JPS6220868B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for effectively treating an aqueous solution containing at least arsenic and iron, such as heavy metal-containing water produced in a smelting process, using iron-oxidizing bacteria. In general, non-ferrous metal minerals contain toxic substances such as arsenic and cadmium in addition to the metals to be extracted, and these can cause various problems in the smelting process or be mixed into products and by-products, causing a decline in quality. It's summery. In particular, arsenic is volatilized during the process of melting raw material concentrate in a smelting furnace and concentrated in smoke ash. In recent years, as flash-smelting furnaces have been adopted as primary smelting furnaces, the SO ₂ concentration in the exhaust gas is high and it is used as raw material for sulfuric acid, so arsenic that does not settle in the flue is discarded in the sulfuric acid process. Since it is collected in sulfuric acid, a method is known in which sodium hydrogen sulfide or the like is added to this to precipitate and remove it as As ₂ S ₃ . Other methods include co-precipitating arsenic with Fe ³⁺ ions such as ferric sulfate in a sulfuric acid solution, and co-precipitating As ³⁺ with hydrogen peroxide, etc. as in Japanese Patent Application Laid-open No. 49-20952. Another method is to oxidize it to As ⁵⁺ using an oxidizing agent, and then remove it by coprecipitation with a hydroxide such as calcium hydroxide in an alkaline solution. However, all of these methods require the use of a large amount of reagent to remove arsenic, and in cases where arsenic is particularly concentrated, operations such as two-step processing are required, which increases the amount of reagent required. This resulted in an increase in the amount of sediment and precipitate produced, leading to increased costs. The present inventors focused on the fact that the sulfuric acid acidic solution produced in the hydrometallurgical process of wet smoke ash processing factories contains a large amount of Fe ²⁺ ions in addition to a high concentration of arsenic. This using oxidizing bacteria
We have found an effective and low-cost method to oxidize Fe ²⁺ to Fe ³⁺ and then react this Fe ³⁺ with arsenic to remove it. Conventional methods for oxidizing Fe ²⁺ to Fe ³⁺ include adding oxidizing agents such as MnO ₂ , KMnO ₄ , and Cl ₂ , and oxidizing and precipitating by blowing air under conditions of high temperature, high pressure, and high pH. These methods are known, but all of them consume large amounts of chemicals and energy and are expensive. Additionally, Fe ²⁺ can be extracted using iron-oxidizing bacteria.
There are examples of substances that oxidize to Fe ³⁺ , such as Japanese Patent Publication No. 47-38981, which was proposed by the applicant, but these are mainly used for the treatment of underground drainage, and they contain a high concentration of Fe ²⁺ and a large amount of arsenic. The smelting process product liquid contained therein was considered unsuitable for use by the bacteria. The present invention provides a method for efficiently removing and recovering arsenic from the smelting process liquid etc. using this iron-oxidizing bacteria. Describe. First, a neutralizing agent such as calcium carbonate is added to a liquid to be treated, such as a liquid produced in the smelting process, containing at least arsenic and Fe ²⁺ ions in an amount equal to or more than the equivalent of arsenic, the pH is adjusted to 2.0 to 2.8, and the reaction is carried out. Solid-liquid separation is performed, the resulting precipitates such as gypsum are separated and recovered, and the liquid is sent to a de-arsenization tank. In this case, as a neutralizing agent, in addition to the above calcium-based neutralizing agent, alkali metal-based sodium hydroxide,
Potassium hydroxide, sodium carbonate, magnesium-based magnesium oxide, magnesium hydroxide,
Magnesium carbonate, ammonia, etc. can also be used, but especially if a neutralizing agent containing K ⁺ , Na ⁺ , NH ₄ ⁺ etc. is used, a large amount of dialosite, which is a basic iron precipitate, will be produced in the bacterial oxidation tank in the third step, which will be described later. It is difficult to control the amount of metal that is generated, and when such a strong alkali is used, a high PH area is generated locally during the reaction, causing heavy metals such as copper and zinc to precipitate, which can hinder recovery in subsequent processes. Become. In addition, the inventors' tests have confirmed that the same arsenizing effect can be obtained even if the precipitates such as gypsum generated in the above neutralization process are sent to the next process, the arsenizing tank, without being separated and recovered. However, commercially available gypsum can be obtained by separating and recovering it in the neutralization process as described above. The arsenization tank contains Fe ³⁺ oxidized in the oxidation tank described later.
The ions are returned and undergo the following reaction with arsenic. AsO ₃ ^3- +2Fe ³⁺ +H ₂ O→AsO ₄ ^3- +2Fe ²⁺ +2H ⁺
…(1) AsO ₄ ^3- +Fe ³⁺ →FeAsO ₄ …(2) This results in the precipitation of white FeAsO ₄ (iron arsenate), and since this reaction occurs instantaneously, the reaction can be completed with just a few minutes of stirring. ends. In this case, Fe ³⁺ /As=
More than 90% of arsenic can be separated by precipitation in about 1 hour. In the arsenization step, the PH value decreases due to the introduction of the Fe ³⁺ liquid from the next oxidation step and the generation of free acid by the reaction between arsenic and the Fe ³⁺ liquid, so the same procedure as in the neutralization step is performed. PH 2.0-2.8 with calcium carbonate
Adjust to the range of . Figure 1 is a graph showing the relationship between pH and residual arsenic concentration in the solution as determined by a beaker test. The residual arsenic concentration in the liquid after solid-liquid separation after neutralization is (-○
-), and the residual arsenic concentration in the liquid after solid-liquid separation after neutralization treatment in which the stock solution was neutralized with calcium carbonate while reacting with Fe ³⁺ solution is shown by (-△-). The difference between (-○-) and (-△-) in this figure (part A in the figure) is true precipitation as iron arsenate, and the arsenic removal rate shown in Table 1 below is the first.
It was calculated using the formula (A)/((A)+(B)) in the figure. In addition, the experimental conditions at this time were: liquid volume: above stock solution 2, temperature: 30°C, amount of Fe ₂ (SO ₄ ) ₃ solution added:
103c.c. (concentration 100gFe/), reaction time: 1 hour. Furthermore, the change in Zn shown in this figure (―×―)
shows the behavior of the Zn concentration in the liquid after solid-liquid separation when Fe ³⁺ solution and calcium carbonate are added to the above stock solution and reacted (-△-). If arsenization treatment is performed in the range of ~2.8, Zn
It can be seen that a sufficient arsenic removal effect can be obtained with less loss. According to the tests conducted by the present inventors, if the amount of gypsum produced in the neutralization reaction in the first step does not affect the dearsenization step in the second step, the neutralization reaction in the first step can be carried out at a pH of 1. We have confirmed that it is acceptable to set the value to around 5.

