Phosphorus Adsorption Capacity Research Articles

Synthesis, characterization, and phosphorus adsorption of Mg/Fe-modified biochar from cotton stalk pretreated with Coriolus versicolor.

In recent years, the research potential in utilizing biochars as adsorbents in adsorption processes has grown due to their eco-friendly and economical nature. However, biochar often possesses a negative surface charge that limits its affinity for binding anions. Nitric acid washing and pretreatment with Coriolus versicolor can break down the lignocellulosic structure in cotton stalk waste, facilitating the subsequent impregnation of Mg and Fe metal oxides. These pretreatment steps can lead to the production of diverse and functionalized biochars with higher adsorption capacities. In this study, cotton stalk waste was first washed with diluted nitric acid and then subjected to biological pretreatment by incubation with C. versicolor, followed by impregnation with Mg and Fe to obtain CV-CS/Fe and CV-CS/Mg biochars. The results showed that the applied pretreatments altered the physicochemical properties and significantly increased the phosphorus adsorption capacity. The adsorption capacities of CV-CS/Fe and CV-CS/Mg biochars were found to be 277.88 and 507.01 mg g-1, respectively. The results indicate that the incorporation of multiple metal oxide impregnates enhances P adsorption. Furthermore, in the kinetic study, pseudo-first-order and pseudo-second-order models provided a well fit, determining chemical adsorption as the main adsorption mechanism for phosphorus adsorption. The biochars demonstrated compatibility with Langmuir-Freundlich models. Overall, the findings suggest the possibility of synthesizing biochars with improved adsorptive properties through pretreatment, and these engineered biochars hold promising potential as effective adsorbents in the field. PRACTITIONER POINTS: Eco-friendly, natural, and economical biochar was synthesized. Biochar was produced via Coriolus versicolor pretreatment. High adsorption capacities of CV-PS/Mg biochars were found to be 507.01 mg g-1. Adsorption capacities of biochars can be improved by pretreatment.

Soil Properties Related to Phosphorus Sorption and Prediction of Maximum Phosphorus Adsorption Capacity of Soils from Southern Brazil

Soil Properties Related to Phosphorus Sorption and Prediction of Maximum Phosphorus Adsorption Capacity of Soils from Southern Brazil

Adsorption of phosphate over a novel magnesium-loaded sludge-based biochar.

The production of sludge-based biochar to recover phosphorus (P) from wastewater and reuse the recovered phosphorus as agricultural fertilizer is a preferred process. This article mainly studied the removal of phosphate (PO4-P) from aqueous solution by synthesizing sludge-based biochar (MgSBC-0.1) from anaerobic fermentation sludge treated with magnesium (Mg)-loading-modification, and compared it with unmodified sludge-based biochar (SBC). The physicochemical properties, adsorption efficiency, and adsorption mechanism of MgSBC-0.1 were studied. The results showed that the surface area of MgSBC-0.1 synthesized increased by 5.57 times. The material surface contained MgO, Mg(OH)2, and CaO nanoparticles. MgSBC-0.1 can effectively remove phosphate in the initial solution pH range of 3.00-7.00, with a fitted maximum phosphorus adsorption capacity of 379.52 mg·g-1. The adsorption conforms to the pseudo second-order kinetics model and Langmuir isotherm adsorption curve. The characterization of the adsorbed composite material revealed the contribution of phosphorus crystal deposition and electrostatic attraction to phosphorus absorption.

Evaluation of Phosphorus Enrichment in Groundwater by Legacy Phosphorus in Orchard Soils with High Phosphorus Adsorption Capacity Using Phosphate Oxygen Isotope Analysis.

