Sequential Chemical Extraction Research Articles

Phosphorus bioavailability and recycling potential in various organic Wastes: Assessment by enzymatic hydrolysis and 31P NMR

Phosphorus(P) recycling from waste streams is crucial to mitigate the P depletion crisis. P forms and contents in organic waste are critical for determining the recycling method and efficiency. We constructed an approach to characterize P forms in seven organic waste by combining chemical sequential extraction, enzymatic hydrolysis, and nuclear magnetic resonance(NMR). Livestock manure and straw exhibited a higher active P(H2O-P&NaHCO3-P)(70.54%-84.40% and 65.78%-85.26% of total P) than sewage sludge(18.22%) and food waste(43.90%). Enzymatic hydrolysis revealed over 10% P in the so-called active P of corn(11.30%) and rice straw(13.32%) was phytate-like P, which is not bioavailable. These findings indicate the chemical sequential extraction inaccurately gauges bioavailable-P and underscores the need to convert phytate into plant-available P in recycling processes(biogas, composting), especially for crop straws and chicken manure. This work introduces a novel methodological framework for assessing P potential bioavailability in organic waste, providing fundamental knowledge for the P recycling process optimization.

Chemical Fingerprinting of PM2.5 via Sequential Speciation Analysis Using Electrochemical Mass Spectrometry.

Chemical fingerprinting to characterize the occurrence state and abundance of organic and inorganic constituents within fine particulate matter (PM2.5) is useful in evaluating the associated health risks and tracing pollution sources. Herein, an analytical strategy for the rapid analysis of metal and organic constituents in PM2.5 was developed employing a combination of sequential chemical extraction coupled with mass spectrometry detection. H2O, CH3OH, EDTA-2Na, electrochemical oxidation, and electrochemical reduction were sequentially utilized to extract the chemical constituents in PM2.5 samples on a homemade device employing simultaneous online detection using two linear trap quadrupole mass spectrometers (LTQ-MS) with electrospray ionization (ESI) in positive and negative modes. After a single analytical procedure, dozens of metals (e.g., Pb, Cr, and Cu), organic compounds (e.g., amines, polycyclic aromatic hydrocarbons, and aliphatic acids), and negative ions (e.g., NO3-, NO2-, and Cl-) were comprehensively detected in the water-soluble, liposoluble, insoluble, oxidizable, and reducible fractions of PM2.5 samples, and their physical and chemical relationships were established.

Mechanisms of roasting for improving rare earth element leaching from coal gangue

ABSTRACT Coal resources represent an important potential source for the future extraction of rare earth elements (REEs). This study, combining microscopic characterization techniques and experimental analysis, investigates the occurrence characteristics of REEs in coal gangue and the roasting activation mechanisms. The study reveals that phosphate minerals are the primary carriers of REEs, and sequential chemical extraction results further confirm the close association between REEs and phosphate minerals. Roasting at around 600°C facilitates the release of REEs from organic matter and clay minerals like kaolinite, significantly improving leaching efficiency. Under leaching conditions of 20 g/L, 50°C, 0.5 M HCl, and 1000 RPM, the leaching of REEs can reach approximately 80%. However, when the roasting temperature exceeds 1000°C, the formation of mullite leads to mineral surface sintering, reducing the recovery of REEs. This study emphasizes the importance of optimizing roasting conditions and understanding mineral phase changes to maximize REEs recovery, which is crucial for sustainable resource management and environmental remediation.

Coupling mechanism of trace elements and maceral in medium and high sulphur coal in the Jurassic terrestrial environment of Zhongyuan mine in the Hengshan mining area and adjacent areas

