2.3. Adsorption kinetics
A volume of 100 mL aqueous solutions containing Hg2+ and
Pb2+ at concentration of 1 mg/L for each was transferred to capped
polypropylene bottles. The solutions were adjusted to pH 6.5
±
0.05
using 0.1 M HNO3 and NaOH. After 1 mg of SH-mSi@Fe3O4 was
added, the solutions were agitated on a rotatory oscillator at
200 rpm at room temperature (25 ◦C). Samples were pipetted at
certain intervals and the adsorbent was separated using a magnet.
The sample solutions were then spiked with HNO3 to 3% (v/v) and
injected to ICP-MS for analysis.
The pseudo-second-order kinetics was used to evaluate the
sorption kinetics and calculate the rate constants, initial sorption
rates and adsorption capacities: