JP5187199B2 - Fluorine separation method from fluorine-containing wastewater - Google Patents

Description

  The present invention relates to a method for separating fluorine from fluorine-containing wastewater containing sodium sulfate from a nonferrous metal smelting process.

  In the smelting process of non-ferrous metals such as copper and lead, raw ore is put into a furnace and melted, impurities are separated as calami and sulfur is separated as sulfurous acid gas, and the target metal is purified. The raw ore may contain fluorine, but the fluorine volatilizes when the ore is melted, and is collected together with sulfurous acid gas as an exhaust gas in a scrubber and collected in an alkaline cleaning liquid.

  The cleaning liquid in which the exhaust gas is collected by a scrubber or the like is sequentially taken out and processed as cleaning waste liquid, and fluorine is separated and recovered. The cleaning waste liquid after the removal of fluorine was subsequently sent to a wastewater treatment facility, where it was rendered harmless by separating heavy metal ions and organic substances other than fluorine ions by methods such as neutralization and oxidation reduction together with general wastewater. It will be discharged later.

  As a general method for removing fluorine contained in an aqueous solution such as waste water, a calcium compound such as calcium chloride or calcium sulfate is added, and the fluorine is precipitated as hardly soluble calcium fluoride, thereby removing fluorine from the aqueous solution. A method of separation is known.

  For example, Japanese Patent Laid-Open No. 2000-140863 (Patent Document 1) discloses a gel-like aluminum hydroxide generation step for neutralizing an aqueous solution of an acidic or alkaline aluminum salt to generate gel-like aluminum hydroxide, and fluorine-containing waste water. A treatment method for fluorine-containing wastewater is described which includes an adsorption step of adsorbing the calcium fluoride and gel aluminum hydroxide produced by adding the calcium compound and the gel aluminum hydroxide.

  According to the method described in Patent Document 1, since the generated calcium fluoride is adsorbed on the gelled aluminum hydroxide, the fluorine separation effect can be enhanced. However, since gelled aluminum hydroxide adsorbing calcium fluoride has poor filterability, it takes time to filter the gel-like starch and the subsequent treatment, resulting in a very inefficient.

  In addition, the wastewater containing fluorine from the nonferrous metal smelting process, such as the cleaning waste liquid from the scrubber described above, volatilizes from the furnace due to fluctuations in the operational load and the fluorine quality contained in the raw ore. As a result of the variation in the amount of fluorine, the concentration of fluorine in the cleaning waste liquid varies. Therefore, it has been difficult to efficiently and reliably remove fluorine by the method of precipitation separation using fluorine as calcium fluoride.

  On the other hand, as another method for separating fluorine in a solution, for example, as shown in Japanese Patent Application Laid-Open No. 10-113672 (Patent Document 2), a rare earth hydroxide is adsorbed on an adsorbent supported on a resin or the like. There is a way to remove it. This method is a method in which an aqueous solution containing fluorine ions and heavy metal ions is treated by adding a sulfur compound-based heavy metal fixing agent and solid-liquid separation, and then contacting with a fluorine adsorption resin.

  However, in this method, the pH of the solid-liquid separated water is adjusted to 2 to 5, and a chlorine agent is added to bring the oxidation-reduction potential to 600 mV or more, and the treatment is performed with a fluorine adsorption resin made of granulated cerium oxide. Therefore, if a practical fluorine ion adsorption rate is to be obtained, the pH of the aqueous solution containing fluorine must be adjusted to an acidic region of 5 or less, and thus pH adjustment is required before and after the adsorption treatment. There was a problem that labor and drug costs increased.

  Further, Patent Document 2 does not specifically describe a method of separating and recovering fluorine from the adsorbed resin after adsorbing fluorine to regenerate the resin, the adsorption performance of the resin after regenerating, and the like. However, it is generally known that the adsorption of fluorine ions and rare earths in the resin is strong, and in order to separate the fluorine ions from the rare earth surface and regenerate the resin, concentrated sodium hydroxide is used repeatedly. Need to be cleaned. If the resin is not sufficiently washed and fluorine ions remain in the resin, the fluorine adsorption performance is lowered.

  Furthermore, the alkali fluoride solution generated in a large amount must be fixed in a stable form of fluorine, for example, by adding a calcium compound to form calcium fluoride. As described above, the method described in Patent Document 2 requires a lot of cost and labor for waste liquid treatment, and it is difficult to say that it is a practical method because there are disadvantages such as a significant increase in the amount of drainage.

