentration value of the post-reaction liquid component contained in the washing solution used for washing scorodite is lowered to 0.3 mg / L or less. Including methods.   The method according to claim 1 or 2, wherein the concentration of the at least one post-reaction liquid component is a Cu ion concentration. Step 1 of heating an acidic aqueous solution containing pentavalent As and trivalent Fe at a temperature and time effective for the synthesis of crystalline scorodite;
-Step 2 of separating the synthesized scorodite from the post-reaction liquid by solid-liquid separation;
-After that, after washing the scorodite with water and separating the scorodite from the washing solution by solid-liquid separation,
A method for producing scorodite, comprising:
The sulfuric acid leaching solution of electrolytically precipitated copper is used as a raw material for the acidic aqueous solution in Step 1, the As ion concentration in the post-reaction solution is 0.1 to 3 g / L, the Cu ion concentration is 10 to 60 g / L, and Step 3 is 1 Washing is performed as a ratio of 100 to 300 g (dry weight) of scorodite per liter of water, and the Cu ion concentration contained in the washing solution used for scorodite washing is measured, and the measured Cu ion concentration is 10 mg / L. A method comprising repeating until reduced below.   The manufacturing method of Claim 3 or 4 which performs the Cu ion density | concentration analysis contained in the water washing liquid used for the water washing of a scorodite by a colorimetric analysis method.   6. The method according to any one of claims 1 to 5, wherein the water washing in step 3 is carried out by repulping and stirring after adding water to scorodite.   Step 2 is carried out by natural filtration on the funnel, and Step 3 pours wash water onto the scorodite installed on the funnel, and keeps the entire scorodite covered with wash water while the wash water is being poured. The manufacturing method as described in any one of Claims 1-6 implemented by gravity or suction filtration including this.   The process 3 is a manufacturing method as described in any one of Claims 1-7 implemented by compressing, after arrange | positioning a scorodite in a vertical filter press and supplying wash water.