Experimental Study On Tl~+ Adsorption And Desorption In Red Soil And Loess

Thallium (Tl) is one of the severe toxicity and scattered heavy metals. It has very low concentration in the earth crust, so the attention on the TI Pollution is not so much. Tl pollution and Tl poisoning affair caused by the exploitation of mineral resource seriously imperil human health, and has caused public concerns. The study for edaphic geochemistry action has been the accented term. Adsorption-desorption action is the inevitable outcome once Tl enter into the soil, the study of adsorption-desorption characteristics of Tl in the soil is to be acquainted with the characteristic of migration of Tl in the soil. It will provide theoretic basis for pollution control and also has significance on theoretics and practice.This study, based on the simulator investigation in the laboratory and combined with field sampling, is to study the adsorption-desorption characteristics of Tl in the soil. Using a batch method to distinguish the thermodynamic behaviour and dynamic behaviour of Tl's adsorption-desorption in Red soil and Loess, investigate the influence of pH and organic matter to the Tl adsorption-desorption, analyse the characteristics of Tl adsorption-desorption from diggings containing Tl, and estimate the Tl pollute degree and potential hazard. The result were shown as follows:(1) Langmuir equation is the most suitable method to analyse isothermal adsorption in Red soil and Loess. The correlation coefficient is remarkable or the most remarkable. The Loess has greater capability of adsorption than Red soil has and has a more exceedable adsorption quantity than Red soil. The rate of Tl~+ desorption in Loess is a little higher than it in Red soil. Freundlich equition is the most suitable method to analyse desorption.Desorption has certain hysteresis effect and the desorption value increases with the adsorption value. The relationship between them coincides with quadratic equation.(2) Tl~+ has a large adsorption-desorption speed in Red soil and Loess. When in Red soil, it spents 5min achieving to the 90% of the adsorption values and desorption values, 20min to the nearly equation. With the increase of initial concentrtion, it spents more time achieving the adsorption equation, about 120min. When in loess, it spents 20min achieving to more than 85% of the desorption equation, and it spents about 120min achieving the equation. Two-constant-equition is the optimal equation to describe the Tl~+ kinetics process.(3) the adsorption value increases with the increase of pH, which ranges from 2 to 10. When pH is 2, the adsorption value is small and the adsorption rate is less than 5% . When pH ranges 2 to 6, the increase of adsorption value is greatly. The rate of Tl~+ adsorption in Red soil achieve to the 48.3% and 71.2% in Losse. So the influence of pH to the adsorption in Red soil and Loess is great when the pH is low. When pH is 2, the adsorption value of Red soil and Loess is small, while the rate of adsorption is high. This explains that if the pH is low, it is not good for Tl~+ adsorption. In the contrary, it is benefit to the adsorbed Tl~+ desorption. When pH ranges from 4 to 10, desorption in Red soil has certain hysteresis phenomena, while the increase of desorption in loess approximates linear and has no hysteresis phenomena.(4) After removing the organic matter, the rates of Tl adsorption in Red soil and Loess are lower than them befor removing, but the rates of desorption are higher than them befor removing. So the influence to Tl~+ adsorption in Loess is greater than it in Red soil, while the influence of the organic matter to the rate of desorption in Red soil and Loess has no significant difference.(5)Tl adsorption-desorption is quite different in each section area of different levels of soil sample, which is pyrite soil including Tl. The adsorption value in top soil is obviously less than it in subsoil layer and substratum. The adsorption value in subsoil layer soil and substratum has little difference. The desorption value increases with the increase of adsorbed Tl and the extent of increase in top soil is larger than in sub soil layer and substratum. So the top soil has a weak Tl~+ adsorption capability .It is easy to desorption and migration in top soil and does harm greatly. In tne contrary, subsoil layer and substratum have a little buffer.