Method for disposal and recycling of gallium production waste

Abstract

This application relates to a method for the disposal and recycling of gallium production waste, belonging to the field of metal recycling technology. The method includes: melting gallium production waste to obtain a gallium production waste melt, wherein the mass fraction of metallic gallium in the gallium production waste is greater than 95%; acid washing the gallium production waste melt to obtain pretreated gallium production waste; directional crystallizing the pretreated gallium production waste to obtain a solid crystalline phase with a purity ≥99.99wt% and an impurity-enriched liquid phase, wherein the difference between the cold and hot temperatures of the directional crystallization is 4℃~20℃; and alkaline dissolution treatment of the impurity-enriched liquid phase to obtain a gallium-containing solution. This application transforms gallium production waste into a reusable product through four sequentially linked steps.

Description

Technical Field

[0001] This application relates to the field of metal recycling technology, and in particular to a method for the disposal and recycling of gallium production waste. Background Technology

[0002] Gallium is an important rare-dispersed metal. Gallium and its compounds possess excellent optoelectronic and chemical properties and are widely used in semiconductor materials, solar cells, alloys, chemicals, and medical fields, making it a key raw material for modern high-tech development. Gallium has a very low melting point of 29.76℃ and is liquid at room temperature.

[0003] In industrial gallium production, losses are unavoidable due to gallium slurry splashing, container wall residue, and filter residue. These losses are typically accumulated as waste. In high-purity gallium production, if a crystallization process is used, a significant percentage of production waste is also generated, such as crystallization tailings and incompletely crystallized liquid residue. While these wastes still contain a high content of metallic gallium, their insufficient purity or high impurity content makes them unsuitable for direct use as products. Currently, the utilization rate of industrial gallium and high-purity gallium production waste is generally low, and treatment methods need improvement. Summary of the Invention

[0004] This application provides a method for the disposal and recycling of gallium production waste to solve the following technical problem: how to develop a method that can efficiently dispose of gallium production waste and make full use of the gallium resources therein. This application provides a method for the disposal and recycling of gallium production waste, the method comprising: Gallium production waste is melted to obtain gallium production waste melt, wherein the mass fraction of metallic gallium in the gallium production waste is greater than 95%. The gallium production waste melt is acid-washed to obtain pretreated gallium production waste; The pretreated gallium production waste is subjected to directional crystallization to obtain a solid crystalline phase with a purity ≥99.99wt% and an impurity-enriched liquid phase. The difference between the cold field temperature and the hot field temperature of the directional crystallization is 4℃~20℃. The impurity-enriched liquid phase is subjected to alkali dissolution treatment to obtain a gallium-containing solution.

[0005] Optionally, the melting temperature is 30℃~50℃.

[0006] Optionally, the pickling uses dilute hydrochloric acid as the pickling solution, the mass fraction of the dilute hydrochloric acid is 0.5% to 5%, and the volume ratio of the dilute hydrochloric acid to the volume of the gallium production waste melt is 1:10 to 1:1.

[0007] Optionally, the pickling temperature is 30℃~50℃, and the pickling time is 0.5h~4h.

[0008] Optionally, the cold zone temperature is 20℃~29℃, and the hot zone temperature is 31℃~40℃.

[0009] Optionally, the alkaline solution used in the alkaline dissolution treatment is a sodium hydroxide solution, a potassium hydroxide solution, or a sodium carbonate solution; the mass fraction of the alkaline solution is 12% to 32%.

[0010] Optionally, the volume ratio of the impurity-enriching liquid phase to the alkaline solution is 1:20 to 1:100.

[0011] Optionally, the alkali dissolution treatment satisfies the following conditions: reaction temperature of 100℃~160℃, stirring speed of 500r / min~1000r / min, reaction time of 5h~12h, and reaction pressure of 0.5MPa~2.5MPa.

[0012] Optionally, the gallium production waste is splash waste generated during industrial gallium production, or crystal tailings generated during high-purity gallium crystallization.

