Method for reducing lead grade in crude bismuth

Abstract

The invention discloses a method for reducing the grade of lead in crude bismuth. The method comprises the following steps: 1) melting the crude bismuth; 2) oxidizing and refining to remove arsenic and antimony; 3) adding alkali to remove tellurium; and 4) removing lead by using quartz sand, namely controlling the temperature of the bismuth pot to be 350-400 DEG C, introducing compressed air, positively and negatively stirring for 8-9 hours in different directions by using a stirrer, adding the quartz sand while stirring to enable the generated lead silicate to float on the surface, and removing slag manually to obtain the lead-removed bismuth. According to the method, no waste gas is produced in the lead removal process, the field operation environment is friendly, the energy consumption is greatly reduced, and the lead removal cost is greatly reduced; according to the method, quartz sand is adopted to remove lead, and a proper reaction temperature is matched, so that not only can the formation of lead silicate be effectively promoted, but also the formation of bismuth silicate can be effectively inhibited, further the lead removal effect can be effectively improved, the lead grade is reduced, and the bismuth grade is improved; the quartz sand is not easy to decompose in the reaction process, the utilization rate of the quartz sand is high, the cost of removing lead from crude bismuth is reduced, and the method is suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of crude bismuth impurity removal, and in particular to a method for reducing the lead grade in crude bismuth. Background Art

[0002] As a green metal, bismuth is mainly used in metallurgy, chemical industry, nuclear industry and other fields. Crude bismuth is the direct raw material for the production of bismuth ingots. The main impurities in crude bismuth are Pb, As, Sb, Te, etc. Impurity lead is a key factor affecting the refining production cycle and production cost of crude bismuth. Therefore, it is necessary to effectively control the grade of impurity lead in crude bismuth to shorten the refining cycle of crude bismuth and reduce the refining cost of crude bismuth.

[0003] In order to solve the above technical problems, there are many existing technologies for lead removal. For example:

[0004] CN202110108548.8 discloses a method for efficient lead removal during bismuth refining. The method first adds alkali to remove impurities such as arsenic, antimony, and copper, and then preliminarily removes lead by introducing chlorine gas. When the lead content drops to 1%, a vacuum distillation furnace is used. Finally, borax and an impurity remover (one or both of ammonium dihydrogen phosphate and potassium dihydrogen phosphate) are added for deep lead removal.

[0005] The method is used for removing lead during bismuth refining. Chlorine is first used for removing lead, and then one or both of ammonium dihydrogen phosphate and potassium dihydrogen phosphate are used for removing lead. Chlorine removal of lead will cause a large amount of chlorine to be contained in the crude bismuth, which is highly corrosive to the equipment during the distillation process, has high equipment maintenance costs, and has a bad on-site environment. At the same time, the required temperature for vacuum distillation is high, and the cost of lead removal is high. When ammonium dihydrogen phosphate and potassium dihydrogen phosphate are used for lead removal, at the reaction temperature of 500-600°C, the impurity remover is very easy to decompose, resulting in a significant increase in the amount used, and the price is expensive, so it is only suitable for trace lead removal, and is not suitable for large-scale lead removal.

[0006] CN201910317277.X discloses a Kaldo furnace oxygen-enriched blowing method, comprising the following steps: inserting a blowing lance with a Laval nozzle into the Kaldo furnace; connecting the pure oxygen pipeline with the compressed air pipeline to obtain oxygen-enriched air; adding quartz sand, passing oxygen-enriched air, reacting at a temperature of 1100°C to 1200°C for 40min to 60min, releasing the blowing slag, sampling and testing, until the lead content is less than 5%; passing oxygen-enriched air, reacting at a temperature of 1100°C to 1200°C for 120min to 180min, releasing the blowing slag, sampling and testing, until the selenium content is less than 2%; adding 20kg to 80kg of sodium carbonate, passing oxygen-enriched air, reacting at a temperature of 1100°C to 1200°C for 40min to 60min, releasing the blowing slag, sampling and testing, until the selenium, tellurium, lead, antimony and bismuth contents are all less than 0.01%, and the copper content is less than 1.5%.

