Synthetic Precipitation Leaching Procedure Research Articles

Evaluating the effectiveness of sulfidated nano zerovalent iron and sludge co-application for reducing metal mobility in contaminated soil

Sewage sludge has long been applied to soils as a fertilizer yet may be enriched with leachable metal(loid)s and other pollutants. Sulfidated nanoscale zerovalent iron (S-nZVI) has proven effective at metal sorption; however, risks associated with the use of engineered nanoparticles cannot be neglected. This study investigated the effects of the co-application of composted sewage sludge with S-nZVI for the stabilization of Cd, Pb, Fe, Zn. Five treatments (control, Fe grit, composted sludge, S-nZVI, composted sludge and S-nZVI), two leaching fluids; synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) fluid were used, samples were incubated at different time intervals of 1 week, 1, 3, and 6 months. Fe grit proved most efficient in reducing the concentration of extractable metals in the batch experiment; the mixture of composted sludge and S-nZVI was the most effective in reducing the leachability of metals in the column systems, while S-nZVI was the most efficient for reducing about 80% of Zn concentration in soil solution. Thus, the combination of two amendments, S-nZVI incorporated with composted sewage sludge and Fe grit proved most effective at reducing metal leaching and possibly lowering the associated risks. Future work should investigate the longer-term efficiency of this combination.

Utilization of phosphoric acid-modified biochar to reduce vanadium leaching potential and bioavailability in soil

Remediating vanadium (V) polluted soil has garnered widespread attention over the past decade. Yet, few research projects have investigated the stabilization of soil V using modified biochar, so the effects and interacting mechanisms between soil properties and modified biochar for V immobilization and stabilization remain unclear. Hence, this gap is addressed by determining the leaching behavior and mechanisms of soil V on different dosages of phosphoric acid (H3PO4) impregnated biochar (MLBC, 0.5%–4%). The applicability and durability in soil V immobilization was investigated under acid precipitation. The MLBC effect on V bioavailability and mobility was assessed first by CaCl2, Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) extractions in different periods. The V concentrations significantly reduced in CaCl2, TCLP, and SPLP extract with MLBC at each dosage (30 d), while slight to significant increase in SPLP and TCLP extract V was recorded in a long-term incubation (90 d). Column leaching test further demonstrated the high durability of 4% MLBC in V stabilization under continuous acid exposure. Compared to the control (no-biochar), the accumulated V content in the leaching solution significantly decreased in MLBC-amended soil. Acid soluble fraction of V showed significant negative correlation with both soil organic matter (SOM) and available P, which was positively correlated with pH, suggested that pH, available P and SOM were key factors affecting the bioavailability of V in soil. Moreover, combining with the characterization results of MLBC and amended soil, the results revealed that H3PO4 modified biochar played a vital role on V immobilization and soil improvement by forming electrostatic adsorption, ion exchange, redox reaction or complexation with the increase of functional groups. These revealed an efficient and steady development of soil quality and treatment for soil V contamination, under MLBC operation to soil polluted with exogenous V.

Evaluation of the effects of L-cysteine addition on the bioleaching of zinc and cadmium from sphalerite flotation concentrate

The primary zinc ore in the world is sphalerite, and roasting-leaching-electrowinning (RLE) is the most typical method of processing. This method has different disadvantages, and bioleaching is an alternative and eco-friendly method for sphalerite treatment. The major drawback of bioleaching is its slow kinetics. In this study, an evaluation of the effects of L-cysteine addition on the bioleaching of zinc and cadmium from a concentrate of sphalerite was investigated in the presence of mixed cultures of mesophilic and moderately thermophilic microorganisms. The results showed that L-cysteine addition increased the dissolution rates of zinc and cadmium while reducing them at higher concentrations. The optimal conditions were achieved by using 0.1 g/L of L-cysteine in mesophilic cultures with zinc recovery of 73.92% and cadmium recovery of 81.45%, respectively. Similarly, zinc recovery was 92.54% in thermophilic cultures, while cadmium recovery was 88.66%. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analyses have detected the formation of jarosite and elemental sulfur on sphalerite surfaces in mesophilic conditions, as well as ammoniojarosite and elemental sulfur in moderately thermophilic conditions. Fourier transform infrared (FTIR) spectroscopy was employed to identify molecular structures and functional groups on the surface of bioleached residues in mesophilic and moderately thermophilic conditions. To assess the environmental risk of residues, a combination of synthetic precipitation leaching procedure (SPLP) and toxicology characteristic leaching procedure (TCLP) methods were used.

