The flasks were shaken for 90 min at constant temperature
and stirring (25 °C and 200 rpm) in thermostat water bath, and
then 10 mL aliquots were centrifuged for 5 min at 3000 RPM,
in order to separate the adsorbent from the aqueous solution,
and subsequently to determine the concentrations of Cd, Pb and
Cr in the solution by FAAS (Welz & Sperling, 1999).