[0007] The method is used for removing selenium, tellurium, lead, antimony and bismuth when smelting copper anode mud. The method adopts quartz sand lead removal technology to reduce the lead content, and the temperature of quartz sand lead removal is 1100-1200°C. When the quartz sand lead removal technology is applied to remove impurity lead in crude bismuth at this temperature, it is found that the quartz sand lead removal temperature is much higher than the conventional distillation lead removal temperature, which greatly increases energy consumption and greatly increases equipment requirements. Moreover, when quartz sand is used to remove lead at this temperature, bismuth will form bismuth silicate and be removed, which reduces the direct recovery of bismuth, and the formation of bismuth silicate will also reduce the lead removal effect, thereby greatly reducing the grade of bismuth. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for reducing the lead grade in crude bismuth, which can effectively reduce the lead grade in crude bismuth and greatly improve the bismuth grade and direct recovery rate.

[0009] The technical solution adopted by the present invention to solve the technical problem is: a method for reducing the lead grade in crude bismuth, comprising the following steps:

[0010] 1) Melting crude bismuth;

[0011] 2) Oxidative refining to remove arsenic and antimony;

[0012] 3) Add alkali to remove tellurium;

[0013] 4) Lead removal by quartz sand: Control the temperature of the bismuth pot to 350-400°C, introduce compressed air, and use a stirrer to stir in different directions for 8-9 hours. Add quartz sand while stirring to make the generated lead silicate float on the surface, remove the slag manually, and obtain lead-free bismuth.

[0014] In the method of the present invention, arsenic, antimony and tellurium in crude bismuth are first removed by oxidation refining and alkali treatment before quartz sand is used for lead removal. The reason is that when quartz sand is used for lead removal, if the reaction substrate contains a large amount of arsenic, antimony and tellurium, these impurities will affect the floating of lead silicate to the surface, greatly reducing the effect of quartz sand for lead removal, prolonging the reaction time of quartz sand for lead removal, and at the same time, it is not conducive to the subsequent vacuum distillation for silver separation.

[0015] The inventors found in the experimental process that when the temperature of quartz sand for lead removal is 350-400°C, the oxidation order of impurities is Pb, Bi, and Cu, and the elemental lead in the crude bismuth can be preferentially oxidized to PbO, and then the silicon dioxide in the quartz sand reacts with lead oxide to form lead silicate. Since the density of lead silicate is less than that of bismuth, it will float on the surface and be removed by artificial slag removal to achieve the purpose of lead removal.

[0016] When the temperature is lower than 350℃, the melting rate of crude bismuth will be slow, which is not conducive to the reaction;

[0017] When the temperature is higher than 400°C, not only will the reaction rate decrease, resulting in an extension of the reaction time and a significant increase in energy consumption; the inventors have also found that the degree of oxidation of bismuth will also increase significantly, causing a significant increase in the amount of bismuth silicate formed by combining with silicon dioxide, thereby reducing the combination of silicon dioxide and lead oxide, weakening the removal effect of lead, and greatly improving the bismuth grade in lead silicate slag; in addition, bismuth silicate will also be removed when the slag is removed, resulting in an increase in the loss of bismuth, thereby greatly reducing the direct recovery rate of bismuth.

[0018] Further, the crude bismuth is put into a bismuth pot, the temperature of the bismuth pot is controlled to be 500-600° C. for melting, and the surface molten slag is removed after it is completely melted.

[0019] Further, the specific operation steps of step 2) are: controlling the temperature of the bismuth pot to 650-750°C, introducing compressed air into the bismuth pot, and the flow rate of the compressed air is 800m 3 / h, react for 48h-72h, oxidize arsenic and antimony and volatilize in the form of arsenic oxide and antimony oxide.