Long-term stability and toxicity effects of three-dimensional electrokinetic remediation on chromium-contaminated soils

The three-dimensional electrokinetic remediation (3D EKR) achieved efficient removal of chromium (Cr) from the soil through mechanisms including electromigration, electroosmosis, and redox reactions. In this study, the long-term stability, leaching toxicity, bioavailability, and phytotoxicity of Cr in remediated soils were systematically analyzed to comprehensively evaluate the effectiveness of the 3D EKR method. The results showed that the concentration of hexavalent chromium (Cr (VI)) in the leachate of the 3D EKR system with sulfidated nano-scale zerovalent iron (S-nZVI) was more than 40% lower than those of the other 3D electrode groups, and the time required to reach the level III standard of groundwater quality criterion in China (0.05 mg/L, GB/T 14848-2017) was significantly shortened. The stabilization of Cr(VI) in contaminated soil after 3D EKR was maintained for 300 pore volumes (PVs), indicating that the treated Cr(VI) had good long-term stability. The leaching toxicity and bioaccessibility of Cr were assessed by the synthetic precipitation leaching procedure (SPLP), the toxicity characteristic leaching procedure (TCLP), and the physiologically based extraction test (PBET). The concentration of Cr(VI) in the SPLP, TCLP, and PBET leachates of the S-nZVI group decreased by more than 25% compared to the other 3D electrode groups, corresponding to the decrease in leaching toxicity and bioavailability of the treated Cr during the 15-day remediation period. In addition, the germination rate of wheat seeds and the average biomass of wheat seedlings in the S-nZVI group under alkaline conditions (EE) were higher than those in the non-polluting group (Blank-OH), indicating that the remediated soil had no obvious toxicity to wheat. In summary, 3D EKR achieved a satisfactory and stable remediation effect on Cr-contaminated soil, especially when using S-nZVI as the 3D electrode.

Firing mechanism and benefit evaluation of high-strength fired water permeable brick containing vanadium-titanium iron ore tailings

Introduction: The vanadium-titanium iron ore tailings (VTIOTs) has a significant amount of discharge, and serious pollution, which makes it difficult to use directly as a resources resource.Methods: High-strength fired water permeable brick (HSFWPB) was prepared using VTIOTs as the main raw material. The orthogonal test, X-ray diffraction analysis (XRD), scanning electron microscope (SEM), energy dispersive spectrometry (EDS), and synthetic precipitation leaching procedure (SPLP) were obtained to study the basic properties and firing mechanism of HSFWPB containing VTIOTs, and an economic benefit evaluation was conducted on the project investment of HSFWPB containing VTIOTs.Results: The results show that when the content of VTIOTs in HSFWPB is 78%, the firing temperature (FT) is 1080°C and the holding time is 120 min, the compressive strength and permeability coefficient of the fired product reach 70.4 MPa and 0.055 cmˑs−1, respectively, which meet the requirements of Cc60 grade products in Water permeable brick (JC/T 945–2005). The products of HSFWPB containing VTIOTs after firing are diopside (CaMgSi2O6) and augite (Ca (Mg, Fe, Al) (Si, Al)2O6), with the increase of FT and the extension of HT, the low melting point elements of P, Na, K dissolve out, and the content of Fe and Al in the firing products increases, most of Ca2+ in diopside is replaced by Fe3+, so that augite becomes the main crystal phase. With the increase of FT, the pores in the fired products are changed from: closed pores with different sizes→ connected pores with irregular diameters→ irregular collapse pores→ small and uniform circular pores, which provides a guarantee for the permeability of HSFWPB containing VTIOTs.Discussion: The full investment payback period of the project of HSFWPB containing VTIOTs is 1.77 years. When the production reaches 48.585% of the design output, it reaches a breakeven point, and the project has strong risk resistance ability. The research has improved the utilization rate of VTIOTs and provided a new approach for the large-scale application of VTIOTs.

