Study On Cadmium Removal From Water By Cellulose/Zeolite Composite Materials

In recent years,the events that cadmium pollution phenomenon in groundwater and surface water happened frequently.Cadmium is a kind of heavy metal with toxicity,and it will seriously threaten human health once it enters the water.So it is urgent to remove cadmium ion from water.Adsorption method has become a research hotspot because of its advantages of widespread application,simple operation,and no secondary pollution to the environment.Therefore,this study aims to find a kind of adsorbent with low cost and good adsorption performance.In this paper,the cellulose extracted from wheat straw by acid-alkali cooking method,was mixed with salt modified zeolite at a mass ratio of 1:5 to prepare cellulose/zeolite composite materials.According to the images of SEM and FTIR,cellulose and zeolite can be well combined,indicating a new porous material was formed.The characteristic of porosity is beneficial to remove cadmium from water.Compared with the single material zeolite or cellulose,the removal rate of cadmium was increased significantly.Cellulose/zeolite composite materials were used as the adsorbent to remove Cd²⁺with the initial concentration of 100?g/L in water,and the vacuum filter was carried out with0.22?m microfiltration membrane to achieve the solid-liquid separation.Residual cadmium concentration was determined with graphite furnace atomic absorption spectrometry,and turbidity was determined with portable turbidimeter.The single factor experiment and orthogonal experiment were applied to optimize the experimental conditions of Cd²⁺adsorption.The results suggested that the adsorbent dosage and adsorption temperature posed the greater influence on the removal rate;when the adsorption time was 30min,the adsorbent dosage was 1.2g/L,pH was 8.5,adsorption temperature was 20?,the Cd²⁺removal rate reached 98.31%.The values of effluent turbidity in all adsorption experiments were below 1NTU.In the study of adsorption isotherm model and adsorption kinetics,the process of cellulose/zeolite composite materials adsorption to Cd²⁺agreed well with the Freundlich adsorption isotherm model and the Lagergren two stage rate equation.In the Freundlich isotherm model,adsorption sites on the surface of cellulose/zeolite composite materials were uneven,and the adsorption index value was 1.386,within the range of 1 to 10,which indicated that the adsorption process was easy.In the study on adsorption kinetics,the experimental saturated adsorption amount of cellulose/zeolite composite materials to trace cadmium was 96.386?g/g,close to the theoretical value of 98.039?g/g calculated based on the adsorption kinetics.The consistency between the values indicated that the adsorption process conformed to the Lagergren two stage rate equation and the equation could predict the effect of adsorption time on the process.The results in the experiment on regeneration of adsorbents showed that the desorption effect of NaCl solution was better than that of CaCl₂ solution,and the regeneration rate was more than 97%,indicating a good regeneration effect.In the competitive adsorption experiments of cadmium ions,it was found that the presence of Cu²⁺in water inhibited the adsorption of Cd²⁺,which could be explained that Cu²⁺with smaller ionic radius was easier to occupy the adsorption sites.When the concentration of Cu²⁺increased from 0 to 100?g/L,the adsorption amount of Cd²⁺decreased from 91.280?g/g to 79.655?g/g.