Method for inhibiting secondary white tungstic acid sodium in sodium tungstate of tin smelting furnace slag alkali fusion water quenching slag

Abstract

The application discloses a method for inhibiting secondary white tungstenization of sodium tungstate in tin smelting slag alkali fusion water-quenched slag, the alkali fusion water-quenched slag is slag after water quenching of tin smelting fuming furnace slag after alkali fusion treatment, and the method is characterized in that, during water quenching of the tin smelting fuming furnace slag after alkali fusion treatment, alkali is added to water for water quenching, the pH value of the water for water quenching is controlled to be 10-12, the dissolution of Ca 2+ is inhibited, and the thermodynamic driving force of reverse reaction is reduced; under the alkaline condition, Ca 2+ generates Ca(OH)2 or CaCO3 precipitate, the free Ca 2+ concentration is reduced, and the reverse reaction of Na2WO4 and Ca 2+ is inhibited. The method can effectively improve the water-soluble recovery rate of tungsten and reduce the secondary white tungstenization rate in the water quenching process. The method is simple to operate, can be seamlessly connected with the main production process, and significantly improves the tungsten recovery efficiency in the alkali fusion slag of the tin smelting fuming furnace after alkali fusion.

Description

Technical Field

[0001] This invention belongs to the field of secondary comprehensive utilization technology of non-ferrous metal smelting slag, specifically relating to a method for suppressing the reaction of sodium tungstate (Na2WO4) and calcium ions (Ca) in the alkaline fusion recovery of tungsten from tin smelting furnace slag by controlling water quenching conditions. 2+ A method for generating insoluble scheelite (CaWO4) precipitate through a reverse reaction (i.e., secondary scheelization). Background Technology

[0002] Tin smelting in fuming furnaces employs the sulfide volatilization method, which converts tin in tin-bearing minerals into easily volatile sulfide vapors that escape and are then oxidized into flue dust for recovery. The slag produced during tin smelting is typically discharged and then quenched in water, resulting in water-quenched slag. This slag contains approximately 0.5% tungsten (mainly in the form of calcium tungstate, iron-manganese tungstate, and tungsten oxide, with CaWO4 being the dominant component, accounting for over 97%). Scheelite accounts for approximately 93% of the tungsten-bearing minerals, and also contains approximately 35% Fe, 12% Si, 6% Ca, and 4% Al. Because CaWO4 is dispersed in the iron-silicon matrix as micron to submicron particles, existing beneficiation methods cannot effectively recover it.

[0003] The applicant has developed an alkali fusion process that involves in-situ addition of Na2CO3 at the end of the sulfidation and volatilization phase in a fuming furnace. This process utilizes the high temperature of 1100-1350°C within the furnace to convert CaWO4 into soluble Na2WO4. After water quenching, the tungsten is then recovered by entering an aqueous solution. This process integrates tungsten recovery into the main flow of the fuming furnace, eliminating the need for a separate process and external heating source. It achieves significant energy savings and a tungsten conversion rate exceeding 85%.

[0004] However, in practical operation and experimental research, a critical problem seriously affecting the tungsten recovery rate was found during the water quenching process after alkali melting: a large amount of calcium-containing phases in the slag (CaSiO3 generated by alkali melting, unreacted CaO, and calcium-containing iron silicates, etc.) dissolve Ca during water quenching. 2+ Na2WO4 and Ca 2+ The reverse reaction can occur: Na₂WO₄ + Ca 2+ → CaWO4↓ + 2Na + This reaction generates an insoluble CaWO4 precipitate, known as secondary scheelization. This process causes tungsten, which had already been converted to water-soluble Na2WO4, to revert back to the insoluble CaWO4 precipitate, resulting in a significant decrease in the water-soluble recovery rate of tungsten.

[0005] Experimental data show that, without any suppression measures, after conventional neutral water quenching (pH 6-8), the secondary scheelization rate can reach 20-30%, meaning that 20-30% of the tungsten converted by alkali fusion will reprecipitate as CaWO4 due to the reverse reaction, which seriously restricts the industrial application effect of the alkali fusion process.

[0006] The essence of the secondary scheelization problem lies in the following aspects: (1) The existence of thermodynamic driving force: Na2WO4 and Ca 2+ The reaction solubility product Ksp(CaWO4) for the formation of CaWO4 precipitate is 8.7 × 10⁻⁶. -9 (25°C), at room temperature, this reaction has a significant thermodynamic driving force, as long as WO4 is present in the aqueous solution. 2- and Ca 2+ The reverse reaction can proceed spontaneously.

