In situ immobilization of cadmium in soil by stabilized biochar-supported iron phosphate nanoparticles

The potential for nanoscale phosphate amendments to remediate heavy metal contamination has been widely investigated, but the strong tendency of nanoparticles to form aggregates limits the application of this technique in soil. This study synthesized a composite of biochar-supported iron phosphate nanoparticle (BC@Fe₃(PO₄)₂) stabilized by a sodium carboxymethyl cellulose to improve the stability and mobility of the amendment in soil. The sedimentation test and column test demonstrated that BC@Fe₃(PO₄)₂ exhibited better stability and mobility than iron phosphate nanoparticles. After 28 days of simulated in situ remediation, the immobilization efficiency of Cd was 60.2 %, and the physiological-based extraction test bioaccessibility was reduced by 53.9 %. The results of sequential extraction procedures indicated that the transformation from exchangeable (EX) Cd to organic matter (OM) and residue (RS) was responsible for the decrease in Cd leachability in soil. Accordingly, the pot test indicated that Cd uptake by cabbage mustard was suppressed by 86.8 %. Compared to tests using iron phosphate nanoparticles, the addition of BC@Fe₃(PO₄)₂ to soil could reduce the Fe uptake of cabbage mustard. Overall, this study revealed that BC@Fe₃(PO₄)₂ could provide effective in situ remediation of Cd in soil.     

Lead phosphate formation in soils

Pyromorphite (Pb5(PO4)3Cl) is one of the most thermodynamically stable lead minerals under the geochemical conditions prevailing in the surface environment. It is therefore expected to form in soils contaminated with Pb if sufficient phosphorus is available. Pyromorphite has previously been identified in mine-waste and industrially contaminated soils but has not previously been identified in urban soils. This paper reports on the presence of a Pb phosphate in urban and roadside soils. This phase has formed in the soil as a weathering product of Pb-bearing grains. Quantitative EDX analyses indicated that the Pb phosphate phase is pyromorphite with Ca frequently substituting for Pb between 21-31 atomic percent. However, positive identification of this phase by XRD was hindered by the deviation from pure end-member and possibly also by the poorly crystalline nature of the phase. Pyromorphite accounted for less than 2% of the total Pb in these soils. However, phosphate amendments to the soil could induce further formation of pyromorphite. As pyromorphite is a highly insoluble mineral, this may be effective in reducing the bioavailability of Pb in urban soils.     

Dissolution of mimetite Pb5(AsO4)3Cl in low-molecular-weight organic acids and EDTA

Due to its relatively low solubility, mimetite Pb₅(AsO₄)₃Cl may control Pb and As(V) solution levels at a low value in contaminated soils. The time-dependent dissolution of mimetite by low-molecular-weight organic acids (LMWOAs) such as acetic, lactic, citric, and ethylene diamine tetra-acetic acid (EDTA) was determined. At pH 3.5, the presence of citric acid or EDTA significantly increases the solubility of mimetite while acetic or lactic acids show little effect. The effect of all organic anions on the dissolution of mimetite increased with the increase in solution pH. The rate of mimetite dissolution depended on the kind and concentration of organic solvents in the sequence r_EDTA > r_lactate > r_acetate > r_citrate. Soluble Pb and As(V) released in LMWOAs and EDTA were higher than the WHO guideline value for these elements in drinking water (10 μg As(V) L⁻¹, 10 μg Pb L⁻¹). This suggests that soil organic acids in rhizosphere can potentially liberate Pb and As(V) from mimetite in contaminated soils.     

The impact of EDTA on lead distribution and speciation in the accumulator Sedum alfredii by synchrotron X-ray investigation

The in vivo localization and speciation of lead (Pb) in tissues of the accumulator Sedum alfredii grown in EDTA-Pb and Pb(NO₃)₂ was studied by synchrotron X-ray investigation. The presence of EDTA-Pb in solution resulted in a significant reduction of Pb accumulation in S. alfredii. Lead was preferentially localized in the vascular bundles regardless of treatments but the intensities of Pb were lower in the plants treated with EDTA. Lead was predominantly presented as a Pb-cell wall complex in the plants regardless of its supply form. However, a relatively high proportion of Pb was observed as Pb-EDTA complex when the plant was treated with EDTA-Pb, but as a mixture of Pb₃(PO₄)₂, Pb-malic, and Pb-GSH when cultured with ionic Pb. These results suggest that EDTA does not increase the internal mobility of Pb, although the soluble Pb-EDTA complex could be transported and accumulated within the plants of S. alfredii.     

