Study Of Adsorption And Desorption Behavior Of Cd On Bentonite

As an important physico-chemical wastewater treatment method, adsorption has already been used widely in treating wastewater because it is simple and efficient. The exploitation of the cheap and effective adsorption materials has attracted the interest of many scholars. Bentonite is a kind of clay minerals that is abundant in our country. It has unique sandwich structure and powerful adsorption ability. Bentonite has lots of advantages in the treatment of wastewater, such as simple process, high efficiency and low cost.This paper described the properties and applications in environmental protection of bentonite. Using single factor experiment method and choosing simulated water samples contaminated with Cd²⁺ as research objects, the main factors affecting bentonite's adsorption performance and its adsorption isothermal aquation and dynamics have been investigated and the effect of ionic strength was discussed in details. The adsorption study of the wastewater samples collected from our school's Yan Hu lake, Dong Feng canal and the power plant was made. It was desorption experiments by means of acidic solution and hydrochloric acid that were carried out, and its best conditions were determined. And it was the main factors affecting bentonite's adsorption performance in the condition of the addition of Humic Acid and its adsorption isothermal aquation and dynamics that were investigated.The bentonite used in the experiment was the Ca-bentonite from GuangZhou province. The optimum conditions obtained are: the optimum pH is 6, shaking time is 30min, bentonite quantity is 20.0g/L, ionic strength is 0.1mol/L. The ionic strength experiment showed that the effect of ionic strength to adsorption was obvious, and electric adsorption and specific adsorption coexited. The behaviors of adsorption of Cd²⁺ in wastewater on bentonite are fitted to the Freudlich Model and Langmuir Model. The adsorption kinetics is fitted well with the Lagergren quasi-second reaction rate model. When was used to treat real wastewater, the adsorption rate to Cd²⁺ reached 82.29%—86.63%. So, the bentonites can play a great role on the wastewater treatment and environment remediation. In a word, the bentonites have extensive prospect on the treatment of wastewater contaminated with Cd²⁺.The results of desorption experiment showed that the desorption rate of acidic solution reached to equilibrium in a short time, then which did not change significantly with the prolonged time, and the adsorption kinetics is fitted well with the Lagergren quasi-second reaction rate model. The desorption rate of acidic solution firstly decreased rapidly with increasing pH, then decreased slowly. The desorption rate decreased from 30.62% to 5.12% when pH values varied from 2 to 3.5, and decreased from 5.12% to 1.10% when pH values varied from 3.5 to 5.5. The desorption rate decreased gradually with the increasing nekeated desorption number. The desorption rate constantly increased with increasing ionic strength, reaching 10.68% when ionic strength was 2.964mmol/L. The experiment showed that when eluted by hydrochloric acid, the desorption rate is getting higher and higher with the concentration of hydrochloric acid increasing. when the concentration of hydrochloric acid was greater than or equal 0.5mol/L, the desorption rate of Cd²⁺ was all to 100%.The best experiment conditions of bentonite adsorpbing cadmium ions in the condition of adding Humic Acid are: the optimum pH is 6, the concentration of Humic Acid is 1g/L. After addition of Humic Acid, the adsorption increased obviously, and the saturated adsorption capacity was increased from 3.231mg/g to 8.425 mg/g when the concentration of Humic Acid added was 1g/L. The behaviors of adsorption of Cd²⁺ on bentonite are also fitted to the Freudlich Model and Langmuir Model, and its adsorption kinetics also fitted well with the Lagergren quasi-second reaction rate model.The above findings have certain theoretical and practical significances for using the adsorption performance of bentonite to treat wastewater, especially the cadmium-containing wastewater. An alternation new way to enhance the application value of bentonite in our country has been developed.