Heavy Metal-contaminated Water Research Articles

Isolation and characterization of native microalgae with potential for phycoremediation of heavy metal contaminated water

ABSTRACT The capacity of living algal cells to efficiently eliminate metals from water is well known and achieved through the mechanisms of biosorption and bioaccumulation. These investigations highlight the potential of indigenous microalgae for the elimination of toxic elements such as cadmium (Cd), cobalt (Co), chromium (Cr), nickel (Ni), and lead (Pb) from aqueous solutions. To identify algal strains that are effective in removing heavy metals, samples of soil and water were collected from areas contaminated with industrial and municipal effluents. Among the 11 isolates obtained from various sites contaminated with heavy metals, three isolates (designated as A, I and K) were able to tolerate both the threshold and double threshold levels of the tested heavy metals. Subsequent liquid assays confirmed the efficiency of the three selected algal isolates in removing heavy metals, with isolates A and I demonstrating effectiveness in removing all tested heavy metals, exhibiting removal rates of cadmium ranging from 40% to 80%, cobalt ranging from 20% to 60%, chromium up to 90%, nickel ranging from 40% to 90%, and lead ranging from 50% to 70%. Isolate K displayed the highest efficiency in only removing lead, specifically 86.23% at 21 DAI (Days After Inoculation), and therefore was not chosen for further characterization. Through morphological and molecular characterization, isolates A and I were identified as Coelastrella thermophila AAU BR A and Chlorella sp. AAU BR I, respectively. In conclusion, the results demonstrate that the native algal isolates have the potential to serve as eco-friendly agents for remediating heavy metal-contaminated water.

Bacterial and microalgal co-fixation for remediation of industrial wastewater contaminated with arsenic, mercury, and other pollutants

Microbial remediation is an efficient approach for improving heavy metal-contaminated water environments. Herein, this article developed a composite bacterial agent (CBA) with a high heavy metal tolerance. Within 12 h, the CBA demonstrated removal efficiencies of 65.18 ± 1.53% for As and 60.73 ± 0.94% for Hg in wastewater. This study prepared bacterial–algal fixed spheres (BAFS) to further enhance the removal efficiencies of As and Hg. Moreover, during desorption using 0.1 mol/L HNO3 for 60 min, the BAFS maintained high removal efficiencies for As and Hg after five adsorption–desorption cycles. Applying BAFS to industrial wastewater collected from factory outfall caused substantial reductions in chemical pollutants and other heavy metals. Scanning electron microscopy analysis further revealed that the internal cavities formed through the crosslinking of immobilized materials provided excellent survival carriers for bacteria and microalgae. Infrared spectroscopy analysis demonstrated the involvement of three functional groups, namely -OH, -CH2-, and C-O-C, in pollutant adsorption. Additionally, microbial community diversity analysis indicated that immobilization effectively preserved the pollutant adsorption ability of the microorganisms, increasing the abundance of functional microbial populations. These characteristics improved the efficiency of industrial wastewater treatment while promoting recycling.

Assessing the Lead Removal Potential of Pineapple Waste Hydrochar in Simulated Wastewater Treatment

This study explores the viability of utilizing biochar and hydrochar derived from pineapple waste as adsorbents for removing lead (Pb) from water. Pineapple residues, including stems, leaves, and fruit, were subjected to pyrolysis and Hydrothermal Treatment to produce biochar (PWB) and hydrochar (PWH) respectively. Fourier Transform Infrared (FT-IR) analysis was employed to characterize the surface properties of PWB and PWH, validating their potential as adsorbents. A series of adsorption experiments assessed the impact of pH (ranging from 2 to 6), contact time (ranging from 15 to 90 minutes), and temperature (ranging from 30 to 90°C) on the adsorption efficiency of both materials. Results indicate PWH to be markedly more effective, with an average Pb removal efficiency of 84.07% compared to PWB's 55.68%. The optimal contact time was determined to be 60 minutes for both materials. Moreover, pH 4.0 was identified as the optimal condition for Pb adsorption, showcasing a significant increase in biosorption capacity within this pH range. Additionally, higher temperatures corresponded to enhanced Pb2+ removal efficiency, rising from 75.02% to 87.58% as temperature increased from 30°C to 90°C. Overall, these findings underscore the potential of pineapple waste-derived biochar and hydrochar as promising, environmentally friendly adsorbents for addressing heavy metal contamination in water, particularly in wastewater treatment applications.

