Phosphate Adsorption Isotherms Research Articles

Production of N–Mg doped biochars for phosphate adsorption from renewable sources

It is crucial for the environment, the economy, and society to create low-cost adsorbents from renewable resources to remove phosphate from aqueous effluents. Here, two renewablecarbon and nitrogen sources (Douglas fir and Chitosan) were used to produce engineered N-doped biochars modified with Mg for PO43− adsorption. Mg–N doped biochars were prepared using an impregnation-carbonization process. A central composite experimental design was used to select combinations of independent variables to maximize phosphate adsorption capacity. Phosphate adsorption isotherms were fitted with Langmuir and Freundlich isotherms. The biochar produced at 700 °C, 12 wt % MgCl2, and Douglas Fir/Chitosan ratio: 1/1, which has the highest PO43− adsorption capacity, was further studied. Proximate analysis, elemental composition, surface area, pore size distribution, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX) were used to characterize this biochar. This biochar has an adsorption capacity of 112.4 mg PO43−/g char. Its phosphate adsorption rate was adjusted to a pseudo-second-order kinetic model. The phosphate adsorption capacity of the biochar produced was comparable with the most effective biochar reported in the literature.

Chitosan Biocomposites with Variable Cross-Linking and Copper-Doping for Enhanced Phosphate Removal.

The fabrication of chitosan (CH) biocomposite beads with variable copper (Cu2+) ion doping was achieved with a glutaraldehyde cross-linker (CL) through three distinct methods: (1) formation of CH beads was followed by imbibition of Cu(II) ions (CH-b-Cu) without CL; (2) cross-linking of the CH beads, followed by imbibition of Cu(II) ions (CH-b-CL-Cu); and (3) cross-linking of pristine CH, followed by bead formation with Cu(II) imbibing onto the beads (CH-CL-b-Cu). The biocomposites (CH-b-Cu, CH-b-CL-Cu, and CH-CL-b-Cu) were characterized via spectroscopy (FTIR, 13C solid NMR, XPS), SEM, TGA, equilibrium solvent swelling methods, and phosphate adsorption isotherms. The results reveal variable cross-linking and Cu(II) doping of the CH beads, in accordance with the step-wise design strategy. CH-CL-b-Cu exhibited the greatest pillaring of chitosan fibrils with greater cross-linking, along with low Cu(II) loading, reduced solvent swelling, and attenuated uptake of phosphate dianions. Equilibrium and kinetic uptake results at pH 8.5 and 295 K reveal that the non-CL Cu-imbibed beads (CH-b-Cu) display the highest affinity for phosphate (Qm = 133 ± 45 mg/g), in agreement with the highest loading of Cu(II) and enhanced water swelling. Regeneration studies demonstrated the sustainability and cost-effectiveness of Cu-imbibed chitosan beads for controlled phosphate removal, whilst maintaining over 80% regenerability across several adsorption-desorption cycles. This study offers a facile synthetic approach for controlled Cu2+ ion doping onto chitosan-based beads, enabling tailored phosphate oxyanion uptake from aqueous media by employing a sustainable polysaccharide biocomposite adsorbent for water remediation by mitigation of eutrophication.

Sorption studies of Tetraoxophosphate (v) ions on some agricultural soils in Akwa Ibom State, eastern Niger Delta, Nigeria