Long-term phosphorus (P) fertilization results in P accumulation in agricultural soil and increases the risk of P leaching into water bodies. However, evaluating P leaching into groundwater is challenging, especially in clay soil with a high P sorption capacity. This study examined whether the combination of PO4 oxygen isotope (δ18OPO4) analysis and the P saturation ratio (PSR) was useful to identify P enrichment mechanisms in groundwater. We investigated the groundwater and possible P sources in Kubi, western Japan, with intensive citrus cultivation. Shallow groundwater had oxic conditions with high PO4 concentrations, and orchard soil P accumulation was high compared with forest soil. Although the soil had a high P sorption capacity, the PSR was above the threshold, indicating a high risk of P leaching from the surface orchard soil. The shallow groundwater δ18OPO4 values were higher than the expected isotopic equilibrium with pyrophosphatase. The high PSR and δ18OPO4 orchard soil values indicated that P leaching from orchard soil was the major P enrichment mechanism. The Bayesian mixing model estimated that 76.6% of the P supplied from the orchard soil was recycled by microorganisms. This demonstrates the utility of δ18OPO4 and the PSR to evaluate the P source and biological recycling in groundwater.

Removal of phosphorus from water bodies using high-performance ceramsite prepared from solid wastes

This study successfully prepared a high-performance ceramsite for phosphorus adsorption using the sintering method, incorporating regolith granite sand-washing sludge (RGSWS) and phosphate tailings as raw materials. The optimal conditions for ceramsite preparation were determined as a ratio of RGSWS to phosphate tailings at 6:4, and sintering at 900 °C for 30 min. The impacts of various factors, such as the prepared ceramsite dosage, different initial phosphorus concentrations, temperature, pH, and co-existing ions were explored, and the reusability and safety of the ceramsite were also investigated. The results show that the ceramsite has a high adsorption capacity for phosphorus (20.40 mg/g) at pH 7 with broad applicability in the pH range of 3–11 and good selective adsorption in the presence of coexisting ions. Additionally, the application of ceramsite does not cause secondary pollution, and the ceramsite still maintains a high removal rate after being reused five times. XRD, FT-IR, XPS, and SEM-EDS analysis showed that chemical precipitation, surface complexation, and electrostatic attraction were involved in the adsorption process. It can be well described by the pseudo-second-order kinetic model and the Langmuir model, and the phosphorus adsorption by ceramsite was a spontaneous endothermic reaction process with increasing chaos. This research presents an effective solution for phosphorus removal from water bodies and offers a sustainable approach toward solid waste utilization.

Study on the removal efficacy and mechanism of phosphorus from wastewater by eggshell-modified biochar.

The excessive discharge of phosphorus from rural domestic sewage is a problem that worthy of attention. If the phosphorus in the sewage were recovered, addressing this issue could significantly contribute to mitigating the global phosphorus crisis. In this study, corn straw, a common agricultural waste, was co-pyrolytically modified with eggshells, a type of food waste from university cafeterias. The resulting product, referred to as corn straw eggshell biochar (EGBC) was characterized using SEM, XRD, XPS, XRF, and other methods. Batch adsorption experiments were conducted to determine the optimal preparation conditions of EGBC and to explore its adsorption characteristics. EGBC showed strong adsorption effectiveness within a pH range of 5-12. The adsorption isotherm closely followed the Sips model (R2 > 0.9011), and the adsorption kinetics were more consistent with the pseudo-second-order model (R2 > 0.9899). The process was found to be both spontaneous and endothermic. Under optimal conditions, the phosphorus adsorption capacity of EGBC was measured to be 288.83 mg/g. This demonstrates the high efficiency of EGBC for phosphorus removal and illustrates an effective method of utilizing food waste for environmental remediation. PRACTITIONER POINTS: Biochar prepared from waste eggshell was used to removal and recovery phosphorus in wastewater treatment. EGBC has an impressive adsorption capacity that can reach up to 288.83 mg/g. EGBC has excellent adsorption and filtration capabilities, and there is a sudden increase in concentration at 900 min in the breakthrough curve of EGBC. EGBC has good regeneration performance, with an adsorption effect of 65% and an adsorption capacity of 121 mg/g after four desorption and regeneration cycles.

Construction of 3D network aluminum sludge-based hydrogel beads: combination of macroization, amino functionalization, and resource utilization.

