Lead Immobilization Research Articles

Mechanistic insight into lead immobilization on bone-derived carbon/hydroxyapatite composite at low and high initial lead concentration

The contamination of heavy metal lead has a serious impact on the natural environment and organisms. Among various materials for lead removal, animal bone derived hydroxyapatite has received extensive attention. However, there are different opinions among researchers regarding the mechanism of lead removal by hydroxyapatite, possibly due to varying initial lead concentrations used in different studies and lack of accuracy in the study of lead removal mechanisms. In present work, we synthesized a carbon-containing hydroxyapatite (CHAP) through pyrolysis of bovine bone with excellent lead removal efficiency, and further investigated the lead removal mechanism of CHAP under high and low initial lead concentrations by combining XRD Rietveld refinement, FTIR, XPS, HRTEM etc. methods. The results showed that under low initial Pb2+ concentration condition, the main mechanism of lead removal by CHAP was chemical precipitation (94.1 %), with small contributions of lead complexation with carbon functional groups and cation-π interactions on the amorphous carbon in CHAP, and surface adsorption on the precipitates. Under high initial Pb2+ concentration condition, chemical precipitation remained the main mechanism (74.68 %), but the contributions of the other three mechanisms increased, and ion exchange appeared in the later stage of the removal process. This study provides new insights on the lead immobilization mechanism by CHAP at different initial Pb2+ concentrations in water.

Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment

Multi-metals/metalloids contaminated soil has received extensive attention because of their adverse health effects on the safety of the food chain and environmental health. In order to provide additional insight and aid in mitigating environmental risks, a pot experiment was directed to assess the impacts of biochars derived from rice straw (BC), and modified biochars i-e., hydroxyapatite modified (HAP-BC) and oxidized biochars (Ox-BC) on the redistribution, phytoavailability and bioavailability of phosphorus (P), lead (Pb), and Arsenic (As), as well as their effects on the growth of maize (Zea mays L.) in a Lead (Pb)/Arsenic (As) contaminated soil. The results showed that HAP-BC increased the soil total and available P, compared with raw biochar and control treatment. HAP-BC improved soil properties by elevating soil pH and electric conductivity (EC). The Hedley fractionation scheme revealed that HAP-BC enhanced the labile and moderately labile P species in soil. Both HAP-BC and Ox-BC assisted in the P build-up in plant roots and shoots. The BCR (European Community Bureau of Reference) sequential extraction data for Pb and As in soil showed the pronounced effects of HAP-BC towards the transformation of labile Pb and As forms into more stable species. Compared with control, HAP-BC significantly (P ≤ 0.05) decreased the DTPA-extractable Pb and As by 55% and 28%, respectively, subsequently, resulting in reduced Pb and As plant uptakes. HAP-BC application increased the plant fresh and dry root/shoot biomass by 239%, 72%, 222% and 190%, respectively. The Pb/As immobilization by HAP-BC was mainly driven by precipitation, ion exchange and surface complexation mechanisms in soil. In general, HAP-BC application indicated a great capability to be employed as an effective alternative soil amendment for improving P acquisition in soil, simultaneously immobilizing Pb and As in the soil-plant systems.

Lead immobilization for environmentally sustainable perovskite solar cells.

Lead halide perovskites are promising semiconducting materials for solar energy harvesting. However, the presence of heavy-metal lead ions is problematic when considering potential harmful leakage into the environment from broken cells and also from a public acceptance point of view. Moreover, strict legislation on the use oflead around the world has driven innovation in the development of strategies for recycling end-of-life products by means of environmentally friendly and cost-effective routes. Lead immobilization is a strategy to transform water-soluble lead ions into insoluble, nonbioavailable and nontransportable forms over large pH and temperature ranges and tosuppress lead leakage if the devices are damaged. An ideal methodology should ensure sufficient lead-chelating capability without substantially influencing the device performance, production cost and recycling. Here we analyse chemical approaches to immobilize Pb2+ from perovskite solar cells, such as grain isolation, lead complexation, structure integration and adsorption of leaked lead, based on their feasibility to suppress lead leakage to a minimal level. We highlight the need for a standard lead-leakage test and related mathematical model to be established for the reliable evaluation of the potential environmental risk of perovskite optoelectronics.

