Fluorine contamination, mobility, and risks in soils at a phosphate-gypsum waste landfill: a new analytical method and comparison with previous methods.

This study used a new X-ray fluorescence (XRF)-based analytical method with better precision and sensitivity to evaluate the fluorine concentrations in soil. It was hypothesized that the XRF method with a pellet-synthesizing procedure may effectively analyze the fluorine concentrations in soil with ease and reliability. The total fluorine concentrations determined using XRF were compared with those determined using three different types of analytical protocols-incineration/distillation, alkaline fusion, and aqua regia extraction procedures. Among the three procedures, the incineration/distillation procedure did not show reliable precision and reproducibility. In contrast, the total fluorine concentrations determined using the XRF analysis were linearly correlated with those determined using the alkaline fusion and aqua regia extraction procedures. Based on the results of the Korean waste leaching procedure and toxicity characteristics leaching procedure, the leachability of fluorine from soil and waste was not directly related to total fluorine concentrations in soil. Risk assessment also revealed that the fluorine-rich soils did not show non-carcinogenic toxic effects, despite exceeding the regulation level (800 mg/kg) in South Korea for total fluorine concentrations in soil. Our results suggest that XRF analysis in combination with the newly developed pretreatment method may be a promising alternative procedure for easily and rapidly determining the total fluorine concentration in soil. However, further efforts are needed to evaluate fluorine leachability and its associated risks in fluorine-contaminated soils.

[Research progress in pharmacological effects of Gypsum Fibrosum and material basis for its heat-clearing effect].

Gypsum Fibrosum, as a classic heat-clearing medicine, is widely used in the clinical practice of traditional Chinese medicine(TCM). However, debates exist about the material basis and mechanism of its efficacy. Therefore, this paper reviewed the recent research progress in the heat-clearing effect and mechanism of Gypsum Fibrosum and discussed the material basis for the heat-clearing effect of this medicine. Ca~(2+) may inhibit the upward movement of temperature set point by regulating the Na~+/Ca~(2+) level in the heat-regulating center. Moreover, trace elements may inhibit the rise of body temperature by regulating the immune system, promoting the absorption of Ca~(2+), and affecting the synthesis of prostaglandin E2(PGE2). This review aims to enrich the knowledge about the mechanism of Gypsum Fibrosum in clearing heat and provides a scientific basis for the clinical application and further development of Gypsum Fibrosum.

Gypsum lichens: A global data set of lichen species from gypsum ecosystems.

Lichens are significant components of the biological soil crust communities in gypsum ecosystems and are involved in several processes related to ecosystem functioning, such as water and nutrient cycles or protection against soil erosion. Although numerous studies centered on lichen taxonomy and ecology have been performed in these habitats, global information about lichen species from gypsum substrates or their distributional ranges at a global scale is lacking. Thus, we compiled a global data set of recorded lichen species growing on gypsum. This review is based on systematic searches in two bibliographic databases (Web of Science and the more specialized database Mattick's Literature Index) using various keywords related to the substrate or ecology (i.e., gypsum, gypsiferous, semiarid, saxicolous, terricolous). In addition, we revised lichen literature from countries with gypsum soils using Mattick's, Hamburg University's Worldwide checklist, and different national lichen checklists. Ultimately the review includes a total of 321 studies. This data set included 6114 specimen records belonging to 336 recorded lichen species from 26 countries throughout the world. The results showed large differences in the number of species recorded among countries, reflecting differences in the sampling effort. We provide a table with the number of studies and species in relation to gypsum surface in order to account for the bias produced by sampling effort. The number of studies carried out per country was not related to the gypsum surface but probably to other factors, such as accessibility to field sampling, economic or political factors, or the presence of a wider community of lichenologists. Thus, Spain and Germany hosted the highest number of recorded species (160 and 114 species, respectively). Outside the European continent, only a few countries had a large number of species: Morocco (46), United States (42), and Iran (37). Remarkably, countries from the southern hemisphere (i.e., Australia, Chile, Namibia, and South Africa) showed a low number of studies from gypsum lands, supporting the stated biases observed in sampling efforts among countries. Considering the most studied countries, the results show that Teloschistaceae was the most represented family in gypsum ecosystems followed by Verrucariaceae and Cladoniaceae. Regarding particular species, Psora decipiens and Squamarina lentigera were some of the most widespread and abundant species in these habitats. This data set constitutes a basic and first step toward a much more comprehensive database, to be periodically updated in future releases, which also serves to identify countries or territories where future studies should be accomplished. There are no copyright restrictions on the data; please cite this data paper if the data are used in publications and teaching events.

