A method for removing fluoride ions from zinc sulfate solution

Abstract

The present invention relates to a method for removing fluoride ions from zinc sulfate solution, belonging to the technical field of hydrometallurgical zinc smelting. The present invention comprises the following steps: (1) adding calcium hydroxide powder to the zinc sulfate solution, and simultaneously introducing an inert gas into the zinc sulfate solution, so that calcium ions react with fluoride ions to form calcium fluoride precipitate; (2) filtering the solution after the reaction in step (1) to obtain supernatant and precipitate residue; (3) adding water to the precipitate residue obtained by filtration in step (2), then adding sodium hydroxide to adjust the pH value, and then adding a complexing agent to cause a complexation reaction of the precipitate residue; (4) filtering the liquid after the complexation reaction in step (3) to separate calcium fluoride and zinc fluoride in the precipitate residue; The present invention removes fluoride ions through chemical reactions, improves the removal rate and efficiency, reduces the volatilization amount of hydrogen fluoride, reduces the probability of the occurrence of the situation where the adsorbent has no contact with hydrogen fluoride, separates zinc fluoride for reuse, and reduces the zinc loss rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrometallurgical zinc smelting. Specifically, it relates to a method for removing fluoride ions from zinc sulfate solution. Background Art

[0002] During the process of hydrometallurgical zinc smelting, when the fluoride ion content in the zinc sulfate solution is too high and the fluoride ions are continuously enriched, it will cause corrosion of the cathode aluminum plate in the zinc electrodeposition process, resulting in the zinc deposited on the aluminum plate being difficult to peel off. The aluminum plate cannot be reused, causing waste. Moreover, it also hinders the continuous and normal operation of production. At the same time, fluoride ions will combine with hydrogen ions to form hydrogen fluoride, and the volatilization of hydrogen fluoride causes air pollution. Therefore, during the process of hydrometallurgical zinc smelting, it is necessary to remove fluoride ions from the zinc sulfate solution.

[0003] Existing fluoride ion removal processes usually use adsorbents for removal. For example, the patent with the application number 201210470338.4 discloses a method for removing fluorine from the sulfuric acid leaching solution of bastnaesite using an aluminum-containing adsorbent. It adsorbs fluorine through the adsorption performance of alumina. First, there are problems of slow removal rate and relatively low removal efficiency when removing fluorine through adsorption. Second, after fluoride ions in the zinc sulfate solution form hydrogen fluoride, a large amount of it volatilizes and is mixed in the flue gas. Currently, the flue gas is usually sprayed with an adsorbent in reverse to adsorb hydrogen fluoride to achieve fluoride ion removal. However, the gas capture itself is difficult, and when spraying the flue gas in reverse, there is more likely a situation where the adsorbent has no contact with hydrogen fluoride, affecting the removal effect. Finally, due to the presence of zinc ions in the zinc sulfate solution, zinc fluoride formed by the combination of zinc ions and fluoride ions is extremely insoluble in water. Therefore, there is inevitably some water-insoluble zinc fluoride in the zinc sulfate solution. After filtration, zinc fluoride enters the precipitation slag, and the precipitation slag also contains a large amount of precipitates generated from removing fluoride ions. So the precipitation slag cannot be returned to the subsequent processes of hydrometallurgical zinc smelting for zinc smelting treatment, resulting in waste and a reduction in the final product quantity.

[0004] Therefore, it is necessary to provide a method for removing fluoride ions from zinc sulfate solution to overcome the above defects. Summary of the Invention

[0005] In order to overcome the problems existing in the background art, the present invention provides a method for removing fluoride ions from zinc sulfate solution. Calcium ions react with fluoride ions to form calcium fluoride precipitate for fluoride ion removal. The removal rate and effect of the chemical reaction are improved compared with the adsorption method. Inert gas is used to inhibit the volatility of hydrogen fluoride, so that most of the hydrogen fluoride reacts with calcium hydroxide in the solution, reducing the amount of hydrogen fluoride volatilized into the flue gas and the amount of hydrogen fluoride removed by reverse spraying, thereby reducing the probability of the adsorbent having no contact with hydrogen fluoride. Utilizing the difference in the ease of forming complexes between zinc ions and calcium ions, zinc fluoride and calcium fluoride are separated through complexation reaction, and zinc fluoride is used as a raw material for hydrometallurgical zinc smelting, reducing the zinc loss rate and increasing the output of the final product.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] The method for removing fluoride ions from zinc sulfate solution includes the following steps:

[0008] (1) Add calcium hydroxide powder to the zinc sulfate solution, and at the same time introduce inert gas into the zinc sulfate solution. Calcium ions react with fluoride ions to form calcium fluoride precipitate;

[0009] (2) Filter the solution after the reaction in step (1). After filtration, the supernatant and precipitate residue are obtained;

[0010] (3) Add water to the precipitate residue obtained by filtration in step (2), then add sodium hydroxide to adjust the pH value, and then add a complexing agent to cause the precipitate residue to undergo a complexation reaction;

[0011] (4) Filter the liquid after the complexation reaction in step (3) to separate calcium fluoride and zinc fluoride in the precipitate residue.

[0012] Preferably, the inert gas in step (1) is argon.

[0013] Preferably, the complexing agent in step (2) is ethylenediaminetetraacetic acid.

