Precipitator Research Articles

Design and Fabrication of an Air Purifier by Combining HEPA and Activated Carbon Filter

The air purifier industry has seen a growth in terms of demand and sales lately. All credit goes to massive industrialization in developing countries such as India and China. As a result, a lot of research has been focused into the various methods of purifying air. The most harmful of the pollutants are PM 2.5 particulates and NOx emissions. The aim has been to bring down the costs without compromising on efficiency as efficient air purification is an expensive deal. This article presents a study of the current scenario of the problems of air pollution. Severity of the issues have been highlighted. A compilation of the most common and significant methods of purifying air such as those employing the use of HEPA filters, electrostatic smoke precipitators, activated carbon and UV light has been presented and their use in air purifiers manufactured by OEMs has been mentioned. Some of the most modern methods of purifying air such as those using transparent PAN filters, photochemical materials, soy proteins and silk Nano fibrils have been studied and reviewed. It has been found that these methods provide an attractive and economical pathway of filtering out PM 2.5 when compared to the conventional HEPA filters Keywords: Air Purifier, PM 2.5, NOx Emissions, Bio Materials

Co-pyrolysis of alkali-fused fly ash and corn stover to synthesize biochar composites for remediating lead-contaminated soil

Fly ash (FA) is mainly composed of silica, alumina, and other metal oxide components, and has a positive stabilizing effect on soil heavy metals. Biochar composites produced from FA and corn stover (CS) can improve its remediation performance. Therefore, a batch of biochar composites (alkali-fused FA-CS biochars, ABs), synthesized via co-pyrolysis of CS and alkali-fused FA (AFFA) at different temperatures of 300, 500, and 700 °C (AB300-1, AB500-1, and AB700-1) and CS to AFFA mass ratios of 10:1, 10:2, and 10:5 (AB500-1, AB500-2, and AB500-5), was used to remediate lead (Pb)-contaminated soil. Compared with pristine biochars (BCs), ABs were enriched with oxygen-containing functional groups (Si–O–Si and Si–O) and aromatic structures. The ABs prepared at lower pyrolytic temperature (≤500 °C) and lower ratio of CS to AFFA (10:1) showed higher yield and stability. The contents of Toxicity Characteristic Leaching Procedure (TCLP)-extractable Pb and DTPA-CaCl2-triethanolamine (DTPA)-extractable Pb were generally lower in the soils amended with ABs than BCs. Compared with other ABs such as AB300-1, AB500-2, AB500-5, and AB700-1, the soil amended with AB500-1 had lower contents of TCLP and DTPA-extractable Pb (24% reduction), exhibiting superior performance in stabilizing Pb in the soil. The gradual decrease of DTPA-extractable Pb content in the soil with increasing dosage of AB500-1 amendments suggests that AB500-1 facilitated the conversion of bioavailable Pb to the stable and less toxic residual fractions. Specifically, the highest percentage of residual fraction of Pb in soil amended with AB500-1 was 14%. Correlation analyses showed that the soil DTPA-extractable Pb content decreased with the increase of soil pH and cation-exchange capacity (CEC) value. ABs stabilize Pb in the soils mainly via electrostatic attraction, precipitation, cation-π interaction, cation exchange, and complexation. These findings provide insights for producing functionalized biochar composites from industrial waste like FA and biomass waste for remediating the soils polluted by heavy metals.

Enhanced size-dependent efficiency of removal of ultrafine particles: New solution of two-stage electrostatic precipitator with thermophoresis