[0013] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for the disposal and recycling of gallium production waste. The method includes: melting the gallium production waste to obtain a gallium production waste melt, wherein the mass fraction of metallic gallium in the gallium production waste is greater than 95%; acid washing the gallium production waste melt to obtain pretreated gallium production waste; directional crystallizing the pretreated gallium production waste to obtain a solid crystalline phase with a purity ≥99.99wt% and an impurity-enriched liquid phase, wherein the difference between the cold field temperature and the hot field temperature of the directional crystallization is 4℃~20℃; and alkali dissolving the impurity-enriched liquid phase to obtain a gallium-containing solution. This application first utilizes the low melting point of gallium to melt gallium production waste into a homogeneous liquid state. Then, acid washing removes floating ash, organic matter, and reactive metallic impurities from the liquid gallium surface, exposing a pure metal interface. Subsequently, based on the physicochemical principle that the equilibrium distribution coefficients of impurities such as copper, mercury, lead, nickel, iron, and zinc during gallium solidification are much less than one, directional crystallization technology is employed to preferentially crystallize high-purity gallium into a solid crystalline phase, while impurities are repelled and enriched in the remaining liquid phase. This allows for the direct separation of most gallium in a low-cost physical manner. For impurities enriched in the liquid phase that cannot be further purified by crystallization, the chemical reaction that allows metallic gallium to form soluble gallates under high-temperature, strongly alkaline conditions is utilized to perform alkaline dissolution treatment on the impurity-rich liquid phase, completely converting the remaining metallic gallium into a reusable gallium-containing solution. Ultimately, this achieves efficient disposal of gallium production waste and recovery of gallium resources, solving the technical problems of gallium production waste accumulation and low gallium utilization rates in existing technologies. Attached Figure Description

[0014] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart illustrating a method for the disposal and recycling of gallium production waste provided in an embodiment of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0019] Figure 1 This is a schematic flowchart illustrating a method for the disposal and recycling of gallium production waste provided in an embodiment of this application.

[0020] Please see Figure 1 This application provides a method for the disposal and recycling of gallium production waste, the method comprising: S1. The gallium production waste is melted to obtain gallium production waste melt, wherein the mass fraction of metallic gallium in the gallium production waste is greater than 95%; S2. The gallium production waste melt is acid-washed to obtain pretreated gallium production waste; S3. The pretreated gallium production waste is subjected to directional crystallization to obtain a solid crystalline phase with a purity ≥99.99wt% and an impurity-enriched liquid phase. The difference between the cold field temperature and the hot field temperature of the directional crystallization is 4℃~20℃. S4. The impurity-enriched liquid phase is subjected to alkali dissolution treatment to obtain a gallium-containing solution.

[0021] This application transforms gallium production waste into reusable products through four sequentially linked steps.

[0022] The first step involves melting gallium production waste to obtain a gallium production waste melt. This step utilizes gallium's low melting point to transform the gallium production waste from a solid state into a homogeneous liquid state, providing a sufficient contact interface for subsequent acid washing and ensuring that the acid washing solution can act uniformly on the surface of the gallium production waste. It should be noted that the acid washing includes a first water wash, an acid wash, and a second water wash in sequence: first, the first water wash removes water-soluble dust from the surface of the gallium production waste melt; then, dilute hydrochloric acid is used to dissolve or peel off surface oxides and organic matter; finally, the second water wash removes residual acid and reaction products, restoring the cleanliness of the metallic gallium surface.

[0023] The second step involves acid washing the gallium production waste melt to obtain pretreated gallium production waste. Acid washing utilizes dilute hydrochloric acid to react with the floating ash, oxides, and some active metal impurities on the surface of the gallium production waste, dissolving or peeling off the floating ash, oxides, and active metal impurities, thereby removing non-gallium components that interfere with subsequent directional crystallization, resulting in a clean surface and uniform composition of the pretreated gallium production waste.

[0024] The third step involves directional crystallization of the pretreated gallium production waste to obtain a solid crystalline phase and an impurity-enriched liquid phase. This step is based on the difference in the equilibrium distribution coefficients between gallium and impurities during solidification: impurities such as copper, mercury, lead, nickel, iron, and zinc tend to remain in the liquid phase during gallium solidification, while high-purity gallium preferentially crystallizes into a solid. By controlling the temperature gradient (the difference between the cold and hot zones is 4℃ to 20℃), the gallium production waste is gradually solidified from one end to the other. High-purity gallium forms a solid crystalline phase and is directly output as a high-purity gallium product, while impurities are repelled and enriched in the remaining liquid phase, forming an impurity-enriched liquid phase. Thus, most of the gallium in the gallium production waste is recovered in high-purity solid form, with only a small amount remaining in the impurity-enriched liquid phase.

[0025] The fourth step involves alkaline dissolution of the impurity-enriched liquid phase to obtain a gallium-containing solution. While the impurity-enriched liquid phase still contains a considerable amount of metallic gallium, its high impurity content prevents further purification through directional crystallization. The alkaline dissolution process utilizes the principle of reacting metallic gallium with alkaline solutions such as sodium hydroxide, potassium hydroxide, or sodium carbonate to form soluble gallates (e.g., sodium gallate or sodium tetrahydroxygallate). This process converts the metallic gallium in the impurity-enriched liquid phase into ionic gallium, which then enters the solution, resulting in a gallium-containing solution. In this solution, gallium exists as gallate ions and can be directly used for electrolytic gallium extraction, enrichment and recovery, or returned to the alumina production process.

[0026] In some embodiments, the gallium production waste is splash waste generated during industrial gallium production, or crystal tailings generated during high-purity gallium crystallization.

