Established 1983

Old News is new News... again!

Soda blasting used to remove PCB's and radioactive particles

 Remember when you were a kid and your family ran out of toothpaste? You might have used baking soda, also known as sodium bicarbonate, to put an extra sparkle in your smile. That same sodium bicarbonate was used by O'Brien & Gere Technical Services, Inc. during a demonstration of soda blasting to decontaminate U.S. Department of Energy facilities and equipment at the Oak Ridge K-25 Site in Tennessee. The soda blasting technique removed greater than 95 percent of radioactive and polychlorinated biphenyl (PCB) surface contamination to a level below DOE's unrestricted use release limits. And after treatment of the blasting residual; aqueous radionuclides, heavy metals, and PCBs were removed below DOE and U.S. Environmental Protection Agency treatment objectives.

O'Brien & Gere won a Program Research and Development Announcement for a pilot-scale demonstration of the effectiveness of soda blasting to remove uranium isotopes, technetium-99, heavy metals, and PCBs on both concrete structures and metal equipment. The soda blasting system aimed abrasive sodium bicarbonate under pressure and at high speed at contaminated surfaces to mechanically remove surface contamination while leaving structures and equipment intact for further use.

The demonstration was conducted in building K-29, where a gaseous diffusion process separated uranium-235 from uranium ore for use in atomic weapons and commercial reactors. The project, conducted between December 1993 and September 1994, also included cleanup of the wastewater from the blasting operations.

Soda blasting test
To meet health and safety concerns during the soda blast, a blasting enclosure was built to contain hazardous and radioactive waste. Blasting personnel were fitted with special protective clothing and supplied-air gear. The test was designed to evaluate the effects of six variables on the operation of the blasting system.

• air pressure,
• water pressure,
• nozzle hole diameter,
• nozzle hole design,
• media type, and
• media flow rate.

A concrete floor at K-29 was gridded into ten one-meter squares. Major contaminants for each square were recorded. After scouring with sodium bicarbonate, the contaminants in the squares were measured again to test the effectiveness of the soda blast. The soda blast was also used on such metal surfaces as an aluminum circuit breaker handle, steel trash can, and compressor blade.

For surfaces tested using selected blasting variables, test results showed contaminant removal averaged between 95 and 100 percent for beta/gamma radioactivity and between 0 and 100 percent for alpha radioactivity. The lower percent removal for alpha was caused by pre-blast readings approaching background levels. In each test, the post-blast alpha readings were below the release limit of 5,000 disintegrations per minute (dpm).

After each blasting test, the tested surfaces were hosed down with tap water to remove the loosened waste. The surfaces were then vacuumed with a wet/dry vacuum and the resulting slurry (water, used sodium bicarbonate, and hazardous and radioactive waste) was transferred to 55 gallon drums in preparation for treatment.

Pretreatment of blasting residuals
Several physical methods were used to remove uranium, other heavy metals, and PCBs from the slurry. The first step was the addition of a 70 percent nitric acid solution to 450 gallons of blasting residual. This nitric acid addition lowered the pH value and facilitated the removal of aqueous phase carbon dioxide following two hours of aeration. The pH level was then elevated by adding sodium hydroxide, which facilitated the formation of insoluble uranium and other heavy metal hydroxides, which settled to the bottom of the holding tank and were removed. Unsettled particulates were further treated by filtration. The last phase of the pretreatment removed dissolved PCBs with an activated carbon system.

The pilot pretreatment system effectively removed more than 97 percent of uranium and more than 99 percent of PCBs and lead. Also, 61 percent removal of technetium was achieved during pretreatment.

Technetium removal
Two technetium removal methods were tested. The first test involved the setup of an ion exchange system employing commercially available resins from Dow Chemicals and Reilly Industries arranged in column beds. During testing, 50 gallons of pretreated blasting residual solution were processed through each column. Column effluents were sampled at 30-minute time intervals. Analysis of the samples demonstrated technetium removal below the 100 pCi/1 treatment objective for both types of resins. However, the Dow resins were more efficient in meeting the standard than were the Reilly resins.

Removing technetium using a chemical reduction method did not prove effective.

Benefits
Soda blasting and the associated waste treatment system hold promise as a surface decontamination method. Sodium bicarbonate is non-toxic and water soluble. Its dissolution in water means it is easily removed from contaminants, thus reducing waste volume. Soda blasting is cost effective and energy efficient. The average amount of sodium bicarbonate used was 1.39 pound per square foot blasted. It is estimated approximately 1 pound per square foot would be used during a full-scale decontamination. The volume of waste generated during the demonstration project averaged 11.9 gallons per test grid. It is estimated the volume of waste generated during full-scale decontamination would be approximately 1.0 gallon per square foot. Treatment of the residual waste achieved a significant 71 percent waste volume reduction.