[0007] (2) Ca 2+ Significant leaching: After alkali melting, calcium-containing phases such as CaSiO3 in the slag come into contact with water during water quenching, causing Ca... 2+ The continuous dissolution into the aqueous solution provides sufficient reactants for the reverse reaction.

[0008] (3) Long-term contact: In conventional water quenching operations, after the slag is water quenched, it is left to settle in the slag pool. The tungsten-containing aqueous solution and the calcium-containing slag phase are in continuous contact for tens of minutes to several hours, providing sufficient reaction time for the reverse reaction. As the contact time is extended, the secondary scheelization rate continues to increase.

[0009] (4) When the water quenching liquid-to-solid ratio is low, the Na2WO4 concentration is high, and at the same time, Ca 2+ The concentrations are also high, and both have high concentrations within a limited volume, resulting in a faster reverse reaction rate.

[0010] Currently, no publicly reported methods exist for suppressing secondary scheelization during the alkaline fusion and water quenching process. Existing research on the alkaline fusion process mainly focuses on the conversion efficiency of CaWO4 during the fusion stage, with insufficient attention paid to the potential reverse reactions during the water quenching stage. Therefore, a method is needed to effectively suppress secondary scheelization of Na2WO4 in alkaline fusion and water quenching slag to improve the water-soluble recovery rate of tungsten. Summary of the Invention

[0011] The purpose of this invention is to address the issue of Na2WO4 and Ca reacting during water quenching in the alkaline fusion recovery of tungsten from slag in tin smelting furnaces. 2+ The reverse reaction generates insoluble CaWO4 precipitate (secondary scheelization), which reduces the water-soluble recovery rate of tungsten. This paper proposes a method to effectively suppress the secondary scheelization of sodium tungstate in alkaline quenched slag. By controlling the water quenching conditions, the reverse reaction can be effectively suppressed, thereby improving the water-soluble recovery rate of tungsten.

[0012] The technical solution adopted in this invention is as follows: A method for inhibiting secondary scheelization of sodium tungstate in alkaline-melted water-quenched slag of tin smelting furnace slag, wherein the alkaline-melted water-quenched slag is the slag material obtained after alkaline melting treatment and subsequent water quenching of tin smelting furnace slag. The method involves adding alkali to the water quenching water during the water quenching process after alkaline melting treatment of the tin smelting furnace slag, controlling the pH value of the water quenching water to 10-12, thereby inhibiting the formation of calcium carbonate. 2+ The dissolution of Ca reduces the thermodynamic driving force of the reverse reaction; under alkaline conditions, Ca... 2+ The formation of Ca(OH)2 or CaCO3 precipitate reduces the free Ca content. 2+ Concentration, inhibiting the reaction of Na2WO4 and Ca 2+ The reverse reaction.

[0013] Furthermore, the alkali added to the water quenching water is Na2CO3 or NaOH; when Na2CO3 is added to adjust the pH, the concentration of Na2CO3 in the water quenching water is 5~30g / L; when NaOH is added to adjust the pH, the concentration of NaOH in the water quenching water is 1~10g / L.

[0014] Furthermore, during the slag water quenching process, the liquid-to-solid ratio of the quenching water to the slag is controlled to be ≥5:1. When the liquid-to-solid ratio is lower than 5:1, the Ca in the aqueous solution... 2+ and WO4 2- The concentrations are all high, and the reverse reaction rate is fast; when the liquid-to-solid ratio is ≥5:1, Ca 2+ When the concentration is diluted, the reverse reaction rate decreases.

[0015] Furthermore, solid-liquid separation is performed immediately after water quenching to separate the tungsten-containing aqueous solution from the calcium-containing slag. The contact time between the tungsten-containing aqueous solution and the calcium-containing slag generated during water quenching is controlled to be ≤5 min, cutting off the supply of reactants for the reverse reaction and reducing its occurrence. The contact time between the tungsten-containing aqueous solution and the calcium-containing slag is crucial. After 5 min, the secondary scheelization rate increases significantly with time; within 5 min, the secondary scheelization rate can be controlled below 5%.

[0016] Furthermore, a complexing agent is added to the separated water-quenched water to chelate Ca. 2+ Reduce free Ca 2+ Concentration; the amount of complexing agent added is 2-8 g / L; the complexing agent is selected from one or more of EDTA, sodium citrate, and sodium tartrate. The complexing agent will react with Ca... 2+ Formation of stable chelates, enabling Ca 2+ It no longer participates in the reverse reaction in the form of free ions.

