Magnesium polypeptide combined with microbially induced calcite precipitation for remediation of lead contamination in phosphate mining wasteland soil.

Soil Pb contamination is inevitable, as a result of phosphate mining. It is essential to explore more effective Pb remediation approaches in phosphate mining wasteland soil to ensure their viability for a gradual return of soil quality for cultivation. In this study, a Pb-resistant urease-producing bacterium, Serratia marcescens W1Z1, was screened for remediation using microbially induced carbonate precipitation (MICP). Magnesium polypeptide (MP) was prepared from soybean meal residue, and the combined remediation of Pb contamination with MP and MICP in phosphate mining wasteland soil was studied. Remediation of Pb using a combination of MP with MICP strain W1Z1 (WM treatment) was the most effective, with the least exchangeable Pb at 30.37% and the most carbonate-bound Pb at 40.82%, compared to the other treatments, with a pH increase of 8.38. According to the community analysis, MP moderated the damage to microbial abundance and diversity caused by MICP. Total nitrogen (TN) was positively correlated with Firmicutes, pH, and carbonate-bound Pb. Serratia inoculated with strain W1Z1 were positively correlated with bacteria belonging to the Firmicutes phylum and negatively correlated with bacteria belonging to Proteobacteria. The available phosphate (AP) in the phosphate mining wasteland soil could encapsulate the precipitated Pb by ion exchange with carbonate, making it more stable. Combined MP-MICP remediation of Pb contamination in phosphate mining wasteland soil was effective and improved the soil microenvironment.

Highly efficient recovery of phosphate and fluoride from phosphogypsum leachate: Selective precipitation and adsorption.

Phosphogypsum, a typical by-product in the phosphorus chemical industry, could generate a large amount of leachate containing phosphate and fluoride in the process of rainfall and long-term stacking, which not only causes serious environmental pollution, but also leads to a waste of resources. In this study, a united treatment of calcium hydroxide precipitation and lanthanum zeolite (La-ZFA) adsorption was proposed to achieve the recovery of phosphate and fluoride from phosphogypsum leachate. In phosphogypsum, most phosphorus could be leached except P in the residual occurrence form, while for fluoride, only water-soluble F could be effectively leached. The optimum leaching amounts of phosphate and fluoride were 22.59 and 4.64 mg/g, respectively, at liquid-solid ratio of 400:1, leaching time of 120 min, pH of 6.0, particle size of >200 mesh (<0.075 mm), and leaching temperature of 25°C. Using Ca(OH)2 as the precipitant, the phosphate could be precipitated selectively from phosphogypsum leachate by controlling pH and time, and the concentrations of it decreased significantly to 0.29 mg/L at pH 10.0, with a removal efficiency of 99.48%. XRD, SEM and Visual MINTEQ software analysis proved that the main component of the precipitate was hydroxyapatite (Ca5(PO4)3(OH)). After P precipitation, a series of sorbents for fluoride were investigated, and La-ZFA sorbent was chosen and utilized to recover the fluoride from the leachate through a cyclic fixed-bed column. The efficiency of La-ZFA was basically not affected by the high concentration sulfate, and it can selectively adsorb fluoride from phosphogypsum leachate, leading to a final fluoride concentration of 0.29 mg/L in the effluent. The characterization demonstrated that fluoride might be adsorbed onto the La-ZFA via ligand exchange with hydroxy groups. The proposed method in this study is expected to sequentially recover phosphate and fluorine from the leachate of phosphogypsum, and it has great guiding significance for resource utilization and management of phosphogypsum.

Treating waste with waste: Adsorption of anionic dyes in wastewater with surfactant-modified phosphogypsum.

