Crushed Glass Grit vs Coal Slag

ContractorTalk.com is a great resource for contractors looking for help from their peers on a variety of topics. There was recently a thread started by a contractor that uses coal slag who was looking for other user's preferences as well as similarities and differences between Crushed Glass Grit and coal slag. Some of the comments included:

"I use the glass because of the area I am in...Maine is going greener..."
"I use coarse glass on heavy rust and heavy equipment"
"'Medium grade good for autos and bikes"
"Glass cleans faster...large media for heavy scale and rust...fine for everything from log and cedar homes to thin sheet metal auto panels"
"My {powder} coaters like glass because it is clean and takes very little prep work before coating"
"I used to use slag and it's filthy. Even my hands were dirty from being around it."

Coal Slag & EPA

The EPA released a statement last week regarding the regulation of coal ash waste. Due to the 'complexity of the analysis' the EPA has delayed their decision. In a previous post, including a link to a 60 Minutes story, the potential hazards of using coal byproducts - including coal slag - was noted. I hope that the delay with the ruling is so that the EPA maintains the priority on the safety and science of this issue (whatever that analysis shows) over the politics.

Coal Slag

When coal is burned in a boiler to produce energy, the incombustible materials constitute three components: fly ash, bottom ash and bottom slag. There is growing concern about the potential hazards of coal waste due to contamination with heavy metals such as chromium, lead and arsenic.

Fly ash is the light 'dust' that is exhausted from the burning process. Improvements over the past 20 years at coal fired facilities has allowed as much as 99% of this ash to be captured for re-use in other applications. Bottom ash is the unburned material and fine particulate that is not expelled in the flue. A recent 60 Minutes expose discusses some of the hazards of fly ash:

Watch CBS News Videos Online

Boiler slag is the molten material (ash and incombustible) that is sent to a quenching water bath. The quenching process immediately fractures the molten material producing a coarse, hard, black, angular, glassy material sometimes call black beauty. This coal slag is used for a variety of industrial applications including abrasive blasting. The concern is that once the coal slag is blasted, the process releases the heavy metals into the air or they get absorbed by ground water.

While coal slag (which contains minimal crystalline silica) has historically been considered to be a safe alternative to silica sand, the EPA is reviewing whether to classify fly ash and other coal burning wastes as a hazardous material. There is no need to wait for the EPA to make a final determination. There are many alternatives to coal slag for blasting such as crushed glass grit and other more specialty types of blasting media.