An aluminum sludge-based composite material was constructed against the problems of phosphorus pollution and the waste of aluminum sludge resources. Utilizing metal Ce doping and hydrogel microbeads with pore preparation, the adsorption performance of the original sludge was improved. Meanwhile, the macroscopic body was constructed, and on this basis, polyethyleneimine (PEI) was introduced to complete the amino functionalization further to enhance the adsorption of phosphorus by the adsorbent, and NH-CeAIS-10 microbeads were successfully prepared. In adsorption, microbeads with larger specific surface area and richer functional groups are better choice compared to original sludge. The results of SEM, BET, FT-IR, and XPS analyses indicate that the adsorption of phosphorus by the microbeads is mainly achieved through electrostatic interactions, ligand exchange, and the formation of inner-sphere complexes. According to the Langmuir model, the maximum phosphorus adsorption capacity of NH-CeAIS-10 was 29.56mgg-1, which was four times higher compared to native aluminum sludge. This also confirms the significant enhancement of phosphorus adsorption through the modification of aluminum sludge. Besides, in dynamic adsorption column experiments, the material exhibited up to 99% removal in simulated wastewater for up to 30days, demonstrating the great adsorption potential of NH-CeAIS-10 in engineering applications.

Phosphorus adsorption characteristics and release risk in saline soils: a case study of Songnen Plain, China.

The Songnen Plain is one of the three major saline-alkali areas in China, covering a vast area, where drought and overgrazing have exacerbated the salinization trend, and will have great potential for development if utilized rationally. Phosphorus, as one of important soil nutrients, plays a crucial role in plant growth. How to minimize its loss and migration has become a current research hotspot. The objective of the present study was to elucidate the adsorption properties of phosphorus in soils affected by salinization and to establish the correlation between the potential for phosphorus release and soil properties. A batch treatment test was conducted in this study using three soils with the various salinization degrees to examine the impact of environmental factors on the adsorption properties and potential release of phosphorus. It was found that the maximum phosphorus adsorption by the three salinization soils in 0-360 minutes accounted for 86.8%-90.5% of the total adsorption capacity; the equilibrium adsorption capacity was: HS> MS> LS. In cases where the phosphorus level in the surrounding liquid is low, the three levels of salinized soils exhibited varying levels of phosphorus discharge, with the adsorbent acting as the origin of contaminants. The Pseudo-second-order model kinetics and Langmuir equation can well describe the adsorption process, and the adsorption process is spontaneous heat absorption with entropy increase. Increasing the pH led to an increase in the adsorption of phosphorus from the three salinized soils. Additionally, the adsorption was enhanced by introducing varying concentrations of Na+, Ca2+, and Al3+ to the background solution. The phosphorus eutrophication release risk (ERI) demonstrated a gradual decline as temperature increased. Correlation analysis revealed a noteworthy positive correlation between TN, TP, and ERI, as well as a significant negative correlation between CEC, K+, and ERI. Furthermore, there was a highly significant negative correlation between coarse silt and fine silt. Considering local climatic and environmental factors is crucial for controlling the adsorption capacity of phosphorus in various salinized soils, as it can unveil the mechanism of phosphorus adsorption and impact its migration and release risk.

Experimental Study on Enhanced Phosphorus Removal Using Zirconium Oxychloride Octahydrate-Modified Efficient Phosphorus Removal Composite

In addressing eutrophication and enhancing water quality, this study builds upon previous research involving the development of an Efficient Phosphorus Removal Composite (EPRC), a material created using modified industrial wastes (steel slag and fly ash) as adsorbent substrates, supplemented with a binder and porosity-forming agent. In this investigation, the EPRC was further enhanced through the addition of zirconium oxychloride octahydrate, resulting in the production of Zr-EPRC particles as reinforced phosphorus removal materials. Comparative experiments were conducted to assess different methods for preparing Zr-EPRC, the static adsorption performance, and dynamic adsorption behavior. The optimal preparation of Zr-EPRC was achieved by separately modifying the base materials, steel slag and fly ash. Loading with mass ratios of zirconium chloride octahydrate to fly ash and steel slag at 0.4 and 0.6, respectively, for a duration of 12 h at a pH of 10 yielded the best results. In static adsorption experiments conducted at temperatures of 15 °C, 25 °C, and 35 °C, Zr-EPRC exhibited saturated phosphorus adsorption capacities of 11.833 mg/g (variance = 0.993), 12.550 mg/g (variance = 0.993), and 13.462 mg/g (variance = 0.996), respectively. Zr-EPRC emerges as a cost-effective and readily available solution with promising stability for general wastewater treatment applications, contributing significantly to the mitigation of eutrophication and the improvement of water quality.

