| With the rapid development of urbanization and industrialization,more and more pollutants were discharged into water.Excess of pollutants have caused serious environmental pollution,which is a challenge for environmental remediation technology Heavy metals are difficult to be biodegradation,and it can be enriched in the food chain then accumulated and amplified in plants,animals and humans,which is a serious threat to human health and ecosystems security.In recent years,the researchers have paid attention to the nanoscale zero-valent iron(nZVI)due to their high reactivity and large specific surface area.However,the bare nZVI are easy to agglomerate,and the surface is easily blunt during the reaction.The sulfidation of nZVI nanoparticles(S-nZVI)can inhibit the agglomeration of bare nZVI,increase their dispersibility and reactivity,and improve their service lifeIn this paper,bare nZVI were prepared by liquid phase reduction method.S-nZVI and Fe/FeS nanoparticles were synthesized by one-step method and two-step method The adsorption of heavy metal Cu(?)and Cd(?)in aqueous solution were discussed The experimental results show that S-nZVI(S/Fe=0.25)have better removal effect on Cu(?)than the bare nZVI.One-step synthesis of S-nZVI(S/Fe=0.2)have better removal of Cd(?)than the bare nZVI.According to the characterization results of SEM and TEM,the bare nZVI are small spherical particles gathered together,and the surface is smooth and chain-like.The S-nZVI contain lamellar structure represent the FeSx,and the particles are more dispersion.The BET characterization analysis shows that the specific surface area of S-nZVI is much larger than the nZVI's.According to the characterization results of XPS,it is known that the nZVI have an S2p characteristic peak after sulfidation,indicating the formation of sulfideCompared with nZVI,S-nZVI have better removal effect on Cu(?)and Cd(?).The adsorption capacity of nZVI on Cu(?)and Cd(?)is 288.27 mg/g and 40.025 mg/g respectively,while the adsorption amount of Cu(?)and Cd(?)by S-nZVI is as high as 388.60 mg/g and 66.275 mg/g.The adsorption of Cu(?)and Cd(?)by the two materials is consistent with pseudo-secondary kinetics,ie the adsorption rate is controlled by a chemical process.The pH of the initial solution has a great influence on the removal of Cu(?)and Cd(?).With the initial pH of the solution,the removal effect under acidic conditions is better.According to the adsorption isotherm model,the Langmuir adsorption isotherm model is more suitable for describing the adsorption process of S-nZVI for Cu(?)removal.The maximum adsorption capacity is 460.83 mg/g.The single layer adsorbs and no interaction occurs between the adsorbed Cu(?).The initial concentration of Cu(II)and coexisting substances are the factors that affect adsorption process.As the initial concentration of Cu(?)increases,the amount of adsorption was increased.It was found that the presence of coexisting ions like Cl-,Ca2+,Mg2+and humic acid could reduce the removal efficiency of Cu(?).This experiment also explored the competitive adsorption of Cu(?)and Cd(?)at the same time.The results showed that the adsorption effect of S-nZVI on Cu(?)is better than that of Cd(?),and the coexistence of Cu(?)during the adsorption of Cd(?)has a strong inhibitory effectFrom the XPS characterization before and after the reaction,the following results could be obtained.The removal process of Cu(?)by S-nZVI was a mixing process:first,Cu(?)in solution was adsorbed onto the surface of S-nZVI,and then Cu(?)was reduced to Cu2O and Cu0 by nZVI on the material.Finally,Cu2O and Cu0 was attached to the surface of the material.At the same time,S2-can be combined with Cu(?)to form CuS,so as the Cu(?)could be removed from the aqueous solution.The mechanism of Cd(?)removal by S-nZVI mainly included surface complexation and adsorption:first,Cd(?)in solution was adsorbed onto S-nZVI,and then surface complexation occured,meanwhile FeSx was dissolved to generate S(-?),then combined theCd(?)to form metal sulfide precipitates. |
PDF Full Text Request