Pb mobility and extractant optimization for contaminated soils

Alternative technologies for the remediation for inorganic lead contaminated soils must be evaluated in addition to conventional standard technologies, such as stabilization, to help ensure the best technology was selected for implementation of the remediation solution. Innovative technologies such as extractive soil washing may provide an economical alternative to reaching remediation cleanup goals while, at the same time, protecting human health and the environment. Extraction of inorganic Pb from contaminated soils has been previously demonstrated using strong acids or chelating reagents. For example, aqueous solutions of chelating agents such as citric acid, diethylenetriaminepentaacetic acid (DPTA), sodium ethylenediaminetetraacetate (EDTA), sodium nitrilotriacetate (NTA) have been used to desorb metals from soils [1, 2]. Also investigated were strong acids, having concentrations up to 2 N, for extraction of metals from sandy soils [3]. Commercial pilot scale systems have been reported to utilize HCl at an extraction pH range of 1.8–2.2 to recover lead from contaminated soils [4]. Chloride complexation of lead can greatly enhance the solubility of lead in solution [5, 6]. Lead also will complex in solution with acetic or citric acid [7]. Incorporating acids or chelating agents with soil washing technologies may extract inorganic Pb species from contaminated soils. However, the feasibility of aqueous based extraction of organic lead species such as tetraethyl lead, and its related byproducts produced by weathering, was unknown. Weathered, contaminated soil core samples were obtained, composited and homogenized in 5 gallon HDPE buckets, and the homogenized sample was characterized. The soils were contaminated predominantly with inorganic Pb as well as trace quantities of organic Pb species. Therefore, a research program was carried out to investigate the feasibility of in‐situ or ex‐situ extractive soil washing to recover inorganic and organic lead contaminants from soil. Literature approaches utilizing acids, chelating agents, or combinations of these, were tested for extraction efficiency. Additional goals included optimizing lead extraction while minimizing extractant chemistry strength to ensure safety and to minimize cost. Both in‐situ and ex‐situ extraction techniques were simulated at bench scale, and the effects of these methodologies on organic lead species were also investigated.