JP6377460B2 - Method for treating sulfate starch - Google Patents

Description

  The present invention relates to a method for treating a sulfated starch, and more particularly to a method for treating a sulfated starch produced during the production of sulfuric acid during a non-ferrous smelting process and containing Hg and Se.

As described in Patent Document 1, sulfuric acid is conventionally produced during the nonferrous smelting process. When producing sulfuric acid, sulfurous acid gas (oxygen disulfide: SO ₂ ) that is also generated during the nonferrous smelting process is used. When producing sulfuric acid, the sulfurous acid gas is purified and impurities are removed from the sulfurous acid gas. In addition, what collected the said impurity is called a sulfated starch. This sulfated starch is a muddy substance and is also called sulfuric acid sludge or sulfuric acid thickener residue.

  The sulfated starch often contains Hg (mercury) and Se (selenium) for non-ferrous smelting. It is a heavy metal harmful to both Hg and Se. Therefore, even when the sulfated starch is disposed of, it is necessary to remove these harmful heavy metals. In order to cope with this, in the invention described in Patent Document 1, sulfuric acid starch (sulfuric acid sludge) is subjected to an attrition treatment, and then the sulfated starch subjected to the attrition treatment is subjected to a flotation treatment, and then subjected to a sulfidation treatment to produce Hg. Then, the flotation process is performed again to remove Hg and Se from the sulfated starch.

  Although different from the technique of removing Hg and Se from sulfated starch in a series of steps, various techniques for removing specific harmful heavy metals are known.

  For example, Patent Document 2 describes a technique for processing molten fly ash generated when melting and solidifying municipal waste or the like. Patent Document 2 describes that Hg is leached from molten fly ash using NaClO (sodium hypochlorite) in order to remove Hg contained in molten fly ash.

  Non-Patent Document 1 describes a method of adding Zn (zinc) powder to the waste liquid so as to reduce and collect Hg in the waste liquid.

  Patent Document 3 describes that in order to remove Se from the Se-containing liquid, sulfur dioxide gas is blown into the selenium-containing liquid and subjected to a reduction reaction, and the hydrochloric acid concentration of the selenium-containing liquid is adjusted to a specific value. Yes.

Japanese Patent Publication No. 60-47335 JP-A-8-41558 JP 2009-292660 A

The Chemical Society of Japan, 1989, (11), p. 1942-1948

  In the invention described in Patent Document 1, an apparatus for performing attrition processing is separately required. For this reason, the processing of Hg and Se becomes large, and the complexity of the process is unavoidable, which is disadvantageous in terms of cost.

In addition, as the inventor conducted diligent research, he faced a situation where it was difficult to remove Hg and Se quickly and reliably by simply applying each of the prior arts listed above.
More specifically, as described in Patent Document 1, the present inventor has intensively studied a technique for removing Hg and Se from sulfated starch. However, in this case, the present inventor used NaClO as described in Patent Document 2 to leach Hg and Se from the actual sulfated starch, and according to the contents described in Patent Document 2, It was found that the final removal of Hg and Se cannot be performed properly. Specifically, for example, Hg and Se are mixed with other metals, or the recovery rate of Hg and Se is low. That is, the present inventor has obtained the knowledge that the contents described in Patent Document 2 cause various problems at least with respect to sulfated starch generated during sulfuric acid production in the nonferrous smelting process.

  An object of the present invention is to propose a technique for quickly and reliably removing Hg and Se from sulfated starch by a relatively simple method.

  The present inventor who came into contact with the above findings conducted intensive research. As a result, the following knowledge was obtained.

In [0017] of Patent Document 2, the oxidation reaction changing from mercuric chloride (Hg ₂ Cl ₂ ) to mercuric chloride (HgCl ₂ ) when NaClO is added to the molten fly ash is balanced. The ORP (oxidation-reduction) potential when reaching the value of +900 mV (hereinafter, the oxidation-reduction potential is simply referred to as “potential”, and + is omitted in the potential). However, when the inventor independently conducted a test, when NaClO was added to an actual sulfated starch, as shown in a comparative example described later, 800 mV immediately before 900 mV, which was considered to be an equilibrium potential. In the case of using a potential, almost no leaching of Hg occurred. This is presumably because the mercury compound contained in the actual sulfate starch remains mercuric chloride (Hg ₂ Cl ₂ ), that is, monovalent Hg (ie, Hg ⁺ ). This finding has been obtained for the first time by the inventors' diligent study.