Two-stage electrostatic precipitators (ESPs) are effective at removing ultrafine particles (UFPs) from gases; however, they fall short in capturing particles with diameters of less than 100 nm. In this study, an effective solution for removal of particles smaller than 300 nm was proposed. Our self-designed system combines a two-stage ESP with thermophoresis. We employed a combination of experimental and numerical simulation methods to examine the effects of temperature and thermophoresis on particle removal efficiency influenced by electrostatic forces. In our experiments, particle removal efficiency was positively correlated with gas temperature up to 75 °C, beyond which removal efficiency was no longer correlated with temperature. The findings also indicate that the introduction of thermophoresis improves particle removal efficiency, with the maximum increase approaching 8 %. However, this effect only occurs for particles smaller than 50 nm. The increase in the length of the thermophoresis segment and the decrease in inlet gas flow rate both enhance particle removal efficiency due to thermophoresis. Numerical simulations confirmed the experimental finding that nanoscale particles are more easily captured at higher temperatures. The simulations also revealed that the primary reasons for the enhanced removal efficiency are twofold: greater electric field strength and higher particle charge resulting from a higher temperature.

A New Kind of Anti-bending and Anti-deformation Cathode Frame for Electrostatic Precipitators

A New Kind of Anti-bending and Anti-deformation Cathode Frame for Electrostatic Precipitators

Towards real-time airborne pathogen sensing: Electrostatic capture and on-chip LAMP based detection of airborne viral pathogens

Considerable loss of life, economic slowdown, and public health risk associated with the transmission of airborne respiratory pathogens was underscored by the recent COVID-19 pandemic. Airborne transmission of zoonotic diseases such as the highly pathogenic avian influenza (HPAI) and porcine reproductive and respiratory syndrome virus (PRRSV) has caused major disruptions to domestic and global food security. Current ambient air pathogen monitoring systems involves the collection of air samples from indoor settings suspected of viral contamination, followed by subsequent processing of capture samples to determine the presence and species of airborne viral matter. Nucleic acid amplification techniques are considered the gold standard for pathogen diagnostics. Currently, the necessary extraction and purification of viral RNA from air collector systems prior to sample analysis is both time consuming and performed manually. A monitoring system with separate air sampling and biochemical detection procedures is prone to delay the response to emergent viral threats. In this paper, we present a pathogen monitoring system that overcomes these limitations related to extraction and purification of viral samples and lays the groundwork for a real-time monitor for airborne viral pathogens. We demonstrate a high flow electrostatic precipitator system, that uses small collection wells as counter electrodes for pathogen collection. Integrated reverse-transcriptase loop-mediated isothermal amplification (RT-LAMP) is used for detection of captured viral matter within wells. On-chip heating of collection wells is enabled by integrated planar heaters and small volumes of reagent (30 μL) directly to the collection wells. We present the design of such a system and show experimental results that demonstrate the use of this device for detection of aerosolized SARS-CoV-2 virus like particles (VLPs), a model pathogen for SARV-CoV-2.

Efficiency Improvement and Market Value Analysis of Guide Vane Electrostatic Precipitators

Urbanization and industrialization accelerate, the issue of atmospheric environmental pollution has become increasingly severe, particularly the impact of indoor air quality on human health and well-being. This study introduces a novel guide vane electrostatic precipitator that significantly enhances dust removal efficiency through optimized airflow channels and electrostatic field design. Experimental data demonstrate that this device can effectively reduce PM2.5 concentrations, improving dust removal efficiency by approximately 10% compared to traditional electrostatic dust removal technologies. Applications in various scenarios, including hotels, dust workshops, and steel foundries, indicate that the device not only improves air quality, enhancing employee productivity and well-being, but also features low energy consumption and intelligent operation. Furthermore, it holds considerable potential market value, contributing to the promotion of green and low-carbon development objectives. This research provides a comprehensive analysis and evaluation of the structure, working principle, mechanism of efficiency improvement, practical application effects, and market value of the guide vane electrostatic precipitator, looking forward to its application prospects in the field of air purification.