Phosphogypsum (PG) is a solid waste generated during the wet process of phosphoric acid production. The environmental-friendly disposal and recycling of PG is vital in the field of environmental solid waste treatment. In this study, PG is used for adsorbent of dyes in wastewater to achieve the goal of recycling waste with waste. Surfactant-modified phosphogypsum (ODBAC@PG) was prepared using octadecyl dimethyl benzyl ammonium chloride (ODBAC) as modifier. ODBAC@PG exhibits high adsorption capability for anionic dyes (methyl blue (MeB) and indocyanine carmine (IC)). The pseudo-second-order kinetic model fits the kinetic experimental data for the adsorption of two organic anionic dyes. Langmuir adsorption isotherm fits the adsorption characteristics of MeB and IC on ODBAC@PG, exhibiting a monolayer adsorption pattern. Thermodynamic parameters indicate the spontaneous and exothermic properties of MeB and IC on ODBAC@PG. MeB and IC have antagonistic effects on each other in binary adsorption system. High adsorption capacity after six cycles of experiments demonstrates the high reusability of ODBAC@PG. The nature for the adsorption includes electrostatic interaction, hydrogen bond and hydrophobic interaction. Using ODBAC@PG for dyes wastewater treatment can accomplish the goal of treating waste with waste and turning waste into treasure.

Mechanisms of combined bioremediation by phosphate-solubilizing fungus and plants and its effects on cadmium contamination in phosphate-mining wastelands.

Owing to uncontrolled mining activities and lack of ecological protection measures, phosphate-mining wastelands are contaminated with the heavy metal Cd. In this study, Penicillium oxalicum strain ZP6, a Cd-resistant phosphate-solubilizing fungus, was used in combination with the fast-growing, high-biomass plant Brassica juncea L. to enhance Cd remediation in phosphate-mining wastelands. Further, the bioremediation mechanisms were explored and elucidated. In pot experiments, strain ZP6 and Brassica juncea L. alone were significantly effective in removing Cd from phosphate-mining wastelands; however, their combination was more effective, exhibiting a high removal rate of 88.75%. The presence of phosphorite powder increases soil-enzyme activity, promotes plant growth, and reduces the bioaccumulation and translocation factors. However, Cd-inhibited plant growth and chlorophyll content increased malondialdehyde accumulation, which was alleviated by inoculation with strain ZP6. The results from the study indicate that bioremediation using a combination of strain ZP6 and plants is a restoration strategy with appreciable potential to resolve Cd contamination in phosphate-mining wastelands.

A Critical Review of the Enhanced Recovery of Rare Earth Elements from Phosphogypsum.

The increasing demand for rare earth elements (REEs), especially from new and innovative technology, has strained their supply, which makes the exploration of new REE sources necessary, for example, the recovery of REEs from phsophogypsum (PG). PG is a byproduct during the wet production of phosphoric acid, which is an attractive secondary resource for REEs due to a large amount of REEs locked in them. In most cases, REEs contained in PG are mainly encapsulated in the gypsum crystal, leading to a low leaching efficiency. Therefore, it is particularly important to use various methods to enhance the leaching of REEs from PG. In this review, we summarized and classified various enhanced leaching methods for the recovery of REEs from PG, and the advantages and disadvantages of different methods were compared. A joint method of recrystallization and RIL may be a promising enhanced leaching approach for the recovery of REEs from PG. Recrystallization could achieve both the complete REE release and simultaneous preparation of industrial materials with high value added, such as high-strength α-hemihydrate gypsum by phase transformation of PG, and the RIL technology could adsorb the releasing REEs and realize their efficient extraction. Such a combination appears to show significant advantages because of high REE recovery, as well as high value-added product preparation at low cost.

Dynamic elution of residual ammonium leaching agent from weathered crust elution-deposited rare earth tailings by magnesium chloride.