  Therefore, even if Hg and Se are leached using NaClO for sulfuric acid starch generated during sulfuric acid production in the non-ferrous smelting process, Hg is monovalent unless leaching is performed at a considerably high potential. As a result, the solubility becomes remarkably small and is mixed with other metals in the residue immediately after leaching.

  The present inventor has also found that the potential at the time of leaching using NaClO is not irrelevant to Se separated in the subsequent steps.

When the present inventor conducted a test to remove Hg and Se from an actual sulfate starch, as far as Se is concerned, if leaching is not performed at a considerably high potential, oxidation is insufficient and tetravalent (Se ⁴⁺ ) The inventor has gained the knowledge that it will remain. Then, when Zn powder is added to collect Hg as described in Non-Patent Document 1, Se precipitates unintentionally, or when Hg is sulfided and precipitated as described in Patent Document 1. Se precipitates unintentionally.

In other words, the contents of the above are different from the sulfated starch generated during the production of sulfuric acid during the non-ferrous smelting process in removing Hg and Se from the sulfated starch in a series of steps. By leaching with NaClO at a considerably high potential, Hg can be made highly soluble Hg ^2+, and Se is previously changed to Se ⁶⁺ that can avoid unintended precipitation. The present inventor has obtained the knowledge that this is possible.

Aspects of the present invention based on the above findings are as follows.
The first aspect of the present invention is:
In a method for treating a sulfated starch produced during the production of sulfuric acid in a non-ferrous smelting process and containing Hg and Se,
An oxidation leaching step in which Hg and Se are oxidized and leached from the sulfated starch using hypochlorite at a potential of 900 mV or more (in the case of a silver / silver chloride electrode);
After the oxidative leaching step, a metal-substituted powder is added to the filtrate obtained by solid-liquid separation, and Hg in the filtrate is precipitated by substituting the metal-substituted powder, thereby separating Hg in the precipitate from Se in the filtrate. A first separation step;
A second Hg separation step of adding an S source, which is a compound containing S, to the filtrate obtained by solid-liquid separation after the first Hg separation step, and sulfidizing and precipitating Hg remaining in the filtrate;
This is a method for treating sulfate starch.

According to a second aspect of the present invention, in the invention according to the first aspect,
The hypochlorite is sodium hypochlorite or potassium hypochlorite.

According to a third aspect of the present invention, in the invention according to the first or second aspect,
A Se separation step of reducing Se in the filtrate by solid-liquid separation after the second Hg separation step and precipitating metal Se.

According to a fourth aspect of the present invention, in the invention according to the third aspect,
The reduction occurring in the Se separation step is reduction using sulfurous acid gas.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects,
The metal substitution powder is a Zn-containing powder.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects,
The S source used in the second Hg separation step is sodium hydrosulfide.

  According to the present invention, it is possible to provide a technique for quickly and reliably removing Hg and Se from sulfated starch by a relatively simple method.

It is a flowchart which shows the processing method of the sulfated starch in this embodiment.

Hereinafter, embodiments of the present invention will be described in the following order. In the description, FIG. 1, which is a flowchart showing a method for treating sulfate starch, will be referred to as appropriate.
1. Method for treating sulfate starch 1-A) Oxidative leaching step 1-B) Hg first separation step 1-C) Hg second separation step 1-D) Se separation step 1-E) Others 2. Effects of the embodiment Modifications etc. In this specification, “to” refers to a value that is greater than or equal to a predetermined value and less than or equal to a predetermined value.

