Research On Chemical Time Bomb In The Beijing Suburb Sewage-Irrigated Soil

In our country, sewage irrigation is one of the main sources, but chemical time bomb (CTB) of heavy metal brings the people disaster. So it is of great importance to study the CTB of heavy metal. In this thesis, about 110 samples have been collected from YMK sewage-irrigated area in southeast suburb of Beijing and analyzed, and some issues on formation, eruption and mechanism of CTB have been discussed.Firstly, the content of Cr, Cd and Pb has been measured and compared with standard of environment quality. The main researching results have showed that the irrigated sewage has exceeded standard, which has lead to polluting of heavy metal in investigated soil. CTB maybe have formed and erupted in the soil.Secondly, formation process and mechanism on CTB have been simulated by using the batch and continuous sorption experiments. The results have showed that adsorption mechanisms of Cd, Cr and Pb follow the model of Freundlich in the soil; Accumulation order of heavy metals is Cr, Pb and Cd at the same condition, but time of arriving at maximum by accumulation is same in the area. Through proceeding adsorption influence of heavy metal experiment, we have concluded: pH can not influence on adsorption of Cd and Pb, but when pH decreases adsorption of Cr increases.Thirdly, proceed simulating release of heavy metal experiment in order to confirm key factor to CTB eruption in the area. In the experiment, pH, temperature and water/soil have been discussed. The results have showed that the most important factor is pH on releasing influence of heavy metal, and it is similar that pH influence on releasing heavy metal. When pH is litmusless, the degree of releasing heavy metals is the smallest. Otherwise, experiments that proceed rainwater washing out simulation show the same conclusion.At last, heavy metal fractions have been measured; models on CTB of heavy metal have been constituted. By evaluation heavy metal fractions, we have concluded: cadmium and chromium have the latent threat to erupt chemical time bomb.