Toxicity characteristic leaching procedure over- or under-estimates leachability of lead in phosphate-amended contaminated soils

Sima, Jingke; Cao, Xinde; Zhao, Ling; Luo, Qingzhi

doi:10.1016/j.chemosphere.2015.07.028

Cited by 35 publications

(4 citation statements)

References 28 publications

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“…4 Our thermodynamic models highlight the need for more comprehensive atomistic/nanoscale studies with coupled kinetic models to clarify under what circumstances scales may form, in part because Pb−P solid formation has been tied to mitigating Pb dissolution rates. 8,64 It should also be noted that phosphate anions may inhibit corrosion kinetics without the detection of stable phosphate-based scales. At the center of the lead-release problem is the kinetically dependent accumulation of consumable lead in the drinking water, whether through the direct dissolution of the pipe or through a multi-step pipe-film-electrolyte process.…”

Section: ■ Discussionmentioning

confidence: 99%

Density Functional Theory-Based Thermodynamic Model for Stable Scale Formation in Lead-Water Systems

et al. 2022

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Current safety standards for water treatment to reduce indigestible lead in drinking water utilize decades-old data and models to define risk mitigation. Limitation is achieved in part by utilizing additives to control particulate and soluble Pb(II) release through scale formation in lead pipes that rely on thermodynamic and kinetic factors. Advances in state-of-the-art computational materials science techniques allow fresh comparisons to older thermochemical data and thereby enable the formulation of new ab initio-based thermodynamic models. Here, we perform first-principles calculations to simulate electrochemical Pb Pourbaix and stability diagrams that include a limited number of non-ideal solution effects and account for variable concentration, additives, and temperature. Our data show that lead carbonates are thermodynamically driven to form a cerussite scale across a large range of conditions. Orthophosphate is a known lead corrosion inhibitor; however, the formation of lead phosphate scales, such as Pb (PO ) (OH) 5 4 3 2(s) , may rely on transient high Pb(II) concentrations with trace alkaline-earth elements. Moreover, their previously reported stability may be due to overestimated free energies of formation. Acceptable thermodynamically stabilized soluble lead levels in water can only be maintained under specific thermal and aqueous boundary conditions. Our work defines critical environmental limits on lead scale formation and provides a renewed look of E-pH lead stability and solid stabilities of lead (II) carbonate and phosphate species as a function of Pb(II) and pH using here-to-fore unavailable computational approaches for comparison to other data.

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Section: ■ Discussionmentioning

confidence: 99%

Density Functional Theory-Based Thermodynamic Model for Stable Scale Formation in Lead-Water Systems

et al. 2022

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“…However, kinetics plays an important role as well as thermodynamics in this process of Pb stabilization. Sima et al [26] investigated the remediation effect of phosphates on Pb-contaminated soils spiked with Pb(NO 3 ) 2 , PbSO 4 and PbCO 3 and found that the rate of Pb-phosphate mineral formation was limited by the dissolution kinetics of the original Pb compounds.…”

Section: Introductionmentioning

confidence: 99%

Pb Mineral Precipitation in Solutions of Sulfate, Carbonate and Phosphate: Measured and Modeled Pb Solubility and Pb2+ Activity

Azimzadeh

Martı́nez

et al. 2021

Minerals

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Lead (Pb) solubility is commonly limited by dissolution–precipitation reactions of secondary mineral phases in contaminated soils and water. In the research described here, Pb solubility and free Pb2+ ion activities were measured following the precipitation of Pb minerals from aqueous solutions containing sulfate or carbonate in a 1:5 mole ratio in the absence and presence of phosphate over the pH range 4.0–9.0. Using X-ray diffraction and Fourier-transform infrared spectroscopic analysis, we identified anglesite formed in sulfate-containing solutions at low pH. At higher pH, Pb carbonate and carbonate-sulfate minerals, hydrocerussite and leadhillite, were formed in preference to anglesite. Precipitates formed in the Pb-carbonate systems over the pH range of 6 to 9 were composed of cerussite and hydrocerussite, with the latter favored only at the highest pH investigated. The addition of phosphate into the Pb-sulfate and Pb-carbonate systems resulted in the precipitation of Pb3(PO4)2 and structurally related pyromorphite minerals and prevented Pb sulfate and carbonate mineral formation. Phosphate increased the efficiency of Pb removal from solution and decreased free Pb2+ ion activity, causing over 99.9% of Pb to be precipitated. Free Pb2+ ion activities measured using the ion-selective electrode revealed lower values than predicted from thermodynamic constants, indicating that the precipitated minerals may have lower KSP values than generally reported in thermodynamic databases. Conversely, dissolved Pb was frequently greater than predicted based on a speciation model using accepted thermodynamic constants for Pb ion-pair formation in solution. The tendency of the thermodynamic models to underestimate Pb solubility while overestimating free Pb2+ activity in these systems, at least in the higher pH range, indicates that soluble Pb ion-pair formation constants and KSP values need correction in the models.

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“…However, while the results indicate that biochar may be able to stabilize metals in contaminated sediments under certain conditions as clear decreases in C p and C DGT and clear increases in F3 and F4 in this study, it is clear that biochar is not as effective as phosphate or iron-bearing materials, the removals and transformations reported in other related studies are much higher than those reported in this and other biochar-related studies (Zhang et al, 2017;Igalavithana et al, 2017;Lu et al, 2017). For example, when phosphate compounds were added to contaminated soils, the concentrations of extractable heavy metals decreased by more than 90% (Ahn et al, 2015;Sima et al, 2015), while the oxidizable and residual phases of Pb and Cu increased by between 70%…”

Section: Possible Mechanisms Of Stabilization Induced By Biocharmentioning

confidence: 46%

Assessing the capacity of biochar to stabilize copper and lead in contaminated sediments using chemical and extraction methods

Wang

Ren

Wang

et al. 2019

Journal of Environmental Sciences

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Toxicity characteristic leaching procedure over- or under-estimates leachability of lead in phosphate-amended contaminated soils

Cited by 35 publications

References 28 publications

Density Functional Theory-Based Thermodynamic Model for Stable Scale Formation in Lead-Water Systems

Density Functional Theory-Based Thermodynamic Model for Stable Scale Formation in Lead-Water Systems

Pb Mineral Precipitation in Solutions of Sulfate, Carbonate and Phosphate: Measured and Modeled Pb Solubility and Pb2+ Activity

Assessing the capacity of biochar to stabilize copper and lead in contaminated sediments using chemical and extraction methods

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