  Sulfuric acid starch is a by-product generated in a sulfuric acid process for producing sulfuric acid from gas generated when roasting concentrate is roasted in non-ferrous smelting operations. In addition to sulfates, most of the types of elements contained in the original sulfide concentrate ore include variations in quantity. For example, sulfated starch from zinc smelting includes not only zinc and sulfur but also mercury, selenium, lead, iron, cadmium, arsenic, aluminum, cobalt, nickel, copper, noble metals, and rare metals. The compounded state of these elements is a complex state with both compound species and composition ratios being complex. Looking at the composition by element, Hg (mercury) is 5 to 20% by mass (dry), Se is 1 to 6% by mass (dry), and other metals except mercury and selenium are mostly zinc and lead. It is about ˜50 mass% (dry). In addition, oxides, halogens and the like are also included in a few percent.

<1. Method for treating sulfate starch>
1-A) Oxidative leaching step In this step, at least Hg and Se are oxidized and leached from sulfated starch using hypochlorite (as a specific example in this embodiment, sodium hypochlorite (NaClO)). . One of the major features of this embodiment is that this step is performed at a potential of 900 mV or higher. Note that the potential 900 mV referred to here is a potential when a silver / silver chloride electrode is used, and is simply referred to as “potential 900 mV” hereinafter. Detailed knowledge about the potential of 900 mV or more is as described above.

Thanks to this process, first, regarding Hg, even if an actual starch sulfate is used, mercuric chloride (Hg ₂ Cl ₂ or Hg ⁺ ) having low solubility is changed to mercuric chloride (HgCl ₂ or Hg ²⁺ ). It can be reliably oxidized. As a result, most of the Hg can be leached from the actual sulfated starch.

In addition to Hg, with respect to Se, by performing this step at a potential of 900 mV or higher, Se can be oxidized to Se ⁶⁺ through Se ⁴⁺ . As described above, if Se ⁴⁺ is left as it is, Se is unintentionally precipitated when Zn powder is added to collect Hg, or Se is intended to precipitate when Hg is sulfided. It will settle without. On the other hand, if Se is oxidized to Se ⁶⁺ in this step, it is possible to suppress unintended Se precipitation.
The chemical reaction formula that brings about the oxidation of Se is as follows.
Hg-Se + 3NaClO + 2H ₂ SO ₄ → HgCl ₂ + H ₂ SeO ₄ + Na ₂ SO ₄ + H ₂ O + NaCl + O ₂

  That is, in addition to the original position of leaching Hg and Se, this process also serves as a preparation process for reliably separating Se in the subsequent Se separation process.

  In addition, it is preferable that the density | concentration of the solution of the hypochlorite (in this embodiment NaClO) used at this process is 10 mass% or more (preferably 10-20 mass%). If the concentration is within this range, the amount of NaClO solution can be adjusted to an appropriate amount. The amount of NaClO solution affects the total amount of subsequent filtrate. Therefore, in consideration of work efficiency, it is preferable to set the concentration within the above range so as to reduce the NaClO solution. Note that a commercially available NaClO may be used, or a waste liquid containing NaClO may be used. Hypochlorite can be used. Among these, sodium hypochlorite (NaClO) and potassium hypochlorite (KClO) are preferable.

Incidentally, the precipitate in this step (hereinafter also referred to as residue) contains Au and Ag that are often contained in sulfated starch, and these elements may be separately collected. If this step is not performed at a potential of 900 mV or higher, monovalent Hg (Hg ₂ Cl ₂ ) is mixed with Au or Ag in the residue. This process also has a role of suppressing the occurrence of the phenomenon.

  In this step, the potential is set to 900 mV or more (silver / silver chloride electrode). However, in order to achieve the effects described above, the potential exceeds 900 mV, further, the potential is 950 mV or more, and the potential is 980 mV or more. Is more preferable. Incidentally, although it is not necessary to set the upper limit of the potential in particular, good results can be obtained up to at least 1000 mV.

1-B) Hg first separation step In this step, Zn powder is added to the filtrate after the oxidation leaching step, and Hg in the filtrate is precipitated by substituting with Zn, and Hg in the precipitate and in the filtrate Of Se.

  The reason for using Zn powder in this step is as follows. That is, when metallic Zn powder is added to the filtrate, a substitution reaction occurs between Zn and Hg on the surface of the Zn powder due to the reducing action of the Zn powder in the filtrate. Fixed. For this reason, since it becomes a stable immobilization state, it is excellent in filterability and collection | recovery of Hg becomes easy.