The release of residual ammonium (RA) leaching agent from weathered crust elution-deposited rare earth tailings would cause serious environmental pollution, and it was necessary to efficiently remove it from the ore body before the mine closure. In this study, occurrence states of the RA were determined and dynamic elution of RA from rare earth tailings by using magnesium chloride as eluent was investigated. Effects of initial concentration, pH, flow rate, and particle size on the ammonium removal efficiency were investigated, and variations of ammonium occurrence states before and after elution were determined. Lastly, elution mechanism was discussed. Results showed that removal efficiency of RA by magnesium chloride was significantly higher than that by deionized water, and elution efficiency of RA could reach about 95.7% at the optimum laboratory experiment conditions. Energy dispersive spectrometer (EDS) analysis illustrated that the residual ammonium was replaced by Mg2+ during the elution process, and occurrence state experimental results showed that 94.0% of water-soluble and adsorbable ammonium was eluted. The empirical kinetic equation of eluting RA by magnesium chloride was established as 1-2/3α-(1-α)2/3= 0.02*C00.6t. This study provided a valuable method for reducing environmental pollution caused by the release of the residual ammonium from the rare earth tailings.

Selective recovery of glyphosine from glyphosate mother liquor using a modified biosorbent: Competitive substitution adsorption.

Here, an easy to prepare, environmentally friendly, and highly efficient biosorbent was synthesized for the selective recovery of glyphosine from glyphosate mother liquor. Batch adsorption and continuous fixed-bed column experiments were conducted to determine its adsorption properties and evaluate its potential towards practical applications. The results showed that the biosorbent exhibited a fast adsorption rate and high adsorption capacity (296.1 mg/g) toward glyphosine. Further, the biosorbent performed better under acidic conditions, and was easily regenerated using an alkaline solution, maintaining a high removal efficiency even after 5 adsorption-desorption cycles. Competitive adsorption experiments in binary and ternary systems revealed that the biosorbent showed a higher adsorption affinity toward the target glyphosine compared with glyphosate and phosphorous acid (which are the other main constituents of glyphosate mother liquor), enabling the selective recycling of glyphosine. These observations were further supported through density functional theory (DFT) calculations of the adsorption energy. Moreover, fixed-bed column experiments showed that the prepared biosorbent could maintain its high performance in actual glyphosate mother liquor. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses revealed that the adsorption mechanism is strongly associated with electrostatic attraction and hydrogen bonding between -NH3+ and glyphosine. Overall, the prepared biosorbent can be considered as an excellent candidate for the selective recovery of glyphosine from complicated industrial wastewater systems.

CSAC-Net: Fast Adaptive sEMG Recognition through Attention Convolution Network and Model-Agnostic Meta-Learning.

Gesture recognition through surface electromyography (sEMG) provides a new method for the control algorithm of bionic limbs, which is a promising technology in the field of human-computer interaction. However, subject specificity of sEMG along with the offset of the electrode makes it challenging to develop a model that can quickly adapt to new subjects. In view of this, we introduce a new deep neural network called CSAC-Net. Firstly, we extract the time-frequency feature from the raw signal, which contains rich information. Secondly, we design a convolutional neural network supplemented by an attention mechanism for further feature extraction. Additionally, we propose to utilize model-agnostic meta-learning to adapt to new subjects and this learning strategy achieves better results than the state-of-the-art methods. By the basic experiment on CapgMyo and three ablation studies, we demonstrate the advancement of CSAC-Net.

Flotation purification of waste high-silica phosphogypsum.

High-silica phosphogypsum (PG) is a kind of industrial by-product with great utilization potential. However, it is difficult to reuse PG directly due to the related gangue minerals (e.g., SiO2), and thus efficient purification is required to allow its further applications. Herein, a typical high-silica phosphogypsum waste was purified by a new "reverse-direct flotation" method. The organic matters and fine slimes were removed by reverse flotation, and then, the silica impurity was removed by direct flotation. Via the closed-circuit flotation process, the whiteness of the PG concentrate is improved from 33.23 to 63.42, and the purity of gypsum in the PG concentrate increases from 83.90% to 96.70%, with a gypsum recovery of 85%. Additionally, the content of SiO2 is significantly reduced from 11.11% to 0.07%. In-depth investigations suggest that the difference in the floatability of gypsum and quartz is prominently intensified by flotation reagents at pH = 2-2.5, and thus leads to good desilication performance. Further characteristics of the PG concentrate prove that impurities have been well removed, and the PG concentrate meets the requirement of related standards for gypsum building materials. The flotation method reported here paves the way for the purification of high-silica phosphogypsum, which can be extended to the purification and value-added reutilization of other industrial solid wastes.

