Mobilization of heavy metals from urban contaminated soils under water inundation conditions

A microcosm experiment was conducted to investigate heavy metal release from the urban soils heavily contaminated by past industrial activities. The aim was to assess the mobility of various heavy metals under inundation with water. The results show that reductive dissolution of iron and manganese compounds was markedly enhanced by organic matter. However, mobilization of Fe and Mn was affected by the abundance of these metals in the soils. The dissolution of Fe and Mn oxides led to the release of As and Zn that were bound to them. However, mixed temporal variation patterns were observed for As, suggesting complication of As mobility by other factors. It is likely that the added organic matter played a role in the formation of organic matter–Fe(III)–arsenic association, leading to partial re-immobilisation of the liberated As at the latter stage of the experiment. Zn showed a consistent trend where it was initially released with reductive dissolution of Fe and Mn compounds and then re-immobilised, possibly through hydrolysis to form insoluble zinc hydroxide. In spite of abundant presence, release of Pb was limited due to its low solubility under less acidic conditions. It appears that anaerobic environment stabilized the soil-borne Cr by forming insoluble Cr(OH)3

The effect of pitch-based carbon fiber microstructure and composition on the formation and growth of SiC whiskers via reaction of such fibers with silicon sources.

The formation and growth of silicon carbide whiskers (SiCw) have been investigated by reaction of silicon sources at 1400 ºC with pitch-based carbon fibers possessing various microstructures. Isotropic and anisotropic pitch-based carbon fibers treated at various temperatures were employed as carbon sources. Silicon sources include silicon powder and a mixture of silicon and silica powder. The reaction of 1000 ºC heat-treated carbon fibers containing a certain content of oxygen with silicon powders is also reported. A reasonable yield of monocrystalline and polycrystalline SiC whiskers can be achieved by the reaction of the isotropic and anisotropic pitch-based carbon fibers treated at 1000 and 2000 ºC with the mixture of silicon and silica. The critical factors for promoting the formation of SiC whiskers are that the carbon sources should possess turbostratically stacked graphite structure and appropriate grain size. The presence of SiO, which originated from the reaction of silicon with silica or with water vapor derived from pyrolysis of carbon fibers, is another necessary condition for formation of SiCw during these reaction processes