The phosphate sorption capacity regulates principally the phosphorus concentration and available phosphorus in any soil solution. This work aims to study the phosphate sorption characteristics of five agricultural soils in Akwa Ibom State, Nigeria. The phosphate adsorption isotherm was obtained by shaking each soil sample with 20, 40, 60, 80, 100 and 120 mgL–1 for 24 h with 20 mL of KH2PO4 in 0.01 M CaCl2 solution. The Langmuir, Freundlich, Van Huay and Temkin isotherms were applied to study the PO43-sorption characteristics of the soil samples. The Freundlich model provided the best choice for phosphate sorption with mean R2 value of 0.9872. Results obtained for the phosphate sorbed (µg g–1soil) with 120 mgL-1 solution, heterogeneity factor of adsorption sites (nF), and the Freundlich constant (KF) (Lg–1) were 101(84.3), 0.515 and 7.355 for Onna soil; 62.8(52.3), 0.641 and 2.464 for Ikot-Amama 2; 60.6(50.5), 0.708 and 3.985 for Ogu-Itumbonuso soil; 59.3(49.5), 0.652 and 2.505 for Ikot-Amama 1 soils; 58.0(48.3), 0.704 and 3.682 for Ikot-Nkon soils, respectively. The equilibrium concentration for phosphates (EC-P) were used as desorption index to determine whether the soils could serve as potential sources for their bioavailability to plants and results ranged from 5.0 to 9.90 mgL–1, indicating high vulnerability to phosphate loss. The relationship between phosphate sorption parameters and soil physicochemical properties showed that the Freundlich adsorption intensity factor, nF, strongly correlated negatively with organic carbon and organic matter (r = -0.953 and -0.947; P<0.01), Fe and Mn (r = -0.911 and -0.812, P<0.05). The EC-P correlated strongly with soil pH(H2O) (r = 0.959, P<0.01), clay (r = 0.913, P<0.05), cation exchange capacity (CEC) (r = -0.824, P<0.05), Mn (r = -0.792, P<0.05) and Fe (r = -0.826, P<0.05). The study illustrated that soil management practices which involves the using organic fertilizers as the basis for PO43- sorption in relation to soil properties can be a useful tool for sustainable crop production and environmental soil-water contamination.

Porous MgO-modified biochar adsorbents fabricated by the activation of Mg(NO3)2 for phosphate removal: Synergistic enhancement of porosity and active sites

Engineering magnesium oxide (MgO)-modified biochar (MgO-biochar) with high porosity and active MgO load is a feasible pathway to enhance phosphate adsorption capacity. However, the blockage to pores caused by MgO particles is ubiquitous during the preparation, which seriously impaired the enhancement in adsorption performance. In this research, with the intent to enhance phosphate adsorption, an in-situ activation method based on Mg(NO3)2-activated pyrolysis technology was developed to fabricate MgO-biochar adsorbents with abundant fine pores and active sites simultaneously. The SEM image revealed that the tailor-made adsorbent has well-developed porous structure and abundant fluffy MgO active sites. Its maximum phosphate adsorption capacity was coming up to 1809 mg/g. The phosphate adsorption isotherms are in accordance well with the Langmuir model. The kinetic data, which agreed with the pseudo-second-order model, indicated that chemical interaction is existing between phosphate and MgO active sites. This work verified that the phosphate adsorption mechanism on MgO-biochar was composed of protonation, electrostatic attraction, monodentate complexation and bidentate complexation. In general, the facile in-situ activation method using Mg(NO3)2 pyrolysis illuminated biochar activation with fine pores and highly efficient adsorption sites for efficient wastewater treatment.

Mechanistic insights into the selective adsorption of phosphorus from wastewater by MgO(100)-functionalized cellulose sponge

Metal oxides have remained state-of-the-art adsorbents for recovering phosphorus from aqueous solutions, but their practical application is still limited by their unsatisfactory adsorption capacities and selectivities in wastewater. Here, using MgO as a model metal oxide, the strategy of employing porous cellulose sponge to support metal oxides featuring exposed specific crystal facets was proposed to develop promising phosphate adsorbents. The phosphate adsorption isotherms and kinetics were measured and the phosphate adsorption mechanism was explored. The results show that cellulose sponge-supported MgO(100) (C-MgO(100)) has a saturation capacity of 28.3 mg P/g, over ten times higher than MgO(100) particles. Importantly, the phosphate adsorption properties of C-MgO(100) are almost not affected in wastewater, demonstrating its exceptional selectivity for phosphate adsorption. In contrast, the saturation capacity of MgO(111)-functionalized cellulose sponge is obviously declined in wastewater. Experimental together with theoretical analyses indicate that phosphate is chemically adsorbed on C-MgO(100) with obvious electrons transfer from the p-orbital of phosphate, and the adsorption energy of C-MgO(100) towards phosphate is maintained in the presence of coexisting anions. Ultimately, regeneration experiments reveal that a regenerant formulation composed of KOH (wt.1 %) and tap water is suitable for the regeneration of C-MgO(100) with >82.6 % phosphate desorption efficiencies after 5 cycles, further confirming its potential in practical application for the treatment of real water.

