Separation and recovery method for trace silver in sintering ash

Abstract

The invention provides a method for separating and recovering trace silver in sintered ash, which comprises the following steps: obtaining a mixed solution containing sintered ash, a sodium thiosulfate solution and a cuprous reagent, sequentially carrying out heating leaching and solid-liquid separation on the mixed solution, and collecting a liquid phase to obtain a silver-containing leaching solution; wherein the molar concentration of the cuprous reagent in the mixed solution is 0.003 mol / L to 0.005 mol / L or is not lower than 0.04 mol / L; mixing the leaching solution with a first precipitant, carrying out first precipitation reaction and solid-liquid separation, and collecting a liquid phase to obtain a silver-containing purified solution; and mixing the silver-containing purified liquid with a second precipitant, carrying out a second precipitation reaction, carrying out solid-liquid separation, and collecting a solid phase to obtain silver sulfide. The method is easy and convenient to operate and environmentally friendly, the silver recovery efficiency is remarkably improved, a new technical approach is provided for recovering silver from industrial waste, and the method has important significance on sustainable utilization of resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste recycling, and particularly relates to a method for separating and recovering trace silver in sintering ash. Background Art

[0002] Silver, with its unique physical and chemical properties such as excellent corrosion resistance, high electrical conductivity, and catalytic activity, is widely used in fields such as electronics and industrial catalysis. However, the scarcity of global silver resources poses a huge challenge to the supply chain. According to the statistics of the World Silver Association, the total global silver demand in 2023 reached 35,551 tons, while the supply was only 31,100 tons, resulting in a supply-demand gap of approximately 4,400 tons. It is expected that by 2024, although the production of mined silver is expected to recover and drive a 2%-3% increase in supply, reaching 31,700 tons, the supply-demand gap will still widen to around 5,000 tons. Therefore, the recycling of waste silver has become increasingly important, especially the recovery of silver resources from industrial waste, which will play a key role in future silver supply.

[0003] In the process of iron and steel metallurgy, silver enters the smelting process with iron ore and finally concentrates in sintering ash. Although the silver content in sintering ash is only about 100 g / t, considering the huge global crude steel production, which reached 1.83 billion tons in 2022, and the production of sintering ash accounts for 1.5%-2.0% of the total crude steel production, it means that the amount of silver that can be recovered from sintering ash is quite considerable. Therefore, the recovery of silver resources from sintering ash has important economic and environmental value. Currently, hydrometallurgy is the most commonly used technology for extracting and recovering silver from silver-based waste, and among them, the chloride leaching method has become the mainstream method due to its low toxicity and cost. This method dissolves silver with a chloride solution and recovers it through precipitation or electrowinning processes. Although the chloride leaching method has certain advantages, it still requires high temperature and strong acidic conditions, which greatly increases the operation difficulty and environmental burden.

[0004] Based on this, it is necessary to provide a method for separating and recovering trace silver in sintering ash to alleviate or solve the above problems. Summary of the Invention

[0005] Aiming at solving the technical problems of harsh process conditions, complicated steps, and environmental unfriendliness in the above-mentioned common technologies, the present invention provides a method for separating and recovering trace silver in sintering ash, including the steps:

[0006] Obtain a mixed solution containing sintering ash, sodium thiosulfate solution, and cuprous reagent. After the mixed solution is heated and leached and then solid-liquid separated in sequence, collect the liquid phase to obtain a silver-containing leaching solution; wherein, the molar concentration of the cuprous reagent in the mixed solution is 0.003-0.005 mol / L or not less than 0.04 mol / L;

[0007] The silver-containing leaching solution is mixed with a first precipitating agent, and through a first precipitation reaction, solid-liquid separation is carried out, and the liquid phase is collected to obtain a silver-containing purified solution;

[0008] The silver-containing purified solution is mixed with a second precipitating agent, and through a second precipitation reaction, solid-liquid separation is carried out, and silver sulfide is collected as the solid phase.

[0009] Furthermore, the separation and recovery method further includes, before the step of obtaining a mixed solution containing sintered ash, sodium thiosulfate solution and cuprous reagent, performing a water washing treatment on the sintered ash. In the water washing treatment, the solid-liquid ratio of the sintered ash to the solvent is 1:3.5 - 4.5 g / mL, the duration of the water washing treatment is not less than 40 min, and the solvent includes water.

[0010] Furthermore, a dispersant is added externally during the water washing treatment. The types of the dispersant include sodium dodecylbenzenesulfonate, and the addition amount of the dispersant is 0.08 g - 0.1 g / 100 g of sintered ash.

[0011] Furthermore, the concentration of the sodium thiosulfate solution is 40 - 50 g / L, and the liquid-solid ratio of the sodium thiosulfate solution to the sintered ash is 6 - 10 ml / g.

[0012] Furthermore, the temperature of the heating leaching is 55 - 65 °C, and the duration of the heating leaching is not less than 120 min.

[0013] Furthermore, the first precipitating agent includes a hydrogen peroxide solution, the concentration of the first precipitating agent is 20 - 40%, the second precipitating agent includes a hydrogen peroxide solution, and the concentration of the second precipitating agent is 20 - 40%.

[0014] Furthermore, the volume ratio of the first precipitating agent to the silver-containing leaching solution is 1.25 - 1.6 ml / 100 ml, the duration of the first precipitation reaction is 0.4 - 1.5 min, and the temperature of the first precipitation reaction is 20 - 40 °C.

[0015] Furthermore, the volume ratio of the second precipitating agent to the silver-containing purified solution is not less than 1.2 ml / 100 ml, the duration of the second precipitation reaction is not less than 30 min, and the temperature of the second precipitation reaction is 20 - 40 °C.

