Enhanced nitrate removal by novel bimetallic Fe/Ni nanoparticles supported on biochar

In this study, a novel bimetallic iron/nickel nanoparticles supported on biochar (BC@Fe/Ni) was established to degrade nitrate pollution in water. The nanocomposite was prepared from steel pickling waste liquor and sugarcane bagasse, which are made at low cost. The particle sizes of the nanocomposite ranged from about 10 nm to 20 nm and its specific surface area (59.83 m2/g) was about 71% bigger than that of nanoscale zero valent iron prepared from steel pickling waste liquor (S-NZVI), which proved that biochar had an excellent dispersal effect on bimetallic iron/nickel particles. Without controlling the pH, high nitrate removal rates over 93% could be realized in nitrate concentrations below 50 mg/L. The results of batch experiments demonstrated that the kinetics curves fitted the pseudo-first-order reaction well. And it was also found that higher dosages of the nanocomposite, lower initial nitrate concentrations, and acid medium facilitated nitrate degradation. In addition, the observed pseudo-first order rate coefficient in nitrate (20 mg/L) degradation rate by 4 g/L of the bimetallic iron/nickel supported on biochar was 30% faster than that by 2 g/L the bimetallic iron/nickel nanoparticles, due to the existence of biochar. And it was 75% faster than that by 2 g/L the nanoscale zero valent iron due to the existence of both biochar and the nanoscale zero valent nickel catalyst. Furthermore, iron and nickel ion pollution occurred in the denitrification system with bimetallic iron/nickel nanoparticles but not in that with the bimetallic iron/nickel nanoparticles supported on biochar, due to the biochar's adsorption. After denitrification by the bimetallic iron/nickel nanoparticles supported on biochar, most of nitrate turned into ammonia (17.04 mg/L) and there only was a small amount of nitrite (0.024 mg/L) with high nitrate removal rate (99.5%). And most of ammonia can be absorbed by cation exchange resin with finial ammonia concentration of 0.58 mg/L. At last, the concentrations of nitrate (0.24 mg/L), nitrite (0.021 mg/L), and total nitrogen (0.84 mg/L) were lowest in the nanocomposite system. Overall, the bimetallic iron/nickel nanoparticles supported on biochar exhibited clear advantages over bimetallic iron/nickel nanoparticles and nanoscale zero valent iron with respect to degrading nitrate efficiently, preventing iron and nickel pollution and removing ammonia pollution in combination with cation exchange resin.