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Variations of the aerosol chemical composition during Asian dust storm at Dushanbe, Tajikistan
Aerosol chemical composition was characterized during the Central Asian Dust Experiment (CADEX) at Dushanbe (Tajikistan). Aerosol samples were collected during a period of 2 months from March to May 2015 using a high volume DIGITEL DHA-80 sampler on quartz fiber filters. The filters were analyzed for their ionic, trace metals as well as organic and elemental carbon (OC/EC) content. The aerosol mass showed strong variation with mass concentration ranging from 18 μg/m3 to 110 μg/m3. The mineral dust concentrations varied between 0.9 μg/m3 and 88 μg/m3. Days of high aerosol mass loadings were dominated by mineral dust, which made up to about 80% of the aerosol mass while organic matter and inorganic ions made up about 70% of the aerosol mass during days of low aerosol mass loadings. The mineral dust composition showed different trace metal signatures in comparison to Saharan dust with higher Ca content and Ca/Fe ratios twice as high as that observed in Saharan dust. Strong influence of anthropogenic activities was observed in the trace metal concentrations with Zn and Pb concentrations ranging from 7 to 197 ng/m3 and 2 to 20 ng/m3, respectively. Mineral dust and anthropogenic activities relating to traffic, combustion as well as metallurgical industrial emissions are identified as the sources of the aerosol during this period. © 2019 The Authors, published by EDP Sciences.
Preparation of clay mineral samples for high resolution x-ray imaging
In the development of optimum ceramic materials for plastic forming, it is of fundamental importance to gain insight into the compositions of the clay minerals. Whereas spectroscopic methods are adequate for determining the elemental composition of a given sample, a knowledge of the spatial composition, together with the shape and size of the particles leads to further, valuable insight. This requires an imaging technique such as high resolution X-ray microscopy. In addition, fluorescence spectroscopy provides a viable element mapping technique. Since the fine particle fraction of the materials has a major effect on physical properties like plasticity, the analysis is focused mainly on the smallest particles. To separate these from the bigger agglomerates, the raw material has to pass through several procedures like centrifugation and filtering. After that, one has to deposit a layer of appropriate thickness on to a suitable substrate. These preparative techniques are described here, starting from the clay mineral raw materials and proceeding through to samples that are ready to analyze. First results using high resolution x-ray imaging are shown.
Modelling mineral dust in the Central Asian region
In Central Asia, climate and air quality are largely affected by local and long-travelled mineral dust. For the last century, the area has experienced severe land-use changes and water exploitation producing new dust sources. Today global warming causes rapid shrinking of mountain glaciers with yet unknow consequences for dust and its climate effects. Despite the importance for a growing population, only little is known about sources, transport pathways and properties of Central Asian dust. A transport study with a global aerosol-climate model is undertaken to investigate the life cycle of mineral dust in Central Asia for the period of a remote-sensing campaign in Tajikistan in 2015-2016. An initial evaluation with sun photometer measurements shows reasonable agreement for the average amount of dust, but a significant weakness of the model in reproducing the seasonality of local dust with maximum activity in summer. Source apportionment reveals a major contribution from Arabia throughout the year in accordance with observations. In the model, local sources mainly contribute in spring and autumn while summer-time dust production is underestimated. The results underline the importance of considering long-range transport and, locally, a detailed representation of atmospheric dynamics and surface characteristics for modelling dust in Central Asia. © 2019 The Authors, published by EDP Sciences.
Synthesis of hydroxy-sodalite/cancrinite zeolites from calcite-bearing kaolin for the removal of heavy metal ions in aqueous media
A hydroxy-sodalite/cancrinite zeolite composite was synthesized from low-grade calcite-bearing kaolin by hydrothermal alkali-activation method at 160 °C for 6 h. The effect of calcite addition on the formation of the hydroxy-sodalite/cancrinite composite was investigated using artificial mixtures. The chemical composition and crystal morphology of the synthesized zeolite composite were characterized by X-ray powder diffraction, infrared spectroscopy, scanning electron microscopy, and N2 adsorption/desorption analyses. The average specific surface area is around 17–20 m2·g−1, whereas the average pore size lies in the mesoporous range (19–21 nm). The synthesized zeolite composite was used as an adsorbent for the removal of heavy metals in aqueous solutions. Batch experiments were employed to study the influence of adsorbent dosage on heavy metal removal efficiency. Results demonstrate the effective removal of significant quantities of Cu, Pb, Ni, and Zn from aqueous media. A comparative study of synthesized hydroxy-sodalite and hydroxy-sodalite/cancrinite composites revealed the latter was 16–24% more efficient at removing heavy metals from water. The order of metal uptake efficiency for these zeolites was determined to be Pb > Cu > Zn > Ni. These results indicate that zeolite composites synthesized from natural calcite-bearing kaolin materials could represent effective and low-cost adsorbents for heavy metal removal using water treatment devices in regions of water shortage.