Recent advances in electrostatic precipitation of particles from flue gases generated by domestic heating appliances. A brief outlook

Winter season is the time of increased emission of exhaust gases from household heating appliances containing particulate matter (PM) and other noxious contaminants. Many old buildings and single houses, particularly at rural and small town regions, still use stoves, fireplaces or ovens to flat heating. Besides qualified fuels like coal or biomass pellets, all kinds of wastes are also burned in many cases, producing not only mineral particles but also toxic volatile organic compounds or other carcinogenic species. To solve the problem of high level of emission of solid particles and organic-compound molecules different constructions of electrostatic precipitators, which can remove such particles, have been developed in last two decades, which were designed to operate downstream of small domestic boilers. Such electrostatic precipitator must comply with the ECODESIGN emission limits, which set the emission level at 20 mg/m3, for biomass. The mass collection efficiency should be higher than 95 % to obtain this emission level. This brief review presents different constructions of electrostatic precipitators designed to be used for the removal of fly ash particles from domestic heating appliances.

Industrial application and numerical simulation on discrete dynamics of fine particulate matters: Condensational growth, deposition and agglomeration

The removal effects of multiple discrete dynamic mechanisms on particulate matters (PMs) are of great significance for industrial application and basic research. In this work, a wet phase transition agglomerator (WPTA) is installed between a wet electrostatic precipitator (WESP) and a stack at a 280 t/h coal-fired power plant. The removal effects of the WPTA are compared with those of the WESP by field measurement. Meanwhile, a numerical model for predicting particle size distributions is developed and verified through the experimental data. The results indicate that the WPTA reduces the emission concentrations of PM1 and PM2.5 to 0.64 mg/Nm3 and 0.89 mg/Nm3, respectively. The PM1 removal efficiencies for the independent WPTA, the independent WESP and the combined method are 33.07 %, 40.31 % and 58.36 %, respectively. The microscopic morphologies of the fine PMs in the particle size range of 0.98–1.64 μm exhibit blocky, spherical and crystal structure. The simulated errors of PM1, PM2.5 and PM10 are 7.81 %, 7.87 % and 12.27 %, respectively. The boundary layers of the tube bundle are conducive to strengthening thermophoretic force and supersaturation. Consequently, the WPTA can effectively replace the WESP to achieve the emission control of fine PMs in industrial applications. The developed numerical model can accurately predict the particle size distributions in the WPTA.

Combined control of PM and NOx emissions by corona discharge

This work investigates the potential of corona discharge to control particulate matter and NOx emissions from small-scale biomass combustion. The electrostatic precipitator (ESP) was designed and used to suppress emissions from a 15-kW heating unit. The ESP was operated at different power modes at both polarities and demonstrated the capability to reduce NOx emissions with a removal efficiency of 78 % while PM concentration was reduced to a magnitude of particle content in ambient air. The efficiency of ESP was evaluated considering the technological parameters, namely the reduced electric field, Nt-product, and specific input energy. The growth in NOx abatement was observed when the energy input exceeded 1 J/L for both polarities and Nt-product exceeded 4.5 × 108 s/cm3/1 × 109 s/cm3 for negative/positive corona. The results of this work may contribute to understanding the processes in corona discharge and optimising corona discharge systems for various applications.

Molecular insights into the simultaneous removal mechanisms of As(Ⅴ) and Cd(II) in iron tailings slag-biochar composites

Arsenic and cadmium contamination frequently coexist in the real environment. However, it remains a challenge for their simultaneous removal due to their distinct physicochemical properties at low cost. To this end, a cost-effective magnetic biochar adsorbent (ITBNa800) was prepared using biomass waste and iron tailings slag. This composite adsorbent exhibits excellent performance in the simultaneous removal of aqueous As(V) and Cd(II) even at high concentrations with removal efficiencies of up to 99.98% and 96.04%, respectively. Electrostatic action, precipitation, and complexation were adsorption mechanisms. As(V) and Cd(II) were synergistic and competitive adsorption. As(V) removal was mainly due to physical and chemical adsorption, and 42.40%-58.59% of As(V) had been converted to As(III). Cd(II) removal was mainly due to chemical adsorption. Iron oxide and aluminum oxide in ITBNa800 were the keys to As(V), As(III), and Cd(II) adsorption. DFT calculations revealed iron oxide complex As(V), As(III), and Cd(II) molecular clusters through bidentate binuclear, bidentate binuclear, and monodentate binuclear pathways, respectively. Aluminum oxide complex Cd(II) molecular cluster through a bidentate mononuclear pathway. We hope the ITBNa800 adsorbent and its involved mechanism could offer inspiration in the simultaneous treatment of As and Cd pollution.

