Virginia S.T. Ciminelli

Biosorption of metals in brown seaweed biomass

Biosorption of Cd by biomass of the brown seaweeds Durvillaea, Laminaria, Ecklonia and Homosira presaturated with Ca, Mg or K was coupled with the release of these light ions. The feasibility of biomass pre-treatment to develop a better biosorbent was evaluated by its biosorption performance, the degree of its component leaching (measured by the weight loss and TOC) as well as by the number of ion-exchange sites remaining in the biomass after the pre-treatment. Multicomponent Langmuir and ion exchange models applied to the equilibrium sorption data for pH 4.5 confirmed the ion exchange mechanism involved in the biosorption of metals. Both models fitted well the experimental data and their parameters can be used in the derivation of dimensionless ion-exchange isotherms which are instrumental in predicting the behavior of the biosorbents in dynamic flow-through biosorption systems. The sequence of biomass affinities established for the selected heavy metals can be correlated with the chemical pretreatment of the biomass.

Mechanism of anion retention from EXAFS and density functional calculations: Arsenic (V) adsorbed on gibbsite

Abstract X-ray absorption fine structure spectroscopy and density functional calculations were used to determine the structural model of arsenic surface complex on gibbsite mineral. The structural environment of arsenic at the solid surface may determine its potential for remobilization and stability. Data were collected for arsenate adsorbed on gibbsite surface at pH 5.5. The X-ray absorption fine structure spectroscopy results showed that As(V) forms an inner sphere bidentate binuclear complex on the surface of Al oxyhydroxyl octaedra. Quantitative results showed an average interatomic As(V)-Al distance of 3.19 ± 0.05 A and a coordination number of 1.3 ± 1.0 atoms. Four different adsorption sites in which arsenate can interact with gibbsite have been studied using density functional calculations, i.e., bidentate binuclear complex, bidentate mononuclear complex, monodentate mononuclear complex, and monodentate binuclear complex. The density functional calculations confirm that the most stable structure predicted for As(V)-gibbsite system is the bidentate-binuclear complex.

ARSENIC SORPTION ONTO SOILS ENRICHED IN Mn AND Fe MINERALS

The As sorption capacity of a natural Mn and Fe mineral-containing sample from the Iron Quadrangle province, Brazil, was investigated. A detailed mineralogical identification was obtained by combining X-ray diffraction analyses (with Rietveld refinement), X-ray fluorescence spectroscopy, optical microscopy, and scanning electron microscopy coupled with X-ray energy dispersive spectrometry-EDS. The oxidation state of the adsorbed As species was determined by X-ray absorption near edge structure spectroscopy. The results demonstrate that the presence of naturally occurring Mn oxides promotes the effective oxidation of As (III) to As(V). Also, the Mn minerals show a significant uptake of both the trivalent and pentavalent As species. This study demonstrates that the combined influences of As(III) depletion by oxidation and adsorption on a natural oxide sample consisting of Mn minerals and Fe oxides may effectively contribute to the reduction the As concentration in waters.

The effect of magnesite calcination conditions on magnesia hydration

The aim of this work was to analyze the effect of magnesite calcination conditions, i.e. kiln temperature and residence time, on magnesia response to activity tests and, further, the relationship of this response with MgO hydration behavior under different reaction conditions. The calcination of magnesite was carried out at various temperatures and residence times, in lab-scale Herreshoff and electrical kilns. The solids were characterized with respect to their chemical and physical properties, and then hydrated under different temperature and time. Magnesia activity was compared to the sample surface areas and the corresponding hydration levels. It is demonstrated that the activity test should be used with caution once its suitability to predict hydration behavior of magnesia depends on the samples characteristics and the conditions in which hydration will take place.

A comparative study of As(III) and As(V) in aqueous solutions and adsorbed on iron oxy-hydroxides by Raman spectroscopy

The sorption of the arsenite (AsO(3)(3-)) and the arsenate (AsO(4)(3-)) ions and their conjugate acids onto iron oxides is one of main processes controlling the distribution of arsenic in the environment. The present work intends to provide a large vibrational spectroscopic database for comparison of As(III) and As(V) speciation in aqueous solutions and at the iron oxide - solution interface. With this purpose, ferrihydrite, feroxyhyte, goethite and hematite were firstly synthesized, characterized in detail and used for adsorption experiments. Raman spectra were recorded from As(III) and As(V) aqueous solutions at various pH conditions selected in order to highlight arsenic speciation. Raman Scattering and Diffuse Reflectance Infrared Fourier Transform (DRIFT) studies were carried out to examine the respective As-bonding mechanisms. The collected data were curve-fitted and discussed according to molecular symmetry concepts. X-ray Absorption Near Edge Spectroscopy (XANES) was applied to confirm the oxidation state of the sorbed species. The comprehensive spectroscopic investigation contributes to a better understanding of arsenic complexation by iron oxides.