[0016] Furthermore, the solid-phase product obtained by solid-liquid separation in the first precipitation reaction includes lead sulfate, and an insoluble intermediate product of a metal ion-peroxo structure-ligand ternary complex formed by the combination of superoxide radicals and cuprous thiosulfate.

[0017] Further, in terms of mass fraction, the elemental composition of the sintering ash includes: K 15% - 20%, Na 2% - 3%, Fe 10% - 20%, Pb 1% - 2%, Cu 0.1% - 0.5%, Ag 100 g / t - 200 g / t;

[0018] The elemental composition of the product after the water washing treatment includes: K 0% - 3%, Na 0% - 1%, Fe 50% - 80%, Pb 5% - 10%, Cu 1% - 2%, Ag 400 g / t - 600 g / t.

[0019] Compared with the prior art, the present invention has at least the following advantages:

[0020] The present invention uses the sintering ash produced by a certain iron and steel plant as the raw material, and researches and develops a process for separating and recovering trace silver in the sintering ash, including steps such as complex leaching by the Na2S2O3 - CuCl method, purification by hydrogen peroxide solution, and precipitation conversion. This process is simple to operate, environmentally friendly, and also significantly improves the silver recovery efficiency, providing a new technical approach for recovering silver from industrial waste, and is of great significance for realizing the sustainable utilization of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0022] Figure 1 It is the X-ray diffraction pattern of the sintering ash before and after the water washing treatment in Analysis Example 1 of the present invention;

[0023] Figure 2 It is the physical diagram of the sintering ash before and after the water washing treatment and the sieved water-washed ash in Analysis Example 2 of the present invention, where Figure 2 (a) is the physical diagram of the sintering ash before the water washing, Figure 2 (b) is the physical diagram of the sintering ash after the water washing, Figure 2 (c) is the physical diagram of the sieved water-washed ash;

[0024] Figure 3 It is the particle size distribution diagram of the sieved water-washed ash in Analysis Example 2 of the present invention;

[0025] Figure 4 It is the schematic diagram of the influence of various factors on the KCl removal rate in the sintering ash in Analysis Example 3 of the present invention, where Figure 4 (a) is the schematic diagram of the influence of the solid-liquid ratio on the KCl removal rate in the sintering ash, Figure 4(b) Schematic diagram of the effect of temperature on the removal rate of KCl in sintered ash; Figure 4 (c) Schematic diagram of the effect of time on the removal rate of KCl in sintered ash; Figure 4 (d) Schematic diagram of the effect of stirring speed on the removal rate of KCl in sintered ash.

[0026] Figure 5 Schematic diagram of the effect of liquid-solid ratio (L / S) on the leaching efficiency of various metal elements in sintered ash in Analysis Example 4 of the present invention.

[0027] Figure 6 Schematic diagram of the effect of the concentration of sodium thiosulfate solution on the leaching efficiency of several metal elements in sintered ash in Analysis Example 5 of the present invention;

[0028] Figure 7 Schematic diagram of the effect of the dosage of cuprous chloride on the leaching efficiency of several metal elements in sintered ash in Analysis Example 6 of the present invention.

[0029] Figure 8 Schematic diagram of the effect of leaching temperature on the leaching efficiency of several metal elements in sintered ash in Analysis Example 7 of the present invention.

[0030] Figure 9 Schematic diagram of the effect of leaching time on the leaching efficiency of several metal elements in sintered ash in Analysis Example 8 of the present invention.

[0031] Figure 10 Schematic diagram of the effect of different recovery agents on the separation effect in Analysis Example 9 of the present invention.

[0032] Figure 11 Schematic diagram of the effect of the dosage of the first precipitant on the conversion rate in Analysis Example 10 of the present invention.

[0033] Figure 12 Schematic diagram of the effect of the reaction duration of the first precipitation on the conversion rate in Analysis Example 11 of the present invention.

[0034] Figure 13 Schematic diagram of the effect of the dosage of the second precipitant on the silver precipitation effect in Analysis Example 12 of the present invention.

[0035] Figure 14 Schematic diagram of the effect of the reaction duration of the second precipitant on the silver precipitation effect in Analysis Example 13 of the present invention.

[0036] Figure 15 XRD pattern of the separated and recovered product in Analysis Example 14 of the present invention.

[0037] Figure 16 Schematic diagram of the effect of different temperatures on the silver leaching rate in Analysis Example 15 of the present invention.

[0038] Figure 17Fitting results of different diffusion rate equations in Analysis Example 15 of the present invention, where Figure 17 (a) is the rate equation of chemical reaction and external diffusion; Figure 17 (b) is the rate equation of internal diffusion.

[0039] Figure 18 (a) is the Arrhenius equation fitted for chemical reaction and external diffusion control in Analysis Example 15 of the present invention Figure 18 (b) is the Arrhenius equation fitted for internal diffusion control in Analysis Example 15 of the present invention.

[0040] Figure 19 (a) is the infrared spectrum of the reaction product of the silver-containing leaching solution and hydrogen peroxide solution in Analysis Example 16 of the present invention; Figure 19 (b) is the infrared spectrum of the reaction product of copper thiosulfate and hydrogen peroxide solution in Analysis Example 16 of the present invention; Figure 19 (c) is the infrared spectrum of the reaction product of lead thiosulfate and hydrogen peroxide solution in Analysis Example 16 of the present invention. Detailed implementation manners

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0043] When the embodiments give a numerical range, it should be understood that unless otherwise specified in the present invention, any value at both ends of each numerical range and any value between the two ends can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention, based on the understanding of those of ordinary skill in the art of the prior art and the description of the present invention, can also use any methods, devices, and materials of the prior art similar to or equivalent to those in the embodiments of the present invention to implement the present invention.

