Factors Influencing the Effectiveness and Stability of Aqueous Lead Immobilization by Hydroxyapatite

Abstract

The effects of Ca, K, Na, calcite, and EDT A on Pb immobilization by hydroxyapatite [CaIO(P04)6(OHh; HAl were investigated. The stability of hydroxy pyromorphite [PbIO(P04MOHh; HPJ (a reaction product of HA with Pb) and the effectiveness of using HA to immobilize Pb in Pb-contaminated soils also were examined. Neither Na nor K affected Pb immobilization. Aqueous Ca and calcite slightly inhibited Pb immobilization, but HA still reduced aqueous Pb > 97% in the presence of these species; however, EDTA significantly reduced the effectiveness of HA to immobilize Pb from Pb-EDTA solutions, with only 24 to 31 % resultant reduction in aqueous Pb. Hydroxypyromorphite was stable in the presence of HA up to 8 wk. Both higher Ca and lower P concentrations (following P removal by anion exchange resin) dissolved HP from a mixture of HA and HP, but the final aqueous Pb concentrations remained low «168 nmol L-I). High EDT A concentrations dissolved most (>85%) of the Pb from the same mixture. Hydroxyapatite effectively immobilized >71 % of the aqueous Ph in four PbHAs04 contaminated soils. The effectiveness of HA to immobilize aqueous Ph in the presence ofCa, K, Na, and calcite, and to immobilize aqueous Pb from Pb-contaminated soil .. , together with the stability of HP in the presence of high Ca and low P concentrations support our previous conclusion that HA has the potential to treat Ph contaminated water, soils, and wastes and that such a treatment can result in long-term in situ Pb stabilization; however, HA did not effectively immobilize Pb, nor was HP, stable in the presence of high EDTA concentrations. Thus, HA treatment will be ineffective in EDTA rich environments.

Lead(II) retention by Alfisol and clinoptilolite: cation balance and pH effect

“…Another method to immobilize lead is application of organic fertilizers or phosphates. In particular, solution lead concentration in Pb-enriched soil can be substantially reduced by adding hydroxyapatite [Ca 5 (PO 4 ) 3 (OH)] (Ma et al, 1992;Ma, 1996), monocalcium phosphate [Ca(H 2 PO 4 ) 2 Á2H 2 O] (Kalbasi et al, 1995), or Na 2 HPO 4 (Rabinovitz, 1993). This response is attributed to the precipitation of hydroxypyromorphite [Pb 10 (PO 4 ) 6 (OH) 2 ].…”

Disponibilidade dos metais pesados tóxicos cádmio, chumbo e cromo no solo e tecido foliar da soja adubada com diferentes fontes de NPK+Zn

“…Ainda segundo Cotter-Howells e Caporn (1996) e Ma (1996), o uso de fosfatos em solos contaminados com Pb pode reduzir a biodisponibilidade desse elemento, graças à formação de fosfato de Pb (por exemplo, piromorfita).…”

Stability of in situ immobilized lead and zinc in rhizosphere soil of phosphorus amended metal contaminated soils.

“…The formation of pyromorphite is a step-wise process which involves the dissolution of the Pb and P minerals and the precipitation of pyromorphite, hence the dissolution of either Pb or P minerals will determine the rate of pyromorphite formation in the soil (Arnich et al, 2003;Ma, 1996;Yang et al, 2001). In most cases, however, soil P availability is greater than Pb (Lindsay, 2001) and pyromorphite formation is limited by the dissolution of Pb 2+ into soil solution.…”

“…On the other hand, a laboratory study using hydroxy-pyromorphite and anion resins to remove P from solution simulating P-uptake by plants indicated that pyromorphite was still stable in a P depleted environment (Ma, 1996). It is very clear that, however, the role of plants in mineral dissolution is beyond a simple P uptake.…”

“…Previous laboratory studies showed that using hydroxypyromorphite and anion resins to remove P from solution to simulate P-uptake by plants indicated that PY was still stable in P depleted environments as well (Ma, 1996). However, the formation of PY in soil systems often can be incomplete because of factors such as ion competition to the added P, adsorption to solid phases and Pb/P chelation with dissolved organic carbon that reduce the formation of PY where intense interactions between PY with roots, soil minerals, microbes, and root exudates including low molecular weight organic acids (LMWOA) are expected Zwonitzer et al, 2003;.…”