[0020] Furthermore, the specific operation steps of step 3) are: controlling the temperature of the bismuth pot to 500-600° C., adding alkali to remove tellurium, reacting for 8h-10h, and removing tellurium slag in time.

[0021] Furthermore, the alkali is flake alkali.

[0022] Furthermore, the flow rate of the compressed air in step 4) is 800m 3 / h.

[0023] Furthermore, the particle size of the quartz sand is 0.8-1.5 mm, and the content of silicon dioxide contained in the quartz sand is ≥99%.

[0024] The particle size of quartz sand mainly affects the reaction surface area and pore structure between substances, thus affecting the removal efficiency of lead. When the particle size is greater than 1.5mm, the larger the particle, the smaller its reaction surface area, and the lead adsorption capacity is greatly reduced; when the particle size is less than 0.8mm, part of the quartz sand is sucked into the dust collection system during the addition process, which greatly reduces the utilization rate of the quartz sand and also reduces the removal effect of lead.

[0025] The main component of quartz sand is silicon dioxide, and it also contains impurity elements such as iron, aluminum, and zinc. The lower the silicon dioxide content, the more other impurity elements there are, which greatly increases the refining time and difficulty in the production of refined bismuth.

[0026] Preferably, the particle size of the quartz sand is 1.0 mm.

[0027] Preferably, the temperature in step 4) is 400° C. and the stirring time is 8 hours.

[0028] Furthermore, the quartz sand is added into the bismuth pot in equal amounts in 2-3 batches.

[0029] Adding quartz sand in batches can make the quartz sand react deeply with the lead oxide in the melt, thereby improving the utilization rate of the quartz sand. Since the density of quartz sand is relatively low, if it is added all at once, part of the quartz sand will be isolated to the surface by the lead silicate slag produced by the reaction and cannot participate in the reaction, thereby reducing the lead removal effect.

[0030] Furthermore, the total amount of the quartz sand is 40-60 kg / t crude bismuth.

[0031] Beneficial effects of the method for reducing the lead grade in crude bismuth of the present invention:

[0032] (1) The method is simple to operate, no waste gas is produced during the lead removal process, the maximum temperature used in the entire method does not exceed 750°C, the on-site operation environment is friendly, the energy consumption is greatly reduced, and the equipment requirements are greatly reduced, which greatly reduces the cost of lead removal;

[0033] (2) In this method, quartz sand is used to remove lead and the reaction temperature is appropriately adjusted, which can not only effectively promote the formation of lead silicate, but also effectively inhibit the formation of bismuth silicate, thereby effectively improving the removal effect of lead, greatly reducing the grade of lead, and improving the grade and direct recovery rate of bismuth;

[0034] (3) When the method uses quartz sand to remove lead, the quartz sand is not easy to decompose during the reaction process, and the utilization rate of the quartz sand is high, which can effectively reduce the use of the impurity remover and reduce the cost of removing lead from crude bismuth, and is suitable for large-scale production. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to examples, but these specific embodiments do not limit the protection scope of the present invention in any way.

[0036] Example 1

[0037] A method for reducing the lead grade in crude bismuth comprises the following steps:

[0038] 1) Melting crude bismuth: 15t crude bismuth is loaded into a bismuth pot, and the temperature of the bismuth pot is controlled to be 500-600°C for melting. After complete melting, the surface molten slag is removed to obtain melt 1;

[0039] 2) Oxidation refining to remove arsenic and antimony: Control the temperature of the bismuth pot to 650-750℃, and introduce compressed air into the bismuth pot with a flow rate of 800m 3 / h, react for 48h-72h (specifically 60h in this embodiment), oxidize arsenic and antimony and volatilize in the form of arsenic oxide and antimony oxide to obtain melt 2;

[0040] 3) Adding alkali to remove tellurium: Control the temperature of the bismuth pot to 500-600° C., add caustic soda flakes, the amount of which is 90-100 kg / t crude bismuth (specifically 95 kg / t crude bismuth in this embodiment) to remove tellurium, react for 8 h-10 h (specifically 9 h in this embodiment), remove tellurium slag in time, and obtain melt 3;

