Investigation of the Process of Increasing Bismuth Content in Lead Alloys Using the Oxygen Oxidation Method

Abstract

Bismuth is a promising and environmentally safe metal widely used in various industries, including electronics, medicine and metallurgy. Despite this, its production is associated with a number of technological difficulties due to the low content of bismuth in natural ores and its presence mainly as a by-product of lead processing. The present article is devoted to the study of the method of increasing the content of bismuth in lead alloys using oxygen oxidation. It is shown that lead, which has a high affinity for oxygen, is effectively oxidized and passes into the slag phase, whereas bismuth is concentrated in the metallic phase. Experiments were carried out at 650 °C using boric acid to lower the melting point of the slag and improve its flowability. As a result of five enrichment steps, the bismuth content in the alloy increased from 4.0% to 48.8%. The proposed method demonstrates high selectivity and economic efficiency, which makes it promising for industrial application. The results of the study can be used to develop more environmentally safe and energy-efficient technologies for bismuth lead enrichment, which is especially relevant in the context of growing demand for bismuth in various industries.

1. Introduction

Lead and bismuth compounds are widely used in various areas of modern technology. Bismuth occurs in nature in the form of various minerals, including bismuthinite (Bi₂S₃ sulfide), bismuthite (Bi₂O₂(CO₃) carbonate), bismite (Bi₂O₃ oxide) and copper–bismuth ore (3Cu₂S⋅4Bi₂S₃) [1,2]. In natural conditions, bismuth is usually part of complex ores containing lead, tungsten, tin and copper [3].

As a consequence, obtaining bismuth requires the use of special technological processes of enrichment and processing [4]. Globally, about 90–95% of all mined bismuth is recovered as a by-product of metallurgical processing of lead–zinc, copper, tin ores and concentrates containing hundredths and sometimes tenths of a percent of bismuth [5].

Global bismuth reserves are generally estimated based on the bismuth content of lead ores, as bismuth is usually a by-product of their processing. In 2017, the USGS estimated global bismuth reserves [5], shown in Figure 1, totaling 370,000 metric tonnes [6], of which the bulk are concentrated in China, Bolivia, Mexico, Canada, Vietnam and other countries. China possesses about two-thirds of the world’s reserves, ranking first.

According to the data of the United States Geological Survey (USGS) for 2018–2023 [5,6,7,8,9], the structure of the global production of metallic bismuth is presented in Figure 2. In 2023, China was the main producer of bismuth, accounting for about 16,000 tonnes of bismuth [7,8,9,10,11], which is about 81.6% of the total production. The remainder (18.4%) is distributed among other countries, including Laos (10.2%), South Korea (4.3%), Japan (2.6%), Kazakhstan (0.82%) and states such as Mexico, Bulgaria, Canada and Bolivia.

Bismuth is a metal which, due to its low toxicity and high environmental safety, is very much in demand in the pharmaceutical industry [2,12].

In addition, it has unique physicochemical properties, including its low melting point and ability to expand upon crystallization. These characteristics make it indispensable in a number of key industries, including nuclear power [13], the semiconductor industry [14,15], creation of superconductors [16], the development of bismuth-based photocatalysts [17,18,19], medical technology [20] and solar energy [21,22]. The major application of bismuth is in the pharmaceutical and animal feed additive industries, which together account for 62% of global consumption [23].

Recently, many papers have been published on the extraction of bismuth and lead using pyro- and hydrometallurgical methods [3,13]. In the review article [24], a comprehensive analysis of the methods of extraction and separation of rough bismuth from bismuth ores and metallurgical dusts was carried out, focusing on four key technologies, namely pyrometallurgy, hydrometallurgy, gravity purification and crystallization, which facilitate the transition of rough bismuth into refined metal. The article also discusses modern methods for producing high-purity bismuth, including electrolysis, vacuum distillation and zone smelting.

