In this paper, we conduct the soil-column experiment on underground soil in a laboratory of Changping, Beijing, to simulate the effect of water table fluctuation on the cadmium migration law after twice pollution. The main job of the experience is to test the adsorption and desorption characteristics of the soil as well as the temporal and spatial distribution of cadmium ions in soil column. The experimental data show that (1) the two kinds of soil used in the test both have a strong adsorption capacity to cadmium ions, and the values could reach to 1026mg/kg and 2804mg/kg. (2) The dominant factor on cadmium ions migration under water table fluctuation is the soil adsorption when a small amount of cadmium ions are poured into soil column. On the other hand, convection plays a significant role in migration when plenty of cadmium ions are injected. (3) When plenty of cadmium nitrate are injected, the concentrations of cadmium ions in fluctuating zone increase with water table rise, and decrease with water table decline. The concentrations of cadmium ions, which exist in the saturated zone decrease when the water table rises and increase with water table decline.
In low-middle temperature porous geothermal field, precipitation of carbonate from solution to form carbonate scale is confirmed as the main obstacle to efficient reinjection from the used hot fluids in Xianyang city, NW China. The carbonate deposits cause operational problems and may even clog pipeline and reinjection drillholes. For this reason, it's important to understand how impact of carbonate precipitation on the second-hand geothermal water before reinjection has been operated, which concern sustainable utilization of the geothermal water in Xianyang, the famous porous geothermal field in China. In this paper, firstly, different possible minerals precipitation from used geothermal fluid were discussed, and carbonate scaling was regarded as mineral for chemical clog by using combined with lab and chemical simulation method. Secondly, the key impacts of carbonate scaling on clog in reinjection holes such as temperature, degassing, pH, mixing, mineralization were demonstrated based on coupled simulation both in lab experiment and theoretical method. Lastly, the distribution of carbonate scaling and its degree in study area were calculated. The results show that, as the main mineral for precipitation, carbonate exist in most thermal-water wells of study area with the minor or medium scaling, and the carbonate scaling vary increasingly from bottom to top in a single reinjection drillhole, north to south in the study area. According to mineral-dissolution-precipitation equilibrium calculation carbonate saturated tend growth with the temperature and pH increases in study area. The influence of mineralization on carbonate clog is different, common-ion effect in the south of study area is given priority, but in the north salt effect is showed main effect. The analysis for impacts on carbonate clog reflect that carbonate deposit effect are very complicated, which interact each other.
Combined with the Guanzhong basin tectonic evolution, the data of Sr content,87Sr/86Sr ratio and hot water hydrochemistry has been used to study the supply origin and flow path of deep geothermal water in the Guanzhong central region. The Sr isotope study result shows that when accepting recharge, the geothermal water in the northwest and southeast of Xianli terrace both mainly come from northwest direction. A small amount supply source of geothermal water in the Xi 'an city is from Qinling mountain and the principal supply source comes from the west and north direction, however, geothermal water of Chang’an accepts supply from the north of Qinling mountain. Keywords: geothermal water; strontium isotope; basin type; indicating significance
Shaizhudong spring is the largest one in the central of north of the Weihe river, Shaanxi Province, China. For its supply source, forefathers have done a lot of research. It was considered that Jinghe leakage is the main supply source of Shaizhudong spring, and it is the concentrated discharge points of Shaizhudong spring area hidden karst system. In this paper, we have different understanding on recharge of Shaizhudong spring, based on the research achievements of strontium isotope.
In this experiment, we simulated the migration and transformation law of nitrate under the condition of water table rise caused by rainfall in Changping District of Beijing. Two types of experimental apparatus were used in the experiment to simulate the distribution of NO3--N, NO2--N and NH4+-N, which were named soil column 1 and soil column 2. Soil column 2 was under the condition of rainfall and soil column 1 was for comparison. It took 50.3 hours for the experiment during which simples were taken and tested. The test items were the concentration of NO3--N, NO2--N and NH4+-N. The results indicated that (1) In unsaturated zone, the influence of leaching caused by rainfall on the concentrations of NO3--N and NH4+-N were significant. The decreasing range could reach to 95.9% and 90% which means that it was easily to lead to the contamination of groundwater. In saturated zone, NO3--N concentrations were mainly influenced by dispersion and could achieve balance between the dilution and dispersion with the increase of rainfall. The increasing range of NO3--N concentration was large, and the value could reach to 675%. In addition, the NH4+-N concentration had a slight trend of decrease. (2) Under the condition of rainfall, NO3--N concentrations increased in saturated zone, decreased in the path of water table rise and unsaturated zone. The NH4+-N concentrations had a decreasing trend in saturated-unsaturated zone. (3) NH4+-N concentrations in medium sand were more easily influenced by leaching from rainfall than those in silt.
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