A method for improving germanium recovery from zinc oxide fume by inhibiting silica gel

Abstract

This invention relates to a method for improving germanium recovery from zinc oxide fume by inhibiting silica gel, and pertains to the field of hydrometallurgical technology. The method includes the following steps: adding high-silica zinc oxide fume to sulfuric acid with a pH of 0.5–1.5, performing ultrasonic leaching, and then adjusting the pH of the leaching solution to 2 using calcium oxide to achieve the leaching of zinc and / or germanium from the high-silica zinc oxide fume. This invention employs a combination of ultrasonic-enhanced leaching and calcium oxide-adjusted solution pH to achieve highly efficient leaching of zinc and germanium from high-silica zinc oxide fume, solving the problem of low zinc and germanium leaching rates caused by silica gel formation during leaching. It also features a simple process flow, clean and efficient operation, and a high comprehensive recovery rate of valuable metals, enabling the resource utilization, reduction, and harmless treatment of high-silica zinc oxide fume.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and in particular to a method for improving germanium recovery from zinc oxide fumes by inhibiting silica gel. Background Technology

[0002] Germanium is an important rare metal that is widely used in aerospace, defense, electronics and semiconductors. However, with the rapid development of science and technology, the global demand for germanium is increasing day by day. Germanium metal and its compounds are of great significance to the development of many aspects of the country.

[0003] Currently, the main raw materials for germanium extraction include byproducts from metal smelting processes such as lead and zinc, and flue ash from lignite combustion. However, due to the extremely low germanium content in these materials, it is often necessary to employ a method to enrich germanium before centralized separation and extraction. In zinc smelting, the fumigation method is commonly used to enrich germanium in zinc oxide flue dust, where the germanium content can reach approximately 500 g / t.

[0004] Currently, domestic and international companies mainly utilize conventional acid leaching, pressure acid leaching, acid-alkali stepwise leaching, and microwave treatment to recover germanium from high-silicon zinc oxide dust. However, these methods all have certain drawbacks: Atmospheric pressure acid leaching typically employs a two-stage leaching process, which is convenient to operate, but the leaching rates of zinc and germanium are low for high-silicon zinc oxide dust. Pressure acid leaching offers advantages such as high overall metal recovery rate, fast reaction, and short process flow, but it cannot solve the problem of silica gel formation caused by the high silicon content in high-silicon zinc oxide dust during leaching. Silica gel can adsorb or encapsulate germanium during leaching, forming co-precipitates and reducing the final leaching rate. To address this challenge, some researchers have proposed acid-alkali stepwise leaching, utilizing the solubility of silicon in alkaline systems to first leach some silicon in an alkaline solution, followed by acid leaching to extract valuable metal elements. This method can fundamentally solve the adverse effects of high silicon content, but it increases the difficulty of separating silicon and germanium in the leaching solution and the loss of valuable metal elements. Some scholars have also used microwave treatment to pyrolyze silicates in flue gas before leaching. This method can effectively avoid the formation of silica gel during the leaching process, but at the same time, some zinc is pyrolyzed and volatilized, leading to increased zinc loss.

[0005] High-silicon zinc oxide dust is an important method for recovering zinc and germanium. With the significant increase in market demand for zinc and germanium and the current shortage of germanium resources, the failure to effectively utilize zinc leaching residue will not only lead to resource waste but also seriously pollute the environment. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving germanium recovery from zinc oxide dust by inhibiting silica gel, thereby solving the problems existing in the prior art and achieving efficient recovery of zinc and germanium from high-silicon zinc oxide dust.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a method for leaching zinc and / or germanium from high-silica zinc oxide fume using ultrasound-enhanced calcium oxide, comprising the following steps:

[0009] High-silicon zinc oxide dust is added to sulfuric acid with a pH of 0.5–1.5 (concentration of 1.0–3.0 M / L) and ultrasonically leached. Then, the pH of the leachate is adjusted to 2 using calcium oxide to achieve the leaching of zinc and / or germanium from the high-silicon zinc oxide dust.

[0010] After leaching, vacuum filtration is performed to separate the leachate and leach residue.

[0011] In high-silicon zinc oxide dust, zinc mainly exists in the form of zinc sulfate, zinc oxide, and zinc silicate.

[0012] Experiments have shown that the initial acidity of sulfuric acid has a significant impact on the leaching rate. Acidity control plays a role in dissolving high-silicon zinc oxide dust. Thermodynamic analysis of germanium shows that stronger acidity is beneficial for the leaching of germanium.

