The predominant exterior charges and speciation characteristics of the soluble metallic ions are highly dependent upon the pH of the examined aqueous solution (Jiang et al., 2020). The pH impact was followed throughout a range of pH levels that varied from 2 to 8. All other parameters were kept constant at specific levels: an interaction period of 120 min, a temperature of approximately 35°C, a tested volume of 100 mL, a pollutant concentration equal to 100 mg/L, and Mth/EXG dosage of 0.2 g/L. The adsorption results for both SFR and Cd²⁺ demonstrate a significant improvement whenever higher pH levels are tested, reaching pH 8. The adsorption capacities for Cd²⁺ and SFR are 54.2 mg/g and 106.4 mg/g, respectively (Figure 5). The speciation profile of soluble cadmium ions indicates that there are either Cd²⁺ cations or [Cd (H₂O₆)]²⁺ cations at a pH around 8 (Jiang et al., 2020). Furthermore, the SFR molecules have been identified as cationic molecules throughout the pH limit that was examined. Moreover, the expected deprotonation of the reactive chemical groups across the exterior of Mth/EXG with the increased basic situations results in the complete saturation of its exterior with hydroxyl ions bearing negative charges. Consequently, the alkaline pH levels provide an ideal environment for powerful electrostatic attractive forces to occur between the water-soluble pollutants (SFR and Cd²⁺) and the exterior of Mth/EXG (Salam et al., 2020; Fu et al., 2018; Li et al., 2023).

The binding of phosphate ions demonstrates varying responses depending on the adapted pH. The highest removal values occurred at pH 5, with a capacity of 73.4 mg/g. However, after pH 5, the effectiveness of Mth/EXG decreased until reaching pH 8 (Figure 5). The ionizing characteristics of soluble phosphate have been determined under the influence of various pH constraints. Within acidic environments (pH < 3), phosphate could be identified as a neutral type (H₃PO₄). Within the pH range between 3 and 6, it existed in its acidic H₂PO^4- class. Within neutral and alkaline situations at a pH beyond 6, phosphate existed in two additional acidic types, specifically HPO₄ ^2- and PO₄ ^3- (Saleh et al., 2024; Fu et al., 2018). Based on the ionizing behaviors and protonation/deprotonation characteristics of Mth/EXG within the assessed pH levels, it possessed a low uptake effectiveness in acidic environments. This can be explained owing to the protonated exterior of the blended structure, which exhibits weak electrostatic binding to the neutral type of phosphate (H₃PO₄). The electrostatic attraction forces steadily increased as the pH increased, leading to the predominance of the acidic phosphate species (H₂PO₄ ⁻) throughout the solution. This resulted in a significant increase in the established capacity of Mth/EXG until pH 5. Further, the deprotonation of the Mth/EXG beneath neutral pH levels led to the formation of negatively charged chemical groups. These groups exhibit significant repellent characteristics with primarily existing phosphate types such as HPO₄ ^2- and PO₄ ^3- (Shi et al., 2019; Abukhadra and Mostafa, 2019). The previous finding were supported with the determined values of pH value of zero point charge (pH_(pzc)). The determined pH_(pzc) values during the uptake of PO₄ ^3-, SFR, and Cd²⁺ are pH 6.3, pH 7.2, and pH 6.6, respectively. The surficial charges beyond these values are mainly negative which induce the electrostatic attractions of SFR and Cd²⁺. Also, during pH levels below these values, the surficial charges on the surface of the adsorbent are mainly positive which induce the uptake of PO₄ ^3- (Neolaka et al., 2018; Neolaka et al., 2021; Neolaka et al., 2022).

