This additive is known as Blastox® and it was developed by the TDJ Group, Inc. of Cary, Ill. First offered as a proprietary chemistry in 1991, the technology now has been used on thousands of production jobs, with over 30,000,000 square feet of steel blasted and coated successfully. Among these jobs are about 20 state Departments of Transportation (DOTs) and many national contractors that have specified and/or used the technology for their lead abatement projects.
The Basic Facts
Features of this blasting additive include:
- Reduces potentially hazardous wastes to a non-hazardous condition for lead;
- Reduces the leachability of many heavy metals including lead, chromium, cadmium, mercury, and zinc;
- Remains non-hazardous long term after put in a landfill;
- Used by industry and military on a wide variety of products such as pipe systems, water towers, plant facilities, tanks, and bridges;
- Used with any abrasive media and equipment for either a dry or wet blast; and
- Helps to reduce the lead in the air generated during blasting.
This additive is abrasive with a Mohs hardness greater than 6.0, and it has a similar bulk density to sands or slags. Blastox is a calcium silicate technology and contains no free iron or steel. It can be shipped to a job site in bag or bulk, and is supplied pre-blended with various abrasive media through a network of regional blending facilities consisting of abrasive manufacturers and independent blenders.
It is typically added to abrasives at a 15 percent weight ratio. This engineered ratio is based on an average application rate of six to eight pounds of blast media per square foot of paint removed.
At that average rate, 15 percent of Blastox represents about one pound of chemicals per square foot to stabilize the lead. With this ratio, TDJ guarantees that if it is properly blended and used, it will reduce the leachable levels of lead from up to 100 mg/l to 5.0 mg/l. When a user's application rate is less than the recommended pounds per square foot rate, TDJ consults with him individually.
No Waste Permits Required
All 50 states and the EPA have indicated that as long as the product is added prior to blasting, the process is not considered treatment. Therefore, no waste treatment permits are required. However, if a waste is characterized as a hazardous waste and Blastox is added after that determination, a permit may then be required from the state or the U.S. EPA.
The 15 percent ratio will reduce the leachability of most metals found in paint systems to below hazardous levels. Chromium may require additional stabilization steps to achieve non-hazardous levels. If chromium is present on a structure, TDJ can assist users in finding a ratio or mixture to stabilize the metals present.
The stabilization mechanisms are summed up by the following: encapsulating hydration reactions, as well as addition and substitution reactions between heavy metal cations and calcium silicates and a pH adjustment. The pH adjustment is a result of hydration reactions, immobilizing the lead ions and allowing the remaining chemical reactions to occur. The lead is chemically converted from a soluble form (such as lead oxide or lead hydroxide) to a stable lead salt (such as lead silicate). In addition, Blastox employs an EPA Best Demonstrated Available Technology (BDAT) stabilization process, the details of which are available through TDJ.
Long term stability data on Blastox indicates that its stabilized abrasives can pass more than five consecutive TCLP tests on the same waste sample. Blastox has also been subjected to and passed the EPA MEP (Multiple Extraction Procedure) test by the Federal Highway Administration and the Army Corps of Engineers. That test subjects the same sample to 10 back-to-back tests and is designed to simulate the acid rain a landfill would be exposed to over extended periods of time. The testing suggests the material is stable under conditions that far exceed agency test standards.
Even though stability data may indicate long term compliance, many generators are hesitant to put any material in a landfill. The TDJ Group, Inc. has been working on alternate disposal methods for spent abrasives. Several areas have been identified where spent abrasive residue with Blastox may be reused as a raw material for other manufacturing processes, rather than landfilled. This option has been operational in the Western United States for the past several years.
Last year TDJ expanded its beneficial reuse capabilities into the Southeastern United States and may soon be operational nationwide. This could greatly reduce liability for the generator, since a non-disposal alternative will be used.
Blastox blended abrasives have also been known to lower the amount of lead that is generated in the air inside containment, provided that a site has a proper containment design and good air flow. Studies have shown that Blastox may reduce the amount of lead in the air as much as three to five times versus straight abrasive. New data shows that Blastox blends combined with wet abrasive blast systems can produce lead in the air levels below the OSHA Action Level of 30/mg/m3.
Effects on New Coatings
In order to study the performance of coatings used over Blastox surfaces, Tnemec Company, Inc. of Kansas City, Mo., did a year of testing and reported the following: "We have completed our testing of various Tnemec coating systems applied over hot rolled steel prepared by sandblasting to an SSPC Sp-10 Near White blast using a Blastox blended abrasive. Based on the results of our testing, the use of Blastox containing abrasives has no effect on immersion service when properly coated with both our two-coat Series 20 Pota-Pox system and our two-coat Series 140 Pota-Pox Plus system.
"Our testing has also shown that the use of Blastox containing blast media had no effect on the performance of various exterior coating systems. The systems tested included our silicone alkyd system, organic zinc/ epoxy/urethane system and two epoxy/urethane systems."