3.5. Effect of natural water matrices
Natural waters are very complicated matrices, containing various
inorganic and organic substances. These constituents are able to
interact with the adsorbents used in water purification. To study the
availability and the effectiveness of SH-mSi@Fe3O4 on the uptake
of heavy metal ions in natural water sources, different water matrices
spiked with single metal ion were mixed with the adsorbent.
The removal efficiencies for single metal ion were determined after
the adsorption.
It was found from Table 3 that SH-mSi@Fe3O4 exerted good
adsorption for Hg2+, Pb2+ and Ag+ in different natural water sources,
with removal efficiencies of over 95%. While, adsorption of Cu2+
was the worst with the removal efficiency not more than 80%. The
distribution coefficient (Kd) between water and the adsorbent is
also used to evaluate the adsorption performance in different water
matrices [27]. The Kd values of the metal ions in tested water matrices
were at the magnitude of 105, which is much higher than the
value of 103 categorized as good performance [43].
It is also found that the SH-mSi@Fe3O4 adsorbed more heavy
metals from groundwater than from other water sources. This is
probably due to the groundwater used in the experiment contains
less competing metal cations like Ca2+ and Mg2+ and organic matter
(total organic carbon, TOC). Although the affinity to thiol group is
weak, Ca2+ and Mg2+ could still bind with a portion of the adsorption
sites on the surface of SH-mSi@Fe3O4 through Coulomb force.
Organic matters also have strong effect on heavy metal removal.
Suspended large molecular organic substances could block the
pores of the mesoporous adsorbents, which leads to the decrease
of adsorption efficiency on the one hand, and organic functional
groups like carboxylate and hydroxylate could counteract the
adsorption on the other [44]. Therefore, the performance of SHmSi@
Fe3O4 in groundwater was better.