[0027] In this embodiment, the gallium production waste is either splash waste generated during industrial gallium production or crystallization tailings generated during high-purity gallium crystallization. The gallium production waste is primarily composed of metallic gallium, but its surface and interior contain floating ash, organic matter, and metallic impurities such as copper, mercury, lead, nickel, iron, and zinc.

[0028] In some embodiments, the mass fraction of metallic gallium in the gallium production waste is greater than 95%.

[0029] Gallium production waste contains more than 95% metallic gallium by mass. This mass fraction refers to the percentage of elemental gallium in the total mass of the gallium production waste. The remaining components, less than 5%, include floating ash, organic matter, and metallic impurities such as copper, mercury, lead, nickel, iron, and zinc. Gallium production waste is solid at room temperature, which is determined by the fact that the mass fraction of metallic gallium is greater than 95% and the melting point of gallium (29.76℃). When metallic gallium constitutes the majority of the gallium production waste and the ambient temperature is below 29.76℃, the gallium production waste generally appears as solid blocks or granules.

[0030] The gallium production waste processed in this application is not low-grade gallium-containing raw material, but a production by-product with metallic gallium as the main component. Specifically, it can originate from splash waste generated during industrial gallium production or crystallization tailings generated during high-purity gallium crystallization. Since the mass fraction of metallic gallium in the gallium production waste is greater than 95%, the disposal and recycling of metallic gallium in gallium production waste has significant economic value.

[0031] In some embodiments, the melting temperature is 30°C to 50°C.

[0032] Melting treatment refers to the process of heating gallium production waste to above the melting point of gallium, transforming it from a solid or semi-solid state into a completely liquid state. The melting treatment temperature is between 30°C and 50°C; that is, the heating equipment raises the gallium production waste to a certain temperature within the range of 30°C to 50°C and maintains it. The purpose of melting treatment is to obtain a homogeneous and well-flowing gallium production waste melt, providing a liquid material with sufficient contact interface for subsequent acid washing steps.

[0033] If the melting temperature is below 30°C, the gallium production waste cannot be completely melted. The unmelted solid areas may contain impurity-rich regions or unmelted gallium particles. Directly acid-washing the incompletely melted material results in the acid solution only contacting the surface and not penetrating the interior, leaving the pre-treated gallium production waste with heterogeneous components. When this heterogeneous material enters the directional crystallization step, it cannot form a uniform temperature and concentration field, leading to impurity segregation and inclusions in the solid crystalline phase, preventing the solid crystalline phase purity from reaching the required 99.99 wt%.

[0034] If the melting temperature exceeds 50°C, it will accelerate gallium oxide formation, exacerbate hydrochloric acid volatilization, increase energy consumption, and increase the risk of container corrosion. At the same time, if the melting temperature exceeds 50°C, some low-melting-point impurities (such as mercury) in gallium production waste may be more easily volatilized or dispersed into the gallium production waste melt, increasing the impurity load for subsequent directional crystallization.

[0035] In some embodiments, the pickling uses dilute hydrochloric acid as the pickling solution, the mass fraction of the dilute hydrochloric acid is 0.5% to 5%, and the volume ratio of the dilute hydrochloric acid to the volume of the gallium production waste melt is 1:10 to 1:1.

[0036] In this embodiment, dilute hydrochloric acid is used as the pickling solution. If the mass fraction of dilute hydrochloric acid is less than 0.5%, the acidity of the pickling solution is too weak, resulting in insufficient dissolution of floating ash and oxide film on the surface of gallium production waste, and low dissolution efficiency for metal impurities such as copper, iron, and zinc. If the mass fraction of dilute hydrochloric acid is greater than 5%, the acidity of the pickling solution is too strong, and metallic gallium can be oxidized to gallium ions under acidic conditions, leading to the dissolution and loss of some metallic gallium and reducing the gallium recovery rate. In addition, high-concentration hydrochloric acid (mass fraction greater than 5%) reacts with metallic gallium to produce hydrogen gas. Hydrogen gas bubbles form at the solid-liquid interface and float to the surface, which may carry a small amount of liquid gallium, causing splashing and resulting in material loss. If the volume ratio of dilute hydrochloric acid to the volume of gallium production waste melt is less than 1:10, the amount of acid is insufficient to cover the entire gallium surface or the total amount of hydrogen ions is insufficient, resulting in uneven or incomplete pickling, which may affect the subsequent directional crystallization effect. If the volume ratio of dilute hydrochloric acid to gallium production waste melt is higher than 1:1, then there is an excess of acid, which increases the loss of gallium dissolution, increases the amount of waste acid to be treated, and may cause partial solidification of the gallium production waste melt due to cooling.

[0037] In some embodiments, the pickling temperature is 30°C to 50°C, and the pickling time is 0.5h to 4h.

