Deep dechlorination method for bismuth oxychloride based on hydrothermal crystallization method
By combining hydrothermal crystallization with hydrogen chloride hydrolysis and mixed heat treatment with an alkaline conversion agent, the problems of difficulty and high cost in deep dechlorination of bismuth oxide were solved, and efficient, low-cost purification and high-purity preparation of bismuth oxide were achieved.
Patent Information
- Application Number
- CN202510900573.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-01
- Publication Date
- 2025-09-23
AI Technical Summary
Existing methods for preparing and purifying bismuth oxide have problems such as high cost, low efficiency, severe equipment corrosion, and environmental pollution. In particular, deep dechlorination of chloride-containing bismuth oxide is difficult. Existing methods have problems such as high energy consumption, complex equipment, and difficulty in waste liquid treatment.
The hydrothermal crystallization method is adopted to achieve deep dechlorination of bismuth oxychloride through hydrogen chloride hydrolysis, filtration and impurity removal, alkaline conversion agent mixed heat treatment and calcination steps, combined with appropriate temperature and time control, to prepare high-purity bismuth oxycarbonate and bismuth oxide of different crystal forms.
The system achieves efficient and low-cost purification of bismuth oxide, with high product purity, less agglomeration, uniform particles, low energy consumption, avoiding repeated operations and secondary pollution, and a dechlorination efficiency of up to 99.9%.
Smart Images
Figure CN120681786A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of bismuth oxide preparation, in particular to a deep dechlorination process of bismuth oxychloride using a hydrothermal crystallization method. Background Art
[0002] Bi2O3 actually has many crystal forms. Among these, the stable α-form and the metastable β-form are the most common and widely used. Dechlorination of bismuth oxychloride yields easily reducible bismuth oxide. Reduction treatment can then produce metallic bismuth, which, due to its excellent properties, is widely used in a variety of fields, including nuclear energy, semiconductors, electronics, and superconductors.
[0003] Bismuth often coexists with other metals, including lead, copper, tungsten, molybdenum, and tin. Bismuth smelting raw materials primarily consist of coexisting ores and byproducts (such as lead-tin anode mud, copper dust, blast furnace dust from pig iron smelting, and lead-bismuth alloys from furnace bottoms). Bismuth is typically obtained through pyrometallurgical smelting of coexisting ores and hydrometallurgical smelting of byproducts. Chloride leaching is typically used to extract the byproducts, resulting in bismuth-containing products with chloride contents typically as high as 10-30% by mass. Due to the highly corrosive and environmentally toxic nature of chloride ions, direct recovery or discharge can lead to equipment corrosion and heavy metal pollution. Therefore, deep dechlorination of bismuth oxychloride has become a core technology for bismuth resource recovery and harmless treatment of industrial solid waste.
[0004] As demand for bismuth oxide continues to grow, production technologies are becoming increasingly diverse, including high-temperature alkaline washing and regeneration, ion exchange dechlorination, and pyrolysis. However, these methods often have limitations when used alone. For example, high-temperature alkaline washing requires a highly concentrated alkaline solution, which introduces a large amount of metal cations into the bismuth oxide solid, significantly reducing its purity. Furthermore, high-temperature strong alkaline solutions can corrode equipment, and wastewater containing high concentrations of alkaline is difficult to process. In anion resin exchange, resin saturation requires frequent regeneration or replacement, a complex regeneration process and the potential for secondary contamination due to poor regeneration reagent quality. The resin is susceptible to organic or microbial contamination, resulting in reduced adsorption efficiency and potentially dissolution of organic matter or the generation of particulate debris, which can affect the stability of bismuth oxychloride dechlorination. Pyrolysis requires high temperatures, consumes significant energy, and generates chlorine-containing exhaust gases, making tail gas treatment complex. Therefore, developing an efficient and convenient bismuth oxychloride dechlorination process is crucial to promoting the standardization and industrialization of the bismuth industry. Summary of the Invention
[0005] In order to solve the problems of the existing difficulty in preparing and purifying bismuth oxide, especially the high cost and limited effect of dechlorination purification of crude chlorine-containing products, the present invention provides a deep dechlorination method of bismuth oxychloride based on hydrothermal crystallization.
