Recycling of complexometric extractants to remediate a soil contaminated with heavy metals.
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 approximately 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 approximately 49% of the Pb, approximately 18% of the Zn and approximately 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.
Lee
Chia Chi
CC
Department of Food Science and Agricultural Chemistry, McGill University, Ste-Anne-de-Bellevue, Qué., Canada.
Marshall
William D
WD
D001682:Biological Availability; D002614:Chelating Agents / Q000737:chemistry; D011232:Chemical Precipitation; D003247:Conservation of Natural Resources; D004492:Edetic Acid / Q000737:chemistry; D004787:Environmental Pollution / Q000517:prevention & control*; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000032:analysis* / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility
D002614:Chelating Agents; D019216:Metals, Heavy; D012989:Soil Pollutants; D004492:Edetic Acid