[0038] The pickling temperature refers to the temperature of the mixture of gallium production waste melt and dilute hydrochloric acid during the pickling process. The pickling time refers to the duration from the addition of dilute hydrochloric acid to the gallium production waste melt until the pickling solution separates from the pretreated gallium production waste. In the embodiments of this application, stirring can be performed during the pickling process to ensure continuous renewal of contact between the pickling solution and the gallium surface.

[0039] If the pickling temperature is below 30℃, the gallium production waste melt may partially solidify. Gallium has a melting point of 29.76℃. When the temperature approaches or falls below this melting point, the fluidity of the gallium production waste melt decreases sharply, and it may even solidify locally. An oxide film will quickly form on the solidified gallium surface, and the solidified gallium cannot effectively contact dilute hydrochloric acid. The pickling solution can only act on the areas that remain liquid, resulting in uneven pickling. Secondly, at temperatures below 30℃, the chemical reaction rate between dilute hydrochloric acid and floating ash, oxides, and metallic impurities decreases significantly. If the pickling temperature is below 30℃, even extending the process to more than 4 hours will not achieve the desired impurity removal effect, and impurities may still remain on the surface of the pretreated gallium production waste.

[0040] If the pickling temperature exceeds 50°C, the evaporation rate of dilute hydrochloric acid will significantly accelerate. The hydrogen chloride gas in the dilute hydrochloric acid escapes into the air, causing a rapid decrease in the effective acid concentration in the pickling solution. This decrease in effective acid concentration weakens the pickling and impurity removal ability, requiring the addition of acid solution or an extended pickling time to achieve the same impurity removal effect. Secondly, at temperatures above 50°C, the reaction rate between metallic gallium and dilute hydrochloric acid significantly increases, leading to increased unnecessary losses of metallic gallium in the gallium production waste melt and reducing the gallium recovery rate.

[0041] The chemical reaction between dilute hydrochloric acid and the floating ash, oxides, and metallic impurities on the surface of gallium production waste melt requires sufficient time to complete. The floating ash typically has a multi-layered structure, requiring the pickling solution to penetrate and dissolve each layer; the oxide film requires the acid to penetrate micropores and react with the underlying metal to generate hydrogen for stripping. In the embodiments of this application, the pickling time is 0.5 hours to 4 hours to complete the removal of surface impurities.

[0042] In some embodiments, the cold zone temperature is 20°C to 29°C, and the hot zone temperature is 31°C to 40°C.

[0043] Directional crystallization involves establishing low-temperature and high-temperature regions at both ends of the gallium production waste melt, utilizing the difference in equilibrium distribution coefficients between gallium and impurities during solidification to achieve separation. The cold zone temperature refers to the temperature of the low-temperature region at the front end of the gallium production waste melt during directional crystallization, while the hot zone temperature refers to the temperature of the high-temperature region at the rear end of the gallium production waste melt. The cold and hot zone temperatures together form a temperature gradient that gradually decreases along the crystallization direction. As the gallium production waste melt slowly moves from the hot zone to the cold zone, gallium preferentially solidifies at the cold zone temperature to form a solid crystalline phase, while impurities such as copper, mercury, lead, nickel, iron, and zinc, due to their equilibrium distribution coefficients in gallium being much less than 1, are repelled and retained in the still liquid impurity-rich liquid phase.

[0044] Gallium has a melting point of 29.76℃. If the cooling zone temperature is higher than 29℃, the gallium production waste melt cannot solidify effectively, directional crystallization cannot be initiated, and gallium and impurities cannot undergo solid-liquid phase separation. If the cooling zone temperature is lower than 20℃, the excessively low temperature may cause two problems: First, the solidification rate is too fast, and impurities do not have enough time to be fully expelled into the liquid phase, resulting in some impurities being encapsulated in the solid crystalline phase, reducing the purity of the solid crystalline phase; second, the excessively low cooling zone temperature may cause some low-melting-point impurities in the gallium production waste (such as mercury, with a melting point of -38.8℃) to also solidify, thus mixing into the solid crystalline phase and reducing the separation effect. Controlling the cooling zone temperature between 20℃ and 29℃ ensures that the gallium production waste melt can gradually solidify in the cooling zone, while also providing a sufficient time window for impurities to diffuse into the liquid phase, thereby obtaining a high-purity solid crystalline phase.