Phosphate binding to allophane and ferrihydrite with implications for volcanic ash soils

AbstractThe occurrence of allophane and ferrihydrite in volcanic ash soils contributes to the high P sorption capacity of the soils. The objective of this study was to investigate the distribution of phosphate between allophane and ferrihydrite in the systems of their mixtures as a function of sorbed phosphate and aqueous citrate concentrations. The results were compared with those from phosphate in volcanic ash soils rich in allophane and ferrihydrite. Phosphate adsorption isotherm for allophane–ferrihydrite mixtures was described as a linear combination of Freundlich isotherm models for each single compound system. Phosphate sorption across single‐ and binary‐compound systems decreased with increasing aqueous citrate concentrations. Phosphorus K‐edge X‐ray absorption near edge structure (XANES) showed that phosphate had a higher affinity for allophane than ferrihydrite, particularly at low to intermediate sorbed phosphate concentrations. Such a preferential distribution of phosphate for allophane were attenuated at 10 mM aqueous citrate with increasing sorbed phosphate concentrations. Changes in the full width at half‐maximum height of the white‐line peak in the P K‐edge XANES spectra provided evidence for Al‐phosphate precipitation in the systems of allophane and allophane‐ferrihydrite mixtures, but not in the ferrihydrite systems. The XANES results from volcanic ash soils demonstrated that 61–92% phosphate was associated with Al, thus confirming a high affinity of phosphate for Al over Fe in the soils.

Iron and Magnesium Impregnation of Avocado Seed Biochar for Aqueous Phosphate Removal

There has been increasing interest in using biochar for nutrient removal from water, and its application for anionic nutrient removal such as in phosphate (PO43−) necessitates surface modifications of raw biochar. This study produced avocado seed biochar (AB), impregnated Fe- or Mg-(hydr)oxide onto biochar (post-pyrolysis), and tested their performance for aqueous phosphate removal. The Fe- or Mg-loaded biochar was prepared in either high (1:8 of biochar to metal salt in terms of mass ratio) or low (1:2) loading rates via the co-precipitation method. A total of 5 biochar materials (unmodified AB, AB + High Fe, AB + Low Fe, AB + High Mg, and AB + Low Mg) were characterized according to their selected physicochemical properties, and their phosphate adsorption performance was tested through pH effect and adsorption isotherm experiments. Fe-loaded AB contained Fe3O4, while Mg-loaded AB contained Mg(OH)2. The metal (hydr)oxide inclusion was higher in Fe-loaded AB. Mg-loaded AB showed a unique free O–H functional group, while Fe-loaded AB showed an increase in its specific surface area more than 10-times compared to unmodified AB (1.8 m2 g−1). The effect of the initial pH on phosphate adsorption was not consistent between Fe-(anion adsorption envelope) vs. Mg-loaded AB. The phosphate adsorption capacity was higher with Fe-loaded AB in low concentration ranges (≤50 mg L−1), while Mg-loaded AB outperformed Fe-loaded AB in high concentration ranges (75–500 mg L−1). The phosphate adsorption isotherm by Fe-loaded AB fit well with the Langmuir model (R2 = 0.91–0.96), indicating the adsorptive surfaces were relatively homogeneous. Mg-loaded biochar, however, fit much better with Freundlich model (R2 = 0.94–0.96), indicating the presence of heterogenous adsorptive surfaces. No substantial benefit of high loading rates in metal impregnation was found for phosphate adsorption. The enhanced phosphate removal by Mg-loaded biochar in high concentration ranges highlights the important role of the chemical precipitation of phosphate associated with dissolved Mg2+.

