Selective regulation and control and directional enrichment method and system for metal arsenic crystal form in arsenic-containing gypsum slag and alpha crystal form-metal arsenic product

Abstract

The invention discloses a selective regulation and control and directional enrichment method and system for metal arsenic crystal forms in arsenic-containing gypsum residues and an alpha crystal form-metal arsenic product, and belongs to the technical field of nonferrous metallurgy and secondary resource recovery. The method comprises the following steps: under an anaerobic condition, carrying out a reduction reaction on the arsenic-containing gypsum slag and a reducing carbonaceous material to obtain metal arsenic vapor; carrying out gradient condensation on the metal arsenic steam to obtain a solid metal arsenic product; the gradient condensation comprises three condensation zones: the temperature of the first condensation zone is 420-450 DEG C, the temperature of the second condensation zone is 360-390 DEG C, and the temperature of the third condensation zone is 300-330 DEG C; and the solid metal arsenic product is cooled to 80 DEG C or below at the cooling rate not lower than 50 DEG C / min, and an alpha crystal form-metal arsenic product is obtained. According to the method, the high-valued arsenic is realized, the sulfur element is synergistically cured, the resource utilization of the residues is realized, and finally, the near-zero emission of the whole treatment process is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to a method and system for selective regulation and directional enrichment of metal arsenic crystal form in arsenic-containing gypsum slag, and an alpha crystal form-metal arsenic product, belonging to the field of non-ferrous metallurgy and secondary resource recycling. BACKGROUND

[0002] Arsenic-containing gypsum slag is a high-risk solid waste generated in the process of non-ferrous metal smelting, sulfuric acid production and flue gas desulfurization, and its environmental risk and resource attribute coexist. The current mainstream treatment technology still has the following defects:

[0003] (1) Solidification / stabilization technology: such as cement solidification, the technical essence of which is to physically wrap the waste slag with cement or other cementitious materials or to convert arsenic into low-solubility compounds through chemical reagents, thereby achieving harmlessness. However, this scheme does not realize the recovery of arsenic resources at all. The volume of the treated solidification body increases by 1.3-1.5 times, which not only permanently loses arsenic resources but also occupies a large amount of land resources for landfill, failing to fundamentally solve the resource recycling problem.

[0004] (2) Wet process: mainly using alkaline or acidic leaching agent to selectively extract valuable metals such as copper and zinc from the slag. However, this method pays little attention to the simultaneous and efficient leaching and recovery of arsenic. After the process is completed, most of the arsenic is still enriched in the leaching residue, and its toxicity and environmental risk have not been eliminated. It is only a transformation from one solid waste to another dangerous waste that may need to be treated again, and the environmental pollution problem has not been fundamentally solved. Moreover, there are few reports on industrial application.

[0005] (3) Traditional carbon thermal reduction technology: under high temperature and strong reduction conditions, arsenic, lead, zinc and other heavy metals in the slag are volatilized and separated. However, this technical route aims to recover sulfur resources (such as elemental sulfur or calcium sulfide), but the treatment of arsenic is extremely rough and has high environmental risk. In the strong reduction and specific temperature range, as much as 45% or more of arsenic will be volatilized into toxic As2O3 dust in the flue gas, not only causing the dispersion loss of arsenic resources, but also producing highly toxic secondary pollutants that need to be treated deeply. In essence, the safe recovery and resource utilization of arsenic have not been achieved.

[0006] Existing technologies have not been able to achieve the three goals of "arsenic high-value recovery-calcium and sulfur resource utilization-near-zero emission", forming a fragmented dilemma between pollution control and resource recovery. In particular, in terms of arsenic recovery, the international community has not yet achieved effective control of the crystal form of metal arsenic. The products of traditional condensation technology are mainly amorphous arsenic or metastable β-arsenic, which are chemically active and have low value, and cannot be used as high-value products.