  As another reason, in order to precipitate Hg, there is also a technique in which Hg is sulfided as described in Patent Document 1. However, when the present inventor conducted a test, when Hg was sulfided, the filterability of the precipitated Hg sulfide was extremely poor. This is a more prominent issue due to the increased amount of precipitate when the Hg leaching rate is increased in the oxidation leaching step. As a result, it becomes impossible to quickly separate Hg sulfide and thus Hg as a base.

  Thus, as a result of intensive studies by the present inventors, it has been found that when Zn powder is added to the filtrate after the oxidative leaching process, precipitation of Hg with very good filterability can be obtained. That is, by using Zn powder in this step, the filterability of precipitated Hg can be improved, and as a result, Hg can be separated quickly.

  Another reason for using Zn powder is that it is relatively inexpensive, easy to handle, and easily available. In addition, about those reasons, the preferable example of this process is given below.

  Instead of the Zn powder, a substituted metal powder made of a metal that can replace Hg may be used. For example, there are silver, copper, iron and the like. The composition of the substitution metal powder may be an alloy such as zinc or copper, and a substitution reaction may occur as appropriate, and the particle diameter may be 5 mm or less. About a composition, when using in a nonferrous smelting process, it is good to use according to the recovery metal of nonferrous smelting. In particular, zinc is the most suitable for the present invention because it is also a recovered metal in the zinc smelting process and is a metal excellent in substitution reactivity. Therefore, it is more preferable to use Zn-containing powder.

  The Zn powder used in the first Hg separation step is preferably produced from Zn contained in a precipitate generated in the method for treating sulfate starch. As described above, the Zn powder not substituted for Hg precipitates with Hg. In other words, by recovering Zn from this precipitate and regenerating Zn powder, it becomes possible to recycle the regenerated Zn powder in the Hg first separation step in the processing method of sulfate sulfate in another cycle. As described above, it is possible to establish a kind of circulation processing step by using a waste liquid containing NaClO and using sulfurous acid gas generated during sulfuric acid production in the Se separation step described later.

  The amount of Zn powder is preferably 2 to 3 equivalents relative to the concentration of Hg. Of course, Zn powder may be added beyond this range, but eventually, the Zn powder remaining without being replaced with Hg is contained in the Hg residue. In addition, it is preferable that the Zn powder is charged in several degrees in terms of improving the substitution efficiency for Hg.

1-C) Hg second separation step In this step, an S source that is a compound containing S (sulfur) is added to the filtrate between the previous Hg first separation step and the Se separation step described later. Thus, Hg remaining in the filtrate is sulfided and precipitated.

  As the positioning of this step, first, there is a role of separating Hg remaining in the filtrate without being completely separated in the previous Hg first separation step.

  However, the role of this process in this embodiment does not stop there. More specifically, it also means a preparation for separating Se quickly and reliably in the Se separation step described later. As will be described in detail later, Se is reduced and precipitated in the Se separation step described later. As described in the item of the example, for example, when this step is not performed and the Se separation step is performed with sulfurous acid gas and hydrochloric acid 3N, the time required for the reduction reaction is 180 minutes. Thus, the time required for the reduction reaction can be shortened to 60 minutes. Moreover, according to the study by the present inventor, it is clear that the effect of shortening the time is further increased when the concentration of hydrochloric acid is lowered.

In the present embodiment, preparations are made twice in order to separate Se quickly and reliably. That is, “the oxidation leaching step is performed at a potential of 900 mV or more and Se is pre-changed to Se ⁶⁺ ” and “the Hg second separation step is performed using the S source, and S is present in the filtrate. Is a preliminary preparation.

The S source used in this step may be a known one, but sodium hydrosulfide (NaSH) is preferable in terms of availability and handling. In addition, hydrogen sulfide may be used.
Further, the amount of S source is preferably about 10 equivalents relative to the concentration of Hg remaining in the filtrate. Of course, the S source may be input outside this range. However, if the S source is excessively input excessively, unintended sulfide precipitation or sulfide complex ions may occur. May be affected. It is preferable to determine the amount of the S source in consideration of this point.

