| Adsorption is widely used in the treatment of heavy metal wastewater.In this study,the modified vermiculite was prepared by modifying the natural vermiculite.By mixing with humic acid,the composite adsorbents with good adsorption effect on cadmium,arsenic and cadmium arsenic were obtained.In this paper,the best preparation conditions of composite adsorbent were studied,and the adsorption mechanism of composite adsorbent for cadmium and arsenic was studied.The main achievements are as f-ollows:1.In this paper,the influence of single modification factors such as calcination temperature,time,ferric chloride concentration and humic acid proportion on the modification effect was studied.Through orthogonal experiment,the combination with the highest removal rate of cadmium(composite adsorbent A15),arsenic(composite adsorbent A7)and cadmium arsenic(composite adsorbent A8)was obtained respectively.Through the test and characterization of the adsorption performance of composite adsorbent As,it can be found that the adsorption performance of composite adsorbent is significantly higher than that of single vermiculite or humic acid.The characterization analysis shows that the microporous structure of the composite adsorbent increases,and there are iron hydroxide particles attached to it.The active groups such as hydroxyl,carboxyl,amino and carbonyl in the composite adsorbent play a key role in the adsorption.2.The study on the adsorption of cadmium by composite adsorbent A15 shows that under the condition of strong acidity(pH<5),it is not conducive to the removal of Cd2+;the adsorption equilibrium time is about 240 min.Response surface analysis showed that the significant factors of interaction effect were:adsorption time and amount of adsorbent,adsorption time and initial pH.Through simulation,the optimal adsorption conditions are:time 296min,adsorbent dosage 479g/L,pH 6,initial concentration of Cd2+ to 55mg/L,the actual removal rate is 97.20%,and the order of the influence degree of each factor on the response value of removal rate is:adsorption time>pH>adsorbent dosage>initial ion concentration.The isothermal adsorption analysis showed that the adsorption process of Cd2+ on adsorbent could be well expressed by Langmuir model.The theoretical maximum adsorption capacity qm of the adsorbent for Cd2+can reach 30.39mg/g(293k).The analysis of adsorption kinetics shows that the quasi second order kinetics is more suitable for the actual adsorption process.The thermodynamic analysis shows that the main force of adsorption is hydrogen bond force and dipole force.The study of adsorption rate control shows that the main control of adsorption is particle diffusion and chemical adsorption.3.The optimal pH for As(?)removal by composite adsorbent A7 is 5?6,and the adsorption equilibrium time is about 480 min.Response surface analysis showed that the interaction between adsorption time and the amount of adsorbent was significant.The best adsorption conditions were:time 383min,dosage of adsorbent 8.89g/1.pH 5.0,initial concentration of As(?)14mg/L,and the actual removal rate was 97.85%.The order of influence degree of each factor on the response value of removal rate is:initial pH>adsorbent dosage?adsorption time>As(?)initial concentration.The results of isothermal adsorption fit showed that the adsorption process of As(?)by the adsorbent was in accordance with Langmuir model,and the maximum adsorption capacity was 5.01mg/g.The analysis of adsorption kinetics shows that the quasi second order kinetics is more accurate.The adsorption thermodynamics analysis shows that the adsorption behavior is spontaneous endothermic reaction,and the main force of adsorption is hydrogen bond force and dipole force.The study of adsorption rate control shows that the main control of adsorption is particle diffusion and chemical adsorption. |
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