[0041] 4) Lead removal by quartz sand: Control the temperature of the bismuth pot to 400°C and continue to introduce compressed air at a flow rate of 800m 3 / h, stirring in different directions of a stirrer for 8h, adding quartz sand with a particle size of 1.0mm (containing a silicon dioxide content of ≥99%) in equal amounts in two times while stirring, that is, 30kg / t crude bismuth (specifically 450kg quartz sand in this embodiment) is added at the beginning of the reaction, and then after reacting for 4h, the lead silicate slag floating to the surface in the pot is scooped out and then the remaining quartz sand is added, the total amount of quartz sand is 60kg / t crude bismuth (specifically 900kg quartz sand in this embodiment), so that the generated lead silicate floats on the surface, and the slag is removed manually to obtain lead-free bismuth, which is bismuth with lead removed.

[0042] Example 2

[0043] The difference between this embodiment and embodiment 1 is that: the temperature used in step 4) of removing lead from quartz sand is 350° C., and the total amount of quartz sand used is 40 kg / t of crude bismuth.

[0044] Example 3

[0045] The difference between this embodiment and embodiment 1 is that the temperature used in step 4) of removing lead from quartz sand is 400° C., and the total amount of quartz sand used is 50 kg / t of crude bismuth.

[0046] Example 4

[0047] The difference between this embodiment and embodiment 1 is that: in step 4), the quartz sand in the quartz sand lead removal is added in three equal batches, that is, 20 kg / t crude bismuth (specifically 450 kg quartz sand in this embodiment) is added at the beginning of the reaction, and then 20 kg / t crude bismuth is added after the lead silicate slag floating to the surface in the pot is scooped out after reacting for 3 hours, and the remaining quartz sand is added after the lead silicate slag floating to the surface in the pot is scooped out after reacting for another 3 hours.

[0048] The present invention measures the grade of each impurity element in crude bismuth and the grade of each impurity element in melt 2, melt 3 and lead-removed bismuth of Examples 1-4 (grade = weight of each impurity element in lead-removed bismuth / weight of lead-removed bismuth × 100%). The measurement method refers to GB T 915-2010 Bismuth. The results are shown in Table 1:

[0049] Table 1 Grades of impurity elements in crude bismuth, melt 2, melt 3 and lead-free bismuth of Examples 1-4

[0050]

[0051]

[0052] The direct recovery rate, lead removal rate and energy consumption of crude bismuth corresponding to Examples 1-4 are shown in Table 2, where lead removal rate = (weight of lead in crude bismuth - weight of lead in lead-removed bismuth) / weight of lead in crude bismuth × 100%, direct recovery rate = weight of lead in lead-removed bismuth / weight of lead in crude bismuth * 100%.

[0053] Table 2 Direct recovery rate, lead removal rate, energy consumption of Examples 1-4

[0054]

[0055] It can be seen from Table 1 and Table 2 that when the method of the present invention (Examples 1-4) is used to reduce the lead in crude bismuth, not only can the bismuth grade in the obtained lead-removed bismuth reach more than 84%, and the lead grade can be reduced to less than 7%, but also the direct recovery rate of bismuth can reach more than 90%, so that the bismuth in the crude bismuth can be effectively and fully enriched and recovered;

