Flake Caustic Soda is the common name for flaked sodium hydroxide, with the chemical formula NaOH. It is a strong alkaline basic chemical raw material. Known for its strong reactivity, degreasing, and scouring properties, caustic soda plays an important role in pulp and paper, textiles, petroleum refining, chemical synthesis, and water treatment.

To help industrial users and trade partners better understand its physicochemical properties, production methods, quality standards, and operational safety, here is a structured FAQ guide:

Frequently Asked Questions (FAQ)

Q1: What are the fundamental physicochemical parameters of flake caustic soda? How does it behave when exposed to air?

A:

• Basic Information: CAS No. 1310-73-2, Molecular Weight: 40.00, Relative Density: 2.130, Melting Point: 318.4 ℃, Boiling Point: 1390 ℃.

• Solubility: Readily soluble in water with strong heat release; the aqueous solution is strongly alkaline and slippery to the touch. Soluble in ethanol and glycerol, but insoluble in acetone and ether.

• Hygroscopicity & Deliquescence: Highly hygroscopic. When exposed to air, it absorbs moisture and gradually dissolves on the surface (deliquescence). It also absorbs atmospheric carbon dioxide to form sodium carbonate (Na2CO3). Therefore, it must be stored tightly sealed.

Q2: What are the main industrial production processes for flake caustic soda, and what are their features?

A: Industrial preparation of sodium hydroxide falls mainly into caustification and electrolysis:

• Caustification Method (Soda Ash / Trona Caustification): Soda ash solution or natural trona liquor reacts with lime milk at 95–101 ℃. After clarification, the liquor is concentrated by evaporation and solidified into flake form.

• Diaphragm Electrolysis: Purified brine undergoes electrolysis. The liquor is evaporated, salt-separated, and cooled to yield liquid caustic soda, which is further concentrated into solid form.

• Ion-Exchange Membrane Process: Chelating resin towers perform secondary brine purification, reducing calcium and magnesium impurities below 0.002%. The cation-exchange membrane selectively allows Na+ to pass, yielding 30%–32% caustic soda in the cathode compartment, which can be used as liquid caustic or evaporated into flake form.

Q3: What are the primary industrial applications of flake caustic soda?

A: As a fundamental chemical raw material, flake caustic soda serves key functions across multiple sectors:

1. Pulp & Paper: Used in cooking wood or non-wood fibers to remove lignin and produce cellulose pulp.

2. Textiles & Dyeing: Serves as a desizing, scouring, and mercerizing agent for cotton fabrics.

3. Chemical Industry: Used to manufacture borax, sodium cyanide, formic acid, oxalic acid, phenol, and to synthesize downstream sodium salts and hydroxides.

4. Petroleum & Oleochemicals: Used for refining petroleum products, formulating oilfield drilling muds, making soap and detergents, and refining fats and oils.

5. Metallurgy & Surface Treatment: Used in alumina production (Bayer process) and surface treatment for zinc and copper metals.

Q4: What quality indicators and testing standards apply to flake caustic soda?

A: According to pharmaceutical and industrial standard specifications, quality requirements include:

• Assay & Carbonates: Calculated as NaOH, total alkali content should be 97.0% – 100.5%; sodium carbonate (Na2CO3) impurity shall not exceed 2.0%.

• Key Quality Parameters:

  • Alkalinity & Clarity: A 0.1 mg/mL aqueous solution exhibits pH not less than 11.0. A 1.0 g sample in 20 mL water should yield a clear, colorless solution.

  • Impurity Limits: Chlorides ≤ 0.005%, Sulfates ≤ 0.015%, Iron ≤ 0.001%, Heavy Metals ≤ 20 ppm.

• Assay Method: Measured via double-indicator titration (phenolphthalein and methyl orange) with 0.5 mol/L sulfuric acid titrant to determine total alkali and sodium carbonate content separately.

Q5: What are the safety handling and emergency response requirements for flake caustic soda?

A: Flake caustic soda carries the hazard symbol C (Corrosive) and Risk Phrase R35 (Causes severe burns).

• Protective Equipment: Personnel handling solid caustic soda must wear full protective gear, including work clothing, dust masks, goggles, rubber gloves, aprons, and rubber boots. Airborne dust concentrations should not exceed 0.5 mg/m³.

• First Aid for Burns: In case of contact or burns, immediately flush or soak the affected area with cold water or saline solution for at least 15 minutes, followed by applying 2% sodium bicarbonate solution. Seek immediate medical attention for severe cases.

• Storage & Transport: Store in tightly closed containers with clear hazard labels. Keep in a cool, dry, well-ventilated area, away from moisture and acids. Ensure containers remain intact during transit. In case of fire, water spray or dry sand may be used, provided handlers avoid direct contact with corrosive runoff.