The traditional hydrometallurgical methods of bismuth processing include leaching in FeCl₃ + HCl, HCl-NaClO₃ and HNO₃ systems to obtain BiCl₃ solutions [25], followed by bismuth extraction by precipitation with iron powder and electrolysis through a diaphragm or hydrolysis to form sponge bismuth or bismuth oxychloride (BiOCl) [26]. The selective chlorination leaching and electrochemical treatment of suspensions are also used [27]. In [28], an efficient approach to extract metallic Bi from Pb–Bi slag, using selective leaching, followed by the electroleaching of Bi, was demonstrated.

Modern bismuth pyrometallurgy includes conventional precipitation smelting, reduction smelting, and combined methods. In addition, new technologies such as low-temperature alkaline smelting [29,30], oxygen-enriched smelting [31,32] and processes using iron oxides as sulfur-fixing agents to produce bismuth products have been developed [33,34].

Bismuth (about 90–95%) is mostly extracted as a by-product in the processing of lead-zinc ores [35,36]. Lead obtained from smelting by reduction contains a significant amount of impurities. These impurities in raw lead make it impossible to use it for technical purposes. Therefore, lead refining is expedient both from the point of view of obtaining pure lead that is used in industry and from a commercial point of view, since lead impurities have an economic value [37].

Bismuth lead obtained during lead refining (containing no more than 6–8% Bi) is processed using two-stage electrolysis in molten media [38]. To date, the method of the electrolytic extraction of bismuth from bismuth lead in molten electrolytes is widely used at lead smelters. This process relies on the higher electropositive potential of bismuth compared to metals such as lead, copper and silver, which favors the deposition of bismuth at the anode while lead is released at the cathode

Although electrolysis can produce fairly pure metallic bismuth, this method has several disadvantages, including complex operations, high reagent consumption, large amounts of waste and low metal recovery rates. In addition, as the electrolysis time increases, the current efficiency gradually decreases and the energy consumption increases, which may further reduce economic efficiency.

It is shown in [38] that the energy consumption per 1 tonne of bismuth in two-stage electrolysis is 32,530–36,640 kWh/t. And 78.5–80.9% of the total power consumption falls on the first stage of electrolysis.

In recent years in bismuth metallurgy, there has been an intensive development of technologies aimed at increasing efficiency, reducing energy consumption and improving environmental safety of processes. In this regard, the search for innovative approaches to optimize bismuth production and increase its content in metal alloys while maintaining environmental and economic efficiency becomes particularly relevant.

In light of the above-mentioned limitations, we propose an alternative approach to the bismuth lead recycling process—replacing the first stage of electrolysis with the high-temperature oxidation of bismuth lead.

This paper presents the results of laboratory studies of increasing the bismuth content in bismuth lead by oxygen oxidation of lead and its conversion to the slag phase. The oxidizing agent is oxygen contained in air, which is a cheap and safe reagent. Lead, having a high affinity for oxygen, is subject to oxidation to a greater extent than bismuth, which leads to its partial transfer to slag in the form of lead oxides. At the same time, bismuth remains in the metallic phase, which enables an increase in its concentration in the metallic phase. This method is more economical than other methods, as it promotes the efficient separation of components with minimum energy and reagent consumption.

2. Materials and Methods of Research

2.1. Research Materials

This research was carried out at the Veritas Scientific Center of the D. Serikbayev East Kazakhstan Technical University and the experimental site of Kazzinc LLP, located in Kazakhstan.

The chemical compositions of the initial materials and the resulting products were determined in accordance with certified methods: GOST 20580.0-80 (Lead. General requirements for chemical analysis methods) for lead and GOST 20580.4-80 (Lead. Methods for determining bismuth) for bismuth, as well as using an ICP-MS 7500cx mass spectrometer.

The object of the study was an alloy of bismuth and lead (bismuth lead), which was formed during the refining of crude lead at one of the metallurgical enterprises in Kazakhstan that produces lead and bismuth. Figure 3 shows the appearance of bismuth lead.

The chemical composition of bismuth lead is presented in

Table 1. Chemical composition of bismuth lead.