[0007] Therefore, it is of great significance to develop a method for directional enrichment and obtaining specific crystal form of metal arsenic from arsenic-containing gypsum slag. SUMMARY

[0008] In order to overcome the technical bottlenecks of low recovery rate of arsenic resources, low product value, uncontrollable crystal form and secondary pollution caused by the existing arsenic-containing gypsum slag treatment technology, one of the purposes of the present application is to provide a method for selective regulation and directional enrichment of metal arsenic crystal form in arsenic-containing gypsum slag, which realizes short process and high efficiency recovery of arsenic from arsenic-containing gypsum slag to metal products. Further, by revealing and utilizing the nucleation, growth and phase transition rules of metal arsenic under different temperature control strategies, a precise regulation method for selectively preparing high-purity and thermodynamically stable alpha crystal form metal arsenic is established. While realizing the high value of arsenic, the method also cooperatively solidifies sulfur elements and realizes the resource utilization of residues, finally achieving near-zero emission of the entire treatment process.

[0009] The second purpose of the present application is to provide an alpha crystal form-metal arsenic product, which has high purity and the proportion of alpha crystal form metal arsenic in the total metal arsenic is not less than 90wt%.

[0010] The third purpose of the present application is to provide a system for selective regulation and directional enrichment of metal arsenic crystal form in arsenic-containing gypsum slag. The process core equipment of the present application is a reduction furnace, a multi-temperature zone condenser and a rapid cooling device, which are all modular combinations and upgrades of mature equipment in the metallurgical and chemical industries. Therefore, the present technical solution does not require revolutionary equipment invention, but mainly based on innovative integration of existing unit equipment and innovative setting of process parameters, which has low engineering amplification risk and clear industrialization conversion path.

[0011] In order to achieve the above-mentioned purposes, the first aspect of the present application is to provide a method for selective regulation and directional enrichment of metal arsenic crystal form in arsenic-containing gypsum slag, which comprises:

[0012] (1) under oxygen-free conditions, reducing reaction of arsenic-containing gypsum slag and reducing carbonaceous material is carried out to obtain metal arsenic vapor;

[0013] (2) gradient condensation of the metal arsenic vapor is carried out to obtain solid metal arsenic product;

[0014] The gradient condensation comprises three condensation zones: the temperature of the first condensation zone is 420-450℃, the temperature of the second condensation zone is 360-390℃, and the temperature of the third condensation zone is 300-330℃;

[0015] (3) the solid metal arsenic product is cooled to below 80℃ at a cooling rate of not less than 50℃ / min to obtain an alpha crystal form-metal arsenic product.

[0016] Firstly, the present application abandons the traditional single-stage condensation, and innovatively adopts the gradient condensation strategy of multi-temperature platform. The present application utilizes the different nucleation barriers and growth rates of different arsenic crystal forms (α-As and β-As) in different temperature intervals.

[0017] The first condensation zone temperature is 420-450℃, which is a high-temperature nucleation zone. This temperature is much lower than the sublimation point of arsenic (about 614℃ under normal pressure), and in this interval, arsenic vapor has a higher supersaturation and suitable atomic migration rate, which is most conducive to the preferential formation of thermodynamically stable α-arsenic nuclei. In this temperature interval, the supersaturation of gaseous arsenic atoms is controlled at a moderate level. According to the theory of crystal growth, the critical nucleation work required for the nucleation of α-arsenic, as a thermodynamically stable phase, is more advantageous at this temperature than that of β-arsenic (metastable phase). In this stage, a large number of fine and stable α-arsenic nuclei can be preferentially induced to form.

[0018] The second condensation zone temperature is 360-390℃, which is a crystal growth zone. As the temperature decreases, the supersaturation increases. At this time, the already formed and more stable α-arsenic nuclei will become the preferential growth center, consuming arsenic atoms in the gas phase and continuously growing, while the metastable β-arsenic is effectively inhibited due to insufficient nucleation driving force and poor stability. This stage is the key to the preferential epitaxial growth of α-arsenic crystals.

[0019] The third condensation zone temperature is 300-330℃, which is a crystal ripening zone. In this temperature range, the crystal growth rate slows down, but it helps to further relax and perfect the crystal structure, reduce crystal defects, and make the α-arsenic crystal have higher crystallinity and more stable structure.

