Comment: Problems/issues with immobilizing As in cement
- I would caution against immobilizing spent arsenic media in cement.
Arsenic is bound strongly to both iron and alumina-based materials at pH values between about 4 and 9 but at higher pH values, the arsenic is stripped from the media and becomes mobile. (In fact, stripping at high pH is the general method for regenerating spent arsenic media!).
Thus the high pH encountered in cement is not conducive to keeping the arsenic immobilized. You would be better using a methodology that maintains the pH closer to environmental levels.
- I agree with Dr.Paul Sylvester's cautionary note. That is why we have to construct a heavy concrete vault to dispose the cement mixed arsenic waste so that the waste is contained within the vault. The vault must be covered so that rain and flood water do not come in contact with waste.
Although arsenic is strongly bonded with iron and alumina based materials, if the waste is disposed in open environment (as many scientists proposed and has been practicing indiscriminate disposal as a safe method based on the same concept), it will cause severe environmental problems due to mechanical/chemical weathering, erosion, transportation by wind and water and other man made practices.
In underdeveloped nations(due to absence of sanitary and hazardous waste landfills,poor socio-economic conditions, I strongly feel cement mixed waste should be disposed into heavy concrete vault until other sophisticated method is invented.
With best regards,