Research On Adsorption Characteristics Of Cadmium From Different Shell Powder

Water resources is of great importance in our lives,but utilizing of water resources in our country is not optimistic.With the progress of society and the impact of human activities,a large number of sewage and waste run into the river,however,the amount of pollutants in the water are far more than the self-purification capacity of water,resulting in seriously pollution of water.At present,the pollution of heavy metals in water is the most seriously,especially the pollution of cadmium.polluted water will not only affect the survival of aquatic organisms,but also influence the crops,agriculture products through food chain because of sewage irrigation and transpiration,resulting great harm on human health.At present,the treatment methods of polluted water about cadmium include chemical precipitation method,adsorption method,ion exchange method and so on.In this paper,the static adsorption experiment analysised the effects of time,temperature,initial concentration and pH on the adsorption capacity,and the thermodynamics and dynamic characteristics of adsorption of Cd²⁺ of shell powder.The results are as follows:?1?According to the XRD pattern,the shell powder is divided into two types:aragonite and calcite.Razor clam powder,powder,powder crab,conch powder,Haihong powder,white clams,abalone and clam shell powder are all aragonite.Oyster powder and scallop powder are calcite.?2?The results of static adsorption showed that the adsorption capacity of manite shell powder about Cd²⁺ is higher than that of calcite shell powder at room temperature under the conditions of 100mg·L-1 cadmium stress for 24 hours at room temperature.There is a great difference in the adsorption of cadmium among aragonite shells.The adsorption capacity of Cd²⁺ in rainbow and clam shell powder were the strongest.The saturated adsorption of Cd²⁺ in the aqueous solution was 145.8mg kg^-1-197.8mg·kg^-1,and the saturated adsorption capacity of calcite shell powder was 29.19 mg·kg^-1-30.01 mg·Kg-1.?3?Different Shell's adsorption of Cd²⁺ is divided into rapid adsorption period and saturation period.The effect of pH value on the adsorption about Cd²⁺ of shell powder was significant.Both the calcite shell powder and the aragonite shell powder had the best adsorption effect at the pH about 4.7-5.0,and the increasing of ion concentration made the exchange capacity increased as well.?4?Compared the thermodynamics model of Cd²⁺ adsorption about shells with Langmuir,Freundlich and Temkin respectively,the expriment find out that the adsorption process of Cd²⁺ in aqueous solution was monomolecular layer,according to the Gibbs free and the entropy values showed that the reaction is exothermic reaction.The kinetics is divided into the rapid adsorption and equilibrium stages,and the rapid adsorption stage is also in accordance with the Lagergren quasi-first order kinetic model,while the whole process is in accordance with the quasi-second order kinetic model.