Synergistic Humidification and Chemical Agglomeration to Improve Capturing the Fine Particulate Matter by Electrostatic Precipitator

The wet electrostatic precipitator (WESP) overcomes the shortcomings of traditional electrostatic precipitators, such as dust re-entrainment and back corona. It can effectively remove high-specific-resistivity dust, with a good removal effect on PM2.5. It is proposed to adopt chemical agglomeration and humidification agglomeration technology in the wet electrostatic precipitators to achieve ultra-low dust emissions from coal-fired power plants. The results show that the addition of chemical agglomerates, surfactants, and water vapor all affect the dust diameter of coal-fired power plants. After adding sesbania gum (SG), the D50 of dust particles increases from 28.29 μm to 48.22 μm. And the D50 of dust particles is 36.46 μm when spraying 3.6 kg/h water vapor only. With the cooperation of chemical agglomeration agents and water vapor, the dust agglomeration effect and removal efficiency can be further improved. When 10 mg/L SG is synergistically combined with 2.9 kg/h water vapor, the D50 is 64.75 μm, and the dust removal efficiency reaches 97.88%. On this basis, by adding 5 mg/L of Hexadecyltrimethylammonium bromide (CTAB), the D50 is 83.06 μm, and the dust removal efficiency increases to 98.62%. The synergistic effect of chemical agglomeration and humidification agglomeration promotes the aggregation of dust from coal-fired power plants. It can improve the removal efficiency of WESP for fine particulate matter but has little impact on the operation of existing equipment. The synergistic effects of multiple agglomeration technologies are also the direction for future research on the removal efficiency of fine particulate matter.

Mn-TiO2 catalyst collaborates with trace O3 to enhance the removal of mercury in ESP environment

Ozone, known for its strong oxidizing properties, is commonly utilized in water pollution control. However, the catalytic ozonation of gaseous pollutants also shows potential as an emission reduction technology. The challenge lies in the high concentrations of ozone required in the catalytic process, which increases costs and complexity, hindering widespread adoption. Industrial electrostatic precipitators (ESPs) powered by high-voltage sources can produce ozone during operation, potentially causing environmental pollution if not managed. This study suggests utilizing a catalyst in the low-concentration ozone environment generated by an ESP for the catalytic oxidation of Hg0 in flue gas. The removal efficiency of Hg0 by either the catalyst alone or ozone alone (O3: 10 ppm) is modest at 43 % and 8 % respectively. However, when combined, the catalyst and ozone demonstrate a remarkable removal efficiency of over 98 %, significantly outperforming their individual capabilities. Furthermore, this process exhibits consistent high efficiency in a wide temperature range of 50–150 ℃. The study reveals that in the absence of O3, adsorbed oxygen acts as the primary oxidant, limiting the oxidation of Hg0. The introduction of O3 enhances electron transfer within the Mn-Ti catalyst, optimizing the electronic structure of oxygen and enhancing the oxidizing capacity of lattice oxygen, resulting in superior Hg0 removal efficiency. These findings offer valuable insights for the catalytic ozonation of Hg0.

Recovery of phosphate from aqueous solution by modified biochar with concentrated seawater and its potential application as fertilizer