Name	Mass Share, %		Mass Fraction, g/t
	Pb	Bi	Au	Ag
Original bismuth lead	95.7	4	0.1	31.8

.

The slag formed during lead oxidation (PbO) is characterized by a high melting point of 888 °C [35]. To reduce the melting point of slag, the solubility of oxides was improved and the viscosity of slag in the process of lead oxidation was reduced, and a flux based on boric acid (H₃BO₃) of grade B GOST 18704-78 was chosen. The mass fraction of the main substance was at least 99.9%. Boric acid effectively lowers the melting point of slag and enables the easier removal of oxides, which improves phase separation and provides more stable and efficient slag removal from the melt surface. This allows the optimization of the lead oxidation process, thus achieving the desired results with minimal energy and time.

The main reaction by which the process of slag formation takes place is as follows:

$$4{\mathrm{H}}_3{\mathrm{B}\mathrm{O}}_3+{\mathrm{O}}_2+2\mathrm{P}\mathrm{b}=6{\mathrm{H}}_2\mathrm{O}+2\mathrm{P}\mathrm{b}\mathrm{O}·{\mathrm{B}}_2{\mathrm{O}}_3/\mathsf{\Delta }\mathrm{G}=-508.191 \mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$$

(1)

Lead metaborate PbO·B₂O₃ is an inorganic compound, a salt of lead and metaboric acid, used in the manufacture of special glasses and electrically conductive ceramic coatings.

2.2. Equipment Preparation and Selection of Optimal Test Parameters

Experimental studies to increase the bismuth content in bismuth lead were carried out in accordance with the scheme presented in Figure 4. To increase the rate of the oxidation reaction when supplying compressed air, an impeller was used, which contributed to improving the melt mixing and the uniform distribution of oxygen in the volume.

The experiment consisted of several consecutive stages and the following operations: the melting of bismuth lead at 650 °C, oxidation with air for 1–2 h with periodic flux loading (with an interval of 15 min), cooling to 500 °C as the slag accumulates and its subsequent removal. Then, the cycle was repeated. To obtain the required bismuth content, the operations were repeated, and the next operation on the resulting bismuth lead was carried out without the addition of the original lead. Thus, the mass of lead after each operation decreased and the content of bismuth increased.

The oxidation of bismuth lead was carried out in a cast iron boiler (Figure 5) heated using a laboratory electric furnace NABERTHERM K 1/10. The temperature was recorded by a thermocouple CA (K), with an operating range of −40 ÷ 1100 °C. A stainless steel pipe with an inner diameter of 16 mm and an outer diameter of 20 mm was used to supply oxygen, through which air was passed into the molten metal. For the accurate measurement of the volumetric air flow, an LZT-08A08M rotameter was installed, which made it possible to control the oxygen supply during the process.

During the experiment, various parameters were studied: temperature (500–650 °C), air consumption (50–1,000,020 L/h) and the amount of flux injected (40–100 g/h).

In order to determine the optimal parameters of the experiment, the above-mentioned parameters ensured the maximum increase in the concentration of bismuth in the metal phase with the minimum transition of bismuth into slag and exploratory experiments were carried out, the results of which are presented in

Table 2. Search modes.

Mode Number	No. 1	No. 2	No. 3	No. 4
Temperature, °C	500	550	600	650
Consumption air, L/h	75	75	75	75
Boric acid loading, g/h	60	60	60	60
Duration, h	4	4	4	4
Bi content in the initial lead, %	4.82	5.01	4.85	5.1
Bi content in the intermediate slag	4.3	0.6	0.15	0.1
Bi content in the lead obtained, %	5.01	5.4	5.2	6.12

. To ensure the correct comparison of oxidation conditions, a fixed process duration of 4 h was set.

The exploratory experiment was carried out at a temperature of 500 to 650 °C with a bubbling supply of compressed air through a layer of molten lead weighing 5 kg in a boiler with a volume of 2.6 × 10⁻³ m³ at an air flow rate of 75 L/h, which prevented the splashing of the melt. Boric acid was added in portions to form liquid slag and minimize bismuth losses.