Simultaneous removal of lead, manganese, and copper released from the copper tailings by a novel magnetic modified biosorbent.

Potentially toxic elements including lead (Pb), manganese (Mn), and copper (Cu) released from copper tailings would cause severe long-term environmental risks and potential threats to human health. To prevent these negative effects caused by the release of the metals, a novel magnetic carboxyl groups modified bagasse with high adsorption affinity and strong magnetism was synthesized through an in-situ precipitation method and used to simultaneously remove Pb, Mn, and Cu from the eluate of copper tailings. Results showed that release of Pb, Mn, and Cu from the copper tailings was pH, time, and particle size dependent, and maximum concentrations of them released in the eluate was 1.7, 1.9, and 4.1 mg L-1 under weak acid conditions. Batch adsorption experiment showed that the as-synthesized magnetic modified bagasse could selectively absorb Pb, Mn, and Cu from a complex solution with adsorption capacity of 137.3, 13.1, and 90.0 mg g-1, respectively. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy-mapping (EDS-mapping) demonstrated that Pb, Mn, and Cu interacted with the magnetic modified biosorbent mainly through coordination and ion exchange. Column experiments showed that higher than 99.5% of the released Pb, Mn, and Cu could be simultaneously removed by the magnetic modified bagasse, and the maximum concentrations of them released in the eluate of the copper tailings were all decreased to lower than 0.01 mg L-1, which reached the discharge standards. After recycled by a magnet, the magnetic modified bagasse could be collected easily and used repeatedly. Because of the high efficiency and easy recovery, the used method had great practical application value in removal of potentially toxic elements released from metallic tailings.

Vertical distribution and occurrence state of the residual leaching agent (ammonium sulfate) in the weathered crust elution-deposited rare earth ore.

Weathered crust elution-deposited rare earth ore (WCE-DREO) are rich in middle and heavy rare earth, and ammonium sulfate ((NH4)2SO4) was often used as leaching agent to leach rare earths by in-situ leaching method. However, much of (NH4)2SO4 would remained in the ore body during the leaching process, and release of it would cause seriously environmental pollution after the mine closure. To efficiently remove it, the rare earth ore properties and vertical distribution and occurrence state of the residual leaching agent at mine roof (GP1), mine waist (GP2), and mine foot (GP3) with different depth were investigated and efficient elution method was proposed in this study. Results showed that the rare earth ore mainly consist of quartz, clay minerals (halloysite, illite, and kaolinite) and rock-forming minerals, and pH and moisture contents of them were ranged from 4.0 to 5.0 and 10-20%, respectively. Residual agent was mainly enriched in the middle and deep layer of the ore body with the main form of ammonium nitrogen (NH4+-N), and content of it at the three sites followed the order of GP1>GP3>GP2, which was related to the content of the clay minerals and the moisture. Occurrence state experimental results illustrated that about 95% of the NH4+-N existed as water-soluble ammonium (WS-AN) and adsorbable ammonium (AS-AN), and 5% of it existed as fixed ammonium (FX-AN), and concentration ratio of them was in order: WS-AN > AS-AN â‰« FX-AN. Based on the results above, MgCl2 solution was used as an eluent to remove the leaching agent from the ore, and results showed that higher than 90% of residual ammonium could be removed from the ore by it. This study provided a valuable guidance for the residual leaching agent removal from the WCE-DREO body.

Remediation of soil cadmium pollution by biomineralization using microbial-induced precipitation: a review.

