Geochemical Fraction, Mobility And Bioavailability Of Lead In Unsaturated Soil Of Yogyakarta City, Indonesia

Lead (Pb) is one of common heavy metals found inthe soil of urban environment. In Yogyakarta City,Indonesia, lead content in the soil was already reported by some researchers, however all of the report were only reveals the distribution of lead concentration in the soil. Therefore, this research paper aims to understand the geochemical fraction leadin the soil of Yogyakarta City and assess the mobility and bioavailability of lead release to the environment. The soil sampling location is selected on Kotagede District, representing the oldest urban area of Yogyakarta city. A shallow bore hole was drill until about 7 m below the surface and soil/sediments weresampled for each 1 m depth started from the surface. Six steps of sequential extraction procedures were carried out to assess the geochemical fraction of Pb for each of soil samples. The sequential extraction shows that the highest amount of Pb in thesoil of Yogyakarta City is found in amorphous ironoxide, crystalline iron oxide and non residual fraction form of Pb. Based on the results of geochemical fraction, the mobility factor of lead can be calculated and reveals low mobility factor range from 0.4 to 3.3%. The mobility of lead is decreased from the surface to the deeper soil, on the other hand the bioavailability of Pb calculated from exchangeable and carbonate fraction is also show low risk of bioavailability. Therefore, it can be concluded that although Pb concentration is high in non-residual fraction, Pb isin low risk condition due to its poor mobility and bioavailability. But, concern on lead contamination should be considered because if the concentration of Pb is enriched over the adsorption capacity of ironoxide, it can easily release to the environment and can impact to human in the future.Keywords: Yogyakarta city, Lead, Sequential extraction, Geochemical fractio

On the nature of structural disorder in calcium silicate hydrates with a calcium/silicon ratio similar to tobermorite

International audienceFour calcium silicate hydrates (C-S-H) with structural calcium/silicon (Ca/Si) ratios ranging from 0.82 +/- 0.02 to 0.87 +/- 0.02 were synthesized at room temperature, 50, 80, and 110 degrees C. Their structure was elucidated by collating information from electron probe micro-analysis, transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and powder X-ray diffraction (XRD). A modeling approach specific to defective minerals was used because sample turbostratism prevented analysis using usual XRD refinement techniques (e.g. Rietveld analysis). It is shown that C-S-H with Ca/Si ratio of similar to 0.8 are structurally similar to nano-crystalline turbostratic tobermorite, a naturally occurring mineral. Their structure thus consists of sheets of calcium atoms in 7-fold coordination, covered by ribbons of silicon tetrahedra with a dreierketten (wollastonite-like) organization. In these silicate ribbons, 0.42 Si per bridging tetrahedron are missing. Random stacking faults occur systematically between successive layers (turbostratic stacking). Layer-to-layer distance is equal to 11.34 angstrom. Crystallites have a mean size of 10 nm in the a-b plane, and a mean number of 2.6-2.9 layers stacked coherently along the c* axis. (C) 2013 Elsevier Ltd. All rights reserved

Dissolution kinetics of synthetic Na-smectite. An integrated experimental approach

International audienceThe effect of pH and Gibbs energy on the dissolution rate of a synthetic Na-montmorillonite was investigated by means of flow-through experiments at 25 and 80 degrees C at pH of 7 and 9. The dissolution reaction took place stoichiometrically at 80 degrees C, whereas at 25 degrees C preferential release of Mg over Si and Al was observed. The TEM-EDX analyses (transmission electronic microscopy with quantitative chemical analysis) of the dissolved synthetic phase at 25 degrees C showed the presence of newly formed Si-rich phases, which accounts for the Si deficit. At low temperature, depletion of Si concentration was attributed to incongruent clay dissolution with the formation of detached Si tetrahedral sheets (i.e., alteration product) whereas the Al behaviour remains uncertain (e. g., possible incorporation into Al-rich phases). Hence, steady-state rates were based on the release of Mg. Ex situ AFM measurements were used to investigate the variations in reactive surface area. Accordingly, steady-state rates were normalized to the initial edge surface area (11.2 m(2) g(-1)) and used to propose the dissolution rate law for the dissolution reactions as a function of Delta G(r) at 25 degrees C and pH similar to 9: r(mol m(-2) s(-1)) = 3.82 x 10(-12) [1 - exp(-8.23 x 10(-10)vertical bar Delta G(r)/RT vertical bar(5.47))]