1-D) Se separation step In this step, after the second Hg separation step, Se in the filtrate by solid-liquid separation is reduced to precipitate metal Se. More specifically, Se is reduced and precipitated by adding a substance having reducibility to the filtrate (hereinafter, also simply referred to as “reducing substance”). Since the potential is set to 900 mV or more in the oxidation leaching step, Se changes to Se ⁶⁺ instead of Se ⁴⁺ , and it becomes possible to separate most of Se contained in the sulfate starch for the first time in this step. . Further, by performing this step, Se (metal selenium) having a quality of 90% or more can be recovered.

Incidentally, the reducing agent in this step is also may be used known ones, preferred is sulfur dioxide (SO ₂₎ and sodium bisulfite (NaHSO _3). In particular, for sulfurous acid gas, it is preferable to use sulfurous acid gas generated during the production of sulfuric acid. As described above, this makes it possible to establish a kind of circulation process.

1-E) Others Through the above steps, Hg and Se are removed from sulfated starch. In addition, you may provide processes other than said process suitably. For example, you may provide the process of processing the filtrate after passing through said process suitably and discharging | emitting to nature.

<2. Advantages of the embodiment>
According to this embodiment, there are mainly the following effects.

By removing Hg and Se from the sulfate starch in a series of steps, the sulfate starch generated during the production of sulfuric acid during the non-ferrous smelting process is leached with NaClO at 900 mV or higher. , Hg can be Hg ²⁺ having high solubility, and Se can be changed in advance to Se ⁶⁺ that can avoid unintended precipitation.

  As a result, according to this embodiment, it is possible to provide a technique for quickly and reliably removing Hg and Se from sulfated starch by a relatively simple method.

<3. Modified example>
The technical scope of the present invention is not limited to the above-described embodiments, and includes various modifications and improvements as long as the specific effects obtained by the constituent elements of the invention and combinations thereof can be derived.

  In the present embodiment, it is very preferable to provide a Se separation step, but even when the Se separation step is performed separately, for example, preparations for obtaining metal Se up to the Hg second separation step are sufficiently prepared, Hg is already well separated. Therefore, the effect of the present invention is sufficiently achieved even if the Se separation step is not included in the series of steps.

  Next, an Example is shown and this invention is demonstrated concretely. Of course, the present invention is not limited to the following examples.

  In Examples 1 and 2 and Comparative Example 1, a series of steps corresponding to this embodiment were performed from the sulfated starch to the removal of Hg and Se. In Example 1, the test was performed in a relatively small scale (so-called laboratory level), and in Example 2-1, Example 2-2, and Comparative Example 1, the test was performed under a larger scale. went.

On the other hand, in Examples 3-4, the test for proving that the example given by this embodiment was suitable was done.
For example, in Example 3, Comparative Example 2 (using H ₂ O ₂ ) and Comparative Example 3 (using KMnO ₄ powder) were compared in order to prove that it is preferable to use NaClO in the oxidative leaching process. A test was conducted.
Moreover, in Example 4, in order to prove the improvement degree of the filterability by using Zn powder in the Hg first separation process, a test was conducted with Comparative Example 4 (Hg precipitated by sulfurization) as a comparison target.

<Example 1>
In this example, a 1 L test tank was used. The blade shape of the stirrer was a three-paddle paddle, and the rotation speed was 250 to 300 rpm. In addition, the sulfated starch used as a process target used the thing produced from the company. The quality of Hg contained in the sulfated starch was 20.0% by mass, and the quality of Se was 2.5% by mass. The quality of other metal components (Zn, Pb, Ag, Cu, As, Ti, Al) is 38.2% by mass, and the rest is other contents (sulfur, oxygen, halogen, etc.).

1-A) Oxidation Leaching Step In this step, 1 L of NaClO solution was used. Then, the above-mentioned sulfated starch was immersed in a NaClO solution in a test tank, and Hg and Se were leached. At that time, the amount of sulfated starch was set to 100 g / L in the NaClO solution. The reaction time was 30 minutes and the end point temperature was 40 ° C. The potential was set to exceed 900 mV. As potential measurement conditions, a silver / silver chloride electrode was used at the end of the reaction time, and the end point temperature was 40 ° C. The same applies hereinafter.
As a result, the leaching rates of Hg and Se were both 98 to 99%, which was a very good result. The leaching rate of Hg and Se was determined from the composition of the sulfated starch and the amounts of Hg and Se contained in the solution after completion of the reaction. The amounts of Hg and Se were determined using an ICP emission spectrometer manufactured by thermo. Hereinafter, the measurement method for the amounts of Hg and Se is the same.

