E-pH diagram of Fe-N-H_2O system and its application in nitrate removal from water by SSI

摘要

Spherical sponge iron (SSI) with high activity and intension could be utilized to remove nitrate from wastewater. Reduction product of nitrate by SSI was investigated through static state experiment combined with E-pH diagram of Fe-N-H_2O system. In a certain range of pH and redox potential, the speciation of iron include Fe~0, Fe~(2+), Fe~(3+), Fe(OH)_2 and Fe(OH)_3, and the speciation of N was (NO_3)~-, N_2, (NH_4)~+, or NH_3 as the initial speciation of N was nitrate. pH in solution increased to above 10 in 6min because of quick erosion battery reaction of zero-valent iron in solution. Moreover, the E value in solution declined quickly to the minimum and then increased slightly because of dissolution of oxygen from atmosphere. It was suggested that nitrite was the intermediate product during reduction of nitrate by SSI, and ammonium was the finial product of nitrate and nitrite reduction. Nitrate removal from wastewater was related with escape of ammonia, which was gas state of ammonium in water, when the water solution was alkaline.