[0017] Complexing agent EDTA and Ca 2+ The stability constant lgK = 10.7, indicating strong chelating ability; sodium citrate and sodium tartrate are food-grade safe reagents and are environmentally friendly.

[0018] Complexing agents such as EDTA are mainly used in the metallurgical field for leaching solution purification, while this invention innovatively uses them to suppress the reverse reaction in the water quenching stage.

[0019] Furthermore, when using EDTA as a complexing agent, the concentration of EDTA in the water-quenched water is 0.3–5 g / L. When the EDTA concentration is below 2 g / L, it chelates Ca. 2+ Insufficient capacity, costs increase when the concentration exceeds 8 g / L, and excessively high EDTA concentration in the recovered solution may affect subsequent ion exchange operations.

[0020] The core idea of ​​this invention is to take measures to suppress the reverse reaction from Na₂WO₄ to CaWO₄ during water quenching, thereby reducing the Ca content. 2+ Secondary scheelization is inhibited by reducing activity, decreasing reaction time, and lowering the reverse reaction rate. The pH of the quenching water is adjusted by adding Na₂CO₃ or NaOH, controlling the pH to 10–12. When the pH is below 10, Ca… 2+ High dissolution rate results in insignificant inhibition; excessive alkali consumption above pH 13, coupled with the high requirements for equipment materials, makes it economically impractical. Na₂CO₃ combines pH adjustment with CO₃²⁻ supply. 2- Make Ca 2+ The dual function of generating CaCO3 precipitate, and the fact that Na2CO3 is a raw material used in the alkali fusion process of pretreatment slag, eliminates the need for additional material types. NaOH is highly alkaline, requires only a small amount, and is suitable for applications where a higher pH value needs to be adjusted.

[0021] In the conventional understanding of this technical field, the purpose of water quenching is to rapidly cool and solidify high-temperature slag. Neutral water at room temperature is typically used, and pH control is not a standard operating parameter. Adjusting the quenching water to alkaline (pH ≥ 10) allows the Ca²⁺ slag to solidify. 2+ Ca(OH)₂ precipitate is formed (Ksp = 5.5 × 10⁻⁶). -6 The critical pH of [Ca] can be accurately calculated using the solubility product: the pH of [Ca] in the solution is... 2+ ]·[OH - ] 2 =Ksp, if [Ca] 2+ When the concentration of [OH] decreases from 300 mg / L to below 10 mg / L, then [OH] - ] ≥3.2×10 -3 mol / L, i.e., pH ≥ 11.5. Setting the lower pH limit to 10 in this invention is a suitable and reasonable lower limit.

[0022] Furthermore, the conventional practice for those skilled in the art in water quenching operations is to let the slag-water mixture settle in the slag pool for tens of minutes to several hours, and they never thought of completing solid-liquid separation quickly within 5 minutes to reduce the occurrence of reverse reactions.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) Effectively inhibits secondary scheelization and significantly improves the water-soluble recovery rate of tungsten. This invention controls the alkaline environment of the water quenching water to make Ca 2+ Under alkaline conditions, Ca(OH)₂ or CaCO₃ precipitates are formed, significantly reducing the amount of free Ca. 2+ Concentration fundamentally inhibits the reaction between Na₂WO₄ and Ca. 2+ The reverse reaction. Compared with conventional neutral water quenching (pH 6–8), the water-soluble recovery rate of tungsten under alkaline water quenching conditions can be increased by 15–25 percentage points. From a thermodynamic perspective, the driving force of the CaWO4 precipitation reaction increases with the amount of Ca. 2+ The effect weakens as the concentration decreases; an alkaline environment reduces the amount of Ca. 2+ Activity effectively weakens the thermodynamic driving force of the reverse reaction. Thermodynamic calculations show that when [Ca...] 2+ When the concentration drops below 10 mg / L, the driving force of the CaWO4 precipitation reaction decreases to an insufficient level to overcome the kinetic energy barrier, and the reverse reaction rate approaches zero.

[0024] (2) Synergistic inhibition by multiple means, with strong adaptability. This invention provides inhibition methods such as alkaline environment control, shortening contact time, and adding complexing agents, which can be used alone or in combination to adapt to different production conditions and changes in slag composition. The combined inhibition effect of multiple means is superimposed, and the water-soluble recovery rate of tungsten can reach more than 91%, while the secondary scheelization rate is reduced to below 0.5%.