[Table] The iron arsenate produced in the arsenic removal tank has few impurities.
Since arsenic is sufficiently concentrated, it can be used as a raw material for arsenous acid.The arsenic precipitate is separated by sedimentation, and the dearsenic solution containing a large amount of unreacted Fe ²⁺ ions is sent to an oxidation tank to oxidize iron. by bacteria
Oxidation treatment is performed on Fe ³⁺ . The oxidation tank contains iron oxidizing bacteria (Ferrobacillus).
Ferrooxidans, Thiobacillus Ferrooxidance, etc.)
is present, and an acid-resistant porous material such as diatomaceous earth is added as a carrier agent to retain the bacterial cells.
In addition, in order to increase bacterial growth if necessary,
Nutrient sources such as N, P, K, etc., such as (NH ₄ ) ₂ CO ₃ ,
(NH ₄ ) ₂ SO ₄ , KCl, K ₂ HPO ₄ , KH ₂ PO ₄ ,
Add MgSO ₄ .7H ₂ O, Ca(NO ₃ ) ₂ , etc. In addition, SS, F, Cl, Zn,
If bacteria-inhibiting elements such as Hg and Ag are included, it is desirable to remove them in advance through pretreatment.For example, SS should be removed by a settler during the smelting process, F at 100ppm, and Cl at 1000ppm. ,
It has been confirmed in a beaker test that bacteria can grow up to about 20g/Zn, so if the concentration is higher than that, dilution may be used. Furthermore, in this oxidation tank, oxidation by bacteria takes place sufficiently within the pH range of 1.0 to 5.0.
When the pH reaches 2.2 or above, a large amount of iron precipitates as goethite, etc., as described above, making it difficult to control the concentration of the returned mud. On the other hand, when the pH is around 1.0, the activity of bacteria decreases slightly, so it is preferable to oxidize at a pH in the range of 1.8 to 2.0. Next, perform solid-liquid separation of the liquid after the oxidation treatment,
Part or all of the precipitate containing diatomaceous earth carrying bacteria is repeatedly fed into the oxidation tank to convert Fe ²⁺ →Fe ³⁺
The required amount of the liquid oxidized to Fe ³⁺ (equivalent to arsenic) is returned to the dearsenic tank and used for the arsenic removal reaction described above, and the remaining liquid is used for the next step of oxidizing iron. Sent to neutralization tank. Further, according to the tests conducted by the present inventors, it has been confirmed that the same effect can be obtained even if the iron precipitate generated in the oxidation tank is sent directly or after being dissolved to the arsenization tank. Most of the liquid after solid-liquid separation after oxidation is sent to the iron neutralization tank.
Ca salts such as CaO, _CaCO3 , Ca(OH) ₂ , sodium hydroxide, sodium carbonate, ammonium hydroxide,
Alkaline agents such as magnesium hydroxide are added,
The produced iron precipitates such as iron hydroxide and goethite are recovered by solid-liquid separation. According to the method of the present invention, as described above, Fe ²⁺ ions present in large quantities in the liquid to be treated are oxidized by iron-oxidizing bacteria and used effectively to remove arsenic. It is very economical because there is no need to add special reagents for Fe ²⁺ oxidation. Furthermore, by adding a small amount of neutralizing agent to the remaining liquid after bacterial oxidation, Fe content can also be recovered at a high yield. Example 1 The raw solution to be treated is the decopper-removed solution from the wet smoke ash treatment plant of smelter A, and its composition is as shown in Table 2.

