Sodium Lignosulfonate is a byproduct of the sulfite pulping process. It is the most commercialized lignin derivative in the world, which accounts for more than 90% of the Lignin market. It is a brown powder or liquid with excellent water solubility and is widely used across several industries, including construction, agriculture, and mining.
To explore the possibility of replacing the current synthetic chemicals, their potential for sustainable development is being investigated. In the following, the basic knowledge and industrial applications will be explained.
1. What is Sodium Lignosulfonate?
Sodium Lignosulfonate (Chemical formula C2OH24Na2O1OS2, CAS Registry Number 8061-51-6) is a type of anionic polyelectrolyte polymer. Its molecular weights range from 1,000 to 140,000 Da, which depends on the wood sources and the processing conditions. It appears as a brown to black powder or liquid, with viscosity increasing with concentration. It mainly serves as a dispersant, a binder, and an emulsifier.
The Sulfo group (-SO3一) is negatively charged; it can be adsorbed onto the surface of a positively charged particle, which can prevent the aggregation of particles. This is the working principle of its function as a dispersant, and is also the chemical foundation of the general application in industries such as concrete, ceramics, and mining.
The ordinary Lignin is not water soluble, and Sodium Lignosulfonate becomes water soluble because of the addition of the Sulfo group. It expands the application scope greatly because of the convenience and solvent-free use.
2. Where Does Sodium Lignosulfonate Come From?
Sodium Lignosulfonate comes from the waste solution of Sulfite pulping process. After the processing under high temperature and high pressure by the paper factory using Sulfurous acid and Sulfite, the cellulose is extracted from the wood, and a large amount of Sodium Lignosulfonate is left in the waste solution. The final product can be made after concentration and purification. The raw materials are mainly softwoods (such as spruce and pine) and hardwoods, and approximately 7 million tons of Sodium Lignosulfonate are made annually using these raw materials.
Other than Sodium Lignosulfonate, hemicellulose, sugars, and other organic matter also remained in the waste solution. The modern factory will extract ethanol and cultivate yeast from the waste solution, which can fully utilize the waste solution and achieve zero waste.
China is the world’s largest producer of Sodium Lignosulfonate. The main raw material is the waste solution from a paper factory, while some factories may also produce from Kraft Lignin using the post-sulfonation method, due to the large demand from the market.
3. Who Invented Sodium Lignosulfonate?
An American called Benjamin Tilghman applied for a patent of sulfite pulping process in Philadelphia, US in 1867. The inspiration is said to come from the observation of the softening of wood after soaking in sulfur water. This discovery laid the foundation for the modern sulfite pulp and paper industry.
In 1874, a Swedish chemical engineer called Carl Daniel Ekman commercialized this technology, with the establishment of the first Sulfite paper factory. Sodium Lignosulfonate, as the byproduct of this technology, is treated as waste to be discharged directly and pollutes the rivers.
Researchers started to investigate the commercial value of the waste solution until the 20th century. Due to the tightening of environmental regulations, the factories are forced to find a way to treat the waste solution, which turns out to discover the general application of Sodium Lignosulfonate.
4. Types of Sodium Lignosulfonate
Lignosulfonate can combine with different cations, such as sodium (Na⁺), calcium (Ca2⁺), magnesium (Mg²⁺), or ammonium (NH₄⁺). Sodium Lignosulfonate is a combination of Lignosulfonate and sodium. It is commonly seen in the market with excellent water solubility and a wide range of applications. The water solubility of Calcium Lignosulfonate is lower, but the cost is relatively reasonable. Magnesium Lignosulfonate is used for certain specific purposes.
When Sodium Lignosulfonate is categorized by physical form, dry powder accounted for approximately 58% of global production in 2024. Its main application is the concrete additive. Liquid form accounted for 42%, and it is mainly used in agricultural animal feed. When Sodium Lignosulfonate is categorized with purity, standard grade is used in construction and agriculture, and refined grade is used in animal feed and the food industry, while high-purity grades are used in pharmaceuticals and fine chemicals.
It is notable to pay attention to the moisture content, pH value (usually 8-11), and reducing sugar content of the dry powder during procurement, as these indicators affect the application performance of concrete. Product specifications may vary significantly between different suppliers, and it is recommended to ask for a completed technical data sheet (TDS).
5. How is Sodium Lignosulfonate Produced?
There are several steps in the manufacturing process:
Wood chips are placed in a digester soaked with sulfurous acid solution under the condition of 130-160°C and pH 1.5-5 for 4-14 hours. |
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Lignin is being sulfonated, and hydrophilic sulfonic acid groups are induced and become water-soluble. |
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The waste solution that contains 50-60% dry solids of Lignosulfonate is processed by evaporative concentration, ultrafiltration, and ion exchange purification. |
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The final powder product is obtained after spray drying. |
The key to the entire production is the sulfonation process, which converts hydrophobic Lignin to hydrophilic, and is the fundamental source of all the functions of Sodium Lignosulfonate.