Characterization of endophytic Rahnella sp. JN6 from Polygonum pubescens and its potential in promoting growth and Cd,Pb, Zn uptake by Brassica napus

Microbe-assisted phytoremediation has been considered as a promising measure for the remediation of heavy metal-polluted soils. In this study, a metal-tolerance and plant growth-promoting endophytic bacterium JN6 was firstly isolated from roots of Mn-hyperaccumulator Polygonum pubescens grown in metal-contaminated soil and identified as Rahnella sp. based on 16S rDNA gene sequence analysis. Strain JN6 showed very high Cd, Pb and Zn tolerance and effectively solubilized CdCO₃, PbCO₃ and Zn₃(PO₄)₂ in culture solution. The isolate produced plant growth-promoting substances such as indole-3-acetic acid, siderophore, 1-aminocyclopropane-1-carboxylic deaminase, and also solubilized inorganic phosphate. Based upon its ability in metal tolerance and solubilization, the isolate JN6 was further studied for its effects on the growth and accumulation of Cd, Pb and Zn in Brassica napus (rape) by pot experiments. Rape plants inoculated with the isolate JN6 had significantly higher dry weights, concentrations and uptake of Cd, Pb and Zn in both above-ground and root tissues than those without inoculation grown in soils amended with Cd (25 mg kg^?1), Pb (200 mg kg^?1) or Zn (200 mg kg^?1). The isolate also showed a high level of colonization in tissue interior of rapes. The present results demonstrated that Rahnella sp. JN6 is a valuable microorganism, which can cost-effectively improve the efficiency of phytoremediation in soils contaminated by Cd, Pb and Zn.     

Products and stability of phosphate reactions with lead under freeze-thaw cycling in simple systems

Orthophosphate fixation of metal contaminated soils in environments that undergo freeze-thaw cycles is understudied. Freeze-thaw cycling potentially influences the reaction rate, mineral chemical stability and physical breakdown of particles during fixation. This study determines what products form when phosphate (triple superphosphate [Ca(H₂PO₄)₂] or sodium phosphate [Na₃PO₄]) reacts with lead (PbSO₄ or PbCl₂) in simple chemical systems in vitro, and assesses potential changes in formation during freeze-thaw cycles. Systems were subjected to multiple freeze-thaw cycles from +10 °C to −20 °C and then analysed by X-ray diffractometry. Pyromorphite formed in all systems and was stable over multiple freeze-thaw cycles. Low temperature lead orthophosphate reaction efficiency varied according to both phosphate and lead source; the most time-efficient pyromorphite formation was observed when PbSO₄ and Na₃PO₄ were present together. These findings have implications for the manner in which metal contaminated materials in freezing ground can be treated with phosphate.     

Characterization of Fugitive Material within a Primary Lead Smelter

ABSTRACT

The primary production of Pb via the sinter plant-blast furnace method resulted in a large number of Pb and other phases, reflecting the complex reactions occurring within each of the processes. Optical microscopy and X-ray diffraction (XRD) techniques have been used to characterize fugitive emissions and dusts generated during sintering, smelting, Cu drossing, refining, and slag fuming at a primary Pb-Zn smelter. The results displayed a complex array of phases, with the mineralogy of the dusts and fume reflecting conditions of the particular metallurgical operation. The principal Pb species followed a transformation from PbS through PbSO₄ and PbO to Pb° (metal) from raw materials to the refinery. The fugitive emissions generated by the blast furnace were of a finer size with more complex chemistry than fugitive material from other source areas. XRD identified a mixture of PbS, ZnO, and ZnS, associated with one or more of the Cl-bearing phases Pb(OH)Cl, PbCl₂, Pb₄O₃Cl₂, Na₃Pb₂(SO₄)₃Cl, Pb₁₀(SO₄)Cl₂O₈, Pb₄SCl₆, and Pb₇S₂Cl₁₀. The presence of Cl-bearing phases in the fume has possible health implications.     