[0013] Silicic acid is charged in solution. It is generally believed that the isoelectric point of orthosilicic acid is around pH 2. When the pH value is < 2, positively charged silicic acid dimers will form, and polysilicic acid will be formed on this basis. When the pH value is > 2, negatively charged silicic acid dimers will form, and polysilicic acid will also be formed on this basis. Regardless of the form of polysilicic acid, it will gradually produce silica gel. Therefore, controlling the final pH value of the leachate to around 2 can effectively inhibit the formation of silica gel.

[0014] As a further preferred embodiment of the present invention, the solid-liquid ratio of the high-silicon zinc oxide dust to sulfuric acid is 1g:(5-8)g.

[0015] As a further preferred embodiment of the present invention, the ultrasonic leaching process further includes a stirring step, with a stirring speed of 100 to 400 rpm.

[0016] As a further preferred embodiment of the present invention, the temperature during ultrasonic leaching is 60°C to 90°C.

[0017] As a further preferred embodiment of the present invention, the ultrasonic power of the ultrasonic leaching process is 200-600W and the ultrasonic frequency is 25KHz.

[0018] As a further preferred embodiment of the present invention, the ultrasonic immersion time is 30 to 60 minutes.

[0019] More preferably, after adjusting the pH of the reaction system to 2, the reaction is further continued for 30 minutes.

[0020] The present invention also provides the application of the above method in the leaching of zinc and / or germanium in high-silica zinc oxide dust.

[0021] This invention combines calcium oxide with ultrasound. On the one hand, the cavitation effect of ultrasound technology increases the overall leaching reaction rate and shortens the leaching time (in conventional acid leaching, the leaching time is generally long, usually 2-5 hours). At the same time, the strong stirring environment brought about by the mechanical effect of ultrasound disperses the silica gel to a certain extent, thereby reducing its adsorption capacity. On the other hand, after a period of leaching, calcium oxide is used to adjust the final pH value of the leaching solution to 2, thereby increasing the acid leaching reaction rate and preventing the polymerization reaction of silicic acid. Ultimately, this controls the formation of silicic acid gel, thereby increasing the leaching rate of zinc and germanium.

[0022] The present invention discloses the following technical effects:

[0023] This invention combines ultrasonic technology with pH adjustment using calcium oxide to produce a synergistic effect, which helps to suppress the formation of silica gel during the leaching of zinc oxide dust, reduces the adsorption of zinc and germanium elements, and improves the leaching rate.

[0024] This invention uses calcium oxide to adjust the pH value of the leachate, which does not introduce new impurity ions, leaves no harmful components in the leachate after leaching, has no adverse effects on subsequent processes, and generates no waste gas during the reaction, making it environmentally friendly.

[0025] This invention employs a combination of ultrasonic-enhanced leaching and calcium oxide-based solution pH adjustment to achieve efficient extraction of valuable metals from high-silica zinc oxide dust. It enables highly efficient leaching of zinc and germanium from high-silica zinc oxide dust, with zinc leaching rates reaching over 95% and germanium leaching rates reaching approximately 85%. This solves the problem of low zinc and germanium leaching rates caused by the formation of silica gel during leaching of high-silica zinc oxide dust. Furthermore, it features a simple process, clean and efficient operation, and a high comprehensive recovery rate of valuable metals, enabling the resource utilization, reduction, and harmless treatment of high-silica zinc oxide dust. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1A simplified diagram illustrating the formation of silica gel during the leaching of zinc and germanium from high-silicon zinc oxide dust.

[0028] Figure 2 The XRD patterns of high-silicon zinc oxide dust used in the embodiments and comparative examples of this invention are shown. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] The zinc oxide dust used in the following embodiments and comparative examples of this invention is high-silica zinc oxide dust, and its XRD pattern is shown in [reference needed]. Figure 2 Zinc in zinc oxide dust mainly exists in the form of ZnO, ZnSO4, and ZnSiO4. The main chemical components are shown in Table 1.

[0035] Table 1

[0036]

[0037] Example 1

[0038] Sulfuric acid was used as the leaching agent, with its initial acidity controlled at 2.5M. At this initial pH, the leaching agent had an initial pH of 0.5. Zinc oxide dust was mixed with the leaching agent at a liquid-to-solid mass ratio of 6:1 (g / g). After mixing, ultrasonic leaching was performed at a power of 300W and a frequency of 25kHz. The leaching reaction was carried out for 60 minutes at 90℃ and a stirring speed of 200rpm. Then, an appropriate amount of calcium oxide was added to adjust the pH of the leachate to 2, and the reaction continued for another 30 minutes. After the reaction was completed, the leachate and leaching residue were obtained through liquid-solid separation. The leaching rates of zinc and germanium were 90.25% and 80.42%, respectively.