[0044] In common technologies, the thiosulfate method, as a green alternative technology, has been widely studied. It has achieved remarkable results especially in the field of gold recovery and has gradually been applied to silver recovery. This method uses divalent copper as a catalyst and ammonia as a complexing agent, enabling thiosulfate to form stable complexes with gold and silver. However, the use of ammonia may produce irritating odors and pollute the environment. At the same time, the complex reaction system also increases the process difficulty.

[0045] To solve these problems, this paper proposes a new process based on the Na2S2O3-CuCl system for recovering silver from steel metallurgy sintering ash. This process does not require the addition of ammonia, avoiding environmental pollution caused by ammonia, and optimizes the silver leaching process by gradually adding hydrogen peroxide solution, effectively removing impurity ions such as copper and lead. This paper systematically investigated the effects of different single factors (such as temperature, thiosulfate concentration, reaction time, etc.) on the leaching process. Finally, by optimizing the process conditions, high-purity silver sulfide products were obtained. This new process is not only simple to operate and environmentally friendly, but also significantly improves the silver recovery efficiency, providing a new technical approach for recovering silver from industrial waste and having important significance for realizing the sustainable utilization of resources.

[0046] The present invention provides a method for separating and recovering trace silver in sintering ash, including the steps:

[0047] S1. Obtain a mixed solution containing sintering ash, sodium thiosulfate solution, and cuprous reagent. After the mixed solution is heated and leached and then solid-liquid separated in sequence, collect the liquid phase to obtain a silver-containing leaching solution; wherein, the molar concentration of the cuprous reagent in the mixed solution is 0.003 - 0.005 mol / L or not less than 0.04 mol / L.

[0048] In the present invention, the step of mixing the sintering ash, sodium thiosulfate solution, and cuprous reagent to obtain a mixed solution further includes washing the sintering ash. In the washing treatment, the solid-liquid ratio of the sintering ash to the solvent is 1:3.5 - 4.5 g / mL, the duration of the washing treatment is not less than 40 min, and the solvent includes water.

[0049] In some embodiments, a dispersant can be added externally during the washing treatment. The types of the dispersant include sodium dodecylbenzenesulfonate, and the addition amount of the dispersant can be 0.08 g - 0.1 g / 100 g of sintering ash.

[0050] In the present invention, the concentration of the sodium thiosulfate solution is 40 - 50 g / L, and the liquid-solid ratio of the sodium thiosulfate solution to the sintering ash is 6 - 10 ml / g.

[0051] In the present invention, the cuprous reagent can be cuprous chloride.

[0052] In the present invention, the temperature of the heating extraction can be 55 to 65 °C, and the duration of the heating extraction is not less than 120 min. In some more specific embodiments of the present invention, the duration of the heating extraction can be 120 to 150 min.

[0053] In the present invention, by mass fraction, the elemental composition of the sintered ash includes: K 15% to 20%, Na 2% to 3%, Fe 10% to 20%, Pb 1% to 2%, Cu 0.1% to 0.5%, Ag 100 g / t to 200 g / t;

[0054] The elemental composition of the product of the water washing treatment includes: K 0% to 3%, Na 0% to 1%, Fe 50% to 80%, Pb 5% to 10%, Cu 1% to 2%, Ag 400 g / t to 600 g / t. In some more specific embodiments, the elemental composition of the product of the water washing treatment includes: K 1% to 3%, Na 0.5 to 1%, Fe 50% to 80%, Pb 5% to 10%, Cu 1% to 2%, Ag 400 g / t to 600 g / t

[0055] S2. The leaching solution is mixed with a first precipitating agent, and through a first precipitation reaction, solid-liquid separation is carried out, and the liquid phase is collected to obtain a silver-containing purified solution.

[0056] In the present invention, the first precipitating agent includes a hydrogen peroxide solution, the concentration of the first precipitating agent is 20 to 40%, the second precipitating agent includes a hydrogen peroxide solution, and the concentration of the second precipitating agent is 20 to 40%.

[0057] In the present invention, the addition amount of the first precipitating agent can be 1.25 to 1.6 ml / 100 ml of the leaching solution, the duration of the first precipitation reaction is 0.4 to 1.5 min, and the temperature of the first precipitation reaction is 20 to 40 °C; in some more specific embodiments, the duration of the first precipitation reaction can be 0.4 to 1 min.

[0058] In the present invention, the solid-phase product obtained by solid-liquid separation through the first precipitation reaction includes lead sulfate and an insoluble intermediate product of a ternary complex of a metal ion-peroxyl structure-ligand formed by the combination of superoxide radicals and copper thiosulfate.

[0059] S3. The silver-containing purified solution is mixed with a second precipitating agent, and through a second precipitation reaction, solid-liquid separation is carried out, and the solid phase is collected to obtain silver sulfide.

[0060] In the present invention, the addition amount of the second precipitating agent is not less than 1.2 ml / 100 ml of the silver-containing purification liquid, the duration of the second precipitation reaction is not less than 30 min, and the temperature of the second precipitation reaction is 20 - 40 °C; in some more specific embodiments, the addition amount of the second precipitating agent can be 1.2 - 5 ml / 100 ml of the silver-containing purification liquid, and the duration of the second precipitation reaction can be 30 - 100 min.

[0061] For the convenience of those skilled in the art to further understand the present invention, the following is an example for illustration:

[0062] The present invention conducts phase analysis, elemental analysis, particle size analysis, and structural analysis on the sintering ash raw material and the products of each step. Specifically:

[0063] (1) Phase analysis. The D / max2550 type X-ray diffractometer prepared by Rigaku Corporation of Japan is used to detect and analyze the phases of the experimental raw materials, namely, iron and steel metallurgical sintering ash, sintering ash after water washing, filter residue after leaching, intermediate product, and final product. The test conditions are as follows: rotating anode 18 kw, tube voltage 40 kV, tube current 300 mA, scanning angle range 5 - 90°, step size 0.02°, and scanning speed 14° / min. The XRD patterns are analyzed using Jade5.0 software.