By analyzing the results of the search experiments, it can be seen that the most effective was mode No. 4. At a temperature of 650 °C, slag acquired a liquid and fluid consistency, which enabled its easy separation from the metal phase (Figure 6). This contributed to the achievement of clear phase separation, allowing the removal of slag with minimal mechanical losses of the metal phase.

During the experiments in mode No. 4, the Bi content in the original lead sample was 5.1%, and after 4 h of oxidation with the addition of flux, the alloy was enriched to 6.12% (Table 2). In order to remove the slag with less mechanical loss, it was decided to reduce the temperature to the slag hardening temperature of 500 °C and only then remove the hardened slag (Figure 7).

Thus, the results of this study showed that the use of mode No. 4 is the most effective for the oxidation of bismuth lead. This mode made it possible to achieve optimal phase separation, increase the bismuth content in the metal phase to 6.12% and reduce its transition to slag. The use of boric acid as a flux significantly improved the separation of slag–metal phases, which reduced metal losses and simplified the process of metal removal. Given the high efficiency, this mode was adopted as the basis for further experiments.

3. Experiment Results

3.1. Main Part of the Experiment

The experiment included several sequential operations. Each operation involved melting the lead to 650 °C, oxidizing it, batch loading flux (every 15 min), cooling to 500 °C and removing dross (slag). In the first stage of the process, the lead was initially charged, enriched with bismuth and cooled to 500 °C, then the slag was removed and the lead was poured into the mold. To achieve the required bismuth content, the process was repeated, with the resulting lead being processed in the next step without adding more starting material.

As a result of this process, the mass of lead gradually decreased, and the bismuth content in the alloy increased, which continued until the required level of bismuth in the final product was reached. As part of the experiment, the initial bismuth lead, weighing 5020 g, was loaded into the refining kettle, after which 306 g of bismuth lead with an increased bismuth content was obtained as a result of five oxidation operations. To reduce mechanical losses and improve the properties of the slag, boric acid was introduced as a flux, which reacted with PbO to form lead metaborate (PbO·B₂O₃). As a result of adding boric acid, the slag acquired a liquid state, which improved its fluidity and the phase separation of “metal–slag” and promoted the more efficient removal of oxide inclusions, while reducing the removal of bismuth with the slag.

It should be noted that in previous studies, we used sodium tetraborate (borax) as a flux, namely Na₂B₄O₇ × 10H₂O. But in the process of these experiments, we observed the following: During melting, borax started to lose crystallization moisture and rapidly expanded, thus causing the foaming of the materials, which led to the overflow of the materials and their loss. Therefore, we replaced sodium tetraborate with boric acid. As is known, boric acid, when heated, forms boron oxide, which has a strong slag-forming ability.

To visualize the sequence of operations and key steps of the bismuth lead beneficiation experiment, Figure 8 shows a process diagram. The diagram also shows changes in the bismuth content of the alloy at each stage of the process and a gradual decrease in the mass of lead during the experiment. This approach allows the visualization of the key points of the experiment and demonstrates the relationship between technological operations aimed at achieving the required bismuth content in the final product.

The initial lead sample was taken after reaching a temperature of 650 °C, with an initial bismuth (Bi) content of 4.0%. During the experiment, the slag was removed as it accumulated, and after each slag removal, a sample of bismuth lead was taken. The first flux-added oxidation operation continued continuously for 18 h, resulting in an increase in the bismuth content of the alloy to 8.5%.

Further operations were carried out exclusively during daytime working hours. As the weight of the alloy decreased in order to prevent melt splashing, the intensity of the air supply decreased (see

Table 3. Amount of slag and lead obtained in bismuth lead analyses.