[0025] (3) Simple operation and easy to industrialize. All measures of the present invention can be achieved by adjusting the water quenching operation parameters and adding conventional chemical reagents, without the need for large-scale modification of the existing water quenching system. Na2CO3 or NaOH is a commonly used chemical raw material for pH adjustment, which is inexpensive; the amount of complexing agents such as EDTA is small, and the cost increase per ton of water quenched slag does not exceed RMB50.

[0026] (4) Consideration to subsequent tungsten recovery processes. The alkaline water quenching water and complexing agent used in this invention will not adversely affect the subsequent ion exchange enrichment of tungsten and CaCl2 precipitation to prepare artificial scheelite. Na2CO3 and NaOH are both commonly used reagents for wet tungsten recovery, and an alkaline environment is actually beneficial to subsequent ion exchange operations (strongly basic anion exchange resins react with WO4 under alkaline conditions). 2- (The adsorption selectivity is better). Complexing agents such as EDTA react with Ca under acidic desorption conditions (pH 2-3). 2+ Dissociation, releasing Ca 2+ It can be retained by the resin or discharged with the waste liquid without interfering with the ion exchange of tungsten and the CaCl2 precipitation process.

[0027] (5) Significant economic benefits. After suppressing secondary scheelization, the water-soluble recovery rate of tungsten increases by 15 to 25 percentage points, which means that 0.06 to 0.1 kg of tungsten can be recovered per ton of water-quenched slag. Based on an annual production of more than 100,000 tons of water-quenched slag, the annual recovery of tungsten is more than 6 to 10 tons. Based on the current market price of tungsten concentrate, the annual economic benefits are significant, while the increased operating costs of the suppression measures are only several hundred thousand yuan per year, resulting in a high input-output ratio. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are used to illustrate the content of the present invention, but are not intended to limit the scope of protection of the present invention. Example 1

[0029] The slag from a tin smelting furnace in a tin smelting enterprise contains 0.511% W, 34.659% Fe, 12.019% Si, and 6.315% Ca. Alkali fusion treatment is performed immediately inside the furnace (Na₂CO₃ is added to the furnace 20 minutes before slag discharge, furnace temperature 1250°C). During this process, CaWO₄ in the slag is converted to Na₂WO₄, with a CaWO₄ conversion rate of approximately 88%.

[0030] The slag containing Na₂WO₄ (alkali molten slag) was discharged from the slag discharge port into a water quenching tank for water quenching treatment. To inhibit the secondary scheelization of sodium tungstate during water quenching of the aforementioned Na₂WO₄-containing slag, Na₂CO₃ was added to the water quenching tank at a concentration of 5 g / L, and the pH of the quenching water was measured to be 10.1. The liquid-to-solid ratio of the quenching water to the alkali molten slag was 6:1. After the alkali molten slag fell into the water quenching tank, it was allowed to stand for 30 minutes, and a solution sample was taken for analysis. The water-soluble tungsten recovery rate was 74.8%, and the free Ca... 2+ At a concentration of 98 mg / L, the secondary scheelization rate was 12.8%. Compared with conventional neutral water quenching (recovery rate 62.3%, secondary scheelization rate 24.7%), under the lower limit of alkalinity at pH=10, the free Ca... 2+ The concentration decreased by 74.5%, the secondary scheelization rate decreased by 11.9 percentage points, and the tungsten water-soluble recovery rate increased by 12.5 percentage points. This example demonstrates that the lower limit of pH=10 has a significant inhibitory effect on secondary scheelization. Example 2

[0031] The same alkali slag as in Example 1. The pH of the water quenching water was adjusted to 11.5 with Na2CO3 (Na2CO3 concentration 18 g / L), and the liquid-to-solid ratio of the water quenching water to the alkali slag was 7:1. Immediately after water quenching, solid-liquid separation was performed using a vacuum filter, with the total time from water quenching contact to completion of separation controlled within 5 minutes. Solution samples were analyzed; the water-soluble tungsten recovery rate was 88.2%, and the free Ca... 2+With a concentration of 8 mg / L, the secondary scheelization rate was 1.6%. Compared to Example 1 with pH=10.1 and a standing time of 30 min, this example, through the synergistic effect of increasing pH and shortening contact time, further reduced the secondary scheelization rate from 12.8% to 1.6%, increasing the recovery rate by 13.4 percentage points. This scheme takes into account the effects of an alkaline environment on Ca. 2+ The inhibition and short-term contact limit the reaction time, the inhibitory effect is superimposed, and no complexing agent needs to be added, which is low cost and makes it the preferred solution for industrial applications. Example 3

