Adsorptive removal of phosphate from aqueous solutions using iron–lanthanum‐doped foam glass adsorbent

Abstract

The purpose of this study was to develop an adsorbent for phosphate using iron–lanthanum‐loaded foamed glass recycled from colored glass bottles. The optimal preparation conditions for the adsorbent were 0.1% iron and 1% lanthanum loaded onto the foam glass and calcined at 350°C for 2 h. Adsorption kinetics for phosphate onto the adsorbent were fitted to pseudo‐second‐order model. The phosphate adsorption was identified as chemisorption, which occurred due to ligand exchange. The adsorption isotherm for phosphate on the adsorbent was expressed as a Langmuir model. The maximum adsorption capacity was calculated to be 1.3 mg‐P g⁻¹. The equilibrium constant (3.1 L mg⁻¹) of the adsorbent was significantly higher than that of previous studies. Hence, the adsorbent developed in this study demonstrated favorable adsorption at low phosphate concentrations, indicating that it can remove phosphate from domestic wastewater and natural water. The adsorbent is a promising and cost‐effective phosphate adsorbent that promotes waste glass recycling.

Practitioner Points

• Adsorbent for phosphate using iron–lanthanum‐loaded foamed glass recycled from colored glass bottles was developed.

• The adsorbent demonstrated favorable adsorption at low concentrations of phosphate.

• The adsorbent is effective in removing phosphate from domestic and natural waters.

The adsorbent developed in this study is a promising and cost‐effective phosphate adsorbent that promotes waste glass recycling.

INTRODUCTION

The excessive discharge of nutrients, such as phosphorus and nitrogen, from farmlands, municipal sources, and industrial wastewater into enclosed water bodies causes eutrophication, leading to harmful algal blooms and the degradation of water quality (Akinnawo, 2023). An effective strategy for controlling eutrophication is to remove phosphorus from domestic and industrial wastewater using wastewater‐treatment plants or on‐site wastewater‐treatment systems. A septic tank is an on‐site wastewater‐treatment system for domestic sewage in rural areas and developing countries where sewage networks cannot be installed. Developed countries also use on‐site wastewater‐treatment systems. For example, 23% of single‐family and mobile homes in the United States continue to use on‐site wastewater‐treatment systems (Jordan et al., 2023). However, 3.6 billion people worldwide lack access to safe sanitation services (WHO and UNICEF, 2021). Globally, approximately 80% of municipal wastewater is untreated and directly discharged into the environment (Malone & Newton, 2020). Hence, it is desirable to develop cost‐effective nutrient removal systems where advanced wastewater‐treatment systems cannot operate.

Another environmental issue is the disposal of glass. According to the US Environmental Protection Agency, although 10.37 million tons of glass is generated in the municipal solid waste stream, only 27% of waste glass is recycled (Mohajerani et al., 2017). One strategy for recycling waste‐colored glass is to produce foam glass, which is a lightweight material prepared by heating crushed waste glass with foaming agents (König et al., 2015). Foam glass is conventionally used in construction and as a water‐folding material (Attila et al., 2013).

In this study, we focused on developing phosphate adsorbents using foam glass for on‐site domestic wastewater treatment in developing countries. Various adsorbents have been developed to remove phosphate, including zinc ferrite (Gu et al., 2016), zerovalent iron (Wen et al., 2014), iron‐loaded biosorbents (Nguyen et al., 2013), and iron–zirconium‐modified activated carbon nanofibers (Xiong et al., 2017). However, the phosphorus adsorption performance of these adsorbents decreases owing to competing adsorption of coexisting anions. Lanthanum modified, lanthanum carbonate, zirconium oxide, and zirconium‐modified adsorbents are highly selective and effective for phosphate adsorption (Asaoka et al., 2021; Bui et al., 2021; He et al., 2022; Lu et al., 2021; Qiu et al., 2015; Rathinam et al., 2021; Wang et al., 2016; Yang et al., 2021). A hybrid adsorbent based on iron–lanthanum was reported in previous studies (Liu et al., 2013; Lu et al., 2021). Lanthanum and phosphate interact through various mechanisms, including inner‐sphere complexation, electrostatic attraction, and ligand exchange (Razanajatovo et al., 2021). In this study, a phosphate adsorbent was prepared using iron–lanthanum‐loaded foam glass (ILFG). We increased the specific surface area of a foam glass by loading it with iron (III) oxide‐hydroxide because an increase in the specific surface area of the adsorbent enhances phosphate adsorption. Iron also adsorbs phosphate by forming an inner‐sphere complex (Lu et al., 2021). Subsequently, the oxide‐hydroxide‐loaded foam glass was loaded with lanthanum, which exhibits a high selectivity for phosphate. This study aimed to develop a phosphate adsorbent using foam glass for use in septic tanks to treat domestic wastewater.

