Method for separating and purifying tellurium from casting slag through multi-property synergistic reduction

Abstract

The invention discloses a method for separating and purifying tellurium from casting slag through multi-property synergistic reduction. The method comprises the following steps that the casting slag is subjected to ball milling; uniformly mixing the casting slag powder with a carbon-sulfur dual-function synergistic reducing agent; placing in a vacuum reaction device, carrying out a multi-property synergistic reduction reaction, carrying out carbon thermal reduction deoxidation on the tellurium oxide, carrying out sulfuration volatilization on impurity elements, and collecting a volatile product to obtain crude tellurium; selective volatilization of impurities and recondensation purification of tellurium are achieved on the obtained crude tellurium under the conditions of different temperature zones and pressure intensities, and finally high-purity tellurium with the purity larger than or equal to 99.99 wt% is obtained. According to the method, high-purity tellurium with the purity larger than 99.99% is prepared through efficient separation and purification from the casting slag, efficient resource recovery and protection of solid waste residues in the metallurgical process can be synchronously achieved, the casting slag is fully utilized, the whole process is easy to operate, no secondary oxidizing slag is generated, and a new thought is provided for resource recovery of the casting slag and high-purity preparation of tellurium.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of scattered metal metallurgy and high-value utilization of secondary resources, and particularly relates to an integrated process based on carbon-sulfur bifunctional synergistic reduction into a precursor and vacuum stepwise evaporation purification. BACKGROUND

[0002] Tellurium-based scattered metals have become irreplaceable functional materials in the fields of semiconductor devices, thin-film solar cells, infrared detection and other cutting-edge fields due to their excellent photoelectric properties, and are listed in the strategic key metal list. More than 90% of the global industrial tellurium is derived from copper smelting by-products, i.e., copper anode slime. The 4N-5N high-purity tellurium ingot can be prepared from the anode slime through traditional processes such as roasting, leaching, reduction and purification. However, during the casting stage, the molten tellurium is oxidized instantly upon contact with air, forming a "melting and casting slag" rich in TeO2. At present, this slag is generally returned to the anode slime system for recycling, causing tellurium to accumulate and disperse repeatedly in the metallurgical circuit, which seriously restricts the efficient utilization of scattered metal resources. So far, there has been no systematic research or industrialization report on the efficient separation and purification of tellurium from the melting and casting slag.

[0003] The melting and casting slag is a typical waste secondary resource and an important raw material for recovering tellurium, but purifying it to 4N (99.99%) and above high-purity tellurium is a necessary process and a key link to realize its high-value conversion. However, this link faces the challenge of separating tellurium from some impurity elements with similar physical and chemical properties, and the traditional purification process is often long, low in efficiency, high in cost, and easy to cause secondary pollution, making the large-scale and stable production of high-purity tellurium face significant technical challenges. This purification difficulty is also directly reflected in the market value stratification of tellurium products. At present, the price of crude tellurium is about 560 yuan / kg, while the price of 4N tellurium can reach 720-740 yuan / kg, and the price of 5N tellurium further rises to 840-860 yuan / kg. The obvious price gradient not only reflects the decisive influence of purity on product value, but also confirms the technical threshold and added value space borne by the preparation process of high-purity tellurium. Therefore, developing an efficient, green and low-cost crude tellurium purification technology to realize the short-process and high-quality conversion from waste resources to high-purity tellurium has urgent practical significance for improving the economic benefits of resource recycling and supporting the development of downstream high-end industries.

[0004] The prior art mainly focuses on "crude tellurium" or "copper telluride slag", for example, the patent with publication number CN117776118A mentions mixing crude tellurium with concentrated sulfuric acid. A slurry is obtained, and the slurry is subjected to rotary roasting under the condition of passing a current-carrying gas to obtain roasting slag and smoke containing selenium dioxide, respectively. The roasting slag is subjected to water immersion and solid-liquid separation to obtain water immersion liquid and water washing slag, respectively. The water washing slag is subjected to alkali leaching and solid-liquid separation to obtain alkali leaching liquid and alkali leaching slag, respectively. The alkali leaching liquid is subjected to acid leaching and neutralization and solid-liquid separation to obtain acid leaching liquid and acid leaching slag, respectively. The acid leaching slag is mixed with carbon material to form pellets, and the pellets are subjected to vacuum carbon thermal reduction to obtain high-purity tellurium. This method effectively recovers and purifies metal tellurium from crude tellurium, but the process involves multiple steps such as roasting, acid / alkali leaching, solid-liquid separation, pelletizing, and carbon thermal reduction, which has the disadvantages of long process and high reagent consumption. Currently, there is no direct method for processing smelting slag, so it is of great significance to develop a short-flow, green, and environmentally friendly tellurium extraction and purification technology suitable for smelting slag. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction, which is used to obtain 4N high-purity tellurium directly from waste resources, significantly improving product value and reducing process complexity.

