Effect of pH
The pH of the solution has a significant impact on the
uptake of heavy metals since it may affect the ionization
degree of the sorbate and the surface property of the
sorbent [32]. Moreover, the selectivity of metal ion by
zeolites is influenced by the character of the metal complex
that predominates at a particular solution pH [33]. The
contact of the zeolite surface with water leads to the
ionization of surface hydroxyl groups (Si–OH and Al–OH).
The degree of ionization is affected by pH, and the acid/
base reaction taking place at the hydroxyl groups may
results in surface charge development [34]. Zeolites are not
only affected by pH but likewise are able of influencing
solution pH especially in batch system and zeolites tend to
have a higher internal pH. In fact, the zeolite surface may
be influenced by the ambient pH, which is different from
the external solution pH value and precipitation within the
channels of zeolites and at the surface of zeolites may
occur.
Fig. 5 illustrates the variation of Cu (II), Co (II) and Cr (III)
removal on the synthesized zeolite at different pH values. rate of adsorption of single metal ions increased with pH.
In fact, the adsorption percentages increased clearly after
pH 5 for all metals.
Copper ions adsorption remains almost constant up to
4, and then increased sharply to 94% adsorption around pH
6. At higher pH, the adsorption percentage was rather slow
and decreased to 91% adsorption at pH 9. A similar