METHODS

Characterization of the foam glass

Foam glass (Supersol L2, Cocco Co., Japan) was prepared by adding a foaming agent to waste glass powder and foaming at 800–900°C for 1 h. Carbonaceous materials were conventionally used as foaming agent to generate CO₂ gas (Ji et al., 2019; Owoeye et al., 2020). After cooling to ambient temperature, the prepared foam glass was sieved to obtain particles with diameter in the range of 2–10 mm. We analyzed the chemical composition and the specific surface area of the foam glass using a wavelength‐dispersive X‐ray fluorescence analyzer (Supermini200; Rigaku, Japan) with the fundamental parameter method and a surface area analyzer (FlowSorb III; Micromeritics) by the Brunauer–Emmett–Teller method with nitrogen gas adsorption, respectively. Scanning electron microscopy (SEM) images of the foam glass were obtained using an electron probe microanalyzer (JXA‐iSP100 super probe; JEOL, Japan). The point of zero charge (PZC) of the prepared adsorbent was determined by titration method (Miura et al., 2004).

The valences of the chromium and iron species in the foam glass and the prepared adsorbent were identified using the X‐ray absorption fine structure (XAFS) beamline BL‐3 at the SR Center, Ritsumeikan University (Asaoka et al., 2012). The analytical conditions are described in detail in the Supporting information.

Elution experiments on environmentally regulated elements from foam glass were based on the standard for soil contamination countermeasures in Japan with minor modifications (Ministry of the Environment Goverment of Japan, 2003). The analytical conditions are described in detail in the Supporting information.

Preparation of the optimum ILFG

The optimum iron‐ and lanthanum‐loading percentages on the ILFG were 0.1% and 1%, respectively. Herein, 8 g of foam glass was impregnated into iron (II) solution prepared with iron chloride tetrahydrate (FUJIFILM Wako Chemicals, Japan) and agitated for 1 day in a 50 mL centrifuge tube in an incubator (LTE‐1010, EYELA, Japan) at 100 rpm and 25°C. The foam glass was transferred to a 50 mL polypropylene disposable cup to evaporate the iron (II) solution in a constant temperature oven (DO‐300FA: AS ONE, Japan) at 100°C for 10 h. After evaporation, the iron‐loaded foam glass was impregnated into lanthanum solution for lanthanum loading, and similar procedures as those in the case of iron loading were followed. Thereafter, the ILFG was calcined at 350°C for 2 h in the air using an electric furnace (HPM‐0N, AS ONE, Japan) and then allowed to cool naturally in the furnace.

The amount of iron–lanthanum loading in the foam glass was controlled by dissolving different amounts of iron chloride tetrahydrate or lanthanum chloride heptahydrate in pure water. The lanthanum‐loading percentage of ILFG was determined using a wavelength‐dispersive X‐ray fluorescence analyzer (Supermini200; Rigaku, Japan).

Optimization of preparation for ILFG

The optimum calcination temperature and the optimum iron‐loading percentage were investigated using the 1.75% lanthanum‐loaded foam glass in the range of 250–750°C and 0%–0.5%, respectively. The optimum lanthanum‐loading percentage was investigated in the range of 0.25%–1.75% using foam glass with 0.1% iron loading.

Batch experiment for phosphate adsorption onto ILFG

A phosphate solution was prepared by dissolving potassium dihydrogen phosphate (FUJIFILM Wako Chemicals, Japan) in ultrapure water. A total of 50 mL of 10 or 100 mg L⁻¹ phosphate solution was added to 0.5 or 1.5 g of prepared adsorbents, respectively, and agitated for 3 h at 100 rpm and 25°C in an incubator. Thereafter, the phosphate solution was filtered through a 0.45 μm pore syringe filter (SLHN033NB; Merck, Germany). The phosphate concentration in the filtrate was analyzed by molybdenum blue adsorption photometry (Murphy & Riley, 1962) using a spectrophotometer (UV‐2600; Shimadzu, Japan). In addition, batch experiments were conducted without adsorbent addition, using the same procedure as that used for the control. The experiments were conducted in triplicates. The phosphate removal percentage (R) was calculated by the following expression (Equation 1).

$$R\left(\%\right)=\frac{C_o-C_f}{C_o}\times 100$$ (1)

where $C_o$ and C_f are the initial and final concentrations of phosphate in the aqueous solution (mg L⁻¹), respectively.

Adsorption behaviors of phosphate onto ILFG

A total of 500 mL of 1 and 10 mg‐P L⁻¹ phosphate solutions were added to 1.0 g of ILFG. Phosphate solutions were collected at suitable intervals.

To describe the adsorption isotherm of phosphate onto ILFG, 1 g of ILFG was added to 500 mL phosphate solution with 1–40 mg‐P L⁻¹. After 48 h, the phosphate solutions were collected. The experiments were conducted in triplicates. Phosphate analyses were conducted as described in Section 2.4.

Desorption study

Fifty milliliters of 3 mol L⁻¹ NaOH solution was added to 1 g of ILFG with 0.6 mg‐P g⁻¹ phosphate adsorbed, and the mixture was agitated for 3 h at 100 rpm and 25°C in an incubator. The NaOH solution was then filtered through a 0.45 μm pore syringe filter (SLHN033NB; Merck, Germany). To calculate the amount of phosphate desorbed from ILFG, the phosphate concentration in the filtrate was analyzed as described in Section 2.4.

Bench‐scale experiment on the removal of phosphate from domestic wastewater

The ILFG (60 g) with 10–20 mm was filled with an acrylonitrile–styrene copolymer column (ϕ 5.3 cm, 32 cm long), which is 1/1000th scale of Johkasou, a Japanese compact‐scale advanced wastewater‐treatment system. Subsequently, the desired wastewater solutions of 2 L each were prepared by dissolving NH₄Cl (Nagai Chemical Industrial, Japan) and K₂HPO₄ (Kishida Chemical, Japan) in domestic wastewater discharged from Johkasou (chemical composition is shown in Table S1) and adjusting the concentrations of 25 mg N L⁻¹ and 5, 15, and 50 mg P L⁻¹. The prepared domestic wastewater was circulated and supplied to the column at an upward flow rate of 160 mL min⁻¹ by a tube pump (PT‐EP1‐500‐KA, Tsukasa, Japan) at 20°C. The domestic wastewater was sampled at suitable intervals and filtered through filter paper (No. 5C, Advantec, Japan). The phosphate concentration in the filtrate was analyzed as described in Section 2.4. As a control, the column was filled with foam glass, and the column experiment was performed following the same protocol.

RESULTS AND DISCUSSION

Characterization of foam glass used in this study

The foam glass used in this study was primarily composed of silicon (31.0%), calcium (7.89%), and sodium (6.62%; Table 1). Chromium as a colorant and lead as a fining agent were detected (Abdel‐Baki & El‐Diasty, 2006). The valence state of chromium in the foam glass was determined by XAFS (Figure 1). The hexavalent chromium standard shows a pre‐edge peak at approximately 5992 eV, representing the 3d⁰ electron configuration. By contrast, the trivalent chromium standard has no pre‐edge peak owing to its 3d³ electron configuration (Hori et al., 2011). The K‐edge XANES spectrum of chromium in the foam glass showed no pre‐edge peak at approximately 5992 eV, indicating that the chromium contained in the foam glass used in this study was mainly trivalent. The amounts of dissolved heavy metals are listed in Table S2 and are below the standard levels for environmental criteria in Japan. The specific surface area of the foam glass was determined as 0.04 m² g⁻¹. The SEM images of the foam glass revealed uniformly distributed pores with a diameter of 10–900 μm (Figure 2a). Few pores could be observed inside the bubbles (Figure 2b).

TABLE 1.

Chemical composition of foam glass used in this study.

Elements	Concentration (wt.%)
Na	6.62
Mg	0.719
Al	0.802
Si	31.0
P	0.0115
S	0.0729
Cl	0.0183
K	0.874
Ca	7.89
Cr	0.0433
Fe	0.127
Sr	0.0172
Zr	0.009
Pb	0.0124
Others	9.52

FIGURE 1.

Chromium K‐edge XANES spectra of standards and a foam glass used in this study.

FIGURE 2.

SEM images of the foam glass: (a) 45 times magnification; (b) 1700 times magnification.

Optimization of calcination temperature to prepare ILFG

The optimum calcination temperature for preventing lanthanum phosphate exfoliation after phosphate adsorption has been investigated (Asaoka et al., 2021). For the initial phosphate concentration of 10 mg‐P L⁻¹, the phosphate adsorption percentages were 99.3%–99.9% up to the calcination temperature of 350°C (Figure 3). However, the phosphate adsorption percentage decreased when the calcination temperatures exceeded 350°C. For the initial phosphate concentration of 100 mg‐P L⁻¹, the phosphorus adsorption percentage was 85.6%–86.9% up to a calcination temperature of 250°C. However, the adsorption percentage of phosphate decreased sharply over a calcination temperature of 350°C. Turbidity (absorbance at 660 nm; JISK0101, 1998), which was used as an indicator of the exfoliation of lanthanum phosphate precipitate, was also monitored after the adsorption of phosphate (Figure S1). At an initial phosphate concentration of 10 mg‐P L⁻¹, turbidity was low (0.008–0.031), which did not depend on the calcination temperature. However, at an initial phosphate concentration of 100 mg‐P L^‐1, turbidity was high (0.443) without calcination, owing to the exfoliation of lanthanum phosphate precipitation. For a calcination temperature greater than 350°C, turbidity decreased to 0.021–0.034. Hence, the optimum calcination temperature of the lanthanum‐doped foam glass was 350°C.

FIGURE 3.

Effect of calcination temperature on the removal of phosphate.

Optimization of iron‐loading percentage on the ILFG

When the initial phosphate concentration was 10 mg‐P L⁻¹, 99.9% of the phosphate was removed using the lanthanum‐loaded foam glass. However, in the case of 100 mg‐P L⁻¹ phosphate, only 42.8% was removed. Therefore, the optimum loading percentage of iron on foam glass was investigated to improve the phosphate adsorption percentage. Iron is well‐known for its high selectivity for phosphate adsorption (Fulazzaky et al., 2022). At an initial phosphate concentration of 100 mg‐P L⁻¹, the phosphate adsorption percentage increased to 82.9% when 0.1% iron was loaded onto ILFG (Figure S2). The phosphate adsorption percentage did not increase further for iron loading over 0.25%. In addition, turbidity of the phosphate solution was minimal at 0.1% iron loading (Figure S2). The increase in turbidity of phosphate solution with increasing iron‐loading percentage can be attributed to the exfoliation of iron due to the overloading of iron onto the ILFG. However, turbidity of the phosphate solution did not show statistical significance between 0.1% iron‐loaded ILFG and ILFG without iron‐loaded (p < 0.5), indicating that iron did not exfoliate from 0.1% iron‐loaded ILFG. Thus, the optimum iron‐loading percentage for the ILFG was 0.1%. The specific surface area of the ILFG increased to 1.34 m² g⁻¹, 30 times higher than that of the foam glass. An increase in specific surface area is advantageous for phosphate adsorption.