ABSTRACT Considering the urgency of resource utilization and environmental protection, the geochemistry of anomalous trace transition metal elements in coal formed in terrestrial environments has been studied using methods such as inductively coupled plasma atomic emission spectrometry analysis, electron probe micro-area analysis, sequential chemical extraction procedures, and correlation analysis. The results indicate that minerals in the coal samples included pyrite, kaolinite, quartz, dolomite, calcite, and celestite. Furthermore, compared with the average values of coals in China and the upper continental crust, the coal samples were rich in transition metal trace elements such as Ni, Cr, and Sr and were deficient in Be, Cd, Cu, Co, Ga, Mo, Sb, Tl, V, Zn, and Ti. We found that Ni preferentially occurred in the organic matter over minerals, while Cr primarily bonded with sulfide minerals and to a lesser extent with the iron-manganese oxide minerals. Sr had a low correlation with organic matter but adhered to clay minerals and celestite. Ni enrichment in coal samples was the result of terrigenous input, while the Cr enrichment was related to intrusion of magmatic hydrothermal fluids. Sr enrichment was caused by the presence of SO4 2- in the terrigenous debris and the influence of Sr-rich water underground.

Efficient extraction of rare earth elements from coal-series kaolin by combining alkali fusion and sulfamic acid leaching

As a solid waste produced by coal mining, the comprehensive utilization of coal-series kaolin is the focus of attention. In this paper, the extraction of rare earth elements (REEs) from coal-series kaolin was carried out by alkali fusion and sulfamic acid leaching. The occurrence modes of REEs in coal-series kaolin was analyzed by means of inductively coupled plasma-mass spectrometry analyse and sequential chemical extraction. The influence of alkali fusion conditions on the leaching of REEs was investigated, and the activation mechanism of alkali fusion was revealed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and field emission scanning electron microscope (FESEM) analysis. In addition, the effect of key operating parameters on the leaching efficiency of REEs from coal-series kaolin was further investigated. The results show that REEs mainly existed in silicate & aluminosilicate state of coal-series kaolin. The mineral structure was destroyed by alkali fusion, and the leaching efficiency of REEs was increased by 59.08 %. At the sulfamic acid concentration of 0.5 mol/L, H2O2 concentration of 0.2 mol/L, solid to liquid ratio of 1/50, the leaching efficiencies of total rare earth elements, light rare earth elements and heavy rare earth elements were 84.91 %, 88.43 % and 71.03 %, respectively.

Assessment of contamination, mobility and application of selected technology-critical elements as indicators of anthropogenic pollution of bottom sediments

The study investigates the potential of technology-critical elements (TCEs) in the bottom sediments of the Biała Przemsza River as indicators of anthropogenic activities. The mass fractions of TCEs: Ge, Ga, In, Tl, Sb and Te (and other elements) in the sediment were analysed by inductively coupled plasma mass spectrometry with the maximum mass fractions: 2.46, 25.6, 0.528, 27.7, 12.5 and 0.293 mg/kg, respectively. Distribution and identification of TCE sources were supported by statistical analysis (principal component analysis coupled with varimax rotation and hierarchical cluster analysis). Assessments of TCE contamination using the geoaccumulation index, pollution index, contamination factor, enrichment factor and the antimony-to-arsenic ratio highlighted the high contamination of bottom sediments by Sb, Ga, Tl, Cd, As, Zn, Pb and moderate contamination by Co, In and V. Distinct behaviour patterns were observed among TCEs, revealing Sb and Tl as potential indicators of Zn-Pb ore mining activities. Co, V, Ge and, to a lesser extent, Te emerged as promising indicators of coal and coal fly ash effluents. Sequential chemical extraction of TCEs showed that Sb, In and Tl had the highest mobility from sediments. The Risk Assessment Code calculations suggest, that in the Biała Przemsza River bottom sediments, there is an average risk of contamination by As, Tl and Mn. Soluble forms of Tl, Ge, Sb, Te and In were identified in descending order, indicating their bioavailability.

Modes of Occurrence, Migration, and Evolution Pathways of Lithium and Gallium during Combustion of an Al-Rich Coal, Inner Mongolia, China