[Table] This stock solution was led to a neutralization tank at a flow rate of 2200 ml/min, and a 5% CaCO ₃ solution was added at a rate of 400 ml/min, the pH was adjusted to 2.6, and the mixture was reacted with the precipitated gypsum using a thickener. It was separated into overflow water (flow rate 1400ml/min). The composition of the overflow water is shown in Table 3.

[Table] Next, the overflow water is sent to the dearsenization tank and the ferric sulfate solution (flow rate
600 ml/min) and separated into iron arsenate precipitate and overflow water (flow rate 2000 ml/min) using a thickener. Table 4 shows the composition of this precipitate and the dearsenization overflow water.

[Table] Overflow water after de-arsenization contains iron-oxidizing bacteria (concentration of carrier mud with bacteria in the oxidation tank is 15%)
and diatomaceous earth as a carrier agent to reduce runoff loss (tank concentration
50mg/) and ammonium phosphate (concentration in the tank: 5mg/) as a nutrient are added to the oxidation tank for oxidation treatment.The oxidized liquid is subjected to solid-liquid separation. is returned to the arsenic removal tank,
The precipitate was returned to the oxidation tank. As a result, as can be seen from Table 4, nearly 90% of the arsenic in the highly concentrated arsenic-containing liquid was removed. Example 2 The stock solution to be treated is a decopper-removed solution from the same wet smoke ash treatment plant as in Example 1, and its composition is as shown in Table 5.

[Table] 5% CaCO ₃ solution (400ml/min) was added to this stock solution (flow rate 2200ml/min) to automatically adjust the pH to 2.2.The neutralized solution was then mixed with gypsum and overflow water (14000ml/min). The overflow water was sent to a de-arsenization tank and reacted with Fe ³⁺ ions from the oxidation tank. The composition of the overflow water after neutralization is shown in Table 6.

[Table] Table 7 also shows the precipitation of iron arsenate from the arsenic removal tank and the composition of the arsenic solution.

[Table] As in Example 1, this dearsenized solution was introduced into an oxidation tank to which diatomaceous earth containing iron-oxidizing bacteria and ammonium phosphate had been added for oxidation treatment. The oxidized liquid was separated into precipitate and overflow water using a thickener, a portion of the precipitate was returned to the oxidation tank, and excess precipitate was extracted from the system. In addition, some of the overflow water is returned to the arsenic removal tank and used for reaction with arsenic.
The rest was sent to the iron neutralization tank. The composition of the overflow water after bacterial oxidation is shown in Table 8.

[Table] Slaked lime solution was added to the iron neutralization tank, and after the reaction, it was separated into precipitate and overflow water. The precipitate was an iron precipitate mainly composed of iron hydroxide, and the compositions of the precipitate and overflow water are shown in Table 9.

[Table] As mentioned above, according to the method of the present invention, As in the stock solution
It shows a removal rate of about 96% for arsenic and 99.9% for Fe, making it possible to remove arsenic more efficiently and economically than conventional methods.

[Brief explanation of the drawing]

Figure 1 shows the relationship between pH and residual arsenic concentration in the solution when the raw solution to be treated is neutralized with calcium carbonate alone and when the addition of a ferric solution and neutralization with calcium carbonate are used together, and the latter case. 2 is a graph showing the behavior of the zinc concentration in the liquid, and FIG. 2 is a flow sheet showing an example of the method of the present invention.

Claims (1)

[Claims] 1. A first step of neutralizing an aqueous solution containing at least arsenic and ferrous ions to pH 2.0 to 2.8, and arsenic in the solution after the first step reaction is returned from the third step described later. A second step of reacting with ferric ions to precipitate and remove them as iron arsenate, and introducing the arsenically removed solution in the second step to an oxidation tank where the ferrous ions in the solution are converted into ferric ions by iron-oxidizing bacteria. A method for treating an aqueous solution containing arsenic and iron using iron-oxidizing bacteria, the method comprising the following steps: oxidizing the arsenic and iron solution, and returning the oxidized solution to the second step. 2. The treatment method according to claim 1, wherein the liquid to be treated in the first step contains ferrous ions in an amount equal to or more than an equivalent amount of arsenic. 3. The iron oxidizing bacteria in the third step are recycled to the oxidation tank together with the precipitate generated in the third step, and a part of the post-oxidation liquid is also transferred to the second step.
3. The treatment method according to claim 1 or 2, wherein the remaining liquid is returned to the process and used for recovering iron precipitates. 4. The treatment method according to claim 1, 2 or 3, wherein diatomaceous earth is added as a carrier agent for iron-oxidizing bacteria and nutrients for the bacteria are added to the oxidation tank in the third step. .