No.	Operation	t, °C	Air, L/h	Time, h	Boric Acid, g/h	Loaded, g	Unloaded, g	Bi, %
1	Initial Pb-Bi alloy	650	75	18	60	5020		4.0
	Slag						3728	0.1
	Pb-Bi alloy					2210		8.5
2	Slag	650	50	4.5	60		842	0.11
	Pb-Bi alloy					1627		11.4
3	Slag removal	650	50	4.5	60		666	0.28
	Pb-Bi alloy					1076		15.6
4	Slag removal	650	50	4.5	60		651	0.29
	Pb-Bi alloy					534		30.01
5	Slag removal	650	50	1.5	60		148	0.3
	Pb-Bi alloy					306		48.8

). After the first oxidation operation, the air supply was reduced to 50 L/h. After five enrichment stages, the bismuth content in the bismuth alloy reached 48.8% (see Figure 9). The yield of bismuth lead was 306 g (6.1% of the original weight of bismuth lead), while the weight of slag was 6035 g with an average lead content (Pb) of 73.1%. The distribution of bismuth in the enriched Pb-Bi alloy was 74.37%.

The material balance of the lead beneficiation process carried out in the refining boiler with an initial lead weight of 5020 g is presented in

Table 4. The final mass balance of the experiment.

Loaded	m		Pb			Bi
	g	%	%	m	dist., %	%	m	dist., %
Pb-Bi alloy	5020	68.36	95.7	4804.14	100	4	200.8	100
Oxygen (calculated).	344	4.68
Boric acid	1980	26.96
Total	7344	100		4804.14			200.8
Obtained
Slag	6035	82.18	73.1	4411.59	91.83	0.32	18.71	9.62
Enriched alloy	306	4.17	51.23	156.76	3.26	48.8	149.33	74.37
Samples for analysis (avg. value)	108	1.47	80.54	86.98	1.81	19.44	21	10.46
Vapor (calculated)	862	11.74
Total	7311			4655.332			189.03
Imbalance	33	0.45		148.81	3.1		11.77	5.56

. In the course of the experiment, such parameters as the mass of the initial lead, the mass of the resulting slag, the mass of the resulting bismuth lead, and the content of the main elements (lead and bismuth) in each phase were recorded. The calculation of the material balance enabled the quantification of the redistribution of components between phases and is a key indicator of the efficiency of the process (Table 4).

The general discrepancy in the material balance is explained by the processes of evaporation (volatilization) of lead and bismuth over the course of the experiment. Specifically, lead loss due to evaporation amounted to 148 g and bismuth losses amounted to 11.76 g. These losses are associated with the transition of metals into the gas phase at high temperatures, which is typical for the processes of refining and the beneficiation of metal alloys.

Bismuth losses as a result of its transition to the gas phase amounted to 5.56% of the initial bismuth content in the alloy.

3.2. Oxygen Efficiency Assessment

3.2.1. Calculation of the Theoretical Amount of Oxygen

One of the key aspects characterizing the efficiency of oxidative bismuth enrichment is the degree of involvement of supplied oxygen in target chemical transformations. Within the framework of this study, the main oxidative reactions occurring in the system are as follows:

$$4{\mathrm{H}}_3{\mathrm{B}\mathrm{O}}_3+{\mathrm{O}}_2+2\mathrm{P}\mathrm{b}=6{\mathrm{H}}_2\mathrm{O}+2\mathrm{P}\mathrm{b}\mathrm{O}·{\mathrm{B}}_2{\mathrm{O}}_3$$

(2)

$$\mathrm{P}\mathrm{b}+\mathrm{½}{\mathrm{O}}_2=\mathrm{P}\mathrm{b}\mathrm{O}$$

(3)

$$4\mathrm{B}\mathrm{i}+3{\mathrm{O}}_2=2{\mathrm{B}\mathrm{i}}_2{\mathrm{O}}_3$$

(4)

Based on stoichiometric analysis, the estimated oxygen consumption for these reactions was as follows: 255.5 g for the reaction (2), 85.5 g for the reaction (3) and 2.8 g for the reaction (4). Here, the amount of oxygen involved in the reaction (2) was calculated based on the mass of the original boric acid, while the consumption for the rest of the reactions was calculated according to the residual principle. As a result, the total theoretical oxygen consumption for these processes amounted to 343.8 g, which makes it possible for us to use this indicator to assess the efficiency of oxygen supply to the system and identify possible areas for improving technological parameters.