Effects and mechanisms of meta-sodium silicate amendments on lead uptake and accumulation by rice

The objectives of this research were to study the effects of Na₂SiO₃ application on the uptake, translocation, and accumulation of Pb in rice and to investigate the mechanisms of Pb immobilization by Na₂SiO₃ in paddy rice soils and rice plants. Pot experiments were conducted using a Cd-Pb-Zn-polluted soil and Oryza sativa L. ssp. indica cv. Donglian 5. L₃-edge X-ray absorption spectroscopy was used to identify Pb species in soils and roots. The results showed that the application of Na₂SiO₃ increased soil pH and available soil Si but decreased DTPA-extractable Pb in the soil. High dose of Na₂SiO₃ (12.5 g/kg) reduced the Pb level in brown rice as it inhibited Pb transfer from soil to rice grains, especially Pb transfer from the root to the stem. The Pb X-ray absorption near-edge spectroscopic analysis revealed that application of high dose of Na₂SiO₃ increased Pb-ferrihydrite and PbSiO₃ precipitates in the soil and in the root while it reduced Pb-humic acids (Pb-HAs) in the soil and Pb-pectin in the root. The decrease in Pb availability in the soil can be partly attributed to increase the precipitation of PbSiO₃ and the association of Pb²⁺ with Fe oxides in the soil. The inhibition of the root-to-stem translocation of Pb was partially due to the precipitation of PbSiO₃ on the root surfaces or inside the roots.     

Application of phosphate solubilizing bacteria in immobilization of Pb and Cd in soil

Environmental Science and Pollution Research - In the present study, heavy metal (HM)-tolerant phosphate solubilizing bacteria (PSB) were isolated and their performance during the remediation of Pb...     

Effects of phosphorus amendments and plant growth on the mobility of Pb, Cu, and Zn in a multi-metal-contaminated soil

Purpose

Phosphorus amendments have been widely and successfully used in immobilization of one single metal (e.g., Pb) in contaminated soils. However, application of P amendments in the immobilization of multiple metals and particularly investigations about the effects of planting on the stability of the initially P-induced immobilized metals in the contaminated soils are far limited.

Methods

This study was conducted to determine the effects of phosphate rock tailing (PR), triple superphosphate fertilizer (TSP), and their combination (P+T) on mobility of Pb, Cu, and Zn in a multimetal-contaminated soil. Chinese cabbage (Brassica rapa subsp. chinensis) (metal-sensitive) and Chinese kale (Brassica alboglabra Bailey) (metal-resistant) were introduced to examine the effects of planting on leaching of Pb, Cu, and Zn in the P-amended soils.

Results

All three P treatments greatly reduced CaCl₂-extractable Pb and Zn by 55.2?C73.1% and 14.3?C33.6%, respectively. The PR treatment decreased CaCl₂-extractable Cu by 27.8%, while the TSP and P+T treatments increased it by 47.2% and 44.4%, respectively. All three P treatments were effective in reducing simulated rainwater leachable Pb, with dissolved and total leachable Pb decrease by 15.6?C81.9% and 16.3?C64.5%, respectively. The PR treatment reduced the total leachable Zn by 16.8%, while TSP and P+T treatments increased Zn leaching by 92.7% and 78.9%, respectively. However, total Cu leaching were elevated by 17.8?C178% in all P treatments. Planting promoted the leaching of Pb and Cu by 98.7?C127% and 23.5?C170%, respectively, especially in the colloid fraction, whereas the leachable Zn was reduced by 95.3?C96.5% due to planting. The P treatments reduced the uptake of Pb, Cu, and Zn in the aboveground parts of Chinese cabbage by up to 65.1%, 34.3%, and 9.59%, respectively. Though P treatments were effective in reducing Zn concentrations in the aboveground parts of the metal-resistant Chinese kale by 22.4?C28.9%, they had little effect on Pb and Cu uptake.

Conclusions

The results indicated that all P treatments were effective in immobilizing Pb. The effect on the immobilization of Cu and Zn varied with the different P treatments and evaluation methods. Metal-sensitive plants are more responsive to the P treatments than metal-resistant plants. Planting affects leaching of metals in the P-amended soils, specially leaching of colloid fraction. The conventional assessment on leaching risks of heavy metals by determining dissolved metals (filtered through 0.45-??m pore size membrane) in leachates could be underestimated since colloid fraction may also contribute to the leaching.     