Removal of phosphate from aqueous solution by using thermally modified clamshell

The removal of phosphate (PO[Formula: see text] from an aqueous solution by clamshell treated by heat process was investigated through batch experiments. The effects of initial phosphate concentrations, pH value, and contact time on the phosphate removal were carried out. The phosphate adsorption isotherm was described by the Langmuir and Freundlich models. As the result, the adsorption process correlated well to both models, and the theoretical maximum phosphate adsorption capacity was 319.0 mg/g by the Langmuir isotherm model. The influence of pH was investigated from 5 to 10, and the value of pH had no significant effect on phosphate adsorption capacity. This finding indicated the application of calcined clamshell in the large range of pH for phosphate removal. The phosphate adsorption capacity and phosphate removal efficiency were obtained at 209.0 mg/g and 38.7% at the initial phosphate concentration of 540 ppm at 25∘C for 24 h, respectively. The clamshell modified by heat treatment exhibited its substantial potential for fast and efficient phosphate removal in water and wastewater.

Environmental application of engineering magnesite slag for phosphate adsorption from wastewater.

Herein, magnesite slags (MS), which remain after sulfuric acid extraction from light burnt magnesite in the magnesite industry, were used as phosphate adsorbents in wastewater. The MS were calcined under 700°C to enhance phosphate adsorption. The calcined magnesite slags (CMS) were characterized by nitrogen adsorption-desorption isotherm, X-ray diffraction, and scanning electron microscopy. A series of batch adsorption experiments were carried out to test the phosphate adsorption capacity of CMS. The results showed that the calcific treatment promoted the conversion from Mg, Ca, Fe, etc. compound to metal oxide of the MS. The generated metal oxide particles resulted in 237.4mg/g increase in the phosphate adsorption capacity. The phosphate adsorption isotherm of CMS fitted the Langmuir model better, and the maximum adsorption capacity of CMS was 526mg/g. The adsorption kinetics of phosphate on CMS can be described by the pseudo-second-order model. The phosphate removal efficiency was greater than 98% in 300mg/L phosphate solution. Mechanism investigation results indicated that phosphate was adsorbed by CMS through MgO protonation, electrostatic attraction, Mg-P complexation, and ligand exchange. The results obtained in this work demonstrate that the CMS is a potential effective adsorbent for removal and reutilization phosphate from P-contaminated water, due to it can be employed as a fertilizer after phosphate adsorption.

A comparative study on phosphate removal from water using Phragmites australis biochars loaded with different metal oxides.

Metal oxide-loaded biochars are a promising material to remove phosphate from polluted water to ultra-low concentrations. To facilitate preparing the metal oxide-loaded biochar with the best phosphate adsorption performance, five biochars loaded with Al, Ca, Fe, La and Mg oxides, respectively (Al-BC, Ca-BC, Fe-BC, La-BC and Mg-BC) were produced using Phragmites australis pretreated with 0.1 mol AlCl3, CaCl2, FeCl3, LaCl3 and MgCl2, respectively, characterized, and phosphate adsorption kinetics and isotherms of the biochars were determined. The maximum phosphate adsorption capacities (Qm) of the biochars ranked as Al-BC (219.87 mg g−1) > Mg-BC (112.45 mg g−1) > Ca-BC (81.46 mg g−1) > Fe-BC (46.61 mg g−1) > La-BC (38.93 mg g−1). The time to reach the adsorption equilibrium ranked as La-BC (1 h) < Ca-BC (12 h) < Mg-BC (24 h) = Fe-BC (24 h) <Al-BC (greater than 72 h). Qm of Ca-BC, Fe-BC, La-BC and Mg-BC depend on the molar content of metals in the biochars. The small phosphate adsorption rate of Al-BC is due to the slow intra-particle diffusion of phosphate attributed to the undeveloped porosity and dispersed distribution of AlOOH crystals on the Al-BC surface. Mg-BC is suggested for phosphate removal from water considering adsorption rate and capacity. Al-BC is applicable when a long contact time is allowed, e.g. as a capping material to immobilize phosphate in lake sediments.

