Abstract

Equilibrations were performed with complexing reagent(s) to mobilise Cd, Cu, Mn, Ni, Pb and Zn from a contaminated urban soil. The metal-laden aqueous extract was treated with zero-valent magnesium (Mg⁰) or bimetallic mixture (Pd⁰/Mg⁰ or Ag⁰/Mg⁰) to precipitate the heavy metals from solution while liberating the chelating reagent(s). Post precipitation, the pH of aqueous supernatant fraction was readjusted to ∼5 and the solution was re-combined with the soil particulates to extract more heavy metal pollutants. A sparing quantity of EDTA (10 mmoles) mobilised 32–54% of the 5 mmoles of heavy-metals from the soil with three cycles but only 0.1% of the iron was removed. Three successive extractions with a mixture of complexing reagents (3 mmoles), 1∶1 EDTA plus HEDC [bis-(2-hydroxyethyl)-dithiocarbamate], mobilised ∼49% of the Pb, ∼18% of the Zn and ∼19% of the Mn burden but only 7% of the Cu, and 1% of the Fe from this soil. An appreciable fraction of the mobilised Pb and Cu and a portion of the Zn was cemented to the surfaces of the excess magnesium whereas virtually all of the Fe and Mn was removed from solution as insoluble hydroxides.