Concentrated seawater as a byproduct of seawater desalination, its resource utilization potential has attracted widespread attention because of its rich inorganic salt resources. Concentrated seawater-modified biochar for phosphate recovery is undoubtedly a promising and sustainable option for resource utilization and eutrophication control. In this study, peanut shells as a carbon source, and modified biochar composites were successfully synthesized by co-precipitation with concentrated seawater for phosphate removal from aqueous solution. Meanwhile, the potential of phosphorus-enriched modified biochar as a soil slow-release fertilizer was evaluated. A series of characterization results showed that magnesium/calcium in the form of Mg(OH)2 and CaCO3 were successfully loaded onto the modified biochar composites. Furthermore, the pseudo-second-order kinetic model and Langmuir model can describe the adsorption process more accurately. According to the Langmuir model calculations, the theoretical maximum adsorption of phosphate by modified biochar composite was 173.09 mg/g, which can be compared with those of many Ca/Mg biochar composites. The primary sorption mechanism is electrostatic adsorption, ligand exchange and chemical precipitation interactions between phosphate and modified biochar composites. In addition, it was shown that the phosphorus-rich modified biochar embodied significant effects in improving the germination rate as well as the growth of plants, and had great potential as a slow-release fertilizer for agricultural soils.

Comprehensive effect of increased calcium content in coal on the selenium emission from coal-fired power plants: Combined laboratory and field experiments

Coal combustion is the major contributor to global toxic selenium (Se) emissions. Inorganic elements in coals significantly affect Se partitioning during combustion. This work confirmed that the calcium (Ca) in ash had a stronger relationship with Se retention at 1300 °C than other major elements. Ca oxide chemically reacted with gaseous Se, and its sintering densification slightly affected Se adsorption capacities (44.45 −1840.71→35.17 −1540.15 mg/kg) at 300 − 1300 °C. Therefore, Ca in coals was identified as having potential for hindering gaseous Se emissions, and coals with increased Ca contents (2.74→5.19 wt%) were used in a 350 MW unit. The decreased Se mass distribution (3.54%→2.63%) in flue gas at air preheater inlet (320 −362 °C) confirmed the effectiveness of increased Ca content on gaseous Se emission reduction. More gaseous Se further condensed and was chemically adsorbed by fly ash when passed through an electrostatic precipitator, resulting in a significant increase in the Se content of fly ash. Additionally, the corresponding Se leaching ratio decreased from 4.88 − 35.74% to 1.87 − 26.31%, indicating enhanced stability of Se enriched in fly ash. This research confirmed the feasibility and environmental safety of sequestration of gaseous Se from flue gas to fly ash by increasing the Ca content in coals.

Gas-particle flow induced erosion of economizer in low-low temperature electrostatic precipitators: Numerical prediction and engineering application

In this work, the gas-particle flow and the induced erosion in the economizer region in low-low temperature electrostatic precipitator were investigated by CFD-DPM-EPM coupling approach. The results show that positioning the economizer on the vertical flue or employing a vertical tubes arrangement for the heat exchange tubes, utilizing a small expansion angle (less than 35°) in the expansion section, ensuring a more uniform distribution of inlet gas velocity and dust concentration, and incorporating short and densely positioned guide plates in the expansion section can effectively reduce erosion in the low-temperature economizer. The above results were applied to the economizer equipped with the low-low temperature electrostatic precipitator of a 1000 MW unit in a certain power plant, and the wear situation was significantly improved. The research findings can serve as a reference for diagnosing and analyzing erosion phenomena in low-temperature economizer, and can guide the improvement design to prevent erosion.

Collection of nanoparticles by electrostatic precipitation operating over a wide range of electric fields

ABSTRACT In the electrostatic precipitation of microparticles, it is common to evaluate the voltages between the corona onset voltage and the breakdown point. However, the charging of particles in the nanoscale size range mainly occurs by diffusion, suggesting the possibility of its occurrence, even at low values. This paper investigates the implications of a wide range of electric fields applied in the collection of nanoparticles (6.15–241.4 nm). Two electrostatic precipitators (P.I. and P.II.), both with plates 10 cm high and 30 cm long, but with different plate spacings (4 and 6.5 cm), were tested using three air velocities (1.9, 2.9, and 3.9 cm/s) and 36 electric fields (0.0 − 5.0 kV/cm). Under the highest electric fields, both precipitators showed efficiencies above 99.9%. Furthermore, nanoparticles were collected before the corona onset voltage, with efficiencies of around 28% (P.I.) and 35% (P.II.). Even though no current was detected by the high voltage source, charges on the particles were measured in electric fields lower than 3.0 kV/cm. The higher the applied voltage, the higher the residual charge of the particles at the precipitator outlet. It is expected that the findings of this work should contribute to the technological development of electrostatic processes for air treatment.