[0056] In addition, the method of the present invention can also maintain the energy consumption of the lead removal process of refined bismuth at 540m 3 Natural gas / ton of crude bismuth, and the cost is controlled below 2,500 yuan, which can save energy and cost while ensuring good lead removal effect.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that: in step 4), the traditional vacuum distillation method is used to remove lead. The specific operation steps are: the melt obtained after adding alkali to remove tellurium is transferred to a vacuum distillation furnace, and the temperature in the furnace is controlled to be 920°C and the vacuum degree is 40Pa. Distillation is carried out, and reflux condensation is performed to achieve lead removal.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is that step 3) and step 4) are performed simultaneously, that is, the temperature of the bismuth pot is controlled to be 400° C., and compressed air is continuously introduced into the molten liquid in the bismuth pot after the treatment in step 2) at a flow rate of 800 m / s. 3 / h, stir in different directions of a stirrer for 8h, add caustic soda flakes and quartz sand with a particle size of 1.0mm (containing a silicon dioxide content of ≥99%), the amount of caustic soda flakes is 95kg / t crude bismuth, and the quartz sand is added in equal amounts while stirring in 2 times, that is, 30kg / t crude bismuth (specifically 450kg quartz sand in this embodiment) and caustic soda flakes are added at the beginning of the reaction, and then the remaining quartz sand is added after reacting for 4h, and the total amount of quartz sand is 60kg / t crude bismuth, so that the generated lead silicate floats on the surface, and the slag is removed manually to obtain lead-removed bismuth.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 1 is that the quartz sand in step 4) is added into the bismuth pot at one time, and the specific operation steps are as follows: the temperature of the bismuth pot is controlled to be 400°C, and compressed air is continuously introduced, and the flow rate of the compressed air is 800m 3 / h, stir in different directions of a stirrer for 8h, add quartz sand with a particle size of 1.0mm (containing a silicon dioxide content of ≥99%) while stirring, and the total amount of quartz sand is 60kg / t crude bismuth, so that the generated lead silicate floats on the surface, and the slag is removed manually to obtain lead-free bismuth.

[0063] Comparative Example 4

[0064] The difference between this comparative example and Example 1 is that the lead removal by quartz sand in step 4 is placed between step 1) and step 2), that is, firstly the lead is removed by quartz sand, and then the arsenic and antimony are removed by oxidation refining and the tellurium is removed by adding alkali. The specific operation method is as follows:

[0065] 1) Melting crude bismuth: 15t crude bismuth is loaded into a bismuth pot, and the temperature of the bismuth pot is controlled to be 500-600°C for melting. After complete melting, the surface molten slag is removed to obtain melt 1;

[0066] 2) Quartz sand lead removal: Control the temperature of the bismuth pot to 400°C, introduce compressed air, and the flow rate of compressed air is 800m 3 / h, stirring in different directions of a stirrer for 8h, adding quartz sand with a particle size of 1.0mm (containing a silicon dioxide content of ≥99%) in equal amounts in two times while stirring, that is, adding 30kg / t crude bismuth (specifically 450kg quartz sand in this embodiment) at the beginning of the reaction, and then adding the remaining quartz sand after reacting for 4h, the total amount of quartz sand is 60kg / t crude bismuth (specifically 900kg quartz sand in this embodiment), so that the generated lead silicate floats on the surface, and the slag is removed manually to obtain melt 2;

[0067] 3) Oxidation refining to remove arsenic and antimony: Control the temperature of the bismuth pot to 650-750℃, and introduce compressed air into the bismuth pot with a flow rate of 800m 3 / h, react for 60h, oxidize arsenic and antimony and volatilize in the form of arsenic oxide and antimony oxide to obtain melt three;

[0068] 4) Add alkali to remove tellurium: control the temperature of the bismuth pot to 500-600°C, add 95kg / t crude bismuth flake caustic soda to remove tellurium, react for 9 hours, remove the tellurium slag in time to obtain lead-free bismuth.

