湿式ボールミル中の鉛粒子による硝酸ナトリウム溶液の還元速度

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  • Reduction Rate of Sodium Nitrate by Lead Drops with Wet-Ballmilling.
  • シッシキ ボール ミルチュウ ノ ナマリ リュウシ ニヨル ショウサン ナトリ

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Reduction of sodium nitrate solution by lead drops with wet-ballmilling is studied in order to remove concentrated NO3- from wastewater. Metal oxides forming on the lead drops surfaces in a ballmill reactor was continuously removed by inter-ball contacting<BR>In the 5-80°C temperature range, initial concentration of NaNO3 0.05-0.1 M, and ballmill rotation speed, ω, 80-180 rpm, NO3- is rapidly reduced to NO2-, then slowly to N2 and NH3. NO3- is reduced to NO2- 32-100% in 10 h, but the reduction rate of NO2-is very slow, so the maximum percentages of N2 and NH3 from NO2- are only 6 and 10 %, respectively.<BR>Above 40°C, NO3- is reduced under zero-order reaction and NO2- is formed corresponding to the reduction stoichiometry. The reduction rate is proportional to ω1/2 [rpm1/2], and the apparent activation energy is 27.5 kJ·mol-1, but independent of the NO3- concentration. These results suggest that the rate determining step is the peeling of PbO layers on the particle surface. Below 25°C, the reduction rate decreases with reaction time as the surface is not covered completely with PbO due to the lowering of the rate.

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