Partitioning of trace metals before and after biological removal of metalsfrom sediments

Metal removal by biological solubilization in three strongly contaminated s ediments was carried out in a two-liter stirred bioreactor. Biological trea tment yielded metal removal efficiencies in the range of 11-30%, 43-57%, 60 -79%, 61-90%, 18-21%, 0-10% for Pb,Cu,Zn,Cd,Ni and Cr, respectively. The tr eated sediments were then rinsed with a NaCl solution (0.5 M), resulting in an increase by nearly 47% in Pb removal for the three sediments, while for other metals (Cu, Zn, Cd, Ni, Cr), the NaCl rinse did not seem to allow an y significant increase in metal solubilization. A standard procedure of seq uential selective extraction (SSE) was applied to the sediments before and after each treatment. With regard to Pb, Zn and Cd, the carbonate bound fra ctions (2/3 sediments) represented 18-42% of metals prior to treatment, whi le the iron and manganese oxides bound fraction constituted 39-60% of metal s for the three sediments. Between 90 and 100% of Pb, Zn and Cd removed by the process came from the fractions bound to carbonates and from those boun d to Fe and Mn oxides. The organic matter and sulfide bound fractions conta ined 65-72% of total Cu present before treatment and the process removed, o n average, 63% Cu present in this fraction. In contrast, Ni and Cr were fou nd mainly in the residual fractions (50-80%). Finally, this biological trea tment did not solubilize Cr appreciably, while removal of Ni mostly origina ted from the carbonate and Fe/Mn oxides fractions (70-80%). (C) 2001 Elsevi er Science Ltd. All rights reserved.