Effects of simulated acid rain and carbon-rich water on mercury mobilization in soils amended with aluminum-based drinking water treatment residuals

Mercury (Hg) contamination in soils is of concern because of its known adverse effects on ecosystem functions and human health. Research on how to reduce Hg contamination in soil is still needed, mainly because of the difficulties in remediating Hg-contaminated soils while minimizing adverse effects on treated systems. We investigated the potential of a waste substrate, aluminum (Al)-based drinking water treatment residuals (Al-WTRs), as a low-cost sorbent for immobilizing the mobile fraction of Hg in contaminated soils using column leaching studies. Because of the known role of acidic deposition and dissolved organic matter on the environmental cycling of Hg, columns packed with Hg-contaminated alluvial soils collected from the watershed of Poplar Creek in Tennessee of USA were leached using either the synthetic precipitation leaching procedure (SPLP) to simulate the effects of acid rain or low pH dissolved organic carbon (DOC) rich river water (Suwannee River water, pH 4.20) to mimic soil flooding events with DOC-rich waters. The results show that, for soils with very high mobile Hg fractions, control columns without Al-WTR leached with the SPLP solution retained only 51% of total-Hg, which was significantly less (p ​< ​0.05) than in the Al-WTR treated soil columns (up to 80%). Leaching with DOC-rich river water (53.3 ​mg ​C/L) decreased the sorption capacity of Al-WTR. Using waters with increasing DOC concentrations (from 5.33 to 40 ​mg ​C/L) resulted in the removal of 63% of the initial mass of Hg in the control columns compared to 22–29% in the columns amended with 2 and 5% Al-WTR. Overall, Al-WTR can immobilize Hg under extreme leachability conditions and should be considered as a potential sorbent for in situ remediation of Hg-contaminated soils. However, further studies are needed on the fate of Al-WTR-immobilized Hg.

Basic characteristics and environmental impact of iron ore tailings

Introduction: In our study, various test methods were adopted to explore the mineralogical characteristics, grindability, particle morphology, particle size distribution, and environmental leaching toxicity of iron ore tailings (lOTs).Methods: The methods include petrographic analysis, X-ray diffraction (XRD), scanning electronic microscopy (SEM), synchronous thermal analyzer (DSC-TGA), electron probe X-ray microanalyser (EPMA), and synthetic precipitation leaching Procedure (SPLP).Results: The results show that the used IOTs contained 14.54% iron which was mainly stored in magnetite and pyrite. The content of iron silicate accounted for 11.82% of the total iron content. Most of it existed in silicate minerals, including grunerite and hornblende. A small amount of iron was contained in biotite, chlorite and augite. Besides, the grindability of lOTs was much better than that of granulated blast furnace slag (GBFS). After grinding for 140 min, the mass fraction of lOTs particles with the particle size less than 5 um was 44.19%. These particles could be used to fill in the voids in the cement-powder-packed structure. lOTs also contained a large number of submicron and nanoscale particles.Discussion: With great strength and environmental friendliness, the composite cementitious material (CCM) prepared from lOTs can be well applied to the building material field and environmental remediation.

Combined approach for assessing metal(loid)s leaching, mobility and accumulation in a specific near-neutral (pH) environment of a former Cu-smelting area in the Old Copper Basin, Poland

Topsoils, soil profiles, water, and stream sediments as well as slags and rocks were analyzed to assess the extent and severity of environmental pollution resulting from historical Cu mining and smelting in the vicinity of Leszczyna, Old Copper Basin, SW Poland. Numerous tailings, smelting wastes, and Cu-rich rocks were disposed in the study area, causing long-term leaching and accumulation of various metal(loid)s. Surrounding the anthropogenically impacted area, two types of geochemical background are distinguished, one of which is associated with rocks and soils that are naturally enriched in metal(loid)s and the second one is free of them. The presence of significant anthropogenic changes combined with natural enrichment creates a highly complex environmental situation with regard to different sources of metal(loid)s. Additionally, the ore-hosting carbonate rocks are responsible for specific near-neutral (pH) conditions. With a focus on numerous elements (Cu, Zn, Pb, Ni, As, Cd, Co, Ba, and Cr) we studied spatial and vertical metal(loid)s distributions in soils to determine elements fate under near-neutral conditions. We applied the Synthetic Precipitation Leaching Procedure (SPLP) to evaluate the leaching potential of geogenic and anthropogenic materials and the Acid Neutralization Potential (ANP) test to measure the impact of slags on the pH of local soils. The EDTA extraction indicated high (bio)availability of Cu, Cd, Pb, and Zn, and suggested that metals from Cu-rich rocks are substantially more mobile than these of metallurgical origin. Our data indicate significant metal(loid)s mobility from surface-deposited wastes, especially into soils and stream sediments. The study proves that in the near-neutral conditions wastes are mainly subjected to short-time, rainfall-associated leaching, which is responsible for mobilization of labile metal(loid)s fractions (especially Cu, Pb, Zn, and Cd).

