Sodium sulfide in industry: Applications, precautions and sustainability

Introduction

Sodium sulfide (Na₂S) is a key chemical compound in a variety of industries due to its reducing properties and its ability to interact with a variety of materials. From water treatment to its use in the textile, leather, and chemical manufacturing industries, this compound plays a prominent role. In addition, its application in the production of sodium-ion batteries has become increasingly important in the search for more sustainable energy storage solutions. The versatility of sodium sulfide makes it a fundamental compound for the optimization of different industrial processes.

The objective of this article is to analyze in depth the properties of sodium sulfide (Na₂S), the most relevant applications, the safety precautions necessary for its proper use, and its potential in sustainable technologies such as sodium-ion batteries.

What is sodium sulfide?

Sodium sulfide, also known as sodium sulfide, is an inorganic chemical compound with the chemical formula Na₂S, widely used in various industries due to its properties as a reducing agent and in the synthesis of organic products; it is used in different sectors such as textiles, leather, water treatment, and the chemical industry. At the industrial level, it is presented in solid form, in a yellow color, and soluble in water; therefore, it is applied in processes ranging from the treatment of fibers to water purification.

In a context where efficiency and safety in industrial processes are paramount, N-H sodium sulfide represents an important component with a positive impact on productivity and industrial sustainability.

Characteristics and production

Most outstanding features

• High solubility: It is highly soluble in water, which means that it dissolves easily in aqueous solutions. This makes it ideal for use in applications requiring an alkaline solution.
• Melting and boiling point: Sodium sulfide has a melting point of 1180 °C and a boiling point of 1380 °C; which, means that it is a solid compound at room temperature and requires high temperatures for conversion to a liquid or gaseous state.
• Corrosive properties: Highly corrosive and may cause skin and eye irritation. Handle with care and use appropriate personal protective equipment when working with this chemical compound.
• Storage Hazards: Must be stored in suitable and safe containers as it may react with other chemicals and release toxic fumes. In addition, it is sensitive to moisture and should be kept away from water and other liquids.
• Transportation hazards: Transportation of sodium sulfide must comply with appropriate regulations and safety standards because it can be hazardous if spilled or exposed to high temperatures.

Thanks to these properties, sodium sulfide Na₂S acts as an efficient reducing agent, which means that it facilitates chemical reactions where electron transfer is needed, thus enabling the transformation of other compounds. This behavior is key to its use in a variety of industrial applications.

Experimental and industrial production

1. In the laboratory: Sodium sulfide (Na₂S) is produced from the chemical elements Na and S by the following chemical reaction: 2 Na + S → Na₂S
2. Industrially: Na₂S is produced by reduction of Na₂SO₄ with carbon, in the form of carbon: Na₂SO₄ (aq) + 4 C (s) → Na₂S (aq) + 4 CO (g)
3. From the reaction between sulfur and sodium hydroxide, producing an aqueous solution which, when crystallized, forms the solid compound. Chemically, it is composed of sodium and sulfur atoms.
4. The most common way to obtain sodium sulfide is through the reaction between hydrogen sulfide and sodium hydroxide. This reaction produces sodium sulfide and water as products.
5. It can also be obtained through the reduction of sodium sulfate with coke and iron at high temperatures, but this method is not as common due to its high cost and complexity.

Common applications of sodium sulfide in industry

Sodium Sulfide Na₂S has a wide range of applications in various industries, each according to specific chemical properties:

1. Textile: In the textile industry, sodium sulfide Na₂S is used as a reducing agent during fiber dyeing and processing. Its ability to modify the chemical properties of textile fibers allows greater penetration of dyes, achieving more intense and long-lasting colors. It is also used in fiber disinfection and cleaning processes, which improves the final quality of the textile product.
2. Leather manufacturing: Sodium sulfide Na₂S plays a fundamental role in the tanning of hides, specifically in the removal of hairiness and other unwanted organic components. Its action prepares the hides for further treatment, ensuring the flexibility and strength of the final leather. This process is essential for the production of high-quality leathers, used in a variety of products such as footwear, clothing, and accessories.
3. Chemistry: In the synthesis of organic compounds, sodium sulfide Na₂S acts as an intermediate in the production of essential chemicals such as anhydrous sodium sulfide. The latter is used in applications such as paper manufacturing, metal extraction, and pharmaceutical manufacturing. Its ability to participate in reduction reactions makes it valuable in metal purification processes and in the production of other industrial products.
4. Water treatment: Wastewater conditioning and water purification are other areas where sodium sulfide Na₂S shows its effectiveness. Its ability to precipitate heavy metals makes it a useful tool for cleaning industrial water of hazardous impurities. When combined with these metals, it facilitates their removal, allowing treated water to meet environmental standards. This use not only contributes to sustainability but also reduces the costs associated with industrial water treatment.
5. Mining and Metallurgy: In the mining industry, sodium sulfide Na₂S is used for the flotation of metallic minerals, facilitating the separation of important metals such as copper, lead, and zinc. It is also used in the purification of minerals by precipitating impurities, optimizing extraction processes, and improving ore quality.
6. Battery manufacturing: From liquid sodium (Na) and sulfur (S). This type of battery has a high energy density, high charge/discharge efficiency (89-92%), and long cycle life and is manufactured from low-cost materials. However, due to the operating temperatures of 300 to 350 °C and the highly corrosive nature of sodium polysulfide, such cells are mainly suitable for applications.

