| Recently, with the rapid development of industry and agriculture, nitrate in ground water has become one of main contaminants with the tendency to gradually deteriorae. Using zero-valent iron and modified nanoparticles to remediate nitrate pollution is a new direction of environmental remediation in the world.About the influence of some coexisting ingredients in the ground water on iron materials to remove nitrate, there is no systematic study now. Few reports of nitrate reduction by bimetallic particles in sand column which is more close to the groundwater environment have been surfaced, so we still don’t know much about migration and deposition of nanoparticles in the sand column, and the pollutant removal performance. It is extremely necessary to carry out the systematic study about the sand column with considering actual water chemistry conditions and hydrodynamic conditions of groundwater.Based on the consideration above, liquid-phase synthesized method was applied to prepare nanoscale Fe/Cu compound materials. Nanoparticles were characterized by TEM technique, and were used to reduce nitrate contamination. Firstly the influences of initial nitrate concentration on nitrate removal were studied to determine the optimum dosing amount of nanometer iron. On the basis, the effect of four kinds of inorganic anions (Cl-,SO42-, HCO3- and PO43-) under the condition of insufficient Fe/Cu nanoparticles dosing and sufficient Fe/Cu nanoparticles dosing on nitrate removal and reduction products was studied. Besides, The influence of fulvic acid and the dissolved oxygen on the process of nitrate reduction were studied. Nano-Fe/Cu bimetallic nanoparticles sand column experiment was carried out, analyzing the effect of quartz sand particle size, concentration of the nanoparticles, nanoparticles volume and nitrate initial concentration on migration and deposition of nanoparticles in the sand column, and nitrate removal. Main conclusions are the following:(1) When Fe/Cu nanoparticles dosing is sufficient, nitrate can be thoroughly restored, and the product was only ammonia nitrogen. Otherwise, nitrate can not be thoroughly restored, and the product was ammonia nitrogen and nitrite.(2) When the quantity of nano-Fe/Cu was insufficient, Cl-,SO42-, HCO3- and PO43- all restrained nitrate reduction. The effect order was PO43-> SO42-> HCO3-> Cl-. Including the role of PO43- almost not influenced by the concentration, and for other anions, the greater the concentration, the stronger the effect. In addition, Cl-, SO42- and HCO3- had promoting effect on the production of ammonia nitrogen. The role was:SO42-> HCO3-> Cl-,and the greater the concentration, the stronger the effect.The reasons for these effects are:PO43- significantly inhibited nitrate reduction because of its strong adsorption on the surface of nano-particles and its corrosion products; Fe (Ⅱ), Fe (Ⅲ) and OH- with Cl-, SO42- or HCO3-participating formed green rust which can promote that the nitrate transformed ammonia nitrogen, so Cl-, SO42- and HCO3- can increase the ratio of ammonia nitrogen in the product. When the quantity of nano-Fe/Cu was sufficient, SO42-and HCO3- restrained nitrate and intermediate nitrite reduction. The effect order was HCO3-> SO42-, and effect was stronger with the increase of concentration. The reason was that these anions transformed to green rusts (GR) by combining with Fe(Ⅱ)/Fe(Ⅲ)hydroxides, which were able to reduce nitrate to ammonia. However, Cl- contributed to the reduction of nitrate in the case of enough nanoparticles, because Cl- and Fe (Ⅱ)/Fe (Ⅲ) produced complexation reaction, which reduced iron oxides deposited on the nanoparticles, and raised the chance of NO3- and NO2- to contact with nanoparticles.(3) The fulvic acid reduced the nitrate reduction rate and had no effect on the removal rate, but the dissolved oxygen decreased reduction rate and removal rate of nitrate.(4) Distribution of Fe/Cu bimetallic nanoparticles in the sand column varied along with the factors, but in all case, the entrapment quality in the first half of the sand column was more, and then, in turn, with the migration to the outlet, the quantity was smaller. In the nitrate reduction process, nitrate, ammonia, nitrite and total nitrogen had the same change trend. Firstly, because of the adsorption of nanoparticles to nitrate, the nitrate and total nitrogen was zero. Then, reduction reaction was going on. Because the nanoparticles were enough, so the product was only ammonia nitrogen. With reaction, the activity of nanoparticles droped, so nitrate and nitrite appeared, and ammonia nitrogen decreased at the same time. Nitrate concentrations increased with time, and nitrite concentration declined after the maximum concentration, which showed that the nanoparticles had gradually losted the ability reducing nitrate.(5) The medium size affected the migration of Fe/Cu bimetallic nanoparticles in the sand column. The greater the particles size was, the better the migration of nanoparticles happened. However, medium size had no effect on nitrate removal effect. The injection volume of nanoparticles had no effect on distribution of nanoparticles in the sand column. But the greater injection volume was, ther more conducive to reduction of nitrate because of the greater interception of nanoparticles in the sand column. Likewise, the great Nanoparticles concentration was helpful for migration of nanoparticles and the nitrate removal. The greater initial nitrate concentration made nanoparticles maintain the reactivity in the shorter time. |
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