Reduction of NaNO₃ Solution by in situ Buff Abrasion of Lead Plate

Abstract

Discharges of wastewater containing concentrated nitrate produced in industrial plants into closed water area can promote algal blooms and water pollution with eutrophication has getting worse. Chrome yellow pigment plants are one of the industries discharging concentrated NaNO₃ wastewater.
Nitrate ions were reduced by fine Pb powder produced by continuous abrasion o f Pb plate with buff abrasive in NaNO₃ solution. Under 25-80 °C, initial concentration of NO₃^- 0.01-0.1 M, and rotation speed of buff 100-800 rpm, 20-100% nitrate ion was reduced to NO₂^-, N₂, and/or NH₃ within 12 h. Since reduction rate of NO₂^- was extremely slow, maximum percentages of formed N₂ and NH₃ were 14, 6, respectively at 12 h. Pb was oxidized at 12 h to PbO containing unreacted Pb.
In the case of producing bigger Pb particles (20 μm) by using coarse buff (#120) and increasing rotation speed, the reduction rate of NO₃^- increased due to an increase in amount of abrabed Pb and surface area of Pb by removing PbO layer grown on Pb particles. However, the reduction efficiency of Pb decreased with increasing amount of unreacted Pb core. On the other hand, producing smaller Pb particles by using fine buff (#400) and decreasing rotation speed allow the reduction efficiency to increase. Although, the reduction rate of NO₃^- was high at 1-4 h because of larger surface area of Pb produced by fine buff, it decreased gradually due to decrease in amounts of abraded Pb.