Selective recovery of phosphorus from the leachate of incinerated sewage sludge ash using the Zr-modified acid-leaching residue as adsorbent for two-fold resource utilization

Phosphorus, as an essential nutrient for plant growth, is crucial for the development of agriculture. In this study, a novel strategy using a zirconium-modified acid-leaching residue adsorbent (Zr-AR adsorbent) was proposed for the efficient and selective recovery of phosphorus from incinerated sewage sludge ash (ISSA). 0.2 mol/L HCl were optimized for the phosphorus extraction from ISSA. The acid-leaching residue with large pore structure and high specific surface area was first reused as a support to prepare Zr-AR adsorbent for a twofold resource utilization of ISSA. Without removing impurities from the leachate, the Zr-AR adsorbent could selectively adsorb phosphorus with a maximum phosphorus adsorption capacity of 53.1 ± 0.8 mg/g in the HCl system. During 5 phosphorus adsorption–desorption processes, the adsorption and desorption ratios of phosphorus remained stable at over 90 %, indicating the high stability of the Zr-AR adsorbent for selective phosphorus recovery. Without adjusting the pH, hydroxyapatite was produced from the phosphorus-rich solution with a phosphorus content of 33.4 ± 1.3 % P2O5, which could significantly promote the growth of ryegrass as a phosphorus fertilizer. The cost of the phosphorus recovery from ISSA was also preliminarily evaluated ($3.76 kg-P product), demonstrating the application potential of this strategy.

Enhanced selective adsorption of low-concentration phosphorus via layered La2O2CO3 with high environmental adaptability

The highly selective deep purification of low-concentration phosphorus has garnered increasing attention. This article employs a novel strategy involving the calcination and reconstruction of Mg/La LDH, leading to the successful preparation of La-based adsorbents (LC-1, LC-2, LC-3). Among them, LC-1, which features a layered La2O2CO3 structure, exhibits excellent phosphorus adsorption performance. At a low dosage (0.1 g/L), it rapidly reached adsorption equilibrium within 100 min, ultimately reducing the phosphorus concentration from 10 mg/L to less than 0.02 mg/L. In the pH 2–13 tests and regeneration tests, LC-1 displays minimal La leaching (<0.04 mg/L) and stability of 10 cycles phosphorus removal (adsorption capacity exceeds 90 mg/g), in contrast to the performance of Mg/La LDH (limited to 5 cycles). LC-1 also has extraordinary environmental adaptability, exhibiting a phosphorus adsorption capacity of over 95.7 mg/g in the presence of interfering anions and humic acid (HA), as well as maintaining a phosphorus adsorption capacity of over 85 mg/g at 5 °C. Analysis suggests that the novel preparation strategy was conducive to forming stable La2O2CO3 species, alleviating metal ion dissolution and optimizing the content and proportion of La3+, electrophilic oxygen species (O22−/O−) and interlayer CO32−. The above are critical factors in controlling the adsorption rate, improving the pH resistance and stability of adsorbents. In summary, La2O2CO3 has not only exhibited outstanding adsorption performance but also boasted a simple preparation strategy, rendering it highly promising for applications in the removal of low-concentration phosphorus.

Fabrication of sodium alginate-doped carbon dot composite hydrogel and its application for La (III) adsorption and enhanced the removal of phosphorus.