Emerging mitigation needs and sustainable options for solving the arsenic problems of rural and isolated urban areas in Latin America : A critical analysis

In this work, current information about the contamination of ground- and surface-water resources by arsenic from geogenic sources in Latin America is presented together with possible emerging mitigation solutions. The problem is of the same order of magnitude as other world regions, such as SE Asia, but it is often not described in English. Despite the studies undertaken by numerous local researchers, and the identification of proven treatment methods for the specific water conditions encountered, no technologies have been commercialized due to a current lack of funding and technical assistance. Emerging, low-cost technologies to mitigate the problem of arsenic in drinking water resources that are suitable for rural and urban areas lacking centralized water supplies have been evaluated. The technologies generally use simple and low-cost equipment that can easily be handled and maintained by the local population. Experiences comprise (i) coagulation/filtration with iron and aluminum salts, scaled-down for small community- and household-scale-applications, (ii) adsorption techniques using low-cost arsenic sorbents, such as geological materials (clays, laterites, soils, limestones), natural organic-based sorbents (natural biomass), and synthetic materials. TiO(2)-heterogeneous photocatalysis and zerovalent iron, especially using nanoscale particles, appear to be promising emergent technologies. Another promising innovative method for rural communities is the use of constructed wetlands using native perennial plants for arsenic rhizofiltration. Small-scale simple reverse osmosis equipment (which can be powered by wind or solar energy) that is suitable for small communities can also be utilized. The individual benefits of the different methods have been evaluated in terms of (i) size of the treatment device, (ii) arsenic concentration and distribution of species, chemical composition and grade of mineralization in the raw water, (iii) guidelines for the remaining As concentration, (iv) economical constrains, (v) complexity of installation and maintenance, and infrastructure constraints (e.g. electricity needs).

Soil and sediment geochemistry of the iron quadrangle, Brazil the case of arsenic

Soils and sediments around gold ore deposit and mining sites in the Iron Quadrangle present positive As anomalies (median concentrations > 100 mg kg-1) and wide ranges (< 20 to > 2000 mg kg-1) even in densely populated areas. These anomalies can be related to geological structures, to hydrothermal ore deposits and to their continuous exploitation over the past three centuries. The paper presents new data on both As geochemistry and soil and sediment geochemistry in general, and discusses consequences of the encountered anomalies, their reasons and potential effects and how they compare with current screening and threshold values. While surface soil As-values are reproducible at a given site, sediment anomalies show a strong seasonal variation that can be explained by tropical hydrological variances. Suggestions are presented on how to minimize the As-load in densely populated areas that might otherwise pose a potential health risk.

Pyrite oxidation in alkaline solutions: nature of the product layer

Abstract The nature of the oxides formed during pyrite oxidation by molecular oxygen in alkaline solutions has been investigated with the aid of Eh–pH diagrams and direct analysis of the solid products. X-ray diffraction (XRD) and infrared analyses indicate that the products formed are determined by solution composition. In hydroxide medium, hematite, as the main phase, and small amounts of ferrihydrite are identified. In contrast, in carbonate medium, the main constituent is ferrihydrite, with some iron hydroxide carbonate phase also present. In calcium hydroxide medium, only calcium carbonate was detected on the surface of oxidized pyrite in an amount that increased when the system was opened to the atmosphere. Only by diffuse reflectance infrared spectroscopy (IR) was it possible to identify carbonate compounds among the products formed during pyrite oxidation in aqueous solutions. The morphology of the product layers was also affected by solution composition. In NaOH solutions, the particles are initially covered by a thin oxide layer that fractures after longer reaction times. Most of the oxide reports to the solution, where it remains as a stable suspension. Pyrite oxidation in Na 2 CO 3 /NaHCO 3 solutions results in particles that are initially covered by a discontinuous oxide coating that grows with reaction time, thus increasing the overall pyrite surface coverage. In this case, a precipitation confined to the solid/liquid interface is favored by the higher ionic strength of the sodium carbonate solutions.

Raman scattering and X-ray diffraction investigations on hydrothermal barium magnesium niobate ceramics

Abstract Ba(B′1/3B″2/3)O3 perovskites are important ceramic materials used as resonators in microwave technologies due to their adequate dielectric properties. These properties are mainly determined by the characteristics of the optical polar phonons of the material. A few spectroscopic investigations of lattice vibrations in Ba(B′1/3B″2/3)O3 ceramics were realized in highly ordered samples. In this work, we use Raman spectroscopy and X-ray diffraction to investigate hydrothermal Ba(Mg1/3Nb2/3)O3–BMN–ceramics with different order degree. Spectroscopic and structural data showed sensitivity to the sample microstructural evolution during sintering. Besides, they allowed independent determination of the long range order degree of the materials. The complete Raman mode assignment for the disordered and ordered BMN structure is also presented.

Recovery of europium by chemical reduction of a commercial solution of europium and Gadolinium chlorides

Abstract A chemical reduction–precipitation process was applied to the separation and recovery of high-grade europium oxide from a europium/gadolinium mixture containing 1.90% Eu 2 O 3 . The effects on europium recovery of the presence of mercury in the reducing agent, temperature, aging time, the nature of the sulfate carrier, and the method of addition of the precipitation agent were studied in detail. Similar grades (95.0±0.5% Eu 2 O 3 ) were obtained with both Zn amalgam and pure Zn powders. The precipitation with sulfuric acid was more selective as compared to that with ammonium sulfate (95% and 80% Eu 2 O 3 , respectively, for 95% recovery). The continuous addition of the precipitating agent was the main factor responsible for improving europium grades, which increased from 93% to 97% in the first stage, with less acid requirements (SO 4 2− : Eu molar ratio decreased from 16 to 5.3). After two stages of reduction–precipitation, grades were higher than 99.99% Eu 2 O 3 and recovery was 94%. The levels of individual rare earth impurities in the final Eu 2 O 3 product were below 0.001%.