An experiment was conducted to examine the retention characteristics of Mth/EXG about the period of the removal of PO₄ ^3-, SFR, and Cd²⁺. The examination’s duration varied from 20 to 780 min. The specific impact of different time intervals was evaluated after the verification of critical parameters, involving the level of pollutants (100 mg/L), temperature (35 °C), volume (100 mL), pH (5 for PO₄ ^3- and 8 for Cd²⁺ and SFR), and dosage (0.2 g/L). The effectiveness of Mth/EXG in removing PO₄ ^3-, SFR, and Cd²⁺ has been demonstrated by the significant increase in both the quantities of ions adsorbed and the quantifiable rates of removal observed across the studies. Moreover, it is crucial to acknowledge that the time frame of the trials significantly influences the noticed enhancements in the presented uptake features, totaling around 360 min (Figure 6A). Nevertheless, no substantial alterations or improvements have been observed with respect to the rate of elimination of PO₄ ^3-, SFR, and Cd²⁺ ions, nor in the amount of these ions retained beyond the designated contact durations. Previous findings indicate that Mth/EXG may serve as adsorbed agents for PO₄ ^3-, SFR, and Cd²⁺, achieving stability after certain durations. The retention capacities of PO₄ ^3-, SFR, and Cd²⁺ during equilibration using Mth/EXG are 98.6 mg/g, 142.7 mg/g, and 82.2 mg/g, respectively (Figure 6A). The first phases of the assessment indicated substantial improvements and elevated rates of Mth/EXG removal, accompanied by increased amounts of trapped ions. The improvements were ascribed to the readily available interacting and unbound sites throughout the Mth/EXG (Yuan et al., 2024). As the duration of the examination extends, there has been a notable decrease in the total number of accessible sites. The key cause of this behavior is attributed to the prolonged adsorption of PO₄ ^3-, SFR, and Cd²⁺, which fills the previously identified receptors and reduces the overall quantity of available receptors. Consequently, there was a notable decline in the binding rates of PO₄ ^3-, SFR, and Cd²⁺ after a certain duration. Furthermore, the implementation of Mth/EXG demonstrated little enhancement or steady characteristics in the retention of PO₄ ^3-, SFR, and Cd²⁺, indicating equilibrium conditions. The determination of the equilibrium phases of Mth/EXG may be attained by completely saturation of all effective receptors, hence preventing further binding of PO₄ ^3-, SFR, and Cd²⁺ to their interfaces (Salam et al., 2020).

The investigation investigated the impact of initial concentrations of PO₄ ^3-, SFR, and Cd²⁺ to ascertain the maximum elimination activities employing Mth/EXG, alongside related equilibrium conditions, all over the evaluated range of 50–400 mg/L. The supplementary parameters affecting the elimination of PO₄ ^3-, SFR, and Cd²⁺ were maintained at certain levels: an overall volume of 100 mL, a period of 24 h, a dose of 0.2 g/L, and temperatures ranging from 308 K to 318 K. An relationship exists between elevated levels of PO₄ ^3-, SFR, and Cd²⁺ ions and the corresponding rise in their immobilized amounts using Mth/EXG (Figures 7A–C). An elevation in the levels of PO₄ ^3-, SFR, and Cd²⁺ ions inside a certain volume significantly enhanced the diffusion, driving forces, and mobility features of soluble chemical ions. This enhanced the ability to interact with greater amounts of the active retaining sites abundantly present across the exterior of Mth/EXG. The retention effectiveness of PO₄ ^3-, SFR, and Cd²⁺ using Mth/EXG was significantly improved about the evaluated levels of PO₄ ^3-, SFR, and Cd²⁺ (Ahmed et al., 2024b). The relationship is observable only within specified ranges of PO₄ ^3-, SFR, and Cd²⁺ concentrations. Moreover, augmenting the starting levels of PO₄ ^3-, SFR, and Cd²⁺ seems to have little impact on their interaction with Mth/EXG (Figures 7A–C). Determining the equilibrium phases facilitates the determination of optimal retention effectiveness for PO₄ ^3-, SFR, and Cd²⁺. The adsorption abilities of PO43- were quantified as 260 mg/g at 308 K, 250.5 mg/g at 313 K, and 230 mg/g at 318 K (Figure 7A). The observed values for SFR were 297.8 mg/g at 308 K, 261.6 mg/g at 313 K, and 234.6 mg/g at 318 K (Figure 7B). The Cd²⁺ retention levels at temperatures of 308 K, 313 K, and 318 K were 223.4 mg/g, 201.4 mg/g, and 182.3 mg/g, respectively (Figure 7C). The decrease in the uptake of PO₄ ^3-, SFR, and Cd²⁺ observed while using Mth/EXG at different temperatures suggests that the processes under investigation exhibit exothermic characteristics.

