Whether you have these substances in solid form or in solution, we recommend that you store them for collection by a licenced waste disposal contractor.
Chromium (VI) compounds, such as dichromate and chromate salts, are classified as Category 1 Carcinogens and are toxic to the environment and should be handled with care. Appropriate PPE—including chemical-resistant gloves, such as nitrile gloves—should be worn when handling these substances and an operating fume cupboard should be used where possible.
Water authorities in Australia accept low concentrations of small quantities of chromium salts in waste water; the washing and rinsing water used in removing Cr residues on contaminated glassware would be unlikely to exceed these limits and should be acceptable to discharge to sink.
The chromium ions can be precipitated from solution as the much less hazardous chromium (III) hydroxide, but we generally wouldn’t recommend doing this, due to the hazards involved and because the resulting chromium (III) precipitate would still have to be collected by a waste disposal contractor.
- Karale, R.S., Wadkar, D.V., Nangare, P.B., Removal and recovery of hexavalent chromium from industrial waste water with due consideration to cost optimization, Journal of Environmental Research and Development, 2(2), 2007, p. 209.