1-B) Hg First Separation Step In this step, 2.0 to 2.5 mol equivalent of Hayashi Metal Zn powder was used in a molar ratio with respect to Hg. And said Zn powder was injected | thrown-in with respect to the test tank, Hg in NaClO solution was substituted with Zn, and Hg was precipitated. The reaction time was 30 to 40 minutes and the end point temperature was 10 to 15 ° C. The potential was set to around 0 mV. After completion of the reaction, filtration was performed using a suction filtration device as solid-liquid separation. The conditions at that time were a filtration surface diameter of 8 cm, a filtration area of 0.00503 m ² , and a suction pressure of 0.5 kg / cm ² .
As a result, the time required for the filtration was 9.7 minutes, and the filtration could be performed in a very short time. Further, when the filtrate was examined, the removal rate of Hg was a value exceeding 99%, and the concentration of Hg was below the lower limit of calibration (1 ppm), which was a very good result. Incidentally, the quality of Hg in the precipitate which became a residue was 45 to 50% when examined by an ICP emission analyzer manufactured by thermo, and Hg was present in the residue in an amount of 60% by weight. The molar ratio of Hg / Zn in the residue was 1.8 to 2.0.

1-C) Hg second separation step In this step, the filtrate after the Hg first separation step was transferred to CT (cone tank). Then, 10 mL of 0.3% NaSH is added to the tank, and Hg remaining in the filtrate is precipitated by sulfidation, and S is contained in the filtrate as a preparation for the Se separation step. It was. The reaction time was 10 minutes and the end point temperature was 20 ° C. The final potential was −60 mV, and the pH was 5.8 to 6.0. After completion of the reaction, filtration was performed using a pressure filter as solid-liquid separation in the same manner as in the Hg first separation step.
As a result, when the filtrate was examined, the concentration of Hg was below the lower limit of calibration (1 ppm), which was a very good result.

1-D) Se separation step In this step, after transferring the filtrate after the second Hg separation step to the original test tank, 12N HCl was added to the filtrate so that the HCl would be 3N. Of HCl was added to the filtrate. Then, while the sulfurous acid gas generated at the time of sulfuric acid production in-house was blown in at a flow rate of 500 mL / min for 180 minutes, it was heated to 80 ° C. by a heater to perform a reduction reaction from Se ⁶⁺ to Se. After completion of the reaction, filtration was performed using a suction filtration device in the same manner as in the Hg first separation step.
As a result, when the filtrate was examined, the removal rate of Se was a value exceeding 99%, which was a very good result. The quality of Se in the precipitate that became a residue was 90 to 99% when examined by an ICP emission spectrometer manufactured by thermo, and extremely high quality metal selenium was obtained. The concentration of Hg was 10 ppm or less, and Hg and Se could be reliably separated.

<Example 2-1>
Whereas Example 1 was of a laboratory level scale, in this example, a 100 L test tank was used. In addition, various conditions different from Example 1 are summarized in Tables 1 and 2 below. Table 1 shows the conditions relating to the entire process, and Table 2 shows the results including the contents of Hg and Se in sulfated starch, the conditions of the oxidative leaching process and filterability, and the final Hg and Se recoveries. Note that the waste solution was used as the NaClO solution.

  In addition, the liquid amount in each process, the amount of residue, the data regarding Hg, and the data regarding Se are described below.

