Selective Reduction Of Groundwater Nitrate By Iron-carbon Complexes By Aerosol Method

In this paper,an aerosol-assisted synthesis of Fe⁰/C composite was prepared and tested.The adsorption effect of Fe⁰/C composites on organic matter and the performance of Fe⁰/C composite material to reduce nitrate were also tested.The results show that the process of synthesis can prevent the oxidation of Fe⁰ surface.The newly prepared Fe⁰/C composites are spherical with diameters ranging from 0.8μm to 4.3μm,in which Fe⁰ with diameters of 80-120 nm is embedded in particles inside and outside the carbon spheres.In addition,Fe⁰ has a central cube structure with an average crystal thickness of 43.6 nm,and the mass proportion of Fe⁰ is 40.9%.The Fe⁰/C specific surface area is 366.2 m²/g,the average pore volume is 0.557cm³/g,and the average pore diameter is 3.7 nm.The specific surface area is 12.8 times larger than that of the C sphere.The maximum adsorption capacity of Rhodamine B was 853.7 mg/g.The adsorption process was combined with a pseudo-second-order adsorption kinetic model,and the adsorption isotherm conforms to the Langmuir-type isotherm.At the same time,the composite material can effectively remove nitrate and has high nitrogen selectivity,the selectivity of nitrogen for freshly prepared Fe⁰/C composites could reach 52.2%,compared to that of 7.7%for traditional n ZVI.Meanwhile,the removal efficiency of nitrate was slightly increased from 63.5%to 69.9%.Dissolved oxygen competes with nitrate,Fe0/C reacts preferentially with dissolved oxygen,and then reacts with nitrate after dissolved oxygen is consumed.The p H of the solution was reduced from 7 to 4,and the nitrogen selectivity was increased from 52.7%to 70.0%,the nitrate removal efficiency decreased from 71.2%to 65.5%.Various materials including aged Fe⁰/C composites,Fe⁰/Si O₂ composites and n ZVI particles in the deoxygenated and oxygenated systems were assessed for comparison.Furthermore,a variety of methods such as SEM,TEM,XRD,XPS,BET,FTIR and TGA were used to characterize the Fe⁰/C composites before and after the reaction.Hence,four key factors were determined for the effective conversion from nitrate to nitrogen:the surface of zero valent iron particle should be protected from oxidation and its genuine characteristics are well retained;the reaction should be controlled under an anaerobic condition;and the carbon as the carrier to support iron particles is very important;lower initial p H favors nitrogen generation.