Simultaneous and long-term effective immobilization of lead, cadmium and arsenic in multi-contaminated soil by ferrihydrite-supported animal-derived biochar

The multi-contaminants of cationic Pb/Cd and anionic As in soils is difficult to simultaneously immobilize by common chemical amendments. Here, a novel ferrihydrite-supported animal-derived biochar (FAB) was prepared and added to pristine Pb/Cd/As-contaminated soil for incubation of 150 days. The amendment using FAB elevated soil pH and reduced soil electric conductivity and the release of soil dissolved organic carbon. After the addition of 3 %w/w FAB (FAB3 %), the bioavailability of Pb, Cd, and As decreased to 9.2, 57.5, and 7.6 mg/kg, respectively, which were 96 %, 47 %, and 36 % lower than that of the control soil (CK). The exchangeable Pb and Cd and specifically sorbed As were transformed into residual Pb, carbonate- and Fe-Mn oxide-bound Cd, and well-crystallized Fe-Al oxide-bound As, respectively. The diversity of soil bacterial community increased after FAB treatment. Dynamic leaching and first-order attenuation simulation experiments showed that FAB3 % can decrease the leachable heavy metal(loid)s to negligible concentration in real soil within 3–7 years, whereas that in CK soil was around 12 years. X-Ray adsorption near edge structure analysis showed that FAB immobilized heavy metal(loid)s in soil by forming pyromorphite coprecipitate with Pb(II), ion exchange between Cd(II) and Ca(II) in the hydroxyapatite component, and complexation between the ferrihydrite component and As(V).

Bioremediation system consisted with Leclercia adecarboxylata and nZVI@Carbon/Phosphate for lead immobilization: The passivation mechanisms of chemical reaction and biological metabolism in soil

Bioremediation is one of the most promising strategies for heavy metal immobilization. A new remediation system was demonstrated in this research, which combined phosphate solubilizing bacteria (PSB) with nZVI@Carbon/Phosphate (nZVI@C/P) composite to remediate lead contaminated soil. Experimental results indicated that the new system (nZVI@C/P + PSB) could effectively convert the labile Pb into the stable fraction after 30 days of incubation, which increased the maximum residual fraction percentage of Pb by 70.58%. The characterization results showed that lead may exist in the forms of Pb5(PO4)3Cl, PbSO4 and 3PbCO3·2Pb(OH)2·H2O in the soil treated with nZVI@C/P + PSB. Meanwhile, soil enzyme activities and Leclercia abundance were enhanced in the treated soil compared with CK during the incubation time. In addition, the specialized functions (e.g. ABC transporters, siderophore metabolism, sulfur metabolism and phosphorus metabolism) in PSB and nZVI@C/P + PSB group were also enhanced. These phenomena proved that the key soil metabolic functions may be maintained and enhanced through the synergistic effect of incubated PSB and nZVI@C/P. The study demonstrated that this new bioremediation system provided feasible way to improve the efficacy for lead contaminated soil remediation.

Biochar amendment of a metal contaminated soil partially immobilized Zn, Pb, and Cd and reduced ryegrass uptake

