Precipitation Of Pb Research Articles

Efficient removal and recovery of lead from high arsenic antimony oxide powder

The existence of Pb in crude antimony oxide powder(CAOP) hinders the further smelting and recovery of Sb and leads to some environmental problems. Therefore, the selective removal of Pb from CAOP is important for the production of high-purity antimony products. In this work, Pb in CAOP is removed by HNO3 leaching, achieving purification of CAOP. Then H2SO4 is used to recover Pb from the HNO3 leaching solution. The Pb leaching efficiency reaches 98.9 %, resulting in a decrease in the Pb content from 4.56 % to 0.20 % in CAOP. The Sb leaching efficiency is controlled at around 5.0 %. These confirm HNO3 has good selectivity. The HNO3 disrupts the molecular structure of the raw materials during the leaching, resulting in the conversion of Sb2O3 and As2O3 into insoluble AsSbO4. By adding H2SO4 to the leaching solution, the Pb precipitation efficiency reaches 93.6 %. After Pb removal, the leaching solution can be re-used for the leaching of Pb, while the residue can be directly returned to the pyrometallurgical system. The reaction mechanism and a novel approach for removing Pb from CAOP are proposed, which have the advantages of high selectivity, effective Pb separation, and recoverable HNO3.

β-tricalcium phosphate enhanced biomineralization of Cd2+ and Pb2+ by Sporosarcina ureilytica HJ1 and Sporosarcina pasteurii HJ2

Microbiologically induced CaCO3 precipitation (MICP) has been proposed as a potential bioremediation method to immobilize contaminating metals. In this study, carbonate mineralizing bacteria HJ1 and HJ2, isolated from heavy metal contaminated soil, was employed for Cd2+ and Pb2+ immobilization with or without β-tricalcium phosphate addition. Compared with the only treatments amended with strains, the combined application of β-tricalcium phosphate and HJ1 improved the immobilization rates of Cd and Pb by 1.49 and 1.70 times at 24 h, and the combined application of β-tricalcium phosphate and HJ2 increased the immobilization rates of Cd and Pb by 1.25 and 1.79 times. The characterization of biomineralization products revealed that Cd2+ and Pb2+ primarily immobilized from the liquid phase as CdCO3 and PbCO3, and the addition of β-tricalcium phosphate facilitated the formation of Ca4.03Cd0.97(PO4)3(OH) and Pb3(PO4)2. Also, the calcium source was related to the speciation of carbonate precipitation and improved the Cd and Pb remediation efficiency. This research demonstrated the feasibility and effectiveness of MICP combined with β-tricalcium phosphate in immobilization of Cd and Pb, which will provide a fundamental basis for future applications of MICP to mitigate soil heavy metal pollutions.

Atomic Imaging of the Pb Precipitation in Lead-Halide Perovskites.

The lead iodide (PbI2) in lead-halide perovskite (LHP) is both a positive additive for material properties and a site for the formation of device defects. Therefore, atomic-level detection of PbI2 and its derivedPbstructures are crucial for understanding the performance and stability of the LHP material. In this work, the atomic imaging of the LHP, PbI2, and Pb lattices is achieved using low-dose integrated differential phase contrast (iDPC) scanning transmission electron microscopy (STEM). Combining it with the traditional high-angle annular dark field (HAADF)-STEM, the Pb precipitation in different LHPs (CsPbI3, CsPbBr3, and FAPbI3) and under different conditions (light, air, and heat) can be investigated in real space. Then, the features of Pb precipitation (positions and sizes) are visually revealed under different conditions and the stabilities of different LHPs. Meanwhile, the pathway of Pb precipitation is directly imaged and confirmed by the iDPC-STEM during an in situ heating process, supporting the detailed mechanism of Pb precipitation. These results provide the visual evidence for analyzing atomic Pb precipitation in LHPs, which helps better understand the structure-property relation induced by Pb impurity.

Impact of orthophosphate on the solubility and properties of lead orthophosphate nanoparticles.

