| The chemical reduction-precipitation method for treating chromium wastewater has beenmost commonly used at home and abroad in the real engineering practice. Chromium removalfrom wastewater by zero-valent iron is an effective approach in the real engineering practice,for the reason that zero-valent iron is a strong reducing agent with the characteristics such aswide variety of sources, rapid reaction rate, relatively high redox and specific surface area.Influencing factors on treatment of cold rolling wastewater containing high concentrationof chromium with zero-valent iron（Fe~0）and nanoscale zero-valent iron（NZⅥ）wereinvestigated in the paper, moreover, it was summarized the treatment effect, as well as,advantage and disadvantage of nanoscale zero-valent iron method compared to zero-valentiron method. In addition, the mechanism and kinetics for removal of Cr（Ⅵ）by Fe~0werestudied.The dosage of sulfuric acid was the most important influencing factor on the treatment byboth using Fe~0and NZⅥ, and the optimum dosage of sulfuric acid were1.2%（pH was nearly0.93）and0.4%（pH was nearly1.60）respectively. Zero-valent iron method and nanoscalezero-valent iron method both have the significant treatment effect, total chromium andhexavalent chromium of effluent met the requirements of the national discharge standard, andthe removal efficiencies achieved above99.99%. Compared to zero-valent iron method,nanoscale zero-valent iron method was more effective with using less dosage of sulfuric acidand Fe. On the other hand, zero-valent iron method is valuable for the real engineering practicedue to the low cost.The Cr（Ⅵ）removal was mainly attributed to reduction effect of Fe~0, and the precipitationeffect of metal hydroxides containing chromium on the Fe~0surface. The reduction process of Cr（Ⅵ）by Fe~0in wastewater treatment basically follows to pseudo first order reaction law. Theapparent rate constant kobsincreases with the increasing of dosage of Fe~0, dosage of sulfuric acidand reaction temperature. |
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