Soil heavy metals (HM) contamination threatens soil and water quality, which significantly affects humans and animals. This study focuses on the competitive immobilization of zinc (Zn), lead (Pb), and cadmium (Cd) in soils from a contaminated site using ryegrass (Lolium perenne) in a potting experiment amended with biochars. Increased rates of switchgrass- (SGB) and poultry litter-derived biochars (PLB) were applied before ryegrass cultivation. Soil HM phytoavailability and HM concentrations in plant shoots were determined. Multivariate regression models were used to evaluate the influence of several soil chemical attributes on the HM phytoavailability. The increased rates of both biochars reduced the Zn, Pb, and Cd availability (p < 0.001). Langmuir models showed that the maximum HM immobilization (IMAX) was 169.2 ± 29.5 mg kg–1 for Zn with SGB, and 20 ± 7.4 (Pb) and 1.08 mg kg–1 (Cd) with PLB. The extended Langmuir model (EL) showed competitive HM immobilization since there was a decrease in the IMAX of Zn (∼90 ± 28 mg kg–1 from SGB) and Cd (∼0.70 ± 0.21 mg kg–1). Negative values of Pb and Cd immobilization at low rates of SGB indicated an increase in those HM availabilities and preferential immobilization for Zn. The reduced Zn and Pb uptake in ryegrass shoots ranged from 70% to 98% and were optimum at rates of 0.50% ± 0.00%–0.60% ± 0.06% for both biochars, and 1.6% ± 0.4% of SGB for Cd. The stepwise multiple linear regression (SMLR) and partial least squares (PLS) revealed that pH and organic matter (OM) were the most responsible factors for reducing Zn bioavailability while OM was more impactful in decreasing Pb and Cd levels. This suggests that the preferential immobilization for Zn relies on its higher sensitivity to the pH increase. Also, the ubiquitous positive relationship among the metals studied shows that competitive immobilization is ceased at high rates of biochars application. Path analysis (PA) showed that pH and OM were the common contributors from both biochars to simultaneously affect Zn, Pb, and Cd availability regardless of the contrasting physicochemical properties of the two bioproducts. This work proved the potential of applying low rates of two contrasting feedstock-derived biochars to remediate the contaminants and safely grow ryegrass.

Lead remediation is promoted by phosphate-solubilizing fungi and apatite via the enhanced production of organic acid.

Lead (Pb) is one of the most common heavy metal pollutants in the environment, which can indirectly or directly threaten human health. Lead immobilization by apatite can reduce the effectiveness of Pb cations via the formation of pyromorphite (Pyro). However, the formation of Pyro is always depending on the release of phosphorus (P) from apatite. Phosphate-solubilizing fungi (PSF) can secrete large amounts of organic acid to promote the release of P from apatite. Although the combination of PSF and apatite has shown a huge potential in Pb remediation, this pathway needs to be more attention, especially for organic acid secretion by PSF. This research mainly reviews the possible pathway to strengthen Pb immobilization by PSF and apatite. Meanwhile, the limitation of this approach is also reviewed, with the aim of a better stabilizing effect of Pb in the environment and promoting the development of these remediation technologies.

Enhancing lead immobilization by biochar: Creation of “surface barrier” via bio-treatment

The long-term effectiveness of heavy metal immobilization is always a concern. This study proposes a completely novel approach to enhance the stability of heavy metals by combined biochar and microbial induced carbonate precipitation (MICP) technology, to create a “surface barrier” of CaCO3 layer on biochar after lead (Pb2+) immobilization. Aqueous sorption studies and chemical and micro-structure tests were used to verify the feasibility. Rice straw biochar (RSB700) was produced at 700 °C, which shows high immobilization capacity of Pb2+ (maximum of 118 mg g−1). But the stable fraction only accounts for 4.8% of the total immobilized Pb2+ on biochar. After MICP treatment, the stable fraction of Pb2+ significantly increased to a maximum of 92.5%. Microstructural tests confirm the formation of CaCO3 layer on biochar. The CaCO3 species are predominantly calcite and vaterite. Higher Ca2+ and urea concentrations in cementation solution resulted in higher CaCO3 yield but lower Ca2+ utilization efficiency. The main mechanism of the “surface barrier” to enhance Pb2+ stability on biochar was likely the encapsulation effect: it physically blocked the contact between acids and Pb2+ on biochar, and chemically buffer the acidic attack from the environment. The performance of the “surface barrier” depends on both the yield of CaCO3 and their distribution uniformity on biochar's surface. This study shed lights on the potential application of the “surface barrier” strategy combining biochar and MICP technologies for enhanced heavy metal immobilization.

