動電学的反応性バリアシステムを六価クロム汚染土壌の処理に適用する際に用いる還元材の選定

抄録

Soil contamination by heavy metals including hexavalent chromium is a worldwide environmental issue. The objective of this study was to evaluate zero-valent iron, magnetite, and activated carbon as potential reductants used in the electrokinetic-PRB hybrid system for the treatment of soils contaminated by hexavalent chromium. The batch experimental results showed that the reduction of hexavalent chromium by these reductants was consistently enhanced by acid, which was a desirable result because PRB in the electrokinetic-PRB hybrid system is strongly acidified by the acid generated at the anode via water electrolysis. However, zero-valent iron and activated carbon were concluded not to be suitable reductants for our objective because of the following reasons. For zero-valent iron, acid dissolution of zero-valent iron released a significant amount of ferrous ion which migrates toward the cathode and as a result, high recovery of chromium in the PRB cannot be expected because ferrous ion reduces hexavalent chromium outside the PRB. For activated carbon, it was found that the generated trivalent chromium was dissolved in the aqueous phase meaning positively charged trivalent chromium migrates toward the cathode without remaining in the PRB. On the contrary, magnetite did not release ferrous ion under the acid exposure. Additionally, the generated trivalent chromium was sorbed to the magnetite without being released in the aqueous phase. Thus, it was concluded that magnesium is a suitable reductant for the electrokinetic-PRB hybrid system providing a high recovery of trivalent chromium in the PRB.