[0069] The differences in the lead removal process steps corresponding to Example 1 and Comparative Examples 1-4 are shown in Table 3:

[0070] Table 3 Differences in lead removal process steps between Example 1 and Comparative Examples 1-4

[0071]

[0072] The present invention measures the grade of each impurity element in the lead-removed bismuth after the crude bismuth is treated with the lead removal method corresponding to Comparative Examples 1-4, and the results are shown in Table 4:

[0073] Table 4 Grades of impurity elements in lead removal of bismuth in comparative examples 1-4

[0074]

[0075] The direct recovery rate, lead removal rate and energy consumption of the lead removal methods corresponding to Example 1 and Comparative Examples 1-4 after treating crude bismuth are shown in Table 5:

[0076] Table 5 Direct yield, lead removal rate, energy consumption of Example 1 and Comparative Examples 1-4

[0077]

[0078]

[0079] Analysis of Tables 4 and 5 shows that, compared with the various treatments, Comparative Example 1 directly treated the crude bismuth by vacuum distillation, and the bismuth grade corresponding to the lowest, the lead grade was the highest, and the energy consumption was the largest, indicating that vacuum distillation was directly performed without oxidation refining to remove arsenic, antimony and tellurium, and the distillation effect was extremely poor. Almost as soon as the material was fed, the feeding pipe was blocked, resulting in the inability to continue distillation, which seriously affected the smooth progress of the subsequent lead removal process, making the lead removal rate and the direct recovery rate of bismuth significantly lower than those of other treatment groups, and the energy consumption was much higher than that of other treatment groups;

[0080] When the lead removal by quartz sand and the tellurium removal by adding alkali are carried out simultaneously, there is no significant difference in the energy consumption between the first adding and subtracting tellurium removal and then the lead removal by quartz sand, but the grade and direct recovery of bismuth will be reduced, and the removal rate of lead will be reduced (compared with Example 1 and Comparative Example 2);

[0081] The energy consumption of adding quartz sand in batches is slightly higher than that of adding it all at once, and the production cost is higher, but its lead removal effect is significantly better than that of adding it all at once (comparison between Example 1 and Comparative Example 3);

[0082] There is no significant difference in energy consumption between using quartz sand to remove lead before oxidative refining of crude bismuth to remove arsenic and antimony and using quartz sand to remove lead after removing arsenic, antimony and tellurium, but the effect is weaker than using quartz sand to remove lead after removing arsenic, antimony and tellurium (compared with Example 1 and Comparative Example 4).

[0083] Therefore, the effect of lead removal from crude bismuth (including lead grade, bismuth grade, direct recovery rate and energy consumption) is not only related to the order of quartz sand and other processes, but also to the way quartz sand is added. The coordination and cooperation between the various steps play a role in the lead removal effect.

[0084] Experimental Example 1

[0085] This experimental example investigates the effect of the particle size of quartz sand on the lead removal rate and direct recovery rate. The specific method is: refer to the method of Example 1 to remove lead, and study the effect of the particle size of quartz sand on the lead removal rate and direct recovery rate in crude bismuth. The results are shown in Table 6:

[0086] Table 6 Effect of different quartz sand particle sizes on lead removal rate and direct recovery rate

[0087] Particle size / mm Lead removal rate / % Direct yield / % 0.5 63.39 73.1 0.8 75.21 92.4 1.0 76.97 93.7 1.5 75.44 92.1 2.0 65.28 73.7

[0088] From the above table, it can be seen that when the quartz sand particle size is 0.8-1.5mm, the corresponding lead removal rate and direct recovery rate are relatively large, both higher than 75% and 90% respectively, and when the particle size is 1mm, the lead removal effect is the best, and the lead removal rate and direct recovery rate reach 76.97% and 93.7% respectively;

[0089] When the particle size is greater than 1.5 mm, the particle size of the quartz sand is larger, and the lead removal effect decreases. The reason is that when the particle size is larger, the quartz sand is easily wrapped by the lead silicate produced in the production process and does not react with the oxidized lead, which reduces the lead removal rate and direct recovery rate.

[0090] When the particle size is less than 0.8mm, the smaller the particle size of the quartz sand, the worse the lead removal effect. The reason is that the quartz sand with a smaller particle size is easily sucked into the dust collection system during the addition process, resulting in a decrease in the utilization rate of the quartz sand, and a decrease in the amount of reaction between the quartz sand and the oxidized lead, which in turn leads to a decrease in the lead removal rate and direct recovery rate.