[0064] (2) Elemental analysis. Accurately weigh 0.1000 g of sintering ash, completely cover it with 2 g of sodium hydroxide, calcine it in a nickel crucible at 700 °C for 2 h, then dissolve the solid in the crucible with 4 mol / L hydrochloric acid, and make the solution up to 100 ml after filtration. Dilute it by a certain multiple, and analyze the contents of the main valuable metal elements in the sintering ash using an atomic absorption spectrometer.

[0065] (3) Particle size analysis. Using anhydrous ethanol as the dispersion medium and nitrogen as the carrier, the Mastersizer2000 type laser particle size distribution analyzer is used to analyze the particle size of the sintering ash after water washing, drying, and sieving.

[0066] (4) Structural analysis. The Nicolet 6700 type Fourier transform infrared spectrometer is used to detect and analyze the structures of the experimental raw materials, namely, iron and steel metallurgical sintering ash, sintering ash after water washing, filter residue after leaching, intermediate product, and final product. The instrument test conditions: resolution 4 cm -1 , using the KBr tablet pressing method for sample preparation, scanning 4 times, and scanning range 4000 - 400 cm -1 .

[0067] Example 1 Sintering Ash Water Washing Treatment

[0068] Add 50.0 g of gas ash (dry basis, i.e., sintered ash) and 0.04 g of sodium dodecylbenzenesulfonate to 200 ml of deionized water, stir in a water bath at 45 °C with a stirrer at a speed of 400 r / min for 45 min, perform vacuum filtration, and rinse the filter cake with deionized water for 5 min after filtration to remove the residual soluble alkali metal compounds on the surface of the filter cake. Then dry the filter cake in an oven at 105 °C for 10 h, crush it and set aside to obtain washed ash.

[0069] Sieve the washed ash to obtain sieved washed ash.

[0070] Example 2 Washing treatment of sintered ash

[0071] Add 50.0 g of gas ash (dry basis, i.e., sintered ash) and 0.04 g of sodium dodecylbenzenesulfonate to 200 ml of deionized water, stir in a water bath at room temperature with a stirrer at a speed of 400 r / min for 40 min, perform vacuum filtration, and rinse the filter cake with deionized water for 5 min after filtration to remove the residual soluble alkali metal compounds on the surface of the filter cake. Then dry the filter cake in an oven at 105 °C for 10 h, crush it and set aside to obtain washed ash. In this example, the removal rates of KCl and NaCl in the sintered ash are 93.97% and 85.92% respectively.

[0072] Analysis example 1 Composition of sintered ash and washed ash

[0073] Use a polarized Zeeman atomic spectrophotometer to measure the main metal elements before and after the washing treatment of the sintered ash in Example 1, and the contents of several main metal elements are shown in Table 1.

[0074] Table 1 Contents of main metal elements before and after washing treatment of sintered ash (%)

[0075]

[0076] The data in Table 1 show that the contents of Fe and K elements in the sintered ash are high, and at the same time, it also contains a small amount of Na, Pb elements and trace amounts of Cu, Ag and other elements, which is consistent with the XRD analysis results.

[0077] Use an X-ray powder diffractometer (XRD) to characterize and analyze the main phases before and after the washing treatment of the sintered ash, and the results are as Figure 1 shown. From Figure 1 it can be seen that the diffraction peak with the largest intensity on the XRD pattern of the sintered ash raw material is the characteristic peak of KCl, and other characteristic peaks are not observed. It may be because the potassium element content in the sintered ash is high, and a large amount of X-rays are absorbed by the potassium element during the measurement, while other elements show weak absorption, resulting in the KCl peak intensity being too large to mask other characteristic peaks.

[0078] In the XRD pattern of the sintered ash after water washing treatment, the characteristic peak signals of KCl and NaCl are significantly weakened. This is because KCl and NaCl are highly soluble in water, and most of the KCl in the sintered ash has been removed after water washing. At the same time, the characteristic peaks of substances such as Fe2O3, PbO, CuO, and Ag2S appear in the pattern, indicating that the main other phases in the sintered ash are Fe2O3, PbO, CuO, and Ag2S.

[0079] Particle size analysis of the sintered ash and water-washed ash in Example 2

[0080] Figure 2 (a) and Figure 2 (b) are the sintered ash before and after water washing in Example 1, Figure 2 (c) is the sieved water-washed ash in Example 1.

[0081] The particle size analysis of the sieved water-washed ash in Example 1 is as follows Figure 3 shown. The detection is carried out with anhydrous ethanol as the dispersion medium and measured with a Mastersizer 2000 laser particle size analyzer. The characteristic parameters are shown in Table 2.

[0082] As Figure 3 shown, the particle size distribution range of the sieved water-washed ash is relatively concentrated, with more than 90% below 135 μm. The difference between the median diameter and the volume average particle size is relatively large, and the particle size distribution of the sample is asymmetric. The difference between the volume average particle size and the surface area average particle size is relatively large, indicating that the particle shape is irregular and the particle size distribution is not concentrated.

[0083] Table 2 Characteristic parameters of the sintered ash

[0084]

[0085] Generally, the specific surface area of the particles of the sieved sintered ash is large, the particle size is small, and it can be in full contact with the leaching solution, which is beneficial to the subsequent leaching recovery. Secondly, through water washing and sieving treatment, the distribution of each element in the sintered ash is more uniform, which is beneficial to the subsequent leaching effect.

[0086] Analysis of Example 3

[0087] Explore the effects of factors such as solid-liquid ratio, temperature, removal time, and stirring speed on the KCl removal rate in Example 2, and the results are as Figure 4 shown.