Orthophosphate (PO4) is a commonly used corrosion control treatment to reduce lead (Pb) concentrations in drinking water. PO4 reduces Pb concentrations by forming relatively insoluble lead phosphate (Pb-PO4) minerals. In some cases, however, Pb-PO4 minerals have been observed to form nanoparticles, and if suspended in water, these nanoparticles can be mobile and reach consumer taps. Although recent research on Pb-PO4 particles has been performed, there remains a need to improve our understanding of the nature of Pb-PO4 nanoparticles. For that reason, Pb precipitation experiments were conducted to generate Pb-PO4 nanoparticles in bench scale studies for analysis. The study objective was to observe how pH, dissolved inorganic carbon (DIC), and PO4 impacted the properties of Pb-PO4 particles. Specifically, particle size, surface charge, mineralogy, and solubility were analysed. Hydrocerussite was precipitated when no PO4 was present, hydroxypyromorphite (Pb5(PO4)3OH) nanoparticles (<100 nm diameter) were precipitated when excess PO4 relative to Pb necessary to completely precipitate the mineral was present, and a mixture of the two minerals was precipitated when an insufficient amount of PO4 was present. Hydroxypyromorphite particles were less soluble than hydrocerussite by up to two orders of magnitude. The estimated K sp,OH of 10-66.87 in this work closely aligned with previous K sp,OH estimates that ranged from 10-66.77 to 10-62.79. Hydroxypyromorphite particles would not settle in water which was likely due to their small size and high negative charge. The mobility and size of these particles indicates that there are potential implications for such particulate Pb to remain suspended in water and thus be present in the tap water.

Different responses of Sinorhizobium sp. upon Pb and Zn exposure: Mineralization versus complexation

Lead (Pb) and zinc (Zn) have been discharged into environment and may negatively impact ecological security. Rhizobia has gained attention due to their involvement in the restoration of metal polluted soils. However, little is known about the responses of rhizobia under Pb and Zn stress, especially the roles played by extracellular polymeric substances (EPS) in the resistance of these two metals. Here, Sinorhizobium sp. C10 was isolated from soil around a mining area and was exposed to a series of Pb/Zn treatments. The cell morphology and surface mineral crystals, EPS content and fluorescent substances were determined. In addition, the extracellular polysaccharides and proteins were characterized by attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS). The results showed that Zn stress induced the synthesis of EPS by C10 cells. Functional groups of polysaccharides (CO) and proteins (C–O/C–N) were involved in complexation with Zn. In contrast, C10 resisted Pb stress by forming lead phosphate (Pb3(PO4)2) on the cell surface. Galactose (Gal) and tyrosine played key roles in resistance to the Zn toxicity, whereas glucosamine (N-Glc) was converted to glucose in large amounts during extracellular Pb precipitation. Together, this study demonstrated that C10 possessed different strategies to detoxify the two metals, and could provide basis for bioremediation of Pb and Zn polluted sites.

Dissolved Lead Removal from Soil-washing Process Using Electrocoagulation

Soil-washing using ethylenediamine-tetraacetate (EDTA) is an effective method for the remediation of lead (Pb) contaminated land. In practice, it is necessary to manage wastewater from this remediation process. The Electrocoagulation technique is an alternative method to remove Pb from soil-washing wastewater. The primary purpose of this study is to determine optimum conditions for the electrocoagulation process of Pb removal from soil-washing wastewater. This study used an electrochemical batch reactor with a monopolar parallel circuit. Based on the initial research, the Pb concentration in soil-washing wastewater was 3600 mg/L. Several parameters were used to obtain the optimal condition for Pb removal: operational voltage, type of electrode used, and time. The result showed that the optimum condition for Pb removal is on the operational voltage of 7 volt (V), using aluminium electrode pair, at an operating time of 80 min within the Pb removal efficiency of 96%. Furthermore, the kinetics study showed the highest Pb precipitation was 0.041/min following the first-order model. Using these optimal parameters, the Pb precipitation and removal efficiencies for real soil-washing wastewater were 0.0416/min and 96.7%, respectively. The electrocoagulation method is efficient for simultaneously removing lead from polluted effluents.

Effect of Annealing Process on Anode Discharge Performance of Aluminum-Air Batteries

This paper investigates the effect of annealing process on the discharge performance of aluminum air battery anode, the results show that. The annealing treatment after rolling can make the grain of aluminum anode be refined, and the surface of aluminum anode with lower morphology has Bi and Pb precipitation, resulting in pitting corrosion. With the increase of morphology, the element distribution is uniform, and the precipitated phase is dissolved in the aluminum matrix, and the corrosion performance is improved. At the same time, the fine grain reduces the internal potential difference of aluminum anode and improves the corrosion resistance of the anode. The microstructure of aluminum anode with large morphology variable becomes more uniform after annealing, which improves the corrosion resistance of aluminum anode. Compared with the aluminum anode with low morphology, the energy density and specific capacity of the anode with high morphology were increased by 584.35 Wh·kg−1 and 579.61 mAh·g−1, respectively, and the anode efficiency was also increased by 19.45%. The anode efficiency of the high-variant sample was increased by up to 10.74% after annealing. The fine-crystalline aluminum anode exhibited higher discharge voltage and electrochemical performance than the coarse-crystalline aluminum anode at constant current density.