Synthesis of MgO-Coated Canna Biochar and Its Application in the Treatment of Wastewater Containing Phosphorus

In order to treat phosphorus-containing wastewater and realize the resource utilization of wetland plant residues, biochar was prepared by the pyrolysis of canna aquatic plant waste at 700 °C, and the adsorption characteristics of phosphorus by MgO-modified biochar (MBC) were explored. The main results are as follows: the adsorption capacity of the MBC was eight times that of unmodified biochar (BC), and the adsorption capacity was up to 244 mg/g. The isothermal adsorption data were consistent with the Langmuir equation, which indicates monolayer adsorption. The functional groups changed little before and after the modification, but a new diffraction peak appeared after the modification. Compared with the standard card, it was suggested that there were MgO crystals with a higher purity. SEM images showed that the BC had a smooth surface, an obvious pore structure, and a thin pore wall, while the MBC had a rough surface and a layered structure, which can provide more adsorption sites for phosphate adsorption. In addition, an XPS analysis showed that Mg3(PO4)2 crystals appeared on the surface of the MBC after adsorption. The mechanism analysis showed that MgO is an important substance for MBC to adsorb phosphorus, and electrostatic adsorption and complex precipitation play key roles. In the test to verify the removal of actual phosphorus-containing wastewater by MBC, it was found that the removal rates for wastewater with 2.06 mg/L and 199.8 mg/L of phosphorus by MBC were as high as 93.4–93.9% and 99.2–99.3%, respectively. MBC can be used as an efficient adsorbent for phosphorus removal.

Oyster shell-modified lignite composite in globular shape as a low-cost adsorbent for the removal of Pb2+ and Cd2+ from AMD: Evaluation of adsorption properties and exploration of potential mechanisms

A low-cost composite adsorption material has been synthesized from fishery wastes and natural minerals to address challenges such as ecological balance destruction caused by high concentrations of Pb and Cd in acid mine drainage (AMD), unreasonable use of low-caloric lignite, and environmental pollution caused by idle accumulation of oyster shells. This new adsorbent can effectively treat AMD by improving acidity and adsorbing Pb2+ and Cd2+. In this study, oyster shell-modified lignite composite in globular shape (OSL-G) was synthesized by using pyrolyzed oyster shell and lignite, with the addition of bentonite adhesive. The adsorption properties of OSL-G on AMD were evaluated, and the potential mechanism of OSL-G repairing AMD was explored. The results showed that when the mass ratio of oyster shell to lignite was 1:1, oyster shell-modified lignite composite (OSL) was synthesized at 900 °C for 20 min. When the adhesive content was 15.50 %, the roasting temperature was 640 °C, and the roasting time was 2.35 h, OSL-G was synthesized and the adsorption effect was the best. The OSL-G could effectively treat AMD with pH 4 ∼ 5 and initial Pb2+ and Cd2+ concentrations of 10 mg/L within 600 min at a dosage of 4 g/L. The OSL-G adsorption process followed the quasi-second-order kinetic model and the Freundlich model. The maximum adsorption saturation capacities of Pb2+ and Cd2+ were 107.2821 mg/g and 8.3777 mg/g at 298.15 K, respectively. The adsorption process was a multistep controlled spontaneous endothermic process. The potential mechanism was mainly the adsorption-condensation coexistence results of electrostatic adsorption, neutralization precipitation, ion exchange, and surface complexation. The removal rates of Pb2+ and Cd2+ of the recovered OSL-G (ROSL-G) were still high, reaching 57.26 % and 50.38 % after 5 times of adsorption–desorption, respectively. The applicability of ROSL-G after adsorption–desorption for other heavy metal components in AMD proved its good application potential. This study suggested that OSL-G can be used as a promising environmentally friendly adsorbent for AMD. This study provided a broad picture of the management and reuse possibilities of fishery wastes and natural mineral resources, and addressed established, current, and potential strategic needs, particularly in terms of sustainability challenges and ecological civilization construction.