Limestone and yellow gypsum can reduce cadmium accumulation in groundnut (Arachis hypogaea): A study from a three-decade old landfill site.

Cadmium (Cd) toxicity has cropped up as an important menace in the soil-plant system. The use of industrial by-products to immobilise Cd in situ in polluted soils is an interesting remediation strategy. In the current investigation, two immobilizing amendments of Cd viz., Limestone (traditionally used) and Yellow gypsum (industrial by-product) have been used through a green-house pot culture experiment. Soil samples were collected from four locations based on four graded levels of DTPA extractable Cd as Site 1 (0.43 mg kg-1), Site 2 (0.92 mg kg-1), Site 3 (1.77 mg kg-1) and Site 4 (4.48 mg kg-1). The experiment was laid out in a thrice replicated Factorial Complete Randomized Design, with one factor as limestone (0, 250, 500 mg kg-1) and the other being yellow gypsum (0, 250, 500 mg kg-1) on the collected soils and groundnut was grown as a test crop. Results revealed that the DTPA-extractable Cd content in soil and Cd concentration in plants decreased significantly with the increasing doses of amendments irrespective of initial soil available Cd and types of amendment used. The effect of amendment was soil specific and in case of Site 1 (low initial Cd) the effect was more prominent. The reduction in DTPA-extractable Cd in combined application of limestone and yellow gypsum @500 mg kg-1 over the absolute control in soil under groundnut for the sites was by far the highest with the values of 83.72%, 77.17%, 48.59% and 40.63% respectively. With the combined application, Target Cancer Risk (TCR) of Cd was also reduced. Hence, combined application of limestone and yellow gypsum can be beneficial in the long run for mitigating Cd pollution.

Ultrafast and highly efficient Cd(II) and Pb(II) removal by magnetic adsorbents derived from gypsum and corncob: Performances and mechanisms.

The utilization of gypsum and biomass in environmental remediation has become a novel approach to promote waste recycling. Generally, raw waste materials exhibit limited adsorption capacity for heavy metal ions (HMIs) and often result in poor solid-liquid separation. In this study, through co-pyrolysis with corncob waste, titanium gypsum (TiG) was transformed into magnetic adsorbents (GCx, where x denotes the proportion of corncob in the gypsum-corncob mixture) for the removal of Cd(II) and Pb(II). GC10, the optimal adsorbent, which was composed primarily of anhydrite, calcium sulfide, and magnetic Fe3O4, exhibited significantly faster adsorption kinetics (rate constant k1 was 218 times and 9 times of raw TiG for Cd(II) and Pb(II)) and higher adsorption capacity (Qe exceeded 200 mg/g for Cd(II) and 400 mg/g for Pb(II)) than raw TiG and previous adsorbents. Cd(II) removal was more profoundly inhibited in a Cd(II) + Pb(II) binary system, suggesting that GC10 showed better selectivity for Pb(II). Moreover, GC10 could be easily separated from purified water for further recovery, due to its high saturation magnetization value (6.3 emu/g). The superior removal capabilities of GC10 were due to adsorption and surface precipitation of metal sulfides and metal sulfates on the adsorbent surface. Overall, these waste-derived magnetic adsorbents provide a novel and sustainable approach to waste recycling and the deep purification of multiple HMIs.

Gypsum amendment of agricultural fields to decrease phosphorus losses - Evidence on a catchment scale.

