Adsorption of cadmium, nickel and lead on modified natural zeolite
Date
2012-02-14
Authors
Taenzana, Blessing
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Abstract
Environmentally friendly treatment methods for heavy metals prior to discharge are
considered favourable so as to protect ecosystems. The performance of modified zeolite from
two different sources (South African and the USA) for the adsorption of Ni2+, Cd2+ and Pb2+
from synthetic industrial effluent contaminated with metal concentration levels at 50, 150 and
500mg/L was assessed. The selectivity of the zeolite for the adsorption of Ni2+, Cd2+ and Pb2+
was investigated at mixed feed solutions containing all three ions in equal concentrations and
single component concentrations containing only one of the ions. The homoionic forms of the
zeolite were made Na+, K+ and Ca2+. Batch experiments were then conducted to measure the
uptake of metals by the zeolites. The zeolites were characterised using XRD and BET. The
South Africa clinoptilolite has a higher surface area and pore volume (17.52m2/g and
0.047cm3/g respectively) than the USA zeolite (12.26m2/g and 0.028cm3/g respectively) for
the Na+ homoionic form. According to the equilibrium studies, the selectivity sequence can
be given as Pb2+ >Cd2 >Ni2+, with good fits being obtained using Langmuir and Freundlich
adsorption isotherms for low metal concentrations as compared to higher concentrations. The
adsorption was found to depend on the homoionic form of the zeolite and to a lesser extent
the source of the zeolite. The selectivity of a particular zeolite for a particular heavy metal
can be altered by the homoionic form of the zeolite. Generally, the adsorption capacity of the
USA clinoptilolite is higher than the capacity of the RSA clinoptilolite revealing the potential
of clinoptilolite in industrial effluent treatment.