[0006] The technical solution adopted by the present application to solve the above technical problems is:

[0007] A method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction, wherein the smelting slag is subjected to ball milling to obtain smelting slag powder with uniform particle size distribution; the obtained smelting slag powder is uniformly mixed with a carbon-sulfur dual-functional synergistic reducing agent in a certain proportion to form a reaction precursor; the reaction precursor is placed in a vacuum reaction device and subjected to multi-property synergistic reduction reaction under specific temperature, vacuum degree and temperature rising program, so that tellurium oxide is subjected to carbon thermal reduction and deoxidation, and impurity elements are subjected to sulfidation and volatilization, and the volatile product is collected to obtain crude tellurium; the obtained crude tellurium is subjected to two-stage gradient temperature control volatilization process (which can be placed in the same or another vacuum purification device) under different temperature zones and pressure conditions to realize selective volatilization of impurities and recondensation and purification of tellurium, and finally high-purity tellurium with purity ≥99.99 wt% is obtained.

[0008] Preferably, the vacuum reaction apparatus is a two-stage vacuum distillation furnace. In the multi-property synergistic reduction reaction, most highly volatile impurities such as As, Na, Ca, and Mg preferentially volatilize into the second-stage graphite condenser and separate from tellurium. Tellurium volatilizes into the first-stage graphite condenser, while most low-volatile impurities such as Cu, Fe, Si, Sn, and Ni do not volatilize and remain in the graphite crucible. During the crude tellurium purification process, after a two-stage stepped temperature-controlled volatilization, highly volatile impurities such as As, Na, Ca, and Mg volatilize into the second-stage graphite condenser and separate from tellurium. Tellurium volatilizes into the first-stage graphite condenser, while low-volatile impurities such as Cu, Fe, Si, Sn, and Ni do not volatilize and remain in the graphite crucible.

[0009] In the aforementioned method for separating and purifying tellurium from molten casting slag through multi-property synergistic reduction, preferably, the ball milling is a micron-level mechanical ball mill with a rotation speed of 450-650 r / min. The ball-to-material ratio used in the ball milling is 5:1-10:1 (preferably 8:1). The particle size D50 of the molten casting slag powder obtained after ball milling is 10-20 µm. The purpose of ball milling is to achieve micron-level refinement of the molten casting slag, increase the specific surface area of ​​the reaction, and promote the subsequent reduction reaction. Studies have shown that excessively low ball milling speed leads to insufficient energy input, low ball milling efficiency, difficulty in reaching the target particle size within a reasonable time, and easily results in uneven powder particle size distribution and excessively large particles, affecting the uniformity of subsequent mixing and the reaction rate. Excessively high ball milling speed leads to local overheating, powder agglomeration, and even oxidation or phase transformation, while also aggravating the wear of the grinding balls and the jar, introducing impurities (such as Fe, Si, etc.), and affecting product purity. Maintaining the ball-to-material ratio is to ensure sufficient collision energy and grinding efficiency to achieve efficient and uniform powder refinement. If the ball-to-material ratio is too low, there will be insufficient grinding balls, resulting in a low collision frequency, poor grinding effect, and the emergence of "dead zones," causing some materials to not be sufficiently refined. If the ball-to-material ratio is too high, the powder will be too fine and agglomerate severely, while increasing energy consumption and equipment wear, and impurities may be introduced due to over-grinding.

[0010] In the above-mentioned method for separating and purifying tellurium from molten casting slag through multi-functional synergistic reduction, preferably, the carbon component of the carbon-sulfur bifunctional synergistic reducing agent is high-purity graphite powder with a carbon content of not less than 99.99 wt%; the sulfur component is sublimed sulfur with a purity of not less than 99.9 wt%.

[0011] Preferably, in the carbon-sulfur bifunctional synergistic reducing agent, the molar amount of sulfur is 80%-120% of that of carbon. Mixing method: Wet the carbon component and the sulfur component with neutral water, and then mix.