Amending agricultural fields with gypsum has been proposed as a cost-effective measure to reduce P load on coastal waters. We treated 1490 ha of clayey fields with phosphogypsum (4 t ha-1) in Southwest Finland and monitored the recipient river with online sensors and water sampling for the preceding spring and 5 years after the amendment. Gypsum immediately decreased the riverine fluxes, the effect lasting at least 5 years for particulate P (PP), total suspended solids (TSS), and dissolved organic C (DOC) and 1-2 years for dissolved reactive P (DRP). Compared with an upstream control area, the fluxes of PP, TSS, and DOC decreased by 15%, 25%, and 8.9%, respectively, as a 5-year average. Assuming the change in the fluxes occurred only due to gypsum, the amended fields showed 35%, 59%, and 64% lower losses for PP, TSS, and DOC than the unamended ones. More than half of the gypsum remained in the soil even after 5 years; thus, although the efficiency of gypsum lessened over time, its residual effect may be present. However, the difference in the erodibility between the control and treatment areas impacted the validity of the results, especially as the pre-gypsum period was short. In addition, the performance of gypsum showed spatial variation.

Assessing the hepatotoxicity of phosphogypsum leachate in zebrafish (Danio rerio).

The improper disposal of large amounts of phosphogypsum generated during the production process of the phosphorus chemical industry (PCI) still exists. The leachate formed by phosphogypsum stockpiles could pose a threat to the ecological environment and human health. Nevertheless, information regarding the harmful effects of phosphogypsum leachate on organisms is still limited. Herein, the physicochemical characteristics of phosphogypsum leachate were analyzed, and its toxicity effect on zebrafish (Danio rerio), particularly in terms of hepatotoxicity and potential mechanisms, were evaluated. The results indicated that P, NH3-N, TN, F-, As, Cd, Cr, Co, Ni, Zn, Mn, and Hg of phosphogypsum leachate exceeded the V class of surface water environmental quality standards (GB 3838-2002) to varying degrees. Acute toxicity test showed that the 96 h LC50 values of phosphogypsum leachate to zebrafish was 2.08 %. Under exposure to phosphogypsum leachate, zebrafish exhibited concentration-dependent liver damage, characterized by vacuolization and infiltration of inflammatory cells. The increased in Malondialdehyde (MDA) content and altered activities of antioxidant enzymes in the liver indicated the induction of oxidative stress and oxidative damage. The expression of apoptosis-related genes (P53, PUMA, Caspase3, Bcl-2, and Bax) were up-regulated at low dosage group and down-regulated at medium and high dosage groups, suggesting the occurrence of hepatocyte apoptosis or necrosis. Additionally, phosphogypsum leachate influenced the composition of the zebrafish gut microbiota by reducing the relative abundance of Bacteroidota, Aeromonas, Flavobacterium, Vibrio, and increasing that of Rhodobacter and Pirellula. Correlation analysis revealed that gut microbiota dysbiosis was associated with phosphogypsum leachate-induced hepatotoxicity. Altogether, exposure to phosphogypsum leachate caused liver damage in zebrafish, likely through oxidative stress and apoptosis, with the intestinal flora also playing a significant role. These findings contribute to understanding the ecological toxicity of phosphogypsum leachate and promote the sustainable development of PCI.

Rare Earth Extraction from Phosphogypsum by Aspergillus niger Culture Broth.

The extraction of rare earth elements (REEs) from phosphogypsum (PG) is of great significance for the effective utilization of rare earth resources and enhancing the resource value of PG waste residues. This study used Aspergillus niger (A. niger) fungal culture filtrate as a leaching agent to investigate the behavior of extracting REEs from PG through direct and indirect contact methods. According to the ICP-MS results, direct leaching at a temperature of 30 °C, shaking speed of 150 rpm, and a solid-liquid ratio of 2:1, achieved an extraction rate of 74% for REEs, with the main elements being yttrium (Y), lanthanum (La), cerium (Ce), and neodymium (Nd). Under the same conditions, the extraction rate of REEs from phosphogypsum using an A. niger culture filtrate was 63.3% higher than that using the simulated organic acid-mixed solution prepared with the main organic acid components in the A. niger leachate. Moreover, the morphological changes observed in A. niger before and after leaching further suggest the direct involvement of A. niger's metabolic process in the extraction of REEs. When compared to using organic acids, A. niger culture filtrate exhibits higher leaching efficiency for extracting REEs from PG. Additionally, using A. niger culture filtrate is a more environmentally friendly method with the potential for industrial-scale applications than using inorganic acids for the leaching of REEs from PG.