Phosphorus modified graphitic carbon nitride activated by guanidine phosphate enables fast, efficient and selective immobilization of aquatic lead

With the assistance of preinstalled silica templates, polymeric graphitic carbon nitride with enhanced porosity suffers from complicated procedures and by-product wastes. Besides, it is still difficult to achieve the incorporation of phosphate groups with high contents on carbon-based materials (mostly < 1.0 at.% of P) via a one-step preparation since phosphate species on the surfaces of sorbents could complex heavy metals strongly from wastewaters. Given the porosity engineering of guanidine phosphate (GP) for carbonaceous materials, GP activated graphitic carbon nitrides (GPCNs) with developed surface area (4.2–4.8 fold of enhancement than inactivated one) and abundant phosphate groups (9.9–16.7 at.% of P) were fabricated via a one-step pyrolysis at 450, 500, and 550 °C. On this basis, the sorption of Pb(II) on GPCNs were studied under geochemical conditions including contact time, solution pH, ionic strength, humic acid concentration, interfering cations and anions, and temperature. GPCN pyrolyzed at 500 °C could capture Pb(II) rapidly (20.0 min) with superior maximum capacities (81.8–217.1 mg/g at pH 5.0, T 298 K), excellent selectivity coefficients (8.10–16.54) and favorable reusability (81.4% of capacity remained). The formation of minerals was dominant for the selectivity rather than ion exchange or surface coordination, etc. This work starts up the facile activation of carbon nitride with developed porosity and surface functionality to manage aquatic pollutants.

Investigation of autoclave curing impact on the mechanical properties, heavy metal stabilization and anti-microbial activity of the green geopolymeric composite based on received/thermally-treated glass polishing sludge

Recycling Pb-containing-sludge, as industrial hazardous waste, in the fabrication of eco-friendly construction material with high mechanical characteristics and antimicrobial activity is the nominal target behind this investigation. The received sludge (RS) has been thermally treated at 500 °C to weed out the entire organic content to benefit from received (RS) and treated (TS) sludges in preparation for geopolymer pastes as an alternative to commercial Portland cement. OPC paste cured up to 28-days at normal conditions was used as a reference, and two other geopolymer pastes were prepared by 5%NaOH-activation; slag containing 50%RS (AAS-RS) and 50%TS (AAS-TS). Two curing regimes treated geopolymer pastes: high humidity at 25 °C for 28-days and hydrothermal treatment at different steam pressures (2, 5, 8 bars) and different time intervals (2, 4, 8 h). The formed binding phases are detected by XRD, TGA/DTG and SEM techniques. A microbial resistivity test was conducted using two different fungi (Aspergillus-terreus and Mucor-circinelloide) and two different bacteria (K.pneumonia-ATCC13883 and Bacillus-subtilis-ATCC6633). The overall outcomes of this study confirmed that the AAS-TS composite possessed higher compressive strength than AAS-RS. Moreover, autoclaving at 5 bars/4hrs for AAS-TS paste was the best condition to reach high strength (72 MPa) compared to OPC (68 MPa). The inhibition zone data confirmed that OPC pastes have no resistance against mentioned microbes, while the composite AAS-RS (cured under humidity for 28-days) possessed the highest antimicrobial action among all geopolymer pastes. Successful immobilization of toxic lead in all geopolymeric pastes, whatever the curing conditions, was achieved according to the toxicity characteristics leaching procedure (TCLP).

From dangerous wastes to green construction materials, as thermally stable-radiation blocker, in presence of meso-porous magnesia and alumina

