No abstract

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.

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.

The dumping of the mining tailings dam from Mariana, Brazil released about 34 million mining tailings in the Doce river basin, containing many toxic metals. The biomasses of banana and rice were used as adsorbents in the removal of Cu (II) and Pb (II) metals from contaminated water. Quantification of metals was performed using NexION 300D PerkinElmer (USA) ICP-MS. The pH effect studies indicated that the adsorption analyzed in the present work did not undergo significant changes with the variation of the pH values, thus for both banana and rice the best adsorption capacity of Cu (II), 34.11 mg g−1 and 34.37 mg g−1, was at pH 5. For Pb (II), the highest adsorption capacity was also at pH 5 with 36.06 mg g−1 for banana and 36.04 mg g−1 for rice. There was a rapid adsorption where, in all cases in the first 30 minutes of adsorption, more than 60% of the metals had already been adsorbed. Finally, tests were carried out using real samples from Doce river contaminated by the metals under study due to the Mariana disaster. The biomasses presented excellent performance in Cu (II) and Pb (II) removal, reaching concentrations close to zero after adsorption process.

If not properly treated, water contaminated with chromium (Cr(VI)) and lead (Pb(II)) can cause severe damage to health due to the accumulation of those toxic metals in the human body. Therefore, in this work, three iron oxides, i.e., δ-FeOOH, cystine-functionalized δ-FeOOH (Cys-δ-FeOOH), and Fe3O4, were synthesized and used as adsorbents for Cr(VI) and Pb(II) in water. The results indicated that the Cr(VI) is best adsorbed on cys-δ-FeOOH followed by δ-FeOOH and Fe3O4. It was because of the enhanced interaction between Cr(VI) and the cysteine functional groups on the δ-FeOOH surface. The Cr(VI) adsorption capacity of cys-δ-FeOOH, δ-FeOOH, and Fe3O4 was 217, 14, and 8 mg g−1, respectively. On the other hand, Pb(II) was preferentially adsorbed directly on δ-FeOOH achieving a maximum Pb(II) adsorption capacity of 174 mg g−1. The Pb(II) adsorption capacity of cys-δ-FeOOH and Fe3O4 was 97 and 74 mg g−1, respectively. The Cr(VI) adsorption on cys-δ-FeOOH was best described by the Langmuir-Freundlich model, whereas Pb(II) adsorption on δ-FeOOH followed the Langmuir model. Both Cr(VI) and Pb(II) adsorption on the adsorbents was well-fitted to pseudo-second-order kinetics. The Cr(VI) was more quickly adsorbed by cys-δ-FeOOH (h0 = 0.10 mg g−1 min−1) while the initial adsorption rate of Pb(II) onto δ-FeOOH was significantly faster (h0 = 16.34 mg g−1 min−1). Finally, the synthesized adsorbents were efficient to remove Cr(VI) and Pb(II) from water samples of the Doce river after the environmental disaster of Mariana city, Brazil, thus showing its applicability to remediate real water samples.