Removal of heavy metals from aqueous solutions using pretreated natural zeolitic materials: The case of mercury(II)

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Abstract
The mercury(II) removal from its aqueous solutions (concentration range 10 to 500 mg/1) by NaCl‐pretreated pure heulandite crystals and NaCl‐pretreated clinoptilolite‐containing rock samples has been studied using 203Hg as radioactive tracer and radioanalytical techniques (γ‐ray spectrometry and RIXRF). The mercury(II) uptake by the zeoliferous rock was found to be higher than of the heulandite and reached the value of 43.0 mg/g for the highest solution concentration investigated. The corresponding value for the heulandite was found to be 16.3 mg/g. The increased metal uptake of the rock samples is attributed to the contribution of the other microporous minerals (phyllosilicates) present in the material. The uptake distribution coefficient values (Kd) indicated, that the relative maximum uptake for both materials takes place for initial solution concentrations between 25 and 100 mg/1. The mercury(II) binding is due to ion‐exchange, adsorption and surface precipitation processes. The applied chemical pretreatment, causing only a chemical modification to the minerals, played a critical role to the whole procedure and could be proposed for natural zeolitic materials used for the heavy metals removal from industrial wastewaters, sewage effluents and drinking water.