[0020] Secondly, the present application adopts rapid cooling and solidification to realize "kinetic locking of target crystal form" of α-arsenic crystals formed by gradient condensation. If it slowly passes through some specific temperature intervals during the subsequent cooling process, solid-state phase transition may still occur, and part of it may be converted into β-arsenic or amorphous arsenic. The present application immediately adopts the strategy of rapid cooling (≥50℃ / min) after gradient condensation. The principle is to "freeze" the α-arsenic crystal lattice structure formed by extremely high cooling rate, so as to prevent its transformation to metastable phase, and to ensure the high proportion and high stability of α-arsenic crystal form in the final product.

[0021] Further, the main component CaSO4·2H2O in arsenic-containing gypsum slag not only is the treatment object in this system, but also plays the role of in-situ sulfur fixation agent. Under reducing conditions, CaSO4·2H2O is reduced to CaS, effectively fixing sulfur elements and avoiding the generation of SO2, realizing the clean separation of arsenic-sulfur (CaSO4 + 2C → CaS + 2CO2(g) ↑).

[0022] Through the synergistic effect of the above technical features, and in combination with the remaining technical features of the present application, the finally obtained alpha crystal form-metallic arsenic product has high stability, and has a high content of alpha-arsenic crystal form, and also achieves the simultaneous valorization of arsenic, the simultaneous solidification of sulfur elements, and the resource utilization of residues, and finally achieves near-zero discharge of the entire treatment process.

[0023] As a preferred scheme, the content of As in the arsenic-containing gypsum residue is 5-10 wt%, the content of Ca is 15-20 wt%, the content of S is 10-15 wt%, the content of Pb is 1.5-4 wt%, and the content of Zn is 0.5-3 wt%.

[0024] As a preferred scheme, the residence time of the metallic arsenic vapor in each condensation zone is independently 10-30 min.

[0025] As a preferred scheme, the reducing carbonaceous material is coke and / or coal powder.

[0026] As a preferred scheme, the mass ratio of the arsenic-containing gypsum residue to the reducing carbonaceous material on a dry basis is 1:0.15-0.25.

[0027] The oxygen-free condition is an inert atmosphere.

[0028] By controlling the ratio of the reducing carbonaceous material to the arsenic-containing gypsum residue, and assisted by the protection of the inert atmosphere, the present application constructs a unique reaction environment of "strong reduction but not excessive reduction". The oxygen partial pressure (the oxygen partial pressure in the present application refers to the oxygen potential, specifically the tendency of oxygen-containing components (such as arsenate, sulfate) in the system to lose oxygen atoms) in this atmosphere is just enough to efficiently reduce the stable arsenate (such as Ca3(AsO4)2) in the residue to the target product-metallic arsenic (As 0 ), while maximally inhibiting the excessive reduction to generate As 3- (such as existing in As2O3) or side reactions with other metals to form arsenides, thereby improving the purity of arsenic. The main chemical reaction is: Ca3(AsO4)2 + 3C → 3CaO + 2As(g) ↑ + 3CO(g) ↑.

[0029] As a preferred scheme, the inert atmosphere is a nitrogen atmosphere.

[0030] As a preferred scheme, the temperature of the reduction reaction is 900-1150°C, and the time is 40-80 min.

[0031] As a further preferred solution, in step (1), the method further comprises: first mixing the arsenic-containing gypsum residue with the reducing carbonaceous material, and then heating at a heating rate of 5-10℃ / min to 900-1150℃, and keeping for 40-80min.

[0032] As a more preferred solution, the temperature of the reduction reaction is 950-1150℃. The temperature range of 950-1150℃ is a "golden window" determined based on thermodynamic calculation and kinetic experiment. If the temperature is too low, the kinetics of the reduction reaction is slow, and the conversion rate is insufficient; if the temperature is too high, although the reaction can be accelerated, it may lead to sintering of the furnace charge, a sharp increase in energy consumption, and may exacerbate the co-evaporation of other impurities. The keeping time of 40-80min ensures that the gaseous products have enough time to diffuse from the interior of the slag phase and volatilize, thereby achieving efficient enrichment and separation of arsenic.

[0033] It should be noted that the time of the reduction reaction does not include the heating time to 900-1150℃.

