NITRATE REDUCTION BY METALLIC IRON

Chemical reduction of nitrate by metallic iron (Fe-0) was studied as a potential technology to remove nitrate from water. The effects of pH and the iron-to-nitrate ratio on both nitrate reduction rate and perce nt removal were investigated. Rate constants and the apparent reaction order with respect to nitrate were determined and a mass balance was obtained. Rapid nitrate reduction by iron powder was observed only at pH less than or equal to 4. pH control with sulfuric acid significantl y prolonged nitrate reduction and increased the percent removal. At hi gh nitrate loadings, both the rate and the percent removal increased w ith decreasing pH. An iron-to-nitrate ratio of 120 m(2) Fe-0/mol NO3 o r higher was required to completely remove nitrate within an hour. An apparent reaction order of 1.7 with respect to nitrate was observed, w hich may be partly due to the inhibitory effect of sulfate. Ammonia wa s the end product of nitrate reduction and accounted for all nitrate t ransformed under our experimental conditions. Acidity is the principal factor which controls the rate and the extent of nitrate removal by F e-0. The rapid reduction of nitrate at low pH was most likely due to e ither direct reduction by Fe-0 or indirect reduction by surface hydrog en derived from proton. Ferrous species, Fe2+ and Fe(OH)(2), were prob ably not involved in this reaction. (C) 1998 Elsevier Science Ltd. All rights reserved.