Visualization of water transfer channel in sludge dewatering conditioned with skeleton builders by X-ray micro-computed tomography.

Skeleton builders were normally deemed to improve the high porosity and newly-generated permeability of sludge cakes by building water transfer channel during high pressure filtration, thus enhancing sludge dewaterability. However, currently a direct visualization proof of water transfer channel was still lacking. This study provided the direct proof for visualizing water transfer channel in dewatered sludge cakes conditioned with a typical skeleton builder (i.e., phosphogypsum (PG)) by X-ray micro-computed tomography (micro-CT) for the first time. After the addition of PG, the pixel value and image luminance increased significantly, indicating the presence of high density substances from both two-dimensional (2D) cross section and three-dimensional (3D) reconstruction CT images. Moreover, the CT numbers showed strong and negative correlations with specific resistance to filtration (SRF) (R = - 0.99, p < 0.05), capillary suction time (CST) (regression coefficient (R) = - 0.87, probability (p) < 0.05), and water content of the dewatered sludge cake (R = - 0.99, p < 0.05), respectively. These results indicated that the X-ray micro-CT could be a potential technique for analyzing the water distribution in sludge samples conditioned with skeleton builders.

Research on the inhibitory properties and mechanism of carboxymethyl cellulose-modified sulfur quantum dots towards calcium sulfate and calcium carbonate.

An eco-friendly antimicrobial sulfur quantum dot scale inhibitor (CMC-SQDs) synthesized using carboxymethyl cellulose (CMC) showed strong inhibition of calcium sulfate (CaSO4) at a concentration just below 1 mg/L, with an inhibition efficiency exceeding 99 %. However, the precise interaction process between CMC-SQDs and CaSO4 remains unclear. This article investigates the effectiveness of SQDs in inhibiting the formation of CaSO4 and calcium carbonate (CaCO3) scales. Through static scale inhibition tests, molecular dynamics simulations, and quantum chemical calculations, the study aims to elucidate the different impacts of CMC-SQDs on CaSO4 and CaCO3 scale formation. The research focuses on understanding the relationship between the structural activity of CMC-SQDs and their scale-inhibiting performance and delving into the underlying mechanisms of scale inhibition. The findings describe the role of SQDs in a water-based solution, acting as persistent "nanodusts" that interact with calcium (Ca2+) ions and sulfate ions. CMC forms complexes with Ca2+ ions, and the presence of SQDs enhances the van der Waals force, indirectly increasing the resistance of associated ions and the binding energy on the surface of precipitated gypsum. Conversely, SQDs exhibit weak surface stability and have minimal binding energy when interacting with calcite, leading to limited occupation of available adsorption sites.

hsa_circ_0008500 regulates Benzo(a)pyrene-loaded gypsum-induced inflammation and apoptosis in human bronchial epithelial cells via activation of Ahr/C-myc pathways.

