Effectiveness Research Of The Remediation Of Cr(?) Pollution In Groundwater By Sulfidated Nanoscale Zerovalent Iron

There are different levels of chromium pollution in the world.The discharge and accumulation of sewage and chromium slag from industrial processes are the main sources of chromium pollution in the environment.These contaminated wastes further contaminate groundwater through infiltration and leaching.Hexavalent chromium is highly soluble and can migrate and spread in the environment,posing a threat to human health.Therefore,the remediation of chromium-contaminated groundwater is a pressing task.At present,in-situ chemical reduction technology is the most commonly used chromium-contaminated groundwater remediation method,in which nanoscale zero-valent iron?nZVI?is the most effective and most promising reducing agent.Though unmodified nZVI has high reduction,low cost and magnetic,it at the same time has a narrow range of active pH value,the surface is easily passivated,which resulting in reduced reactivity.Therefore,it is often improved by modifying nZVI.Recent studies have shown that sulfidation will be an effective means of nZVI modification.However,the application of sulfidated nanoscale zero-valent iron?S-nZVI?is still in the research stage of the laboratory,and the removal efficiency and influence effects of various pollutants are not yet clear.The excellent reducibility of S-nZVI has been demonstrated in the literature,but the adsorption of S-n ZVI is rarely explain.In this paper,the Cr???in groundwater is the object of treatment,and removal efficiency of S-n ZVI on Cr???and its own application performance,and the reaction mechanism between S-n ZVI and Cr???analyzed by the product and kinetic are studied in order to provide some reference and help for the application of S-nZVI as a remediation agent for the in situ restoration of groundwater Cr???pollution.It mainly includes the following contents:?1?S-n ZVI was synthesized by two-step method and characterized by TEM-EDX,XRD,XPS and Zeta potential.The results show that under the effect of magnetic properties,S-nZVI appears the same chain structure as nZVI with a size of about 100nm.S-nZVI has an obvious shell-core structure.The Fe⁰ core is covered with amorphous ferrous sulfide and polysulfide.The isoelectric point of S-n ZVI is 6.2,which is smaller than nZVI?8.4?.The sulfidation has little change in the morphology of nZVI.It mainly changes the chemical composition of the nZVI surface,which changes the physicochemical properties of some materials;?2?The effect of different influencing factors on the removal of hexavalent chromium by S-nZVI was explored.The results showed that the optimism S/Fe removal rate of Cr???was 0.14.With the increase of S-nZVI dosage,the removal efficiency of Cr???increased.When the dosage is 2.0 g/L,the removal efficiency of Cr???by S-nZVI reaches 98%,and the removal rate of nZVI by the same dosage is 82%.When the pH was increased from 3 to 11,the removal efficiency of Cr???by S-nZVI was gradually decreased,but at the same pH,the removal efficiency and removal rate of Cr???by S-n ZVI was always higher than that of nZVI.When pH=5,the removal efficiency of Cr???by S-nZVI can still reach 100%,while n ZVI can only remove 85%.Therefore,S-n ZVI can be applied in a larger pH range than n ZVI.Increasing the temperature favors the progress of the reaction.The reaction is endothermic and the activation energy is 20.58 kJ/mol.K⁺,Na⁺,Ca²⁺,Mg²⁺,SO₄^2-,NO₃^-,and Cl^-all promoted the removal of Cr???by S-n ZVI.The efficiency of S-nZVI is higher than that of nZVI.The increase of pH of HCO₃^-solution inhibited the removal of Cr???,and its inhibitory effect on n ZVI system was higher than that of S-nZVI system.?3?Considering the application performance of performance,the results show that the settling performance and oxidation resistance of S-nZVI are better than nZVI.Especially after exposure to air for 15 days,the removal efficiency of S-nZVI on Cr???decreased only by 6%,while that of n ZVI decreased by 47%.Dissolved oxygen in water has little effect on the removal of Cr???by S-nZVI.?4?The reaction kinetics of S-n ZVI and Cr???were fitted and the total chromium,Cr???,Cr???and S-nZVI after reaction were analyzed.The results showed that the reaction process between S-nZVI and Cr???includes both adsorption and reduction,and is first adsorption and then reduction process.The reaction of S-n ZVI with Cr???followed pseudo second-order adsorption kinetics?R²>0.99?,chemical adsorption was the rate-limiting process of the reaction.The reaction between Cr???and S-nZVI occurs mostly on the solid phase instead of the aqueous phase,it reduces the electron loss caused by hydrogen evolution,and accelerates the electron transfer between S-nZVI and Cr???.Cr???undergoes a reduction reaction with S-nZVI after adsorbed on the surface of S-n ZVI.Fe?II?and S^2-on the surface reduced Cr???to Cr???,while itself oxidized to Fe?III?and S_n^2-;Fe⁰ core in S-nZVI transfers electrons to Cr???and reduce it to Cr???,and itself oxidized to Fe?II?.S_n^2-and Fe?II?produced by the above process continue to react with Cr???to form SO₄^2-and Fe?III?.Finally,as the reaction proceeds,the pH of the system gradually increases,and Fe?III?and Cr???are converted to Fe₂O₃,Cr₂O₃,or co-precipitation of iron and chromium,respectively.