Traditional equilibrium assessments of adsorption responses were conducted to evaluate the spatial distribution of water-soluble pollutants in aqueous solutions and the materials that adsorb them after stability levels. Conventional equilibrium modeling approaches significantly impact the elucidation of processes. The prevalent isotherm functions provide critical insights into three dimensions: (a) the sorbate’s selectivity for the adsorbent’s reactive surface; (b) the possible amount of soluble chemical ions that may engage with these surfaces; and (c) the ultimate binding features. The binding properties of PO₄ ^3-, SFR, and Cd²⁺ were analyzed for their equilibrium features using the Langmuir (Figures 8A–C), Freundlich (Figures 8D–F), and Dubinin-Radushkevich (D-R) (Figures 8G–I) equilibrium models. The degree of concordance between the proposed equilibrium assumptions outlined in the aforementioned models and the measurable retaining behaviors of PO₄ ^3-, SFR, and Cd²⁺ has been evaluated by non-linear fitting methods. The inquiry included analyzing the correlation coefficient (R²) and the Chi-squared (χ²) data. Assessment of R² and X² indicates that the Mth/EXG particles have a stronger affinity for binding PO₄ ^3-, SFR, and Cd²⁺, conforming more closely to Langmuir’s concepts than to the Freundlich concept. The equilibrium behavior mentioned above demonstrates that PO₄ ^3-, SFR, and Cd²⁺ display consistent and uniform binding affinities across both the reactive and available sites of Mth/EXG particles. This leads to the formation of monolayers of adsorbed PO₄ ^3-, SFR, and Cd²⁺ ions (Huang et al., 2018; Dawodu et al., 2012). Furthermore, the analysis established that Mth/EXG particulates have favorable adsorption characteristics for PO₄ ^3-, SFR, and Cd²⁺, as shown by the RL values, which are less than 1 (Wu et al., 2023; El Qada, 2020). The mathematical study determined the maximum adsorption capacities (Q_max) of PO₄ ^3- as 268.07 mg/g at 308 K, 257.5 mg/g at 313 K, and 234.1 mg/g at 318 K. The predicted values for SFR are 312.3 mg/g at 308 K, 270 mg/g at 313 K, and 237 mg/g at 318 K (Table 3). The calculated concentrations of Cd²⁺ were 234.9 mg/g at 308 K, 211 mg/g at 313 K, and 187.9 mg/g at 318 K (Table 3).

The equilibrium parameters of the D-R hypothesis provide a comprehensive understanding of the energy variations shown by Mth/EXG nanoparticles throughout the purification processes of PO₄ ^3-, SFR, and Cd²⁺, irrespective of the particle’s degree of heterogeneity or homogeneity depending on Gaussian energy distribution (El Qada, 2020). The examination of the D-R modeling results provides critical insights into the calculation of free adsorption energy (E) and its relevance in understanding fundamental mechanisms, regardless of whether they are chemical or physical in nature. The energy levels related to retaining activities may be categorized into three separate groups: below 8 kJ/mol, between 8 and 16 kJ/mol, and beyond 16 kJ/mol. At these energy levels, the primary mechanisms consist mostly of significant physical interactions, weak chemical reactions, or a combination of physical and chemical processes, together with significant chemical activities (Sayed et al., 2022). The determined E values for SFR uptake procedures using Mth/EXG were below the permissible energy limits (below 8 kJ/mol) for the physical processes (Table 3). The established levels for PO₄ ^3- and Cd²⁺ align with the hypothesized range for weak chemical or complicated interactions between chemical and physical reactions (8–16 kJ/mol) (Table 3).