3.2.2. Calculation of the Actual Amount of Oxygen

The experimental air supply was carried out in two stages:

• At the first stage (for 18 h), the air consumption was 75 L/h;
• At the second stage (for 15 h), the air supply was reduced to 50 L/h.

The total volume of air supplied to the system was calculated using the following formula:

$${\mathrm{V}}_{\mathrm{a}\mathrm{i}\mathrm{r}}=75 \mathrm{L}/\mathrm{h}\times 18 \mathrm{h}+50 \mathrm{L}/\mathrm{h}\times 15 \mathrm{h}=2100 \mathrm{L}=2.1 {\mathrm{m}}^3$$

(5)

Considering the volumetric fraction of oxygen in the air (21%), the calculated amount of supplied oxygen was as follows:

$${\mathrm{V}}_{{\mathrm{O}}_2}=2.1 {\mathrm{m}}^3\times 21/100\mathrm{\%}=0.441 {\mathrm{m}}^3$$

(6)

The mass of supplied oxygen was calculated based on the ideal gas law, assuming standard conditions (GOST 2939-63) at T = 20 °C and P = 101325 Pa. Using the molar mass of oxygen μ = 32 g/mol and the universal gas constant R = 8.31 J/(mol·K), the mass of supplied oxygen was determined as follows:

$$\mathrm{m}={\displaystyle \frac{\mathrm{P}\mathrm{V}\mathsf{\mu }}{\mathrm{R}\mathrm{T}}}={\displaystyle \frac{101325 \mathrm{P}\mathrm{a} \mathrm{\ast } 0.441 {\mathrm{m}}^3 \mathrm{\ast } 32 \mathrm{g}/\mathrm{m}\mathrm{o}\mathrm{l}}{8.314 \mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}·\mathrm{K} \mathrm{\ast } 293 \mathrm{K}}}=587.27 \mathrm{g}$$

(7)

The efficiency of oxygen utilization was determined as the ratio of the calculated amount of oxygen required for the reactions (343.8 g) to the total amount supplied (587.27 g):

$${\mathsf{\eta }}_{{\mathrm{O}}_2}={\displaystyle \frac{343.8 \mathrm{g}}{587.27 \mathrm{g}}}\times 100\mathrm{\%}=58.5\mathrm{\%}$$

(8)

Thus, the oxygen utilization efficiency in experiment was 58.5%.

4. Discussion

According to the data of a Kazakhstani bismuth producer, the average consumption of electrical energy at the first stage of electrolysis in terms of 1 tonne of metal is 20,428 kWh/t (Bi).

The results of various studies have shown that in the process of the high-temperature oxidation of bismuth lead, energy consumption per 1 tonne of bismuth decreases by 23.8–31.4% and amounts to 14,022–15,580 kWh.

The conducted experiments confirmed that the process of oxidation of bismuth-containing lead using boric acid as a flux is an effective method for increasing the concentration of bismuth in the metallic phase. The optimal process parameters, including a temperature of 650 °C, air consumption of 50–75 L/h and a boric acid feed rate of 60 g/h, allowed an increase in bismuth content in the alloy from 4.0% to 48.8%. This demonstrates the high selectivity of the process, where lead predominantly transitions into the slag phase while bismuth remains in the metallic phase. The use of boric acid significantly improved the slag–metal separation by lowering the melting point of the slag, enhancing its fluidity and facilitating the removal of oxidized lead, which resulted in improved phase separation and reduced mechanical metal losses. The formation of lead metaborate (PbO·B₂O₃) ensured the stability of the process, simplified slag removal and increased the purity of the final product. The results showed that at 650 °C, the slag remained in a liquid state, providing easy separation from the metallic phase, whereas at lower temperatures, the slag became more viscous, making its removal difficult and leading to greater losses of bismuth in the slag phase. Increasing the air flow beyond 75 L/h led to excessive turbulence in the melt, increasing metal losses due to splashing.