A ratiometric electrochemical sensor for simultaneous detection of multiple heavy metal ions in water and herbal medicines based on methylene blue-functionalized metal–organic framework

Heavy metal contamination in water and herbal medicine poses a global threat to human health. There is a pressing need for the development of a simple and rapid method for simultaneous quantification. In this study, a ratiometric electrochemical sensor was first constructed using a hybrid material composed of methylene blue functionalized metal–organic framework (MB-UiO66-NH2) and multi-walled carbon nanotubes (MWCNTs). Then, MB-UiO66-NH2/MWCNTs harnessed the large specific surface area of UiO66-NH2 and good conductivity of MWCNTs, resulting in a sensor with superior analytical performance for Cd2+, Pb2+, and Hg2+ detection. Meanwhile, the ratiometric probe uses MB as an internal reference, with the ratio signal (Imetalion/IMB) serving as output. This ratiometric electrochemical sensor was able to enhance the reproducibility and reliability and eliminate interference, particularly in complex environments. Importantly, based on this ratiometric electrochemical platform, the low detection limit were 11.08 nM for Cd2+, 5.47 nM for Pb2+, and 6.42 nM for Hg2+, which realized the simultaneous, sensitive, and reliable detection. In addition, it has been successfully applied in real water and representative herbal medicine sample analysis. Therefore, this work provides a new approach for the risk assessment of heavy metal accumulation, which is conducive to safeguarding people's lives and health.

Improving Pb(II) Removal via Ascorbic Acid-Enhanced Red Mud Adsorption: Kinetics and Isotherm Analysis

This study explored the efficacy of red mud, an aluminum production by-product, as an adsorbent for Pb(II) ion removal from contaminated water and assessed the adsorption isothermal model and kinetics. Red mud, characterized by its richness in oxide minerals with reactive surfaces, has potential for heavy metal adsorption, but its capacity for larger ions like Pb(II) is limited. This research aimed to enhance red mud’s adsorption properties through modification with ascorbic acid. The modification process involved heating a mixture of red mud and ascorbic acid to its boiling point, followed by the formation of adsorbent beads using red mud and Na-alginate mixture dropped into a 2 % CaCl2 solution at −2 °C. The beads were tested over varying durations ranging from 30 to 210 min. The results indicated that ascorbic acid modification led to the transformation of minerals in red mud, improving its pore diameter, pore volume, and specific surface area of the adsorbent. The modified and unmodified red mud adhered to both Langmuir and Freundlich isotherms, with R² values converging to one, and displayed pseudo-second-order kinetics. Notably, the introduction of ascorbic acid augments the adsorption efficacy of red mud for Pb(II) ions from 84.8 % to a compelling 99.3 %. This underscores the augmented capability of ascorbic acid-modified red mud, highlighting its prospective applicability as a potent adsorbent in the remediation of heavy metal-contaminated water. HIGHLIGHTS Innovative Use of Red Mud: Explored the potential of red mud, a by-product of aluminum production, as an adsorbent for removing Pb(II) ions from contaminated water Ascorbic Acid Modification: Developed a novel modification process using ascorbic acid, including heating the red mud and ascorbic acid, enhancing the adsorption properties of red mud as pore diameter, pore volume, and specific surface area of the adsorbent Adsorption Isotherms and Kinetics: Conducted a comprehensive assessment of adsorption isothermal models and kinetics, with modified and unmodified red mud adhering to Langmuir and Freundlich isotherms and displaying pseudo-second-order kinetics Enhanced Adsorption Efficacy: the adsorption effectiveness is enhanced from 84.8 to 99.3 %, emphasizing its potential applicability for Pb(II) GRAPHICAL ABSTRACT

A novel green synthesis of MnO2-Coal composite for rapid removal of silver and lead from wastewater

