3.2.3. Effect of MNHAP amount
The relationship between MNHAP amount and the heavy metals
adsorption quantities was shown in Fig. 6. The results showed that
the amount of heavy metals adsorbed increased rapidly with the
increasing of MNHAP amount at the beginning. When the amount
of the MNHAP was 0.1 g L−1, the adsorption amount reached maximum
followed by a decrease of the adsorption amount as the
MNHAP dosage increased. The reason for this phenomenon was
that, for a fixed initial concentration of heavy metals, the amount
of metal retained by gram of MNHAP increased with the amount
of MNHAP (increases the no. of sites available) before the maximum (conditions of saturation), and when more MNHAP were
added after the maximum (the retention is almost total), the same
cations were distributed on greater amount of surface and therefore
resulted in the reduction of adsorption amount on unit mass
adsorbent. Since the adsorption capacity reached maximum at
the point of 0.1 g L−1, this dosage was chosen in the following
experiments.