The reduction of an ammonium nitrate solution by lead pellets during wet ba
ll milling was studied, as a method of removing concentrated NO3- from wast
ewater. Metal oxides forming on the surface of lead pellets in a ball mill
reactor are continuously removed by contact between the pellets. At tempera
tures between 25 and 80 degrees C and a ball mill rotation speed, omega, of
80-180 rpm, initial concentrations of NH4NO3 between 0.05 and 0.1 M, NO3-
rapidly reduce to NO2-, and then to N-2 and NH3. 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 NO3- and NO2-. As the
temperature increases, the rate of reduction of NO3- increases and the prop
ortion of NH3 formed increases, as that of N-2 decreases. The rate of reduc
tion of NO3- is governed by the rate of wear of the outer layer of the Pb p
ellets, which is determined by the speed of rotation of the ball mill. In t
his system, there are three competitive reactions: the reduction of NO3- an
d NO2- by Pb, the reduction of NO2- by NH4+ and the precipitation of basic
lead (II) salts. (C) 1999 Elsevier Science Ltd. All rights reserved.