[0045] The thermal zone temperature must be higher than the melting point of gallium to maintain the tail end of the gallium production waste melt in a completely liquid state during directional crystallization. If the thermal zone temperature is below 31°C, it becomes too close to the melting point of gallium, reducing the fluidity of the gallium production waste melt, slowing down impurity diffusion, reducing impurity enrichment efficiency, and making it easier for irregular crystal nuclei to form prematurely in the thermal zone, interfering with the uniformity of directional crystallization. If the thermal zone temperature is above 40°C, the temperature gradient between the cold and hot zones is too large, and the solidification front of the gallium production waste melt moves too quickly, which can also cause impurities to be captured and enter the solid crystalline phase. At the same time, a thermal zone temperature above 40°C increases energy consumption and may exacerbate the reaction between the gallium production waste and the container. Controlling the thermal zone temperature between 31°C and 40°C can maintain good fluidity and impurity diffusion ability of the gallium production waste melt. Combined with a cold zone temperature of 20°C to 29°C, this forms a temperature gradient range of 4°C to 20°C, ensuring that directional crystallization proceeds at a stable rate and that impurities migrate sufficiently to the impurity-enriched liquid phase.

[0046] In some embodiments, the purity of the solid crystalline phase is ≥99.99 wt%.

[0047] Solid crystalline phase purity refers to the percentage of gallium mass in the total mass of the solid crystalline phase. A solid crystalline phase purity of not less than 99.99 wt% means that the mass fraction of gallium in the solid crystalline phase is greater than or equal to 99.99 wt%, and the total mass fraction of all impurity elements (including metallic impurities such as copper, mercury, lead, nickel, iron, and zinc, as well as any possible residual non-metallic impurities) does not exceed 0.01%.

[0048] The purity of the solid crystalline phase is no less than 99.99 wt%, demonstrating the core technological effectiveness of the gallium production waste disposal and recycling method. This method, through the synergistic action of four steps—melting, acid washing, directional crystallization, and alkali dissolution—directly transforms most of the gallium in the originally low-utilization and easily accumulated gallium production waste into high-value-added industrial-grade high-purity gallium products, which can be directly used in fields requiring high gallium purity, such as semiconductor materials, solar cells, and alloy preparation.

[0049] In some embodiments, the alkaline solution used in the alkaline dissolution treatment is a sodium hydroxide solution, a potassium hydroxide solution, or a sodium carbonate solution; the mass fraction of the alkaline solution is 12% to 32%.

[0050] Alkali dissolution treatment refers to the process of mixing an impurity-enriched liquid phase obtained from directional crystallization with an alkaline solution, and then reacting the metallic gallium in the impurity-enriched liquid phase with the alkali under heating, stirring, and pressurization conditions to form soluble gallate. The purpose of alkali dissolution treatment is to convert the metallic gallium in the impurity-enriched liquid phase into a gallium-containing solution, which is a soluble gallate solution such as sodium gallate, potassium gallate, or sodium gallate (sodium gallate is formed when sodium carbonate is used as the alkali solution), facilitating subsequent use for electrolytic gallium extraction, gallium enrichment and recovery, or return to the alumina production process. A closed reaction vessel can be used as the reaction vessel for alkali dissolution treatment. Sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution provide different hydroxide concentrations at the same mass fraction. Therefore, the actual reaction intensity varies depending on the alkaline solution selected. In the embodiments of this application, the mass fraction range is uniformly set to 12%–32%, allowing those skilled in the art to adjust the mass fraction within the range as needed and combine it with the type of alkaline solution to achieve the required reaction intensity.

[0051] In some embodiments, the volume ratio of the impurity-enriching liquid phase to the alkaline solution is 1:20 to 1:100.

[0052] The volume ratio of the impurity-enriched liquid phase to the alkali solution refers to the ratio of the volume of the impurity-enriched liquid phase obtained by directional crystallization to the volume of the alkali solution used in the alkali dissolution treatment. This volume ratio is 1:20 to 1:100, meaning that each unit volume of impurity-enriched liquid phase corresponds to twenty to one hundred units of alkali solution.

[0053] If the volume ratio exceeds 1:100, meaning the volume of the alkali solution is more than one hundred times the volume of the impurity-enriching liquid phase, the excessive alkali solution will result in an excessively low gallium concentration in the gallium-containing solution. A low-concentration gallium-containing solution leads to low current efficiency and high energy consumption during subsequent electrolytic gallium extraction; when used as a gallium enrichment solution, it requires significant energy and reagent consumption for concentration; and when returned to the Bayer process as a seed mother liquor, the excessively low gallium concentration will reduce gallium recovery efficiency. Therefore, 1:100 is the maximum alkali solution volume that maintains the gallium-containing solution concentration within an economically recoverable range. Secondly, excessive alkali solution means higher alkali reagent consumption. The cost of sodium hydroxide, potassium hydroxide, or sodium carbonate increases with the amount used. When the volume ratio exceeds 1:100, the proportion of alkali solution cost in the total processing cost increases significantly, reducing the economic viability of this method.