Bioinspired “cage traps” for closed-loop lead management of perovskite solar cells under real-world contamination assessment

Despite the remarkable progress made in perovskite solar cells, great concerns regarding potential Pb contamination risk and environmental vulnerability risks associated with perovskite solar cells pose a significant obstacle to their real-world commercialization. In this study, we took inspiration from the ensnaring prey behavior of spiders and chemical components in spider web to strategically implant a multifunctional mesoporous amino-grafted-carbon net into perovskite solar cells, creating a biomimetic cage traps that could effectively mitigate Pb leakage and shield the external invasion under extreme weather conditions. The synergistic Pb capturing mechanism in terms of chemical chelation and physical adsorption is in-depth explored. Additionally, the Pb contamination assessment of end-of-life perovskite solar cells in the real-world ecosystem, including Yellow River water and soil, is proposed. The sustainable closed-loop Pb management process is also successfully established involving four critical steps: Pb precipitation, Pb adsorption, Pb desorption, and Pb recycling. Our findings provide inspiring insights for promoting green and sustainable industrialization of perovskite solar cells.

Effects of capping on microbial populations and contaminant immobilization in an old unlined landfill.

This research aimed at evaluating the effects of capping on the mitigation of impacts generated by a closed unlined landfill in São Carlos, SP, Brazil. Physicochemical and microbiological analyses (16S rRNA sequencing) of buried solid waste samples were performed, in capped and uncapped areas. Even though leachate pockets could still be encountered in capped areas, the capping construction reduced oxygen availability and created more reducing conditions, propitiating the development of sulfate-reducing bacteria and possibly contributing to the precipitation of the metals Pb, Cd, Ni, Co, As, and Zn as metal sulfides, causing their immobilization. The microbial populations adapted to the anaerobic conditions created under capped zones belonged to the phyla Firmicutes, Chloroflexi, and Euryarchaeota and the genera Methanosaeta, Hydrogenispora, Smithella, and Gelria. Differently, the phyla Acidobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria were more abundant in samples from the uncapped zones, in which the abundance of different genera varied homogeneously. Methanogenic activity was not impaired by the intervention measure, as assessed by the specific methanogenic activity (SMA). Capping of old unlined landfills brings benefits to the immobilization of metals and does not impair microbial degradation, being effective for the mitigation of impacts on soils and water resources.

Application of ferromanganese functionalized biochar simultaneously reduces Cd and Pb uptake of wheat in contaminated alkaline soils

The reduction of Cd and Pb accumulation in wheat grains grown on Cd and Pb contaminated alkaline soils is a pressing issue that needs to be solved. In this study, ferromanganese functionalized biochar (FM-BC) was used to remediate Cd and Pb contaminated alkaline soils and mitigate Cd and Pb accumulation in wheat grains. The immobilization capacity and mechanism of FM-BC were investigated by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) characterization and chemical analysis. Fe and Mn loaded on FM-BC improved the removal efficiencies of DTPA-Cd and DTPA-Pb in soil with DTPA-Cd removal of 22.99%− 52.04% (JM22) and 25.54%− 53.32 (AK58) and DTPA-Pb removal of 11.39%− 22.36% (JM22) and 5.38%− 13.00% (AK58). The FT-IR and XRD results indicated that the complexation and precipitation of Cd and Pb with the Fe-Mn oxides and the oxygen-containing functional groups on biochar surface stabilized the Cd and Pb in soil for the observation of Cd2Mn3O8, PbHPO4, CdCO3, and PbO2 on FM-BC isolated from contaminated soils. FM-BC with excellent adsorption capacity reduced the available Cd and Pb in the soil, therefore, thereby inhibiting the Cd and Pb accumulation in wheat. In the 3% FM-BC treatment, Cd and Pb contents in wheat grains were lower than 0.10 mg/kg and 0.20 mg/kg, respectively, reaching the national safety standards. And FM-BC increased the Fe, Mn, Na and Zn contents in wheat grains, and improved the growth and yield of wheat. These findings suggest that FM-BC can be considered a prospective and effective material for remediation of alkaline soils contaminated with Cd and Pb.

