Study On Adsorption Properties And Mechanism Of Modified Rice Husk On Pb²⁺ And Cd²⁺ In Contaminated Water

In this paper,the modified rice hull adsorbent was obtained by using KMnO₄、HNO₃、acid CH₂O and CH₂H₆O.The structure and composition of modified rice husk were characterized and analyzed by infrared spectrometer,scanning electron microscope,energy spectrum,etc.,and then by static test.The effects of modified rice husk adding,pH of solution,reaction time and initial concentration of Pb²⁺and Cd²⁺on the removal of Pb²⁺and Cd²⁺from water were studied,and the optimal experimental conditions were determined.The adsorption isotherm model and adsorption Kinetics model were used for fitting analysis,the adsorption mechanism was discussed,and the removal effects of Pb²⁺and Cd²⁺on water under different hydraulic load and initial concentration of Pb²⁺and Cd²⁺were studied by continuous experiments.Through the research,this paper has obtained the following results and understanding:（1）The adsorption performance of rice husk after KMnO₄ modification is the best.Using infrared spectroscopy,scanning electron microscopy and energy spectrum analysis:1)SEM map analysis,KMnO₄ modified rice husk cellulose with large pore will significantly increase the adsorption capacity of rice husk and suspended solids retention;2)spectrum of the modified rice husk for adsorption of Pb²⁺and Cd²⁺after the energy spectrum analysis shows that the emergence and change of pore a variety of cations,effectively enhance the modified rice husk adsorption efficiency for various heavy metals;3)X ray diffraction analysis of rice husk:the emergence of a large number of hydroxyl and carboxyl groups,can be used as adsorption sites of metal elements.（2）The static test results show that when the pH of water is 5,the reaction time is90min,the initial concentration of Pb²⁺is 20 mg/L,and the modified rice husk is added0.1 g（1.0 g/L）,the removal rate of lead can reach 75.98%,and the corresponding maximum adsorption amount is 15.76 mg/g,the adsorption process accorded with the Langmuir adsorption isotherm model and the quasi-primary kinetic model;When the pH of water is 6.0,the reaction time is 120 min,the initial concentration of Cd²⁺was 40mg/L,the modified rice husk admixture is 0.1g（1.0 g/L）,the cadmium removal rate can reach35.76%.The corresponding maximum adsorption amount is 13.15 mg/l,which is in line with Freundlich isothermal adsorption model and quasi-secondary kinetic model.（3）Continuous experiment:1)The continuous adsorption results of 0.981 mg/L and9.125 mg/L Pb²⁺showed that the modified rice husk has a good adsorption effect on Pb²⁺,reaching 90%.The adsorption process includes two mechanisms:the chemical exchange adsorption of Pb²⁺with hydroxyl and carboxyl H⁺on the surface of the rice hull and other cations;Pb²⁺complexes formed by the increase of the pH of the system are physically adsorbed and adsorbed in the rice shell column;2)The continuous adsorption results of1.373 mg/L and 13.732 mg/L Cd²⁺showed that the modified rice husk had a certain adsorption effect on Cd²⁺,but the removal rate was worse than that of Pb²⁺,and the high concentration removal rate was higher than the low concentration,The main reasons are:Cd²⁺mainly exists in the form of simple ions or simple ions in the solution,with fewer other forms,strong migration ability,and weak adsorption ability;The contribution of Cd²⁺adsorption to the pH growth of the system is weaker than that of Pb²⁺.Therefore,the pH growth of the Cd²⁺adsorption system is less,and it is difficult to form Cd（OH）₂ flocs that are easily adsorbed and intercepted.