In recent years, with industrial pollution and the application of agricultural fertilizers with high cadmium (Cd) content, soil Cd pollution has become increasingly serious. A large amount of Cd is discharged into the environment, greatly endangering the stability of the ecological environment and human health. The use of microorganisms to induce Cd precipitation and mineralization is an important bioremediation method. Itis highly efficient, has a low cost, enables environmental protection, and convenient to operate. This article summarizes the pollution status, pollution source, biological toxicity and existing forms of Cd, as well as the biomineralization mechanism of microbial induced Cd(II) precipitation, mainly including microbial-induced carbonate precipitation, microbial-induced phosphate precipitation and microbial-induced sulfide precipitation. Factors affecting the bioremediation of Cd, such as pH, coexisting ions, and temperature, are introduced. Finally, the key points and difficulties of future microbe-induced Cd(II) biomineralization research are highlighted, providing a scientific basis and theoretical guidance for the application of microbe-induced Cd(II) immobilization in soil.

Selective removal of phosphate from aqueous solution by MIL-101(Fe)/bagasse composite prepared through bagasse size control.

MIL-101(Fe)/sugarcane bagasse (SCB) with high adsorption capacity and selectivity toward phosphate was prepared through in-situ synthesis method. Effects of bagasse size on the morphology and performances of the composites were investigated, and adsorption behavior and mechanism of phosphate on the composite prepared at the optimum bagasse size were studied. Results showed that composite prepared with bagasse size of 200-300 mesh (MIL-101(Fe)/SCB3) showed much higher adsorption capacity than SCB, blank MIL-101(Fe) and the composites prepared with the other bagasse size, which was due to the more positively charged surface and the more exposed adsorption active sites including FeOHx and exchangeable Cl-. Co-ions experimental results illustrated that the as prepared MIL-101(Fe)/SCB3 showed high adsorption affinity toward phosphate, and the common cationic and anionic ions exhibited negligible effects on phosphate adsorption capacity and rate. The optimum pH range for phosphate adsorption on MIL-101(Fe)/SCB3 was from 3.0 to 10.0, and in this range Fe release was less than 0.03%. Adsorption mechanism showed that phosphate was adsorbed mainly through electrostatic force, ion-exchange, and inner-sphere surface complex. Simulated wastewater treatment experiment showed that MIL-101(Fe)/SCB3 could efficiently remove phosphate from aqueous solution.

Simultaneous removal of cationic and anionic dyes from aqueous solution by double functional groups modified bagasse.

Double functional groups modified bagasse (DFMBs), a series of new zwitterionic groups of carboxyl and amine modified adsorbents, were prepared through grafting tetraethylenepentamine (TEPA) onto the pyromellitic dianhydride (PMDA) modified bagasse using the DCC/DMAP method. DFMBs' ability to simultaneously remove basic magenta (BM, cationic dye) and Congo red (CR, anionic dye) from aqueous solution in single and binary dye systems was investigated. FTIR spectra and Zeta potential analysis results showed that PMDA and TEPA were successfully grafted onto the surface of bagasse, and the ratio of the amount of carboxyl groups and amine groups was controlled by the addition of a dosage of TEPA. Adsorption results showed that adsorption capacities of DFMBs for BM decreased while that for CR increased with the increase of the amount of TEPA in both single and binary dye systems, and BM or CR was absorbed on the modified biosorbents was mainly through electrostatic attraction and hydrogen bond. The adsorption for BM and CR could reach equilibrium within 300 min, both processes were fitted well by the pseudo-second-order kinetic model. The cationic and anionic dyes removal experiment in the binary system showed that DMFBs could be chosen as adsorbents to treat wastewater containing different ratios of cationic and anionic dyes.

Phosphate rock solubilization and the potential for lead immobilization by a phosphate-solubilizing bacterium (Pseudomonas sp.).