[0091] Therefore, the particle size of quartz sand will have different effects on the removal of lead in crude bismuth, and the preferred particle size of quartz sand is 0.8-1.5 mm, and most preferably 1 mm.

[0092] Experimental Example 2

[0093] This experimental example investigates the effect of the temperature of quartz sand lead removal on the lead removal rate and direct recovery rate. The specific method is: refer to the method of Example 1 for lead removal, and in step 4), the temperature of the bismuth pot is controlled to be 200°C, 300°C, 350°C, 400°C, 450°C, 600°C, and 1000°C, respectively. The effect of different reaction temperatures during quartz sand lead removal on the lead removal rate and direct recovery rate in crude bismuth is studied. The results are shown in Table 7:

[0094] Table 7 Effect of different quartz sand lead removal reaction temperatures on lead removal rate and direct recovery rate

[0095] Temperature / ℃ Lead removal rate / % Direct yield / % 200 12.3 58.6 300 27.49 60.3 350 75.6 92.2 400 76.97 93.7 450 77.02 94.02 600 60.48 71.4 1000 28.02 61.3

[0096] It can be seen from the above table that when the reaction temperature of quartz sand for lead removal is 350-450℃, the corresponding lead removal rate and direct recovery rate are relatively large, both higher than 75% and 90% respectively, and there is no significant difference between the lead removal rate and direct recovery rate between 400℃ and 450℃; when the temperature is less than 350℃, the lead removal rate is less than 28% and the direct recovery rate is less than 61%. The reason is that: when the reaction temperature is lower than 350℃, the melting rate of crude bismuth is very slow, so that the lead in the crude bismuth cannot be effectively combined with quartz sand to form lead silicate for removal, resulting in a significant reduction in the lead removal rate and direct recovery rate;

[0097] When the temperature increases to 600°C, the reaction rate decreases, and the inventors also found that above 450°C, bismuth silicate will gradually be produced, which will not only prolong the reaction time and significantly increase energy consumption, but also reduce the lead removal effect;

[0098] When the temperature continues to increase to 1000°C, the formation of bismuth silicate becomes more dominant, which sharply reduces the formation of lead silicate, and further reduces the lead removal rate and direct recovery rate more significantly.

[0099] Therefore, in order to save energy and inhibit the formation of bismuth silicate to improve the removal effect of lead, the preferred reaction temperature is 350-400°C, and 400°C is most preferred.

[0100] Experimental Example 3

[0101] This experimental example investigates the effect of quartz sand dosage on lead removal rate and direct recovery rate. The specific method is: refer to the method of Example 1 for lead removal, and in step 4), the quartz sand dosage is controlled to be 20kg / t, 30kg / t, 40kg / t, 50kg / t, 60kg / t, 70kg / t, and 80kg / t, respectively. The effect of quartz sand dosage on lead removal rate and direct recovery rate in crude bismuth is studied. The results are shown in Table 8:

[0102] Table 8 Effect of different quartz sand dosage on lead removal rate and direct recovery rate

[0103] Dosage / kg / t Lead removal rate / % Direct yield / % 20 50 69.6 30 62.5 72.6 40 75.6 91.5 50 76.1 92.2 60 76.97 93.7 70 77.08 93.8 80 77.12 93.9

[0104] It can be seen from the above table that when the dosage of quartz sand is 40-60kg / t, the corresponding lead removal rate and direct recovery rate are relatively large, both higher than 75% and 90% respectively, and when the dosage of quartz sand continues to increase, the corresponding lead removal rate and direct recovery rate do not change significantly, indicating that the lead removal effect of quartz sand has reached saturation, even if the dosage of quartz sand is further increased, it will not have a significant impact on the lead removal rate and direct recovery rate.

[0105] Therefore, considering the lead removal effect and the cost of quartz sand, the preferred amount of quartz sand is 40-60 kg / t, and the most preferred amount is 60 kg / t.