Employing statistical physics methods to mimic the equilibrium characteristics of adsorption activities can give an in-depth investigation of the distinctive characteristics of the processes. This study uses mathematical models to assess the interactions between water-soluble pollutants and external reactive chemical groups present as binding spots onto adsorbent interfaces. The mathematical formulas used in this investigation provide calculated parameters that accurately describe the principal activities, such as energetic and steric aspects. The simulations include several steric factors, notably Nm, which denotes the total number of occupied adsorption sites over the contact surface of Mth/EXG. The estimations also include the quantity of held ions (n) within an individual receptor and the maximum retention efficacy of PO₄ ^3-, SFR, and Cd²⁺ using Mth/EXG at full saturation (Q_sat). The evaluated energetic parameters, derived from the model’s fitting variables, include internal energy (E_int), entropy (Sa), retention energies (E), and free enthalpy (G). Non-linear regression analyses have been used to examine the aforementioned hypotheses of the established models. The prior inquiry was effectively conducted using multivariable nonlinear regression algorithms with the Levenberg-Marquardt iterative approach. The derived fitting values were later used to evaluate and describe the adsorption processes of PO₄ ^3-, SFR, and Cd²⁺ by Mth/EXG. The analysis was completed using a closely analogous model, namely the monolayer model of a single active site (Figures 8J–L). Table 4 displays the calculated variables and the fitting quality.

The recycling and reuse potential of Mth/EXG as an adsorption material is a significant factor when evaluating its qualities for practical and large-scale water treatment activities. The residual particulates of Mth/EXG, obtained after conducting adsorption experiments for PO₄ ^3-, SFR, and Cd²⁺, were subjected to a 10-min washing process utilizing distilled water. This washing process has been repeated four times. Subsequently, the cleansed Mth/EXG particulates had been carefully dried inside an electric oven at a temperature of 55 °C for duration of 8 h and then used in subsequent adsorption cycles. The recyclable adsorption experiments of PO₄ ^3-, SFR, and Cd²⁺ have been performed, implementing specific values of pH (pH 5 for PO₄ ^3- and pH 8 for Cd²⁺ and SFR), Mth/EXG dose (0.2 g/L), investigated levels (400 mg/L), interaction time (24 h), temperature (308 K), and volume (100 mL) (Figure 11). The results of the five recycling experiments demonstrate the excellent stability and potential to be reused of Mth/EXG particulates for successful use in removal operations throughout the five cycles (Figure 11). The amounts of PO₄ ^3- adsorbed throughout the examined rounds are as follows: 260 mg/g (Cycle 1), 260 mg/g (Cycle 2), 254 mg/g (Cycle 3), 243.4 mg/g (Cycle 4), and 231.7 mg/g (Cycle 5). The binding levels of SFR are as follows: 297.8 mg/g (Cycle 1), 294.7 mg/g (Cycle 2), 286.5 mg/g (Cycle 3), 277.5 mg/g (Cycle 4), and 263.7 mg/g (Cycle 5) (Figure 11). The adsorption amounts of Cd²⁺ during the examined rounds are as follows: 223.4 mg/g (Cycle 1), 220.6 mg/g (Cycle 2), 214.6 mg/g (Cycle 3), 202.6 mg/g (Cycle 4), and 184.8 mg/g (Cycle 5) (Figure 11). The noticeable reduction in the effectiveness of Mth/EXG after repeat reusing runs may be attributed to the ongoing development of a complex among the ions that were absorbed, together with the chemical composition of the composite material.

Glauconite has a highly environmental clay structure and is commonly used as fertilizer for its content of potassium and iron. The synthetic glauconite-based adsorbents display remarkable recyclability to be used several times, and after the complete exhaustion of the structure, each spent product after the adsorption of each pollutant can be disposed of and recycled by different techniques. The spent sample after the adsorption of phosphate can be applied directly as fertilizer. Following cadmium adsorption, the exhausted material can potentially be utilized for recovering the cadmium ions using acidic washing as well as magnetic extraction, and the remaining materials can be repurposed as an adsorbent on its own or in combination with other types of structures. Furthermore, the structure may undergo heat treatment or microwave exposure, resulting in a cadmium oxide-supported EXG or cadmium iron silicate framework suitable for many applications. After safranin adsorption, the spent structure can undergo carbonization or activation, resulting in a type of activated carbon/EXG composite suitable for various applications.