The presence of Ag(I) and Pb(II) ions in wastewater poses a significant threat to human health in contemporary times. This study aims to explore the development of a novel and economical adsorbent by grafting MnO2 particles onto low-rank coal, providing an innovative solution for the remediation of water contaminated with silver and lead. The synthesized nanocomposites, referred to as MnO2-Coal, underwent thorough characterization using FTIR, XRD, BET, and SEM to highlight the feasibility of in-situ surface modification of coal with MnO2 nanoparticles. The adsorption of Ag(I) and Pb(II) from their respective aqueous solution onto MnO2-Coal was systematically investigated, with optimization of key parameters such as pH, temperature, initial concentration, contact time, ionic strength, and competing ions. Remarkably adsorption equilibrium was achieved within a 10 min, resulting in impressive removal rates of 80–90 % for both Ag(I) and Pb(II) at pH 6. The experimental data were evaluated using Langmuir, Freundlich, and Temkin isotherm models. The Langmuir isotherm model proved to be more accurate in representing the adsorption of Ag(I) and Pb(II) ions onto MnO2-Coal, exhibiting high regression coefficients (R2 = 0.99) and maximum adsorption capacities of 93.57 and 61.98 mg/g, along with partition coefficients of 4.53 and 71.92 L/g for Ag(I) and Pb(II), respectively, at 293 K. Kinetic assessments employing PFO, PSO, Elovich, and IPD models indicated that the PFO and PSO models were most suitable for adsorption mechanism of Pb(II) and Ag(I) on MnO2-Coal composites, respectively. Moreover, thermodynamic evaluation revealed the spontaneous and endothermic adsorption process for Ag(I), while exothermic behavior for adsorption of Pb(II). Importantly, this approach not only demonstrates cost-effectiveness but also environmental friendliness in treating heavy metal-contamination in water. The research suggests the potential of MnO2-Coal composites as efficient and sustainable adsorbents for water purification applications.

Heavy metal concentrations in water from Bakkhali River estuary, Cox’s Bazar, Bangladesh

Heavy metals contamination of water is considered as severe global issues for developing countries like Bangladesh. Because heavy metal pollution ruined aquatic ecosystem especially fish diversity which contribute important share on economy of a country. The present study designed to investigate the contamination level of lead (Pb), chromium (Cr), cadmium (Cd), copper (Cu) and zinc (Zn) in surface water of Bakkhali river estuary in Bangladesh. The decreasing order of metals concentration was Cu>Zn >Cr>Pb>Cd with the mean value of 2.6> 0.825 > 0.355 > 0.056 >0.003 mg/L, respectively. The results showed a significant seasonal variation of heavy metals concentration in water. Higher contamination occurred during post monsoon, while lower during the monsoon season. Among the all studied heavy metals Cu concentration was higher (2.6 mg/L) and lower (0.003 mg/L) concentration was Cd. Metal concentrations in water samples exceeded the safe limits of drinking water which indicated that the water from this estuarine river is not fully safe for using/drinking. The study area was not entirely polluted in terms of all metal concentrations. But level of metal concentration in polluted sites supposed risk to ecological health. The findings of present study recommended that continuous monitoring of water should be aimed to evaluate the risk which could help to maintain healthy coastal ecosystem and improve management strategy of this estuarine river.

β particles enhance the modulating lattice distortion of Mn-doped BiFeO3 and photo-responsive catalyzing of As(III) and Sb(III)

In this work, metal Mn was doped into BiFeO3(BFO) to modulate the lattice, and a high-energy β electron beam was used to irradiate the Mn-BiFeO3(BFMO) to produce lattice distortions, resulting in reducing the photogenerated carrier complexation rate of the material and improving the photocatalytic activity for arsenic and antimony. The physical properties of the BFMO with lattice distortion also produced some changes, with the Bi: O ratio on the surface decreasing from 1.0: 3.0–1.0: 1.6 and the band gap decreasing from 1.5 eV to 1.3 eV. In addition, the experiment results show that the structure of Bi-Mn-Fe-O can efficiently enhance the photocatalytic oxidation of As(III) and Sb(III) at different initial pH values, and the elimination rates of As(III) and Sb(III) can reach 100% and 79.9%, respectively. Characterization by PL, Mott-Schottky, transient photocurrent response, and DFT calculations demonstrated that BFMO-450 (irradiated at a dose of 450 KGy) has excellent charge mobility, which is conducive to the separation and transfer of photogenerated carriers. The XPS results showed that the BFMO-450 surface has optimal Mn4+/Mn2+ and Fe2+/Fe3+ ion pairs, and the formation of the Fe-Mn structure is favorable for the generation of superoxide radicals (·O2−, whereas the most prominent radicals in the photocatalytic process are the ·O2−, which was proved by the electron paramagnetic resonance (EPR) and bursting experiments. This study provides a novel approach to modifying BFMO composites and demonstrates that materials possessing lattice distortion have advantages in treating heavy metal-contaminated water.

Heavy Metal Contamination of Water and their Toxic Effect on Human Health Area of Kishangarh Block of Alwar District (Rajasthan)

Heavy Metal Contamination of Water and their Toxic Effect on Human Health Area of Kishangarh Block of Alwar District (Rajasthan)

Optical Method for Detection and Classification of Heavy Metal Contaminants in Water Using Iso-pathlength Point Characterization.