The nominal objective behind this study is to recycle iron-rich slag (GGBFS) and lead-rich glass waste (LRGW) as industrial solid wastes in the presence of meso-porous magnesia or alumina to produce sustainable, eco-friendly, and high-performance binding materials. Four NaOH-activated composites (AACs) pastes have been prepared: Pure alkali-activated slag (AAS), AAS-20%LRGW, AAS-20%LRGW-3% meso-porous MgO, and AAS-20%LRGW-3% meso-porous Al2O3. After the hardening process, the compressive strength was measured at 1, 7 and 28-days of normal curing (high humidity at 25 °C). Thermal stability test for all AACs, after 28-days, was conducted at 250, 500 and 750 °C. Two different radio-active isotopes (Cs-137 and Co-60) were used, as gamma radiation sources, to investigate the attenuation performance of all prepared AACs. The results confirmed that, among the four composites, AAS-20%LRGW-3% meso-porous MgO composite pastes possessed the highest compressive strength (29.3 MPa), highest thermal stability (25 MPa, 18.2 MPa and 10 MPa at 250 °C, 500 °C and 750 °C, respectively). Moreover, this composite has the highest gamma radiation shielding performance, whatever the intensity of the gamma-ray or firing temperature. At cesium isotope, it was found that the μ values were 0.199 ± 0.003, 0.197 ± 0.003, 0.194 ± 0.005 and 0.188 ± 0.005 cm−1 at 25, 250, 500 and 750 °C, respectively. This efficiency is attributed to the role of meso-porous MgO; it has a high surface area (8891 cm2/g), high adsorption capacity (2.042 cm3/g), and low average pore diameter (37.17 nm); these textural characteristics helped much in the generation of additional hydrates/binding phases such as calcium-silicate-hydrates (CSHs), calcium-aluminate-hydrates (CAHs), calcium-alumino-silicate hydrates (CASHs as gehlenite or hydrogarnet), hydrotalcite, magnesium silicate hydrates (MSHs) as well as sodium-alumino-silicate-hydrates (NASHs) and lead silicates (Pb3SiO5). All these phases were detected via XRD, TGA/DTG as well as SEM/EDX techniques. Moreover, the inclusion of meso-porous MgO enhanced the immobilization of hazardous lead according to the obtained data from the toxicity characteristics leaching procedure (TCLP). Hence, we recommend using AAS-20%LRGW-3%MgO composite as gamma-radiation blocker in medical fields and concrete landfills containing dangerous radioactive wastes.

Enhanced immobilization of lead, cadmium, and arsenic in smelter-contaminated soil by sulfidated zero-valent iron

Soils contaminated with multiple heavy metal(loid)s (HMs) such as lead (Pb), cadmium (Cd), and arsenic (As) are of great concern in many countries. In this study, taking three lead-zinc smelter soils, the performance of sulfidated zero-valent iron (S-ZVI) toward Pb, Cd, and As immobilization was systemically investigated. Results showed that more than 88% of water-extractable Pb and Cd could be immobilized and transformed into reducible, oxidizable, and/or reducible forms by S-ZVI within 3 h, whereas only 3–56% of them could be immobilized by unsulfidated ZVI even after 72 h. Meanwhile, the phytoavailability of the tested HMs could be effectively reduced by 79% after S-ZVI amendment. More importantly, anoxic/oxic incubation tests revealed that the dissolved concentrations of HMs were much lower in S-ZVI-treated soils than in the untreated or unmodified ZVI-treated soils. Speciation analysis further suggested that unmodified ZVI seemed to reduce the long-term soil stability by changing the residual HMs species to mild-acid soluble and/or reducible ones. In contrast, S-ZVI could effectively alleviate the remobilization of HMs under the changeover of soil redox environments. All these findings indicate that S-ZVI may be a promising amendment for the immobilization of Pb, Cd, and As in smelter-contaminated soil.

Efficient lead immobilization by bio-beads containing Pseudomonas rhodesiae and bone char

Mineralization of lead ions (Pb2+) to pyromorphite using phosphorus-containing materials is an effective way to remediate lead (Pb) contamination. Bone char is rich in phosphorus, but its immobilization of Pb2+ is limited by poor phosphate release. To utilize the phosphorus in bone char and provide a suitable growth environment for phosphate-solubilizing bacteria, bone char and Pseudomonas rhodesiae HP-7 were encapsulated into bio-beads, and the immobilization performance and mechanism of Pb in solution and soil by bio-beads were investigated. The results showed that 137 mg/g of phosphorus was released from bone char in the presence of the HP-7 strain. Pb2+ removal efficiency reached 100 % with an initial Pb2+ concentration of 1 mM, bone char content of 6 g/L, and bio-bead dosage of 1 %. Most Pb2+ was immobilized on the surface of the bio-beads as Pb5(PO4)3Cl. The soil remediation experiments showed a 34 % reduction in the acid-soluble fraction of Pb. The bio-beads showed good stability in long-term (30 d) soil remediation. The present study shows that bone char can be turned into an efficient Pb immobilization material in the presence of phosphate-solubilizing bacteria. Thus, bio-beads are expected to be used in the remediation of Pb-contaminated environments.