Optimization of lanthanum‐loading percentage on ILFG

The phosphate adsorption percentages increased with increasing lanthanum loading, reaching 94.6% at 1% lanthanum loading (Figure 4). When the lanthanum‐loading percentage exceeded 1%, the phosphorus adsorption percentage did not show a statistical difference due to the overloading. Hence, the optimum La‐loading percentage was 1%.

FIGURE 4.

Effect of lanthanum‐loading percentage on phosphate removal.

Identification of iron species on the surface of ILFG

The Fe species in the foam glass were FeO (OH) (32.3%), FeO (26.4%), and Fe (OH)₂ (41.3%) (Table 2 and Figure S3). The ILFG was composed of FeO (OH) (50.1%) and Fe₃O₄ (49.9%). The Fe₃O₄ present on the ILFG may have been derived from the oxidation of FeO through calcination. After the adsorption of phosphate on ILFG, Fe (OH)₃ (37.1%), FePO₄ (39.0%), and FeO (OH) (23.9%) were identified. Fe (OH)₃ is expected to form through the hydrolysis of Fe³⁺ derived from the oxidation of Fe²⁺ in ILFG. Fe (OH)₃ and FeO (OH) have important roles in the adsorption of phosphate via ligand exchange and formation of surface complexes, respectively (Abdala et al., 2015; Yan et al., 2010). Therefore, iron on the surface of ILFG played a crucial role in both phosphate adsorption and increasing the specific surface area of ILFG.

TABLE 2.

Composition of iron species on the surface of foam glass, initial iron–lanthanum‐loaded foam glass (ILFG), and phosphate adsorbed ILFG.

Composition (%)	FeO	Fe (OH)2	Fe3O4	Fe (OH)3	FeO (OH)	FePO4
Foam glass	26.4	41.3	‐	‐	32.3	‐
ILFG (initial)	‐	‐	49.9	‐	50.1	‐
ILFG (adsorbed phosphate)	‐	‐	‐	37.1	23.9	39.0

Adsorption behaviors of phosphate onto ILFG

The phosphate adsorption reached equilibrium after 48 h (Figure 5). The adsorption kinetics of phosphate onto ILFG were fitted using three models: the pseudo‐first‐order model (Ho & McKay, 1999), the pseudo‐second‐order model (Ho & McKay, 1999), and the intra‐particle diffusion model (Wu et al., 2009). The equations for these models are expressed as Equations (2)–(4).

$$\log \left(Q_e-Q_t\right)=\mathit{log}{Q}_e+\frac{k₁}{2.303}t$$ (2)

$$\frac{t}{Q_t}=\frac{1}{k_2{Q}_t^2}+\frac{t}{Q_e}t$$ (3)

$$Q_t=k_i{t}^{\frac{1}{2}}$$ (4)

where t is the contact time (h), $Q_e$and $Q_t$ (mg‐P g⁻¹) indicate the amount of phosphate adsorbed per unit weight (g) of the 0.1%iron–1%lanthanum‐doped foam glass at equilibrium, and the amount of phosphate adsorbed per unit weight (g) of 0.1%iron–1%lanthanum‐doped foam glass at time t (h), respectively. $k_1$ (h⁻¹), $k_2$ (g mg⁻¹ h⁻¹), and $k_i$(mg g⁻¹ h^‐1/2) are the rate constants for the pseudo‐first‐order, second‐order, and intra‐particle diffusion models, respectively.

FIGURE 5.

Phosphate adsorption kinetics of iron–lanthanum‐loaded foam glass (ILFG).