[0034] As a preferred solution, in step (3), the cooling rate of the solid metallic arsenic product is 60-100℃ / min. The inventors have found that in this preferred case, the α crystal content in the α crystal type-metallic arsenic product prepared is higher.

[0035] As a preferred solution, in step (1), the arsenic-containing gypsum residue is first subjected to drying treatment and crushing treatment, and then subjected to a reduction reaction with the reducing carbonaceous material.

[0036] As a preferred solution, the arsenic-containing gypsum residue subjected to drying treatment and crushing treatment has a water content of less than 5wt% and a particle size of <100 mesh.

[0037] The second aspect of the present application is to provide an α crystal type-metallic arsenic product prepared by the preparation method of the first aspect. The high α crystal product is a more inert, less perishable and safer commodity form, and its storage stability is far superior to that of metastable products, greatly reducing the environmental and safety risks throughout the life cycle. α-arsenic has definite parameters such as density, melting point, resistivity, and reactivity. If the raw material is a mixture of mixed crystal types, the α / β / amorphous ratio may fluctuate in different batches or even different parts of the same batch, resulting in uncontrollable reaction rate, conversion rate and impurity introduction in subsequent reactions, which seriously affects the quality uniformity and qualification rate of the terminal product. Therefore, high content of α crystal type can improve the "product stability" and "application reliability" of arsenic products.

[0038] As a preferred solution, the purity of the α crystal type-metallic arsenic product is not less than 98wt%, and the proportion of α crystal type metallic arsenic in the total metallic arsenic is not less than 90wt%.

[0039] The third aspect of the present application provides a system for selective regulation and directional enrichment of metal arsenic crystal form in arsenic-containing gypsum residue, which comprises a reduction furnace, a multi-stage condensation system and a quenching device.

[0040] The flue gas outlet of the reduction furnace is connected to the multi-stage condensation system, the multi-stage condensation system is connected to the quenching device, and the multi-stage condensation system comprises a first condensation chamber, a second condensation chamber and a third condensation chamber connected in sequence.

[0041] In the system of the present application, the reduction furnace is used for carrying out a thermal reduction reaction, the quenching device is used for rapidly cooling the condensation product, and the three condensation chambers are used for realizing gradient condensation.

[0042] As a preferred scheme, the temperature control range of the first condensation chamber is 420-450℃, the temperature control range of the second condensation chamber is 360-390℃, and the temperature control range of the third condensation chamber is 300-330℃.

[0043] Compared with the prior art, the present application has at least the following advantages:

[0044] (1) Significant improvement in arsenic recovery efficiency and product value: In the present application, the volatilization enrichment rate of arsenic is increased from 85% in the traditional technology to more than 92%, and more importantly, the product is directly upgraded from low-value amorphous arsenic to high-value crystal metal arsenic with a purity of >98wt% and an α-crystal form proportion of >90wt%, realizing a leap from "waste treatment" to "product manufacturing".

[0045] (2) Environmental friendliness and resource synergy: By "in-situ sulfur fixation" and residue resourceization, the paths of SO2 pollution and solid waste storage are fundamentally cut off, and the synergistic recovery of arsenic, sulfur and calcium and near-zero emission in the whole process are realized.

[0046] (3) Wide industrial application prospect: The process provided by the present application has high compatibility with existing metallurgical equipment, clear parameter control logic, and is easy to realize industrialization and automatic control, thereby providing a feasible technical solution for solving the green and high-value utilization of large-scale arsenic-containing gypsum residue in China. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a process flow diagram of the present application.

[0048] Figure 2 is a TEM and XRD diagram of the metal arsenic product obtained in Example 1 and Comparative Example 1; Figure 2 (a) in is a TEM diagram of the metal arsenic product prepared in Example 1; Figure 2 (c) in is an XRD diagram of the metal arsenic product prepared in Example 1; Figure 2(f) in the figure is the XRD pattern of the metal arsenic product prepared by the preparation of Comparative Example 1; from the figure, it can be seen that the peak shape of the metal arsenic product prepared by the preparation of the example is symmetrical and sharp, showing sharp, narrow and high-intensity diffraction peaks, perfectly matching the characteristics of α-arsenic crystal (trigonal system), the baseline is flat, and the peak intensity is significantly higher than the baseline, directly reflecting high crystallinity and high crystal purity; the peak type of the metal arsenic product prepared by the preparation of Comparative Example 1 is diffuse, and the whole presents a broad steamed bun peak, the baseline is slightly higher than the crystal curve, reflecting the structural characteristics of disordered crystal, and directly proving that the product is amorphous arsenic. Figure 2 DETAILED DESCRIPTION