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Copyright © 2002 The Harmon Group
Last modified: 04/12/03

APPROACH

Harmon Distributing Systems uses Soda or Sand to remove most coatings from almost any surface. The equipment & media is combined for a wide use of applications to remove paint, rust, dirt, carbon, oil and grease from steel, stainless steel, aluminum, galvanized metal, concrete, glass and more.....

SODA BLASTING
SANDBLASTING

Cob blasting

What is it?
Uses

Why It Works
Examples

Advantages

Examples

SODA BLASTING EXAMPLES

WHAT IS SODA BLASTING?
It is a process where a surface is cleaned or paint is removed or coatings of any kind are stripped from a substrate. It is very similar to traditional sand blasting yet has the significant advantage of cleaning the surface without causing any harm to the substrate or the environment.

APPLICATIONS

From the removal of graffiti from brick and concrete to the cleaning of boat bottoms, from the removal of carbon, char, and odors from buildings damaged by fire to refurbishing stainless steel kitchen equipment, from removing oil and grease from engines to removing offensive odors in stairwells, from cleaning washrooms in manufacturing facilities to removing paint from brick and steel, from removing rust and paint from cars to the line removal off highways, this approach has proved to be successful time and time again. The system has been used for:

Paint Removal
Engine Parts
Brick & Concrete
Hard Wood
Odor Elimination
Cleaning Boats
Anilox Rolls
Fiberglass
Rust Removal
Cars-Paint/Rust
Airplane Parts
Stain Removal
Graffiti Removal
Fire Restoration
Conveyor Systems
And More!

WHY THIS APPROACH

Equipment is easy to use
Equipment is transportable, in many cases a one-man operation
Short set-up time
Media is environmentally sensible (USDA Approved as an A1 cleaner)
Media is water soluble, gentle yet effective
Safer than solvents, caustics and acids
Media is an odor-eater
Clean up is relatively easy


WHY IT WORKS...

The cleaning effectiveness of blast soda is a direct result of its physical properties. These qualities allow the media to be used in a wide variety of applications.

The magic of baking soda is due to: Granulation resulting in consistent sizing of the cleaning media
Shape is multi sided leads to an improved cleaning capability
Hardness is such that it will not damage delicate substrates
Friability (easily crumbled) enhances the cleaning process
pH of media (8.2) greatly reduces any
caustic effect


These properties provide the cleaning power of media:
1. High friability with consistent angular fractures results in smaller, uniformly angular cleaning particles. This feature ensures that all surfaces of a part can be cleaned effectively.

2. media is very soft (2.4 on Mohs Scale of Hardness) and is a friable cleaning agent. This means that blasting with soda is like throwing a snowball at a fence whereas other less friable media (plastic at 3.5 and glass at 5.0 on Mohs Hardness Scale) is like throwing a stone at a fence.

3. media imparts a cleaning effect where other abrasives use a hit and cut method to clean or chop away the coating.

4. soda crystals begin at less than 70 microns. At impact the crystal crumbles and gently imparts the energy into a cleaning mass. Much of this energy is transferred perpendicular to the angle of the blast across the entire structure. The result is a clean surface.

5. Easily remove carbon, grease, oils, gasket material, surface corrosion, paint and coatings from a variety of alloys, plastics and composites without substrate damage or distortion, even leaves hard anodized coatings intact.

6. Reduce cycle time by cleaning, de-greasing, de-painting in one step. Unlike glass beads or plastic media, soda requires no pre-wash and its water solubility allows for complete rinsing, eliminating the risk of spent media lodging in tight spaces or critical passageways.

ADVANTAGES...

Cleaning & De-Coating in One Step
Standard abrasive blasting is a dirty process, often loading and even embedding the surface with contaminants (grease, oil, tar & abrasive particles) in the process of removing the coating. Recycled abrasives compound this problem by loading increasing amounts of contaminants into the substrate. Soda blast media's effectively de-coats and cleans the substrate in one step; producing a level of surface cleanliness not seen with most processes. The media is not reusable thus eliminating the issue of blasting with re-used media. Coating adhesion relies heavily on surface cleanliness and a surface profile has been used to offset this lack of cleanliness.

Unique Cutting Action
Soda blast media offers the unique properties of sodium bicarbonate, the primary ingredient. The softness (Mohs Hardness = 2.4) and friable nature of this crystal produces a unique cutting action with little or no effort on most substrates. For example, thick coatings can be removed from glass without any etching effect. With proper care, delicate substrates can be cleaned without damage.

No Pre-Cleaning Required
For projects where the coating is covered with grease, carbon, salt or other contaminants, the more traditional blasting methods require the coating to be fully cleaned before blasting. This is required so that the contaminants on the surface of the coating not be driven through the coating and into the surface of the substrate, causing future coating failure.