[0006] The main objectives of the present invention are: 1. Ability to cleanly and efficiently prepare high-purity bismuth oxycarbonate crystals; Second, different crystal forms of bismuth oxide can be obtained by calcination to meet the application of different situations; 3. High-purity bismuth can be prepared through further hydrogen reduction process.
[0007] To achieve the above objectives, the present invention adopts the following technical solutions.
[0008] A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization. The method comprises: 1) Pre-treating bismuth oxide coarse powder and then dissolving it in a hydrogen chloride aqueous solution to prepare a pre-solution; 2) filtering the pre-solution to remove impurities, adding water to hydrolyze it, filtering to obtain a bismuth oxychloride intermediate, and washing it to neutrality to obtain bismuth oxychloride; 3) bismuth oxychloride is mixed and dispersed with water to form a suspension, an alkaline transition agent is prepared as a transition solvent, the suspension is added to the transition solvent for mixing and heat treatment, and then filtered to obtain a precursor; 4) Calcining the precursor to obtain dechlorinated bismuth oxide. The calcination temperature and calcination time can be adjusted according to the target crystal form. The adjustment can directly refer to the existing process for calcining bismuth oxycarbonate ((BiO)2CO3) into bismuth oxide.
[0009] As a preference, The pretreatment in step 1) includes grinding, and the grinding process makes the particle size of the bismuth oxide coarse powder ≤100 μm.
[0010] As a preference, In step 1), the bismuth concentration in the pre-solution is 100-500 g / L, and the hydrogen chloride concentration is 3-8 mol / L.
[0011] As a preference, Step 2) The filtration and impurity removal process is performed using a 0.44 μm filter membrane; Step 2) When adding water for hydrolysis, the amount of precipitate in the solution system no longer increases after the water is added, and stirring is maintained for at least 1 hour during and after the addition; In step 2), the washing to neutrality is performed using water as the washing liquid and washing until the pH value of the washing liquid is 6.5 to 7.5.
[0012] As a preference, Step 3) the bismuth oxychloride and water are mixed at a solid-to-liquid ratio of 1:(10-25); Step 3) The alkaline conversion agent is ammonium carbonate, and the concentration of ammonium carbonate in the conversion solvent is 10 to 200 g / L.
[0013] As a preference, Step 3) the suspension and the transformation agent are mixed in a volume ratio of 1: (0.8-1.2) and subjected to a mixing heat treatment; The mixed heat treatment process controls the reaction temperature to be 80-150° C. and the reaction time to be 2-24 h.
[0014] As a preference, Step 4) The calcination temperature is ≥320°C and the calcination time is ≥1 h.
[0015] like Figure 1 The preparation method of the present invention is shown in step 2) deep impurity removal through chloride-coupled hydrolysis to achieve solid-liquid redistribution of the main metal and impurities, thereby improving the purity of the main metal, achieving a metal recovery rate of about 96%, and obtaining a relatively high-purity BiOCl product; step 3) dispersing bismuth oxychloride powder in water to form a suspension, significantly increasing its contact area with an alkaline conversion agent (dechlorinating agent, such as ammonium carbonate, alkali, etc.), accelerating the ion exchange reaction and promoting the dechlorination reaction, and using a hydrothermal crystallization method to convert BiOCl into (BiO)2CO3 using a (NH4)2CO3 solution to achieve the purpose of dechlorination. The main mechanism is that (NH4)2CO3 generates NH4 in the aqueous solution. + and CO3 2- , NH4 + Hydrolysis forms an alkaline system. BiOCl in alkaline conditions - Can be CO3 2- Substitution, the following reaction occurs: 2BiOCl + CO3 2- → (BiO)2CO3↓ + 2Cl - Under high temperature conditions, the ion migration ability is enhanced, which promotes the - The Cl generated by the reaction is separated from the BiOCl lattice. - With NH4 in solution + It is combined into NH4Cl and separated by subsequent filtration or crystallization steps, with a dechlorination efficiency of 99.9%; finally, (BiO)2CO3 is decomposed into bismuth oxide of different crystal forms by calcining at different temperatures.