Adsorption is an effective method for the removal of hazardous substances from wastewater. In this work, a low-cost and environmental-friendly composite hydrogel material of sodium alginate doped with nitrogen doped carbon dots (SA@NCDs) was fabricated by impregnation for lanthanide and enhanced phosphorus adsorption in wastewater. The effects of NCDs doping amount, dosage, pH, initial solution concentration, adsorption time and temperature on the process of La (III) adsorption by SA@NCDs were investigated. The adsorption isotherms fitted to Langmuir isotherm model (R2 = 0.9970-0.9989) and the adsorption kinetics followed pseudo-second-order kinetic model (R2 = 0.9992). The maximum adsorption capacity of the adsorbent for La (III) was 217.39mg/g according to the Langmuir model at 298.15K. After five cycles, the removal efficiency of La (III) adsorbed by SA@NCDs was still 85.1%. Moreover, the loaded La (III) enhanced the adsorption of phosphorus. The La (III)-SA@NCDs-5 hydrogel adsorbent greatly improved the adsorption capacity for phosphorus compared with the La (III)-free adsorbent, and the adsorption amount can reach 9.64mg-P/g. The SA@NCDs complex hydrogels for rare earth adsorption were prepared by introducing NCDs rich in amino group into SA hydrogels. The introduction of NCDs increases the adsorption sites of hydrogels, and also overcomes the problem that NCDs itself is difficult to recover in wastewater treatment applications. The lanthanide adsorbed material has a stable structure and can be used to remove phosphorus to deal with waste using the waste. It indicates the SA@NCDs hydrogel composite adsorbent have good potential for wastewater treatment.

Effect of filling materials on reconstructed soil phosphorus adsorption and desorption in mining area

Utilization of alternative soil substrates for minesoil reconstruction can affect the nutrient status of reclaimed minesoil (RMS), particularly the availability of phosphorus. This study investigated the adsorption and desorption capacities of phosphorus in three typical reclamation lands using coal gangue (CGR), lake mud (LMR), and Yellow River sand (YSR) as filling materials. The results showed that (i) the phosphorus adsorption capacity of all RMS samples was lower than that of the normal cultivated soil (NCS), the YSR was lower than the CGR and LMR in phosphorus adsorption capacities, while the YSR had better phosphorus desorption capacity than the CGR and LMR. (ii) The specific surface area, pore size, soil texture, mineral composition, functional group composition, and iron/aluminum element content of RMS were varied after the filling of alternative soil substrates, and (iii) the surface characteristics played a vital role in driving the phosphorus adsorption-desorption, while soil texture, and organic matter drove the phosphorus desorption behavior via non-linear ways. This study reveals the difference of phosphorus adsorption-desorption in RMS, and provides a theoretical basis for the rational utilization of alternative soil substrates and the improvement of reclamation land in coal mining subsidence areas.

Phosphate recovery from wastewater by rapid adsorption-desorption enrichment over UiO-66@melamine sponge composites

Excessive discharge of phosphorus (P) to natural watercourses not only causes eutrophication of water bodies but also results in the loss of P resources. P-containing wastewater is a crucial secondary P resource. Zirconium-based metal-organic frameworks (MOFs), particularly UiO-66 has been shown great promise in efficiently capturing P from water. In this study, a group of UiO-66@sponge composites was prepared by a facile layer-by-layer in-situ growth approach using melamine sponge (MS) as scaffolds. The as-prepared UiO-66@sponge composites exhibit high chemical and dimensional stability when used as adsorbents for reclaiming P from wastewater. Batch adsorption results show that one UiO-66@sponge composite exhibited the highest phosphorus adsorption capacity of 83.55 mg g−1 at pH 6.0, outperforming most other UiO-66 adsorbents under environmentally relevant conditions. The intrinsic mechanical flexibility and chemical stability of these UiO-66@sponge composites enable us to efficiently enrich phosphorus from a dilute solution by a rapid adsorption-desorption operation. This work provides a promising strategy to integrate MOFs with dimensionally stable and flexible sponges for rapid adsorption and recovery of phosphate from wastewater and could be potentially expanded to the recovery of other value-added or technology-critical elements from waste streams.