The modes of occurrence, migration, and evolution pathways of lithium (Li) and gallium (Ga) during combustion of an Al-rich coal from Inner Mongolia, China, were investigated using methods of simulated combustion experiments, the sequential chemical extraction procedure (SCEP), and the thermodynamic equilibrium calculation. Mineralogical and chemical compositions of the feed coal and combustion ash were analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy (SEM). The study reveals that Li and Ga are significantly enriched in the ash after combustion, with the contents reaching up to 1086 μg/g and 133 μg/g, respectively. The primary modes of occurrence of Li and Ga in the ash are quartz and aluminosilicates, and sulfides, respectively. Li, in the form of LiAlSi4O10 (s), primarily occurs in hematite, glass, and quartz below 800 °C. However, it migrates into the glass phase, mullite, and quartz above 1000 °C. On the other hand, Ga exists as Ga4S5 (s) and transforms into Ga2S (g) as the temperature rises from 800 °C to 1000 °C, maintaining this gaseous form until 1200 °C. Ga4S5 (s) predominantly occurs in the glass phase at 600 °C, whereas mullite and quartz become its dominant modes of occurrence in industrial combustion ashes and ashes obtained from simulated combustion above 600 °C.

The release and migration mechanism of arsenic during pyrolysis process of Chinese coals

Special attention was drawn to the heavy metals contained in coal, due to it will cause harm to the environment during coal processing and utilization. The sequential chemical extraction of Shanxi coal (SX coal) and Wulanchabu coal (WLCB coal) was carried out to investigate the distribution of arsenic (As) in coals. Two raw coals were pyrolyzed at 300–900 °C in horizontal tubular furnace to investigate release behavior of As during pyrolysis process. The results showed that As in SX coal mainly existed in aluminosilicate-bound state (40.25%) and disulfide-bound state (32.51%), followed by carbonate-bound state and organic-bound state. The As in WLCB coal mainly existed in aluminosilicate-bound state (62.50%), followed by disulfide-bound state (19.10%). The As contents of water-soluble, ion-exchange and residue states in the two coals were less than others. The modes of occurrence of As had great influence on its volatilization behavior. As in organic part was easy to volatilize at low temperature. Sulfide-bound state would escape with the decomposition of pyrite. Because SX coal contained higher organic state and sulfide-bound state, the volatilization rate of As was higher than WLCB coal at any temperature, and the difference was more obvious at low temperature. In addition, FactSage simulation value was basically consistent with the experimental value.

Estimating internal phosphorus loading for a water quality model using chemical characterisation of sediment phosphorus and contrasting oxygen conditions

The Finnish Archipelago Sea (AS) has long been subject to intensive anthropogenic phosphorus (P) loading. The area suffers from seasonal hypoxia and cyanobacterial blooms despite reductions in nutrient discharge from the catchment and point sources. Internal loading may even dominate the P budget. Previous estimates of internal P loading have limitations (e.g., in spatial coverage and infrequent measurements). We present the first area-wide estimates of the magnitude of internal P loading based on the long-term release of P stored in the sediments.Modelling the internal P loading in the AS is challenging due to the complexity of biogeochemical processes in the sediment-water interface, as well as the heterogenic topography of the seafloor. Instead, we calculated estimates of internal P loading based on data from previous studies on sequential chemical extraction of sediment P, sediment physical characteristics (e.g., organic content, location of muddy seabed substrates), and near-bottom oxygen (O2) conditions. The estimates in three scenarios of contrasting O2 conditions were based on potentially mobile P pools in the sediments, recycled from sediment to water (i.e., loosely-bound or exchangeable P, P bound to reducible iron oxy(hydr)oxides, and labile organic P). The potentially mobile P pools were determined by chemical extraction methods (modified from Psenner et al., 1984 and Ruttenberg, 1992). The internal P loading under presumable O2 conditions was estimated to be fivefold that of waterborne P input to the AS; comparable to previous estimates for hypoxic areas in the Baltic Sea.Our estimates revealed wide spatial variability in the internal P loading, depending on O2 conditions and seabed sediment substrate. The site-specific P release estimates are included in a water quality model used by regional authorities, which increases the model's reliability for estimating the impact of human activities on the water quality across the AS.

Enhancing Phosphorus Release from Sewage Sludge in Anaerobic Digestion via Thermal Hydrolysis Pretreatment: Insights from Phosphorus Speciation and Molecular Biological Pathways.