[0032] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.8 with Na₂CO₃ (Na₂CO₃ concentration 22 g / L), and EDTA (concentration 2.5 g / L) was added simultaneously. The liquid-to-solid ratio of water quenching water to alkali slag was 6:1. Centrifugation was performed immediately after water quenching for 2.5 min. Solution samples were analyzed; the water-soluble tungsten recovery rate was 91.3%, and free Ca... 2+ Concentration <1 mg / L, secondary scheelization rate <0.5%. EDTA effectively chelates residual Ca. 2+ Free Ca 2+ When the concentration drops below the detection limit, secondary scheelization is almost completely suppressed. This method is applicable to Ca... 2+ In situations where the leaching amount is particularly large or the tungsten recovery rate is required to be extremely high. Example 4

[0033] The same alkali slag as in Example 1. The pH of the water quenching water was adjusted to 12.0 with NaOH (NaOH concentration 3.5 g / L), and the liquid-to-solid ratio of the water quenching water to the alkali slag was 8:1. Solid-liquid separation was completed using a filter press within 3 minutes after water quenching. Solution samples were taken for analysis. The water-soluble tungsten recovered from the solid-liquid separation had a recovery rate of 89.0%, and free Ca... 2+ With a concentration of 4 mg / L, the secondary scheelization rate is 1.7%. NaOH is highly alkaline and requires only a small dosage; 3.5 g / L is sufficient to adjust the pH to 12.0, making it suitable for applications requiring high pH but with large water volumes. Companies can flexibly choose the alkaline raw material for pH adjustment based on reagent costs and ease of procurement. Example 5

[0034] The same alkali slag as in Example 1. The pH of the water quenching water was adjusted to 12.5 with Na2CO3 (Na2CO3 concentration 30 g / L). The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed using a vacuum filter within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 90.6%, and the free Ca... 2+ The concentration was 2.3 mg / L, and the secondary scheelization rate was 1.1%. The Na₂CO₃ concentration was 30 g / L. The high concentration of Na₂CO₃ provided a strongly alkaline environment (pH 12.5) and sufficient CO₃²⁻. 2- Ca 2+It almost completely precipitates in the form of CaCO3, with free Ca... 2+ The concentration was reduced to extremely low levels, resulting in excellent inhibition. Compared to Example 2 (Na2CO3 18 g / L, recovery rate 88.2%), further increasing the Na2CO3 concentration to the upper limit increased the recovery rate by another 2.4 percentage points, but the alkali consumption increased significantly. This method is suitable for applications requiring extremely high tungsten recovery rates or those with high Ca content. 2+ In cases where the dissolution rate is particularly high. Example 6

[0035] The same alkali slag as in Example 1. The pH of the water quenching water was adjusted to 10.5 with NaOH (NaOH concentration 1 g / L). The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1, and solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 82.8%, and the free Ca... 2+ The concentration was 42 mg / L, and the secondary scheelization rate was 6.5%. A NaOH concentration of 1 g / L allowed the pH to be adjusted to 10.5, reaching the effective lower limit of alkaline inhibition (pH ≥ 10). Compared to Example 4 (NaOH 3.5 g / L, pH 12.0, recovery rate 89.0%), the inhibitory effect of the lower limit NaOH concentration was somewhat weakened, but compared to Comparative Example 1 (neutral water quenching, recovery rate 61.8%), the recovery rate was still increased by 21 percentage points, verifying the effectiveness of the lower limit NaOH concentration. This example is suitable for operating conditions where alkali consumption control is sensitive and recovery rate requirements are moderate. Example 7

[0036] The same alkali slag as in Example 1. The pH of the water quenching water was adjusted to 12.8 with NaOH (NaOH concentration 10 g / L). The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1, and solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 90.8%, and the free Ca... 2+ The concentration was 1.8 mg / L, and the secondary scheelization rate was 0.9%. The NaOH concentration was 10 g / L, the pH was as high as 12.8, and the Ca... 2+ Sufficient precipitation in the form of Ca(OH)2 resulted in an inhibition effect comparable to that of Example 5 (Na2CO3 30 g / L). NaOH is highly alkaline and requires only a small amount; 10 g / L is sufficient to achieve an extremely high pH, ​​making it suitable for applications requiring the rapid establishment of a strongly alkaline environment. This example and Example 6 respectively verified the lower and upper limits of NaOH concentration, demonstrating that a concentration range of 1–10 g / L can effectively inhibit secondary scheelization. Example 8