Classification of Mine Drainages in Japan Based on Water Quality: Consideration for Constructed Wetland Treatments

As a passive technology, constructed wetlands (CWs) are promising candidates for mine-drainage treatment. However, the design and operation of CWs have not been fully established because the chemical compositions of mine drainage are diverse. In this study data sets of 100 mine drainages in Japan were classified using multivariate analysis based on water quality. Mine drainage was classified into eight types based on the ratio of the concentrations of Cd, Pb, As, Cu, Zn, Fe, and Mn to the effluent standard: (I) neutral and low metal concentration, (II) weakly acidic and low metal concentration, (III) weakly acidic and high Zn concentration, (IV) weakly acidic and high Mn and Zn concentrations, (V) acidic and high As concentration, (VI) acidic and high Fe concentration, (VII) acidic and extremely high Fe concentration, and (VIII) acidic and high Zn concentration. Mechanisms for removing metals in CWs were discussed based on this classification. Metal hydroxides of Cu, Pb, Zn, and Cd can precipitate with an increasing pH. Under oxidative conditions, dissolved Fe and Mn are oxidized to metal oxides. Under reductive conditions, Pb, Zn, Cd, and Cu precipitate as metal sulfides. This classification of mine drainage will be helpful in the systematic design and operation of CWs.

Phosphate‐Assisted Remediation of Pb(II) From Jarosite

AbstractJarosite is an essential solid industrial waste material which is generated during the hydrometallurgical processing of zinc in smelters. Besides zinc and iron, Jarosite also contains toxic heavy metals like Pb, Cd, Al, Cr, Cu etc. due to which it is environmentally hazardous. Due to the presence of heavy metals, the useful Zn, Fe components cannot be utilized safely. Therefore, it is necessary to remove Pb(II), a major toxic element, to make it useful. In this report, a green process for immobilization of Pb(II) using phosphate materials (physiochemical adsorption) is discussed. Jarosite was used as a precursor for synthesis of the Zn−Fe binary nano‐composite. Mitigation of Pb(II) by this process was assessed by the batch experiments, which showed significant reduction in leaching of Pb(II). The mechanism of Pb(II) immobilization involve the dissolution of phosphate materials (KH2PO4, NH4H2PO4 and CaH2PO4) to a lower pH≤3 followed by precipitation of Pb(II) in the form of pyromorphite complex. The results indicated that the concentration of Pb(II) was reduced by 90–95 % which was pH dependent with a high uptake (325 ppm) of lead ion in the pH range of 5.5–6.0. This physicochemical process brings new perspectives for reuse of a polluting solid industrial waste.

In Situ Electroplating of Ir@Carbon Cloth as High-Performance Selective Oxygen Evolution Reaction Catalyst for Direct Electrolytic Recovery of Lead

The hydrometallurgical technology provides an efficient and sustainable green lead recovery process from lead acid batteries. Methanesulfonic acid has been widely considered as a green solvent for lead electrolytic recovery. However, the competitive precipitation of PbO2 at anode and higher overpotential for OER limit the lead recovery efficiency. In this work, an anodic oxygen evolution reaction (OER) catalyst with a low Ir mass fraction of 7.2% is obtained by electroplating iridium on carbon cloth (CC), exhibiting a lower overpotential of 256 mV, longer lifetime of 10 h, and better stability in the 0.5 M MSA solution. When CC-Ir is used as an anodic catalyst for lead recovery in the lead methanesulfonate electrolyte, only a lesser Pb precipitation product with Pb atom mass fraction of 1.42% is found after electrolysis of 10 h, demonstrating the suppression effect of CC-Ir for a PbO2 side reaction. This work proves that the anodic catalyst plays an important role in the lead electrolytic recovery process, which can inhibit the side reaction, reduce the energy consumption, and increase recovery efficiency.