1-A) Oxidation Leaching Step First, the weight of sulfated starch was 10.27 kg. The quality of Hg contained in the sulfated starch was 20.7%, and the weight was 2126 g. The quality of Se was 2.3% and the weight was 239 g. Other metals (zinc, copper, lead, iron, cadmium, cobalt, nickel, noble metals, gallium, indium) 24.7% by mass, other contents are mercury, selenium, oxygen other than other metals, sulfur, halogen, etc. The remainder is mostly oxygen and sulfur.
And in 106 L of back solutions after performing this process, the density | concentration of Hg is 19 g / L, the weight is 2016 g, and a distribution rate is 94.8 when the distribution rate of a sulfated starch is 100%. %Met. The concentration of Se was 2.29 g / L, the weight was 242.9 g, and the distribution rate was 101.5% when the distribution rate of the sulfated starch was 100%. The method of defining the distribution rate will be the same hereinafter. The distribution rate has an analysis error of 2% or less in the numerical value.
Moreover, in 7.54 kg of residues after performing this process, the quality of Hg was 0.4%, the weight was 27.4 g, and the distribution rate was 1.3%. The grade of Se was 0.1%, the weight was 4.3 g, and the distribution rate was 1.8%.
That is, the residue after this step contained almost no Hg or Se, and most Hg and Se in the sulfated starch could be leached.

1-B) Hg first separation step In the filtrate 106L after this step was performed, the concentration of Hg was 0.006 g / L, the weight was 0.6 g, and the distribution rate was 0.03%. . The concentration of Se was 2.2 g / L, the weight was 228.1 g, and the distribution rate was 95.3%.
Moreover, in the residue 3.38kg after performing this process, the quality of Hg was 58.6%, the weight was 1984.3g, and the distribution rate was 93.3%. The grade of Se was 0%, the weight was 0 g, and the distribution rate was 0%.
In other words, most of the residue after this step was composed of Hg, and Se was not contained at all. On the other hand, the filtrate contained almost no Hg, and Hg and Se could be reliably separated.

1-C) Hg Second Separation Step In the filtrate 106L after this step was performed, the concentration of Hg was 0.002 g / L, the weight was 0.2 g, and the distribution rate was 0.010%. . The concentration of Se was 2.05 g / L, the weight was 217.5 g, and the distribution rate was 90.85%.
Moreover, in 0.005 kg of the residue after performing this step, the quality of Hg was 14.9%, the weight was 0.84 g, and the distribution rate was 0.04%. The grade of Se was 0.4%, the weight was 0.023 g, and the distribution rate was 0.009%.
That is, Hg remaining in the filtrate after performing this step could be removed.

1-D) Se separation step In the filtrate 140L (increased by the amount of HCl solution) after performing this step, the concentration of Se is 0.00005 g / L, the weight is 0 g, and the distribution rate is 0.0029. %Met.
Moreover, in 0.3 kg of residue after performing this process, the quality of Hg was 0.0002%, the weight was 0 g, and the distribution rate was 0.00002%. On the other hand, the grade of Se was 99.2%, the weight was 0.22 kg, and the distribution rate was 90.77%.
That is, most of the residue after this step is composed of Se, but hardly contains Hg, and Hg and metal Se could be reliably separated. Finally, Hg and Se were successfully removed from sulfated starch quickly, reliably and in a relatively simple manner.

<Example 2-2>
Also in this example, a 100 L test tank was used. Other conditions were the same as in Example 2-1, except that sulfated starch having a different composition of Hg, Se, other metals, and other inclusions was used. The conditions for the composition are described in Table 2 above.

<Comparative Example 1>
In this comparative example, the same conditions as in Example 2-1 were adopted except that the potential in the oxidation leaching step was 818 mV and less than 900 mV. The results are also listed in Table 2 above.

As can be seen from Table 2, Examples 2-1 and 2-2 show very good results in terms of Hg and Se leaching rate, filterability, and final Hg and Se removal rate. And Hg and Se were able to be removed reliably.
On the other hand, in Comparative Example 1, since the leaching rate of Hg and Se was inferior in the first place and the separation property between sulfated starch and Hg and Se was not good, the test itself was stopped. Furthermore, the removal rate decreased with each step, and the test was interrupted.

<Example 3>
As test conditions, 10 g of sulfated starch was repulped into 100 ml of water, and the concentration of sulfated starch was 100 g / L. The stirring speed was 200 to 300 rpm. Then, NaClO having a mass concentration of 14% was added to the sulfated starch, and the leaching rates of Hg and Se were measured while increasing the potential to more than 900 mV. In this example, Comparative Example 2 (using H ₂ O ₂ ) and Comparative Example 3 (using KMnO ₄ powder) were compared in order to prove that it is preferable to use NaClO in the oxidative leaching process. As a test. The results are shown in Table 3 below.