Synergetic effects of hydrothermal treatment on the behavior of toxic sludge-modified geopolymer: Immobilization of cerium and lead, textural characteristics, and mechanical efficiency

Geopolymers have been subjected as a promising strategy for heavy metals immobilization due to their sustainability (environmental and energy saving). This study proposed a novel hydrothermal technology for the solidification/stabilization of lead and cerium present in a sludge resulting from the glass polishing process. Slag and fly-ash (50wt.%slag + 50wt.%fly-ash) activated with 6 wt% NaOH solution were used as base materials for geopolymer fabrication. The sludge was incorporated in the fabricated geopolymeric composite as a fly-ash replacement (10, 20 and 30 wt%). The impact of sludge incorporation and different curing regimes (humidity at 20 °C and 80 °C for 28-days and hydrothermal treatment at 3 and 6 bar for 1, 2, 6, 12 and 24 hrs) on the mechanical and textural characteristics as well as the formed phases were investigated via compression test, N2-adsorption/desorption technique, SEM/EDX, TGA/DSC and XRD. Moreover, the efficiency of the immobilization process was examined by determining the concentration of lead and cerium in the leachate solution (0.1 M HNO3 and 0.1 M CH3COOH) using Inductively Coupled Plasma Mass Spectroscopy to ensure the safety of developed composites. The results indicated that autoclaving at 6 bar/6hrs greatly returned the strength values for all hardened geopolymers, particularly the composite containing 50wt.%slag + 40wt.%fly-ash + 10wt.%sludge; its strength values were 22, 46 and 60 MPa at 20 °C/28 days, 80 °C/28 days and 6 bar/6hrs, respectively. The enthalpy change calculated by the DSC technique has the highest value (122.2 J/g) at 6 bar/6hrs, indicating the formation of additional hydration products. Hydrothermal treatment technology has proven its worth in immobilizing heavy metals in geopolymeric materials; curing at 6 bar/6hrs for specimen containing 30wt.%sludge decreased lead concentration by 95.2 and 97.8 % and cerium by 98.2 and 99.6 % in leachate solutions (HNO3 and CH3COOH, respectively). This may be attributed to the transformation of lead and cerium into insoluble Ce2Si2O7 and Pb3SiO5 as detected by XRD that are physically encapsulated in a cross-linked geopolymer structure. Furthermore, due to pore structure rearrangement that shifted to micro/mesoporous (2–50 nm) under the steam condition with a high BET surface area (31.7 m2/g) and low BJH average pore diameter (10.01 nm).

Hazardous industrial filter sludge immobilization with mayenite and gypsum

Heavy metals escaping from industrial processes and industrial waste are a significant environmental hazard all around the globe. Since they cannot be destroyed, the only way to manage the pollution is to capture and contain the hazardous components. This study focuses on stabilization-solidification of a highly toxic industrial filter slag that contains a range of different heavy metals in extremely high quantities. The stabilization-solidification treatment was executed with a mayenite and gypsum based solid cementitious binder. The major components that were monitored during the study were selenium, lead and sulphate. Different ratios of gypsum addition were tested in order to observe the effect of total sulphate content in the system to the immobilization efficiency of anionic selenium and sulphate. During the experiments, all cationic heavy metals were immobilized efficiently, most of them achieving the immobilization efficiencies of more than 99.9%. By adjusting the sulphate content of the system, the immobilization efficiency of selenium was improved from 95.669% to 99.925% and the immobilization efficiency of sulphate raised from 96.069% to above 99.964%. Controversially, the immobilization of lead was at its highest (99.999%) with high sulphate content and dropped to 98.162% as the sulphate rate decreased. The results show clearly that mayenite has good potential for stabilization-solidification applications.