[0054] If the volume ratio is less than 1:20, meaning the volume of the alkali solution is less than twenty times the volume of the impurity-enriched liquid phase, the amount of alkali solution is insufficient to provide enough hydroxide ions. According to stoichiometry, each mole of gallium metal requires one to two moles of hydroxide ions (depending on the form of the reaction products). Besides gallium metal, the impurity-enriched liquid phase may also contain small amounts of unremoved acidic substances or oxides produced by hydrolysis, which also consume alkali. When the volume ratio is less than 1:20, even with an upper limit of 32% alkali mass fraction, the total number of moles of hydroxide ions in the alkali solution may not be sufficient to convert all the gallium metal in the impurity-enriched liquid phase into gallate ions, leading to a decrease in gallium conversion rate and some unreacted gallium metal remaining. Secondly, if the volume of the alkali solution is too small, it cannot effectively disperse the impurity-enriched liquid phase. During alkali dissolution treatment, the impurity-enriched liquid phase needs to be dispersed into fine droplets to increase the reaction interface. If the volume of the alkali solution is too small, the impurity-enriched liquid phase easily aggregates into larger droplets or a continuous phase, resulting in insufficient contact area with the alkali solution and a slower reaction rate. Even with a stirring speed of 1000 rpm, sufficient dispersion cannot be achieved with a small volume of alkaline solution. Finally, a small volume of alkaline solution leads to insufficient buffering capacity in the reaction system. During the alkaline dissolution process, metallic gallium reacts with the alkaline solution to form gallate and consumes hydroxide ions. If the volume of alkaline solution is small, the hydroxide concentration in the solution decreases rapidly during the reaction, the pH value decreases, and the reaction rate decreases accordingly. Before reaching the reaction endpoint, the reaction may stop prematurely due to the depletion of the alkaline solution, resulting in incomplete gallium conversion.

[0055] In some embodiments, the alkali dissolution treatment satisfies the following conditions: reaction temperature of 100℃~160℃, stirring speed of 500r / min~1000r / min, reaction time of 5h~12h, and reaction pressure of 0.5MPa~2.5MPa.

[0056] Gallium reacts very slowly with alkaline solutions at room temperature, requiring heating to provide the activation energy needed for the reaction. When the reaction temperature is below 100°C, the water in the alkaline solution boils at atmospheric pressure, making it difficult to stably raise the temperature of the reaction system under closed conditions. More importantly, the reaction rate of gallium with alkaline solutions (2Ga + 2NaOH + 2H₂O → 2NaGaO₂ + 3H₂↑) is too low below 100°C, significantly extending the reaction time required to achieve the same conversion rate (exceeding 12 hours), thus reducing economic efficiency. While the reaction rate increases further at temperatures above 160°C, the following adverse effects occur: First, the pressure resistance and corrosion resistance requirements of the reaction vessel increase significantly, raising equipment costs and safety risks; second, excessively high temperatures may exacerbate the corrosion of the reaction vessel materials by the alkaline solution, shortening equipment lifespan; and third, energy consumption increases dramatically.

[0057] The impurity-enriched liquid phase is liquid gallium metal (containing enriched impurities such as copper, mercury, lead, nickel, iron, and zinc), and the alkaline solution is an aqueous solution; the two are immiscible. During the alkaline dissolution process, the gallium metal needs to be in full contact with the alkaline solution to react and form water-soluble gallates. If the stirring speed is below 500 r / min, the stirring intensity is insufficient, and the liquid gallium metal easily agglomerates into large particles or adheres to the bottom and walls of the reaction vessel, resulting in a small contact area with the alkaline solution, a low reaction rate, and incomplete conversion. When the stirring speed is above 1000 r / min, although the mass transfer effect is better, excessive shear force is generated, causing the reaction system to splash and adhere to the upper part of the reaction vessel and the exhaust pipe. At the same time, excessively high stirring speed will exacerbate the fragmentation of hydrogen bubbles, which is not conducive to the smooth discharge of hydrogen from the reaction system and may cause local pressure fluctuations. By controlling the stirring speed between 500 r / min and 1000 r / min, the negative effects of excessive stirring can be avoided while ensuring that the liquid gallium metal is fully dispersed in the alkaline solution. This allows the surface of the gallium metal to be constantly renewed and in contact with fresh alkaline solution, thus maintaining a stable reaction rate.

[0058] The reaction between gallium and alkaline solution is not instantaneous; sufficient time is required for the alkaline solution to penetrate and dissolve the oxide film on the gallium surface, and for the hydrogen bubbles generated in the reaction to escape. In the embodiments of this application, the reaction time is 5 to 12 hours. If the reaction time is less than 5 hours, complete conversion cannot be achieved even under optimal conditions; if it is more than 12 hours, energy consumption and cost increase, the conversion rate improvement is negligible, and economic efficiency decreases.