[0012] Carbon as a strong reducing agent, carbon thermal reduction reaction with TeO2 occurs under vacuum at high temperature, to achieve the deep deoxidation of tellurium oxide, generating metal tellurium and converted into CO2 gas exhaust. As a sulfidation agent, with the impurity metals in the cast slag (such as Cu, Pb, Bi, As, etc.) sulfidation reaction, so that it volatilizes and separates under vacuum conditions. Carbon deficiency / sulfur excess, will not be complete reduction, part of TeO2 residual, resulting in tellurium recovery rate decreased; excess sulfur may be directly with tellurium to generate TeS2 and other sulfides, causing tellurium loss, and excess sulfur vapor may condense mixed into the product, introduce sulfur impurities. Carbon excess / sulfur deficiency, will cause incomplete sulfidation of impurities, residual Cu, Pb and other metal impurities will increase the difficulty in subsequent volatile purification; excess free carbon may be mixed into the volatile dust form, pollute the crude tellurium, increase the burden of purification.

[0013] The above-mentioned multi-nature synergistic reduction method for separating and purifying tellurium from the cast slag is preferably mechanically mixed by dry method, and the mixing time is not less than 30 minutes to ensure uniform distribution of components. The total amount of carbon-sulfur dual functional synergistic reducing agent added is 5%-15% of the mass of the cast slag, and the amount added is determined according to the content of Cu, Pb and other impurities (1% wt); if the content of Cu, Pb and other impurities exceeds 1wt%, more carbon-sulfur dual functional synergistic reducing agent is added, and the amount of carbon-sulfur dual functional synergistic reducing agent added is usually 10%-15% of the mass of the cast slag. If the content of Cu, Pb and other impurities is less than 1%, less carbon-sulfur dual functional synergistic reducing agent is added, and the amount of carbon-sulfur dual functional synergistic reducing agent added is usually 5%-10% of the mass of the cast slag.

[0014] Too much carbon-sulfur dual functional synergistic reducing agent will affect the direct recovery rate of tellurium, causing tellurium loss; too little carbon-sulfur dual functional synergistic reducing agent will cause incomplete sulfidation of impurity metals, and residual metal impurities (such as Cu, Pb) will be dissolved or mixed in the crude tellurium, greatly increasing the difficulty of subsequent vacuum purification, and the purity of the final product is difficult to reach 4N.

[0015] The above-mentioned multi-nature synergistic reduction method for separating and purifying tellurium from the cast slag is preferably mechanically mixed by dry method, and the mixing time is not less than 30 minutes to ensure uniform distribution of components. The total amount of carbon-sulfur dual functional synergistic reducing agent added is 5%-15% of the mass of the cast slag, and the amount added is determined according to the content of Cu, Pb and other impurities (1% wt); if the content of Cu, Pb and other impurities exceeds 1wt%, more carbon-sulfur dual functional synergistic reducing agent is added, and the amount of carbon-sulfur dual functional synergistic reducing agent added is usually 10%-15% of the mass of the cast slag. If the content of Cu, Pb and other impurities is less than 1%, less carbon-sulfur dual functional synergistic reducing agent is added, and the amount of carbon-sulfur dual functional synergistic reducing agent added is usually 5%-10% of the mass of the cast slag.

[0016] The above-mentioned multi-nature synergistic reduction method for separating and purifying tellurium from the cast slag is preferably mechanically mixed by dry method, and the mixing time is not less than 30 minutes to ensure uniform distribution of components. The total amount of carbon-sulfur dual functional synergistic reducing agent added is 5%-15% of the mass of the cast slag, and the amount added is determined according to the content of Cu, Pb and other impurities (1% wt); if the content of Cu, Pb and other impurities exceeds 1wt%, more carbon-sulfur dual functional synergistic reducing agent is added, and the amount of carbon-sulfur dual functional synergistic reducing agent added is usually 10%-15% of the mass of the cast slag. If the content of Cu, Pb and other impurities is less than 1%, less carbon-sulfur dual functional synergistic reducing agent is added, and the amount of carbon-sulfur dual functional synergistic reducing agent added is usually 5%-10% of the mass of the cast slag.

[0017] The method for separating and purifying tellurium from smelting slag by the multi-property synergistic reduction method has the following preferred modes: the heating mode for vacuum purification of the crude tellurium is two-stage gradient temperature control; and the graphite used in the vacuum purification device is high-purity graphite (99.99%, wt, ash content less than 10 ppm).