Modification of cemented paste backfill with calcined layered double hydroxides for lead-containing tailings disposal

Cemented paste backfill (CPB) is the main way to treat tailings at present. Alternative binders are necessary due to the high cost and CO 2 emission of ordinary Portland cement . Besides, the heavy metals contained in the tailings should be immobilized effectively when being used in CPB. In the present work, calcined Mg-Al-layered double hydroxides (CMA) were used to modify the properties of high-volume fly ash (FA) cement to increase its performance in CPB. Isothermal calorimetric, X-ray diffraction, and thermogravimetric analysis were used to explore the reaction kinetics and phase assembles of the binder. The properties of CPB samples were then studied. In addition, the lead (Pb) immobilization effects in CPB samples were studied using toxicity characteristic leaching procedure and semi-dynamic leaching. The experimental results proved that CMA could accelerate binder reaction by providing additional nucleation sites for hydration gel formation. It then increased the compressive strength of CPB samples. Besides, the immobilization effects of Pb were enhanced when adding CMA due to the better immobilization capacity of regenerated LDHs. • CMA provided more nucleation sites for hydration gels formation. • CMA could increase the yield stress of fresh CPB slurry. • The presence of CMA increased Pb immobilization effects of CPB. • The leaching of Pb from CPB was controlled by diffusion.

Penicillium oxalicum augments soil lead immobilization by affecting indigenous microbial community structure and inorganic phosphate solubilization potential during microbial-induced phosphate precipitation

Phosphate-solubilizing microorganisms (PSMs) are critically important for increasing soil phosphate (P) and decreasing lead (Pb) bioavailability during microbial-induced phosphate precipitation (MIPP). However, their relative contributions to the indigenous soil microbial communities and P-cycling genes during the MIPP process remain unclear. In this study, inoculation of the PSM P. oxalicum in hydroxyapatite-cultured and Pb-contaminated soil increased soil phosphatase activities, available P (AP) concentrations and reduced available Pb levels. Metagenomics revealed a 3.9–44.0% increase in the abundance of P-cycling genes by P. oxalicum inoculation. No P-cycling genes were assigned to Penicillium. While P. oxalicum increased the complexity of microbial community co-occurrence networks, and improved the directly interrelationships between Penicillium and genera containing P-cycling gene. These results suggesting that P. oxalicum obviously positively affected the regulation of indigenous P-cycling functional communities during the MIPP process. Inorganic P solubilization genes (gcd, ppa, and ppx) have been shown to affect soil AP, suggesting that inorganic P solubilization is the major driver of Pb immobilization improvement following P. oxalicum inoculation. These results enhance our understanding of the significant ecological role of PSMs in governing soil P-cycling and alleviating Pb2+ biotoxicity during the MIPP process.

Use of Surface Modified Calcium Oxide Nanoparticle in Immobilizing of Lead and Cadmium Contaminated Soil

Remediation is vital in advancing the agriculture yield and decreasing the hazard of food poisoning in contaminated soil. The aim of this study was to remediate lead and cadmium contaminated soil from Evbareke spare parts market using surface modified calcium oxide nanoparticle (SMCON). Soil samples were collected from Evbareke spare parts market, Benin City, Edo state Nigeria, using quadrant sampling method at the depth of 0-15cm using soil auger. The soil samples obtained were physicochemically and geochemically characterized. The SMCON was synthesized and characterized using Fourier Transform-Infra Red, Scanning electron spectroscopy and x-ray diffraction. A leaching experiment was carried out to authenticate the immobilization efficiency and capacity of SMCON on the lead and cadmium in the contaminated soil. The SMCON efficiency for lead and cadmium immobilization in the contaminated soil increased with increase in immobilizer up to the optimum 4% of SMCON in contaminated soil for lead and ≤1% of SMCON for cadmium. Likewise, the immobilization capacity of SMCON in the contaminated soil also revealed that more of lead and cadmium were immobilized as SMCON content in the contaminated soil mixture increased, thereby disallowing leaching of lead and cadmium from the contaminated soil. The SMCON effectively decreased the lead and cadmium in the soil by in situ adsorption, ion exchange and complexation mechanism thus reducing its accessibility for uptake by plants and its transmission to man and animals.

