Formation of Chloropyromorphite from Galena (PbS) in the Presence of Hydroxyapatite

These results suggested that in an aerobic aqueous suspension of galena, the formation of chioropyromorphitewas determined by the oxidation rate of sulfide and the soluble Pb concentration were determined by the solubility of the newly formed chloropyromorphite in the presence of apatite

Pengchu Zhang; James A. Ryan

2002

Scholarcy highlights

  • In-situ immobilization of soil lead by addition of phosphate minerals has been considered a cost effective and environmental benign alternative remediation technology for Pb contaminated soils.This approach transforms the reactive and bioavailable soil Pb species, or labile Pb species, into the chemical forms that a r e stable and have reduced mobility and boiavailability under environmental conditions
  • It has been demonstrated that pyromorphite is o n e of the most stable Pb forms that can be formed under ordinary soil conditions and the bioaccessibility of soil Pb can be drastically reduced when unstable soil P b forms, such as cerrusite,are converted into pyromorphite
  • A s the forms of soil Pb vary and dependent upon the sources of Pb contamination and environmental conditions, knowledge of the reaction behavior of primary Pb forms with phosphate becomes important in assessing the efficiency of' Pb immobilization by addition of phosphate
  • Dissolution of Galena and Hydroxyapatite Dissolution of Galena As measured by soluble Pb concentration, dissolution of galena increased as pH decreased during the initial 180 min reaction time
  • The quantities of galena dissolved in the first 180 min reaction obtained in this study were in general agreement with that reported .Apparently, surface protonation, adsorption of H' on the mineral surface is the first step for most mineral dissolution processes, and was the driving force in the galena dissolution
  • The pH, of galena is between 2 to 4, depending upon the galena sources .At pH 4, the surface is positively chargedbecause of the adsorption of protons, and a higher dissolution of galena can be expected. This was confirmed by the results obtained in the initial 180 min reaction.Between pH 4 and 8, the net charge of the surface is either neutral or negative, t h u s dissolution of galena can be limited by the low surface protonation
  • These results suggested that in an aerobic aqueous suspension of galena, the formation of chioropyromorphitewas determined by the oxidation rate of sulfide and the soluble Pb concentration were determined by the solubility of the newly formed chloropyromorphite in the presence of apatite

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