According to the literature, As (V) can be treated more easily than As (III). As (III) is more commonly found in reducing environments such as groundwater.
Therefore, I want to make sure that the trivalent form is present in my aqueous solution before treatment. I already set pH=4. Could you please tell me a way to reduce ORP in laboratory? (I supplied nitrogen gas but there was no difference according to ORP meter).
I thank you for your kind attention in advance.
Not very pleasant approach is to use hydrogen sulphide. As I understand it, H2S accounts for anoxia at depth in the Black Sea.
Most important is how to ensure the precise occurrence of anoxia. ? . to my mind, best course would be to look at redox potential on negative side , somewhere -200-300 mv , but again the values of soil redox potential as an indicator of anoxia will depend upon soil type.
If I understand your request well, you need to turn your sample of water anoxic... That means with zero oxygen dissolved. If that is what you need, try to add to your sample of water an aliquot of water solution of sodium sulfite (15% w/v ?) which is routinarily used to calibrate the zero oxigen point in oxymetry. You can search detail in the web for this. When I use this solution for O2 elimination in oxymetry for pristine waters the vanishing of all oxygen is nearly instantaneous. Greets. Gustavo.
You cannot use reverse osmosis (RO) to remove oxygen gas, but you can use an additive to bind to oxygen so that the resulting compound is a solid.
Then you can use RO to remove the resulting compound. The water should then become anoxic.
To eliminate the aqueous O2, you can add excess MnSO4 (48% of vol) along with excess KI into water. This will lead to the formation of Mn(OH)3, by consuming DO. Mn(OH)3 will precipitate and the filtrate will contain no or very less amount of O2.
Alternatively you can create anoxic conditions biologically, depends what your sample is and what you want to achieve. Add any organic material that can be transformed by bacteria into CO2 and CH4. I.e. sugar or light hydrocarbon and exclude air. If CO2 is produced let it get out from the bottle.