Minimizing salinity-induced Pb toxicity to microbial N cycling processes in saline Pb-polluted soils amended with biochar

Biochar may affect nitrogen (N) cycling processes and, therefore, plant-available forms of soil N by modifying the activity and composition of the soil microbial community. However, it is unclear how biochar addition can influence microbial N cycling and availability in saline polluted soils. The present study investigated the impact of sugarcane bagasse biochars (SBBs) produced at 400 and 600 °C on potential net ammonification, nitrification and N mineralization, microbial biomass N (MBN), and urease activity in a calcareous soil polluted with lead (Pb) under different levels of NaCl salinity (6 and 10 dS m-1 ) during a 120-day incubation period. NaCl salinity increased soil available Pb concentration, with a greater increase at high than low salinity level. The application of SBBs increased soil organic carbon (SOC, 96–101 % relative to controls), dissolved organic carbon (DOC, 14–110 %), total nitrogen (TN, 6–25 %), cation exchange capacity (CEC, 12–20 %), and immobilized soil Pb (10–25 %). Lead immobilization, which largely resulted from increased soil CEC, was greater with addition of 600 °C (20–25 %) than 400 °C (15–20 %) biochar in saline soils. Addition of SBBs decreased the availability of soil Pb that was enhanced by salinity. Biochar application stimulated potential net ammonification (177–218 %), nitrification (70–83 %) and N mineralization (92–110 %), MBN (114–221 %) and urease activity (66–79 %) in saline Pb-polluted soils. Redundancy analysis revealed that increased DOC, increased TN and Pb immobilization were the most significant factors contributing to the enhanced N bio-transformations, MBN, and urease activity in saline polluted soils amended with SBBs. Our highlights the potential benefits of low-temperature SBBs as an amendment to minimize the impact of metal toxicity associated with salinity on microbial N cycling processes in Pb-polluted soils. In conclusion, biochar application could be a useful practice for enhancing the N turnover rate in saline Pb-polluted soils by increasing substrate availability and decreasing Pb mobility.

A novel and sustainable technique to immobilize lead and zinc in MSW incineration fly ash by using pozzolanic bottom ash

Fly ash (FA) generated from Municipal Solid Waste (MSW) incineration contains high leaching potential of toxic metals. Calcium silicate hydrate (C–S–H) is the main hydration product of cement and can immobilize the leaching of toxic metals, formed by the reaction of Ca with pozzolanic Si in a highly alkaline environment. Toxic metals can be immobilized by the addition of pozzolan to FA residues (in lieu of cement), which is a source of Ca and provides an alkaline condition. The current study proposed a new approach of reusing the fine-fraction of MSW incineration bottom ash (BA), which contains amorphous silica, known as pozzolan for immobilization of lead (Pb) and zinc (Zn) in FA. The dissolved amorphous silica and alumina emerged from the BA, with available Ca ions and in an extremely alkaline condition owing by FA, stimulate the pozzolanic reaction, resulting the formation of cementitious compounds of C–S–H gel and calcium aluminate hydrates (C-A-H) that can immobilize the heavy metals leaching from FA. The existence of calcium hydroxide promotes the carbonation process, reducing pH, and consequently immobilizing heavy metals. The method involves the simple mixing of BA and FA with water. The mixture was settled for 1, 4, 16, and 30 days at room temperature and annealed (120 °C) conditions. The leaching concentrations of Pb and Zn significantly reduced in the stabilized FA samples followed by standard Japanese leaching test (JLT- 46). Pb stabilization efficiency was reached >99.9% after 16-days of settling periods with 10% dosage of BA at room temperature. The added BA to FA residues reacted with Ca(OH)2 and CaClOH produced the C–S–H gel. pH, XRD, and SEM-EDX analyses evaluated the carbonation and pozzolanic reactions that promoted the immobilization of Pb and Zn. Immobilization of heavy metals by using fine-fraction of BA seems to be very effective and technically feasible. The technology can save original material, produce inert material and avoids landfilling of incineration residues. More advanced and detailed experiments have been designed to promote the optimization of the proposed technology for application in industries.