I am performing Pb batch adsorption experiments. While preparing the working solution and adjusting the pH of Pb solution, the solution precipitates at pH above 4. Another issue that i am facing is that after Pb adsorption experiment, the solution precipitates. How should i give sample for atomic absorption spectroscopy? Do I need to filter the solution before the analysis?
The precipiation pH range for lead is 7.2-8.7, therefore your observation is quite strange for me.
If you observed a precipitation in an adsorption experiement, you would not get a proper result for the adsorptions. You would always have the summe of adsorbed + precipitated Pb removed from the solution.
Are you sure that you are using lead? Or that the materilia is not contaminated with something else that starts precipitates a pH of 4?
Dear Noor,
There are too many unknowns in your problem. What lead salt did you use? What water did you use? If it is water that already contains salts, then the ionic strength may influence.
It could also be the effect of common ions. For example, if You have used PbCl2 to which you have added HCl to adjust the pH, then there are too many chlorides and the inverse reaction will occur (Precipitation). This is called the "common ion effect".
Regards
Thank you so much everyone for your kind responses.
Salt of Pb is lead nitrate, i am using distilled water currently previously i was using deionized water. 0.1 N HCl and 0.1 N NaOH for pH adjustment.
Problem 1: Working solution preparation, when NaOH added the precipitation occurs even at pH 5.
Problem 2: After adsorption (working solution pH=4 initially) precipitates are formed. Do i need to filter my sample?
Dalal Z. Husein Thomas Mayer-Gall
Problem 2. If in an adsorptions process a precipitation occours, you won't get a proper result for the loading.
As said before, you will habe probably the precipitation of PbCl2.
For atomic absorption spectroscopy, I think its better to filter your sample before analyses.