Experimental Study of the Adsorption of Nitrogen and Phosphorus by Natural Clay Minerals

Nitrogen and phosphorus are commonly recognized as causing eutrophication in aquatic systems, and their transport in subsurface environments has also aroused great public attention. This research presented four natural clay minerals (NCMs) evaluated for their effectiveness of NH4 + and PO4 3- adsorption from wastewater. All the NCMs were fully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET analysis, and adsorption kinetics and isotherms to better understand the adsorption mechanism-property relationship. The results show that the adsorption efficiency of the four NCMs for phosphate was better than that for ammonia nitrogen. The removal rate of phosphate was higher than 65%, generally in the range of 80%-90%, while the removal rate of ammonia nitrogen was less than 50%. The adsorption kinetic behavior followed the pseudo-second-order kinetic model. The ammonia nitrogen adsorption isotherm was in good agreement with the Freundlich isotherm equilibrium model, and the phosphate adsorption isotherm matched the Langmuir model. Among all the NCMs studied, bentonite (7.13 mg/g) and kaolinite (5.37 mg/g) showed higher adsorption capacities for ammonia nitrogen, while zeolite (0.21 mg/g) and attapulgite (0.17 mg/g) showed higher adsorption capacities for phosphate. This study provides crucial baseline knowledge for the adsorption of nitrogen and phosphate by different kinds of NCMs.

Biochar-Ca and Biochar-Al/-Fe-Mediated Phosphate Exchange Capacity are Main Drivers of the Different Biochar Effects on Plants in Acidic and Alkaline Soils

Because of the low consistency of the results obtained in the field, the use of biochar as a soil amendment is controversial. Thus, in general, in acidic soils, results are positive, while in alkaline soils, they are non-significant or even negative. The results regarding biochar action in acidic soils have been related to a lime-like effect due to its alkaline pH and the high doses normally used. However, the causes of biochar effects in alkaline soils remain unknown. Our objective was to explore the chemical mechanism of biochar interaction in acidic and alkaline soils. We used well-characterized biochar as a component of two complex N and PK granulated fertilizers at two different doses (1% and 5%). These fertilizers were applied to wheat cultivated in pots containing an alkaline soil and grown for 60 days. No effect was shown for the N-biochar fertilizer application. However, the PK-biochar fertilizer application caused a decrease in crop yield. In addition, the adsorption isotherms of Al, Fe, Mo, Mn, and Phosphate (Pi) in biochar were also studied. The results showed that Fe and Al were rapidly adsorbed in biochar, while Pi was only adsorbed on the Fe-, Al-biochar complex. Desorption experiments showed that P and Fe/Al were not desorbed from the P-Fe/Al-biochar complex by water or the Olsen reagent, while partial desorption was observed when HCl 0.1 M was used. This blockage of Fe/Al and P through Fe/Al bridges in biochar could partially explain the negative effects in alkaline soils. After these studies, soil solution sorption experiments were carried out in both acidic and alkaline soils and were complemented with a greenhouse trial using tomato plants. The results showed that biochar enhanced foliar Ca and N content, as well as growth in acidic soil only, and the possible mechanism of the failure in alkaline soils.

