Incorporation of iron (oxyhydr)oxide nanoparticles with expanded graphite for phosphorus removal and recovery from aqueous solutions

Removal of phosphorus by modified bentonite:polyvinylidene fluoride membrane-study of adsorption performance and mechanism

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

La-Ca/Fe-LDH-coupled electrochemical enhancement of organophosphorus removal in water: Organophosphorus oxidation improves removal efficiency

Metal ions or metal (hydrogen) oxides are widely used as active sites in the construction of phosphate-adsorbing materials in water, but the removal of soluble organophosphorus from water remains technically difficult. Herein, synchronous organophosphorus oxidation and adsorption removal were achieved using electrochemically coupled metal-hydroxide nanomaterials. La-Ca/Fe-layered double hydroxide (LDH) composites prepared using the impregnation method removed both phytic acid (inositol hexaphosphate, IHP) and hydroxy ethylidene diphosphonic acid (HEDP) acid under an applied electric field. The solution properties and electrical parameters were optimized under the following conditions: organophosphorus solution pH = 7.0, organophosphorus concentration = 100 mg L-1, material dosage = 0.1 g, voltage = 15 V, and plate spacing = 0.3 cm. The electrochemically coupled LDH accelerates the removal of organophosphorus. The IHP and HEDP removal rates were 74.9% and 47%, respectively in only 20 min, 50% and 30% higher, respectively, than that of La-Ca/Fe-LDH alone. The removal rate in actual wastewater reached 98% in only 5 min. Meanwhile, the good magnetic properties of electrochemically coupled LDH allow easy separation. The LDH adsorbent was characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. It exhibits a stable structure under electric field conditions, and its adsorption mechanism mainly includes ion exchange, electrostatic attraction, and ligand exchange. This new approach for enhancing the adsorption capacity of LDH has broad application prospects in organophosphorus removal from water.

Phosphorus removal and recovery: state of the science and challenges

Phosphorus is one of the main nutrients required for all life. Phosphorus as phosphate form plays an important role in different cellular processes. Entrance of phosphorus in the environment leads to serious ecological problems including water quality problems and soil pollution. Furthermore, it may cause eutrophication as well as harmful algae blooms (HABs) in aquatic environments. Several physical, chemical, and biological methods have been presented for phosphorus removal and recovery. In this review, there is an overview of phosphorus role in nature provided, available removal processes are discussed, and each of them is explained in detail. Chemical precipitation, ion exchange, membrane separation, and adsorption can be listed as the most used methods. Identifying advantages of these technologies will allow the performance of phosphorus removal systems to be updated, optimized, evaluate the treatment cost and benefits, and support select directions for further action. Two main applications of biochar and nanoscale materials are recommended.

Recent advances in developing innovative sorbents for phosphorus removal-perspective and opportunities

Phosphorus is an essential mineral for the growth of plants which is supplied in the form of fertilizers. Phosphorus remains an inseparable part of developing agrarian economics. Phosphorus enters waterways through three different sources: domestic, agricultural, and industrial sources. Rainfall is the main cause for washing away a large amount of phosphates from farm soils into nearby waterways. The surplus of phosphorus in the water sources cause eutrophication and degradation of the habitat with an adverse effect on aquatic life and plants. Phosphate elimination is necessary to control eutrophication in water sources. Among the different methods reported for the removal and recovery of phosphorus: ion exchange, precipitation, crystallization, and others, adsorption standout as a sustainable solution. The current review offers a comparative assessment of the literature on novel materials and techniques for the removal of phosphorus. Herein, different adsorbents, their behaviors, mechanisms, and capacity of materials are discussed in detail. The adsorbents are categorized under different heads: iron-based, silica-alumina-based, calcium-based, biochar-based wherein the metal and metal oxides are employed in phosphorus removal. The ideal attribute of adsorbent will be the utilization of spent adsorbents as a phosphate plant food and a soil conditioner in agriculture. The review provides the perspective on the current research with potential challenges and directives for possible research in the field.

Urchin-like structured magnetic hydroxyapatite for the selective separation of cerium ions from aqueous solutions

In this study, bio-inspired urchin-like structured hydroxyapatite (UHdA) and its magnetic composite (UHdA@Fe₃O₄) were developed for efficient and easy separation of cerium ions (Ce³⁺) from aquatic waste streams. UHdA and UHdA@Fe₃O₄ exhibited superior Ce³⁺ adsorption capacities of 248.39 and 230.01 mg/g-UHdA respectively, compared to a commercial HdA (141.71 mg/g-HdA) due to their hierarchical mesoporous structure and large specific surface area. The adsorption of Ce³⁺ to UHdA and UHdA@Fe₃O₄ were heterogeneous, pseudo-second-order-kinetic, and the rate-limiting step was external mass transfer and intra-particle diffusion. Moreover, thermodynamic studies revealed that the adsorption process was spontaneous and endothermic nature. The high selectivity towards Ce³⁺ in multi-ionic systems is attributed to the strong affinity between strong Lewis acid (Ce³⁺) and base (PO₄^3- and OH^-) interactions. XRD, FTIR, and XPS analysis demonstrated that the adsorption was mainly attributable to the ion exchange of Ce³⁺ with Ca²⁺ and to surface complexation. The desorption of Ce³⁺ was efficiently accomplished using 0.1 M HNO₃. The results suggest that UHdA and UHdA@Fe₃O₄ could be promising choices for the adsorption and recovery of rare earth elements.

Strong Adsorption of Phosphorus by ZnAl-LDO-Activated Banana Biochar: An Analysis of Adsorption Efficiency, Thermodynamics, and Internal Mechanisms

Zn-Al layered bimetallic composites were prepared by ethanol strengthening and co-precipitation using banana straw as a raw material. A high-efficiency phosphorus adsorbent (ZnAl-LDO-BC) was obtained by calcination at a high temperature. The kinetics and thermodynamics of phosphorus adsorption on ZnAl-LDO-BC were then studied. The results showed that the adsorption process of ZnAl-LDO-BC corresponds with the pseudo-second-order (PSO) kinetic equation and the Langmuir model. The theoretical maximum adsorption capacity of ZnAl-LDO-BC is 111.11 mg/g (at 45 °C, 500 mg/L phosphorus initial concentration). The influence of anions on phosphorus adsorption decreased in strength in the following order: CO₃ ^2- > SO₄ ^2- > NO₃ ^-. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) were used to characterize the adsorption of phosphorus on ZnAl-LDO-BC and showed that ZnAl-LDO-BC can efficiently adsorb phosphorus. The adsorption mechanism utilizes both O-H and C-H on the surface of ZnAl-LDO-BC for the adsorption of PO₄ ^3-, forming Zn₃(PO₄)₂·₄H₂O via complexation precipitation; additionally, biochar surface adsorption and interlayer adsorption are indispensable forms of phosphate adsorption. With the systematic study of phosphorus adsorption by ZnAl-LDO-BC, a novel green technology was developed for addressing phosphorus pollution.