Remediation Of Arsenic-Contaminated Groundwater Based On Enhanced Transport Of Nano-Zero Valent Iron

Nano-zero valent iron（nZVI）with cheap and high reactivity features can be used to remove pollutants such as heavy metals,inorganic salts,and chlorine-containing organic compounds in groundwater via in situ remediations.However,nZVIs are easy inactivation,easy aggregation,and difficult migration in the actual application process.Therefore,it is crucial to find an effective way to construct stable nZVI and realize its long-distance transport in the groundwater environment.This dissertation uses flexible carbon（CB）and anionic surfactants as carriers to explore the dispersion stability of nZVI in simulated groundwater,investigate the removal efficiency toward arsenic by adjusting the functional group type,charge structure,hydrophobicity and other parameters of the interface between nZVI and the carrier,and then test the transport in the filling soil.The main research contents and results are as follows:（1）Dispersion stability of modified nZVI.Using commercial nZVI,CB,anionic surfactants（sodium carboxymethyl cellulose:CMC and sodium dodecyl sulfate:SDS）as raw materials,different types of amendments,including Fe⁰（monary）,Fe⁰+CB/CMC/SDS（binary）and Fe⁰+CB+CMC/SDS（ternary）were prepared.The results show that the order of dispersion stability is ternary system>binary system>unmodified nZVI,and the 1:1:2（Fe⁰-CB-CMC）,1:2:1（Fe⁰-CB-SDS）and 2:1:1（Fe⁰-CB-SDS）amendments in the ternary systems exhibited the best dispersion stability.The adsorption experiments further showed that the effluent concentrations of the ternary system for As（Ⅲ）(initial concentration:1 mg L^-1,adsorbent concentration:1 g L^-1,initial p H:7.45)were 0.01,0.008 and0.005 mg L^-1,respectively.All of them can meet the Grade Ⅲ standard of groundwater.(≤0.01 mg L^-1).The results of SEM-EDS and particle size analysis showed that the degree of agglomeration of the ternary system was reduced and a stable dispersion system was formed.The rheological test and Zeta potential analysis showed that the stability of the CMC system in the ternary slurry was greater than that of the SDS system.The above results all indicated that the ternary modified nZVI repairing slurry stably existed in aqueous solution was obtained through the synergistic effect of CB and CMC/SDS.（2）Removal performance of As（Ⅲ）from simulated groundwater by ternary modified nZVI.The adsorption effect of ternary supported nZVI slurry on As（Ⅲ）and the effects of initial p H,dissolved oxygen,coexisting ions and other environmental factors on the adsorption performance were studied by adsorption experiments.From the adsorption isotherms,the three types of adsorbents 2:1:1（Fe⁰-CB-SDS）,1:2:1（Fe⁰-CB-SDS）and1:1:2（Fe⁰-CB-CMC）The maximum adsorption capacities are 109.3,85.1and 79.0 mg g^-1,respectively,which are much larger than the adsorption capacity of Fe⁰ alone,which is 33.7 mg g^-1,and the isotherm curve fitting fits the Langmuir model.The adsorption kinetics showed that the adsorption process was more in line with the pseudo-second-order kinetic model.In addition,when the initial p H increased from acidic（p H=5）to alkaline（p H=10）,the effluent concentration increased and the removal rate decreased by about 30%.Through the dissolved oxygen content experiment,it was found that the increase of O₂ would inhibit the removal of As（Ⅲ）by the slurry.The coexisting anions SO₄^2-and Cl-had no obvious effect on the adsorption effect;while the arsenic removal effects of Mn²⁺and Ca²⁺on the three slurries all became worse with the increase of ionic strength.（3）Study on the migration and influencing factors of modified nZVI in aqueous media.Quartz sand and site fill were used to fill the simulated column,and 1:1:2（Fe⁰-CB-CMC）,1:2:1（Fe⁰-CB-SDS）,2:1:1（Fe⁰-CB-SDS）and unmodified nZVI slurries to study their penetration and retention profiles.The results of the column experiment show that:under the conditions of increasing the flow rate and decreasing the particle size of the medium,the penetration rate of the slurry increases and the retention decreases.In the soil simulation column,the increase of the flow rate had a greater effect on the 1:1:2（Fe⁰-CB-CMC）slurry;the migration distance showed a hysteresis with the increase of the ionic strength,and the migration ability decreased.The higher the p H value,the greater the electrostatic repulsion between the slurry and the medium,which is more conducive to the migration of the slurry.The maximum migration distance L_max can reach 140.37 cm.