RCRA 8 metals
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The RCRA 8 metals is a list made by the EPA over metals not allowed in general waste if it is over a certain level. If it crosses the level it is treated as hazardous waste. It applies to both liquid or solid waste.
The limits for each of the RCRA8 metals are:
- Arsenic 5 ppm (mg/l)
- Barium 100 ppm (mg/l)
- Cadmium 1 ppm (mg/l)
- Chromium 5 ppm (mg/l)
- Lead 5 ppm (mg/l)
- Mercury 0.2 ppm (mg/l)
- Selenium 5 ppm (mg/l)
- Silver 5 ppm (mg/l)
The most common metals found in refining wastes are silver and cadmium.
Definition of limits
The EPA Limits for solid waste is calculated as the amount that can be leached in a test called Toxicity Characteristic Leaching Procedure, TCLP. It simulates landfill conditions and shows if the solids poses a toxic hazard for the environment once it's been deposited.
For example, a piece of stainless steel contains chromium but would probably not pose a problem in solid waste while dried up solutions from dissolving stainless would pose a toxic hazard as the chromium salts are easily leached.
It is the responsibility of the producer of the waste to test and mark the waste according to the result.
Many soluble chromium compounds is both toxic and carcinogenic, especially chromium(VI) compounds. Chromium in metal or oxide form isn't toxic but it needs to be inert so it doesn't leach out.
Hexavalent chromium, Cr6+ can be reduced to the less harmful Cr3+ by mixing it with copperas.