Influence of coexisting calcium ions during on-column phosphate adsorption and desorption with granular ferric oxide

Adsorption and desorption of phosphate by hydrated granular ferric oxide (GFO) were investigated using model phosphate wastewater (2 mg P/dm3) containing that also contained calcium and magnesium ions. The phosphate adsorption isotherm of GFO was fit with the Langmuir equation. GFO particles with an average size of 0.75 mm took up a maximum of 14.2 mg P/g. The intraparticle surface diffusivity (Ds) of phosphate was 1.0 × 10−11 m2/h. Phosphate adsorption breakthrough curves were obtained with a solution that contained alkaline earth metals (Ca, Mg) and one that did not. The breakthrough curves were compared to examine the effects of coexisting alkaline earth metal ions on-column phosphate adsorption. The column breakthrough volume (3800 times volume of the adsorbent bed, BV) with the solution containing Ca and Mg was over four times larger than that (860 BV) obtained with the Ca- and Mg-free solution at the same space velocity (SV 4.3/h). Greater uptake of P in the presence of Ca and Mg was ascribed to the precipitation of Ca salts in the GFO bed. Pretreatment with acid increased the efficiency of phosphate desorption in NaOH to regenerate phosphate-loaded GFO owing to the dissolution of precipitated Ca salts.

La(III)-bentonite/chitosan composite: A new type adsorbent for rapid removal of phosphate from water bodies

It is highly imperative to remove phosphorus from water bodies because the excessive phosphorus content can cause eutrophication of water bodies. In this work, we prepare a kind of environmentally friendly and low-cost adsorbent comprising lanthanum (La)-doped bentonite and chitosan, with a simple, facile and scalable method combining direct calcination and subsequent blending. The optimal adsorbent, La-doped bentonite/chitosan-5, La-BC-5 hereinafter, can rapidly reach equilibrium in 20 min and provide 93.2% adsorption efficiency (initial phosphate concentration, 50 mg/L); and as high as 99.7% could be removed in 5 min under low phosphate concentration (2 mg/L). Fitting result indicates the phosphate adsorption isotherm fits the Freundlich model, meanwhile the adsorptive kinetics follows a pseudo-second-order model. Anti-interference result for some typical anionic species including NO3−, SO42−, Cl−, indicates 97.5% removal efficiency could be achieved under coexisting phosphate concentration of 5 mg/L. Meanwhile, reusability experiment reveals that removal efficiency decreases to 89.1% after five regeneration cycles. Notably, practical water adsorption experiment manifests the La-BC-5 can efficiently reduce the phosphate concentration from 0.30 to 0.07 mg/L. The favorable properties with rapid adsorption, excellent anti-interference for coexisting anions and reusability foresee the enormous potentials for practical phosphate removal in water bodies.

Assessment of phosphorus fixing capacity in contrasting soil orders in central India

Phosphate adsorption by soils is important because adsorbed P equilibrates with soil solution P, which in turn is immediate source of P. While P fixation continues to receive much attention it is more important to know the effect of soil characteristics on P fixation. Phosphorus sorption characteristics of JNKVV, Farm, Jabalpur representative agricultural soils belonging to three soil orders namely Vertisol, Inceptisol and Alfisol were investigated for adsorption behaviour of P and sorption data were fitted to Langmuir equation. The Langmuir constant i.e. adsorption maxima was highest for Vertisol (504.26 μg g-1), followed by Alfisol (480.89μg g-1) and Inceptisol (452.98μg g-1) respectively. The phosphate adsorption isotherm gave good fit adopting Langmuir (r2 = 0.98 to 0.99) for the three soils. The value of equilibrium solution P concentrations were found significantly variation under different soil orders but the adsorb P value was also found significant varied. The equilibrium solution P concentrations minimum in Alfisols 0.03 to 8.95 mgµg mL-1 and maximum in Inceptisols 0.09 to 10.95µg mL-1, but the adsorb P value was minimum in Inceptisols 19.01 to 290.41µg mL-1 and maximum were recorded in Alfisols 19.64 to 310.47µg mL-1. In Vertisols the value of equilibrium solution P concentrations were found in the range of 0.13 to 10.08µg mL-1 and adsorb P values were 18.65 to 299.13µg mL-1. The range of P buffering capacity was 60.07 to 70.89 L kg-1. The highest value of MPBC was found in Alfisols with the mean value 68.89L kg-1and the lowest of MPBC value was found in the Inceptisols with the mean value was 63.72L kg-1. Correlation of Adsorption parameters of Langmuir and were worked out taking all soil types together with pH, EC, organic carbon, clay, CEC and CaCO3. For the Lamgmuir equation, value of ‘r’ indicated that P adsorption maxima (b) was significantly and positively correlated with pH (r=0.993**), clay (0.916**) EC (r= 0.734*).