Engineering mechanical properties and mechanism of carbonated solidified lead-cadmium contaminated clay with steel slag curing agent

Recently, treating heavy metal-contaminated soil in a green, effective and harmless way has gradually become a research hotspot and also a difficulty. Hence, this study presents a novel environmentally friendly composite, formed by sodium hydroxide (used as an activator), desulfurized gypsum, and steel slag (S-GS). The main objective of this study is to synthetically evaluate the potential use of S-GS for solidifying Lead-Cadmium contaminated clay under the condition of carbonation curing. Moreover, the samples’ characteristics are investigated according to the tests of unconfined compressive strength (UCS), freeze–thaw cycle, Synthetic Precipitation Leaching Procedure (SPLP), and a series of microscopic tests. The results indicate that the carbonation curing can effectively improve the strength of the S-GS solidified contaminated clay, and also help to reduce the toxic leaching amount of lead and cadmium in samples, mainly due to the formation of carbonate or basic carbonate precipitation of the heavy metal in the process of carbonation, and the heavy metal is stabilized in the soil through adsorption and the packing effects of cementitious substances. Besides, within 120 days, the strength of solidified soil samples increases in the form of a power function with the increasing standing time. But compared with the uncarbonated samples, carbonation curing has an inhibiting effect on the strength growth of samples at longer ages. Additionally, carbonation curing can effectively improve the ability of the freeze–thaw cycle resistance for the S-GS solidified lead-cadmium composite contaminated clay.

Performance and environmental assessment of microsurfacing mixture using the granulated Blast-Furnace Slag Powder (GBSP) as potential recycled filler

One of the best methods for preventive maintenance of roads is using microsurfacing. The present research focuses on the effect of using Granulated Blast-Furnace Slag Powder (GBSP) as the replacement for Natural Aggregate Filler (NAF) on the performance of microsurfacing mixture. For this purpose, tests such as Wet Cohesion Test, Wet Track Abrasion Test, Loaded Wheel Test-Displacement, and Loaded Wheel Test-Sand Adhesion were performed in five groups. These groups consisted of microsurfacing mixtures containing 10 % NAF (control mixture), 7.5 % NAF + 2.5 % GBSP, 5 % NAF + 5 % GBSP, 2.5 % NAF + 7.5 % GBSP and 10 % GBSP based on the total weight of aggregates. Next, to evaluate the environmental impact of the mixture, the Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) tests were investigated. The results of the performed tests on the specimens showed that the mixtures containing GBSP improved the microsurfacing mixture performance. Among the mixtures, the one containing 10 % GBSP caused increase in the cohesion, reduction of the vertical Displacement, and reduction in the potential of bleeding by 35 %, 57 % and 48.5 %, respectively. Also the moisture damage resistance of all the mixtures containing GBSP was within the allowable limits of the standard (ASTM D6372). The results of the leaching tests also exhibited that the specimens containing GBSP were environmentally friendly mixtures. So that leakage of all the studied heavy metals was lower than the allowable limits and using them in microsurfacing as replacement for filler up to 10 % is acceptable.

Investigating the use of zinc production wastes as filler in asphalt mixtures

This study aimed to evaluate different types of zinc production wastes for using as filler in asphalt mixtures. Four different types of waste, namely, leach cake, nickel cake, cobalt cake and zinc ash have been chosen along with limestone powder as the control filler for evaluation. Elemental analysis of the fillers, the rheological properties of the mastics and some mechanical properties of the mixtures using Marshall and indirect tensile strength (ITS) tests and their environmental effects using Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) tests have been investigated. Results show that, except the nickel cake, for which the cadmium concentration exceeds the legal limit, rest of the fillers can be used as filler in asphalt concrete. The zinc ash filler results in much better performance than the other fillers. Leach and cobalt cake are found to be hydrophilic with low resistance against moisture damage.