This study explores the mechanisms enhancing phosphorus (P) release from sludge in anaerobic digestion (AD) with thermal hydrolysis pretreatment (THP) using sequential chemical extraction, X-ray absorption near-edge structure spectroscopy (XANES), 31P NMR, and multiomics. THP-treated sludge notably increased liquid-phase P by 53.8% over 3 days compared to sewage sludge (SS), identifying solid-phase Fe-P as the primary P source. The THP+AD also provided a higher abundance of bacteria that contributed to P release through multiple pathways (MPRPB), whereas SS+AD enriched some microbial species with single P release pathway. Moreover, species co-occurrence network analysis underlined the pivotal role of P-releasing bacteria in THP+AD, with 8 out of 16 keystones being P-releasers. Among the 63 screened genes that were related to P transformations and release, the poly beta-hydroxybutyrate (PHB) synthesis genes associated with polyphosphate bacteria-mediated P release were more abundant in THP+AD than in SS+AD. Furthermore, the upregulation of genes involved in methyl phosphonate metabolism in the THP-treated sludge enhanced the methane production potential of the AD process. These findings suggested that MPRPB were indeed the main contributors to P release, and enrichment in the THP+AD process enhanced their capability for P liberation.

Effect of Land Use Change on Molecular Composition and Concentration of Organic Matter in an Oxisol.

Land use change from native vegetation to cropping can significantly affect the quantity and quality of soil organic matter (SOM). However, it remains unclear how the chemical composition of SOM is affected by such changes. This study employed a sequential chemical extraction to partition SOM from an Oxisol into several distinct fractions: water-soluble fractions (ultrapure water (W)), organometal complexes (sodium pyrophosphate (PP)), short-range ordered (SRO) oxides (hydroxylamine-HCl (HH)), and well-crystalline oxides (dithionite-HCl (DH)). Coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the impact of land use change on the molecular composition of different OM fractions was investigated. Greater amounts of OM were observed in the PP and HH fractions compared to other fractions, highlighting their importance in SOM stabilization. The composition of different OM fractions varied based on extracted phases, with lignin-like and tannin-like compounds being prevalent in the PP and HH fractions, while aliphatic-like compounds dominated in the DH fraction. Despite changes in the concentration of each OM fraction from native vegetation to cropping, there was little influence of land use change on the molecular composition of OM associated with different mineral phases. No significant selective loss or preservation of organic carbon compounds was observed, indicating the composition of SOM remained unchanged.

Geochemical fractionation, bioavailability, and ascertaining ecological risk of phosphorus in surface and core sediments of mangroves, western coast of India.

Phosphorus (P), a crucial macronutrient, is essential in the maintenance of ecosystem productivity and the biogeochemical processes of other biogenic substances found in marine settings. The aim of the present study is to quantify the different geochemical fractions, bioavailability, and ecological risk of phosphorus in surface and core sediment of mangroves, Gulf of Kachchh (GoK). To better understand the P dynamics, sequential chemical extraction techniques were used to study sediment P pool distribution such as exchangeable P; Fe-bound P; authigenic P; detrital P; and organic P. The total sedimentary P ranged from 539.51 to 7217.24mg/kg in pre-monsoon and 487.04 to 7180.26mg/kg in post-monsoon, and was primarily composed of inorganic P. Authigenic P and Fe-bound P were the dominant fractions of P in surface and core sediments, exhibiting a significant long-term P reservoir. Sources such as riverine inputs, industrial and sewage discharge, aquaculture farms, and seaport operations all have an impact on the P dynamics in GoK. Furthermore, organic matter, pH, ORP, and diagenetic processes in sedimentary environment have influenced P retention and release. FeBD:Fe-P ratio indicates the presence of Fe matrices, having strong adsorption potential for P, with the availability of a surplus of Fe(III) (oxy)hydroxides serving as a significant P pool, governing the P dynamics. The P enrichment index (PEI) showed that sediments were highly impacted by anthropogenic P and could cause a high ecological risk. Bioavailable phosphorus (BAP) suggests the availability of an ample amount of bioavailable P fractions (average of 49.70% post-monsoon and 44.64% post-monsoon) in surface sediments. Sites 3, 13, 14, 20, 21, and 26 exhibited considerably higher BAP. Core 1 comprised significantly higher BAP (60.52%). Thus, sediments of GoK could act as a source of P to the overlying water if released from sediments.