Biochar- and phosphate-induced immobilization of heavy metals in contaminated soil and water: implication on simultaneous remediation of contaminated soil and groundwater

Long-term wastewater irrigation or solid waste disposal has resulted in the heavy metal contamination in both soil and groundwater. It is often separately implemented for remediation of contaminated soil or groundwater at a specific site. The main objective of this study was to demonstrate the hypothesis of simultaneous remediation of both heavy metal contaminated soil and groundwater by integrating the chemical immobilization and pump-and-treat methods. To accomplish the objective, three experiments were conducted, i.e., an incubation experiment was first conducted to determine how dairy-manure-derived biochar and phosphate rock tailing induced immobilization of Cd in the Cd-contaminated soils; second, a batch sorption experiment was carried out to determine whether the pre-amended contaminated soil still had the ability to retain Pb, Zn and Cd from aqueous solution. BCR sequential extraction as well as XRD and SEM analysis were conducted to explore the possible retention mechanism; and last, a laboratory-scale model test was undertaken by leaching the Pb, Zn, and Cd contaminated groundwater through the pre-amended contaminated soils to demonstrate how the heavy metals in both contaminated soil and groundwater were simultaneously retained and immobilized. The incubation experiment showed that the phosphate biochar were effective in immobilizing soil Cd with Cd concentration in TCLP (toxicity characteristics leaching procedure) extract reduced by 19.6 % and 13.7 %, respectively. The batch sorption experiment revealed that the pre-amended soil still had ability to retain Pb, Zn, and Cd from aqueous solution. The phosphate-induced metal retention was mainly due to the metal–phosphate precipitation, while both sorption and precipitation were responsible for the metal stabilization in the biochar amendment. The laboratory-scale test demonstrated that the soil amended with phosphate removed groundwater Pb, Zn, and Cd by 96.4 %, 44.6 %, and 49.2 %, respectively, and the soil amended with biochar removed groundwater Pb, Zn, and Cd by 97.4 %, 53.4 %, and 54.5 %, respectively. Meanwhile, the metals from both groundwater and soil itself were immobilized with the amendments, with the leachability of the three metals in the CaCl₂ and TCLP extracts being reduced by up to 98.1 % and 62.7 %, respectively. Our results indicate that the integrated chemical immobilization and pump-and-treat method developed in this study provides a novel way for simultaneous remediation of both metal-contaminated soil and groundwater.     

Influence of extracellular polymeric substances (EPS) on Cd adsorption by bacteria

The role of extracellular polymeric substances (EPS) in Cd adsorption by Bacillus subtilis and Pseudomonas putida was investigated using a combination of batch adsorption experiments, potentiometric titrations, Fourier transform infrared spectroscopy (FTIR). An increased adsorption capacity of Cd was observed for untreated bacteria relative to that for EPS-free bacteria. Surface complexation modeling of titration data showed the similar pK_a values of functional groups (carboxyl, phosphate and hydroxyl) between untreated and EPS-free bacteria. However, site concentrations on the untreated bacteria were found to be higher than those on the EPS-free bacteria. FTIR spectra also showed that no significant difference in peak positions was observed between untreated and EPS-free bacteria and carboxyl and phosphate groups were responsible for Cd adsorption on bacterial cells. The information obtained in this study is of fundamental significance for understanding the interaction mechanisms between heavy metals and biofilms in natural environments.     

钝化剂在烟草植物修复铅镉污染土壤中的作用简

重金属钝化剂可以改变土壤中重金属的形态,降低其在土壤中的有效浓度、植物毒性及生物有效性,影响污染土壤中植物的生长及其对重金属的吸收。在温室盆栽条件下研究了施加羟基磷灰石（HA）、纳米羟基磷灰石（nHA）、纳米零价铁（nFe⁰）和纳米TiO₂（nTiO₂）对烟草植物修复铅镉污染土壤的作用。结果表明,HA降低土壤中Pb、Cd的有效性、促进烟草生长、增加了烟草叶、茎、根中Cd的吸收量和根系中Pb的吸收量,有利于Pb、Cd的钝化和植物修复。nHA也可以降低土壤中Pb、Cd的有效性,增加了烟草叶中Cd的吸收量,有利于Pb、Cd的钝化和Cd的植物提取。nFe⁰和nTiO₂对于土壤Pb和Cd的钝化作用和植物修复均没有显著影响。综合来看,HA最适合应用于烟草植物修复铅镉污染土壤。     