[0088] Separation and recovery method of trace silver in the sintered ash of Example 3

[0089] S1. Mix the sintered ash, sodium thiosulfate solution, and cuprous reagent after the water washing treatment in Example 1 to obtain a mixed solution. After heating extraction and solid-liquid separation of the mixed solution in sequence, collect the liquid phase to obtain a silver-containing extraction solution. Among them, the heating extraction temperature is 60 °C, the extraction time is 120 min, the molar concentration of cuprous chloride in the mixed solution is 0.005 mol / L, the concentration of the sodium thiosulfate solution is 45 g / L, and the liquid-solid ratio of the sodium thiosulfate solution to the sintered ash is 6 ml / g. The extraction rates of Ag, Cu, and Zn in the sintered ash are measured to be 83.1%, 8.77%, and 3.16% respectively.

[0090] S2. Take 100 ml of the extraction solution and mix it with 1.5 ml of 30% hydrogen peroxide solution. After the first precipitation reaction and solid-liquid separation, collect the liquid phase to obtain a silver-containing purification solution. Among them, the temperature of the first precipitation reaction is 30 °C, the stirring rate of the first precipitation reaction is 100 r / min, and the duration of the first precipitation reaction is 1 min. The lead conversion rate is measured to reach 100%, the copper conversion rate reaches 95%, and the silver loss rate is within 4%.

[0091] S3. Mix the silver-containing purification solution with 1.2 ml of 30% hydrogen peroxide solution. After the second precipitation reaction and solid-liquid separation, collect the solid phase to obtain silver sulfide. The stirring rate of the second precipitation reaction is 100 r / min, and the duration of the second precipitation reaction is 30 min. The conversion rate of silver in the silver-containing purification solution is 100%, and the copper conversion rate is within 5%. The purity of silver sulfide is measured to be about 97% by titration method, and the total silver recovery rate is 80.09%.

[0092] Analysis Example 4 explores the influence of the liquid-solid ratio on the leaching efficiency of metal elements.

[0093] In Example 3, with other conditions unchanged, adjust the liquid-solid ratio of the sodium thiosulfate solution to the sintered ash in step S1, and the results are as Figure 5 shown. It can be seen that the leaching efficiencies of Ag, Cu, and Zn all increase with the increase of the liquid-solid ratio. When the liquid-solid ratio increases from 2 mL / g to 7 mL / g, the leaching efficiency of Ag increases from 25.6% to 81.9%, while Cu and Zn increase from 1.12% and 0.76% to 8.94% and 3.09% respectively. After the liquid-solid ratio is increased to 6 mL / g, the leaching efficiency of Ag is basically stable, while the leaching rate of copper continues to increase slowly. Therefore, the optimal liquid-solid ratio for the experiment is selected as 6 mL / g.

[0094] Analysis Example 5 explores the influence of the concentration of sodium thiosulfate solution on the leaching efficiency of metal elements.

[0095] In Example 3, with other conditions unchanged, adjust the concentration of the sodium thiosulfate solution in step S1, and the results are as Figure 6As shown, it can be seen that the leaching efficiencies of Ag, Cu, and Zn all increase with the increase in the concentration of the sodium thiosulfate solution. With the increase in the amount of the sodium thiosulfate solution, the leaching efficiencies of Cu and Zn increase slowly, while the leaching efficiency of Ag increases rapidly. When the concentration of the sodium thiosulfate solution increases from 10 g / L to 45 g / L, the leaching efficiency increases from 17.3% to 81.4%. When the concentration of the sodium thiosulfate solution is further increased, the change in the leaching efficiency of Ag is not significant. Therefore, the concentration of the sodium thiosulfate solution is selected as 45 g / L.

[0096] Analysis Example 6 explores the influence of the amount of cuprous chloride on the leaching efficiency of metal elements

[0097] Under the condition that other conditions in Example 3 remain unchanged, the amount of cuprous chloride in step S1 is adjusted, and the results are as Figure 7 shown. It can be seen that when the amount of cuprous chloride is 0.005 mol / L, the leaching efficiency of Ag reaches 82.6%. With the increase in the amount of cuprous chloride, the leaching efficiency of silver remains basically stable; the leaching efficiency of Zn has always been very low, and the leaching efficiency of copper shows a trend of first increasing and then decreasing. This is because the added cuprous chloride leads to an increase in the concentration of copper in the leaching solution. Therefore, the amount of cuprous chloride is selected as 0.005 mol / L.

[0098] Analysis Example 7 explores the influence of the temperature of heating leaching on the leaching efficiency of metal elements

[0099] Under the condition that other conditions in Example 3 remain unchanged, the temperature of heating leaching in step S1 is adjusted, and the results are as Figure 8 shown. It can be seen that with the increase in the leaching temperature, the leaching efficiency of Ag first increases and then decreases, and reaches the maximum leaching efficiency of 83.1% at 60 °C. When the temperature is further increased, due to the large amount of Cu present, the thiosulfate ions in the solution are competed, resulting in a slight decrease in the leaching efficiency of Ag. The leaching temperature is selected as 60 °C.

[0100] Analysis Example 8 explores the influence of the time of heating leaching on the leaching efficiency of metal elements

[0101] Under the condition that other conditions in Example 3 remain unchanged, the time of heating leaching in step S1 is adjusted, and the results are as Figure 9 shown. It can be seen that the leaching efficiencies of Ag, Cu, and Zn all increase with the increase in the concentration of the sodium thiosulfate solution. The leaching efficiencies of Cu and Zn increase very little. When the leaching time of Ag is 15 min, the leaching rate reaches 50.1%. With the increase in the leaching time, the leaching efficiency of Ag gradually increases and reaches 82.5% at 120 min. This shows that extending the leaching time has a promoting effect on the leaching of both silver and copper. Because the longer the time, the more sufficient the contact between the complexing agent in the solution and the sintered ash. Therefore, the leaching time is selected as 120 min.

