地球化学模型在土壤重金属形态研究中的应用进展

重金属在土壤中的固-液分配行为和形态分布对于其环境迁移过程和生物有效性有重要意义.基于热力学机制的地球化学平衡模型是重金属形态研究中一项重要手段.本文从形态模型的发展历史出发,对土壤环境中一些常见的地球化学形态模型进行了梳理;对形态模型的使用过程中模型输入值,包括吸附组分和活性态金属含量的确定方法进行了说明;对地球化学形态模型在各方面的应用进行了总结;最后对模型今后的发展方向和应用前景进行了展望.

Thermodynamic simulation of stepwise precipitation of NH_4VO_(3)and NaHCO_(3)from carbonating Na_(3)VO_(4)solution

Thermodynamic simulation was conducted to design a new process of stepwise precipitating NH_4VO_(3)and NaHCO_(3)from regulating the CO_(2)carbonation of Na_(3)VO_(4)solution.Firstly,a new V(V)speciation model for the aqueous solution containing vanadate and carbonate is established by using the Bromley-Zemaitis activity coefficient model.Subsequently,thermodynamic equilibrium calculations are conducted to clarify the behavior of vanadium,carbon,sodium,and impurity species in atmospheric or high-pressure carbonation.To ensure the purity and recovery of vanadium products,Na_(3)VO_(4)solution is initially carbonated to the pH of 9.3-9.4,followed by precipitating NH_4VO_(3)by adding(NH_4)_(2)CO_(3).After vanadium precipitation,the solution is deeply carbonated to the final pH of 7.3-7.5 to precipitate NaHCO_(3),and the remaining solution is recycled to dissolve Na_(3)VO_(4)crystals.Finally,verification experiments demonstrate that 99.1%of vanadium and 91.4%of sodium in the solution are recovered in the form of NH_4VO_(3)and NaHCO_(3),respectively.

Mechanism of slope failure in loess terrains during spring thawing

Slope failure in loess terrains of Northern China during spring thawing period is closely related to the freeze-thaw cycling that surface soils inevitably experienced. Field surveys were carried out on natural and artificial slopes in thirteen surveying sites located in the Northern Shaanxi, the center of Loess Plateau, covering five characteristic topographic features including tablelands, ridges, hills, gullies and valleys. Based on the scale that is involved in freeze-thaw cycling, the induced failures can be classified into three main modes, i.e., erosion, peeling and thaw collapse, depending on both high porosity and loose cementation of loess that is easily affected. Model tests on loess slopes with gradients of 53.1°, 45.0° and 33.7° were carried out to reveal the heat transfer, water migration and deformation during slope failure. The surface morphology of slopes was photographed, with flake shaped erosion and cracks noted. For three slope models, time histories for the thermal regime exhibit three obvious cycles of freeze and thaw andthe maximum frost depth develops downwards as freeze-thaw cycling proceeds. Soil water in the unfrozen domain beneath was migrated towards the slope surface, as can be noticed from the considerable change in the unfrozen water content, almost synchronous with the variation of temperature. The displacement in both vertical and horizontal directions varies over time and three obvious cycles can be traced. The residual displacement for each cycle tends to grow and the slopes with higher gradients are more sensitive to potentially sliding during freeze-thaw cycling.

Morphological Evolution of a Void under Thermal and Mechanical Loads

A model for the morphological evolution of a void under thermal and mechanical loads is established, and the thermodynamics potential of the model is given based on energy principle. Thus, the path and the bifurcation condition of the morphological evolution of the void are described, which gives some insight into the reliability of the interconnect under combined thermal and mechanical loads.

Establishment of a blunt impact-induced brain injury model in rabbits

Objective： To establish an animal model to replicate the blunt impact brain injury in forensic medicine. Methods： Twenty-four New Zealand white rabbits were randomly divided into control group （n=4）, minor injury group （n：10） and severe injury group （n=10）. Based on the BIM- II Horizontal Bio-impact Machine, self-designed iron bar was used to produce blunt brain injury. Two rabbits from each injury group were randomly selected to monitor the change ofintracranial pressure （ICP） during the impact- ing process by pressure microsensors. Six hours after injury, all the rabbits were dissected to observe the injury mor- phology and underwent routine pathological examination. Results： Varying degrees of nervous system positive signs were observed in all the injured rabbits. Within 6 hours, the mortality rate was 1/10 in the minor injury group and 6/10 in the severe injury group. Morphological changes con-sisted of different levels of scalp hematoma, skull fracture, epidural hematoma, subdural hematoma, subarachnoid hemo- rrhage and brain injury. At the moment of hitting, the ICP was greater in severe injury group than in mild injury group; and within the same group, the impact side showed positive pressure while the opposite side showed negative pressure. Conclusions： Under the rigidly-controlled experimental condition, this animal model has a good reproducibility and stable results. Meanwhile, it is able to simulate the morphology of iron strike-induced injury, thus can be used to study the mechanism of blunt head injury in forensic medicine.