[0037] The same alkali slag as in Example 1. The pH of the water used for quenching was adjusted to 11.5 with Na2CO3 (Na2CO3 concentration 18 g / L). The liquid-to-solid ratio of the water to the alkali slag was controlled at 5:1, and solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 85.5%, and the free Ca...2+ At a concentration of 16 mg / L, the secondary scheelization rate was 5.3%. Compared to Example 2 (liquid-to-solid ratio 7:1, recovery rate 88.2%), the recovery rate decreased by 2.7 percentage points, while the secondary scheelization rate increased by 3.7 percentage points. The low liquid-to-solid ratio resulted in lower WO4 concentration in the aqueous solution. 2- and Ca 2+ As the concentration increases, the reverse reaction rate also increases. However, with the aid of an alkaline environment at pH 11.5 and rapid separation, the secondary scheelization rate can still be controlled below 6%. This example verifies the effectiveness of a liquid-to-solid ratio of 5:1. Compared with Comparative Example 4 (liquid-to-solid ratio 3:1, recovery rate 77.5%), it further demonstrates that a liquid-to-solid ratio ≥5:1 is a necessary condition to ensure the inhibition effect. Example 9

[0038] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.5 with Na₂CO₃ (Na₂CO₃ concentration 18 g / L), and sodium citrate 0.3 g / L was added simultaneously. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 87.3%, and free Ca... 2+ At a concentration of 13 mg / L, the secondary scheelization rate was 3.5%. Under the same conditions as without a complexing agent (recovery rate 85.8%, free Ca...),... 2+ Compared to sodium citrate (at a concentration of 20 mg / L, with a secondary scheelization rate of 4.1%), sodium citrate (at 0.3 g / L) already showed a preliminary chelation effect, reducing free Ca2+. 2+ A 35% reduction in concentration resulted in a 0.6 percentage point decrease in secondary scheelization rate. Sodium citrate is a food-grade safe reagent, environmentally friendly, and produces an auxiliary inhibitory effect even at low concentrations. Example 10

[0039] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.5 with Na₂CO₃ (Na₂CO₃ concentration 18 g / L), and sodium citrate 0.5 g / L was added simultaneously. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 88.2%, and free Ca... 2+ At a concentration of 9 mg / L, the secondary scheelization rate was 2.7%. Compared to Example 9 (sodium citrate 0.3 g / L), the free Ca2+ concentration increased to 0.5 g / L. 2+ The concentration was further reduced by 31%, and the secondary scheelization rate decreased by 0.8 percentage points. Sodium citrate at a low concentration range of 0.3–0.5 g / L can produce a considerable auxiliary inhibition effect, and it is low in cost, making it suitable as a supplementary method to alkaline water quenching. Example 11

[0040] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.5 with Na₂CO₃ (Na₂CO₃ concentration 18 g / L), and sodium tartrate 0.3 g / L was added simultaneously. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 86.9%, and the free Ca... 2+ At a concentration of 15 mg / L, the secondary scheelization rate was 3.8%. Sodium tartrate at 0.3 g / L also exhibited preliminary chelation of Ca. 2+ The effect, compared with no complexing agent added, is that free Ca 2+ A 25% reduction in concentration resulted in a 0.3 percentage point decrease in secondary scheelization rate. Sodium tartrate and sodium citrate are both food-grade safe reagents. Sodium tartrate has a slightly lower chelating ability than sodium citrate, but it has a wider range of applications, allowing companies to choose flexibly based on the convenience of reagent procurement. Example 12

[0041] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.5 with Na₂CO₃ (Na₂CO₃ concentration 18 g / L), and sodium tartrate 0.5 g / L was added simultaneously. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 87.8%, and the free Ca... 2+ At a concentration of 11 mg / L, the secondary scheelization rate was 3.1%. Compared to Example 11 (sodium tartrate 0.3 g / L), the free Ca2+ concentration increased to 0.5 g / L. 2+ The concentration decreased by 27%, the secondary scheelization rate decreased by 0.7 percentage points, and the inhibition effect gradually increased. Example 13

[0042] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.5 with Na₂CO₃ (Na₂CO₃ concentration 18 g / L), and 0.3 g / L of EDTA was added simultaneously. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 87.8%, and the free Ca... 2+ At a concentration of 11 mg / L, the secondary scheelization rate was 3.2%. EDTA and Ca... 2+ With a stability constant lgK = 10.7, it exhibits strong chelating ability, and even at a low concentration of 0.3 g / L, it begins to show superior chelating effects compared to sodium citrate and sodium tartrate at the same concentration. In comparison, Control Example 5 (EDTA 0.2 g / L, recovery rate 86.1%, secondary scheelization rate 3.8%) showed that increasing the EDTA concentration from 0.2 g / L to 0.3 g / L improved the recovery rate by 1.7 percentage points, verifying that 0.3 g / L is the starting concentration for effective chelation by EDTA. Example 14