[0016] In addition, in terms of parameters, the present invention uses appropriate high temperature in step 3) during the mixed heat treatment process to greatly accelerate the CO3 2- and Cl - The migration exchange of Cl in the BiOCl lattice - The mobility increases dramatically under high temperature conditions, but if too high a temperature is used, other impurities are easily formed, resulting in a decrease in the yield of the target product bismuth oxycarbonate, which ultimately affects the acquisition of the target product bismuth oxide.
[0017] The present invention provides a deep dechlorination process of bismuth oxychloride by a hydrothermal crystallization method, which has the following beneficial effects: (1) The preparation method of the present invention utilizes a high-acidity chloride system, and the redistribution of impurities between the solid and liquid phases can be achieved through the hydrolysis process. The hydrothermal crystallization method utilizes a relatively low concentration of ammonium carbonate solution, and the entire process has less pollution. No elements such as sodium that are difficult to remove during the crystallization process are introduced. Moreover, the NH4Cl generated by the reaction can be recovered by evaporation and crystallization, and the filtrate is reused to prepare the ammonium carbonate solution, thereby achieving zero discharge of ammonium salts. (2) The process for preparing bismuth oxide of the present invention is simple, does not require complicated processes and related equipment, and the raw materials are easily available and low in cost. The separation process has low energy consumption, avoids repeated operations, and has a high direct material recovery rate. The obtained product has high purity, less agglomeration, and uniform and fine particles. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is a flowchart of the program of the present invention; Figure 2 XRD pattern of BiOCl, (BiO)2CO3 prepared in Example 1 of the present invention; Figure 3 This is the SEM image of (BiO)2CO3 obtained in Example 1 of the present invention. DETAILED DESCRIPTION
[0019] The present invention is further described in detail below with reference to specific embodiments and the accompanying drawings. Based on these descriptions, those skilled in the art will be able to implement the present invention. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.
[0020] Unless otherwise specified, the raw materials used in the examples of the present invention are commercially available or readily available to those skilled in the art. Unless otherwise specified, the methods used in the examples of the present invention are methods within the skill of those skilled in the art. Unless otherwise specified, the chlorine content of the coarse bismuth oxide powder used in the examples of the present invention is 10-30%.
[0021] Example 1 A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization. The method comprises: 1) Grind bismuth oxide coarse powder to a particle size ≤100 μm and dissolve it in aqueous hydrogen chloride solution to prepare a pre-solution with a specific concentration of 250 g / L and a hydrogen chloride concentration of 5 mol / L. 2) The pre-solution was filtered through a 0.44 μm filter membrane to remove impurities, and then water was added until the amount of precipitate in the solution system stopped increasing. During the addition of water, the solution was heated to 50°C and stirred continuously for 1 hour. The bismuth oxychloride intermediate was filtered and washed with deionized water until the pH was approximately 7.0, thereby obtaining bismuth oxychloride. 3) Bismuth oxychloride and water were dispersed in a solid-liquid ratio of 1:15 to prepare a suspension, ammonium carbonate was dissolved in deionized water to prepare a transition solvent, the suspension and the transition agent were mixed in a volume ratio of 1:1, and the mixture was heat-treated at 100°C for 6 hours, followed by filtration to obtain a precursor; 4) The precursor is calcined at 400 °C for 6 h to obtain dechlorinated bismuth oxide, i.e., high-purity α-Bi2O3.
[0022] In this example, different concentrations of transition solvents (i.e., different concentrations of ammonium carbonate aqueous solutions) were used to characterize the chlorine content of the dechlorinated bismuth oxide product prepared with different concentrations of transition solvents, and the dechlorination efficiency was calculated.
[0023] ; The characterization calculation results are shown in the following table.
[0024]
[0025] In addition, the purity of the product dechlorinated bismuth oxide was characterized, and the characterization results are shown in the following table.