[0014] Preferably, the reaction temperature in step (1) is room temperature, the molar mass ratio of the added calcium hydroxide powder to the fluoride ions in the zinc sulfate solution is 1:2, and the end point of the heat release of the solution is used as the end point of the reaction.

[0015] Preferably, the pH value in step (3) is controlled at 9-10, the reaction temperature is room temperature, and the reaction time is 20-30 min.

[0016] Inert gases generally have relatively high densities and low reactivity. They can form a stable gas barrier in the reaction system, and inert gases can also reduce the total pressure of the reaction system, thereby reducing the evaporation rate of hydrogen fluoride. By inhibiting the volatility of hydrogen fluoride with inert gases, the volatilization of hydrogen fluoride can be better inhibited. Furthermore, hydrogen fluoride can react in the solution to remove fluoride ions, reduce the content of hydrogen fluoride in the flue gas, and reduce the probability of the adsorbent having no contact with hydrogen fluoride.

[0017] Zinc has a higher electron affinity and ionization ability than calcium. Therefore, it is more difficult for zinc to lose electrons to form positively charged ions and it is not easy to form complexes. Thus, most of the zinc still exists in the precipitate slag in the form of zinc fluoride, while calcium fluoride is more likely to form complexes and calcium will exist in the form of complexes. Zinc fluoride existing in the form of precipitate can be filtered out through filtration. The filtered zinc fluoride can be reused as a raw material for magnesium removal in zinc hydrometallurgy, and the zinc in zinc fluoride will also be obtained through smelting as the final product, reducing the loss rate of zinc.

[0018] Advantages of the present invention:

[0019] 1. The present invention uses a chemical reaction to remove fluoride ions, and compared with physical adsorption removal, both the removal rate and removal efficiency are improved.

[0020] 2. The present invention uses inert gases to inhibit the volatility of hydrogen fluoride, reduce the amount of hydrogen fluoride volatilizing into the flue gas, and reduce the probability of the adsorbent having no contact with hydrogen fluoride during the reverse spraying process.

[0021] 3. The present invention uses a complexation reaction, utilizes the property differences between zinc ions and calcium ions, separates zinc fluoride for reuse, and reduces the loss rate of zinc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the process flow chart of the present invention DETAILED DESCRIPTION OF THE INVENTION

[0023] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings for the convenience of those skilled in the art to understand.

[0024] The zinc sulfate solution used in the experiments of the present invention is the zinc sulfate solution in the zinc hydrometallurgy process of a certain company in Yunnan Province.

[0025] Example 1

[0026] Take a certain amount of zinc sulfate solution, detect the fluoride ion content in the zinc sulfate solution, record the detection results, then add calcium hydroxide powder to the zinc sulfate solution, and at the same time introduce argon into the reaction space. The addition amount of calcium hydroxide powder and the fluoride ion content in the zinc sulfate solution are added according to a molar mass ratio of 1:2. After the heat release of the solution ends, take out the solution for filtration to obtain the supernatant and the precipitate residue. Detect the fluoride ion content in the supernatant and record it, detect the zinc fluoride content in the precipitate residue and record it. Then add water to the precipitate residue, and then add sodium hydroxide to adjust the pH of the liquid to 9. After reacting for 30 minutes, take out the liquid for filtration, and detect the zinc fluoride content in the precipitate obtained after filtration. The fluoride ion removal rate is calculated to be 87% through the detection data of the fluoride ion content in the initial zinc sulfate solution and the fluoride ion content in the supernatant, and the zinc recovery rate is calculated to be 80% through the zinc fluoride content in the precipitate residue and the zinc fluoride content in the precipitate after the complexation reaction.

[0027] Example 2

[0028] The difference in the experimental process between Example 2 and Example 1 is that sodium hydroxide is added to adjust the pH of the liquid to 10, and the liquid is removed for filtration after reacting for 20 minutes. The rest of the experimental process is the same as that of Example 1. Finally, the fluoride ion removal rate is 90% and the zinc recovery rate is 82%.

[0029] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for removing fluoride ions from zinc sulfate solution, characterized in that: The method for removing fluoride ions from zinc sulfate solution includes the following steps: (1) Add calcium hydroxide powder to the zinc sulfate solution, and at the same time, introduce argon gas into the zinc sulfate solution. Calcium ions react with fluoride ions to form calcium fluoride precipitate; (2) Filter the solution after the reaction in step (1). After filtration, the supernatant and precipitate residue are obtained; (3) Add water to the precipitate residue obtained by filtration in step (2), then add sodium hydroxide to adjust the pH value to 9 - 10, and then add the complexing agent ethylenediaminetetraacetic acid. React at room temperature for 20 - 30 minutes to cause a complexation reaction of the precipitate residue; (4) Filter the liquid after the complexation reaction in step (3) to separate calcium fluoride and zinc fluoride in the precipitate residue, and the zinc fluoride is returned to the hydrometallurgical zinc smelting process for reuse.

2. The method for removing fluoride ions from zinc sulfate solution according to claim 1, characterized in that: In step (1), the reaction temperature is room temperature, and the molar mass ratio of the added calcium hydroxide powder to the fluoride ions in the zinc sulfate solution is 1:

2. The end point of the heat release of the solution is used as the end point of the reaction.

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