[0018] The method for separating and purifying tellurium from smelting slag by the multi-property synergistic reduction method has the following preferred modes: in the two-stage gradient temperature control, the temperature of the first stage is 500-650 DEG C, the pressure is 1-10 Pa, the temperature rising rate is 8-15 DEG C / min, and the holding time is 2-4 h; the temperature of the second stage is 200-350 DEG C, the pressure is 1-10 Pa, the temperature rising rate is 3-6 DEG C / min, and the holding time is 2-4 h. The first-stage temperature control is mainly used for removing low-volatility impurities such as Fe, Si, Cu, Al, Pb and Bi; and the second-stage temperature control is mainly used for removing high-volatility impurities such as Ca, Zn, Cd, As, Se and Mg.

[0019] The method for separating and purifying tellurium from smelting slag by the multi-property synergistic reduction method has the following preferred modes: in the reduction and volatilization process, the change of the volatilization components is monitored by an online mass spectrometry or residual gas analysis system, so as to realize real-time feedback and optimal control of the process parameters.

[0020] Compared with the prior art, the method has the following advantages:

[0021] (1) Mechanism synergistic advantage: the reducing agent used in the method is a carbon-sulfur dual-function synergistic reduction precursor, and the cost of carbon and sulfur is lower than that of other reducing agents; and under vacuum, the carbon-sulfur dual-function synergistic reduction precursor is coupled to deeply deoxidize the smelting slag and convert the oxygen in the smelting slag into harmless gas CO2. In addition, the sulfur can deeply remove impurities, and in the reduction process, the sulfur can simultaneously remove impurities such as Cu, Bi and Pb, thereby greatly reducing the purification difficulty in the vacuum purification process.

[0022] (2) Environmental friendliness: the heat generated by the self-heating of the excess carbon and sulfur in the method can assist in the self-heating reaction of the smelting slag, thereby reducing the energy consumption and saving the electric energy. The carbon thermal reduction of TeO2 is an exothermic reaction, and the sulfuration reaction is an endothermic reaction, and the two reactions complement each other in the heat effect, thereby realizing the self-heating balance of “using the heat energy of the slag to compensate the reduction heat”.

[0023] (3) High process integration degree and good adaptability: the method realizes the “reduction-purification” process in the same vertical vacuum furnace, and the equipment occupies a small area, and compared with the traditional “leaching-reduction-electrolysis” process, the method greatly shortens the preparation process of high-purity tellurium and saves the technical cost. The equipment uses a two-stage gradient temperature control vertical vacuum furnace, and can implement a condensation scheme according to different impurities, thereby realizing the selective volatilization and dynamic condensation of the impurities and providing a “universal” high-value path for various tellurium-containing solid wastes.

[0024] The present application realizes deep deoxidation and synchronous sulfidation and volatilization of tellurium oxide by introducing a carbon-sulfur dual functional synergistic reducing agent at 450-650 DEG C and 1-10 Pa vacuum degree after micron-sized mechanical ball milling pretreatment of smelting slag containing 75-80% tellurium to 10-20 mu m, and one-step collection of crude tellurium is completed. Further, in the same vertical vacuum furnace, a two-stage temperature control volatilization process is adopted, and through fine control of temperature, pressure, heating rate and holding time, directional removal of impurities such as sulfur, sodium and arsenic is realized, and finally tellurium products with purity ≥99.99 wt% are obtained. Compared with the traditional "acid leaching-electrolysis" process, the process is shortened by 60%, and there is no secondary oxidation slag, which provides a general new path for resourceization of smelting slag and high value of scattered metals.

[0025] In summary, the present application realizes efficient separation and purification of high-purity tellurium with a purity of more than 99.99% (4N) from smelting slag by adopting a multi-reduction method, which can simultaneously realize efficient resource recovery and protection of metallurgical process solid waste slag, fully utilize smelting slag, and has simple whole process operation, no secondary oxidation slag, and provides a new idea for resource recovery and high-purification preparation of tellurium.