[0039] The leaching rate is calculated using the following formula:

[0040]

[0041] In the formula: Y(%) represents the metal leaching rate, X1(g / L) represents the concentration of metal ions in the obtained leachate, V(L) represents the volume of the obtained leachate, X2 represents the metal content in the raw material, and m(g) represents the mass of the raw material used.

[0042] Comparative Example 1

[0043] The only difference from Example 1 is that ultrasonic treatment is not used:

[0044] Sulfuric acid was used as the leaching agent, with its initial acidity controlled at 2.5M. At this initial pH, the leaching agent had an initial pH of 0.5. Zinc oxide dust was mixed with the leaching agent at a liquid-to-solid mass ratio of 6:1 (g / g). After mixing, the temperature was controlled at 90℃ and the stirring speed at 200 rpm for 60 minutes of leaching reaction. Then, an appropriate amount of calcium oxide was added to adjust the pH of the leachate to 2, and the reaction continued for another 30 minutes. After the reaction was completed, the leachate and leaching residue were obtained through liquid-solid separation. The leaching rates of zinc and germanium were 86.33% and 70.22%, respectively.

[0045] Example 2

[0046] Sulfuric acid was used as the leaching agent, with its initial acidity controlled at 2.0 M, resulting in an initial pH of 0.7. Zinc oxide dust was mixed with the leaching agent at a liquid-to-solid mass ratio of 6:1 (g / g). After mixing, ultrasonic leaching was performed at a power of 300 W and a frequency of 25 kHz. The leaching reaction was carried out for 60 min at 90 °C and a stirring speed of 200 rpm. Then, an appropriate amount of calcium oxide was added to adjust the pH of the leachate to 2, and the reaction continued for another 30 min. After the reaction was completed, the leachate and leaching residue were obtained through liquid-solid separation. The leaching rates of zinc and germanium were 94.37% and 80.86%, respectively.

[0047] Comparative Example 2

[0048] The only difference from Example 2 is that ultrasonic treatment is not used:

[0049] Sulfuric acid was used as the leaching agent, with its initial acidity controlled at 2.0 M, resulting in an initial pH of 0.7. Zinc oxide dust was mixed with the leaching agent at a liquid-to-solid mass ratio of 6:1 (g / g). The mixture was then subjected to a leaching reaction at 90℃ and a stirring speed of 200 rpm for 60 min. An appropriate amount of calcium oxide was then added to adjust the pH of the leachate to 2, and the reaction continued for another 30 min. After the reaction was complete, the leachate and leaching residue were obtained through liquid-solid separation. The leaching rates of zinc and germanium were 90.53% and 68.93%, respectively.

[0050] Example 3

[0051] Sulfuric acid was used as the leaching agent, with its initial acidity controlled at 2.5M. At this initial pH, the leaching agent had an initial pH of 0.5. Zinc oxide dust was mixed with the leaching agent at a liquid-to-solid mass ratio of 7:1 (g / g). After mixing, ultrasonic oxidation leaching was performed at an ultrasonic power of 300W and an ultrasonic frequency of 25kHz. The leaching reaction was carried out for 60 minutes at a temperature of 90℃ and a stirring speed of 300rpm. Then, an appropriate amount of calcium oxide was added to adjust the pH of the leachate to 2, and the reaction continued for another 30 minutes. After the reaction was completed, the leachate and leaching residue were obtained by liquid-solid separation. The leaching rates of zinc and germanium were 95.51% and 85.18%, respectively.

[0052] In this embodiment, the initial acidity of sulfuric acid is controlled at 2.5M, at which point the initial pH of the leaching agent is 0.5. After a period of reaction, the pH of the leaching solution is adjusted to around 2. At this point, the inhibition effect on silica gel is maximized, and the situation of co-precipitation with zinc and germanium elements entering the slag is avoided to the greatest extent, thus obtaining the maximum zinc and germanium leaching rate.