Some factories may apply the sulfonation process to Kraft Lignin, reacting formaldehyde with sodium sulfite under high temperatures. It can produce products with slightly different structures but similar functions. This method becomes increasingly important as the global availability of Kraft Lignin far exceeds that from the sulfite process.
6. Applications of Sodium Lignosulfonate
The main use of Sodium Lignosulfonate is in the construction industry, which accounts for 40% of the global consumption. As a water-reducing agent for concrete, Sodium Lignosulfonate can reduce water consumption by 12%. It can improve strength and durability, and also delay the setting time. In 2024, this additive is used in approximately 220 million tons of concrete. Other than construction industry, agriculture accounts for about 25%, while 20% of Sodium Lignosulfonate is used in metals and mining.
In the aspect of agriculture, Sodium Lignosulfonate is used for animal feed pellet binder, soil conditioner, and slow-release fertilizer agent. For metals and mining, it is used as a binder for mineral powders and a drilling fluid additive. In addition, the refined products of Sodium Lignosulfonate is approved by the FDA to be used in food contact materials and animal feeds.
Emerging applications are also developing rapidly. Sodium Lignosulfonate is now under investigation for being an electrode additive in the lead-acid battery Industry that may improve the charge and discharge performance. It can also be treated as a heavy metal adsorbent in sewage treatment, which can remove heavy metals such as Lead or Cadmium from wastewater at a relatively low cost.
7. Advantages of Sodium Lignosulfonate
Compared with synthetic water reducer such as Polycarboxylate Superplasticizer (PCE), the cost of Sodium Lignosulfonate is about $50 per ton, which is only one-tenth of that of PCE. The performance is more than sufficient for general construction. Synthetic water reducer is only required in high-rise buildings or high-performance concrete.
The other advantages include the excellent water solubility and the convenience of use. Besides, it is environmental friendly as it is biodegradable and renewable, as it is a byproduct in a paper factory. Sodium Lignosulfonate is also multifunctional as it can be applied across multiple industries. It can be used as a preservative due to its natural antibacterial properties.
One of the limitations of Sodium Lignosulfonate is that it is not suitable for white or light-colored products because of its brownish to blackish appearance. The sulfur content of approximately 5% also makes the product unsuitable for certain high-end applications (such as pharmaceutical uses). This explains why the more costly Organosolv Lignin is still in demand because of its high purity.
8. Why Sodium Lignosulfonate Matters for Sustainability
In the annual production of Sodium Lignosulfonate in a paper factory, the commercial utilization part is equivalent to transforming waste into valuable raw materials. Replacing synthetic chemicals with each ton of Sodium Lignosulfonate can reduce approximately 1.5 tons of CO2 emissions.
The replacement of synthetic additives by Sodium Lignosulfonate is facilitated by the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) and China Green Building Materials Product Certification. The policy direction is beneficial to the long-term development of the industry because of the rising demand for bio-based materials globally. The global market was approximately 4.6 billion RMB (Chinese Yuan) in 2024, and with stable growth, is expected to reach 5 billion in 2030.
9. FAQ About Sodium Lignosulfonate
Q: What is the difference between Sodium Lignosulfonate and Lignosulfonate? A: Lignosulfonate is the common term, and may consist of different cations such as calcium , magnesium, or ammonium . Sodium Lignosulfonate specifically refers to the type containing sodium ions, which is the most commonly seen type in the market, with excellent water solubility. |
Q: What is the specific reaction of Sodium Lignosulfonate and cement? A: The Sulfo group adsorbs on the surface of cement particles and prevents the aggregation of particles, which can make the cement slurry more fluid, reduce the water consumption, and increase final strength. |
Q: Can Sodium Lignosulfonate replace synthetic water reducer completely? A: Sodium Lignosulfonate can replace synthetic water reducer in general construction. However, in the construction of high-rise building or high-performance concrete, synthetic water reducer such as Polycarboxylate Superplasticizer (PCE) is still preferred because of the higher water reduction rate. |
Q: Is Sodium Lignosulfonate safe? A: The refined products of Sodium Lignosulfonate are approved by the FDA to be used in food contact materials and animal feeds. The industrial-grade Sodium Lignosulfonate is also classified as having low toxicity, with only basic protection in daily operation. |
Q: What is the shelf life of Sodium Lignosulfonate? A: The dry powder can be stored for two years under dry and sealed conditions, and the liquid type can be stored for 6-12 months. It is essential to avoid high temperatures and direct sunlight. |
Q: Where are the main suppliers? A: The main suppliers are located in China, such as Kingsun Chemicals and Shenyang Xingzhenghe. It is recommended to ask for a completed technical data sheet (TDS) and third-party testing report during procurement. |
