Rodolfo Fernández-Martínez

Arsenic pollution and fractionation in sediments and mine waste samples from different mine sites

A characterization of arsenic pollution and its associations with solid mineral phases in sediments and spoil heap samples from four different abandoned mines in Spain is performed. Three of them were mercury mines located in the same mining district, in the province of Asturias, and the other one, devoted to arsenic mining, is in the province of León. A sequential extraction procedure, especially developed for arsenic, was applied for the study of arsenic partitioning. Very high total arsenic concentrations ranging 300-67,000 mg·kg(-1) were found. Arsenic fractionation in each mine is broadly in accordance with the mineralogy of the area and the extent of the mine workings. In almost all the studied samples, arsenic appeared predominantly associated with iron oxyhydroxides, especially in the amorphous form. Sediments from cinnabar roasted piles showed a higher arsenic mobility as a consequence of an intense ore treatment, posing an evident risk of arsenic spread to the surroundings. Samples belonging to waste piles where the mining activity was less intense presented a higher proportion of arsenic associated with structural minerals. Nevertheless, it represents a long-term source of arsenic to the environment.

A simplified method for determination of organic mercury in soils

Monitoring levels of organic mercury species at very low concentrations in the environment is of concern due to their high toxicity. However, conventional methods for organic mercury determination are usually expensive and time consuming because they involve many preparation steps and require instrumentation which is not available in most laboratories. In order to make it easier the organic mercury determination this paper presents a simple, fast and reliable extraction method for isolating and quantifying the organic mercury fraction in soil samples. The proposed method is based on one single digestion stage using a CuBr2 solution in HCl to release the organic mercury compounds from the solid matrix and their simultaneous and selective extraction into dichloromethane. After the separation of the organic phase, reextraction into aqueous media using N-acetyl-L-cysteine solution allows the determination of the extracted organic mercury by electrothermal atomic absorption spectrometry with the direct mercury analyzer DMA-80. Experimental and instrumental variables were optimized by the analysis of synthetic samples of methylmercury dispersed in pulverized silica. The method was validated by the analysis of the certified CRM 580 reference material. The detection limit of the procedure is 9.6 ng of organic mercury per gram of dry soil. The applicability of the proposed method to real samples was demonstrated through recovery studies of methylmercury in spiked soils. In addition, the influence of the TOC (Total Organic Carbon) content in soils was studied. The recoveries obtained under optimal experimental conditions ranged from 90% to 105% for all tested samples, indicating the suitability of the proposed method for determination of the organic mercury fraction in soils.

Assessment of a sequential extraction procedure for arsenic partitioning and application to samples from different pollution sources

In this paper, a seven-step sequential extraction procedure (SEP) is proposed to evaluate As fractionation in environmental solid samples of concern. The protocol covers the most relevant As-bearing phases in soils and sediments, stressing the importance of the most mobilizable fractions, in accordance with their potential environmental hazards. The considered fractions are (1) readily soluble As, (2) strongly adsorbed As onto mineral surfaces, (3) As associated with Al oxyhydroxides, (4) As bound to organic matter, (5) As incorporated into amorphous Fe oxyhydroxides, (6) As associated with poorly crystalline Fe (hydr)oxides and (7) As coprecipitated with refractory minerals. Although this protocol is suitable for all kinds of environmental solid samples, it was especially designed for those that are highly polluted. Hence, optimization of some operational parameters in every extraction step such as the extraction time and solid-to-solution ratio was carried out by using highly polluted solids as control samples. The selectivity of the selected agents for every extraction step was assured through experiments with natural and synthetic matrices of As-bearing minerals and As-spiked materials. The validation of the proposed method was accomplished with five certified materials of soils and sediments covering a diverse range of As contents. The results of its application to As-contaminated samples from different geological origins and within a wide range of As contents revealed As fractionation to be largely in accordance with the pollution source of samples and with their geochemical composition, which confirmed this methodology to be suitable for fractionation assessment of As in environmental solid samples of different nature. In addition, one of the strengths of this method is that the simplicity of its steps would easily allow for its automation.

Preparation of graphene thin films for radioactive samples.

A new method for the preparation of conductive thin films is presented. The metallization of VYNS films guarantees the electrical conductivity but it results in the breaking of a high proportion of them. Graphene, a two-dimensional nanostructure of monolayer or few layers graphite has attracted a great deal of attention because of its excellent properties such as a good chemical stability, mechanical resistance and extraordinary electronic transport properties. In this work, the possibilities of graphene have been explored as a way to produce electrical conductive thin films without an extra metallization process. The procedure starts with preparing homogenous suspensions of reduced graphene oxide (rGO) in conventional VYNS solutions. Ultra-sonication is used to ensure a good dispersibility of rGO. Graphene oxide (GO) is prepared via oxidation of graphite and subsequent exfoliation by sonication. Different chemically rGO were obtained by reaction with hydrazine sulfate, sodium borohydride, ascorbic acid and hydroiodic acid as reducing agents. The preparation of the thin graphene films is done in a similar way as the conventional VYNS foil preparation procedure. Drops of the solution are deposited onto water. The graphene films have been used to prepare sources containing some electron capture radionuclides ((109)Cd, (55)Fe, (139)Ce) with an activity in the order of 3kBq. The samples have been measured to test the attainable low energy electron efficiency and the energy resolution of Auger and conversion electrons by 4π (electron capture)-γ coincidence measurements. The 4π (electron capture)-γ coincidence setup includes a pressurized proportional counter and a NaI(Tl) detector. Tests with different pressures up to 1000kPa were carried out. All these tests show similar values in both parameters (efficiency and resolution) as those obtained by using the conventional metallized films without the drawback of the high percentage of broken films.