For heavy metal chromium adsorption experiments from biochar how much concentration of sulphuric acid/ NaOH should I use to maintain pH range 1-10 of potassium dichromate soluion? If use of sulphuric acid is safe as it could make chromium sulphate precipitation which may give false reading. Do I use some other acid/ base to maintain pH, If yes then at which concentration?
When should I maintain pH of the potassium dichromate solution either after adding the biochar or before it as after adding the biochar the solution pH may increase.
Dear Amita... How are you planning to estimate the Cr+6 concentration levels? Have you decided on that? Are you going with ICP-AES or AAS?
Secondly, remember Cr is difficult to handle as it is equally stable at variable pH levels. So, even if Cr is present, the stable form may not allow you to pick up the concentration levels. I had terrible time handling Cr...
Dear Arif SIr,
Thank you for your reply, I am doing it with Diphenylcarbazide method of UV spectroscopy. I did it with a little amount of concentrated sulphuric acid.
But now I am moving ahead for ICP-OES. I am trying to find out how do i prepare my samples for that. Sir, please tell me whether I need to digest my samples of water (the extract), or i could just filter it with .45 micron filter and put it for analysis...???
Dear Amita...
I would prefer ICP-OES. However, I encountered couple of issues with acid digestion technique. Do not use HF as it is known to severely affect the nebulizer of ICP-OES. Check USEPA - 3050B. You can find something useful there.
Further, if you use .45 micron filter, here is what could happen. (Remember I am being devils advocate here)
If the adsorption is taking place in biochar, sometimes, the size of Cr precipitate could be more than 0.45 microns. This will be retained on your filter and in-turn you may get very high adsorption levels (or quite high removal efficiency levels - which ever way you look at). Sometimes, you can even get negative levels. I do not know whether you have encountered this scenario or not. But, it happened with me. As I said earlier, this doesn't mean that Cr is not there in your sample.
Try with glass fiber filters and use more than three aliquots. Try to purge all samples on the same day with ICP-OES. Check the deviation levels and calibrate the instrument to non-linear regression fitting. It will pick up small Cr levels. Remember ICP-OES consumes lot of Argon and Nitrogen. If you are doing batch adsorption testing, you need to do all the samples in one go. In this way, even if there is an error in the testing, it will be equally distributed and the trend can be trustworthy. Make sure the deviation levels between each aliquots is not more than 5% (allowable as per ASTM standards)...
Cheers and Best of Luck :)
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