Simulation And Study On The Adsorption Behavior Of Pb²⁺ In Wastewater By GAC And AC-S

With the aggravation of heavy metal pollution in recent years,this area of watertreatment field has drawn many attentions across the world.Activated carbon adsorption is one of the most effective and widely used methods to remove heavy metal ions from wastewater,but its research usually tends to be tedious,repetitive and long period of large scale experimental studies.There are few studies have been carried out on the efficient analysis of adsorption behavior through the establishment of computational adsorption models,especially in China.Therefore,this topic intends to establish 2 models of granular activated carbon GAC and Na₂S modified activated carbon adsorption on Pb²⁺by the advanced numerical simulation software COMSOL Multiphysics,which are based on the theoretical study on adsorption of heavy metals in water by activated carbon and the experimental data done by Chandra and Jyotsna.After the adsorption model was established,this study investigated the influence of the key parameters such as Pb²⁺initial concentration,hydraulic load and bed height that corresponding to the experiment on the adsorption effect,through 3 diagrams of the changes of Pb²⁺concentration in adsorption column,Pb²⁺breakthrough curve under different parameters and adsorption capacity change with time under different parameters,and by comparing the simulation results with the experimental results to verify the modelling accuracy,as well as the rationality and applicability of the model.At the same time,the simulation results were analyzed by Langmuir and Freundlich adsorption isotherms,and were analyzed by pseudo-first-order and pseudo-second-order reaction kinetics equations.The results are shown as follows:?1?In model 1 and model 2,the time required for penetration,saturation,and achieving maximum adsorption capacity?mg/g?of activated carbon adsorption column decreased with the increasing of Pb²⁺concentration?model 1:20⁶0mg/L,model 2:2⁸mg/L?and hydraulic loading?model 1:4¹6m/h,model 2:3¹0.5m/h?and increased with increasing bed height?model1:50⁸0cm,model 2:40⁸0cm?.The maximum adsorption capacity q_m is directly proportional to the initial Pb²⁺concentration,it however does not depend on the hydraulic loading and the change of the bed height,which wasn't involved in the concentration balance.The 2 parameters only affect the total amount of the total adsorbed Pb²⁺.The simulation results and the experimental results show that the Pb²⁺adsorption law is basically consistent,and the numerical value is highly uniform.?2?The adsorption law of Pb²⁺represented by model 1 simulated data is in good agreement with Langmuir adsorption isotherm,and the correlation coefficient R² with the linear fitting equation y=0.038x+0.24is is as high as 1,and the maximum adsorption capacity q_m calculated by Langmuir isotherm equation is obtained by simulation data and experimental data is respectively 26.32mg/g and 26.55mg/g,the error is only 0.23mg/g.The adsorption law of Pb²⁺ represented by model 2 simulated data is in good agreement with both of Langmuir and Freundlich adsorption isotherms,and the correlation coefficients R² of the fitting equation y=0.033x+0.58?y=0.8137x+0.5792 are all higher than 0.99,and the error calculated by Langmuir isotherm equation is only 0.86mg/g by simulation data and experimental data.This shows that the adsorption laws of GAC and AC-S on Pb²⁺is more consistent with the Langmuir adsorption isotherm.Therefore,we believe that the adsorption of GAC and AC-S on Pb²⁺is single molecule layer adsorption.?3?Compared with the pseudo-first-order reaction kinetics,the kinetic behavior of Pb²⁺adsorption in model 1 and model 2 is more in line with the pseudo-second-order reaction kinetics equation,and the correlation coefficient R² between simulated data and its corresponding linear fitting equation are all above 0.99 at different concentration gradients of Pb²⁺.At the same time,the pseudo-second-order reaction kinetics parameters of equilibrium adsorption capacity q_e is directly proportional to Pb²⁺concentration,and R² is inversely proportional to the concentration of Pb²⁺.However,the rate constantk₂?1/k₂q_e²=b?does not show a fixed change rule due to the influence of two parameters.