<Comparative example 2>
In this comparative example, the test was performed under the same conditions as in Example 3 except that 300 mL of 30% concentration H ₂ O ₂ was used in the oxidation leaching step. The results of this comparative example are also listed in Table 3.

<Comparative Example 3>
In this comparative example, the test was performed under the same conditions as in Example 3 except that 2 g of KMnO ₄ powder manufactured by Kishida Chemical was used in the oxidation leaching step. The results of this comparative example are also listed in Table 3.

  When Example 3, Comparative Example 2 and Comparative Example 3 were compared, in Example 3, a good leaching rate was obtained by using NaClO. On the other hand, in Comparative Examples 2 and 3, even if a potential exceeding 900 mV was set, a good leaching rate could not be obtained.

<Example 4>
In the present Example, in order to prove the improvement degree of the filterability by using Zn powder in the Hg first separation process, a test was conducted with Comparative Example 4 (Hg precipitated by sulfurization) as a comparison target. The results are shown in Table 4 below. This embodiment corresponds to the first embodiment.

<Comparative Example 4>
In this comparative example, the test was performed under the same conditions as in Example 4 except that Hg was precipitated by sulfurization in the Hg first separation step. The results of this comparative example are listed in Table 5 below. The test conditions for precipitating Hg by sulfidation in the first Hg separation step were the same as those in the second Hg separation step in Example 1. Moreover, after completion | finish of reaction made to precipitate by sulfidation, it filtered using the pressure filter machine made from an Advantech company. The conditions at that time were a filtration surface diameter of 12 cm, a filtration area of 0.01131 m ² , and a pressure of 4.2 kg / cm ² . That is, compared with Example 4 (namely, Example 1), the filtration surface diameter was 1.5 times, the filtration area was about 2 times, and the pressure was about 8 times. In other words, in Example 4, the filtration surface diameter is 2/3 compared to Comparative Example 4, the filtration area is about half, and the pressure is 1/8. It has been placed.

  Comparing Example 4 and Comparative Example 4, compared to Comparative Example 4, in Example 4, the filtrate amount of 1 L was filtered in spite of being placed in a more disadvantageous condition than Comparative Example 4. The filtration speed was improved 5 times or more. In Example 4, the filterability with respect to the precipitation of Hg was remarkably improved.

  As a result, according to the above-described examples, it has been clarified that it is possible to provide a technique for quickly and reliably removing Hg and Se from sulfated starch by a relatively simple method.

Claims (5)

In a method for treating a sulfated starch produced during the production of sulfuric acid in a non-ferrous smelting process and containing Hg and Se,
An oxidation leaching step in which Hg and Se are oxidized and leached from the sulfated starch using hypochlorite at a potential of 900 mV or more (in the case of a silver / silver chloride electrode);
After the oxidative leaching step, a metal-substituted powder is added to the filtrate obtained by solid-liquid separation, and Hg in the filtrate is precipitated by substituting the metal-substituted powder, thereby separating Hg in the precipitate from Se in the filtrate. A first separation step;
A second Hg separation step of adding an S source, which is a compound containing S, to the filtrate obtained by solid-liquid separation after the first Hg separation step, and sulfidizing and precipitating Hg remaining in the filtrate;
Se separation step of reducing Se in the filtrate by solid-liquid separation after the Hg second separation step and precipitating metal Se;
A method for treating sulfate starch.   The method for treating a sulfated starch according to claim 1, wherein the hypochlorite is sodium hypochlorite or potassium hypochlorite. The method for treating a sulfated starch according to claim 1 or 2 , wherein the reduction occurring in the Se separation step is reduction using sulfurous acid gas. The method for treating a sulfated starch according to any one of claims 1 to 3 , wherein the metal-substituted powder is a Zn-containing powder. The method for treating a sulfated starch according to any one of claims 1 to 4 , wherein the S source used in the second Hg separation step is sodium hydrosulfide.

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