[0049] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the present application. The endpoints of the ranges and any values are provided as approximations only, and are understood to encompass a range of values unless otherwise indicated. Various exemplary dimensions are provided herein for reference purposes, and the dimensions are not intended to limit the scope of the application.

[0050] In the present application, room temperature refers to 25±2℃.

[0051] The application will be further described in conjunction with specific examples, but the protection scope of the application is not limited to the following specific examples. Obviously, the following described examples are only a part of examples, and all other examples obtained by those skilled in the art without creative labor still belong to the protection scope of the application.

[0052] Unless otherwise specifically indicated, all of the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by the existing method.

[0053] The arsenic-containing gypsum slag comes from a lead-zinc smelting plant, and its main chemical components are: the content of As is 7.8wt%, the content of Ca is 18.5wt%, the content of S is 12.1wt%, the content of Pb is 2.5wt%, the content of Zn is 1.2wt%, and the content of H2O is 12wt%.

[0054] Example 1

[0055] (1) 1.0 kg of wet base arsenic-containing gypsum slag was weighed and placed in an oven for drying treatment at 105℃ for 4 h, so that the moisture content was reduced to below 5wt%. Then, crushing treatment was carried out to obtain dry gypsum slag powder with particle size less than 100 mesh. The mass of the obtained dry slag was about 880 g.

[0056] ​(2) The entire dry slag powder (880 g) obtained in step (1) is mixed with 150 g of coke powder (fixed carbon > 80%) and pressed into a briquette. The briquette is placed in a reduction furnace and heated to 1050°C at a heating rate of 8°C / min under the protection of a nitrogen atmosphere, and kept at this temperature for 60 min to fully reduce and volatilize the arsenic compounds, to obtain high-temperature flue gas containing metallic arsenic;

[0057] (3) The high-temperature arsenic vapor is directly introduced into a gradient condensation system and sequentially subjected to temperature-programmed condensation in three temperature zones:

[0058] The first temperature zone is 450°C, and the residence time is 15 min.

[0059] The second temperature zone is 390°C, and the residence time is 15 min.

[0060] The third temperature zone is 330°C, and the residence time is 15 min.

[0061] The metallic arsenic vapor is gradually condensed and forms solid crystals.

[0062] (4) The solid metallic arsenic product obtained by gradient condensation is quickly transferred to a quenching device and rapidly cooled to room temperature at a cooling rate of 80°C / min. Finally, 73 g of a dense block-shaped product with a silver-gray color and a bright metallic luster is collected.

[0063] It is detected that the purity of metallic arsenic is 98.8%, the arsenic enrichment recovery rate is 92.4%, and the proportion of α-arsenic crystal form is ≥ 95%.

[0064] Example 2

[0065] (1) The same as in Example 1.

[0066] (2) The entire dry slag powder (880 g) obtained in step (1) is mixed with 180 g of coke powder (fixed carbon > 80%) and pressed into a briquette. The briquette is placed in a reduction furnace and heated to 1000°C at a heating rate of 8°C / min under the protection of a nitrogen atmosphere, and kept at this temperature for 60 min to fully reduce and volatilize the arsenic compounds, to obtain high-temperature flue gas containing metallic arsenic;

[0067] (3) The high-temperature arsenic vapor is directly introduced into a gradient condensation system and sequentially subjected to temperature-programmed condensation in three temperature zones:

[0068] The first temperature zone is 430°C, and the residence time is 20 min.

[0069] The second temperature zone is 380°C, and the residence time is 20 min.

[0070] The third temperature zone is 320°C, and the residence time is 20 min.

[0071] The metallic arsenic vapor is gradually condensed and forms solid crystals.

[0072] (4) The solid metallic arsenic product after gradient condensation is rapidly transferred to a quenching device and cooled to room temperature at a cooling rate of 60 °C / min. Finally, 70 g of dark gray compact solid is collected.