[0026] The present application relates to the field of scattered metal metallurgy and high-value utilization of secondary resources, and particularly relates to an integrated process based on carbon-sulfur dual functional synergistic reduction as a precursor and vacuum step-by-step volatilization purification, which is used for efficient separation and preparation of semiconductor-grade high-purity tellurium material from metallurgical smelting slag rich in tellurium oxide. The process is suitable for resource recovery of tellurium-containing solid waste generated in non-ferrous metal smelting process, and provides technical support for short process, low energy consumption and green extraction of scattered metals. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is the product change real object diagram of the process of vacuum synergistic reduction separation and purification of tellurium in Example 1. (a) is the real object diagram of the crude tellurium after reduction of the smelting slag; (b) is the enrichment area of impurities in the reduction process; (c) is the product tellurium obtained in the purification process; (d) is the transition stage real object of the two-stage heating area in the purification process;

[0028] Figure 2 It is a structure schematic diagram of a two-stage vacuum distillation furnace used in each embodiment of the present application. In the figure, 1 is a first heater; 2 is a material; 3 is a heat preservation filler; 4 is a second heater; 5 is a high-purity graphite crucible; 6 is a first graphite condenser tube; 7 is a vacuum device; 8 is a second graphite condenser tube; and 9 is an industrial cold water machine. DETAILED DESCRIPTION

[0029] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all terms used in the description employed herein have the same meaning as commonly understood by one of ordinary skill in the art. As used herein, the following professional terms are intended to have the following meanings.

[0031] Unless otherwise specified, various materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0032] The vacuum reaction device used in each embodiment is a two-stage vacuum distillation furnace (see Figure 2 ), the manufacturer is Shandong Gaomi Pute Electronic Equipment Co., Ltd., model PTVD-70, power 25KVA.

[0033] The composition of the smelted slag used in the following examples and comparative examples is shown in Table 1.

[0034] Table 1 Chemical composition of smelted slag (wt %)

[0035]

[0036] In each embodiment and comparative example, the carbon component of the carbon-sulfur dual functional synergistic reducing agent is high-purity graphite powder, and the carbon content is 99.99 wt%; the sulfur component is sublimed sulfur, and the purity is 99.9 wt%. In the carbon-sulfur dual functional synergistic reducing agent, the number of moles of sulfur is 80%-120% of the number of moles of carbon. Mixing method: the carbon component and the sulfur component are wetted with neutral water and then mixed.

[0037] Example 1:

[0038] The method for separating and purifying tellurium from smelted slag by a multi-component synergistic reduction in this embodiment comprises the following steps:

[0039] (1) After ball milling the smelted slag, smelted slag powder with a particle size D50 of 15 µm is obtained; 250 g of smelted slag powder is taken, and 25 g of carbon-sulfur dual functional synergistic reducing agent is added, wherein the molar ratio of carbon to sulfur is 1:1 (i.e. the number of moles of sulfur is 100% of the number of moles of carbon). The mechanical ball milling method is used for mixing for 30 minutes until the mixture is uniform, forming a reaction precursor;

[0040] The smelted slag ball milling is micron-level mechanical ball milling, and the rotation speed of the mechanical ball milling is 450 r / min. The ball-to-material ratio used in the ball milling is 8:1. The particle size D50 of the smelted slag powder obtained after ball milling is 15 µm.

[0041] (2) The mixed powder reaction precursor of step (1) is compacted, the surface is covered with a high-purity water protective film to prevent the phenomenon of material spraying, and is placed in a high-purity graphite crucible, the temperature of vacuum reduction is set to 650℃, the heating rate is 12℃ / min, the holding time is 8h, and the vacuum degree is 1~10Pa; a multi-property synergistic reduction reaction is carried out to make tellurium oxides undergo carbothermal reduction and deoxidation, and high-volatility impurity elements are volatilized into a second-stage graphite condensing tube by sulfidation, tellurium is introduced into a first-stage graphite condensing tube, and low-volatility impurity elements remain in the graphite crucible;

[0042] (3) The volatilized material (first-stage graphite condensing tube) after reduction in step (2) is collected, and 200g of the volatilized material is placed in a high-purity graphite crucible, the first-stage temperature is set to 600℃, the pressure is 1~10Pa, the heating rate is 15℃ / min, the holding time is 4h, the second-stage temperature is 300℃, the pressure is 1~10Pa, the heating rate is 6℃ / min, and the holding time is 4h;

[0043] (4) The volatilized material (first-stage graphite condensing tube) obtained in step (3) is subjected to ICP-MS detection to determine the average content of impurities and the average content of tellurium, and Table 2 is the detection result of the impurity element content of the product tellurium after purification in Example 1; Figure 1 The product change physical map of the process of vacuum synergistic reduction separation and purification of tellurium in Example 1. The present application mainly includes two stages of slag reduction and purification of the crude tellurium obtained after reduction; (a) is a crude tellurium physical map after slag reduction; (b) is an impurity enrichment area in the reduction process, indicating good impurity removal effect; (c) is the product tellurium obtained in the purification process; (d) is the transition stage of the two heating areas in the purification process.