The impact of several species of soluble chemicals, including Pb²⁺, Zn²⁺, NO₃ ⁻, SO₄ ^2-, malachite green dye (MG), and chlorpyrifos insecticide (CF), on the binding selectivity of the Mth/EXG towards Cd²⁺, PO₄ ^3-, and SFR ions has been investigated. The adsorption experiments for Cd²⁺, PO₄ ^3-, and SFR were done, taking into account particular levels of pH (pH 5 for PO₄ ^3- and pH 8 for Cd²⁺ and SFR), concentrations (400 mg/L), Mth/EXG dose (0.2 g/L), interaction duration (24 h), temperature (308 K), and volume (100 mL) (Figure 12). The presence of the soluble chemical anions (NO₃ ⁻ and SO₄ ^2-) does not significantly affect the removal of Cd²⁺, PO₄ ^3-, and SFR ions using Mth/EXG (Figure 12). This assignment has been assigned to the types of chemical complexes formed as well as the exchange of ligands. The uptake of NO₃ ⁻ along with SO₄ ^2- occurred by forming outer-sphere complexes, which have lower stability compared to the inner-sphere complexes described for ions of the studied pollutants (Saleh et al., 2024). In relation to the presence of different types of organic pollutants (MG and CF), they had a significant competitive effect, particularly during the adsorption of Cd²⁺ and PO₄ ^3-. The quantity of Cd²⁺ and PO₄ ^3- adsorbed decreased to 160.6 mg/g and 127.4 mg/g, respectively, in the presence of CF and to 172.7 mg/g (Cd²⁺) and 121.6 mg/g (PO₄ ^3-) in the presence of MG (Figure 12). In terms of the influence of MG and CF on the uptake of SFR, they have a considerable competitive influence on the binding potential of Mth/EXG for SFR. However, the amount of SFR adsorbed is still greater than the established levels of MG and CF. Furthermore, the existence of metallic cations such as Pb²⁺ and Zn²⁺ had a significant competitive effect on the removal of Cd²⁺, PO₄ ^3-, and SFR using Mth/EXG. This was evident from the decrease in the amount of their adsorbed ions. Nevertheless, the Mth/EXG particulates maintain considerable capacities for Cd²⁺, PO₄ ^3-, and SFR retention, regardless of being interacting with the other metallic ions of Pb²⁺ and Zn²⁺ (Figure 12). The overall results confirm that Mth/EXG is suitable for successfully eliminating Cd²⁺, PO₄ ^3-, and SFR ions, irrespective of whether there are other soluble chemicals, including different anions, cations, and organic compounds. Furthermore, the findings given demonstrate the efficacy of Mth/EXG for removing various types of organic and inorganic contaminants from water.

The determined adsorption capacities of Mth/EXG as adsorbent for PO₄ ^3-, SFR, and Cd²⁺ were compared with studied organic and inorganic adsorbents in literature in addition to the raw galuconite and exfoliated glauconite (Supplementary Table S2). The recognized best capacities of raw galuconite are 91.7 mg/g (PO₄ ^3-), 82.5 mg/g (Cd²⁺), and 104.8 mg/g (SFR). For the exfoliated product prior to the modification with methanol (EXG) the determined values are 196.4 mg/g (PO₄ ^3-), 183.7 mg/g (Cd²⁺), and 260.3 mg/g (SFR) (Supplementary Table S2). Such results demonstrate the impact of the exfoliation followed by methanol modification in inducing the uptake efficacy of the studied pollutants. Also, the presented values reflected the higher adsorption properties of the Mth/EXG composite as compared most of the presented materials in the table (Supplementary Table S2). Therefore, the synthetic structure is a suitable and effective product to be applied as a low-cost and environmental adsorbent in the realistic purification of wastewater from different species of dissolved organic and inorganic chemicals as pollutants. The structure is less expensive than the aforementioned adsorbents, and its uses may attain excellent removal effectiveness with little dosages and in brief timeframes. Furthermore, it is suggested as a non-toxic natural environmental material with extensive applications as a fertilizer.