[0102] In summary, the optimal leaching conditions are as follows: the concentration of sodium thiosulfate solution is 45 g / L, the liquid-solid ratio is 6 mL / g, the leaching temperature is 60 °C, the dosage of cuprous chloride is 0.005 mol / L, and the leaching time is 120 min. Under these conditions, the leaching rates of Ag, Cu, and Zn are 83.1%, 8.77%, and 3.16% respectively.

[0103] Analysis Example 9 explores the influence of the type of the first precipitant on the leaching effect of metal elements.

[0104] The leaching solution obtained by leaching sintered ash with the thiosulfate-cuprous system contains Ag, Cu, and Zn. Since the content of silver ions in the solution is low, adjusting the pH and the displacement method cannot achieve the selective separation of impurity metals and will also cause a large loss of silver. In order to remove the impurity metals (Cu, Zn) and recover silver, this analysis example compares the separation and recovery effects of citric acid, oxalic acid, sodium hypophosphite, sodium dithionite, and hydrogen peroxide solution as separating agents.

[0105] In Example 3, other conditions remain unchanged, and the type of the first precipitant in step S2 is adjusted. The results are as Figure 10 shown. It can be seen that the conversion rates of copper and silver by citric acid, oxalic acid, sodium hypophosphite, hydrogen peroxide solution, etc. are all very low. The conversions of copper and silver by sodium dithionite are 77.35% and 64.23% respectively, with relatively high conversion rates but separation cannot be achieved. The conversion rate of silver by hydrogen peroxide solution reaches more than 99%, and the conversion rate of the impurity metal copper is only 6.74%, which can achieve the effect of preliminary separation. Therefore, hydrogen peroxide solution is selected as the precipitation conversion agent to selectively recover silver. Through experiments, it is found that when the reaction time is short and the concentration of hydrogen peroxide solution is low, copper and lead will react with hydrogen peroxide solution to form precipitates first, and the conversion rate of silver is very low. Therefore, it is decided to utilize this characteristic to add hydrogen peroxide solution step by step for the separation and recovery of silver.

[0106] Analysis Example 10 explores the influence of the dosage of the first precipitant on the leaching effect of metal elements.

[0107] In Example 3, other conditions remain unchanged, and the dosage of the first precipitant in step S2 is adjusted. The results are as Figure 11As shown in the figure, it can be seen that 100 mL of the leaching solution is taken at 30°C, the stirring speed is 300 rpm, the reaction time is 1 min, and 30% hydrogen peroxide solution is added. When the dosage of hydrogen peroxide solution is 0.3 mL, the conversion rate of lead reaches 100%, the conversion rate of copper is 40%, and the conversion rate of silver is only about 5%. As the dosage of hydrogen peroxide solution gradually increases, the conversion rate of lead remains stable, the conversion rate of copper gradually increases, and the conversion rate of silver changes little. When the dosage of hydrogen peroxide solution reaches 1.5 mL, the conversion rate of copper reaches more than 95%, and the conversion rate of silver is still about 5%. Continuing to add hydrogen peroxide solution, the conversion products of copper and lead are partially dissolved, and the conversion rate decreases, while the conversion rate of silver suddenly increases to 83%. In order to separate copper, lead, and silver to the greatest extent, the dosage of hydrogen peroxide solution is selected as 1.5 mL. At this time, the conversion rate of lead is 100%, the conversion rate of copper is 95%, and the loss of silver is 5%.

[0108] Analysis Example 11 explores the influence of the first precipitation reaction duration on the leaching effect of metal elements

[0109] In Example 3, other conditions remain unchanged, and the duration of the first precipitant in step S2 is adjusted. The results are as Figure 12 shown. It can be seen that 100 mL of the leaching solution is taken at 30°C, 1.5 mL of 30% hydrogen peroxide solution is added, the stirring rate is 100 r / min, and the conversion rates of copper and lead reach their peaks within 0.5 min. As the reaction time extends, the conversion rate of copper gradually decreases, and the conversion rate of lead remains basically unchanged. The conversion rate of silver increases with the extension of the reaction time and stabilizes after 5 min. In order to obtain a good separation effect, 0.5 - 1 min is selected as the optimal reaction time.

[0110] Analysis Example 12 explores the influence of the dosage of the second precipitant on the silver precipitation effect

[0111] In Example 3, other conditions remain unchanged, and the dosage of the second precipitant in step S3 is adjusted. The results are as Figure 13 shown.

[0112] Analysis Example 13 explores the influence of the reaction duration of the second precipitant on the silver precipitation effect

[0113] In Example 3, other conditions remain unchanged, and the duration of the second precipitation reaction in step S3 is adjusted. The results are as Figure 14 shown.[[ID=!]]

[0114] When the dosage of H2O2 (30%) is 1.2 mL / 100 mL of the purification solution, the reaction time is 30 min, the reaction temperature is 30°C, and the stirring speed is 300 rpm, a 100% separation recovery rate of silver is achieved.

[0115] Analysis Example 14

[0116] The silver sulfide obtained in step S3 in Example 3 of the present invention was subjected to XRD characterization analysis, and the results were as follows: Figure 15 As shown, it can be seen that at positions such as 2θ=28.98°, 31.52°, 34.38°, 36.81°, 40.74°, and 43.41°, the characteristic peaks of the product basically correspond to the standard spectrum of Ag2S, and the peak shapes are basically consistent with those of pure Ag2S, indicating that the obtained product is Ag2S. The purity of the obtained Ag2S product is determined, and the average value of the Ag2S content in the product is calculated to be 97.2%, that is, the purity of Ag2S is 97.2%.