[0044] Table 2 Product index (mg / kg) in Example 1

[0045]

[0046] In this embodiment, the volatilization rate and direct recovery rate of tellurium in the vacuum synergistic reduction process are 91.14% and 93.04% respectively, the purity of the obtained crude product tellurium is greater than 99.9%, which indicates that the vacuum synergistic reduction process effectively recovers tellurium from the slag, and the synergistic reducing agent has complementary thermal effects, which can selectively separate impurities and achieve self-heating balance of "slag heat energy supplementing reduction heat". Through two-stage temperature control in the purification process, the directional removal of impurities such as S, Na and As is realized, and the average purity of the obtained tellurium product is 99.9935%.

[0047] Therefore, the method for separating and purifying tellurium from slag in this embodiment by using the multi-property synergistic reduction method can provide a new idea for slag resource recovery and high-purity tellurium preparation.

[0048] Example 2:

[0049] The method for separating and purifying tellurium from smelting slag by a multi-element synergistic reduction method in the embodiment comprises the following steps:

[0050] (1) After ball milling of the smelting slag, smelting slag powder with a particle size D50 of 15 µm is obtained; 250 g of the smelting slag powder is taken, and a carbon-sulfur bifunctional synergistic reducing agent is added in an amount of 25 g, wherein the number of moles of sulfur is 80% of that of carbon. The mechanical ball milling method is used for mixing for 30 minutes until the mixture is uniform, and a reaction precursor is formed;

[0051] The ball milling of the smelting slag is micron-level mechanical ball milling, and the rotating speed of the mechanical ball milling is 450 r / min. The ball-to-material ratio used in the ball milling is 8:1. The particle size D50 of the smelting slag powder obtained after the ball milling is 15 µm.

[0052] (2) The powder mixed in step (1) is compacted, the surface is covered with a high-purity water protective film to prevent the phenomenon of material spraying, and is placed in a high-purity graphite crucible. The temperature for vacuum reduction is set to 600 ℃, the heating rate is 12 ℃ / min, the holding time is 8 h, and the vacuum degree is 1~10 Pa. A multi-element synergistic reduction reaction is carried out to make tellurium oxides undergo carbon thermal reduction and deoxidation, and high-volatility impurity elements are volatilized into a second-stage graphite condensing tube by sulfidation, tellurium enters a first-stage graphite condensing tube, and low-volatility impurity elements remain in the graphite crucible;

[0053] (3) The volatilized material (first-stage graphite condensing tube) after the reduction in step (2) is collected, and 200 g of the volatilized material is placed in a high-purity graphite crucible. The first-stage temperature is set to 650 ℃, the pressure is 1~10 Pa, the heating rate is 15 ℃ / min, the holding time is 4 h, the second-stage temperature is 250 ℃, the pressure is 1~10 Pa, the heating rate is 6 ℃ / min, and the holding time is 4 h;

[0054] (4) The volatilized material (first-stage graphite condensing tube) obtained in step (3) is subjected to ICP-MS detection to determine the average content of impurities and calculate the average content of tellurium. The results are shown in Table 3, which is the detection results of the impurity element content of the tellurium product after purification in Example 2.

[0055] Table 3 Product index (mg / kg) in Example 2

[0056]

[0057] In this embodiment, the volatilization rate and direct recovery rate of tellurium in the vacuum synergistic reduction process are 90.04% and 92.83% respectively, and the purity of the obtained crude tellurium product is greater than 99.9%, indicating that the vacuum synergistic reduction process effectively recovers tellurium from the smelting slag, and the heat effects of the synergistic reducing agents are complementary, which can selectively separate impurities and achieve self-heating balance of "using slag heat to compensate for reduction heat". The purification process realizes directional removal of impurities such as S, Na and As through two-stage temperature control, and the average purity of the obtained tellurium product is 99.9908%.