Phosphorus adsorption using chemical and metal chloride activated biochars: Isotherms, kinetics and mechanism study

Efficient treatment of nutrient-rich wastewater is of paramount importance for protecting the ecosystem. In this work, an efficient, abundant, and eco-friendly adsorbent was derived from biochar and employed for phosphorus (P) adsorption. The key factors influencing the P removal efficiency of the activated biochar, including P concentration, pH, dosage, temperature, adsorption time, and influence of co-existing ion type, were investigated. Maximum P adsorption percentage (100%) was obtained with 10 mg/L and zinc chloride activated biochar (BC–Zn) compared to the other activated biochars. Results show that by increasing the P concentration from 5 to 200 mg/L, the phosphorus adsorption capacity increases from 0.13 to 10.4 mg/g biochar. Isotherms and kinetic studies further show that the P adsorption follows the Langmuir and quasi-second-order kinetic models. The mechanistic investigation demonstrated that P adsorption occurred by precipitation reaction. Furthermore, P desorption has been studied at different time intervals to understand the P release rate after adsorption.

Sustainable phosphorus adsorption and recovery from aqueous solution by a novel recyclable Ca-PAC-CTS

Phosphorus removal has been explored for a long time, however sustainable phosphorus adsorption and recovery with adsorbents recycling is rarely reported. This work proposes a sustainable phosphorus recycling route with calcium-modified powdered activated carbon with chitosan (Ca-PAC-CTS). The morphology, functional groups and crystal structure of Ca-PAC-CTS were characterized. The maximum phosphorus adsorption capacity was 16.73 mg/g Ca-PAC-CTS with Langmuir model at 298 K. Stable phosphorus sorption on Ca-PAC-CTS could be observed at the large range of pH (4– 10) when coexisting with NO3−, SO42−, Cl− and F−, except HCO3−. 98.95 % The recovery of adsorbed phosphorus could get to 98.95 % using 0.05 M sulfuric acid solution, and the phosphate adsorption efficiency through Ca-PAC-CTS remained to be more than 80 % after five adsorption-desorption cycles, suggesting that Ca-PAC-CTS was one of the promising adsorbents for sustainable removal and recovery of phosphorus in aqueous solution.

Significant Improvement of Adsorption for Phosphate Removal by Lanthanum-Loaded Biochar.

Due to eutrophication, removing phosphate ions from wastewater has received a lot of attention. In order to improve the phosphorus adsorption capacity of the material, this study used biomass pyrolysis to create a series of biochars modified with metal chloride ions. In accordance with adsorption tests, lanthanum-loaded biochar (LCBC) had a significant phosphorus adsorption capacity of approximately 666.67 mg/g, which was 30 times greater than that of pristine biochar. Adsorption kinetic analysis revealed that the LCBC's adsorption process could be fitted to the pseudo-secondary kinetic equation, indicating that chemical processes were primarily responsible for controlling the adsorption process. Zeta potential, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis showed that the main adsorption mechanism of LCBC for phosphate removal was electrostatic attraction of protonated H+ with negatively charged mono-hydrogen phosphate and dihydrogen phosphate ions and complexation reaction of the C=O on the carboxyl group and P=O on the phosphate group with the oxygen on the phosphate group and hydroxyl group. According to regeneration performance results, LCBC performed relatively better than as-prepared adsorbents, and the phosphate removal rate was approximately 75.1% after the fifth regeneration cycle. The study provided a potential approach for creating and preparing an adsorbent with high adsorption for phosphate removal.

Bi-functional biochar-g-C3N4-MgO composites for simultaneously minimizing pollution：Photocatalytic degradation of pesticide and phosphorus recovery as slow-release fertilizer