Combined Treatment of Cr(VI)-Contaminated Soils by Reduction, Adsorption, and Solidification

Remediation of Cr(VI)-contaminated soil usually includes reducing Cr(VI) to Cr(III) with sub-sequent solidification. In this paper, a treatment technique that combines reduction, adsorption, and solidification was proposed. By introducing an adsorbent into the reduction process, the remediation effectiveness was improved and the amount of reducing and solidified agent was decreased. Synthetic precipitation leaching procedure (SPLP), unconfined compressive strength (UCS) test, and scanning electron microscope (SEM) analysis were carried out to evaluate the remediation effect under different agent combinations and different agent-adding procedures. The results of SPLP showed that the reduction/adsorption/solidification treatment significantly reduced the leachability of Cr. UCS increased with increasing dosage of cement and CaS5, and decreased with an increasing dosage of vermiculite. The best agent dosage was CaS5 of 2 times molar stoichiometric ratio of Cr(VI), 15% of vermiculite, and 20% of cement. Orthogonal test showed that for soil with low Cr(VI) content, CaS5 dosage was the most important factor that affected the leachability of Cr. Cement and vermiculite have greater impact in limiting the leachability of Cr when Cr(VI) content in soil increased.

Remediation of uranium-contaminated acidic red soil by rice husk biochar.

Uranium (U) in the U-contaminated acidic red soil exhibits high mobility. In the present study, rice husk was used to produce biochar to remediate U-contaminated red soil under acid precipitation. Firstly, batch adsorption experiments showed that the dissolution of alkaline substance in biochar could buffer the pH value of acidic solution. The equilibrium pH value had a crucial influence on biochar adsorption capacity of U, and the neutral equilibrium pH value was favorable for adsorption. Then, the incubation experiments of red soil with biochar were performed, and the Synthetic Precipitation Leaching Procedure (SPLP) extraction of amended red soil showed that the short-term leachability of U was decreased from 26.53% in control group (without biochar) to 1.40% in 10% biochar-amended red soil. Subsequently, the sequential extraction showed that the fraction of U was mainly transformed from exchangeable and Fe/Mn oxide fraction to carbonate fraction after biochar amendment, and the total amount of exchangeable U and carbonate fraction U in soil was increased slightly. Finally, simulated acid rain leaching experiments showed that the capability of amended red soil to resist acid rain acidification was enhanced. And the long-term leachability of U in amended red soil was decreased from 26.37% in control group to 3.18% in the 10% biochar-amended red soil under the simulated acid rain leaching conditions. In conclusion, biochar has passivation effect on U in U-contaminated red soil, which can reduce the long-term and short-term mobility of U in acidic environments. This study provided an experimental basis for the application of biochar in remediation and improvement of U-contaminated acidic red soil.

Simultaneous removal of arsenate and arsenite in water using a novel functional halloysite nanotube composite.

This work aims at exploring a novel environment-friendly nanomaterial based on natural clay minerals for arsenic removal in aqueous samples. Halloysite nanotubes (HNTs) were selected as the substrate with Mn oxides loaded on the surface to enhance its arsenic adsorption ability and then grafted onto the SiO2-coated Fe3O4 microsphere to get a just enough magnetic performance facilitating the material's post-treatment. The prepared composite (Fe3O4@SiO2@Mn-HNTs) was extensively characterized by various instruments including Fourier transform infrared spectroscope (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TG), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscope (XPS), and X-ray diffraction (XRD). Batch experiments were carried out to get the optimum test conditions for arsenic adsorption by the composite, including pH, loading amount of Mn oxides, adsorbent dosage, and the co-existing ions. The adsorption of AsIII and AsV on Fe3O4@SiO2@Mn-HNTs were both well fitted with the pseudo-second-order kinetic model as well as the Langmuir adsorption isotherm model revealing the chemisorption between arsenic and Fe3O4@SiO2@Mn-HNTs. The adsorption process of AsIII and AsV were both endothermic and spontaneous displayed by the thermodynamic study. The capacities of the prepared composite are 3.28mgg-1 for AsIII and 3.52mgg-1 for AsV, respectively, which are comparable or better than those of many reported materials in the references. Toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) tests were carried out to access the secondary environmental risk of the composite and showed that it was quite environmentally stable and can be safely disposed. The composite was successfully applied in environmental water samples indicating its great potential applicability in future.

