The adsorption of heavy metals from synthetic wastewater by using natural mixed shell (Krasa) in
Samut Sakhon province was studied. The main elements of Krasa are bivalves such as Carpet shell,
Venus shell and Cockle shell. Effective Size was 0.28 mm and uniformity coefficient was 7.27 .The
adsorption capacities and rates of heavy metal onto Krasa were studied in a batch adsorption system.
Maximum zinc, copper and cadmium adsorption was found at pH 5, shaking time 60 minutes, contact
time 60 minutes. The amount of 0.25 g. and size 2-4.275 mm. can reduce the 40-65 % of heavy metals.
Adsorption isotherm data of the heavy metal could be well explained by both the Langmuir and
Freundlich model. The kinetic experimental data properly more correlated with pseudo-second order
kinetic model than pseudo-first order.