[0059] Reaction pressure refers to the gauge pressure inside the sealed reaction vessel during the alkali dissolution process. If the reaction pressure is below 0.5 MPa, the alkali solution may boil at high temperatures, leading to concentration fluctuations and uncontrolled reaction; if it is above 2.5 MPa, the equipment requirements are too high, increasing investment and operational risks.

[0060] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0061] Example 1 The gallium production waste used in this embodiment comes from splash waste generated during the industrial gallium production process. The main impurities in the gallium production waste are copper, mercury, and lead, with a copper content of 42 ppm, a mercury content of 10 ppm, and a lead content of 30 ppm.

[0062] 1 kg of gallium production waste was melted at 35°C to transform the solid waste into a liquid state, yielding a gallium production waste melt. The melt was then subjected to a water-washing-acid-washing process to obtain pretreated gallium production waste. The acid washing used dilute hydrochloric acid as the washing solution, with a mass fraction of 5% and a volume ratio of 1:10 between the hydrochloric acid and the gallium production waste melt. The acid washing temperature was 35°C for 4 hours, accompanied by mechanical stirring.

[0063] The pretreated gallium production waste was directionally crystallized. The cooling temperature for directional crystallization was 26℃, and the heating temperature was 34℃. Driven by the temperature gradient, the pretreated gallium production waste directionally solidified, yielding a solid crystalline phase and an impurity-enriched liquid phase. The mass ratio of the solid crystalline phase to the impurity-enriched liquid phase was approximately 4:1. The purity of the solid crystalline phase was 99.992%, with the main impurity elements copper content at 6.0 ppm, mercury content at 1.6 ppm, and lead content at 5.0 ppm. Other impurity elements met national standards. The mass of the solid crystalline phase was approximately 800 g.

[0064] The impurity-enriched liquid phase was subjected to alkali dissolution treatment. Sodium hydroxide solution with a mass fraction of 20% was used as the alkali, and the volume ratio of the impurity-enriched liquid phase to the alkali solution was 1:60. The alkali dissolution treatment was carried out in a closed reactor at a reaction temperature of 150℃, a stirring speed of 1000 r / min, a reaction time of 10 h, and a reaction pressure of 1.0 MPa. After the reaction was completed, a gallium-containing solution was obtained, with a sodium gallate concentration of approximately 180 g / L.

[0065] Example 2 The gallium production waste used in this embodiment is derived from waste generated during the high-purity gallium crystallization process. The main impurities in the gallium production waste are copper, mercury, and lead, with copper content at 40 ppm, mercury content at 14 ppm, and lead content at 28 ppm.

[0066] 1 kg of gallium production waste was melted at 36°C to obtain gallium production waste melt. The gallium production waste melt was then subjected to a water wash-acid wash-water wash cycle to obtain pretreated gallium production waste. Dilute hydrochloric acid (5% by mass) was used as the acid wash solution, with a volume ratio of hydrochloric acid to gallium production waste melt of 1:8. The acid wash temperature was 36°C for 3.5 hours, accompanied by mechanical stirring.

[0067] The pretreated gallium production waste was subjected to directional crystallization. The cooling temperature for directional crystallization was 27℃, and the heating temperature was 33℃. After directional crystallization, a solid crystalline phase and an impurity-enriched liquid phase were obtained. The mass ratio of the solid crystalline phase to the impurity-enriched liquid phase was approximately 4:1. The purity of the solid crystalline phase was 99.991%, with the main impurity elements copper content at 6.5 ppm, mercury content at 1.9 ppm, and lead content at 6.0 ppm. Other impurity elements met national standards. The mass of the solid crystalline phase was approximately 800 g.

[0068] The impurity-enriched liquid phase was subjected to alkali dissolution treatment. Sodium hydroxide solution with a mass fraction of 15% was used as the alkali, and the volume ratio of the impurity-enriched liquid phase to the alkali solution was 1:100. The alkali dissolution treatment was carried out in a closed reactor at a reaction temperature of 145℃, a stirring speed of 1000 r / min, a reaction time of 9.5 h, and a reaction pressure of 1.1 MPa. After the reaction was completed, a gallium-containing solution was obtained, with a sodium gallate concentration of approximately 176 g / L.

[0069] Example 3 The gallium production waste used in this embodiment is a mixture of splash waste generated during industrial gallium production and waste generated during the high-purity gallium crystallization process. The main impurities in the gallium production waste are copper, mercury, and lead, with copper content of 50 ppm, mercury content of 20 ppm, and lead content of 23 ppm.

[0070] 5 kg of gallium production waste was melted at 37°C to obtain gallium production waste melt. The gallium production waste melt was then subjected to a water wash-acid wash-water wash cycle to obtain pretreated gallium production waste. Dilute hydrochloric acid (5% by mass) was used as the acid wash solution, with a volume ratio of hydrochloric acid to gallium production waste melt of 1:10. The acid wash temperature was 37°C for 4 hours, accompanied by mechanical stirring.