[0043] The same alkali slag as in Example 1 was used. The pH of the water quenching water was adjusted to 11.5 with Na₂CO₃ (Na₂CO₃ concentration 18 g / L), and 0.5 g / L of EDTA was added simultaneously. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. Solid-liquid separation was completed within 3 minutes after water quenching. Solution samples were analyzed; the water-soluble tungsten recovery rate was 88.8%, and the free Ca... 2+ At a concentration of 7 mg / L, the secondary scheelization rate was 2.2%. Compared to Example 13 (EDTA 0.3 g / L), the free Ca content increased to 0.5 g / L. 2+ The concentration was reduced by 36%, and the secondary scheelization rate decreased by 1.0 percentage point. Compared with Example 3 (EDTA 2.5 g / L, recovery rate 91.3%, secondary scheelization rate <0.5%), the inhibitory effect of 0.5 g / L EDTA, although not as good as the high concentration, is significantly better than the case without adding a complexing agent, and the reagent cost is greatly reduced, making it suitable for industrial scenarios that are cost-sensitive and have moderate recovery requirements.

[0044] Comparative Example 1

[0045] The alkali slag was the same as in Example 1. The quenching water was fresh industrial water with a pH of 7.3, and no alkaline substances or complexing agents were added. The liquid-to-solid ratio of the quenching water to the alkali slag was 6:1. After quenching, the slag-water mixture was allowed to settle in a slag tank for 30 minutes, and then the supernatant was taken for analysis. Solution samples were analyzed, and the tungsten water-soluble recovery rate was 61.8%, with free Ca... 2+ Concentration 392 mg / L, secondary scheelization rate 25.6%. Large amount of free Ca. 2+ With WO4 2- During prolonged contact and full reaction, more than a quarter of the dissolved tungsten reprecipitated as CaWO4. This comparative example demonstrates that, without any inhibitory measures, secondary scheelization severely restricts tungsten recovery efficiency.

[0046] Comparative Example 2

[0047] The same alkali slag as in Example 1 was used. The water quenching water was adjusted with a small amount of Na₂CO₃, with the pH adjusted only to 8.5. The liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1, and the mixture was allowed to stand for 30 minutes. Solution samples were analyzed; the water-soluble tungsten recovery rate was 66.5%, and the free Ca... 2+ At a concentration of 278 mg / L, the secondary scheelization rate was 20.2%. Compared to Comparative Example 1 (pH 7.3), pH 8.5 showed only a slight improvement, with free Ca... 2+ The concentration remained as high as 278 mg / L, and the secondary scheelization rate still exceeded 20%. This comparative example demonstrates that weakly alkaline conditions are insufficient for the effective precipitation of Ca. 2+ The pH must be raised to ≥10 to significantly reduce free Ca. 2+ concentration.

[0048] Comparative Example 3

[0049] The same alkali slag as in Example 1. The pH of the water quenching water was adjusted to 11.5 with Na2CO3, and the liquid-to-solid ratio of the water quenching water to the alkali slag was 6:1. After water quenching, rapid solid-liquid separation was not performed. Instead, the slag-water mixture was continuously stirred and contacted in a stirred tank for 60 minutes before separation, to simulate long-term contact conditions caused by equipment failure or operational delays in industrial production. Solution samples were analyzed, and the water-soluble tungsten recovery rate was 72.3%, with free Ca... 2+ At a concentration of 45 mg / L, the secondary scheelization rate was 14.2%. Although alkaline conditions at pH 11.5 effectively reduced free Ca... 2+ However, prolonged contact (60 min) still caused the reverse reaction to continue to accumulate, increasing the secondary scheelization rate from 1.6% at 3 min to 14.2%, and reducing the recovery rate by 15.9 percentage points. This comparative example verifies the necessity of shortening the contact time between water-quenched water and alkali slag and accelerating solid-liquid separation.

[0050] Comparative Example 4

[0051] The same alkali slag as in Example 1 was used. The pH of the water used for quenching was adjusted to 11.5 with Na₂CO₃, but the liquid-to-solid ratio was only 3:1. Solid-liquid separation was completed within 3 minutes after water quenching. Analysis of the solution sample showed a tungsten water-soluble recovery rate of 77.5%, and free Ca... 2+ At a concentration of 35 mg / L, the secondary scheelization rate was 10.6%. The low liquid-to-solid ratio resulted in high WO4 concentrations in the aqueous solution. 2- and Ca 2+ The concentrations were all concentrated, increasing the reverse reaction rate. Compared to Example 2 with the same pH, contact time, and liquid-to-solid ratio of 7:1, the recovery rate decreased by 10.7 percentage points. This comparative example demonstrates that even with controlled pH and contact time, an excessively low liquid-to-solid ratio can still exacerbate secondary scheelization due to the concentration effect.