Polycyclic aromatic hydrocarbons (PAHs) are major organic pollutants attached to fine particulate matter in the atmosphere. They induce lung inflammation, asthma, and other lung diseases. Exploring the toxic mechanism of PAHs on lung epithelial cells may provide a theoretical basis for the prevention and treatment of respiratory diseases induced by PAHs. In our study, 16 human bronchial epithelial (16HBE) cells were exposed to different concentrations of gypsum dust, Benzo(a)pyrene (BaP), and BaP-loaded gypsum dust for 24 hours. Gypsum dust loaded with BaP significantly increased the cytotoxicity of 16HBE cells, enhanced the production of lactate dehydrogenase (LDH), interleukin-6 (IL-6) and interleukin-8 (IL-8), induced cell apoptosis, and upregulate the expression of hsa_circ_0008500 (circ_0008500). The mechanism was studied with a BaP-loaded gypsum dust concentration of 1.25 mg/mL. StemRegenin 1 (SR1) pretreat significantly reduced the release of LDH, IL-6, and IL-8 and decreased the protein levels of Ahr、XAP2, C-myc, and p53. Second-generation sequencing indicated that circ_0008500 was highly expressed after 16HBE induced by BaP-loaded gypsum dust. Functional experiments confirmed that circ_0008500 promoted the inflammation and apoptosis of 16HBE cells induced by BaP-loaded gypsum dust by regulating the Ahr signaling pathway. Our study showed that fine particulate matter adsorption of BaP significantly increased the toxic effect of BaP on cells. By activating the Ahr/C-myc pathway, circ_0008500 promoted inflammation and apoptosis of 16HBE cells induced by BaP-loaded gypsum dust.

The effect of casing and gypsum on the yield and psychoactive tryptamine content of Psilocybe cubensis (Earle) Singer.

Psychedelic fungi have experienced a surge in interest in recent years. Most notably, the fungal secondary metabolite psilocybin has shown tremendous promise in the treatment of various psychiatric disorders. The mushroom species that produce this molecule are poorly understood. Here we sought to examine for the first time, the response of a psilocybin-producing species Psilocybe cubensis to casing (peat moss and vermiculite) and supplementation with gypsum (calcium sulfate dihydrate), two common practices in commercial mushroom cultivation. Mycelial samples of genetically authenticated P. cubensis were used to inoculate popcorn grain bags. The fully colonized bags of popcorn grain (0.15 kg) were transferred to bins of 0.85 kg pasteurized horse manure, with or without 1 cm thick layer of casing and/or 5 % gypsum. Our results indicate that the use of a casing layer significantly increases the biological efficiency (161.5 %), by approximately four fold, in comparison to control (40.5 %), albeit with a slight delay (∼2 days) for obtaining fruiting bodies and a somewhat reduced total tryptamine content (0.85 %) as gauged by High Performance Liquid Chromatography measurements. Supplementation with both casing and gypsum, however, appears to promote maximal yields (896.6 g/kg of dried substrate), with a biological efficiency of 89.6 %, while also maintaining high total tryptamine expressions (0.95 %). These findings, revealing methods for maximizing yield of harvest and expressions of psychoactive tryptamines, may prove useful for both home growers and commercial cultivators of this species, and ultimately support the growth of a robust industry with high quality natural products.

Innovative methodology for comprehensive utilization of arsenic-bearing neutralization sludge.

Arsenic-bearing neutralization (ABN) sludge is a classical hazardous waste commonly found in nonferrous metallurgy. However, the current storage of these hazardous wastes not only has to pay costly hazardous waste taxes but also poses significant risks to both the environment and human health. To address these issues and achieve the comprehensive utilization and minimization of ABN sludge, this study proposes a new combined process. The process involves selective reduction roasting, leaching, and carbonation, through which, the arsenate and gypsum in the ABN sludge were recovered in the form of As(s), high-purity CaCO3, and H2S. The selective reduction behaviors of arsenate and gypsum were investigated through thermodynamic analysis and roasting experiments. The results indicated that the 95.35 % arsenate and 96.55 % gypsum in the sludge were selectively reduced to As4(g) and CaS at 950 °C by carbothermic reduction. The As4(g) was condensed to As(s) and enriched in the dust (As, 96.78 wt %). In the leaching process, H2S gas was adopted to promote the leaching of CaS, and resulted in 97.41 % of CaS in the roasted product was selectively leached in the form of Ca(HS)2, leading to a 74.11 % reduction in the weight of the ABN sludge. Then, the Ca(HS)2 was subjected to capture CO2 for the separation of Ca2+ and S2-. The result depicted that 99.69 % of Ca2+ and 99.12 % of S2- were separated as high-purity (99.12 wt %) CaCO3 and H2S (24.89 vol %) by controlling the terminal carbonation pH to below 6.55. The generated H2S can be economically converted to sulfur by the Clause process. The whole process realized the comprehensive resource recovery and the minimization of the sludge, which provides an alternative solution for the clean treatment of hazardous ABN waste.