Compared to traditional methods, such as electrolytic refining, the oxygen oxidation method demonstrated several advantages. Electrolysis requires high energy consumption and specialized electrolytes, whereas the oxidation process uses air, boric acid and electrical energy to maintain the melt temperature, making it a more economical and environmentally safe alternative. Electrolytic refining involves complex reagent systems and generates large volumes of waste, whereas the oxidation process minimizes chemical waste generation.

However, the oxygen utilization efficiency in this study was 58.5%, indicating significant losses of oxygen that were not part of oxidation reactions. This suggests potential areas for process optimization, such as modifying the oxygen supply system to improve its interaction with the molten metal or adjusting the oxidation kinetics by changing the flux composition.

To further improve the efficiency of the process, future research should focus on optimizing oxygen utilization by refining the air supply system to enhance gas dispersion and its contact with molten lead. The use of a protective atmosphere or a slight reduction in process temperature while maintaining oxidation efficiency could minimize lead and bismuth evaporation. Conducting large-scale trials in industrial conditions would help confirm the practical applicability of this method and assess its economic efficiency for bismuth production.

The oxygen oxidation method with boric acid as a flux has proven to be effective in enriching bismuth-containing lead, ensuring a significant increase in bismuth concentration while maintaining economic and environmental efficiency. The further optimization of process parameters could enhance oxygen utilization, reduce metal losses, and make the method even more competitive compared to traditional refining methods.

The traditional two-stage electrolytic refining of bismuth lead produces significant amounts of electrolyte waste and harmful gas emissions. In the proposed process, the main wastes are a dust–gas mixture containing mainly lead, which is effectively captured by gas cleaning systems, and slag. Both of these wastes can be sent for processing as part of the metallurgical cycle of lead production. The proposed refining method allows not only the increase in the efficiency of the process and the reduction of its cost but also the minimization of environmental damage by reducing the emission of harmful substances, increasing the recycling of solid waste and reducing energy consumption. Thus, it is a more environmentally friendly alternative to traditional technologies.

5. Conclusions

The proposed oxygen oxidation method using boric acid as a flux allowed an increase in bismuth content in the metallic phase from 4.0% to 48.8%, with minimal losses in the slag phase. This confirms the effectiveness of this approach for enriching bismuth-containing lead.

It has been established that the process of the oxidation of bismuth-containing lead using boric acid as a flux effectively increases the concentration of bismuth in the metallic phase. Optimal process parameters for the initial bismuth-containing lead with a mass of 5020 g include a temperature of 650 °C, air consumption of 50–75 L/h and a boric acid feed rate of 60 g/h.

Bismuth losses due to evaporation amounted to 5.56%, which is acceptable for this method. Possible improvements include using a protective atmosphere or lowering the process temperature.

The oxygen utilization coefficient was 58.5%, indicating significant losses during oxidation, with some oxygen simply escaping into the gas phase without participating in the reaction. To improve efficiency, it is advisable to optimize air supply parameters and flux composition.

The obtained results can be used to develop more economical technologies for bismuth-containing lead enrichment, which is especially relevant in the conditions of growing demand for bismuth in various industries—including the industry in which it is in demand.

The production of 1 tonne of bismuth by electrolysis in molten salts generates approximately up to 2.5 tonnes of waste, namely salt electrolytes. These wastes are subjected to secondary multistage processing, including crushing, the separation of metallic inclusions of lead and bismuth, regeneration, the purification of salts and their return to the process.

Therefore, one of the main environmental advantages of the proposed technology is the absence of the use of chloride-containing materials (in this case, the electrolytes, which are a mixture of sodium, potassium, lead and zinc chlorides) and, consequently, the absence of the possibility of chlorine extraction.

Thus, the proposed method for the enrichment of bismuth-containing lead is a promising direction for further research and practical applications in the metallurgical industry.