[0058] Example 3

[0059] The method for separating and purifying tellurium from smelting slag by a multi-phase synergistic reduction method in this embodiment includes the following steps:

[0060] (1) After ball milling the smelting slag, smelting slag powder with a particle size D50 of 15 µm is obtained; 250 g of the smelting slag powder is taken, and a carbon-sulfur dual-function synergistic reduction precursor is added, with an addition amount of 25 g, wherein the number of moles of sulfur is 120% of that of carbon. The mechanical ball milling method is used for mixing for 30 minutes until the mixture is uniform, forming a reaction precursor;

[0061] The smelting slag ball milling is micron-level mechanical ball milling, and the rotating speed of the mechanical ball milling is 450 r / min. The ball-to-material ratio used in the ball milling is 8:1. The particle size D50 of the smelting slag powder obtained after the ball milling is 15 µm.

[0062] (2) The mixed powder reaction precursor in step (1) is compacted, the surface is covered with a high-purity water protective film to prevent the phenomenon of material spraying, and is placed in a high-purity graphite crucible. The temperature for vacuum reduction is set to 650℃, the heating rate is 12℃ / min, the holding time is 8h, and the vacuum degree is 1~10Pa; a multi-phase synergistic reduction reaction is carried out, so that the tellurium oxide is subjected to carbon thermal reduction and deoxidation, and the high-volatility impurity elements are volatilized and enter the second-stage graphite condensing tube, while the tellurium enters the first-stage graphite condensing tube, and the low-volatility impurity elements remain in the graphite crucible;

[0063] (3) The volatilized material (first-stage graphite condensing tube) after the reduction in step (2) is collected, and 200 g of the volatilized material is placed in a high-purity graphite crucible. The first-stage temperature is set to 550℃, the pressure is 1~10Pa, the heating rate is 15℃ / min, the holding time is 4h, the second-stage temperature is 200℃, the pressure is 1~10Pa, the heating rate is 6℃ / min, and the holding time is 4h;

[0064] (4) The volatilized material (first-stage graphite condensing tube) obtained in step (3) is subjected to ICP-MS detection to determine the average content of impurities and calculate the average content of tellurium, and the results are shown in Table 3.

[0065] Table 4 Product indexes (mg / kg) in Example 3

[0066]

[0067] In this embodiment, the volatilization rate and direct recovery rate of tellurium in the vacuum synergistic reduction process are 88.64% and 91.94% respectively, and the purity of the obtained crude tellurium product is greater than 99.9%, indicating that the vacuum synergistic reduction process effectively recovers tellurium from the smelting slag, and the complementary thermal effects of the synergistic reducing agent can selectively separate impurities and achieve self-heating balance of "smelting slag heat energy to complement reduction heat". The purification process realizes directional removal of impurities such as S, Na and As through two-stage temperature control, and the average purity of the obtained tellurium product is 99.9916%.

[0068] Comparative Example:

[0069] In this comparative example, a traditional carbon reduction method for separating and purifying tellurium from smelting slag includes the following steps:

[0070] (1) After ball milling the smelting slag, smelting slag powder with a particle size D50 of 15 µm is obtained; 250 g of smelting slag powder is taken and carbon is added as a reducing agent, with an addition amount of 25 g. The mechanical ball milling method is used for mixing for 30 minutes until the mixture is uniform, forming a reaction precursor; the smelting slag ball milling is micron-level mechanical ball milling, and the rotation speed of the mechanical ball milling is 450 r / min. The ball-to-material ratio used in the ball milling is 8:1. The particle size D50 of the smelting slag powder obtained after ball milling is 15 µm.

[0071] (2) The powder after mixing in step (1) is compacted, the surface is covered with a high-purity water protective film to prevent the phenomenon of material spraying, and is placed in a high-purity graphite crucible, with a vacuum reduction temperature of 650℃, a heating rate of 12℃ / min, a holding time of 8h, and a vacuum degree of 1~10Pa;

[0072] (3) The volatilized material after reduction in step (2) (first-stage graphite condenser) is collected, and 200 g of the volatilized material is placed in a high-purity graphite crucible, with a heating temperature of 600℃, a pressure of 1~10Pa, a heating rate of 15℃ / min, and a holding time of 4h;

[0073] (4) The volatilized material (first-stage graphite condenser) obtained in step (3) is subjected to ICP-MS detection to determine the average content of impurities and calculate the average content of tellurium, and the results are shown in Table 5.

