Remediation of Groundwater Contaminated with Zn, Pb and Cd using a Permeable Reactive Barrier with Apatite II

Introduction Phosphate-Induced Metal Stabilization (PIMS) using Apatite II stabilizes a wide range of metals, especially Pb, Cd, Zn, U and Pu, in situ or ex situ, by chemically binding them into new stable phosphate phases and other low-solubility phases that are stable over geologic time. The concept resulted from paleochemical oceanographic and chemostratigraphic studies, in the 1970s and 1980s, of phosphatic sedimentary materials from the Cambrian period (570 million years ago) to the Present [1,2]. These studies showed that apatite hard parts of marine animals, and even abiotic phosphorite deposits, developed identical trace metal signatures of the seawater with which they were in contact, but with concentrations enriched by six or seven orders of magnitude. The chemical reactions were relatively fast and the chemical signatures were retained over geologic time, even in the face of multiple destructive events such as burial, lithification, heating, and weathering. Recent laboratory and field studies have demonstrated the applicability of this concept towards remediation of metal-contaminated waters and soil. Results are presented from a field site at Success Mine in Idaho, where a permeable reactive barrier (PRB) filled with Apatite II has been operating for just under two years to remediate Zn, Cd and Pb [3]).