The reduction of an ammonium nitrate solution by lead pellets during wet ball milling was studied, as a method of removing concentrated NO_3-from wastewater. Metal oxides forming on the surface of lead pellets in a ball mill reactor are continuously removed by contact between the pellets. At temperatures between 25 and 80℃ and a ball mill rotation speed. ω, of 80-180 rpm. initial concentrations of NH_4NO_3 between 0.05 and 0.1 M. NO_3-rapidly reduce to NO_2-,and then to N_2 and NH_3. Depending on the pH of the solution, the precipitation of basic lead (II) nitrate and basic lead (II) nitrite occurs simultaneously with the reduction of NO_3 and NO_2-. As the temperature increases. the rate of reduction of NO_3-increases and the proportion of NH_3 formed increases, as that of N_2 decreases. The rate of reduction of NO_3 is governed by the rate of wear of the outer layer of the Pb pellets, which is determined by the speed of rotation of the ball mill. In this system. there are three competitive reactions: the reduction of NO_3-and NO_2-by Pb. the reduction of NO_2 by NH~+_4 and the precipitation of basic lead (II) salts.
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