[0073] The detection shows that the purity of metallic arsenic is 98.3%, the proportion of α-arsenic crystal form is 92%, and the arsenic recovery rate is 88.2%.

[0074] Example 3

[0075] Step (1) is the same as that in Example 1;

[0076] (2) The whole dry residue powder (880 g) obtained in step (1) is mixed with 130 g of coke powder (fixed carbon > 80%) and pressed into a lump. The lump is placed in a reduction furnace and heated to 1100 °C at a heating rate of 8 °C / min under the protection of nitrogen atmosphere, and kept at this temperature for 40 min, so that the arsenic compounds are fully reduced and volatilized to obtain high-temperature flue gas containing metallic arsenic;

[0077] (3) The high-temperature arsenic vapor is directly introduced into a gradient condensation system and sequentially subjected to programmed temperature condensation in three temperature zones:

[0078] The first temperature zone is 420 °C, and the residence time is 10 min.

[0079] The second temperature zone is 370 °C, and the residence time is 10 min.

[0080] The third temperature zone is 310 °C, and the residence time is 10 min.

[0081] The metallic arsenic vapor is gradually condensed and forms solid crystals.

[0082] (4) The solid metallic arsenic product after gradient condensation is rapidly transferred to a quenching device and cooled to room temperature at a cooling rate of 100 °C / min. Finally, 75 g of silver-gray block-shaped product is collected.

[0083] The detection shows that the purity of metallic arsenic is 99.0%, the proportion of α-arsenic crystal form is 96%, and the arsenic recovery rate is 95.2%.

[0084] Example 4

[0085] Step (1) is the same as that in Example 1;

[0086] (2) The whole dry slag powder (880 g) obtained in step (1) was mixed with 180 g of coke powder (fixed carbon > 80%) and pressed into a briquette. The briquette was placed in a reduction furnace and heated to 900℃ at a heating rate of 8℃ / min under the protection of nitrogen atmosphere, and kept at this temperature for 90 min, so that the arsenic compounds were fully reduced and volatilized, to obtain high-temperature flue gas containing metallic arsenic;

[0087] Step (3) was the same as in Example 1;

[0088] Step (4) was the same as in Example 1. Finally, 65 g of dark gray solid with partial metallic luster was collected.

[0089] It was detected that the purity of metallic arsenic was 95.5%, the proportion of α-arsenic crystal form was 80%, and the arsenic recovery rate was 79.6%.

[0090] When the reduction temperature was reduced to 900℃, even if the same gradient condensation and quenching strategy as in Example 1 was used, the arsenic recovery rate, product purity and α-crystal form proportion all showed a comprehensive and significant decrease. The reduction of the reduction temperature led to poor quality of the source arsenic vapor, which restricted the ultimate performance that could be achieved by the subsequent condensation and crystallization process.

[0091] Comparative Example 1

[0092] Step (1) was the same as in Example 1;

[0093] Step (2) was the same as in Example 1;

[0094] Step (3): The high-temperature arsenic vapor was introduced into a single-temperature condenser set at 400℃ for condensation, and then the heat source was turned off, and the product was naturally cooled in the furnace (cooling rate about 10-15℃ / min) to room temperature. 68 g of black, brittle, non-metallic luster powder solid was collected.

[0095] It was detected that the chemical analysis showed that the total arsenic content was 91.5%. The XRD pattern showed a broadened "steamed bun peak", indicating that it was mainly amorphous arsenic. The arsenic recovery rate was 79.7%.

[0096] Reason analysis: The single-stage condensation process has a single condensation temperature, and the product is slowly cooled after condensation, resulting in low condensation collection efficiency (part of the arsenic vapor is not effectively condensed and is lost), and the product has mixed crystal forms, low purity, and the loose powder form is easy to produce dust loss during the collection process, further reducing the total recovery rate.

[0097] Comparative Example 2

[0098] Step (1) was the same as in Example 1;

[0099] Step (2) was the same as in Example 1;

[0100] Step (3) The high-temperature arsenic vapor is directly introduced into a single condenser set at 370°C and resided at this temperature for 45 min (the total residence time is the same as the sum of the three-stage condensation time of Example 1, 45 min), so that the arsenic vapor is condensed.