Experimental Investigation on Gallium and Germanium Migration in Coal Gangue Combustion

Gallium (Ga) and germanium (Ge) critical elements have a wide range of applications and market value. Extracting critical elements from coal gangue and combustion products can alleviate pressures on primary mining resources. Understanding the transformation behavior of Ga and Ge during coal gangue combustion processes is significant for resource utilization and environmental protection. Coal gangue from Xing’an League, Inner Mongolia, was chosen to explore how combustion temperatures (600 °C to 1000 °C) and particle sizes (50, 80, 10, 140, and 200 mesh) influence Ga and Ge migration during combustion. Techniques such as ICP-MS, XRD, XRF, SEM, TG-DSC, and sequential chemical extraction were employed to analyze the transformation of minerals and to quantify the contents and occurrence forms of Ga and Ge. Smaller gangue particle sizes were associated with higher concentrations of Ga and Ge. Approximately 99.19% of Ga and Ge in coal gangue were found in the residual, organic/sulfide-bound, and metal-oxide-bound modes. High temperatures promoted element volatilization and changed the reactions and interactions between elements and minerals. As combustion temperatures rose from 600 °C to 1000 °C, Ga and Ge contents in the products declined progressively. Under high temperatures, minerals like kaolinite, illite, and pyrite in gangue converted to silicate glass phases, mullite, and hematite. Minerals like kaolinite, calcite, and pyrite melted, leading to increased cohesion and agglomeration in the products. Over 90% of Ga and Ge in the combustion products existed in the residual, organic/sulfide-bound, and metal-oxide-bound forms. Moreover, Ga was enriched in combustion products, with its content exceeding critical extraction levels. The results may provide a useful reference for developing critical elements enrichment, extraction, and separation technologies from coal gangue.

Bioleaching ion-unexchangeable rare earth in ion-adsorption type rare earth waste tailing

Ion-adsorption type rare earth ores (IREO) in China serve as the primary source of medium and heavy rare earth globally. With the rapidly growing demand for rare earth elements (REEs) and the dwindling supply of premium IREO, enhancing the recovery of REEs, especially the ion-unexchangeable REEs with ultra-low content and ambiguous speciation from IREO or its tailing, has become a critical trend and challenge. This study identified the occurrences of ion-unexchangeable REEs, primarily detected in Fe-enriched minerals, xenotime, and monazite of IREO using TESCAN integrated mineral analyzer (TIMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analysis. To extract these elusive REEs, a bioleaching technique utilizing Aspergillus niger (A. niger) metabolites was proposed, achieving a leaching yield of 31.4 wt%. Complementary sequential chemical extraction methods (SCEM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations further elucidate the underlying mechanism, involving the carboxylic acid produced by the metabolic process of microbes that dissolves goethite by disrupting FeO bonds and liberating REEs, which complexed with carboxylate (RCOO), to promote further dissolution. This work offers insight into enhancing the recovery of ion-unexchangeable REEs from IREO or its tailing, paving the way for sustainable and efficient rare earth mining practices.

Bioaccessibility Characterization of Organic Matter, Nitrogen, and Phosphorus from Microalgae-Bacteria Aggregates

The quality of microalgae-bacteria biomass as an organic soil fertilizer may depend on the biomass’s microbial composition, morphology, and growth history. This study aims to characterize the molecular complexity and bioaccessibility of organic matter, nitrogen, and phosphorus from microalgae-bacteria aggregates with different morphologies (flocs and granules) grown under nutrient-abundant and starvation conditions. A biochemical fractionation method was used based on sequential chemical extraction and fluorescence spectroscopy. Microalgae-bacteria aggregates were cultured and collected from photobioreactors using contrasting growth conditions to generate (i) loose flocs, (ii) consolidated flocs, (iii) smooth granules, and (iv) filamentous granules. The organic matter, nitrogen, and phosphorus from consolidated flocs were mostly extractable, accounting for up to 94% of their total content. In contrast, the organic matter from loose flocs was up to 50% non-extractable. The extractability of loose flocs was improved under starvation conditions. All microalgae-bacteria aggregates showed a low structural complexity, corresponding to an abundance of simple microbial-related constituents like tyrosine and tryptophane. Differences between the gradients of bioaccessibility for each microalgae-bacteria structure were related to the abundance of microorganisms and their metabolic products. The findings of this study have implications for the development of sustainable and environment-friendly organic fertilizers.Graphical