The correlation coefficients for the pseudo‐second‐order model (r = 0.9979–0.9981, p < 0.01; Figure S4) were higher than those of the other models (Table S3). These results indicated that the adsorption of phosphate onto ILFG occurred mainly via chemisorption (Ho & McKay, 1999). At equilibrium, the pH of the aquatic phase was determined to be approximately 5. The PZC for ILFG was 4. When the pH value is between 2.0 and 8.0, phosphate was mainly adsorbed by the ligand exchange process (Huang et al., 2022; Zhang et al., 2012). Therefore, the adsorption of phosphate onto ILFG may be primarily due to ligand exchange. The calculated second‐order rate constants (k ₂ ) for phosphate adsorption onto ILFG were 1.19 and 0.232 g mg⁻¹ h⁻¹ for initial concentrations of 1 and 10 mg‐P L⁻¹, respectively.

The obtained adsorption isotherms were expressed as Langmuir and Freundlich isotherms (Rajahmundry et al., 2021 Equations (5), (6)).

$$Q_e=\frac{Q_{\mathit{max}}K{C}_e}{1+K{C}_e}$$ (5)

$$\mathit{log}{Q}_e=\mathit{\text{logF}}+\frac{1}{n}\mathit{log}{C}_e$$ (6)

where $C_e$ (mg‐P L⁻¹), K (L mg⁻¹), and Q_max (mg‐P g⁻¹) are the equilibrium phosphate concentration, equilibrium constant, and maximum adsorption capacity, respectively. F and n are the Freundlich constants.

The correlation coefficients for the Langmuir isotherm (r = 0.997, p < 0.01) were higher than those for the Freundlich isotherm (r = 0.965, p < 0.01). The Langmuir model better fitted the observed values (Figure 6). The adsorption equilibrium constant, K (L mg⁻¹), and maximum adsorption capacity, Q_max (mg‐P g⁻¹), obtained by the Langmuir model were 3.1 L mg⁻¹ and 1.2 mg‐P g⁻¹, respectively. The high error bars near the adsorption maximum are attributed to the variations in the amounts of iron and lanthanum loaded on the surface of the foam glass, caused by the heterogeneity of pores on the foam glass. The calculated maximum adsorption capacity is consistent with the observed value (1.3 mg‐P g⁻¹). The dimensionless constant separation factor (R_L) of Langmuir isotherms was calculated using Equation (7) (Togue Kamga, 2019).

$$R_L=\frac{1}{1+K{C}_0}$$ (7)

where K and C ₀ represent the adsorption equilibrium constant obtained by the Langmuir model and the initial concentration of phosphate, respectively.

FIGURE 6.

Langmuir adsorption isotherm of phosphate on iron–lanthanum‐loaded foam glass (ILFG) (La/Fe molar ratio = 4.0).

The R_L value represents the type of adsorption (unfavorable R_L > 1, linear R_L = 1, favorable 0 < R_L, and irreversible R_L = 0). The calculated R_L values for ILFG ranged from 0.0080 to 0.24, indicating favorable adsorption. The observed maximum phosphate adsorption capacity of ILFG (1.2 mg‐P g⁻¹) was lower than that of magnetic zirconium‐based metal–organic frameworks, Mg/Al‐layered double oxide, aluminum impregnated biochar, and lanthanum‐doped coal fly ash‐blast furnace cement composite reported in previous studies (9.90–103.61 mg‐P g⁻¹; Liu et al., 2019; Zhang et al., 2020; Asaoka et al., 2021; Van Truong et al., 2023). However, the equilibrium constant (3.1 L mg⁻¹) of ILFG was significantly higher than that of previous studies (0.07–0.38 L mg⁻¹; Liu et al., 2019; Asaoka et al., 2021; Van Truong et al., 2023), indicating that phosphate adsorption was strong even at low phosphate concentrations.

It has been reported that phosphate adsorbed onto lanthanum adsorbents was desorbed using NaOH (Zhang et al., 2021). Using 3 mol L⁻¹ of NaOH, 42% (SD:6.3, n = 3) of the phosphate adsorbed on the ILFG could be desorbed. Optimal conditions for phosphate desorption will be investigated in future studies.