Significant progress has been made in the development of phosphorus recovery adsorbents and photocatalysts for degradation of pesticides. However, the bifunctional materials for phosphorus recovery and photocatalytic degradation of pesticides have not been designed, and the mechanism of the interaction between photocatalysis and P adsorption remains unexplored. Herein, we develop biochar-g-C3N4-MgO composites (BC-g-C3N4-MgO) with bi-function application to minimize water toxicity and eutrophication. The results show phosphorus adsorption capacity of the BC-g-C3N4-MgO composite reaches 111.0 mg·g-1, and its degradation ratio of dinotefuran reaches 80.1% within 260 min. The mechanism studies show that MgO can play variety roles in BC-g-C3N4-MgO composite, in which can improve the adsorption capacity of phosphorus, enhance the utilization efficiency of visible light and the separation efficiency of photoinduced electron-hole pairs. The biochar existed in BC-g-C3N4-MgO serves as charge transporter with a good conductivity, which promotes the fluent transfer of photo-generated charge carriers. The ESR indicates that both •O2− and •OH generated from BC-g-C3N4-MgO are responsible for dinotefuran degradation. Finally, pot experiments reveal that P laden BC-g-C3N4-MgO promotes the growth of pepper seedlings with high P utilization efficiency of 49.27%.

Physicochemical Properties and Phosphorus Adsorption Capacity of Ceramsite Made from Alum Sludge

Alum sludge is an inevitable by-product from the water purification process, which had been applied as substrates in some constructed wetlands with good performance, especially for phosphorus (P) adsorption. The raw alum sludge is similar to a clay lump with an irregular shape, and there is a concern of it leaching into water. For better reuse, herein, some sludge was fired to produce alum sludge ceramsite (ASC) with a uniform spherical shape via a four-step process of kneading the sludge ball, air drying, preheating at 400 °C for 10 min, and firing at 600 °C for 5 min. Meanwhile, an air-dried alum sludge ball (adASB) was manufactured for comparison. The physicochemical properties and P adsorption ability of ceramsite were investigated subsequently. Through XRD and FT-IR tests, there was no obvious difference between ASC and adASB on the phase structure, but there was a certain amount of Al-OH group loss on the surface of ASC. The structure of ASC was still amorphous, similar to adASB, while ASC possessed more micropore structure and a bigger specific surface area than adASB. Adsorption experiments showed the P adsorption behaviors of ASC and adASB were much similar, and their adsorption kinetics were in accordance with the two-step adsorption kinetics rate equation and pseudo-second-order kinetics equation. The maximum adsorption capacities of ASC and adASB fitted by the Langmuir model were 1.66 mg/g and 1.89 mg/g, respectively. It should be pointed out that, compared with other adsorbents, the ASC produced in this study still had a greater ability to adsorb P. Therefore, ASC should have a great application potential for P removal in wastewater treatment in China.

Potentially migrating and residual components of biochar: Effects on phosphorus adsorption performance and storage capacity of black soil

Biochar has great potential to increase the soil nutrient storage capacity. However, with aging, biochar gradually disintegrates and releases fractions with migration potential, resulting in unknown effects on soil nutrient regulation. Based on this problem, we used ultrasound to separate original biochar (TB) into potentially migrating biochar (DB) and residual biochar (RB). The elemental composition and pore characteristics of TB, DB and RB were analyzed. Different fractions of biochar were applied to black soil, and the kinetic model and isothermal adsorption models were used to explore the adsorption characteristics of different treatments. Then, the effects of initial pH and coexisting ions on adsorption were compared. The adsorption mechanism and potential leaching process of phosphorus in soil were investigated. The results showed that RB had higher O and H contents and was less stable than TB, while RB was more aromatic. The phosphorus adsorption capacity of different treatments was SRB (1.3318 mg g−1) > STB (1.2873 mg g−1) > SDB (1.3025 mg g−1) > SCK (1.1905 mg g−1). SRB had optimal phosphorus adsorption performance and storage capacity, with a maximum adsorption capacity of 1.6741 mg g−1 for the Langmuir isotherm, and it also showed excellent applicability in a pH gradient and with coexisting ions. The main adsorption mode of phosphorus by different treatments was monolayer chemisorption, related to electrostatic repulsion and oxygen-containing functional groups. DB was less effective in inhibiting soil phosphorus migration, with the cumulative leaching of SDB reaching 8.99 mg and the percentage of phosphorus in the 0–6 cm soil layer reaching only 15.42%. Overall, the results can help elucidate potential trends in the adsorption performance and migration process of soil phosphorus by biochar, and improve the comprehensive utilization efficiency of biochar.