Sustainable and reagent-free cathodic precipitation for high-efficiency removal of heavy metals from soil leachate

Heavy metal pollution of soils has become a serious environmental problem. Soil washing with degradable reagents is an effective remediation technique of heavy metal pollution, and the generated leachate must be appropriately treated before discharge. However, the existing methods usually have the problems of large consumption of regents, high cost, and secondary pollution. This study proposed a reagent-free electrochemical precipitation method to remove mixed heavy metal ions extracted from soils by citrate using inert electrodes (IrO2–Ta2O5/Ti anode and graphite cathode). The results showed that the low potential of cathode led to the electrodeposition of Cd; the local alkaline environment provided by electro-mediated water reduction caused the hydrolytic precipitation of Zn and Pb; and the precipitation of Fe washed out from Fe-rich soil resulted in the coprecipitation of As on cathode surface. These combined cathodic precipitation processes decreased the concentrations of toxic heavy metals by over 99.4% after 12 h of electrolysis at 26 mA cm−2. The electrodes exhibited high stability after multiple successive cycles of reuse. The concentrations of As, Zn, Pb and Cd in the leachate decreased to below the limits of industrial wastewater discharge in each cycle, and those in soils could be reduced by 53.8%, 58.8%, 25.5%, and 70.2% at the initial concentrations of 1549, 1016, 310 and 50 mg kg−1, respectively. The heavy metal removal rate increased with increasing current density in the range of 0–52 mA cm−2. This work provides an efficient and sustainable method for the remediation of site soils polluted by mixed heavy metals.

Geochemical Characteristics of the Mineral Assemblages from the Niukutou Pb-Zn Skarn Deposit, East Kunlun Mountains, and Their Metallogenic Implications

The Niukutou Pb-Zn deposit is typical of skarn deposits in the Qimantagh metallogenic belt (QMB) in the East Kunlun Mountains. In this study, based on detailed petrographical observations, electron microprobe analyses (EMPAs), and laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses, we report the major and trace element compositions of the typical skarn mineral assemblages (garnet, pyroxene, ilvaite, epidote, and chlorite) in this deposit. Three hydrothermal mineralization stages with different mineral assemblages of the prograde metamorphic phase were determined, which were distributed from the inside to the outside of the ore-forming rock mass. Grt1+Px1 (Stage 1), Grt2+Px2 (Stage 2), and Px3 (Stage 3) were distinguished in the Niukutou deposit. Furthermore, the ilvaites in the retrograde metamorphic phase can be divided into three stages, namely Ilv1, Ilv2, and Ilv3. The ore-forming fluid in Stage 1 exhibited high ∑REE, U, and Nd concentrations and δEu, δCe, and LREE/HREE values, which were likely derived from a magmatic–hydrothermal source and formed at high temperatures, high fO2 values, and mildly acidic pH conditions, and probably experienced diffusive metasomatism in a closed system with low water/rock ratios. In Stages 2 and 3, the ore-forming exhibited lower ∑REE, U, and Nd concentrations and δEu, δCe, and LREE/HREE values, with high Mn content that had likely experienced infiltrative metasomatism in an open system with high water/rock ratios. From Ilv1 to Ilv3, the δEu and U contents decreased, whereas the Mn content increased, indicating that the oxygen fugacity of mineralization was in decline. The ore-forming fluid evolution of the Niukutou deposit can be characterized as follows: from Stage 1 to Stage 3, the hydrothermal fluid migrated from the deep plutons to the shallow skarn and marble; the environment altered from the high fO2 and temperature conditions to low fO2 and temperature values, and the pH and Mn contents increased. The fluids contained considerable metal ore-forming materials that were favorable for the enrichment and precipitation of the Fe content. In the retrograde metamorphic phase, with the decrease in oxygen fugacity (from Ilv1 to Ilv3), the temperature and oxygen fugacity of the theore-forming fluid environment decreased, ultimately becoming conducive to the dissolution and precipitation of Pb and Zn elements.

Metallography on a sickle fragment from the Drassburg/Burgenland hoard find

Abstract The Drassburg Bronze Age hoard find (approx. 25 kg) also comprises some sickles and sickle fragments. One of these sickle fragments was provided for metallographic examinations. A XRF analysis revealed 94.5 wt.% Cu, 4.31 wt.% Sn, 0.61 wt.% Pb, and 0.12 wt.% S in the alloy. It can therefore be attributed to tin bronzes. The material has a uniform dendritic microstructure. Higher concentrations of Sn, S, and Pb were measured in the interdendritic areas. This suggests a precipitation of the phases Pb and Cu2S from the residual melt. Klemm II etching also revealed the dendritic areas which exhibited different orientations. Deformations were observed in thin edge areas of the sickle fragments. They were introduced in the course of mechanical postprocessing of the bronze or during its use. The surface of the sickle exhibits a patina with a layered structure and a thickness of up to 500 μm. The Sn contents measured in the outer layers are somewhat higher than in the inner layers.

