UV-Solar Photocatalysis for the Simultaneous Removal of Arsenic and Mercury in Washing Solutions from Polluted Marine Sediments

Abstract

An environmentally sustainable strategy has been developed for simultaneously removing arsenic and mercury from wastewater, potentially coming from washing of polluted marine sediments. Citric acid (CA), a biodegradable chelating agent, forms stable complexes with both metals, which can be extracted from contaminated sediments through ex situ sediment washing. A solar photocatalytic method has been developed to separate toxic metals from wastewater and degrade CA. Increasing the TiO₂ photocatalyst load enhances arsenic adsorption under dark conditions. Total arsenic removal is achieved during photocatalytic decontamination using 1000 ppm of TiO₂. Fe(III)–hydroxides formed in the presence of Fe(III) further adsorb arsenic. Nearly total arsenic removal is achieved even under seawater conditions and visible light irradiation only. The removal of arsenic in different oxidation states has been successfully demonstrated. The UV–vis/TiO₂/CA photocatalytic system has also proven highly effective for mercury removal from wastewater. Although seawater conditions slightly slow the removal process, complete mercury removal is achieved even under visible light irradiation. Finally, a combined photocatalytic approach has been developed for the removal of both arsenic and mercury, achieving 100% removal within few minutes of light irradiation. The reaction mechanism has been depicted based on intermediates and reaction products detected during the photocatalytic process.