Silver refining method for pyrogenic tellurium removal

Abstract

The invention belongs to the field of precious metal pyrometallurgy, and particularly relates to a silver refining method for pyrogenic tellurium removal, which comprises the following steps: drying tellurium-containing silver alloy, crushing into powder after drying, weighing, adding tellurium removal agents sodium carbonate and sodium nitrate, fully stirring, uniformly mixing, adding into an intermediate frequency furnace, controlling the smelting temperature to be 1025 + / -25 DEG C and 1125 + / -2 DEG C, keeping the constant temperature for more than 60 minutes, and cooling to room temperature; a titanium rod is used for stirring during the constant temperature period, cooling is carried out after the constant temperature is finished, a crucible is used for slag receiving treatment, a casting cake obtained after residues are poured out is the reduced silver ingot, the tellurium removal rate is higher than 99.9% by using the method, and the obtained silver ingot meets the national standard IC-Ag99.99 silver standard and the new national standard IC-Ag99.999 standard.

Description

Technical Field

[0001] The invention belongs to the field of precious metal pyrometallurgy, and in particular relates to a method for refining silver by removing tellurium through pyrometallurgy. Background Art

[0002] Tellurium is a metalloid with a crustal abundance of l×10 -7 %, and no independent industrial minerals containing tellurium have been found. Tellurium ore resources are sparsely distributed, mostly associated with other minerals or existing in other mines as impurities, with a content of only 0.001%-0.1%; the main tellurium minerals are tellurium lead ore, tellurium bismuth ore, tellurium bismuth ore, tellurium gold ore, tellurium copper ore, etc. Although the grade of tellurium is low, the floatability of this type of mineral is good. In silver purification, the more mature process is that after the tellurium-containing gold concentrate is leached by cyanide and replaced by zinc powder, part of the tellurium is enriched in the anode mud, and the anode mud is cast into anode plates for electrolysis to obtain high-purity silver and anode mud slag, and the tellurium element enters the electrolyte, anode mud slag and high-purity silver. The main effects of tellurium on the refining process are: first, it affects the quality of electrolytic silver powder, causing the tellurium content in the electrolytic silver to exceed the standard and not meet the national standard 2# silver; second, it seriously pollutes the electrolyte and increases the frequency of electrolyte purification.

[0003] Existing methods of tellurium precipitation cannot meet production requirements and process flow in many aspects. For example, CN113201650A discloses a process for treating high-silver tellurium-containing anode mud, which first uses a wet method to separate gold and silver, and then adds a pyrometallurgical alkaline smelting slag to remove tellurium. A large amount of reducing agent needs to be added, the process flow is long, the operation is complicated, and the tellurium of electrolytic silver product quality needs to be treated by at least two alkaline smelting slag removal methods, which greatly prolongs the production cycle, has a low reduction rate, and is not conducive to industrial production; after treatment by this process, the tellurium content of silver powder is reduced to 0.0008%, which can only reach the national standard IC-Ag99.99. In most of the national standard No. 2 silver ingots and below sold from tellurium-gold ores in China, the tellurium content is almost around 0.001%. If the new national standard IC-Ag99.999 standard (Te≤0.00005%) is to be achieved, the tellurium content must be further reduced. How to further reduce the tellurium content is an important research topic in this industry. Summary of the invention

[0004] The purpose of the present invention is to provide a method for refining silver by pyrometallurgical detellurization in view of the shortcomings of the above-mentioned prior art, which can further reduce the tellurium content in silver powder to above the national standard IC-Ag99.99.

[0005] The specific technical scheme is: a method for refining silver by fire-removing tellurium, comprising the following steps: (1) drying the tellurium-containing silver alloy, crushing and sieving to obtain tellurium-containing silver powder; (2) weighing the tellurium-containing silver powder, adding tellurium-removing agents sodium carbonate and sodium nitrate, and mixing them evenly; (3) adding the mixture in step (2) into a medium frequency furnace, controlling the temperature at 1025±25℃ and 1125±2℃, and maintaining the temperature for more than 60 minutes; (4) stirring with a titanium rod during the constant temperature process, cooling for more than 5 minutes after the constant temperature ends, using a crucible for slag treatment, and pouring out the residue to obtain a reduced silver ingot, wherein the tellurium content of the reduced silver ingot is ≤0.0008% and ≤0.00005%.

