The surface complex formation of K+, NO3-, SO42-, Ca2+, F-, Co2+, Cr3+ ions was examined on the surface of silica gel. Experimental data obtained by acid-base titration of a solution containing adsorbent were calculated using the Fiteql fitting program applying a triple layer model. The value the of the deprotonation constant is log K=7.6±0.2. The value of the protonation constant of silica gel is log K+=2.2±0.6, depending strongly on the model used. The ion-pair formation constants of K+, NO3-, Ca2+, SO42- are: log KipK = 0.5±0.3; log KipN03∼0 (it is not measurable), log KipCa: 0.7±0.3 and logKipSO4: 0.3±0.2. These values are around zero, therefore these ions can be considered as non-specifically binding ions in the investigated pH range of pH= 2.6-9. The determined surface complex formation constant of F- is logK SiF = 4±0.4. The ion-pair formation constants of Co2+, Cr3+ ions are: log-KipSOCo[+] = 4.35±0.36, logK ipSOCr(OH)2= 3.6±0.36. It is shown that the goodness of optimization itself, i. e. WSOS/DF < 20, is not a good test for the applied equilibrium model. The results are affected by the relatively large error of the values of ion-pair formation constants used for inert ions. This uncertainty can be reduced using the modified triple layer model.
|Number of pages||11|
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - Nov 1 1999|
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