[0053] Example 4

[0054] Sulfuric acid was used as the leaching agent, with its initial acidity controlled at 2.5M. At this initial pH, the leaching agent had an initial pH of 0.5. Zinc oxide dust was mixed with the leaching agent at a liquid-to-solid mass ratio of 7:1 (g / g). After mixing, ultrasonic leaching was performed at a power of 500W and a frequency of 25kHz. The leaching reaction was carried out for 60 minutes at 80℃ and a stirring speed of 300rpm. Then, an appropriate amount of calcium oxide was added to adjust the pH of the leachate to 2, and the reaction continued for another 30 minutes. After the reaction was completed, the leachate and leaching residue were obtained through liquid-solid separation. The leaching rates of zinc and germanium were 95.57% and 85.18%, respectively.

[0055] This invention further investigates the effect of the final pH value of the leachate on the leaching rate of zinc and germanium in zinc oxide flue dust.

[0056] Under the same conditions as in Example 3, the final pH value of the leachate was controlled to investigate the effect of the final pH value on the leaching rate. The results are shown in Table 1.

[0057] Table 1. Effect of final pH value of leachate on leaching rate

[0058] Final pH value of leachate Zinc leaching rate % Germanium leaching rate % 0.5 80.31 68.64 1 79.77 67.59 1.5 84.23 71.66 2 96.51 85.18 2.5 91.81 72.07

[0059] The final pH value of the leachate is closely related to the leaching rates of zinc and germanium. Experimental results show that a final pH value greater than or less than 2 affects the leaching rates of zinc and germanium. This is because during the dissolution of valuable elements zinc and germanium in zinc oxide dust by sulfuric acid, a portion of silicates with a higher content in the dust also enters the solution. The main reaction formula is as follows:

[0060] Zn2SiO4+2H2SO4→2ZnSO4+H4SiO4

[0061] The above formula shows that silicon in zinc oxide fumes enters the solution in the form of H4SiO4. Under leaching conditions, polymerization readily occurs, and the resulting polymer is released along with the SiO4 in the solution. 4- As the concentration gradually increases, a gelation process occurs, forming a hydrogel. This type of hydrogel has extremely poor fluidity and a certain adsorption capacity. Since silicon and germanium belong to the same group of elements, germanium is easily adsorbed by this type of silicon gel, and then forms a co-precipitate that enters the slag, resulting in a decrease in the leaching rate.

[0062] Previous studies have found that silicic acid is charged in solution, and its isoelectric point is generally considered to be around pH 2.0. Different reactions occur depending on the pH of the solution. At pH > 2.0, negatively charged silicic acid dimers form, which then develop into polysilicic acid. At pH < 2.0, positively charged silicic acid dimers form, which also develop into polysilicic acid. Regardless of the form of polysilicic acid, silica sol is gradually formed. The specific reaction process is as follows:

[0063] At pH > 2, some orthosilicic acid dissociates according to the following formula:

[0064] H4SiO4→H3SiO4 - +H +

[0065] When pH < 2, orthosilicic acid reacts with H+ in the solution. + Combined, the reaction equation is as follows:

[0066] H4SiO4+H + →H5SiO4 +

[0067] Generally, silicic acid exists in various forms depending on the degree of reaction in solution. At around pH 2.0, it exists as orthosilicic acid or simple metasilicic acid, at which point polymerization is essentially nonexistent. At pH > 2.0 or pH < 2.0, it forms polysilicic acid, which eventually gradually forms silica sol. Therefore, to minimize the negative impact of silica sol, the final pH of the leachate should be controlled at around 2 to achieve optimal inhibition.

[0068] This invention further investigated the effect of ultrasonic power on the leaching rates of zinc and germanium in zinc oxide fumes:

[0069] Under the same conditions as in Example 3, the ultrasonic power was adjusted to investigate the effect of different ultrasonic powers on the leaching rate. The results are shown in Table 2.

[0070] Table 2. Effect of different ultrasonic powers on leaching rate

[0071] Ultrasonic power / W Zinc leaching rate % Germanium leaching rate % No ultrasound 85.75 78.64 120 89.55 80.58 180 90.89 81.93 240 93.71 83.59 300 96.51 85.18 360 96.92 85.24

[0072] Under the same conditions, the leaching rates of zinc and germanium are significantly reduced without the use of ultrasound. This is mainly because the dissolution rate of zinc and germanium is lower without the synergistic effect of ultrasound, requiring a longer leaching time for the relevant compounds of zinc and germanium to dissolve fully. Therefore, the main purpose of introducing ultrasound is to shorten the leaching time and accelerate the leaching efficiency. During the propagation of ultrasound, ultrasonic "cavitation" is induced. Under cavitation, the shock waves and microjets formed when microbubbles break down have an impact destructive effect on the solid surface of zinc oxide dust, which is conducive to the development of pores and cracks in the dust and the removal of the coating on the particle surface, exposing the particles to their own surface. Under normal conditions, the coating formed before and during the reaction of the solid phase can be destroyed under the action of ultrasound, exposing a fresh surface.