Cd/Pb behavior during combustion in a coal-fired power plant and their spatiotemporal impacts on soils: New insights from Cd/Pb isotopes

Coal power plants annually generate quantities of byproducts that release environmentally hazardous heavy metals like Cd and Pb. Understanding the behavior and spatiotemporal impacts on soils of these releases is crucial for pollution control. This study investigated the concentrations and isotope ratios of Cd/Pb in combustion byproducts, depositions and soils collected from a coal-fired power plant or its surrounding area. The pulverized fuel ash (PFA) and desulfurized gypsum (DG) exhibited heavier Cd isotopes with Δ114Cd values of 0.304‰ and 0.269‰, respectively, while bottom ash (BA) showed lighter Cd isotopes (Δ114CdBA-coal = –0.078‰), compared to feed coal. We proposed a two-stage condensation process that governs the distribution of Cd/Pb, including accumulation on PFA and DG within electrostatic precipitators and desulfurization unit, as well as condensation onto fine particles upon release from the stack. Emissions from combustion and large-scale transport make a significant contribution to deposition, while the dispersion of Cd/Pb in deposition is primarily influenced by the prevailing wind patterns. However, the distribution of Cd/Pb in soils not only exhibit predominant wind control but is also potentially influenced by the resuspension of long-term storage byproducts. The power plant significantly contributes to soil in the NW–N–NE directions, even at a considerable distance (66%–79%), demonstrating its pervasive impact on remote regions along these orientations. Additionally, based on the vertical behavior in the profile, we have identified that Cd tends to migrate downward through leaching, while variations in Pb respond to the historical progression of dust removal.

Efficient Recovery of Phosphate from Water Media by Iron-Magnesium Functionalized Lignite: Adsorption Evaluation, Mechanism Revelation and Potential Application Exploration.

Selective phosphorus removal from aquatic media has become an ideal strategy to mitigate eutrophication and meet increasingly stringent discharge requirements. To achieve phosphorus control and resource utilization of low-calorific-value lignite, iron and magnesium salts were used to functionalize lignite, and iron-magnesium functionalized lignite (called IM@BC) was prepared for phosphate recovery from water media. The adsorption properties of IM@BC were systematically evaluated, especially the influence of ambient pH and co-existing ions. The kinetic, isothermal, and thermodynamic adsorption behaviors of IM@BC were analyzed. The adsorption mechanism was revealed by microscopic characterization. The potential application of phosphate-containing IM@BC (P-IM@BC) was explored. The results show that IM@BC has a strong phosphate adsorption capacity, and the maximum adsorption capacity is 226.22 mgP/g at pH = 3. Co-existing CO32- inhibits phosphate adsorption, while coexisting Ca2+ and Mg2+ enhance the effect. At the initial adsorption stage, the amount of phosphate adsorbed by IM@BC continues to increase, and the adsorption equilibrium state is gradually reached after 24 h. The adsorption process conforms to the pseudo-second-order kinetic model (PSO) and Langmuir isothermal adsorption model, and the adsorption process is mainly chemical adsorption. The phosphate absorption capacity is positively correlated with temperature (283.15 K~313.15 K), and the adsorption process is spontaneous, endothermic, and entropy-increasing. Its adsorption mechanism includes electrostatic attraction, ion exchange, surface precipitation, and coordination exchange. IM@BC can efficiently recover phosphate from actual phosphorus-containing wastewater with a recovery efficiency of up to 90%. P-IM@BC slowly releases phosphate from pH 3 to 11. Plant growth experiments showed that P-IM@BC could be used as a slow-release fertilizer to promote the root growth of cowpeas. The novelty of this work lies in the development of a highly efficient phosphate recovery adsorbent, which provides a feasible method of phosphorus control in water media and resource utilization of lignite.