Understanding White Liquor in the Pulp & Paper Industry

White liquor is a strongly alkaline solution primarily composed of sodium hydroxide (NaOH) and sodium sulfide (Na₂S). It plays a crucial role in the Kraft process, where it breaks down lignin and hemicellulose to separate cellulose fibers from wood chips, facilitating pulp production. ​

Chemical Properties & Safety Considerations

Due to its high alkalinity, white liquor is highly corrosive and poses significant health risks, including chemical burns and respiratory hazards. Proper handling protocols are essential to prevent exposure and ensure environmental safety.

White Liquor 101: Role, Hazards, and Safety in Pulp Mill Operations

White liquor is a caustic aqueous solution consisting primarily of sodium hydroxide and sodium sulfide. It plays a key role in the Kraft process, the dominant method for producing pulp in the paper and packaging industry. Used to digest wood chips under high-pressure steam—typically around 150 psig—white liquor breaks down lignin and hemicellulose to free cellulose fibers. The result is brown stock pulp and a residual by-product known as black liquor.

White liquor is essential to the paper mill digestion phase but is classified as a strong white liquor due to its high alkalinity and reactivity. During the cooking process, organic sulfur compounds are released—responsible for the pungent odor often associated with Kraft mills. These gases, including methyl mercaptan and hydrogen sulfide, present both environmental and occupational safety concerns.

As with other paper mill liquors—green, black, and white—white liquor is highly corrosive and may contain toxic ingredients. It can release hazardous vapors, dust, or mists during handling, especially when transferred or heated, making proper containment, ventilation, and protective equipment critical.

If exposure occurs, the following first aid measures should be taken immediately:

• Move the individual to fresh air to reduce the risk of inhaling vapors.
• Remove any contaminated clothing and wash the affected skin thoroughly with soap and water.
• If the substance has come into contact with eyes, flush them with tepid water for a minimum of 15 minutes.
• If white liquor is ingested, do not induce vomiting; instead, contact a poison control center or seek emergency medical attention.

Understanding what white liquor is and how to safely handle it is essential for every paper mill that uses the Kraft process. With appropriate training, engineered safety systems, and personal protection, the risks associated with white liquor can be significantly reduced in pulp and paper operations.

White Liquor Loading & Unloading Procedures in the Paper Industry

The safe handling of white liquor in pulp mills depends on well-designed loading and unloading systems that minimize exposure to corrosive chemicals and hazardous gases. As a highly caustic component used in the Kraft pulping process, white liquor requires closed-loop systems and dedicated equipment to maintain safety during transfer operations.

Railcar Loading and Unloading

White liquor is typically transferred using closed-loop loading systems that include stainless steel loading arms and vapor return hoses. These systems reduce the risk of operator exposure to hydrogen sulfide and other sulfur gases released during transfer. Railcars used for transporting white liquor are commonly 26,000-gallon DOT-111 insulated tank cars, engineered to handle corrosive chemicals. They typically measure 9 feet in outside diameter and 45 to 50 feet in overall length, featuring 6-by-6-foot center or offset crash box openings for top-loading access.

SafeRack supports pulp and paper facilities with custom-engineered white liquor railcar loading platforms designed for security, compliance, and efficiency. Required equipment includes GX Gangways with safety cages that offer OSHA-compliant fall protection for top-loading operations. Spill containment systems, including track pans and berms, help prevent leaks and environmental contamination. In addition, ventilation systems and gas detectors are used to monitor toxic emissions such as hydrogen sulfide, ensuring a safer working environment.

Tank Truck Loading and Unloading

Tank trucks used for white liquor must meet DOT standards and are typically MC 307 trailers or ISO chemical containers suitable for transporting strong white liquor. These trucks are most often bottom-unloaded using remote-controlled stop valves, limiting direct operator exposure during transfer.

Supporting safe white liquor truck loading systems, SafeRack provides corrosion-resistant pumps and hoses designed specifically for handling caustic liquids. Grounding and bonding systems are installed to prevent static discharge during product flow, while emergency shower stations and eyewash units are strategically placed near loading zones to offer immediate first aid in the event of a spill or splash exposure.

By implementing specialized white liquor handling equipment, SafeRack helps facilities meet regulatory standards and reduce risk throughout every stage of bulk chemical transfer—whether by rail or truck.