Preferentially Biodegradable Gypsum Fibers Endowing Invisible Microporous Structures and Enhancing Osteogenic Capability of Calcium Phosphate Cements.

It is known that hydroxyapatite-type calcium phosphate cement (CPC) shows appreciable self-curing properties, but the phase transformation products often lead to slow biodegradation and disappointing osteogenic responses. Herein, we developed an innovative strategy to endow invisible micropore networks, which could tune the microstructures and biodegradation of α-tricalcium phosphate (α-TCP)-based CPC by gypsum fibers, and the osteogenic capability of the composite cements could be enhanced in vivo. The gypsum fibers were prepared via extruding the gypsum powder/carboxylated chitosan (CC) slurry through a 22G nozzle (410 µm in diameter) and collecting with a calcium salt solution. Then, the CPCs were prepared by mixing the α-TCP powder with gypsum fibers (0-24 wt %) and an aqueous solution to form self-curing cements. The physicochemical characterizations showed that injectability was decreased with an increase in the fiber contents. The µCT reconstruction demonstrated that the gypsum fiber could be distributed in the CPC substrate and produce long-range micropore architectures. In particular, incorporation of gypsum fibers would tune the ion release, produce tunnel-like pore networks in vitro, and promote new bone tissue regeneration in rabbit femoral bone defects in vivo. Appropriate gypsum fibers (16 and 24 wt %) could enhance bone defect repair and cement biodegradation. These results demonstrate that the highly biodegradable cement fibers could mediate the microstructures of conventional CPC biomaterials, and such a bicomponent composite strategy may be beneficial for expanding clinical CPC-based applications.

Comparison of different bone substitutes in the repair of rat calvaria critical size defects: questioning the need for alveolar ridge presentation.

OBJECTIVE: This study aimed to evaluate the effectiveness of biomaterials in bone healing of critical bone defects created by piezoelectric surgery in rat calvaria. METHOD AND MATERIALS: Histomorphologic analysis was performed to assess bone regeneration and tissue response. Fifty animals were randomized into five groups with one of the following treatments: Control group (n = 10), spontaneous blood clot formation with no bone fill; BO group (Bio-Oss, Geistlich Pharma; n = 10), defects were filled with bovine medullary bone substitute; BF group (Bonefill, Bionnovation; n = 10), defects were filled with bovine cortical bone substitute; hydroxyapatite group (n = 10), defects were filled with hydroxyapatite; calcium sulfate group (n = 10), defects were filled with calcium sulfate. Five animals from each group were euthanized at 30 and 45 days. The histomorphometry calculated the percentage of the new bone formation in the bone defect. RESULTS: All data obtained were evaluated statistically considering P < .05 as statistically significant. The results demonstrated the potential of all biomaterials for enhancing bone regeneration. The findings showed no statistical differences between all the biomaterials at 30 and 45 days including the control group without bone grafting. CONCLUSION: In conclusion, the tested biomaterials presented an estimated capacity of osteoconduction, statistically nonsignificant between them. In addition, the selection of biomaterial should consider the specific clinical aspect, resorption rates, size of the particle, and desired bone healing responses. It is important to emphasize that in some cases, using no bone filler might provide comparable results with reduced cost and possible complications questioning the very frequent use of ridge presentation procedures.

A Comparative Evaluation of Three Methods of Disinfection of Gypsum Casts and the Changes in Surface Roughness and Dimensional Accuracy after Disinfection-An Ex Vivo Study.