[0006] Furthermore, in step (1), the tellurium-containing silver alloy is crushed and then passed through a 100-mesh sieve.

[0007] Furthermore, in step (2), the amount of sodium carbonate added as a tellurium removal agent is 5-6% by weight of the tellurium-containing silver powder, and the amount of sodium nitrate added is 3-4% by weight of the tellurium-containing silver powder.

[0008] Furthermore, in step (4), a titanium rod is used for stirring, and the stirring frequency is 10 min / time.

[0009] The present invention dries the tellurium-containing silver alloy and crushes it into powder, adds 5-6% sodium carbonate and 3-4% sodium nitrate as tellurium removal agents based on the weight of the tellurium-containing silver powder, mixes and puts it into a medium frequency furnace for constant temperature, and smelts it by precise temperature control and stirring, so that tellurium in the tellurium-containing silver alloy can be effectively separated. Compared with the existing technology, the process flow of the present invention is simple, the reagents and equipment used are simple, and the operation is easy. The tellurium removal rate in the silver alloy can reach 99.9%, and the obtained silver ingot meets the national standard IC-Ag99.99 silver standard and the new national standard IC-Ag99.999 standard.

[0010] (1) In the present invention, the tellurium removal agent is composed of 5-6% sodium carbonate and 3-4% sodium nitrate containing tellurium silver powder by total weight, the temperature is 1125±2°C, the heat preservation time is more than 60 minutes, and the silver powder is stirred to obtain the new national standard IC-Ag99.999 silver standard (tellurium ≤ 0.00005%); (2) In the present invention, the tellurium content in the reduced silver powder obtained is 0.0008% by mass (IC-Ag99.99 silver standard) when the detellurization agent is 5-6% sodium carbonate and 3-4% sodium nitrate, the temperature is 1025±25°C, the heat preservation time is more than 60 minutes, and the mixture is stirred. (3) The tellurium removal rate of the reduced silver powder obtained by the present invention exceeds 99.9%.

[0011] (4) The present invention has a leading technological level for the purification of rare and precious metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the national standard 1# silver standard Figure 2 Tellurium content test results report DETAILED DESCRIPTION

[0013] Examples 1 to 8 are carried out according to the following steps: (1) Dry the silver alloy containing 0.48% tellurium, crush it and pass it through a 100-mesh sieve to obtain tellurium-containing silver powder; (2) Take 10 kg of tellurium-containing silver powder, add tellurium-removing agents sodium carbonate and sodium nitrate, and mix them evenly; (3) Add the silver powder mixed with the tellurium-removing agent into a medium-frequency furnace, control the reaction temperature, and keep the constant temperature reaction time for 60 minutes; (4) Start stirring with a titanium rod at the 30th minute of the constant temperature, and the stirring frequency is 10 minutes / time, that is, stir once at the 30th minute, 40th minute, 50th minute, and 60th minute of the constant temperature. After the constant temperature ends, cool it for 5 minutes, use a crucible to collect slag, and pour out the residue to obtain a cast cake as a reduced silver ingot. The tellurium content in the obtained reduced silver ingot is tested. Table 1 shows the parameters and tellurium removal results of Examples 1-8.

[0014] Table 1 Parameters and results of Examples 1 to 8

[0015] In Examples 1 and 2, a tellurium removal agent of 5-6% sodium carbonate + 3-4% sodium nitrate is added according to the weight of tellurium-containing silver powder, the reaction temperature of the medium frequency furnace is controlled at 1123 and 1125°C (the applicant found that the temperature is controlled at 1125°C plus or minus 2°C), the constant temperature reaction time is 60-65min, and the titanium rod is used to stir once at the 30th, 40th, 50th and 60th minutes of the constant temperature. Under the conditions, 99.9% of the tellurium element in the silver powder can be removed, and the obtained silver ingot meets the new national standard IC-Ag99.999 standard (tellurium ≤ 0.00005%).