Leaching of heavy metals from wood biomass ash, before and after binding in cement composite

Wood ash is a complex mixture of inorganic and organic compounds. It is heterogeneous in composition, which can vary considerably. Ash is mainly disposed of in landfills, which creates a risk for air, soil and groundwater contamination by trace elements. In order for wood biomass ash to be used as a secondary raw material, it is necessary to perform leaching tests, to determine which microelements it contains, and which of them could be released into the environment during the ash disposal. Sequential extraction (SE) showed that in the exchangeable and carbonate fraction, the most volatile metals As, Cd, Zn and Pb are released the most from the ash of deciduous trees, while the leaching of ash from coniferous trees is significantly lower. The evaluation of risk assessment code (RAC) for the tested biomass ash samples, indicates that Pb is a high-risk leaching element due to its condensation on the ash particles. By performing toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) tests, it was established that the released concentrations of tested metals are below the maximum allowable concentration, given by the regulation. The leaching tests of composites, prepared from wood ash in combination with cement, indicate that the leaching of ash is reduced to a minimum, and that all heavy metals are bound in a cement matrix, which indicates the possibility of using wood ash for construction purposes.

Properties and heavy metal leaching characteristics of leachate sludge-derived biochar.

Heavy metals and metalloids, in sludge and sediments, are environmental pollutants of concern with long-term negative effects on human and ecological health. In this study, sludge from biological treatment of municipal waste leachate was pyrolyzed into leachate sludge-derived biochar (LSDB) at 300°C to 900°C, comprising complex organic and inorganic (particularly heavy metals) species formed from heterogeneous chemical reactions. Based on different advanced material analyses, that is, Thermogravimetric Analysis (TGA), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis, this study revealed that mass loss and microstructural changes of LSDBs occurred primarily due to decomposition of volatiles, aromatic rings, carbonates, and hydroxides. The leaching behaviors of heavy metals from LSDBs were evaluated using the Synthetic Precipitation Leaching Procedure (SPLP). The final pH in SPLP increased from 7.5 to 12.5 with pyrolysis temperature. The pH increase favored the retention of heavy metals in the LSDBs due to the formation of low soluble precipitates at alkaline pH. The heavy metals and metalloids in the LSDBs were present as surface precipitates due to precipitation and cation exchange rather than surface complexation. The leaching contents of metals and metalloids, such as Cr, Cd, Ni, Pb, and As, were all below their respective maximum discharge standards for the first priority pollutants in China.

Desorption and Migration Behavior of Beryllium from Contaminated Soils: Insights for Risk-Based Management.

Factors influencing the desorption, distribution, and vertical migration behavior of Be in contaminated soils are not fully understood. This study examined the desorption and migration of Be in a soil profile from a legacy radioactive waste disposal site using different batch leaching [monofilled waste extraction procedure (MWEP); synthetic precipitation leaching procedure (SPLP); simulated acid rain solution (SARS); and toxicity characteristic leaching procedure] and sequential leaching [community bureau of reference (BCR)] methods for insights relevant to the application of risk-based management. The results showed that Be desorption was higher in the presence of organic than the inorganic leachate composition (MWEP < SPLP < SARS < TCLP < BCR first-step). The desorption followed three diffusion control mechanisms, which resulted in three desorption rate constant estimates of 157, 87.1, and 40.4 Be/kg.h0.5, and the estimated desorption maximum was 556 μg/kg. The desorption process was, spontaneous (ΔG > 0), enthalpically and entropically influenced. Increasing the incubation period and heat treatment resulted in a decrease of Be desorption and migration. The soil clay content and pH were the primary factors influencing Be desorption, and the results suggested that Be was desorbed from metal oxyhydroxides and surfaces of silicates (e.g., reactive surfaces of clay minerals), organic matters, and soil pores. Because of high Kd values, the mobility of Be was limited, and no exceedances of ecological or human health risk index or guidelines were determined for the current contamination levels at the site. However, Be released from the waste trenches has the ongoing potential to increase Be concentration in the soil.