No Need To Re-Profile Steel
Standard grades of soda media (without any hard aggregates) do not profile steel. soda have a Profile grade of baking soda that imparts a profile on steel. When an operator removes a coating from a metal surface, he or she exposes the existing anchor pattern under the coating. Unless corrosion has occurred, there is no reason to re-profile the surface.

Reduced Solid Waste
soda blast media can be dissolved in fresh water. By dissolving the media and filtering out the contaminants the solution can generally be discharged to POTW treatment systems or open waterways, with proper discharge permits. Waste volume is generally reduced to less than 5% of the original waste volume. With increasing landfill costs and liabilities, this advantage becomes more important every day.

Natural Rust Inhibitor
As long as soda is on a ferrous metal surface, rust will not form. For rust to form, free moisture and an acidic condition must exist. In most cases, free moisture combines with carbon dioxide in the atmosphere to form carbonic acid. This acid releases a free metal (ferrous) ion which combines with oxygen (oxidizes) to form rust. soda buffers acids, prevents the release of free metal ions and prevents rust.

Reduced Clean-Up Costs
soda blast media performs roughly the same level of work (somewhat slower) as sand blasting while producing 1/5 to 1/7 of the total waste volume. Although media costs per square foot are higher, site clean-up and residue disposal are significantly lower. The net balance id that total cost per square foot are about the same for both approaches.

Benefits In Waste Disposal
In most non-hazardous applications, the residue from blasting with soda can be rinsed into sanitary drains or sewers which flush the residue to a water treatment facility, greatly reducing the clean-up time. Sodium bicarbonate is actually beneficial to waste water treatment systems.
For industrial treatment systems, where chemical neutralization is a major cost in water treatment, soda blast media can often save significant dollars in waste treatment.

Increased Worker Safety
The safety of sodium bicarbonate to workers is well understood, since it has been in use for some 160 years. The bicarbonate buffer system is the major extracellular buffer in the human body, thus sodium bicarbonate is part of the body's normal chemistry.
Sodium bicarbonate and thus, soda is not toxic via ingestion, inhalation or dermal contact, nor is it a skin or eye irritant as defined by EPA and OSHA. Any risk to workers is primarily the containment or coating removed during the blasting operation. Removes Odors
The same odor absorbing effect seen in the refrigerator at home is present when blasting with soda media. It not only removes the contaminants, it also reduces the unfriendly odors.

Replaces Dangerous Solvents
soda formula is an excellent de-greasing media that eliminates the uses of solvents in most cleaning processes. Hydroflex does not "dissolve" or "emulsify" grease and oils, it simply coats them causing the grease or oil to release from the surface. It also eliminates the translocation of oil and grease.

Does Not Produce Sparks
Standard grades of soda blast media (without hard aggregate) will not produce thermal sparks and are suitable for use in explosion proof areas; including refineries, chemical plants and grain elevators as long as proper grounding techniques are used to prevent a static charge build up.

Improved Crack Detection
When cleaning metal surfaces for crack detection, standard abrasive blasting tends to peen the crack closed or pack the crack with abrasive, making crack detection more difficult. soda media actually cleans out the crack, leaving it exposed and easy to find.

No Residue Problems In Small Passageways
Standard grades of soda blast media (without hard aggregate) are 100% water soluble. They can be used to clean critical engine components including those with small passageways. Once cleaned, the soda residue can be thoroughly rinsed off by dissolving in water.
Traditional blast media are not water soluble and if left after cleaning, can pack into small passageways and possibly damage an engine while on operation.

Reduce Surface Acids
As a strong buffer for acids and alkalis, soda eliminates acidic conditions on the surface of the substrate. For conditions with high acid levels, acid rain or boiler fly ash, blasting with soda will reduce coating failures.

SSPC-NACE Standards
soda will attain a level of clean that will meet the standards of both NACE and SSPC.

NACE 1 (SP-5) White Metal Blast Cleaning
NACE 2 (SP-10) Near-White Blast Cleaning
NACE 3 (SP-6) Commercial Blast Cleaning
NACE 4 (SP-7) Brush-Off Blast Cleaning

Hardness Scale
soda has a hardness of 2.4 on Mohs' scale of Hardness. The softness of this media means that it can be used to remove most materials without harming the substrate.

Benefits Of Process

Environmentally Sensible
Non-Hazardous to Workers
Non-Toxic Media
Water Soluble Media
Low Blasting Pressure
Does Not Generate Explosive Dust
Does Not Pose A Threat Of Silicosis

Where Used

Industrial Maintenance
Chemical & Petro-Chemical
Oil & Gas Production
Pulp & Paper
Food & Beverage Processing
Textile Mills
Foundries & Steel Production
Printing Industry
Electrical Utilities
Mining
Aviation, Military & Commercial
OEM's, Automotive, Electronic
Marine
Transportation, Transit, Highway.