Adsorption and Absorption: What’s the Difference?

Fire and spill professionals often think absorption and adsorption are the same thing. But the truth is there is a fundamental difference in the performance of an absorbent versus an adsorbent, and not understanding these differences during a hazardous materials spill can have serious occupational safety and health implications.

“The easy way to differentiate between the two is to think of the ‘D’ in adsorb as the ‘D’ in dangerous,” says John Brinkman, president of Imbibitive Technologies Corporation (IMBTEC), the manufacturer of an “oil-sensitive”, super-absorbent called Imbiber Beads®.

He cites a circumstance in England involving diesel spills along the country’s highways as an example of why. Whenever spills occurred, responders typically spread clay granules or sand on highways to clean them up. They would scrape up the material after it picked up the visible liquid. The roadway looked clean, but the process left behind an invisible fuel smear.

“It was not possible using these materials to leave a squeaky-clean surface behind,” he says. “Later, a motorist or motorcyclist would hit the fuel smear, especially after a rain event, and lose control of their vehicle. And they’d have fatalities.”

Brinkman says there are three key issues that occur when products fail to fully clean up spills:

• Noxious vapors
• Slipping hazards
• Environmental runoff

He adds industrial fire brigades and hazmat teams can mitigate these concerns better when they use an absorbent instead of an adsorbent for hazmat spills.

What’s the Difference?

The American Society for Testing & Materials (ASTM) defines an adsorbent as “an insoluble material that is coated by a liquid on its surface including pores and capillaries without the solid swelling more than 50% in excess liquid.” These high surface materials enhance the rate at which hazardous materials release vapors, effectively lowering the flash point.

“Adsorbents rely on increased exposed surface area and for liquids to coat the surfaces of clay granules or fill interstitial spaces between matted polypropylene fibers,” Brinkman says. “But the liquid is still available for release as a liquid, which often leads to ‘secondary contamination’ of response personnel and the environment as a result of simple gravitational pull, compression upon retrieval, or leaching in the presence of water.”

Liquids remain in discrete droplets when adsorbents are used, which provides an ongoing source for increased hazardous vapor release. They also lower the flash point and increase the concentration of explosive and toxic vapors in the air.

Though first responders wear personal protective equipment at hazmat incidents, they often approach these scenes without SCBA. “These materials [adsorbents] actually increase the rate at which hazardous vapors are released because they rely on exposed surface area,” Brinkman says. “That’s the real danger. It is the vapors that are toxic when inhaled, and it is the vapors that support combustion.”

This poses serious health risks to first responders who may at the very least get dizzy or nauseous, or suffer permanent injuries to their kidneys, liver and even brain.

Commonly used adsorbents include clay granules, sand, straw and polypropylene. “None of these materials are absorbents,” Brinkman says. “Though they may be labeled as such.”

Conversely, (according to ASTM) he says an absorbent is “a material that picks up and retains a liquid distributed through its molecular structure causing the material to swell (50% or more). The absorbent must be at least 70% insoluble in excess fluid.”

When used in spill control situations, such as an oil/fuel or solvent spill, absorbents physically contain the liquid in a form with a minimum exposed surface area. “The reduction in surface area lowers the rate of hazardous vapor off-gassing. Absorbent materials also minimize human and secondary contamination, as there is no longer any liquid available for release” he says.

To foster an understanding of how absorbents work, Brinkman points out that super absorbent polymers (SAPs) are found in everyday life. Baby diapers, for example, use SAPs to “absorb” water away from babies’ bottoms, leaving the retaining fabric dry to the touch. The water gets absorbed into the polymer. The SAPs in the diapers also are non-leaching, and discrete water droplets within the fabric are eliminated and no longer available for release.

“The liquid diffuses into the polymer and causes it to swell,” he says. “You eliminate the liquid, and it keeps the baby’s bottom dry and hopefully free from rashes and infections. Absorbents for hazmat spills work the same way. They swell when contacted by organic liquids and physically ‘capture and contain’ the liquid, which results in the elimination of secondary contamination of response personnel and the local environment.”