Behavior of potentially toxic elements from stoker-boiler fly ash in Interior Alaska: paired batch leaching and solid-phase characterization

Despite significant investigation of fly ash spills and mineralogical controls on the release of potentially toxic elements (PTEs) from fly ash, interactions with the surficial environment remain relatively poorly understood. We conducted 90-day batch leaching studies with paired analysis of supernatant and solid-phase mineralogy to assess the elemental release and transformation of fly ash upon reaction with aquatic media (18 MΩ cm−1 water and simulated rainwater). The fly ash in this study, collected from the University of Alaska Fairbanks stoker-boiler power plant, is high in unburned carbon (~20% LOI) and highly enriched in several PTEs relative to the upper continental crust. Supernatant concentrations of oxyanion-forming elements (e.g., As, Se, Mo, Sb) remained relatively low and constant, suggesting equilibrium with the solid phase, possibly ettringite [Ca6Al2(SO4)3(OH)12•26H2O], which is known to incorporate and sorb oxyanion-forming PTEs and was identified by X-ray diffraction. Synthetic precipitation leaching procedure (SPLP) results failed to capture important temporal trends. Lead and Ba supernatant concentrations consistently exceeded drinking water standards, as well as others upon exposure to simulated physiological solutions. Seven-day experiments with dissolved organic matter-isolate solutions indicated that for certain elements, liberation was influenced by carbon concentration and/or the identity of the isolate. Overall, this paired approach can serve as a model for future studies, bridging existing gaps between batch leaching and single-element mineralogical, sorption, or speciation studies.

Investigating the potential for microbially induced carbonate precipitation to treat mine waste

In this study, the feasibility of promoting microbially induced carbonate precipitation (MICP) in mine waste piles by using an environmental bacterial enrichment is explored, with goals to reduce metals and acid leaching. MICP has been explored for remediation applications and stabilization of mine waste. Here, we utilize a native bacterial enrichment to promote MICP on seven mine waste samples with variability in acid production and extent of toxic metal leaching. During fifteen applications of MICP solutions and bacteria on waste rock in bench-scale columns, calcium carbonate formed on grain surfaces within all waste samples, though microscopy revealed uneven distribution of CaCO3 coating. The effluent from acid-producing wastes increased in pH during MICP treatment. MICP performance was evaluated with humidity cell and synthetic precipitation leaching procedure (SPLP) tests. Leaching tests revealed reductions in Cd, Pb and Zn concentrations in leachate of all but one sample, mixed results for Cu, and As increasing in all but one leachate sample after treatment. MICP technology has potential for coating mine waste and reducing release of acid and some metals. This study provides a laboratory assessment of MICP feasibility for stabilizing mine waste in situ and mitigating release of toxic metals into the environment.

Immobilization of lead in tailings by Bacillus subtilis through microbially induced phosphate precipitation (MIPP)

The accumulation of heavy metal tailings has raised serious environmental concerns, especially in China. Therefore, remediation and utilization of heavy metal tailings have become urgent and vital. In this paper, an emerging technology MIPP (microbially induced phosphate precipitation) was applied and the commercial Bacillus subtilis were employed to mitigate the Pb contamination risks in tailings. Through aqueous Pb-removal experiments and tailings remediation experiments, the process and mechanism of MIPP treatment for heavy metal tailings were systematically explored. In addition, the optimal Pb-removal conditions were discussed. The results shows that the commercial Bacillus subtilis can be served as a preferable MIPP-stabilization commercial strain with lower application cost, better heavy metal tolerance, and excellent Pb stabilization compared to traditional strains isolated from contaminated sites. The mobile Pb was almost converted into Pb9(PO4)6 through MIPP treatment contributing to the Pb immobilization. According to SPLP (the synthetic precipitation leaching procedure), the leaching concentration of Pb from tailings dropped from 0.86 mg/L before treatment to less than 0.02 mg/L after MIPP remediation, which is far below China’s groundwater environmental requirements (0.1 mg/L). This technology has the advantages of on-site construction and environmental friendliness. The treated tailings are expected to be safely used as construction sand for road base and mine backfilling.