The role of Cu(II) in the reduction of N-nitrosodimethylamine with iron and zinc.

The role of Cu(II) in the reduction of N-nitrosodimethylamine (NDMA) with zero-valent metals was investigated by determining the effects of Cu(II) on the removal, kinetics, products, and mechanism. NDMA removal was enhanced, and all reactions followed a pseudo-first-order kinetic model except for the Fe and Fe/0.1 mM Cu(II) systems. The iron mass-normalized pseudo-first-order rate constants (kMFe) increased with the Cu(II) concentration. The zinc mass-normalized pseudo-first-order rate constants (kMZn) were identical to those with the Cu(II) concentrations from 0.1 mM to 1.0 mM and were higher with 2.0 mM Cu(II). The types of products detected were unchanged. Some unknown products were also found. NDMA was reduced to 1,1-dimethylhydrazine (unsymmetrical dimethylhydrazine, UDMH). Then, UDMH was reduced into dimethylamine (DMA) by the Fe/Cu(II) and Zn/Cu(II) systems. Catalytic hydrogenation was proposed as the reduction mechanism. Several copper species, such as Cu(OH)2 in the Fe/Cu(II) system and Cu2O and Cu(OH)2 in the Zn/Cu(II) system enhanced NDMA reduction. Differences between the Fe/Cu(II) and Zn/Cu(II) systems were caused by the reduction potentials and surface conditions of the different metals and the copper species in the various systems.

[Landscape pattern and its dynamics in typical oasis-desert transitional zone of Minqin Region in 1960-2005].

By using ERDAS and GIS techniques, a systematic analysis was made on the landscape pattern and its dynamics in typical oasis-desert transitional zone of Minqin Region in 1960-2005. Forest land and cultivated land were the dominant factors leading to the landscape change. During the research period, oasis expanded toward the periphery by 2-3 km, and the transitional zone moved toward desert, with its width increased from 4 km in 1960 to about 9 km in 1987 and decreased rapidly then. In 1978-1987, the landscape change reached the historically highest level; but after 1998, the landscape pattern became relatively stable. In the whole transitional zone, the period with higher fragmented index occurred in 1978-1987, during which, the quickest variation among patch types was observed. The fragmentized regions were located in the area 2 km from oasis and in the forestation area. In 1960-1987, arbor forest tended to vanish. Shrubbery area increased widely before 1987, and decreased sharply since then. The intensity of land reclamation kept increasing in 1960-1998 but decreased after 1998, while the abandon rate had a trend of linear increase during the research period.