[0026]
[0027] From the results in the above table, it can be seen that the dechlorination efficiency is positively correlated with the increase of ammonium carbonate concentration within the appropriate range. However, when the concentration of ammonium carbonate is too high, the ammonium carbonate solution produces kinetic inhibition, resulting in an increase in diffusion resistance, which in turn begins to lead to a decrease in dechlorination efficiency. In terms of product purity, it is also lower than theoretical expectations and has produced a more significant decrease, indicating that additional non-removable or difficult-to-remove by-products are produced during the reaction process. Therefore, the concentration of ammonium carbonate solution needs to be strictly controlled. In addition, XRD characterization was performed on the precursor prepared with an ammonium carbonate concentration of 25-150 g / L. The characterization results are as follows: Figure 2 As shown in the middle left figure, the four curves in the left figure correspond to the precursors of 150 g / L, 100 g / L, 50 g / L and 25 g / L ammonium carbonate concentrations from top to bottom, respectively. It can be seen that the dechlorination effect is significant. The product of the 25 g / L ammonium carbonate concentration experimental group was also characterized by SEM. Figure 3 As shown, Figure 3 The product crystal structure is highly uniform and consistent. Based on the 25 g / L experimental group, the solid-liquid ratio of bismuth oxychloride to water in step 3) was changed to 1:10 and 1:7.5, and the precursor was prepared for XRD characterization as shown below. Figure 2 As shown in the middle right figure, the right figure shows the XRD characterization results of the precursor with a solid-liquid ratio of 1:10, the precursor with a solid-liquid ratio of 1:7.5, and BiOCl from top to bottom. It can be seen that within the appropriate solid-liquid ratio range, better preparation effects can be achieved.
[0028] Example 2 A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization. The method comprises: 1) Grind bismuth oxide coarse powder to a particle size ≤100 μm and dissolve it in aqueous hydrogen chloride solution to prepare a pre-solution with a specific concentration of 250 g / L and a hydrogen chloride concentration of 5 mol / L. 2) The pre-solution was filtered through a 0.44 μm filter membrane to remove impurities, and then water was added until the amount of precipitate in the solution system stopped increasing. During the addition of water, the solution was heated to 50°C and stirred continuously for 1 hour. The bismuth oxychloride intermediate was filtered and washed with deionized water until the pH was approximately 7.0, thereby obtaining bismuth oxychloride. 3) Bismuth oxychloride and water were mixed and dispersed at a solid-to-liquid ratio of 1:15 to prepare a suspension, and ammonium carbonate was dissolved in deionized water to prepare a transition solvent with an ammonium carbonate concentration of 25 g / L. The suspension and the transition agent were mixed at a volume ratio of 1:1, and heat-treated at different temperatures for 6 h, followed by filtration to obtain a precursor; 4) The precursor is calcined at 400 °C for 6 h to obtain dechlorinated bismuth oxide, i.e., high-purity α-Bi2O3.
[0029] In this example, different concentrations of transition solvents (i.e., different concentrations of ammonium carbonate aqueous solutions) were used to characterize the chlorine content of the dechlorinated bismuth oxide product prepared with different concentrations of transition solvents, and the dechlorination efficiency was calculated.
[0030] ; The characterization calculation results are shown in the following table.
[0031]
[0032] In addition, the purity of the product dechlorinated bismuth oxide was characterized, and the characterization results are shown in the following table.
[0033]
[0034] From the results in the table above, the dechlorination efficiency and product purity are significantly correlated with the heat treatment temperature. In the range of 60-120 ℃, the dechlorination efficiency is positively correlated with the temperature, but after reaching 120 ℃, the dechlorination effect is negatively correlated with the temperature in the range of 150-180 ℃. This is mainly because although high temperature accelerates ion migration, the reaction equilibrium at high temperature moves towards the endothermic direction, and Cl- It may re-bond to the crystal lattice, resulting in a decrease in the dechlorination effect.
