Cr(VI) REDUCTION BY DISSOLVED Fe(II) IN LOW-BUFFERED AQUEOUS SYSTEMS

Han, Ihn S.

Environmental Engineering Research 1999;4(4): 239-250.

Ihn S. Han^†

Texas A&M University, Civil Engineering Department, Environmental Engineering Specialty

Corresponding Author: Ihn S. Han ,

Received: May 9, 1999; Accepted: September 10, 1999.

ABSTRACT

The effects of pH and DO on the reduction of Cr(VI) to 0(111) by Fe(II) were investigated in aqueous solutions, where ionic strength, initial concentrations of Fe(H) and Cr(VI) were maintained constant. Fe(II) was spiked to Cr(VI)-contaimng solutions. Preadjusted initial pH conditions by adjusting pH of both Cr(VI)-containing and Fe(II) stock solutions and rapid-pH increasing conditions were used for studying the effect of solution pH. The experiments for studying the effect of DO were performed in an anaerobic chamber. Cr(VI) reduction by Fe(II) was closely related with the solution pH. The reduction rate was increased with increasing pH (pH 4~pH 6.0 for oxic and pH 4.0~pH 9.8 for anoxic experiments). When NaOH was added after spiking Fe(II) the reduction rates showed the similar trend (higher rate with increasing pH) but under the oxic conditions the rate increase is steeper than under the anaerobic conditions with respect to pH values measured 1 minute later after adding NaOH. The molar ratios of Fe(ll) oxidized to Cr(VT) reduced were scattered around the theoretical value except that NaOH was added under the aerobic condition. Much more rapid reduction when NaOH was added than when pH of solutions was initially adjusted may be due to the underestimation of solution pH or locally, short-term high pH in the solutions.

Keywords: Cr(VT) reduction | Fe(II) | reduction rate | oxic and anoxic conditions | pH increase