Lead (Pb) pollution is getting more and more serious in phosphate mining wastelands recently. However, seldom studies focused on the bioremediation of Pb pollution in phosphate mining wastelands by phosphate-solubilizing bacterium (PSB). In this study, a PSB named LA with high Pb tolerance was isolated from a phosphate mining wasteland. Based on its cell morphology, physiology, and phylogenetic analysis, it was identified as Pseudomonas sp. Its capabilities to solubilize mid-low-grade phosphate rock (PR) and immobilize Pb were assessed in this study. It was found that LA could effectively solubilize PR on PKO culture medium and release soluble phosphate in the culture medium. PR solubilization and Pb immobilization were investigated at different initial Pb concentrations and pH levels. The results showed that soluble phosphate was highly effective in immobilizing Pb and that when the initial concentration of Pb2+ was 100 mg/L, the immobilization rate of Pb was enhanced. Further, the mechanisms underlying solubilization of PR and biomineralization of Pb ions in LA were evaluated by Fourier transform infrared spectroscopy and X-ray diffraction. The results showed that some functional groups on the PR surface and LA were altered, and LA could form hydroxyapatite and pyrophosphate with Pb ions.

Optimizations of particle size and pulp density for solubilization of rock phosphate by a microbial consortium from activated sludge.

Microbial solubilization of rock phosphate is getting more and more attention recently. However, the microorganisms used in previous studies were mostly single or known species, and seldom studies focused on the mixed microorganisms or microbial consortia from natural environments. In this study, a microbial consortium taken from activated sludge was used to solubilize two different mid-low-grade rock phosphates. The results showed that the microbial consortium could effectively solubilize the rock phosphates in National Botanical Research Institute's phosphate growth medium and released soluble phosphorus in the broth. The biomass increased gradually, whereas the pH decreased sharply during the solubilizing process. The maximum phosphorus solubilization was recorded at particle size of 150 µm. Higher or lower than this optimal particle size, the phosphorus solubilization decreased. The phosphorus solubilization gradually decreased with a larger pulp density from 1 to 5%, and the optimal pulp density was 1%. The solubilization level of microbial consortium varied with different rock phosphates. The results revealed that the soluble phosphorus released from high-silicon ore was higher than which from high-magnesium ore. A strong positive correlation between biomass and phosphorus solubilization in the broth was observed from regression analysis results, and the phosphorus solubilization also had a significant negative correlation with pH in the broth.

Phosphorus immobilization/release behavior of lanthanum-modified bentonite amended sediment under the dual effects of pH and dissolved organic carbon.

Lanthanum modified bentonite (LMB) is typical P-inactivating agent that has been applied in over 200 lakes. Dissolved organic carbon (DOC) and high pH restrict the phosphorus (P) immobilization performance of LMB. However, the P immobilization/release behaviors of LMB-amended sediment when suspended to overlying water with high pH and DOC have not yet been studied. In the present work, batch adsorption and long-term incubation experiments were performed to study the combined effects of pH and DOC on the P control by LMB. The results showed that the coexistence of low concentration of DOC or preloading with some DOC had a negligible effect on P binding by LMB. In the presence of DOC, the P adsorption was more pronounced at pH 7.5 and was measurably less at pH 9.5. Additionally, the pH value was the key factor that decided the P removal at low DOC concentration. The increase in pH and DOC could significantly promote the release of sediment P with a higher EPC0. Under such condition, a higher LMB dosage was needed to effectively control the P releasing from sediment. In sediment/water system with intermittent resuspension, the alkaline conditions greatly facilitated the release of sediment P and DOC, which increased from 0.087 to 0.581 mg/L, and from 11.05 to 26.56 mg/L, respectively. Under the dual effect of pH and DOC, the P-immobilization performance of LMB was weakened, and a tailor-made scheme became essential for determining the optimum dosage. The desorption experiments verified that the previously loaded phosphorus on LMB was hard to be released even under high pH and DOC conditions, with an accumulative desorption rate of less than 2%. Accordingly, to achieve the best P controlling efficiency, the application strategies depending on LMB should avoid the high DOC loading period such as the rainy season and algal blooms.

The investigation of ion association characteristics in lanthanum sulfate solution by the density functional theory and molecular dynamics simulations.