BACKGROUND: One of the major problems of everyday dental practice is cross-contamination. It can place office personnel, dentists, and patients at risk of acquiring serious illness. Disinfection helps in controlling this cross-contamination to an extent. The evaluation was done to find the efficient disinfection method on gypsum casts. AIMS: The aim of this study is to evaluate and compare the efficacy of three methods of disinfection of gypsum casts, namely, chemical disinfection by immersion, spray method, and microwave method, and also to evaluate and compare changes in surface roughness and dimensional accuracy between the three methods after disinfection. MATERIALS AND METHODS: Ex vivo and experimental study. Thirty participants were selected, and impressions of the maxillary arch were made using polyvinyl siloxane impression material. Ninety type IV die stone gypsum casts were poured. It was divided into three groups and was subjected to chemical disinfection by immersion and spray methods, and microwave method. The disinfected casts were evaluated for microbial growth, surface roughness, and dimensional accuracy. It was performed by using the one-way analysis of variance test and paired t-test followed by the Kruskal - Wallis test and Wilcoxon signed rank test (α = 0.05). RESULTS: Microwave disinfection was more effective than both immersion and spray chemical disinfection methods (P < 0.010 and <0.001). The surface roughness of the microwave-irradiated casts had significantly increased after disinfection. However, there were no significant dimensional changes by any of the methods of disinfection. CONCLUSION: Within the limitations of the study, the microwave method of disinfection is more effective in eradicating microorganisms when compared to chemical methods of disinfection by immersion and spray methods.

Mineralogical transformation of arsenic at different copper smelting workshops: The impact on arsenic bioaccessibility.

Soil arsenic (As) contamination associated with the demolition of smelting plants has received increasing attention. Soil As can source from different industrial processes, and also participate in soil weathering, making its speciation rather complex. This study combined the usage of chemical sequential extraction and advanced spectroscopic techniques, e.g., time of flight secondary ion mass spectrometry (ToF-SIMS), to investigate the mineralogical transformation of soil As at different processing sites from a typical copper smelting plant in China. Results showed that the stability of arsenic species decreased following the processes of storage, smelting, and flue gas treatment. Arsenic in the warehouse area was incorporated into pyrite (FeS2) as well as its secondary minerals such as jarosite (KFe3(SO4)2(OH)6). At the smelting area, a large proportion of As was adsorbed by iron oxides from smelting slags, while some As existed in stable forms like orpiment (As2S3). At the acid-making area, more than half of As was adsorbed on amorphous iron oxides, and some were adsorbed on the flue gas desulfurization gypsum. More importantly, over 86% of the As belonged to non-specifically and specifically adsorbed fractions was found to be bioaccessible, highlighting the gypsum-adsorbed As one of the most hazardous species in smelting plant soils. Our findings indicated the importance of iron oxides in As retention and suggested the potential health risk of gypsum-adsorbed As. Such detailed knowledge of As speciation and bioaccessibility is vital for the management and remediation of As-contaminated soils in smelting plants.

Effects of the three amendments on NH3 volatilization, N2O emissions, and nitrification at four salinity levels: An indoor experiment.

The marked salinity and alkaline pH of coastal saline soil profoundly impact the nitrogen conversion process, leading to a significantly reduced nitrogen utilization efficiency and substantial gaseous nitrogen loss. The application of soil amendments (e.g. biochar, manure, and gypsum) was proved to be effective for the remediation of saline soils. However, the effects of the three amendments on soil nitrogen transformation in soils with various salinity levels, especially on NH3 volatilization and N2O emission, remain elusive. Here, we reported the effects of biochar, manure, and gypsum on NH3 volatilization and N2O emission under four natural salinity gradients in the Yellow River Delta. Also, high-throughput sequencing and qPCR analysis were performed to characterize the response of nitrification (amoA) and denitrification (nirS, nirK, and nosZ) functional genes to the three amendments. The results showed that the three amendments had little effect on NH3 volatilization in low- and moderate-salinity soils, while biochar stimulated NH3 volatilization in high-salinity soils and reduced NH3 volatilization in severe-salinity soils. Spearman correlation analysis demonstrated that AOA was significantly and positively correlated with the NO3--N content (r = 0.137, P < 0.05) and N2O emissions (r = 0.174, P < 0.01), which indicated that AOA dominated N2O emissions from nitrification in saline soils. Structural equation modeling indicated that biochar, manure, and gypsum affected N2O emission by influencing soil pH, conductivity, mineral nitrogen content, and functional genes (AOA-amoA and nosZ). Two-way ANOVA further showed that salinity and amendments (biochar, manure, and gypsum) had significant effects on N2O emissions. In summary, this study provides valuable insights to better understand the effects of gaseous N changes in saline soils, thereby improving the accuracy and validity of future GHG emission predictions and modeling.

