Study On Capacity And Mechanisms Of Cadmium Sorption On Several Modified Biochars In Solution

Since heavy metal pollution is becoming more serious in domestic water body and leads to serious results in soils and crops.The treatment for heavy metal pollution in water body has become a focus in recent years.The way of adsorption plays an extraordinary role in heavy-metal removal from water environment because of its unique charterers and received extensive attention among people.The study is designed to mimic wastewater environment under the lab condition and aims to use two experimental methods?static and dynamic experiment?to assess adsorbing effectiveness among four types of adsorbing materials,including coconut shell char?CSC?,bamboo char?BC?,char?CC?and clinoptilolite?CP?,in terms of some factors including:the sorbent usage,original solution concentration,adsorbing timescale,penetrating curve,input flux etc.Meanwhile,CSC and BC are modified with CTAB and ferric nitrate?Fe NO₃·9H₂O?,and then four latest types of adsorbing materials?CTAB-CSC,CTAB-BC,Fe-CSC and Fe-BC?are acquired.In order to detect their adsorbed mechanisms,The isothermal adsorbing model of Langmuir and Freundlich and the kinetic models of pseudo-first order and pseudo-second order are established,while SEM,FTIR and XPS are adopted to characterize them as well.The specific results as shown as below:?1?The four materials?CSC,BC,CC and CP?can remove cadmium?Cd?from water well and the adsorbing capability order is following by:CC>BC>CSC>CP.However,the sorbent usage and solution pH value also have important impact on the process.More usage can lead to better performance on Cd removal.the best effectiveness remains at the initial solution pH=7.Moreover,CC and CP are more allowed to the isothermal model of Langmuir,while CSC and BC are more approaching the isothermal model of Freundich.?2?In dynamic experiment,the initial solution concentration,input flux,input time and depth of packing layer in adsorption column influence the adsorbing effectiveness greatly.The increasing of the initial solution concentration leads to the decrease of adsorbing penetrating time,the higher input flux leads to the higher concentration of output flux,the lower removal rate leads to the shorter time of penetration.The output flux concentration at every location of adsorbing column goes down as the flowing direction and eventually becomes consistent and approaches to the input flux concentration as time change.The order of adsorption performance is following by CC>BC>CSC>CP.?3?It is indicated that the new materials modified with the surfactant?CTAB-CSC and CTAB-BC?can play well in the adsorption of Cd2+in water.According to their largest adsorbing capability,the performance of CTAB-BC is better than CTAB-CSC.The most suitable pH range for CTAB-CSC and CTAB-BC is pH 3?7 and pH 4?7 respectively.The adsorption capability is promoted as the time change,and their adsorption processes match to the isothermal model of Langmuir,the fitted kinetics results demonstrate adsorbing processes of two materials are well allowed to pseudo-second order kinetic model.?4?The new magnetic materials?Fe-CSC and Fe-BC?produced by the way of coprecipitation also can adsorb Cd2+well.The performance of Fe-BC is better than that of Fe-CSC and their best adsorption ability is ranging from pH 5?7.The removal rate of Cd2+is also increasing with the time change.The kinetics-match results show that adsorbing processes of two materials are allowed to pseudo-second order kinetics formation.According to results of isothermal adsorption models,Fe-CSC is more fitted with the Langmuir model,while Fe-BC is allowed to the Freundlich model better.