Preparation of polyaminated Fe3O4@chitosan core-shell magnetic nanoparticles for efficient adsorption of phosphate in aqueous solutions

In this study, novel polyethylenimine (PEI)-grafted chitosan (CS) core-shell (called as Fe3O4/CS/PEI) magnetic nanoparticles were synthesized and applied for adsorbing phosphate in water. The magnetic and physicochemical properties of as-synthesized nanoparticles were first analyzed by means of a superconducting quantum interference device, X-ray diffractometer, X-ray photoelectron spectroscope, Fourier-transform infrared spectroscope, transmission electron microscope, zeta potential analyzer, and nitrogen sorptiometer. The followed experiments indicated that the amount of phosphate adsorbed increased with increasing equilibrium pH to near 4.0 and then decreased when the pH was further increased. The adsorption isotherms of phosphate on Fe3O4/CS/PEI particles were well fit by the Langmuir equation, and its maximum adsorption was 48.2mgg−1 at an equilibrium pH of 3.0 and 25°C. The primary mechanism for phosphate adsorption on Fe3O4/CS/PEI particles was electrostatic attraction. The preferential adsorption of phosphate in the presence of other excess anions including chloride, nitrate, carbonate, and sulfate was presented. Under the conditions studied, more than 90% of phosphate was desorbed from the laden Fe3O4/CS/PEI particles by 0.05mol L−1 of NaOH solution. The remained adsorption efficiency obtained in the five-cycle reusability tests has demonstrated the promising application potential of Fe3O4/CS/PEI particles.

Removal and recovery of phosphate and fluoride from water with reusable mesoporous Fe3O4@mSiO2@mLDH composites as sorbents

Three core/shell/shell MgAl-LDH composites using Fe3O4 microspheres as the core, a SiO2 matrix as the inner layer and a MgAl-LDH layer as the outer shell have been synthesized for the removal and recovery of phosphate and fluoride from water by a magnetic separation technique. The synthetic mesoporous MgAl-LDH composites show good magnetic separability, well-defined pore distributions, and have specific surface areas of 73 m2 g−1, 168 m2 g−1, and 137 m2 g−1 for Fe3O4@SiO2@LDH350, Fe3O4@SiO2@mLDH350, and Fe3O4@mSiO2@mLDH350, respectively. The adsorption isotherms of both phosphate and fluoride on these MgAl-LDH composites can be well fitted with the Langmuir model. The maximum adsorption capacities of 57.07 mg g−1 and 28.51 mg g−1 were obtained on Fe3O4@mSiO2@mLDH350 for phosphate and fluoride, respectively, much higher than those of other LDH-type materials. The adsorbed phosphate and fluoride could be successfully recovered by NaNO3-NaOH solution, and the regenerated MgAl-LDH composites could be reused for phosphate and fluoride removal. Owing to their high adsorption capacities of both phosphate and fluoride, easy magnetic separation from solution, and good reusability, the mesoporous MgAl-LDH composites are expected to have potential applications in removal or recovery of fluoride or phosphate from water.