  As described above, even if the fluorine concentration in the wastewater changes from the fluorine-containing wastewater from the nonferrous metal smelting process such as the cleaning waste liquid from the scrubber, the method for effectively separating the fluorine at a low cost is It was not known. In addition, in the case of fluorine-containing wastewater from non-ferrous metal smelting processes, precipitation of calcium fluoride may be insufficient even when calcium compounds are added, and fluorine removal from the wastewater may be incomplete. .

JP 2000-140863 A Japanese Patent Laid-Open No. 10-113672

  In view of the above-described conventional circumstances, the present invention can easily and efficiently remove and remove fluorine from a fluorine-containing wastewater from a non-ferrous metal smelting process, and regardless of the fluorine concentration in the wastewater, etc. An object of the present invention is to provide a method capable of constantly and reliably separating and removing fluorine.

  As described above, in the fluorine-containing wastewater from the nonferrous metal smelting process, a sufficient amount of calcium compound is added when separating the fluorine by generating poorly soluble calcium fluoride by adding the calcium compound. In some cases, however, the removal of fluorine from the wastewater is incomplete.

  As a result of various studies on the cause, the present inventors have found that the concentration of sodium sulfate contained in the fluorine-containing wastewater from the nonferrous metal smelting process affects the solubility of fluorine, and further the increase in sodium sulfate concentration. As a result, the inventors have found that the fluorine concentration in the waste water is increased and the separation of fluorine becomes incomplete, and the present invention has been made based on the findings.

  That is, the method for separating fluorine from fluorine-containing wastewater provided by the present invention is a method in which a calcium compound is added to fluorine-containing wastewater containing sodium sulfate from a non-ferrous metal smelting step, and fluorine is precipitated as calcium fluoride and separated. The concentration of sodium sulfate contained in the fluorine-containing waste water is controlled to 15 g / l or less.

  According to the present invention, regardless of the content of sodium sulfate contained in the fluorine-containing wastewater from the non-ferrous metal smelting process, fluorine can always be stably precipitated as calcium fluoride and reliably separated and removed. In addition, according to the present invention, the process is simple and does not require special equipment, and expensive rare earths and chemicals are not used. In addition, the precipitation of calcium fluoride is excellent in filterability and easy to process. However, there is an advantage that the cost can be reduced.

It is a graph which shows the relationship between the sodium sulfate concentration and fluoride ion concentration in aqueous solution.

  In the method for separating fluorine from fluorine-containing wastewater according to the present invention, when the added calcium compound reacts with fluorine to form a precipitate of calcium fluoride, it is contained in the fluorine-containing wastewater from the nonferrous metal smelting process. It is important to maintain and control the concentration of sodium sulfate below 15 g / l.

  In general, sodium sulfate is contained in the fluorine-containing wastewater from the nonferrous metal smelting process. Sodium sulfate contained in fluorine-containing wastewater is generated from sodium contained in the neutralizing agent added to the scrubber cleaning liquid that collects fluorine in the exhaust gas, and sulfurous acid gas collected by the scrubber. it is conceivable that.

In a method in which a calcium compound (for example, CaSO ₄ ) is added to fluorine-containing wastewater to form a precipitate of calcium fluoride (CaF ₂ ), when sodium sulfate is present in the wastewater, the generated calcium fluoride is separated from sulfate ions. It was found that by anion exchange, the reaction shown in the chemical formula below progressed to the right side and the fluorine concentration in the wastewater increased.

[Chemical formula]
CaF ₂ + SO ₄ ²⁻ = CaSO ₄ + 2F ⁻

  That is, when the solubility of calcium sulfate and calcium fluoride is compared, the solubility of calcium fluoride is much lower than that of calcium sulfate and tends to precipitate, so in the usual case, the reaction of the above chemical formula tends to proceed to the left. However, if excessive sulfate ions coexist due to the inclusion of sodium sulfate, the equilibrium is inclined to the right, and it is considered that some fluorine ions are eluted.

  Therefore, in order to stably precipitate fluorine as wastewater calcium fluoride by suppressing elution of fluorine ions and allowing the reaction of the above chemical formula to proceed to the left side, sulfate ions contained in the fluorine-containing wastewater, that is, It has been found that the sodium sulfate concentration needs to be controlled below a certain level.

  According to the study by the present inventors, the relationship between the sodium sulfate concentration in the aqueous solution and the fluorine ions is the graph shown in FIG. It can be seen that when the sodium sulfate concentration is 3 g / l or more, the increase in fluorine concentration increases, and when the sodium sulfate concentration exceeds 15 g / l, the fluorine concentration further increases and the re-dissolution of fluorine is accelerated. Therefore, in the present invention, the sodium sulfate concentration in the fluorine-containing waste water is maintained at 15 g / l or less, preferably 3 g / l or less.

