Arsenic Hyperaccumulator Pteris Vittata L.Postnatal Treatment And Disposal

Heavy-metal-contaminating phytoremediation has become the research hot spot at home and abroad. However, the after-treatment of hyperaccumulators has become an issue which the phytoremediation has to face. In this paper, on the one hand utilizes the leaching experiment so as to screen out the extracting agent effective against the arsenic hyperaccumulator of Pteris vittata L., On the other hand, by incineration ashes tube experiments approach to screening and effective solid arsenic, thus resolving the secondary pollution of Pteris vittata L. for phytoremediation.A variety of low concentrations of acid leaching experiments:This research adopts HNO3, Hcl, H2SO4with the concentration of50%and the mixed acid and aqua regia with the same concentration to make arsenic extraction treatment to the Pteris vittata L. planted in contaminated area according to different parts. There are three pretreatment methods for Pteris vittata L., i.e. natural drying, oven drying at70℃and fresh frozen. The leaching is run according to the roots, the blades and petioles of mature leaves, and the blades and petioles of immature leaves respectively. Through LC-AFS, this paper analyzes the effects and differences of arsenic extraction in all the parts of Pteris vittata L. With different extracting agents at100℃for12h. After screening out the extracting agent, orthogonal experiment is designed. The experiment shows that:1.The arsenic in all parts of Pteris vittata L. is mainly inorganic As(Ⅲ) and As(V), and As(III) is more than As(V); The arsenic content in the blades of immature leaves is the highest, reaching1839.39mg/kg to1928.11mg/kg, and the As(III) in the blades is also the highest, accounting for35.7%to44.4%of its total arsenic; the arsenic content in the petioles of mature leaves is the least, and after all kinds of treatments, there is no significant difference in the arsenic extraction effect of the samples under natural drying and oven drying at70℃.2.Under the conditions of this research, the effect of HNO3extraction rate is the best, whose extraction rate is71.6%to82.4%, and after leaching, the As(III) of the sample is reduced significantly; the effect of HCL-H2SO4mixed leaching is the worst, whose extraction rate is only6.5%to15.9%, and most of the arsenic still remains in the extract residue.3.There are big differences in the total arsenic amount and distribution of the arsenic speciation by adopting different extracting agents. From orthogonal experiment, a positive correlation is found between the arsenic extraction rate of the samples and the extracting agent concentration, extraction temperature and time, and the effect of the extracting agent concentration upon the extraction rate is the biggest, then the temperature. During this experiment, when the sample is extracted by75%HNO3at130℃for18h, the arsenic extraction rate reaches the highest, with89.6%.Incineration ashes tube experiments:Different treatment in different parts of centipede grass samples under different experimental conditions (Incineration temperature:200℃、400℃、600℃、800℃, Burning Time:2h、4h、6h、8h), Do orthogonalexperiment with adding three different solid arsenic (CaO、MgO、SiO2), and using diethyl dithiocarbamate method for the determination of silver in each of the absorption liquid arsenic,analysis of the quality of its ashes and arsenic levels before and after the change in the incineration.The results showed that:l.As the sample was burned content have emerged as the temperature increases, the residual ashes As content gradually increases.Within a certain temperature range,its arsenic volatilization with increasing temperature showed a rising trend, Under the experimental conditions,each sample at800℃, the maximum amount of arsenic volatilization.2.On arsenic volatilization rates,When without solid arsenic,samples arsenic volatilization begins at a lower temperature,400℃, more than80%in each sample arsenic volatilization,200℃-800℃, As volatile showing a rising trend, After adding solid arsenic, CaO at600℃and800℃, there certainly have the effect of solid arsenic,dropped from over90%to85.64%and79.38%,The MgO and SiO2were200℃,2h when arsenic volatilization rate declined,respectively,When not added by a68.32%decrease, to49.5%and52.66%,MgO better than SiO2.3.In terms of mass loss rate on the sample,as apparently,Incineration can significantly reduce the quality of the sample, Positively correlated with temperature and time were burned, When not add solid arsenic, the mass loss of the sample reached90%,As the temperature continues to rise, it changes little.4.By analyzing the three solid-arsenic effectiveness shows that,CaO has a good effect of arsenic in the solid in the high-temperature region,which also has the maximum rate of mass loss. The MgO and SiO2were200℃,2h when arsenic volatilization rate declined, but with the burning temperature increases.