[0035] Example 3 A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization. The method comprises: 1) Grind bismuth oxide coarse powder to a particle size ≤100 μm and dissolve it in aqueous hydrogen chloride solution to prepare a pre-solution with a specific concentration of 250 g / L and a hydrogen chloride concentration of 5 mol / L. 2) The pre-solution was filtered through a 0.44 μm filter membrane to remove impurities, and then water was added until the amount of precipitate in the solution system stopped increasing. During the addition of water, the solution was heated to 50°C and stirred continuously for 1 hour. The bismuth oxychloride intermediate was filtered and washed with deionized water until the pH was approximately 7.0, thereby obtaining bismuth oxychloride. 3) Bismuth oxychloride and water were mixed and dispersed at a solid-to-liquid ratio of 1:15 to prepare a suspension, and ammonium carbonate was dissolved in deionized water to prepare a transition solvent with an ammonium carbonate concentration of 25 g / L. The suspension and the transition agent were mixed at a volume ratio of 1:1, and the mixture was heat-treated at 100°C for 1 to 32 hours, followed by filtration to obtain a precursor; 4) The precursor is calcined at 400 °C for 6 h to obtain dechlorinated bismuth oxide, i.e., high-purity α-Bi2O3.
[0036] In this example, different concentrations of transition solvents (i.e., different concentrations of ammonium carbonate aqueous solutions) were used to characterize the chlorine content of the product dechlorinated bismuth oxide prepared with different concentrations of transition solvents, and the dechlorination efficiency was calculated.
[0037] ; The characterization calculation results are shown in the following table.
[0038]
[0039] In addition, the purity of the product dechlorinated bismuth oxide was characterized, and the characterization results are shown in the following table.
[0040]
[0041] The results in the table above show that heat treatment duration is positively correlated with dechlorination effectiveness within an appropriate range. However, as heat treatment time increases, not only does energy consumption increase, but dechlorination efficiency also decreases. This is mainly due to the fact that prolonged heat treatment leads to further structural changes in the pre-product, potentially forming a potential "molecular sieve"-like adsorption structure and potentially capturing and fixing some chloride ions during structural reconstruction and densification, resulting in the inability to effectively remove chloride ions. Therefore, controlling the appropriate heat treatment duration is one of the keys to achieving optimal results.
Claims
1. A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization, characterized in that: The method comprises: 1) Pre-treating bismuth oxide coarse powder and then dissolving it in a hydrogen chloride aqueous solution to prepare a pre-solution; 2) filtering the pre-solution to remove impurities, adding water to hydrolyze it, filtering to obtain a bismuth oxychloride intermediate, and washing it to neutrality to obtain bismuth oxychloride; 3) bismuth oxychloride is mixed and dispersed with water to form a suspension, an alkaline transition agent is prepared as a transition solvent, the suspension is added to the transition solvent for mixing and heat treatment, and then filtered to obtain a precursor; 4) The precursor is calcined to obtain dechlorinated bismuth oxide.
2. A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization according to claim 1, characterized in that, The pretreatment in step 1) includes grinding, and the grinding process makes the particle size of the bismuth oxide coarse powder ≤100 μm.
3. A method for deep dechlorination of bismuth oxychloride based on a hydrothermal crystallization method according to claim 1 or 2, characterized in that, In step 1), the bismuth concentration in the pre-solution is 100-500 g / L, and the hydrogen chloride concentration is 3-8 mol / L.
4. A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization according to claim 1, characterized in that, Step 2) The filtration and impurity removal process is performed using a 0.44 μm filter membrane; Step 2) When adding water for hydrolysis, the amount of precipitate in the solution system no longer increases after the water is added, and stirring is maintained for at least 1 hour during and after the addition; In step 2), the washing to neutrality is performed using water as the washing liquid and washing until the pH value of the washing liquid is 6.5 to 7.
5.
5. A method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization according to claim 1, characterized in that, Step 3) the bismuth oxychloride and water are mixed at a solid-to-liquid ratio of 1:(10-25); Step 3) The alkaline conversion agent is ammonium carbonate, and the concentration of ammonium carbonate in the conversion solvent is 10 to 200 g / L.
6. A method for deep dechlorination of bismuth oxychloride based on a hydrothermal crystallization method according to claim 1 or 5, characterized in that, Step 3) the suspension and the transformation agent are mixed in a volume ratio of 1: (0.8-1.2) and subjected to a mixing heat treatment; The mixed heat treatment process controls the reaction temperature to be 80-150° C. and the reaction time to be 2-24 h.
7. The method for deep dechlorination of bismuth oxychloride based on hydrothermal crystallization according to claim 1, wherein Step 4) The calcination temperature is ≥320°C and the calcination time is ≥1 h.