Performance of an integrated sediment interceptor in removing phosphorus from agricultural drainage water

Reducing phosphorus (P) loss from agricultural drainage water is challenging. In this study, we aimed to remove P from agricultural drainage water by developing an integrated sediment interceptor with adsorbent modules filled with Zr/Zn nanocomposite-modified ceramsite (ZMC-interceptor). The results of sequential chemical extraction and 31P NMR showed that the contents of H2O-P (1.15 % of total P), NaHCO3-Pi (10.48 % of total P), and ortho-P (orthophosphate, 90.6 % of total P) in the sediments of the ZMC-interceptors were higher than those in nearby field soils. The average enrichment ratios of particulate P (PP, >450 nm), medium-colloidal P (MCP, 220–450 nm), fine-colloidal P (FCP, 1–220 nm), and truly dissolved P (Truly DP, <1 nm) in the sediment over the field soil were 1.37, 1.21, 1.70, and 3.01, respectively. No significant differences were found in the sediment P-trapping function with and without ZMC integrated sediment interceptors. However, the ZMC-interceptors remarkably reduced total P (39.7 % for influent concentrations of 0.19–0.68 mg L−1) from agricultural drainage water compared to those unmodified ceramsite-interceptors (21.7 % for influent concentrations of 0.17–0.66 mg L−1) during the drainage ‘window period’ (June–August 2022). This was mainly due to the higher removal efficacies of MCP (19.7 %), FCP (23.3 %), and Truly DP (34.8 %) of the ZMC-interceptors. This study highlighted that the ZMC-interceptor not only trapped P in the sediment but also facilitated the removal of different-sized P fractionated from agricultural drainage water.

Comparative study of chemical speciation and leaching feature of typical heavy metals in coarse and fine slags from the entrained-flow coal gasification

ABSTRACT The dissimilarity in chemical speciation and release properties of heavy metals will result in varying levels of environmental hazards and potential applications of coal gasification coarse and fine slags. The distribution, chemical speciation, leaching features, and potential environmental risks of heavy metals (Cr, Cu, Cd, Zn, Pb, and Mn) in coarse and fine slags from different coal gasification processes were revealed and compared by the sequential chemical extraction method, Horizontal vibration method, and pH-dependent leaching experiments. The results show that Cr (516.78 mg/kg) in coarse slag, Zn (348.50 mg/kg) and Pb (214.78 mg/kg) in fine slag are highly enriched and the content exceeds the screening value, indicating the need for better management during stockpiling and landfilling. The distribution of Cr, Cu, Pb, and Mn in residual state, Zn in Fe-Mn oxide bound state, and Cd in unstable bound state is the highest in both coarse slag and fine slag. The leaching toxicity of heavy metals (HMs) does not exceed the standard, but the leachate is classified as Level V surface water or groundwater quality due to the leaching concentration of Pb exceeding 0.1 mg/L. Furthermore, leaching of Cr, Zn, Cd, and Pb in fine slag is much more dependent on pH compared to coarse slag, and the concentrations of Zn and Pb exceed emission standards at pH < 3.0. The high concentration of heavy metals caught on the surface of fine slag is more harmful to the environment. The properties of HMs in the slags and pH of the application environment must be comprehensively considered before coal gasification slag disposal, especially fine slag.

Fractionation and Lability of Phosphorus Species in Cottonseed Meal-Derived Biochars as Influenced by Pyrolysis Temperature.