[0117] Analysis Example 15: Exploring the Kinetics of the Sodium Thiosulfate Solution Heating Leaching Reaction Process

[0118] Reaction kinetics studies the changes in rate and chemical reaction mechanism during the reaction process. It is a non-equilibrium dynamic system that changes with time. Different models are used for different reaction types. The leaching of silver from sintered ash by thiosulfate system is a typical liquid-solid heterogeneous reaction. Although the composition of sintered ash is complex, the process is simplified through the model. The particle size distribution of the leached sintered ash is uniform and can be regarded as spherical particles. As the reaction proceeds, the part of the particle in contact with the solution gradually dissolves, and the unreacted core gradually shrinks at a uniform rate, which is consistent with the shrinking core model in liquid-solid heterogeneous reactions.

[0119] The leaching process can be divided into five steps: the leaching agent (i.e., sodium thiosulfate solution, the same below) passes through the liquid film on the surface of the solid particles (external diffusion); the leaching agent passes through the solid particles to reach the reaction interface (internal diffusion); the leaching agent undergoes a chemical reaction at the reaction interface, and the reaction products pass through the solid particles to the liquid film (internal diffusion); and the reaction products pass through the liquid film on the surface of the solid particles (external diffusion). The shrinking core reaction model in the leaching kinetics model is a good fit for this leaching process. Each control type corresponds to a different equation.

[0120] Chemical reaction and external diffusion control:

[0121]

[0122] Where ω is the leaching rate of silver and k1 is the chemical reaction and external diffusion rate constant.

[0123] The activation energy controlled by chemical reaction is relatively large, generally 40-300 kJ / mol, while the activation energy controlled by external diffusion is about 8-20 kJ / mol.

[0124] When the reaction is internal diffusion controlled:

[0125]

[0126] Under the conditions that the concentration of sodium thiosulfate solution is 25 g / L and the liquid-solid ratio is 6 mL / g, reactions were carried out at 30, 40, and 50 °C respectively, and the leaching rate obtained varied with time as shown in Figure 16 follows. It can be seen that the leaching rate of silver in the sodium thiosulfate solution increases with the increase of temperature. At low temperatures, the conversion rate changes slightly with time. After the temperature rises, the conversion is rapid and gradually levels off with the extension of time, and it is basically stable at about 130 min.

[0127] To understand the control steps of this leaching process, the leaching rates at different temperatures were substituted into the calculation formula, and the k values under different controls were obtained respectively, as shown in Figure 17 follows. The fitting results are shown in Tables 5 and 6 as follows:

[0128] Table 5 Fitting results of chemical reaction and external diffusion control

[0129]

[0130] Table 6 Fitting results of internal diffusion control

[0131]

[0132] By comparison, it is found that the confidence levels of the two fitting results are similar and cannot be directly judged. The Arrhenius equation was refitted respectively, as shown in Figure 18 follows. The fitting results of the activation energy of chemical reaction and external diffusion control are within the appropriate range and the fitting effect is good. Therefore, it is initially judged to be chemical reaction and external diffusion control. Subsequently, reducing the particle size and increasing the rotation speed to investigate the influence of external diffusion has little effect on the leaching rate, indicating that this process is mainly controlled by chemical reaction, and its activation energy is about 32.53 kJ / mol, which is close to the activation energy range of chemical reaction control.

[0133] At present, the research on the thiosulfate leaching system is mainly focused on the copper-ammonia-thiosulfate system. In this system, copper salts are added in the +1 state and ammonia is not added as a stabilizer, so copper-ammine complexes will not be formed to participate in the reaction. Therefore, the mechanism of the copper-ammonia-thiosulfate system cannot be directly applied. Based on relevant literature and experimental results, the possible reaction process is proposed as shown in Reaction Formulas 1 to 6:

[0134]

[0135]

[0136] Cuprous chloride is insoluble in water, but it can react with thiosulfate to form a cuprous thiosulfate complex. The cuprous thiosulfate replaces the silver in silver sulfide and combines with the sulfur ion to be converted into cuprous sulfide. Secondly, since cuprous chloride carries chloride ions and there are residues of potassium chloride and sodium chloride in the sintered ash, there may also be silver chloro complexes and the conversion between them and thiosulfate complexes, promoting the reaction. The partial elution of silver during the previous water washing process and the effect of the chloride salt method experiment can be used as evidence.

[0137] Secondly, other metals in the sintered ash can also react with thiosulfate to form thiosulfate complexes, consuming thiosulfate in the solution and inhibiting the silver leaching process. At the same time, thiosulfate itself is metastable, and there may also be a conversion process of thiosulfate in the solution.

[0138] Analysis of Example 16 to explore the mechanism of removing copper and lead impurities during the heating leaching reaction

[0139] During the study of the reaction process between the leaching solution and hydrogen peroxide solution, it was observed that the color of the solution quickly changed to brownish-yellow, and then quickly aggregated into brown flocculent products with the appearance of bubbles. Based on the change in the element content in the solution and the color of the obtained filtration product, it is speculated that the products formed may be copper and lead sulfides or oxides. After adding dilute HCl to the product, the solid quickly dissolved with dense bubbles generated, and the solution showed a light blue color after dissolution. It is speculated that the separated product may be a peroxide.

[0140] Prepare lead thiosulfate solution and copper thiosulfate solution, and add hydrogen peroxide solution to them respectively. Almost no reaction occurred in the lead thiosulfate solution within the first 3 minutes. At 5 minutes, the conversion rate of lead was 20%, which is different from the complete conversion of lead in the leaching solution in a short time. It is inferred that the rapid conversion of lead in the leaching solution is related to the presence of copper. Moreover, no bubbles were generated during the reaction of lead thiosulfate, while bubbles were generated during the reaction of copper thiosulfate, indicating the formation of copper peroxide.

