Aqueous solubility of Pb at equilibrium with hydroxypyromorphite over a range of phosphate concentrations.

Hydroxypyromorphite (HPM) is a low-solubility Pb phosphate mineral that has the potential to limit solubility and bioavailability of Pb in soils and water. Because of reported uncertainty regarding the solubility product of this important mineral, we re-evaluated the solubility of Pb and activity of the free Pb2+ ion in aqueous suspensions of microcrystalline HPM equilibrated up to 30 days over a wide range of added soluble phosphate. A small addition of phosphate (0.1 mM) reduced Pb solubility as measured by ICP-OES, but greater phosphate additions (up to 50 mM) had no further effect in lowering HPM solubility. However, free Pb2+ ion activity measured by ion-selective electrode progressively decreased from about 10-6.5 with no added phosphate to 10-9 as soluble phosphate was increased. The effect of soluble phosphate in lowering Pb2+ activity is attributed to inhibited dissolution of HPM as well as increased Pb2+-phosphate ion pair formation in solution at higher solution concentrations of phosphate. Measurement of the ion activity products (IAP) of the solutions at equilibrium with HPM gave highly variable IAP values that were sensitive to pH and were generally not consistent with the reported solubility product of this mineral. The high variability of the IAPs for solutions with variable pH and phosphate concentrations indicates that dissolution-precipitation reactions of HPM are not described by a constant solubility product at equilibrium, possibly because of the incongruent dissolution behavior of this mineral at near-neutral pH.

[1]  M. Nadagouda,et al.  Lead Particle Size Fractionation and Identification in Newark, New Jersey's Drinking Water. , 2020, Environmental science & technology.

[2]  J. Pasteris,et al.  Impact of orthophosphate on lead release from pipe scale in high pH, low alkalinity water. , 2020, Water research.

[3]  C. Dai,et al.  Formation and Aggregation of Lead Phosphate Particles: Implications for Lead Immobilization in Water Supply Systems. , 2018, Environmental science & technology.

[4]  C. D. dos Remedios,et al.  A review of heavy metal cation binding to deoxyribonucleic acids for the creation of chemical sensors , 2018, Biophysical Reviews.

[5]  T. Bajda,et al.  Solubility of pyromorphite Pb5(PO4)3Cl at 5–65 °C and its experimentally determined thermodynamic parameters , 2016 .

[6]  C. Dybowski,et al.  Ion pairing in H2O and D2O solutions of lead nitrate, as determined with 207Pb NMR spectroscopy , 2016, Journal of Structural Chemistry.

[7]  Yinian Zhu,et al.  Characterization, dissolution and solubility of the hydroxypyromorphite–hydroxyapatite solid solution [(PbxCa1−x)5(PO4)3OH] at 25 °C and pH 2–9 , 2016, Geochemical Transactions.

[8]  David R. Brown,et al.  The Identification and Synthesis of Lead Apatite Minerals Formed in Lead Water Pipes , 2016 .

[9]  James Noel,et al.  Effect of water chemistry on the dissolution rate of the lead corrosion product hydrocerussite. , 2014, Water research.

[10]  Y. Xiong,et al.  Experimental determination of solubilities of lead oxalate (PbC2O4(cr)) in a NaCl medium to high ionic strengths, and the importance of lead oxalate in low temperature environments , 2013 .

[11]  T. Bajda,et al.  Solubility of pyromorphite Pb5(PO4)3Cl–mimetite Pb5(AsO4)3Cl solid solution series , 2011 .

[12]  B. Darvell,et al.  Calcium Phosphate Solubility: The Need for Re-Evaluation , 2009 .

[13]  James P. Larentzos,et al.  Aqueous divalent metal-nitrate interactions: hydration versus ion pairing. , 2008, Physical chemistry chemical physics : PCCP.

[14]  D. Giammar,et al.  Equilibrium solubility and dissolution rate of the lead phosphate chloropyromorphite. , 2007, Environmental science & technology.

[15]  K. Scheckel,et al.  Pyromorphite formation and stability after quick lime neutralisation in the presence of soil and clay sorbents , 2007 .

[16]  M. McBride,et al.  Lead phosphate minerals: solubility and dissolution by model and natural ligands. , 2004, Environmental science & technology.

[17]  H. Wolterbeek,et al.  Adsorption of metals to membrane filters in view of their speciation in nutrient solution , 2003, Environmental toxicology and chemistry.

[18]  H. Sigel,et al.  Stabilities of complexes formed between lead(II) and simple phosphonate or phosphate monoester ligands including some pyrimidine-nucleoside 5′-monophosphates (CMP2–, UMP2–, dTMP2–) , 1999, JBIC Journal of Biological Inorganic Chemistry.

[19]  V. Laperche,et al.  Contaminant bioavailability in soils, sediments, and aquatic environments. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[20]  B. Jackson,et al.  The Influence of Extraction Procedure on Ion Concentrations in Sediment Pore Water , 1998, Archives of environmental contamination and toxicology.

[21]  S. Sauvé,et al.  Lead Phosphate Solubility in Water and Soil Suspensions , 1998 .

[22]  H. Sigel,et al.  Stability of metal ion complexes formed with methyl phosphate and hydrogen phosphate , 1996, JBIC Journal of Biological Inorganic Chemistry.

[23]  M. Pagano,et al.  Lead precipitation in the presence of sulphate and carbonate: Testing of thermodynamic predictions , 1995 .

[24]  A. Klug,et al.  Pb(II)-catalysed cleavage of the sugar–phosphate backbone of yeast tRNAPhe—implications for lead toxicity and self-splicing RNA , 1983, Nature.

[25]  E. Atlas,et al.  Solubility behavior of apatites in seawater1 , 1977 .

[26]  J. Nriagu.  Lead orthophosphates—II. Stability of cholopyromophite at 25°c , 1973 .

[27]  J. Nriagu.  Lead orthophosphates. I. Solubility and hydrolysis of secondary lead orthophosphate , 1972 .

[28]  C. Childs.  Potentiometric study of equilibriums in aqueous divalent metal orthophosphate solutions , 1970 .