Defatted cottonseed meal (CSM), the residue of cottonseeds after oil extraction, is a major byproduct of the cotton industry. Converting CSM to biochar and utilizing the goods in agricultural and environmental applications may be a value-added, sustainable approach to recycling this byproduct. In this study, raw CSM was transformed into biochar via complete batch slow pyrolysis at 300, 350, 400, 450, 500, 550, and 600 °C. Thermochemical transformation of phosphorus (P) in CSM during pyrolysis was explored. Fractionation, lability, and potential bioavailability of total P (TP) in CSM-derived biochars were evaluated using sequential and batch chemical extraction techniques. The recovery of feed P in biochar was nearly 100% at ≤550 °C and was reduced to <88% at 600 °C. During pyrolysis, the organic P (OP) molecules predominant in CSM were transformed into inorganic P (IP) forms, first to polyphosphates and subsequently to orthophosphates as promoted by a higher pyrolysis temperature. Conversion to biochar greatly reduced the mobility, lability, and bioavailability of TP in CSM. The biochar TP consisted of 9.3-17.9% of readily labile (water-extractable) P, 10.3-24.1% of generally labile (sequentially NaHCO3-extractable) P, 0.5-2.8% of moderately labile (sequentially NaOH-extractable) P, 17.0-53.8% of low labile (sequentially HCl-extractable) P, and 17.8-47.5% of residual (unextractable) P. Mehlich-3 and 1 M HCl were effective batch extraction reagents for estimating the "readily to mid-term" available and the "overall" available P pools of CSM-derived biochars, respectively. The biochar generated at 450 °C exhibited the lowest proportions of readily labile P and residual P compounds, suggesting 450 °C as the optimal pyrolysis temperature to convert CSM to biochar with maximal P bioavailability and minimal runoff risk.

Extraction of valuable critical metals from coal gangue by roasting activation-sulfuric acid leaching

ABSTRACT Coal gangue is a bulk industrial solid waste produced in the process of coal mining and washing, with the dual attributes of resourcefulness and hazardousness. It can be used as a reserve resource for valuable critical metals such as aluminum (Al), lithium (Li), gallium (Ga), and rare earth elements (REEs). In this paper, the occurrence modes of Li, Ga, and REEs in coal gangue were studied by sequential chemical extraction method. The extraction of valuable critical metals from the coal gangue was systematically studied by roasting activation-sulfuric acid leaching process, and the activation mechanism was elucidated. The results showed that roasting can destroy the inert kaolinite structure in coal gangue and significantly improve the leaching rate of valuable critical metals. Under the optimum conditions, the leaching rates of Al, Li, Ga, and REEs reached 86.51%, 74.46%, 95.45%, and 77.14%, respectively, and the leaching behaviors of Al, Li, and Ga were highly similar. In addition, the characterization of the leaching residue revealed 83.96% silicon oxide content with a loose and porous surface, which could be used to prepare silicon-based products. This study provides the theoretical basis and technical support for the utilization of valuable metals in coal gangue.

Study on modes of occurrence and selective leaching of lithium in coal gangue via grinding-thermal activation

Lithium (Li), an important strategic metal, has been paid attention to by researchers, entrepreneurs, and political circles, especially its recovery from coal-based solid waste. In this paper, the occurrence modes of Li in coal gangue (CG) have been studied through sequential chemical extraction, distribution correlation, and intercalation-leaching test. The CG was pretreated via grinding-thermal activation to selectively leach Li. The correlation between Li and magnesium (Mg) during the leaching process was also investigated. Finally, the migration mechanism of Li during the grinding-thermal activation process was analyzed using solid-state nuclear magnetic resonance for the first time. The results of the first three experiments demonstrated that Li primarily exists within the kaolinite. The extraction of Li from CG after grinding-thermal activation is 44.82 % using 0.2 M (NH4)2SO4 (pH = 4.0), while aluminum (Al) was almost insoluble, exhibiting the selective leaching of Li. 84.76 % of Li and 17.63 % of Al are obtained at pH = 1.0. The correlation analysis result suggests that lithium ions (Li+) exist in the octahedron of the lattice as charge compensation. The migration mechanism is explained by the chemical shift of Li+, which moves from −0.196 ppm (raw, in the octahedron) to −0.319 ppm (ground, octahedral destruction) and further to −0.564 ppm (thermal activation, out of the octahedron). This paper can provide a theoretical basis for the occurrence of Li and a new method for selective extraction of Li from CG.