engleski

Preliminary investigation of sorption of the Hg(II) chloride complexes on the natural zeolite

In this paper, the possibility of using natural zeolite clinoptilolite (NZ) originating from the Vranjska Banja deposit, Serbia for the remediation of mercury-polluted water systems is examined. Namely, it is well-known that the area of the Idrija mine in Slovenia is still contaminated with mercury as a result of the excavation and processing of cinnabar ore, as well as inadequate disposal of mine tailings. Moreover, investigations have shown that runoff waters wash away the Hg species from contaminated soil into the Idrijca and Soča-Isonzo rivers, and finally to the Gulf of Trieste, where complexation of Hg species with chloride ions occurs. Mercury in seawater exists in the form of soluble chloride complexes available for the methylation process, most often in the sediment. Therefore, this paper examines the sorption of Hg(II) species from the HgCl2 aqueous solution on the NZ under different experimental conditions. The results indicate that the optimal pH range is pH=2-5, since above pH>5, Hg(II) precipitation occurs. The optimal solid/liquid ratio in a wide Hg(II) concentration range is 6 g/L. The highest proportion of sorbed Hg(II) is achieved in 120 minutes, with the maximum sorption capacity of 0.07 mmol Hg/g of NZ. The obtained sorption capacity of NZ towards Hg(II) is lower compared to other tested heavy metals. The consequence of this behaviour probably lies in the fact that Hg(II) at pH<5 exists in the form of neutral complexes, HgCl2 and HgOHCl, whereby the effect of electrostatic attraction is reduced on negatively charged NZ. Therefore, for the possible implementation of NZ for remediation purposes, it is undoubtedly necessary to carry out its chemical modification with sulphur species due to the well-known affinity of mercury toward sulphur species. Since NZ and sulphur species are natural constituents of the hydrogeological layer, the obtained material should be compatible with the environment with improved sorption properties.

natural zeolite ; mercury ; mercury chloride complexes ; sorption

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