The ion association behavior in aqueous lanthanum sulfate solutions was investigated using density functional theory (DFT). The structures and properties of [La(SO4)m·(H2O)n](3-2m) clusters, where m = 1 to 3 and n = 1 to 9, were examined at the PBE0/6-311+G(d, p) level. The results show that Lanthanum sulfate hydrated clusters exist in the aqueous solution's microscopic state of contact ion pairs (CIP). [La(SO4)(H2O)n]+ and [La(SO4)2·(H2O)n]-, and [La(SO4)3·(H2O)n]3- clusters approximately reach the saturation of the first water shell at n = 7 and 6 and 3. [La(SO4)2·(H2O)6]- and [La(SO4)3·(H2O)3]3- clusters have lower binding energy than [LaSO4·(H2O)n]+. This indicates that lanthanum sulfate tends to aggregate in an aqueous solution. Compared to the gas-phase cluster structures, the distance of R(La-O)H2O expands in the PCM solvent model, while R(La-O)SO4 contracts. The hydration energy of LaSO4·(H2O)7, La(SO4)2·(H2O)6, and La(SO4)3·(H2O)3 were -76.5, -54.1 and -332.0 kcal/mol, respectively. The molecular dynamics simulation results show that La is more inclined to coordinate with sulfate's oxygen than water's oxygen, and the coordination number of water around La3+ is 6.075. These results are consistent with the calculated results by DFT.

Study on the occurrence state of main components of phosphogypsum dihydrate and its impurity distribution.

The dihydrate phosphoric acid process is the mainstream technique. However, the phosphogypsum (PG) produced contains high levels of impurities such as phosphorus and fluorine, severely constraining its valorization. In order to elucidate the occurrence patterns of phosphorus and fluorine impurities in PG, this study employed analytical methods including XRF, XRD, AMICS (Automated Mineralogy Integrated with Chemistry System), XPS, and chemical element balance analysis. We investigated the occurrence states of phosphorus, fluorine, silicon, iron, and aluminum elements in PG from wet-process phosphoric acid production, as well as the distribution characteristics of phosphorus and fluorine impurities. Additionally, we utilized Density Functional Theory (DFT) calculations to determine the binding energies of major minerals with water-soluble phosphate and fluoride groups, and analyzed the zeta potentials of gypsum and quartz mineral surfaces. The results indicate that the main mineral phases in PG are gypsum, quartz, potassium silicate minerals, aluminosilicate minerals, and hematite, predominantly occurring in monomineralic forms. Phosphorus impurities primarily exist in calcium silicate and hematite minerals, while fluorine is mainly associated with gypsum and potassium silicate minerals. DFT calculations demonstrate strong binding energies between calcium silicate and hematite minerals with PO4 3-, as well as between gypsum and quartz minerals with F-. The acidic conditions in the separation tank during wet-process phosphoric acid production may contribute to the distinctive distribution characteristics of phosphorus and fluorine impurities in PG.

Heterotrophic nitrification processes driven by glucose and sodium acetate: New insights into microbial communities, functional genes and nitrogen metabolism from metagenomics and metabolomics.

Heterotrophic nitrification (HN) bacteria use organic carbon sources to remove ammonia nitrogen (NH4+-N); however, the mechanisms of carbon and nitrogen metabolism are unknown. To understand this mechanism, HN functional microbial communities named MG and MA were enriched with glucose and sodium acetate, respectively. The NH4+-N removal efficiencies were 98.87 % and 98.91 %, with 88.06 % and 69.77 % nitrogen assimilation for MG and MA at 22 h and 10 h, respectively. Fungi (52.86 %) were more competitive in MG, and bacteria (99.99 %) were dominant in MA. Metagenomic and metabolomic analyses indicated that HN might be a signaling molecule (NO) in the production and detoxification processes when MG metabolizes glucose (amo, hao, and nosZ were not detected). MA metabolizes sodium acetate to produce less energy and promotes nitrogen oxidation reduction; however, genes (hao, hox, and NOS2) were not detected. These results suggest that NO and energy requirements induce microbial HN.