Nitrogen doped char from anaerobically digested fiber for phosphate removal in aqueous solutions

This study explores the use of an engineered char produced from the pyrolysis of anaerobically digested fiber (ADF) to adsorb phosphate from aqueous solutions. Two series of engineered chars were produced. The first series was a CO2 activated (CA) char produced via slow pyrolysis between 350 and 750 °C. The second series was a nitrogen doped (ND) char activated in the presence of ammonia at comparable temperatures. Proximate analysis, elemental composition, gas physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray powder diffraction (XRD) techniques were used to characterize properties of resulting products. The surface area of the carbon product increased after nitrogen doping through ammonization (166.6–463.1 m2/g) compared to CO2 activated chars (156.5–413.1 m2/g). Phosphate adsorption isotherms for both CO2 activated and nitrogen doped chars can be described by the Langmuir- Freundlich and Redlich Peterson adsorption models. Nitrogen doped carbon phosphate sorption capacity in aqueous solutions was twice compared to CO2 activated carbons. As carbonization/activation temperature increased the sorption capacity increased from 3.4 to 33.3 mg g-1 for CA char and 6.3–63.1 mg g-1 for nitrogen doped char.

Magnetically separable ZrO2@SiO2@Fe3O4 for selective phosphate removal from wastewater

Phosphorus (P), which is a non-renewable resource, has been extensively used in agricultural and industrial fields. However, the release of P into surface water through agricultural runoffs and wastewater can cause enrichment of P and eutrophication in confined water bodies. Hence, a novel technology that can remove phosphate (major species of P in water) from water bodies for eutrophication prevention and recover phosphate for minimising the loss of P resource is desired. Adsorption is a preferable approach for phosphate removal due to its simplicity of design, effectiveness even at low P concentrations, and potential for recovery. The use of zirconium-based adsorbents for phosphate removal from wastewater has received increasing attention. However, challenges remain to recover zirconium-based adsorbents. In this study, zirconium oxide-based superparamagnetic adsorbents (i.e. ZrO2@SiO2@Fe3O4) were developed for phosphate removal from wastewater. Magnetic separation efficiency, phosphate adsorption kinetics and isotherm, effects of coexisting anions and organic matters, and reusability are reported. The developed ZrO2@SiO2@Fe3O4 has an excellent magnetic separation efficiency of &gt; 98%, fast adsorption kinetics, high adsorption capacity at low phosphate concentrations, and strong selectivity for phosphate even at a competitive anion (i.e. Cl-, NO3-, SO42- and HCO3-) to phosphate molar ratio of 100:1 and humic acid (HA) concentration of 100 mg C/L. Adsorption-desorption cyclic experiments demonstrated the good reusability of the ZrO2@SiO2@Fe3O4.

Enhanced phosphate removal under an electric field via multiple mechanisms on MgAl-LDHs/AC composite electrode

Phosphorus removal is essential to avoid eutrophication in water bodies. Layered double hydroxides (LDHs) are widely used to scavenge phosphate through intercalated ion exchange or surface complexation. Moreover, LDHs have attracted increasing attention as electrode modifiers for supercapacitors. Researchers have begun to re-delve the electrosorption technology according to the fundamental principle of electrical double layers. Herein, we propose a new phosphate removal method inspired by the adsorption characteristic and electrical double-layer capacitive properties of LDHs through electrosorption via capacitive deionization. We present a series of experiments to study the enhanced phosphate removal under an electric field via multiple mechanisms on the MgAl-LDHs/AC electrode. The uptake of phosphate by MgAl-LDHs/AC was investigated as a function of phosphate concentration, applied voltage, electrode materials, and temperature. The MgAl-LDHs/AC electrode possessed a salt removal capacity of 67.92mg PO43−·g−1 (1.2V, 250mg·L−1 KH2PO4, 30°C). The electrosorption kinetics of phosphate ions onto the capacitive deionization electrode followed the pseudo-second-order kinetics model rather than the pseudo-first-order kinetics model. Furthermore, the adsorption isotherms of phosphate on the MgAl-LDHs/AC electrode fitted the Freundlich model better than the Langmuir model. The proposed method could be used for phosphate removal.