Influence of bacteria on Pb and Zn speciation, mobility and bioavailability in soil: A laboratory study

A soil column experiment was carried out to investigate the effects of inoculation of bacteria on metal bioavailability, mobility and potential leachability through single chemical extraction, consequential extraction and in situ soil solution extraction technologies. Results showed that bacteria inoculated, including Azotobacter chroococcum, Bacillus megaterium and Bacillus mucilaginosus, may pose both positive and negative impacts on bioavailability and mobility of heavy metals in soil, depending on the chemical nature of the metals. The activities of bacteria led to an increase of water dissolved organic carbon (DOC) concentration and a decrease of pH value, which enhanced metal mobility and bioavailability (e.g. an increase of water-soluble and HOAc-soluble Zn). On the other hand, bacteria could immobilize metals (e.g. a great reduction of water-soluble Pb) due to the adsorption by bacterial cell walls and possible sedimentation reactions with phosphate or other anions produced through bacterial metabolism.     

复合纳米材料对土壤重金属离子吸持固化的模拟研究

土壤中过量重金属离子可通过食物链和地表水系统危害人群健康。通过土柱淋溶模拟实验,研究了SiO2-Al2O3-Fe2O3等复合纳米材料对土壤溶液中Cu2+、Cd2+、Pb2+、Zn2+和Ni2+的吸持与固化特征。分别向重金属含量4倍于土壤二级标准(GB15618-1995)的土壤中添加0%、4%、6%和10%的复合纳米材料,分析不同深度土壤渗滤液以及土柱上栽培植物不同部位中重金属的含量。结果表明,碱性壤质土壤中重金属向下的迁移量很少;在含4%复合纳米材料土柱中,其吸持固化土壤溶液中63%的Cu、79%的Cd、68%的Pb、89%的Zn和76%的Ni;在含6%复合纳米材料土柱中,其吸持固化土壤溶液中82%的Cu、92%的Cd、76%的Pb、91%的Zn和88%的Ni;再增加土柱中复合纳米材料的含量,其吸持固化效果并不再显著增加。     

Evaluation of the effectiveness of phosphate treatment for the remediation of mine waste soils contaminated with Cd, Cu, Pb, and Zn

The effectiveness of phosphate treatment for Cd, Cu, Pb, and Zn immobilization in mine waste soils was examined using batch conditions. Application of synthetic hydroxyapatite (HA) and natural phosphate rock (FAP) effectively reduced the heavy metal water solubility generally by about 84-99%. The results showed that HA was slightly superior to FAP for immobilizing heavy metals. The possible mechanisms for heavy metal immobilization in the soil involve both surface complexation of the metal ions on the phosphate grains and partial dissolution of the phosphate amendments and precipitation of heavy metal-containing phosphates. HA and FAP could significantly reduce Cd, Cu, Pb, and Zn availability in terms of water solubility in contaminated soils while minimizing soil acidification and potential risk of eutrophication associated with the application of highly soluble phosphate sources.     

Evaluation of three common alkaline agents for immobilization of multi-metals in a field-contaminated acidic soil

We investigated three common alkaline agents (NaOH, CaO, and Mg(OH)₂) for immobilization of four heavy metals (Pb, Zn, Cu, and Cd) in a field-contaminated soil and elucidated the underpinning principles. NaOH caused the highest pH spike in the soil, while CaO and Mg(OH)₂ served as a longer-lasting source of OH^-. Amending the soil with CaO or Mg(OH)₂ at ≥0.1 mol as OH^- (kg·soil)^?1 for 24 h was able to immobilize all four metals, while NaOH failed. NaOH leached up to 3 times more organic carbon than CaO and Mg(OH)₂, resulting in elevated leachability of the metals. Column elution tests showed that amendments by CaO and Mg(OH)₂ lowered the leachable Pb²⁺, Zn²⁺, Cu²⁺, and Cd²⁺ by 52–54%, 71–75%, 69–73%, and 68%, respectively, after 1440 pore volumes of elution. Sequential extraction revealed that the soil amendments converted the exchangeable fraction of the metals to the much less available forms. XRD and FTIR analyses indicated that formation of metal oxide precipitates and complexation with soil organic matter were responsible for the metals immobilization. Taken together the chemical cost, technical effectiveness, and environmental impact, CaO is the most suitable alkaline agent for remediation of soil contaminated with heavy metals.

