The application of synthetic zeolites for the removal of heavy metals from contaminated effluents
The aim of this research was to provide a comprehensive evaluation of the heavy metal
removal performance of two synthetic zeolites, Zeocros CA150 and Zeocros CG180.
Detailed laboratory investigations of the key parameters known to affect zeolitic ion
exchange were performed with respect to lead, zinc, copper, cadmium and nickel by means
of batch equilibrium tests.
The study into the effect of contact time suggests that a near equilibrium state was reached
within two hours. As metal hydroxide precipitation was minimal at pH 6.0 and the structural
integrity of the zeolite was maintained, metal removal at this pH is predominantly by ion
exchange rather than chemical precipitation. Fluctuations in both silicon and aluminium
release from the zeolites suggest that partial dissolution may occur under mildly acidic
conditions, an observation discussed elsewhere in the literature.
Heavy metal removal decreased with increasing metal loading, with the zeolites exhibiting
Significantly lower operating exchange capacities compared to the theoretical ones.
Exchange capacities varied between 1.3-4.9 meq/g and 0.5-4.6 meq/g for CA 150 and
CG180 respectively for the five metals studied. Throughout all of the experimental
investigations, lead was removed preferentially (>99%) and nickel removal effiCiencies were
the lowest «20%). The results from the mixed metal studies demonstrated that lead
removal was the least affected by the presence of other heavy metals whereas cadmium,
copper and zinc removal was suppressed in comparison to that from Single metal solutions.
The presence of competing ions was not found to adversely affect lead removal by CA 150
and CG180, with copper and cadmium removal showing the most suppression in the
presence of calcium, magnesium, potassium and sodium. Zinc uptake by both zeolites
proved the most sensitive to the addition of hardness ions even under soft water conditions.
The zeolites were also demonstrated to achieve up to 100% removal from real effluents,
outperforming a natural zeolite, clinoptilolite. Overall, this research has demonstrated the
considerable potential of these synthetic zeolites to selectively remove heavy metals from
complex contaminated effluents, indicating their possible application as a tertiary technology
for effluent treatment.