Desorption experiments
In order to estimate the reversibility of Cd2+ and Zn2+ sorption,
desorption experiments using solutions with different pH were
performed. Firstly, MNHAP was loaded with Cd2+ or Zn2+ by equilibrating
the adsorbent with 2×10−2 mol L−1 Cd2+ or Zn2+ solution
.The resulting suspensions were separated and the final metal concentrations
were determined. Subsequently, the solid residue was
thoroughly washed several times with distilled water, and dried
at 90 ◦C. Secondly, amount of 0.1000 g of the obtained adsorbents
was added into 20mL of four kinds of eluants including EDTA, HCl,
Ca(NO3)2 and NaOH respectively at room temperature (25±1 ◦C)
under vibration conditions for 24 h. After the completion of the
reaction, the metal concentration in each eluant was measured