I am working on an issue of an environment with Cu and Zn ions prepared by CuSO4.5H2O and ZnSO4.H2O with an adsorbent. when I check the solution after shaking (and use the filter to have Homogeneity the concentration of Zn is logical and it shows that adsorption with adsorbent is done but the main problem is Cu ion. The atomic adsorption display almost no Cu ion even I add more and more concentration of Cu ion but there is no difference, also I decrease the time of shaking but the result same, almost no Cu ion. It could not be accepted so when I check the main container of the experiment I recognize that the precipitation of it without really adsorption of Cu ion on adsorbent. I can not know what the problem is and how I can fix it and what is the good way to investigate adsorbent capacity to adsorb these two ion under an appropriate condition.
Dear Alimohammad,
What adsorbent have you used? Of course, it is not very normal, although to try to give a possible explanation it is necessary to know what type of material you are using.
Best,
Fran
But what is the pH? The solubility of Cu2+ ion changes a lot with pH.
Francisco Manuel Marquez thanks for your consideration, the adsorbent is KMgPO4.6H2O. the article about adsorption of Cu ion on NH4MgPO4.6H2O has been published , and I thought it might be the same process. but as more Cu ion as I add to the sample the result are the same, no Cu concentration in the filtered solution and consequently all of Cu ion are precipitated but Zn is Ok.
Valerio Paolini the pH of starting point is about 5 and the final pH is about 9.
is there a big difference between Zn and Cu ions? cause the Zn does not behave like Cu ions.
Indeed yes, there is big difference: Zn is amphoteric (like Al) and is soluble at pH=9 because it forms Zn(OH)4=. Cu does not. Best regards.
Valerio Paolini thank you very much, is there any way to overcome this phenomenon and investigate the adsorption of Cu ion?
The pKa value of of Cu2+(aq) is around 7.
However, at pH < 6 there is no Cu (OH)2 in aqueous solution.
Akito I Sema thank you very much for your consideration,do you mean that the pH of the solution should be kept under 6 so that the Cu ion would not precipitate and if the pH is more than 7 anyhow the Cu ions definitely would precipitate regardless of other conditions?
i have explained in this paper if you would like to read.
Article A brief commentary on activated carbon material as an effici...
Maybe there is some confusion here. Dear Dr Alimohammad Dehghan Manshady, if you need to calculate the solubility of Cu2+ ion at different pH, the only thing you have to know is the solubility of its hydroxide Cu(OH)2, which is Kps=[Cu2+]×[OH–]^2=2.2×10^-20. So you can easily calculate the maximum concentration of [Cu2+] that can be solved as a function of [OH-] concentration, just using this formula: [Cu2+]=Kps/[OH–]^2. For instance at pH=9.45 you have pOH=14–9.45=4.55 and [OH–]=10^-4.55=2.82×10^-5M, and so [Cu2+]=Kps/[OH–]^2=2.2×10^-20/(2.82×10^-5)^2=7.95×10^-10 M meaning that Cu2+ is "almost insoluble", as you have experimentally observed as well. Other example at pH=5.45 you have [OH–]=3.55×10^-10 M and so [Cu2+]=Kps /[OH–]^2=2.2×10^-20/(3.55×10^-10)^2=0,175 M meaning that Cu2+ is very soluble. Best regards and good luck with your work ;)
PS: I strongly recommend you to use a pH buffer, if I was the reviewer of your manuscript I would be very concerned by the pH variation during adsorption. Is it significant to remove Cu and Zn from a water at pH= 9 ? What is the future application of this adsorption? Likely, you will apply it to a (waste)water with a neutral or slightly acid pH. For instance you might try sodium acetate (pH=5.3) or neutral phosphate buffer, depending on the pH of the (waste)water to which you want to apply your decontamination methodology.