Study on inverse geochemical modeling of hydrochemical characteristics and genesis of groundwater system in coal mine area - a case study of Longwanggou Coal Mine in Ordos Basin.

The exploitation of coal resources has disturbed the equilibrium of the original groundwater system, resulting in a perturbation of the deep groundwater dynamic conditions and hydrochemical properties. Exploring the formation of mine water chemistry under the conditions of deep coal seam mining in the Ordos Basin provides a theoretical basis for the identification of sources of mine water intrusion and the development and utilization of water resources. This paper takes Longwanggou Coal Mine as the research area, collects a total of 106 groups of water samples from the main water-filled aquifers, comprehensively uses Piper trilinear diagram, Gibbs diagram, ion correlation, ion ratio coefficient and mineral saturation index analysis, and carries out inverse geochemical modeling with PHREEQC software, so as to analyze the hydrochemical characteristics and causes of the main water-filled aquifers in deep-buried coal seams in the research area. The results show that the main hydrochemical processes in the study area are leaching and cation exchange, and the groundwater is affected by carbonate (calcite, dolomite), silicate (gypsum) and evaporite. Calculations of mineral saturation indices and PHREEQC simulations have led to the conclusion that the dissolution of rock salt and gypsum in groundwater accounts for most of the ionic action. Na+, Cl- and SO42- are mainly derived from the dissolution of rock salt and gypsum minerals, while Ca2+ and Mg2+ are mostly derived from the dissolution of dolomite and calcite. The results of the inverse geochemical modeling are consistent with the theoretical analysis.

Effect of recycled phosphogypsum and calcium aluminate cement on the strength behavior optimization of cement-treated dredged soil: A co-utilization of solid wastes.

Dredged soil and phosphogypsum (PG) are waste materials that must be treated to reduce their negative environmental effects. Guided by the concept of waste treatment, this study proposed the use of PG as a supplementary cementitious material to stabilize waste-dredged soil, and calcium aluminate cement (CAC) was selected to further improve the strength of the cement-treated dredged soil. Several laboratory tests were conducted to investigate the pH, unconfined compressive strength (UCS), and failure strain of the cement-treated soils in different proportions. Microstructural and mineralogical tests were performed to reveal the mechanisms underlying the strength improvement of PG and CAC. The results showed that both PG and CAC enhanced the strength of cement-treated dredged soil. PG provided SO2- 4 to promote the formation of ettringite (aluminum ferrite trisulfate (AFt)), whereas CAC neutralized the acidity of PG and provided reactants to the reaction system, leading to an increase in the pH and strength with an increase in the relative CAC content. Meanwhile, an exponential relationship was obtained between pH and qu. Mineralogical changes demonstrated that the major hydration products of cementitious materials, such as calcium silicate (aluminate) hydrate (C-(A)-S-H), AFt, and calcium aluminate hydrate (C-A-H), enhanced the strength by filling pores between particles and bridging soil particles. However, excess CAC content may not be favorable for the later strength formation, the relative CAC content is recommended to be in the range of 40%-60%. Compared to using sand, the construction of a square kilometer of reclamation consumed 3.5 million tons of PG, and saved 1.54 billion USD by using dredged soil as raw material. Hence, the use of PG to treat dredged soils will have great environmental sustainability, economic benefits, and engineering value.