[0073] In this invention, the cavitation effect of ultrasound on the leachate is a very complex physicochemical phenomenon. Under the action of ultrasound, the tiny bubble nuclei in the treated liquid are excited, resulting in a series of reactions such as bubble nuclei oscillation, growth, contraction and collapse. The reaction is accompanied by the heating of the vapor phase in the bubble, generating instantaneous high temperature and high pressure. As a result, the water vapor entering the cavitation bubble will undergo a chain reaction to generate hydroxyl radicals (-OH).

[0074] 300W is the optimal ultrasonic power for this invention, and too low or too high power is detrimental during the leaching process. When the ultrasonic power is less than 300W, the leaching rates of zinc and germanium decrease significantly. This may be because the intensity of ultrasonic energy in the solution is too low to produce good mechanical action and cavitation effect. When the ultrasonic power is 300W, the leaching rates of zinc and germanium are higher. This may be because, under the current acidic conditions, the ultrasonic power of 300W can produce a good synergistic effect with the sulfuric acid in the leachate, which enhances the leaching of zinc and germanium. In particular, the leaching rate of germanium is significantly improved when the ultrasonic power is 300W. This may be because the ultrasonic waves of 300W produce a stronger cavitation effect with the encapsulated germanium ions, causing a sudden increase in the decomposition rate of germanium. When the ultrasonic power is greater than this and continues to increase, the rate of change of the leaching rate tends to stabilize, indicating that further increasing the power has little effect on improving the leaching effect. On the other hand, when the ultrasonic power is too high, it may also cause the bubbles generated by cavitation to coalesce, and then weaken the relevant leaching reaction under high ultrasonic power. Therefore, considering all factors, the ultrasonic power of 300W is the best for the optimization effect of this invention.

[0075] This invention further investigated the effect of initial sulfuric acid acidity on the leaching rates of zinc and germanium in zinc oxide dust:

[0076] Under the same conditions as in Example 3, the initial acidity of sulfuric acid was adjusted to investigate the effect of different initial acidities on the leaching rate. The results are shown in Table 3.

[0077] Table 3. Effect of different initial sulfuric acid concentrations on leaching rate

[0078] initial acidity of sulfuric acid Zinc leaching rate % Germanium leaching rate % 1.0M / L 53.25 44.23 1.5 72.71 61.95 2.0 84.58 71.13 2.5 93.13 83.08 3.0 91.21 77.21

[0079] This invention introduces ultrasonic technology in conjunction with the alkaline pH adjuster calcium oxide into the leaching process of zinc and germanium from high-silica zinc oxide flue dust. The cavitation and mechanical effects generated by ultrasonic technology in the liquid system accelerate the reaction rate of the overall leaching process. At the same time, after a period of leaching, an appropriate amount of calcium oxide is added to the solution to adjust the pH value of the leachate to about 2. At this time, the silicon in the solution is dispersed in the form of orthosilicic acid, and little or no polymerization reaction occurs, thereby reducing the formation of silica gel in the subsequent solution and reducing the zinc and germanium elements adsorbed by the silica gel, thus improving the zinc and germanium leaching rate.

[0080] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for leaching zinc and / or germanium from high-silica zinc oxide fume using ultrasound-calcium oxide enhancement, characterized in that, Includes the following steps: High-silicon zinc oxide dust is added to sulfuric acid with a pH of 0.5 to 1.5 and ultrasonically leached. Then, calcium oxide is used to adjust the pH of the leachate to 2 to achieve the leaching of zinc and / or germanium from the high-silicon zinc oxide dust. The temperature during ultrasonic leaching is 60℃~90℃; the ultrasonic power during ultrasonic leaching is 200~600W. The ultrasonic leaching frequency is 25 kHz; the ultrasonic leaching time is 30 to 60 minutes.

2. The method according to claim 1, characterized in that, The solid-liquid ratio of the high-silicon zinc oxide dust to sulfuric acid is 1g:(5-8)g.

3. The method according to claim 1, characterized in that, The ultrasonic leaching process also includes a stirring step; the stirring speed is 100-400 rpm.

4. The application of the method according to any one of claims 1-3 in the leaching of zinc and / or germanium in high-silica zinc oxide dust.

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