[0101] (4) The solid metallic arsenic product after condensation was quickly transferred to a quenching device and rapidly cooled to room temperature at a cooling rate of 80℃ / min. 69 g of dark gray, slightly rough blocky product was collected.

[0102] Testing revealed that the purity of metallic arsenic was 95.2%, with 70% being α-arsenic crystal form. Arsenic recovery rate: 84.2%.

[0103] Comparative Example 3

[0104] Steps (1) to (3) are the same as in Example 1;

[0105] Step (4): Turn off the power of the gradient condensation system and allow the solid metallic arsenic product obtained in step (3) to cool naturally to room temperature. Collect 71 g of gray-black, partially metallic but uneven blocky product.

[0106] Testing revealed that the purity of metallic arsenic was 97.0%, with 82% being α-arsenic crystal form. Arsenic recovery rate: 88.3%.

[0107] This comparative example employed gradient condensation but omitted the rapid cooling step. Its arsenic recovery rate was close to that of Example 1, indicating that gradient condensation is effective for collecting gaseous arsenic. However, its α-arsenic crystal form ratio (82%) was significantly lower than that of Example 1 (≥95%), suggesting that some of the α-arsenic crystals formed by gradient condensation during the slow cooling process underwent deterioration or phase transition.

[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag, characterized in that: The method includes: (1) Under anaerobic conditions, arsenic-containing gypsum slag is reduced with reducing carbonaceous materials to obtain metallic arsenic vapor; (2) The metallic arsenic vapor is subjected to gradient condensation to obtain solid metallic arsenic product; The gradient condensation includes three condensation zones: the first condensation zone has a temperature of 420~450℃, the second condensation zone has a temperature of 360~390℃, and the third condensation zone has a temperature of 300~330℃. (3) Cool the solid metallic arsenic product to below 80°C at a cooling rate of not less than 50°C / min to obtain α-crystalline metallic arsenic product.

2. The method for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag according to claim 1, characterized in that: The residence time of metallic arsenic vapor in each condensation zone is independently 10-30 min; And / or, the reducing carbonaceous material is coke and / or pulverized coal.

3. A method for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag according to claim 1 or 2, characterized in that: In step (1), the arsenic-containing gypsum slag is first dried and crushed, and then reduced with reducing carbonaceous materials. And / or, the reduction reaction is carried out at a temperature of 900~1150℃ for a time of 40~80min.

4. A method for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag according to claim 1 or 2, characterized in that: The mass ratio of the arsenic-containing gypsum residue to the reducing carbonaceous material, on a dry basis, is 1:0.15~0.25; The oxygen-free condition is an inert atmosphere.

5. The method for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag according to claim 3, characterized in that: The reduction reaction is carried out at a temperature of 950~1150℃.

6. A method for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag according to claim 1 or 2, characterized in that: In step (3), the cooling rate of the solid metal arsenic product is 60~100℃ / min.

7. An α-crystalline metallic arsenic product prepared by the method of any one of claims 1 to 6.

8. The α-crystalline metallic arsenic product according to claim 7, characterized in that: The purity of the α-crystalline metallic arsenic product is not less than 98 wt%, and the proportion of α-crystalline metallic arsenic to all metallic arsenic is not less than 90 wt%.

9. A system for selectively controlling and directionally enriching the crystal form of metallic arsenic in arsenic-containing gypsum slag, characterized in that: The system includes a reduction furnace, a multi-stage condensation system, and a quenching device; The flue gas outlet of the reduction furnace is connected to the multi-stage condensation system, which is connected to the quenching device; and the multi-stage condensation system includes a first condensation chamber, a second condensation chamber, and a third condensation chamber connected in sequence.

10. The selective regulation and directional enrichment system for metallic arsenic crystal forms in arsenic-containing gypsum slag according to claim 9, characterized in that: The temperature control range of the first condensing chamber is 420~450℃, the temperature control range of the second condensing chamber is 360~390℃, and the temperature control range of the third condensing chamber is 300~330℃.

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