Sodium sulfide an environmentally friendly alternative?

With the growing demand for a transition to a fossil fuel-free society, sodium sulfide (Na₂S) is emerging as a key alternative in the development of sustainable energy storage technologies, in particular sodium-ion batteries built from this compound.

This salt, known for its applications in industrial processes, is now being considered as an environmentally friendly option to meet the challenges presented by traditional materials such as lithium and cobalt.

Sodium-ion batteries and sodium sulfide: ecological impact

The main challenge facing current battery technologies is the shortage of essential raw materials such as lithium. Molten salt sodium-ion batteries¹, whose key raw materials include sodium chloride, are emerging as a more sustainable option. The use of sodium-derived compounds, such as sodium sulfide, in these batteries could enable cleaner and more affordable production. This is because sodium is an abundant element and its extraction has a lower environmental impact compared to lithium.

Recent research at Chalmers University of Technology in Sweden has shown that sodium-ion batteries have a climate impact comparable to lithium batteries, but with the advantage that they do not have the risk of raw material depletion. Sodium sulfide, as part of this development, further reinforces the focus on battery production that is less dependent on scarce resources and with lower environmental costs.

Under this context, sodium sulfide (Na₂S) is presented as a significant component in the development of batteries representing a major step towards sustainability, reduction of dependence on limited resources, and the possibility of securing energy supply in the future.

Role of sodium sulfide in the oil industry

It plays a fundamental role in the oil industry, mainly as a chemical agent used in refining processes and in wastewater treatment. Its capacity to eliminate impurities and neutralize acid compounds, such as hydrogen sulfide, makes it a significant component in improving the efficiency of crude oil extraction and refining processes. It also contributes to corrosion protection in equipment and pipelines, extending their useful life and ensuring operational safety in challenging industrial conditions.

The following are some of the key applications of this compound in the oil industry:

Industrial water treatment

In Oil & Gas operations, produced water (water that emerges along with oil and gas) often contains heavy metals and other compounds that must be removed prior to reuse or disposal. Sodium sulfide Na₂S can act as a precipitating agent that reacts with heavy metals, such as mercury and lead, forming insoluble compounds that can be separated from the water, improving its quality and facilitating its treatment.

Corrosion prevention

In the Oil & Gas sector, sodium sulfide Na₂S is used to combat certain types of acid-induced corrosion. For example, in the presence of hydrogen sulfide (H₂S), a common by-product in crude oil and natural gas processing, sodium sulfide can be used to neutralize H₂S and reduce its corrosive impact on pipelines and equipment. This is especially relevant in operations that handle sour crude, which contains high concentrations of sulfur compounds.

Mineral flotation and metal separation

In some stages of oil extraction and production, such as in refinery operations, sodium sulfide Na₂S can be used to separate certain heavy metals by flotation or precipitation processes, minimizing contaminants that interfere with the refining or treatment processes.

Toxic gas control

Sodium sulfide Na₂S can also play a role in controlling toxic gases such as hydrogen sulfide (H₂S), which is highly toxic and corrosive. This compound can be used to neutralize H₂S in oil and gas processing facilities, which contributes to a safer working environment and longer equipment durability.

Precautions and safety

Sodium sulfide Na₂S is a very toxic chemical compound, and its handling requires strict safety measures. Despite its usefulness, it can be irritating to the skin and eyes, which makes it necessary to use personal protective equipment (PPE), such as gloves, goggles, and masks, when handling it. In addition, it should be stored in cool and dry places, away from heat sources and flames, to avoid risks of decomposition or dangerous reactions.

It is important to note that sodium sulfide Na₂S is highly soluble in water, which facilitates its use in aqueous solutions for industrial applications. However, this also requires careful handling to avoid accidental release of large quantities into water bodies, which could cause contamination.

Conclusions

Sodium sulfide Na₂S is a versatile chemical compound of great importance in a variety of industrial applications. From textile and leather treatment to water treatment and chemical synthesis, this compound plays an essential role in improving the efficiency of industrial processes. However, it is crucial to handle it with caution due to its irritant properties and potential hazards if not stored properly.

In a context where sustainability and efficiency are increasingly important, the use of sodium sulfide Na₂S must be accompanied by best practices in safety and environmental responsibility.

References

1. Wikipedia; “Molten-salt battery”; https://en.wikipedia.org/wiki/Molten-salt_battery
2. Rickard Arvidsson; “Resource-efficient and climate-friendly with sodium-ion batteries”; News Cision. Chalmers; Dec 13, 2023;  https://worldenergytrade.com/gran-avance-nueva-bateria-sal-marina-litio/