A novel chemical model for burial diagenesis and Zn–Pb sulphide precipitation within the Carboniferous Waulsortian Limestone, Ireland

Basin-scale processes such as regional fluid flow and organic maturation are commonly associated with the precipitation of Pb–Zn sulphide minerals. Despite extensive study, the origin of carbonate-hosted Pb–Zn mineralisation (Mississippi Valley-type and Irish-type) remains controversial, with deposits viewed as exceptional features derived from unusual basin conditions (e.g. regional hydrothermal fluid flux). In order to explore the links between mineralisation and broader-scale basinal processes, we have examined the relationship of base metal sulphides to regional diagenetic phases in the Waulsortian Limestone (Feltrim Formation) of the world-class Irish Midlands Zn–Pb province. Using combined sedimentology, petrography, and trace/rare earth element chemistry of regional calcite cements, we have reconstructed the basinal fluid history before, during and after sulphide mineralisation. The non-bright‐dull cathodoluminescence and trace metal composition of calcite cements indicates that the Waulsortian Limestone was subjected to three major chemical environments during progressive burial diagenesis: 1. Near-surface/shallow-burial oxic conditions; 2. subsurface euxinic conditions; and 3. subsurface ferruginous (ferrosulphidic) conditions. Zn–Pb mineralisation occurred under stage 2 euxinic conditions. We suggest that euxinic conditions were initiated when hydrocarbons entered the Waulsortian succession regionally, associated with the introduction of sour gas (H2S) accumulations. Mixing between more oxic base metal-bearing and H2S-bearing fluids produced ideal conditions for voluminous Zn–Pb sulphide precipitation. Increasing fluid anoxia then led to iron oxide dissolution with consequently increased iron sulphide precipitation, causing eventual depletion of H2S, and marked the onset of ferruginous conditions that terminated metal sulphide precipitation. Base metals were potentially derived from a range of sources that include Carboniferous seawater (and the dissolution of associated Mn/Fe oxyhydroxides), hydrocarbons, and basement-interacted basinal brines. The chemical model proposed by this study is compatible with existing data on the Irish Zn–Pb Orefield and indicates that sulphide mineralisation is linked to normal basin-scale processes such as subsidence, aquifer redox evolution and hydrocarbon generation. These results may explain many other global occurrences of carbonate-hosted Zn–Pb mineralisation and provide new insights into the chemical and redox processes that occur during burial diagenesis.

Performance of oxalate-doped hydroxyapatite as well as relative contribution of oxalate and phosphate for aqueous lead removal

An oxalate-doped hydroxyapatite (O-HAP) was hydrothermally synthesized for aqueous lead (Pb) removal based on the solubility-limiting ability of oxalate and phosphate over pH range 4–9. Free Pb2+ activities in oxalate and/or phosphate systems were controlled by oxalate to form soluble ion pairs Pb-Ox (aq) and Pb-Ox22− at pH 4–7 while in preference to persist as PbHPO4 (aq) when pH ≥ 8. Both phosphate and oxalate exhibited excellent efficiency in reducing Pb solubility, causing over 99 % of Pb precipitated from solution following oxalate < oxalate-phosphate < phosphate. The Visual MINTEQ model overestimated dissolved Pb and free Pb2+ in nearly all of the reaction systems due to the ill-defined stability constants and solubility products for Pb ion-pair formation. The addition of phosphate acting as a buffer in Pb-oxalate systems tended to lessen the spontaneous pH shifts within 24 h to equilibrate proton release from Pb precipitation and hydrolysis, indicating lower solubility products and faster kinetics of Pb-phosphate mineral formation. The TEM-EDS, FTIR and XRD identified a block-shaped Pb-oxalate mineral phase as the only precipitate at acidic pH while substituted by phosphate to form rod-shaped Pb5(PO4)3OH and Pb3(PO4)2 precipitates as pH increased. The optimum hydrothermal conditions of O-HAP were 433 K, pH 9 and P/Ox doping ratio of 0.5 for 24 h. Batch experiments revealed the endothermic process of O-HAP toward Pb with the maximum adsorption capacity reaching 2333 mg/g at a pH of 7, reaction time of 12 h, initial Pb concentration of 600 mg/L and temperature of 308 K, which were best fitted with the pseudo-second-order kinetic model and Langmuir isotherm. The synergetic mechanisms of O-HAP for Pb removal involved dissolution-precipitation, adsorption and ion exchange. This study provides an insight in developing effective remediation strategies for heavy metal contamination by interacting between low-molecular-weight organic acids and secondary mineral phases.