Bench‐scale experiments on the removal of phosphate from domestic wastewater

The percentage of phosphate removed by the foam glass was 0%–4.5% in the treated domestic wastewater from Johkasou (Figure 7). By contrast, the percentage of phosphate removed by ILFG increased with increasing contact time. At an initial phosphate concentration of 5 mg‐P L⁻¹, which is the typical phosphate concentration in domestic wastewater, the phosphate removal percentage reached 99.2% after 24 h (Figure 7). The saturation time was roughly estimated by time course of phosphate concentration obtained by the column experiments. The calculated initial removal rate for phosphate was 0.99–1.11 mg‐P L⁻¹ h⁻¹. The saturation time of the column was 70–79 h. ILFG can adsorb phosphate from domestic wastewater with large amounts of impurities, such as organic matter. However, other nutrients such as NH₄‐N, NO₂‐N and NO₃‐N in the domestic wastewater were not removed by ILFG.

FIGURE 7.

Changes in phosphate removal percentages over time in domestic wastewater with different phosphate concentrations using foam glass (control) and iron–lanthanum‐loaded foam glass (ILFG) (La/Fe molar ratio = 4.0).

CONCLUSION

We prepared a phosphate adsorbent, ILFG, from waste glass. The presence of iron (III) oxide‐hydroxide was observed on the surface of the foam glass, which played a crucial role in both phosphate adsorption and increasing the specific surface area of ILFG. The foamed glass was loaded with lanthanum, which exhibited a high selectivity for phosphate. The optimal loading percentages for iron and lanthanum to prepare ILFG were 0.1% and 1%, respectively. The ILFG was calcinated at 350°C for 2 h to prevent exfoliation of lanthanum. Phosphate adsorption was classified as chemisorption based on ligand exchange. Adsorption kinetics for phosphate onto ILFG could be expressed as the pseudo‐second‐order model. Phosphate adsorption onto ILFG reached equilibrium within 48 h. The adsorption isotherm was expressed as a Langmuir model with 1.3 mg‐P g⁻¹ of adsorption maximum. The ILFG demonstrated favorable adsorption at low concentrations of phosphate. Hence, ILFGs are effective in removing phosphate from domestic and natural waters. Our findings demonstrate the advantages of ILFG as a low‐cost, eco‐friendly, and sustainable adsorbent prepared from waste glass, as well as its potential applications in the on‐site treatment of domestic water.

AUTHOR CONTRIBUTIONS

Yuzu Katsuura: Investigation; formal analysis; writing – original draft. Satoshi Asaoka: Conceptualization; methodology; data curation; validation; supervision; funding acquisition; writing – review and editing; investigation. Kazuhiko Takeda: Formal analysis; data curation. Shinya Nakashita: Formal analysis; data curation. Kodai Hayashi: Investigation; formal analysis; data curation; visualization. Kazuya Tanaka: Resources; formal analysis; data curation. Yasuhiro Inada: Formal analysis; data curation. Tetsuji Okuda: Formal analysis; data curation.

CONFLICT OF INTEREST STATEMENT

This study was a corroborative research project funded by FujiClean Co., Ltd. The authors have no control over the interpretation or publication of this manuscript.

Supporting information

Figure S1. Relationship between calcination temperature and turbidity after adsorption of phosphate.

Figure S2. Effect of iron loading percentage on the removal of phosphate and turbidity.

Figure S3. Iron K edge XANES spectra of standards, and ILFG with and without phosphate adsorption.

Figure S4. Pseudo second order kinetics of phosphate removal by ILFG.

Table S1. Chemical composition of domestic wastewater discharged from Johkasou.

Table S2. Heavy metals dissolved from the foam glass used in this study.

Table S3. Correlation coefficients of each kinetic model for phosphate adsorption.

Katsuura, Y. , Asaoka, S. , Takeda, K. , Nakashita, S. , Hayashi, K. , Tanaka, K. , Inada, Y. , & Okuda, T. (2025). Adsorptive removal of phosphate from aqueous solutions using iron–lanthanum‐doped foam glass adsorbent. Water Environment Research, 97(2), e70025. 10.1002/wer.70025

DATA AVAILABILITY STATEMENT

All relevant data are included in the paper or its Supporting information.