  In the present invention, calcium compounds added to fluorine-containing wastewater containing sodium sulfate can be used as long as they are soluble sulfates such as calcium sulfate and calcium chloride. However, calcium sulfate is used in terms of cost and solubility. Easy and most suitable. Further, when it is necessary to raise the pH of the aqueous solution, calcium hydroxide may be used.

  Moreover, although the production | generation of the calcium fluoride in this invention has a difference by content and temperature of the fluorine ion in waste_water | drain, it can process by general 8.0 or more as pH value. If the reaction temperature of the fluorine-containing wastewater at the time of processing is a practical temperature range which does not boil, it can be processed without problems.

  The step of controlling the concentration of sodium sulfate in the fluorine-containing wastewater to 15 g / l or less and the step of adding calcium compounds to the fluorine-containing wastewater to form calcium fluoride precipitates are generally a concentration control step. Is followed by a calcium fluoride precipitate formation step, but it is also possible to carry out the other step after one of the steps is carried out first.

  In the step of controlling the sodium sulfate concentration in the fluorine-containing wastewater to 15 g / l or less, the sodium sulfate concentration in the fluorine-containing wastewater is measured, and water having a sodium sulfate concentration lower than the obtained measured concentration is added. Is preferred. As such water, for example, wastewater having a low sulfate ion concentration from the nonferrous metal smelting process, treated wastewater having a reduced sulfate ion concentration by treating the wastewater from the nonferrous metal smelting process, and the like are preferably used.

[Example 1]
The relationship between sodium sulfate concentration and fluoride ion concentration in aqueous solution was investigated. That is, 200 g of pure water was added to 16 g of calcium fluoride and suspended by stirring. To this fluorine-containing aqueous solution, anhydrous sodium sulfate (reagent) in an amount corresponding to the sodium sulfate concentration shown in Table 1 below was added, and dissolved by stirring for 60 minutes while maintaining the temperature at 25 ° C. using a stirrer. Then, solid-liquid separation was performed by natural filtration using 5C filter paper. The obtained filtrate was collected and analyzed for fluorine concentration using ICP. The results shown in Table 1 below were obtained.

  As can be seen from Table 1 above, when sodium sulfate is not present in the fluorine-containing aqueous solution, many precipitates are formed, and the fluorine concentration in the filtrate is 2.4 mg / l, which corresponds approximately to the solubility in water. there were. However, as the sodium sulfate concentration increased, calcium fluoride dissolution increased and the fluorine concentration in the filtrate increased.

  From this result, it was confirmed that when the sodium sulfate concentration in the fluorine-containing aqueous solution is high, fluorine is easily dissolved, but when the sodium sulfate concentration is lowered, fluorine cannot be dissolved but precipitates, and the fluorine concentration is lowered. When the compound remaining in the container was identified by X-ray diffraction, calcium fluoride and calcium sulfate were detected.

[Comparative Example 1]
Using the same fluorine-containing aqueous solution in which the same calcium fluoride as in Example 1 was suspended, sodium chloride concentration was added instead of sodium sulfate so as to be the concentration shown in Table 2 below, and 25 ° C. using a stirrer. While maintaining the temperature, the solution was stirred for 60 minutes for dissolution.

  Each aqueous solution obtained was subjected to natural filtration using 5C filter paper to separate into solid and liquid. The obtained filtrate was collected and analyzed for fluorine concentration using ICP. The results shown in Table 2 below were obtained.

  From the results in Table 2 above, even when the aqueous solutions having the same sodium concentration shown in Table 1 were compared, increasing the amount of sodium chloride instead of sodium sulfate did not increase the fluorine concentration in the filtrate. It was confirmed that dissolution was caused by the presence of sodium sulfate.

Claims (2)

In the method of adding calcium compounds to fluorine-containing wastewater containing sodium sulfate from a non-ferrous metal smelting process and precipitating and separating fluorine as calcium fluoride, the concentration of sodium sulfate contained in the fluorine-containing wastewater is 3 g / A method for separating fluorine from fluorine-containing wastewater, characterized by controlling to 1 or less. The sodium sulfate concentration in the fluorine-containing wastewater is measured by measuring the sodium sulfate concentration in the fluorine-containing wastewater, and adding wastewater from a nonferrous metal smelting process having a sodium sulfate concentration lower than the measured concentration or treated wastewater. It controls to 3 g / l or less, The fluorine separation method from the fluorine-containing wastewater of Claim 1 characterized by the above-mentioned.

Images