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FeO nanoparticles were prepared by co-precipitation of Fe and Fe and then modified with Au to produce an effective adsorbent (FeO/Au) for aqueous Hg(II) in contaminated water. Rietveld refinement on the XRD pattern confirmed that the FeO/Au was synthesised. Mössbauer spectra exhibited broad and asymmetric resonance lines with two sextets which can be assigned to tetrahedral Fe; and octahedral Fe/Fe. The quantitative analysis of magnetite confirms that the sample shows around 3 wt.% Au and 97 wt.% partially oxidised FeO. High surface area: 121 m g, average pore sizes: 6.3 nm and pore volume: 1.64 cm g. The kinetics data were better fitted with a pseudo-second-order and Dubinin-Radushkevich isotherm suggests the Hg(II) adsorption onto FeO/Au nanoparticles was mainly by chemical adsorption forming complex with the Au metal immobilised on FeO surfaces. Adsorption capacity of 79.59 mg g. Ionic strength and co-existing ions had a slight influence on the adsorption capacity.

The emission and accumulation of toxic elements such as arsenic in various environmental compartments have become increasingly frequent primarily due to anthropogenic actions such as those observed in agricultural, industrial, and mining activities. An example of environmental arsenic contamination in Brazil exists in the city of Paracatu, MG, due to the operation of a gold mine. The aim of this work is to evaluate the routes and effects of arsenic contamination in environmental compartments (air, water, and soil) and environmental organisms (fish and vegetables) from mining regions as well as the trophic transfer of the element for a risk assessment of the population. In this study, high levels of arsenic were found in the waters of the Rico stream ranging from 4.05 µg/L during the summer season to 72.4 µg/L during the winter season. Moreover, the highest As concentration was 1.668 mg kg−1 in soil samples, which are influenced by seasonal variation and by proximity to the gold mine. Inorganic and organic arsenic species were found above the allowed limit in biological samples, indicating the transfer of arsenic found in the environment and demonstrating a great risk to the population exposed to this area. This study demonstrates the importance of environmental monitoring to diagnose contamination and encourage the search for new interventions and risk assessments for the population.

The contamination of water with arsenic has aroused concern around the world due to its toxic effects. Thus, the development of low-cost technologies for treating water contaminated with toxic metals is highly advisable. Adsorption is an attractive technology for purification of contaminated water, but it only transfers the contaminant from water to the solid adsorbent, which provokes another problem related to solid residue disposal. In this work, we developed a sustainable method for purifying water contaminated with arsenic by using δ-FeOOH nanoparticles. The adsorption capacities of nanomaterial for As and As species were 40 and 41 mg g, respectively, and were highly efficient to purify arsenic-contaminated water from a Brazilian river. The concentration of arsenic in water was close to zero after the water treatment by δ-FeOOH. Once the arsenic is adsorbed, it can be recovered by treatment with NaOH solutions. Approximately 85 % of the total adsorbed arsenic could be recovered and used as a precursor to produce useful material (AgAsO) with excellent photocatalytic activity. It was active under visible light and had a high recyclability for oxidation of rhodamine B. Finally, the simple method described is promising to design sustainable process of environmental remediation with minimum residue generation.

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The high toxicity and potential arsenic accumulation in several environments have encouraged the development of technologies for its removal from contaminated waters. However, the arsenic released into aquatic environment comes mainly from extremely acidic mining effluents, making harder to find stable adsorbents to be used in these conditions. In this work, K-jarosite particles were synthesized as a stable adsorbent in acidic medium for eliminating arsenic from contaminated water. The adsorption capacities of K-jarosite for As, As, and monomethylarsonic acid were 9.45, 12.36, and 8.21 mg g, respectively. Most arsenic in water was adsorbed within the first 10 min, suggesting the fast arsenic adsorption kinetics of K-jarosite particles. Because of that, a K-jarosite filter was constructed for purifying water at a constant flow. The K-jarosite filter was highly efficient to treat arsenic-contaminated water from a Brazilian river, reducing the concentration of arsenic in water to near zero. These data suggest the K-jarosite filter can be used as a low-cost technology for purifying arsenic-contaminated water in acidic medium.

The emission of residues has contributed immensely to the fact that man is susceptible and exposed to toxic chemical products, among them, arsenic. One of the main anthropic sources of arsenic in the world is mining, which can contribute to the contamination of soil, water, air, and food. An example of environmental arsenic contamination in Brazil occurs in the city of Paracatu - MG, due to the operation of a gold mine. Thus, the objectives of this study were: (i) to assess the physical-chemical parameters and the concentration of arsenic in samples of superficial fresh water (sub-basin of the Paracatu River), and soil samples, during winter and summer; (ii) evaluate the arsenic concentration in samples of particulate matter; (iii) determine the concentration and species of As in biological samples and (iiii) evaluate the toxicity of surface waters using the Allium cepa test. There was no change in the physical-chemical parameters. The water samples collected during the winter and all soil samples showed values ​​of As above those allowed by organs regulatory agencies. The values ​​of As in the particulate material showed great variations between the regions under study but were within the limit established by the ATSDR for urban areas. Inorganic and organic As was found above the limit allowed in biological samples The analysis of water toxicity by the Allium cepa test indicated the presence of cytotoxic and genotoxic compounds, demonstrating a great risk for the population exposed to the waters of the Rico stream.