[0141] Perform infrared analysis on the reaction products of different solutions, and the results are as Figure 19 shown. It can be seen that there is a broad absorption peak at 3429 cm -1 , corresponding to the stretching vibration of the hydroxyl group in free water, and its specific peak position will fluctuate slightly with the water content in the sample; the peak at 1626 cm -1 is the bending vibration peak of crystal water, and the infrared characteristic peaks at 1382 cm -1 and 1470 cm -1 are the characteristic peaks of CuO2. It can be inferred that CuO2 exists in this intermediate product. At 619 cm -1 , 882 cm -1 , 1105 cm -1An obvious sulfate characteristic peak appears at [specific location], and it is inferred that the product is mainly lead sulfate. Based on the above inferences, the conversion mechanism of copper in the solution is proposed as shown in Equations 7 to 11.

[0142]

[0143] When hydrogen peroxide solution is added, the reaction between thiosulfate and hydrogen peroxide solution also occurs in the solution, and the conversion reaction is shown in Equations 12 to 19.

[0144]

[0145] In the leaching solution, the reason why lead can be rapidly converted may be that the free radicals generated by copper during the reaction contact and react with thiosulfate, converting into sulfate ions, which combine with lead to form lead sulfate precipitate, accelerating the precipitation of lead. In addition, there is also the possibility of generating sulfate radicals during the reaction process.

[0146] Since this intermediate product is insoluble in water but can react with hydrogen peroxide solution to be re-converted into thiosulfate complex and generate oxygen. This step of reaction is rapid, while the subsequent dissolution and conversion reaction is slower. Therefore, the phenomenon that the conversion rate of copper decreases with the extension of time appears, and separation can be achieved by controlling the reaction time.

[0147] In the above technical solution of the present invention, the above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for separating and recovering trace silver in sintering ash, characterized in that, Comprising the steps of: Obtaining a mixed solution containing sintered ash, sodium thiosulfate solution and cuprous reagent. After the mixed solution is successively subjected to heating leaching and solid-liquid separation, the liquid phase is collected to obtain a silver-containing leaching solution; wherein, the molar concentration of the cuprous reagent in the mixed solution is 0.003 - 0.005 mol / L or not less than 0.04 mol / L; Mixing the silver-containing leaching solution with a first precipitant, performing a first precipitation reaction, followed by solid-liquid separation, and collecting the liquid phase to obtain a silver-containing purified solution; Mixing the silver-containing purified solution with a second precipitant, performing a second precipitation reaction, followed by solid-liquid separation, and collecting the solid phase to obtain silver sulfide.

2. The method for separating and recovering trace silver in sintering ash according to claim 1, wherein The separation and recovery method further includes, before the step of obtaining a mixed solution containing sintered ash, sodium thiosulfate solution and cuprous reagent, performing a water washing treatment on the sintered ash. In the water washing treatment, the solid-liquid ratio of the sintered ash to the solvent is 1:3.5 - 4.5 g / mL, the duration of the water washing treatment is not less than 40 min, and the solvent includes water.

3. The method for separating and recovering trace silver in sintering ash according to claim 2, wherein, Adding a dispersant during the water washing treatment. The types of the dispersant include sodium dodecylbenzenesulfonate, and the addition amount of the dispersant is 0.08 g - 0.1 g / 100 g of sintered ash.

4. The method for separating and recovering trace silver in sintering ash according to claim 1, characterized in that, The concentration of the sodium thiosulfate solution is 40 - 50 g / L, and the liquid-solid ratio of the sodium thiosulfate solution to the sintered ash is 6 - 10 ml / g.

5. The method for separating and recovering trace silver in sintering ash according to claim 1, wherein The temperature of the heating leaching is 55 - 65 °C, and the duration of the heating leaching is not less than 120 min.

6. The method for separating and recovering trace silver in sintering ash according to claim 1, wherein, The first precipitant includes hydrogen peroxide solution, the concentration of the first precipitant is 20 - 40%, the second precipitant includes hydrogen peroxide solution, and the concentration of the second precipitant is 20 - 40%.

7. The method for separating and recovering trace silver in sintering ash according to claim 6, wherein The volume ratio of the first precipitant to the silver-containing leaching solution is 1.25 - 1.6 ml / 100 ml, the duration of the first precipitation reaction is 0.4 - 1.5 min, and the temperature of the first precipitation reaction is 20 - 40 °C.

8. The method for separating and recovering trace silver in sintering ash according to claim 6, wherein, The volume ratio of the second precipitant to the silver-containing purified solution is not less than 1.2 ml / 100 ml, the duration of the second precipitation reaction is not less than 30 min, and the temperature of the second precipitation reaction is 20 - 40 °C.

9. The method for separating and recovering trace silver in sintering ash according to claim 1, characterized in that, The solid-phase product obtained by solid-liquid separation after the first precipitation reaction includes lead sulfate and an insoluble intermediate product of a metal ion-peroxo structure-ligand ternary complex formed by the combination of superoxide radicals and cuprous thiosulfate.

10. The method for separating and recovering trace silver in sintering ash according to claim 2, wherein In terms of mass fraction, the elemental composition of the sintered ash includes: K 15% - 20%, Na% 2 - 3%, Fe 10% - 20%, Pb 1% - 2%, Cu 0.1% - 0.5%, Ag 100 g / t - 200 g / t; The elemental composition of the product of the water washing treatment includes: K 0% - 3%, Na% 0 - 1%, Fe 50% - 80%, Pb 5% - 10%, Cu 1% - 2%, Ag 400 g / t - 600 g / t.

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