     

Phosphate-induced metal immobilization in a contaminated site

To assess the efficiency of P-induced metal immobilization in soils, a pilot-scale field experiment was conducted at a metal contaminated site located in central Florida. Phosphate was applied at a P/Pb molar ratio of 4.0 with three treatments: 100% of P from H3PO4, 50% of P from H3PO4+ 50% of P from Ca(H2PO4)2, and 50% of P from H3PO4+5% phosphate rock in the soil. Approximately 1 year after P application, soil and plant samples were collected to determine mobility and bioavailability of selected metals (Pb, Zn, and Cu) using sequential extraction procedure and mineralogical characterization using X-ray diffraction (XRD) and scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis. Phosphorus distribution and soil pH effects were also evaluated. Phosphate was more effective in transforming soil Pb (to 53%) from the non-residual to the residual phase than soil Zn (to 15%) and soil Cu (to 13%). This was because Pb was immobilized by P via formation of an insoluble pyromorphite-like mineral in the surface and subsurface of the soil, whereas no phosphate mineral Zn or Cu was identified. While P amendment enhanced metal uptake in the roots of St. Augustine grass (Stenotaphrum secundatum), it significantly reduced metal translocation from root to shoot, especially Pb via formation of a pyromorphite-like mineral on the membrane surface of the root. A mixture of H3PO4 and phosphate rock was effective in metal immobilization, with less soil pH reduction and less soluble P. Although H3PO4 was effective in immobilizing Pb, its use should be limited to minimize soil pH reduction and potential eutrophication risk.     

Electrochemical EDTA recycling with sacrificial Al anode for remediation of Pb contaminated soil

Recycling chelant is a precondition for cost-effective EDTA-based soil remediation. Extraction with EDTA removed 67.5% of Pb from the contaminated soil and yielded washing solution with 1535 mg L⁻¹ Pb and 33.4 mM EDTA. Electrochemical treatment of the washing solution using Al anode, current density 96 mA cm⁻² and pH 10 removed 90% of Pb from the solution (by electrodeposition on the stainless steel cathode) while the concentration of EDTA in the treated solution remained the same. The obtained data indicate that the Pb in the EDTA complex was replaced by electro-corroded Al after electro-reduction of the EDTA and subsequently removed from the solution. Additional soil extraction with the treated washing solution resulted in total removal of 87% of Pb from the contaminated soil. The recycled EDTA retained the Pb extraction potential through several steps of soil extraction and washing solution treatment, although part of the EDTA was lost by soil absorption.     

Effect of weathering product assemblages on Pb bioaccessibility in mine waste: implications for risk management

General assessments of orebody types and associated mine wastes with regard to their environmental signature and human health hazards are needed to help in managing present and historical mine waste facilities. Bioaccessibility tests and mineralogical analysis were carried out on mine waste from a systematic sampling of mine sites from the Central Wales orefield, UK. The bioaccessible Pb widely ranged from 270 to 20,300 mg/kg (mean 7,250 mg/kg, median 4,890 mg/kg), and the bioaccessible fraction from 4.53 to >100 % (mean 33.2 %, median 32.2 %), with significant (p?=?0.001) differences among the mine sites. This implies sensitivity of bioaccessibility to site-specific conditions and suggests caution in the use of models to assess human health impacts generalised on the basis of the mineral deposit type. Mineralogical similarities of the oxidation products of primary galena provided a better control over the observed Pb bioaccessibility range. The higher Pb bioaccessibility (%) was related to samples containing cerussite, irrespective of the presence of other Pb minerals in the mineral assemblage; lower Pb bioaccessibility resulted where anglesite was the main Pb mineral phase and cerussite was absent. A solubility diagram for the various Pb minerals in the waste was derived using PHREEQC model, and the experimental Pb concentrations, measured in the simulated gastric solution, were compared with the equilibrium modelling results. For samples containing cerussite, the model well predicted the soluble Pb concentrations measured in the gastric solution, indicative of the carbonate mineral phase control on the Pb in solution for these samples and little kinetic control on the dissolution of cerussite. On the contrary, most mine waste samples containing dominant anglesite and or plumbojarosite (no cerussite) had lower solution Pb values, falling at or below the anglesite and plumbojarosite solubility equilibrium concentrations, implying kinetic or textural factors hindering the dissolution.