Abstract
Presence of hexavalent chromium, Cr(VI), in water is an important environmental and human health problem. Natural zeolites are widely accepted as non-expensive adsorbents for sustainable remediation, however they are not effective in removing metals in anionic form. The paper presents study on use of silver (Ag) modified natural clinoptilolite to immobilize Cr(VI) ions from model and real neutral to slightly alkaline wastewater. Increasing the initial pollutant concentration increases the removed amount (80 % removal from model wastewater in 45 min at initial concentration of 30 mg Cr(VI)/L). The pseudo-second order kinetic equation best describes the Cr(VI) immobilization by the Ag-modified zeolite, which is indicative for the chemical nature of the rate-limiting step of the process. The data obtained are best fitted to the Freundlich adsorption isotherm. The Ag-modified clinoptilolite removes in 30 min over 80 % of Cr(VI), over 75 % of Cu(II) and over 70 % of Zn(II) that present simultaneously in an industrial wastewater. Due to its ability to remove Cr(VI) species, in combination with some heavy metal ions, some organic pollutants and exhibited antibacterial activity, silver loaded clinoptilolite seems to be a possible multifunctional reagent in the water and wastewater treatment and deserves further investigation.
Highlights
Hexavalent chromium, Cr(VI), appears in water due to natural and anthropogenic reasons
It is estimated that more than 70 % of Cr that is found in the environment comes from anthropogenic sources, such as nonferrous metals production, metals finishing and corrosion protection, paper and pulp mills, urban wastewater, etc
The immobilized amounts of Cr(VI) are of the same order of magnitude as the values described by other works for metal-exchanged forms of different aluminosilicate minerals, including natural clinoptilolite [25, 27]
Summary
Hexavalent chromium, Cr(VI), appears in water due to natural and anthropogenic reasons. It is estimated that more than 70 % of Cr that is found in the environment comes from anthropogenic sources, such as nonferrous metals production (minerals beneficiation, metals smelting and refining), metals finishing and corrosion protection, paper and pulp mills, urban wastewater, etc. The effluents from these industries contain Cr(VI) at concentrations ranging from parts of the tenth to hundreds of mg/L [2]. In natural waters Cr(VI) exists mainly as chromate (CrO42-) or hydrogen chromate (HCrO42-) ion [4]
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