[0052] Comparative Example 5

[0053] The same alkali slag as in Example 1 was used. The pH of the quenching water was adjusted to 11.5 with Na₂CO₃, and the liquid-to-solid ratio of the quenching water to the alkali slag was 6:1. Disodium EDTA was added, but at a concentration of only 0.2 g / L. Solid-liquid separation was completed within 3 minutes after water quenching. Analysis of the solution sample showed a tungsten water-soluble recovery rate of 86.1% and a free Ca content of [missing information]. 2+ At a concentration of 22 mg / L, the secondary scheelization rate was 3.8%. Compared to the same conditions without EDTA (recovery rate 85.8%, secondary scheelization rate 4.1%), 0.2 g / L EDTA produced almost no additional inhibitory effect. 2+ The chelation amount is extremely limited. This contrasts with the 91.3% recovery rate achieved in Example 3 with EDTA at 2.5 g / L.

[0054] Unless otherwise stated, all percentages mentioned in this invention are mass percentages.

[0055] The method of this invention can effectively improve the water-soluble tungsten recovery rate and reduce the secondary scheelization rate during water quenching. This method is simple to operate, can be seamlessly integrated with the main production process, and significantly improves the tungsten recovery efficiency in the alkali slag after alkali melting of slag from tin smelting furnaces.

Claims

1. A method for suppressing secondary scheelization of sodium tungstate in alkaline melt-quenched slag of tin smelting furnace slag, wherein the alkaline melt-quenched slag is slag material obtained by alkaline melting treatment followed by water quenching of tin smelting furnace slag, characterized in that, The method involves adding alkali to the water during the water quenching process after the slag from the tin smelting furnace has undergone alkali melting treatment. The pH of the quenching water is controlled to be 10-12 to inhibit calcium buildup. 2+ The dissolution of Ca reduces the thermodynamic driving force of the reverse reaction; under alkaline conditions, Ca... 2+ The formation of Ca(OH)2 or CaCO3 precipitate reduces the free Ca content. 2+ Concentration, inhibiting the reaction of Na2WO4 and Ca 2+ The reverse reaction.

2. The method for suppressing secondary scheelization of sodium tungstate in alkaline melt water-quenched slag of tin smelting furnace slag according to claim 1, characterized in that, The alkali added to the water quenching water is either Na2CO3 or NaOH; when Na2CO3 is added to adjust the pH, the concentration of Na2CO3 in the water quenching water is 5~30 g / L; when NaOH is added to adjust the pH, the concentration of NaOH in the water quenching water is 1~10 g / L.

3. The method for suppressing secondary scheelization of sodium tungstate in alkaline melt water-quenched slag of tin smelting furnace slag according to claim 1, characterized in that, During the slag water quenching process, the liquid-solid ratio of quenching water to slag should be controlled to be ≥5:

1.

4. The method for suppressing secondary scheelization of sodium tungstate in alkaline melt water-quenched slag of tin smelting furnace slag according to claim 1, 2, or 3, characterized in that, Immediately after water quenching, solid-liquid separation is performed to separate the tungsten-containing aqueous solution from the calcium-containing slag, and the contact time between the tungsten-containing aqueous solution and the calcium-containing slag generated during the water quenching process is controlled to be ≤5min.

5. The method for suppressing secondary scheelization of sodium tungstate in alkaline melt water-quenched slag of tin smelting furnace slag according to claim 4, characterized in that, Adding a complexing agent to the water after solid-liquid separation to chelate Ca 2+ Reduce free Ca 2+ concentration.

6. The method for suppressing secondary scheelization of sodium tungstate in alkaline melt water-quenched slag of tin smelting furnace slag according to claim 1, characterized in that, Adding a complexing agent to water quenching water to chelate Ca 2+ Reduce free Ca 2+ concentration.

7. The method for suppressing secondary scheelization of sodium tungstate in alkaline melt water-quenched slag of tin smelting furnace slag according to claim 5 or 6, characterized in that, The complexing agent is selected from one or more of EDTA, sodium citrate, and sodium tartrate, and the amount of EDTA added is 2-8 g / L.