Research On Nitrate Removal From Water By Spherical Sponge Iron Prepared By Direct Reduction

Spherical sponge iron used as a new wastewater treatment material was prepared by direct reduction. Static experimental test has been carried on to investigate the nitrate removal efficiency from polluted water by the spherical sponge iron prepared by charcoal and H2 reduction, and to explore nitrite removal machenism.When the reaction condition could be controlled as solid-liquid ratio being 1:10, initial pH value in solution below 3, and keep dissolved oxygen in solution in a certain concentration, it was suggested that nitrite removal percentage could hold a highest level. As initial nitrate concentration below 10mgN/L, Nitrate removal percent increased with original nitiate concentration increased. But remains of nitrate in solution could retain about 0.5mgN/L. Nitrate removal percentage would significantly decreased with original nitrate concentration increased as it was above 10mgN/L. Nitrate reduction by charcoal reductive spherical sponge iron appeared to be the first-order reaction. The reaction order ranged from 0.827 to 1.310, and the apparent reaction rate constant ranged from 0.122 to 0.247h-1.Spherical sponge iron deoxidized by H2 appeared to be the first-order reaction. The reaction order ranged from 0.959 to 0.993. Reaction rate could keep a higher speed as H2 direct reduction temperature above T2. Whether initial nitrate concentration was high or low, nitrate removal percentage by H2 reductive sponge iron was higher than that of charcoal reductive sponge iron when the reduction temperature was between T1 to T5. Whether initial pH was high or low, pH values could reached above 11 after H2 reductive sponge iron was filled in. It was suggested that initial pH has litte influence on nitrate removal percentage. Nitrate removal percents could read 89.60% and 78.07% respectively, as nitrate original concentration being 5mgN/L and 50mgN/L. Moreover, nitrate reduction by H2 reductive spherical sponge iron appeared to be the first-order or pseudo-first-order reaction.Nitrate was removed rapidly when Fe/N was above 80, and the concentration of nitrate remains could be about 0.4mgN/L as Fe/N mole ratio above 80. Nitrate reduction by H2 reductive sponge iron appeared to be the first-order reaction. The reaction order of nitrate reduction ranged from 0.970 to 1.378, and the apparent reaction rate constant was 0.314~0.536 h-1. Nitrate reactive rate increased with original concentration. It was suggested that ammonium, which was the major product of nitrate reduction, exist in solution as ion-state ammonium. When the quantity of ion-state ammonium in solution exceeded its saturation solubility, ammonia could escape as molecule-state. With electrochemisty going on, ferrous ion concentration increased and achieved the maximum value, and then decreased.It provide a new zero-valent iron material, which deoxidized by charcoal or H2 directly for the first time, to remove nitrate from wastewater. Moreover, nitrate removal mechanism was explored. In summarization, the research work possess important realistic and scientific value for developing and applying of zero-valent iron.