[0071] The pretreated gallium production waste was subjected to directional crystallization. The cooling temperature for directional crystallization was 24℃, and the heating temperature was 35℃. After directional crystallization, a solid crystalline phase and an impurity-enriched liquid phase were obtained. The mass ratio of the solid crystalline phase to the impurity-enriched liquid phase was approximately 4:1. The purity of the solid crystalline phase was 99.990%, with the main impurity elements copper content at 6.9 ppm, mercury content at 1.8 ppm, and lead content at 5.7 ppm. Other impurity elements met national standards. The mass of the solid crystalline phase was approximately 4000 g.

[0072] The impurity-enriched liquid phase was subjected to alkali dissolution treatment. Sodium hydroxide solution with a mass fraction of 12% was used as the alkali, and the volume ratio of the impurity-enriched liquid phase to the alkali solution was 1:100. The alkali dissolution treatment was carried out in a closed reactor at a reaction temperature of 150℃, a stirring speed of 1000 r / min, a reaction time of 10 h, and a reaction pressure of 1.5 MPa. After the reaction was completed, a gallium-containing solution was obtained, with a sodium gallate concentration of approximately 172 g / L.

[0073] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: High-value-added products are produced simultaneously during waste treatment: In the waste disposal process, a solid crystalline phase (high-purity gallium) with a purity of not less than 99.99 wt% can be obtained directly through a directional crystallization step. This product can be directly used as a raw material for high-end application fields such as semiconductors and optoelectronic materials, realizing the simultaneous production of high-purity products and improving the economic benefits of the method.

[0074] It exhibits excellent industrial compatibility and operational flexibility: The pickling, directional crystallization, and alkali dissolution steps used in the embodiments of this application are all mature unit operations. Production enterprises can directly implement them using existing crystallization equipment, reaction vessels, and other production line facilities without large-scale equipment modifications. Furthermore, sodium hydroxide, potassium hydroxide, or sodium carbonate solutions can be selected for the alkali dissolution treatment, and the mass fraction of the alkali solution can be adjusted within a wide range. The volume ratio of the impurity-enriching liquid phase to the alkali solution can also be flexibly selected, allowing production enterprises to adjust process parameters based on factors such as raw material sources, equipment materials, cost budgets, and downstream product demands, demonstrating strong adaptability.

[0075] The process is short, simple to operate, and does not involve toxic organic reagents: The embodiments of this application only involve three main steps: acid washing, directional crystallization, and alkali dissolution. The entire process uses conventional inorganic reagents such as dilute hydrochloric acid and alkaline solutions, without involving the use of organic extractants. The operation is safe, the wastewater treatment is easy, and it is more in line with the requirements of green chemistry and clean production.

[0076] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for disposal and recycling of gallium production waste, characterized by, The method comprises: The gallium production waste is subjected to melting treatment to obtain a gallium production waste melt, the mass fraction of metallic gallium in the gallium production waste being greater than 95%; The gallium production waste melt is subjected to acid pickling to obtain pretreated gallium production waste; The pretreated gallium production waste is subjected to directional crystallization to obtain a solid crystalline phase with a purity of 99.99wt% or above and an impurity-rich liquid phase, the difference between the cold field temperature and the hot field temperature of the directional crystallization being 4-20℃; The impurity-rich liquid phase is subjected to alkali dissolution treatment to obtain a gallium-containing solution.

2. The method of claim 1, wherein, The temperature of the melting treatment is 30-50℃.

3. The method of claim 1, wherein, The acid pickling uses dilute hydrochloric acid as the acid pickling solution, the mass fraction of the dilute hydrochloric acid being 0.5-5%, and the volume ratio of the dilute hydrochloric acid to the gallium production waste melt being 1:10-1:

1.

4. The method of claim 3, wherein, The temperature of the acid pickling is 30-50℃, and the time of the acid pickling is 0.5-4h.

5. The method of claim 1, wherein, The cold field temperature is 20-29℃, and the hot field temperature is 31-40℃.

6. The method of claim 1, wherein, The alkali solution used in the alkali dissolution treatment is a sodium hydroxide solution, a potassium hydroxide solution or a sodium carbonate solution; the mass fraction of the alkali solution is 12-32%.

7. The method of claim 6, wherein, The volume ratio of the impurity-rich liquid phase to the alkali solution is 1:20-1:

100.

8. The method of claim 1, 6 or 7, wherein, The alkali dissolution treatment satisfies the following conditions: the reaction temperature is 100-160℃, the stirring speed is 500-1000r / min, the reaction time is 5-12h, and the reaction pressure is 0.5-2.5MPa.

9. The method of claim 1 wherein, The gallium production waste is splash waste generated in the industrial gallium production process or crystallization tailings generated in the high-purity gallium crystallization production process.

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