Once the liquid is imbibed/absorbed, it is no longer available for release back into the environment. It has been transformed into a leach-resistant, semi-solid, retrievable material. Applying an absorbent polymer to a hazardous and noxious substance (HNS) release can reduce the rate of vapor release by up to 600%, found a Maritime Disaster Prevention Center Study in Yokohama, Japan.

Imbiber Beads®

Not every absorbent works for industrial spill applications involving organic substances. In fact, Brinkman says “the only product that meets the ASTM Performance Standard definition of ‘absorbent’ is Imbiber Beads®.”

However, he notes the product is not a panacea for all types of spills. The product does not work with chlorine but is “engineered” to work on crude oil, gasoline, diesel fuel, benzene, styrene, toluene, xylene, chlorinated solvent spills and literally thousands of others.

Imbiber Beads® function much like a baby’s diaper with a significant difference. Imbiber Beads® are completely unaffected by water. They will “selectively filter fuels and solvents out of water and retain them within their polymer structure,” he says. “This product eliminates the liquid phase and, in doing so, eliminates the chance of re-releasing liquids onto response personnel or the environment during clean-up operations. No amount of squeezing or compression will cause Imbiber Beads® to release their contents as a liquid once imbibed.”

Imbiber Beads® sorption capacity is far more than any adsorbent, adds Brinkman. He explains adsorbent materials list their sorption capacity (the amount of liquid they sorb) in numbers of times their weight. Most adsorbent products are lightweight, so even a substantial number up to 50 times its weight does not represent a significant amount of liquid.

“Adsorbent products cannot pick up more liquid than the amount of space (volume) they occupy,” he says.

However, an absorbent like Imbiber Beads® can absorb many times its volume of spilled liquids (up to 27 volumes of liquid for each Imbiber Beads®). The maximum sorption capacity by volume is up to 27:1, he says.

Imbiber Beads® also reduce hazardous vapor concentrations-in-air to below the “Lower Explosive Limit (LEL).” Raising flashpoints for even the most flammable liquids can significantly reduce fire and explosion risks.

It’s also difficult for hazmat personnel to identify whether their sorbent products are working when fuels and solvents are colorless. “When you try to remove millimeters of colorless product from the surface of the water, it’s practically impossible,” Brinkman says.

IMBTEC created the IMBICATOR® line of color-change spill maintenance products to solve this problem. When Imbiber Beads encounter colorless fuels or solvents, personnel can see the product at work. First, they “puff up” two to three times their normal size, then they go from their original white color to pink at activation and red at saturation.

Hazmat personnel can easily and safely remove “imbibed” liquids off the surface of the water or a hard deck such as a roadway or airport runway and dispose of them. “If the imbibed liquid ends up in a landfill, though I’m not a proponent of that, it cannot be re-released, in accordance with US EPA Code of Federal Regulations because it is an integral part of the Imbiber Beads® polymer structure,” Brinkman says. “But if you did the same with an adsorbent, it would contaminate the environment.”

Lifetime Costs

Often departments opt for adsorption products because they think other products will bust their budgets or are not aware that alternatives such as Imbiber Beads® are available. After all, cat litter or clay granules are “dirt” cheap.

“If a purchasing department only looks at price, they will pick those products every time,” says Brinkman. He recommends looking at efficacy and cradle-to-grave costs before making purchase decisions. It’s important to factor in labor, transportation, storage, disposal costs and occupational safety considerations before deciding which product to buy.

“Studies have shown Imbiber Beads® are 25% to 50% less expensive cradle to grave,” he says. “When you use Imbiber Beads®, the duration of the spill incident is lessened because you’re actually eliminating the contaminant on the first pass. Cleanup is safer and easier. Clean-up time is reduced by as much as 60%, according to a multi-year government study in the UK. Risks associated with public safety and environmental concerns are significantly reduced, which can cause major misery from a liability and public relations perspective.”

Feedback from Hazmat First Responders’ experience when using Imbiber Beads® has been very positive.

Imbiber Beads® are available in several product configurations and solutions for many types of spills. To learn more about Imbiber Beads®, visit www.imbiberbeads.com