Microbial Precipitation of Pb(II) with Wild Strains of Paraclostridium bifermentans and Klebsiella pneumoniae Isolated from an Industrially Obtained Microbial Consortium.

The study focused on determining the microbial precipitation abilities of bacterial strains that were isolated from an industrially obtained Pb(II)-resistant microbial consortium. Previous research has demonstrated the effectiveness of the consortium on the bioprecipitation and adsorption of Pb(II) from solution. The bioremediation of Pb(II) using microbial precipitation provides an alternative option for Pb(II) removal from wastewater. Both strains, Klebsiella pneumoniae and Paraclostridium bifermentans, were successfully isolated from the consortium obtained from a battery recycling plant in South Africa. The experiments were conducted over both 30 h and 5 d, providing insight into the short- and long-term precipitation abilities of the bacteria. Various initial concentrations of Pb(II) were investigated, and it was found that P. bifermentans was able to remove 83.8% of Pb(II) from solution with an initial Pb(II) concentration of 80 mg L, while K. pneumoniae was able to remove 100% of Pb(II) with the same initial Pb(II) concentration after approximately 5 d. With the same initial Pb(II) concentration, P. bifermentans was able to remove 86.1% of Pb(II) from solution, and K. pneumoniae was able to remove 91.1% of Pb(II) from solution after 30 h. The identities of the precipitates obtained for each strain vary, with PbS and Pb being the main species precipitated by P. bifermentans and PbO with either PbCl or Pb(PO) precipitated by K. pneumoniae. Various factors were investigated in each experiment, such as metabolic activity, nitrate concentration, residual Pb(II) concentration, extracellular and intracellular Pb(II) concentration and the precipitate identity. These factors provide a greater understanding of the mechanisms utilised by the bacteria in the bioprecipitation and adsorption of Pb(II). These results can be used as a step towards applying the process on an industrial scale.

Co-precipitation of gold and base metal sulfides during fluid boiling triggered by fault-valve processes in orogenic gold deposits

The extreme fluctuations in pressure during earthquakes are widely regarded as responsible for gold mineralization in quartz-vein-hosted gold deposits. However, it is barely noticed that base metal sulfides can precipitate together with gold during these processes. Here we present the phenomenon and unravel the mechanism of the co-precipitation of Au and base metal sulfides during the fluid boiling via geological study and thermodynamic modeling, respectively. The Bangbu deposit, a lode-type orogenic gold deposit in Tibet shows two mineralization substages of pyrite. The pyrite formed in the later substage is hosted in the wall rock selvages of laminated crack-seal quartz veins formed by the fault-valve processes. The pyrite grains are characterized by anhedral small crystals with porous textures and abundant native gold, chalcopyrite, galena, and sphalerite inclusions. They also contain higher concentrations of Cu, Pb, Ag, Sb, and Au, and lower concentrations of Co and Ni, compared to the euhedral large-grained pyrite formed in the initial substage. The textural and trace element characteristics of the pyrite indicate that vigorous boiling occurred during fault-valve behavior, which decreased the solubilities of Au, Cu, Pb, and Zn in the ore fluid in Bangbu. The co-precipitation of Au and base metal sulfides triggered by fluid boiling has also been reported in other orogenic gold deposits worldwide.Thermodynamic models are designed to acquire the predominant species and solubility of Au, Cu, Pb, and Zn in orogenic ore fluids under varied chemical conditions. The results show that Au, Cu, Pb, and Zn are dominantly transported as hydrosulfide complexes under lower mesozonal to epizonal deposit conditions. At temperatures of about above 350 °C, Au hydrosulfide species still predominates, but the predominant Cu, Pb, and Zn species change from hydrosulfide to chloride complexes. A sudden decrease in the reduced sulfur concentration during fluid boiling may be the most important mechanism controlling the precipitation of Au, Cu, Pb, and Zn in lower mesozonal to epizonal deposits. The decrease of logfS2 during fluid boiling can increase the fluid pH, resulting in the decrease of solubilities of base metal chloride complexes and thus explain the co-precipitation of Au and base metal sulfides in hypozonal deposits.