What is Sodium Silicate Powder?
Sodium silicate powder, also known as solid water glass or powdered sodium silicate, is a convenient form of silicate product for transportation and storage. It has the same composition as liquid water glass but is in the form of a fine white or grayish-white powder. So, how is this widely used powdered sodium silicate produced in industries such as washing, chemical engineering, and construction? This article will delve into the mainstream production processes of powdered sodium silicate, as well as its properties and specific applications.
The production process of powdered sodium silicate: Wet process, also known as liquid phase method
The wet process first prepares liquid sodium silicate and then converts it into powder. This method has higher energy consumption, but the product has better solubility and it is easier to produce high modulus sodium silicate powder.
1. Prepare liquid water glass
Mix solid caustic soda (NaOH) or liquid caustic soda with quartz sand in proportion. In a pressure heat vessel (reactor), introduce high-pressure steam (about 0.5-0.7 MPa) and carry out a liquid phase reaction at a temperature of 150-180℃: 2NaOH + nSiO₂ → Na₂O·nSiO₂ + H₂O
After the reaction is completed, the liquid sodium silicate is obtained after sedimentation and filtration.
2. Spray drying for powder making
This is the core step in the wet process to convert liquid into powder. The liquid sodium silicate is pumped to the top of the spray drying tower by a high-pressure pump. The liquid is atomized into countless micron-sized droplets by an atomizer (pressure type or centrifugal type). High-temperature hot air (usually 500-600℃) generated by the hot air furnace enters the tower from the top or bottom. The fine droplets come into instant contact with the high-temperature hot air, and the water is rapidly evaporated, forming dry fine particles. The dried powder settles at the bottom of the tower and is collected by conveying equipment. This entire process is called spray drying.
3. Cooling and packaging
The collected powder is at a high temperature and needs to be cooled by a fluidized bed cooler or cyclone separator. Finally, it is sieved and packaged.
The following is the specific process flow chart of the wet process:
Caustic soda + Quartz sand → Reaction in high-pressure reactor → Sedimentation and filtration → Liquid sodium silicate → Spray drying → Hot air evaporation → Powder sedimentation → Cooling → Sodium silicate powder
Interpretation of the Specific Properties of sodium silicate powder
1. Physical Properties of sodium silicate powder
Form and Color: Fine white or off-white free-flowing powder.
Solubility: Soluble in water (but dissolves more slowly than liquid products, requiring heating or stirring), insoluble in alcohol and most organic solvents.
Hygroscopicity: Highly hygroscopic, deliquesces and forms lumps when exposed to air. (This is crucial for storage and packaging)
Melting Point: Has a high melting point (approximately 1088°C).
2. Chemical Properties of sodium silicate powder
Chemical Composition: Explains that it is a polymer form of sodium silicate (Na₂SiO₃).
pH Value: Its aqueous solution is strongly alkaline.
Hydrolysis: Undergoes hydrolysis in water, resulting in an alkaline solution.
Reaction with Acids: Reacts with acids to form silicic acid (H₂SiO₃) gel, which is the basis for its use as a binder and coagulant.
Modulus: Reiterates the concept of modulus (SiO₂/Na₂O ratio), explaining the differences in reactivity, bonding strength, and water resistance among powders with different moduli.
Sodium silicate powder uses
1. Detergent industry
Used as a detergent builder in phosphorus-free/concentrated laundry detergents and industrial detergents, replacing phosphates and enhancing decontamination, emulsification and dispersion capabilities.
2. Construction materials
Used as a binder for refractory materials, a fast-drying and strength-enhancing agent for cement, and an acid-resistant mortar, improving material strength, high-temperature resistance and acid resistance.
3. Foundry and ceramics
Used as a sand mold binder and ceramic adhesive, improving casting accuracy and high-temperature stability.
4. Petroleum and mining
Used as a drilling fluid loss control agent, thickener and mineral flotation agent, to stabilize the formation, prevent wellbore collapse and increase mineral recovery rate.
5. Other industries
Mainly used as a binder, filler or pH buffer, such as in paints, soap making, textile auxiliaries and soil stabilizers.
Precautions for the Use and Storage of sodium silicate powder
1. Pay attention to the key parameter “modulus”: The modulus (the molar ratio of SiO₂ to Na₂O) is a crucial indicator affecting its alkalinity and dissolution rate. Different application scenarios have different requirements for the modulus. For instance, a higher modulus may be needed when it is used as a binder for refractory materials.
2. Take safety precautions: Powdered sodium silicate itself is not hazardous, but its aqueous solution is strongly alkaline. Protective gloves and goggles should be worn during operation to prevent direct contact with skin and eyes.
3. Pay attention to storage conditions: The product readily absorbs moisture and forms lumps in the air. It must be stored in a sealed container in a cool, dry, and well-ventilated warehouse, and kept separate from acidic substances.