[0074] Table 5 Product indicators in the comparative example (mg / kg)

[0075]

[0076] Note: The improvement effect is calculated as Cr %= (17.04-12.91) / 12.91*100%

[0077] In the present comparative example, the reducing agent used is a conventional carbon reducing agent, and the conventional primary vacuum distillation used in the purification process has a tellurium volatilization rate and a direct recovery rate of 63.17% and 70.64%, respectively. The purity of the obtained crude tellurium product is only 99.9%, and the removal effect of each impurity element in the tellurium is much lower than that in Example 1. The increase rates of Fe, Cu, Na, Pb, Bi and Se relative to Example 1 are all above 1000%, indicating that the effect of recovering tellurium from smelting and casting slag in the conventional vacuum carbon thermal reduction process is much worse than that of the synergistic reduction of the present application, and subsequent vacuum distillation must be performed again. The present application uses carbon-sulfur dual functional synergistic reduction precursors, and the reduction process uses coupled reducing agents. The purification process is controlled by two-stage temperature gradient, which greatly simplifies the traditional process, improves the industrial efficiency, greatly simplifies the process of separating, recovering and purifying high-purity tellurium from secondary resources, and is a novel method in line with the concept of green metallurgy.

Claims

1. A method for separating and purifying tellurium from molten casting slag through multi-property synergistic reduction, characterized in that, The process includes the following steps: ball milling the molten casting slag to obtain molten casting slag powder with a relatively uniform particle size distribution; uniformly mixing the obtained molten casting slag powder with a carbon-sulfur bifunctional synergistic reducing agent in a certain proportion to form a reaction precursor; placing the reaction precursor in a vacuum reaction device and carrying out a multi-functional synergistic reduction reaction under specific temperature, vacuum degree and heating program, causing tellurium oxide to undergo carbothermic reduction deoxidation, while impurity elements undergo sulfidation volatilization, and collecting the volatile products to obtain crude tellurium; and subjecting the obtained crude tellurium to a two-stage stepped temperature-controlled volatilization process to achieve selective volatilization of impurities and recondensation purification of tellurium under different temperature zones and pressure conditions, finally obtaining high-purity tellurium with a purity ≥99.99 wt%.

2. The method for separating and purifying tellurium from smelting slag through multi-property synergistic reduction according to claim 1, characterized in that, The vacuum reaction apparatus is a two-stage vacuum distillation furnace. In the multi-property synergistic reduction reaction, highly volatile impurities preferentially volatilize into the second-stage graphite condenser and separate from tellurium, while tellurium volatilizes into the first-stage graphite condenser. Low-volatile impurities do not volatilize and remain in the graphite crucible. During the crude tellurium purification process, after a two-stage stepped temperature-controlled volatilization, highly volatile impurities volatilize into the second-stage graphite condenser and separate from tellurium, while tellurium volatilizes into the first-stage graphite condenser. Low-volatile impurities do not volatilize and remain in the graphite crucible.

3. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, The ball milling is a micron-level mechanical ball milling with a rotation speed of 450~650 r / min; and / or, the ball-to-material ratio used in the ball milling is 5:1~10:1; and / or, the particle size D50 of the molten casting slag powder obtained after ball milling is 10~20µm.

4. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, The carbon-sulfur bifunctional synergistic reducing agent uses high-purity graphite powder as the carbon component, with a carbon content of not less than 99.99 wt%; the sulfur component is sublimed sulfur with a purity of not less than 99.9 wt%.

5. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, In the carbon-sulfur bifunctional synergistic reducing agent, the molar number of sulfur is 80%-120% of that of carbon; mixing method: wet the carbon component and the sulfur component with neutral water and then mix.

6. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, The mixing method is mechanical dry mixing, and the mixing time is not less than 30 minutes; and / or, the total amount of carbon-sulfur bifunctional synergistic reducing agent added is 5%-15% of the mass of the molten casting slag.

7. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, The chemical composition of the slag includes: Te 75~80%, O 16~18%, and the contents of Fe, Si, Cu, Al, Pb, Bi, Se, As, and Mg are all <1%.

8. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, The temperature of the multi-functional synergistic reduction reaction is 450~650℃, the heating rate is 8~15℃ / min, the holding time is 6~10h, and the vacuum degree is 1~10Pa.

9. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 1 or 2, characterized in that, The heating method used for vacuum purification of crude tellurium is a two-stage stepped temperature control.

10. The method for separating and purifying tellurium from smelting slag by multi-property synergistic reduction according to claim 9, characterized in that, In the two-stage stepped temperature control, the first stage has a temperature of 500~650℃, a pressure of 1~10Pa, a heating rate of 8~15℃ / min, and a holding time of 2~4h; the second stage has a temperature of 200~350℃, a pressure of 1~10Pa, a heating rate of 3~6℃ / min, and a holding time of 2~4h.

Images