[0106] The working principle and use method of a method for reducing the lead grade in crude bismuth of the present invention are as follows:

[0107] When reducing the lead in crude bismuth, the method of the present invention firstly puts the crude bismuth into a bismuth pot, melts it at 500-600° C., and removes the molten slag on the surface;

[0108] Then, the temperature of the bismuth pot is controlled to be 650-750°C, and the oxidation order at this temperature is As-Sb-Pb-Sn-Cu-Bi. Compressed air is introduced to perform oxidation refining to remove arsenic and antimony. Since the free enthalpy of arsenic and antimony oxides is very different from that of bismuth oxides, and arsenic and antimony oxides are volatile, while bismuth is almost non-volatile at the refining temperature, arsenic and antimony are rapidly oxidized and volatilized, and removed from the crude bismuth.

[0109] Add appropriate amount of caustic soda to remove tellurium at 500℃~600℃, and remove tellurium slag in time;

[0110] Continue to introduce compressed air, and control the temperature at 350-400°C. The oxidation order at this temperature is Pb, Bi, and Cu, and the elemental lead in the crude bismuth can be preferentially oxidized to PbO. Use a stirrer to stir forward and backward in different directions, and add a certain amount of quartz sand into the pot in batches. Lead oxide reacts with silicon dioxide in the quartz sand to form lead silicate. The density of lead silicate is lower than that of bismuth, so that the lead silicate floats on the surface and is removed by manual slag to achieve the purpose of preliminary lead removal.

[0111] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for reducing the lead grade in crude bismuth, characterized in that: The following steps are involved: 1) Melting crude bismuth; 2) Oxidation refining to remove arsenic and antimony; 3) Adding alkali to remove tellurium; 4) Removing lead with quartz sand: Control the temperature of the bismuth pot to 350-400℃, introduce compressed air, use a stirrer to stir in different directions for 8-9 hours, add quartz sand while stirring, so that the generated lead silicate floats on the surface, remove the slag manually, and obtain the lead-free bismuth.

2. A method for reducing the lead grade in crude bismuth as claimed in claim 1, characterized in that: The specific operation steps of step 1) are: putting crude bismuth into a bismuth pot, controlling the temperature of the bismuth pot to 500-600° C. for melting, and removing the surface molten slag after complete melting.

3. A method for reducing the lead grade in crude bismuth as claimed in claim 1, characterized in that: The specific operation steps of step 2) are: controlling the temperature of the bismuth pot to 650-750° C., introducing compressed air into the bismuth pot, and the flow rate of the compressed air is 800m 3 / h, react for 48h-72h, oxidize arsenic and antimony and volatilize in the form of arsenic oxide and antimony oxide.

4. A method for reducing the lead grade in crude bismuth as claimed in claim 1, characterized in that: The specific operation steps of step 3) are: controlling the temperature of the bismuth pot to 500-600° C., adding alkali to remove tellurium, reacting for 8h-10h, and removing tellurium slag in time.

5. A method for reducing the bismuth grade in crude bismuth as claimed in claim 4, characterized in that: The alkali is flake alkali.

6. A method for reducing the lead grade in crude bismuth as claimed in claim 1, characterized in that: In the step 4), the particle size of the quartz sand is 0.8-1.5 mm, and the content of silicon dioxide contained in the quartz sand is ≥99%.

7. A method for reducing the lead grade in crude bismuth as claimed in claim 6, characterized in that: The particle size of the quartz sand is 1 mm.

8. A method for reducing the lead grade in crude bismuth as claimed in claim 1, characterized in that: The temperature in step 4) is 400° C. and the stirring time is 8 hours.

9. A method for reducing the lead grade in crude bismuth as claimed in claim 6, characterized in that: The quartz sand is added into the bismuth pot in 2-3 batches in equal amounts.

10. A method for reducing the lead grade in crude bismuth as claimed in claim 6, characterized in that: The total amount of the quartz sand is 40-60 kg / t crude bismuth.

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