[0016] In Examples 3 and 4, a tellurium removal agent of 5-6% sodium carbonate + 3-4% sodium nitrate was added according to the weight of tellurium-containing silver powder, the reaction temperature of the medium frequency furnace was controlled at 1000 and 1050°C (the applicant found that the temperature was controlled at 1025°C plus or minus 25°C), the constant temperature reaction time was 60-70 minutes, and the titanium rod was used to stir once at the 30th, 40th, 50th, and 60th minutes of the constant temperature. Under the conditions, most of the tellurium elements in the silver powder can be removed, and the obtained silver ingot meets the new national standard IC-Ag99.99 standard (tellurium ≤ 0.0008%). The applicant found that as the reaction temperature is further reduced, the tellurium removal efficiency will decrease accordingly.

[0017] In Examples 5-8, the reaction temperature of the medium frequency furnace was controlled at 1125°C, the constant temperature reaction time was 60 min, and the reaction was stirred once with a titanium rod at 30 min, 40 min, 50 min, and 60 min. The amount of the tellurium removal agent was adjusted. It was found that too high or too low an amount was not conducive to the removal of tellurium from the silver powder.

[0018] In summary, the present invention adds 5-6% sodium carbonate and 3-4% sodium nitrate as tellurium removal agents, the reaction temperature is 1125±2℃ constant temperature for 60min, and the condition of constant temperature stirring can effectively remove tellurium from silver powder to obtain a silver ingot that meets the new national standard IC-Ag99.999 (tellurium ≤ 0.00005%); the reaction temperature is 1025±25℃ constant temperature for 60min, and the condition of constant temperature stirring can effectively remove tellurium from silver powder to obtain a silver ingot that meets the national standard IC-Ag99.99 (tellurium ≤ 0.0008%). The increase or decrease of the reaction temperature will affect the tellurium removal efficiency. The amount of sodium carbonate and sodium nitrate added will also have a great impact on the tellurium removal efficiency. Compared with the prior art, the method adopted by the present invention has simple process, easy operation, low cost, and is at the leading level in the industry.

Claims

1. A method for refining silver by removing tellurium through pyrometallurgy, characterized in that: The following steps are involved: (1) preparing tellurium-containing silver alloy into tellurium-containing silver powder; (2) adding detellurization agents sodium carbonate and sodium nitrate to the tellurium-containing silver powder and mixing them evenly, wherein the amount of sodium carbonate added is 5-6% by weight of the tellurium-containing silver powder, and the amount of sodium nitrate added is 3-4% by weight of the tellurium-containing silver powder; (3) Add the mixture from step (2) into a medium frequency furnace and control the temperature at 1025±25°C for more than 60 minutes; (4) Stirring during the constant temperature process, cooling after the constant temperature ends, and removing the slag to obtain a reduced silver ingot with a tellurium content of ≤0.0008%, which meets the national standard IC-Ag99.99 silver standard, and the tellurium content is measured in mass percentage.

2. A method for refining silver by removing tellurium through pyrometallurgy, characterized in that: The following steps are involved: (1) preparing tellurium-containing silver alloy into tellurium-containing silver powder; (2) adding detellurization agents sodium carbonate and sodium nitrate to the tellurium-containing silver powder and mixing them evenly, wherein the amount of sodium carbonate added is 5-6% by weight of the tellurium-containing silver powder, and the amount of sodium nitrate added is 3-4% by weight of the tellurium-containing silver powder; (3) Add the mixture from step (2) into a medium frequency furnace and control the temperature at 1125±2°C for more than 60 minutes; (4) Stirring during the constant temperature process, cooling after the constant temperature ends, and removing the slag to obtain a reduced silver ingot with a tellurium content of ≤0.00005%, which meets the new national standard IC-Ag99.999 silver standard, and the tellurium content is measured in mass percentage.

3. A method for refining silver by removing tellurium by pyrometallurgy according to claim 1 or 2, characterized in that: In step (1), the tellurium-silver alloy is crushed and then passed through a 100-mesh sieve.

4. The method for refining silver by removing tellurium by pyrometallurgy according to claim 3, characterized in that: In step (4), a titanium rod is used for stirring, and the stirring frequency is 10 min / time.

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