Water pollution caused by hazardous substances, particularly heavy metal (HM) ions, poses a threat to human health and the environment. Traditional methods for measuring HM in water are expensive and time-consuming and require extensive sample preparation. Therefore, developing robust, simple, and sensitive techniques for the detection and classification of HM is needed. We propose an optical approach that exploits the full scattering profile, meaning the angular intensity distribution, and utilizes the iso-pathlength (IPL) point. This point appears where the intensity is constant for different scattering coefficients, while the absorption coefficient is set. The absorption does not affect the IPL point position, it only reduces its intensity. In this paper, we explore the wavelength influence on the IPL point both in Monte Carlo simulations and experimentally. Next, we present the characterization of ferric chloride (FeCl2) by this phenomenon. Eventually, we exhibit the detection of FeCl2 and intralipid mixed in concentrations of 50-100 and 20-30 ppm, respectively. These findings endorse the idea that the IPL point is an intrinsic parameter of a system serving as an absolute calibration point. The method provides an efficient way of differentiating contamination in water. Its characterization technique is easy, precise, and versatile making it preferable for water monitoring.

Spatial Distribution, Risk Assessment, and Provenance of Heavy Metals Contamination in the Sediments of the Gilgit River Basin, Northern Pakistan

ABSTRACT Gilgit River Basin (GRB) is one of the primary fluvial aquatic systems flowing through Gilgit-Baltistan and a water source for recreation, fisheries, irrigation, and drinking to more than 1.8 million people. This study aimed to investigate heavy metals (HM) contamination levels in sediments of GRB, northern Pakistan. Fifty-five samples were picked from the various sections of GRB and examined for HM concentrations. Fe showed the maximum average concentration of 27,743 mg/kg, while Cd was noted with a minimum average of 1.06 mg/kg. HM concentrations were noted within the world river system guidelines except Cd, which also surpassed the sediment quality guidelines set by USEPA. HM concentrations of GRB sediments were used for the geospatial and ecotoxicological risk indices. Geospatial analyses showed higher levels of HM contamination and risk in the sediments of Ishkomen River in GRB. HM contamination in GRB sediments showed low to moderate levels of risk to exposed aquatic ecosystems. Statistical analyses were used for the HM source apportionment in sediments of GRB, suggesting a major contribution from natural activities. This study recommends seasonal variation in HM contamination of water and sediments studies in the GRB.

Green and effective remediation of heavy metals contaminated water using CaCO3 vaterite synthesized through biomineralization

Heavy metal pollution has attracted significant attention due to its persistent presence in aquatic environments. A novel vaterite-based calcium carbonate adsorbent, named biogenic CaCO3, was synthesized utilizing a microbially induced carbonate precipitation (MICP) method to remediate heavy metal-contaminated water. The maximum Cd2+ removal capacity of biogenic CaCO3 was 1074.04 mg Cd2+/g CaCO3 with a high Cd2+ removal efficiency greater than 90% (initial Cd2+ concentration 400 mg/L). Furthermore, the biogenic CaCO₃ vaterite, induced by microbial-induced calcium carbonate precipitation (MICP) process, demonstrated a prolonged phase transformation to calcite and enhanced stability. This resulted in a sustained high effectiveness (greater than 96%) following six consecutive recycling tests. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the semi-stable vaterite type of biogenic CaCO3 spontaneously underwent dissolution and recrystallization to form thermodynamic stable calcite in aquatic environments. However, the presence of Cd2+ leads to the transformation of vaterite into CdCO3 rather than undergoing direct converting to calcite. This transformation is attributed to the relatively low solubility of CdCO3 compared to calcite. Meanwhile, the biogenic CaCO3 proved to be an efficient and viable method for the removal of Pb2+, Cu2+, Zn2+, Co2+, Ni2+ and Mn2+ from water samples, surpassing the performance of previously reported adsorbents. Overall, the efficient and promising adsorbent demonstrates potential for practical in situ remediation of heavy metals-contaminated water.

Effective removal of heavy metals from aqueous solution using CS/OMMT nanocomposite synthesized by gamma irradiation

The current investigation involved the fabrication of nanocomposites CS/OMMT through polymerization initiated by γ-rays irradiation. The product was characterized using FTIR and SEM techniques. The current analysis aimed to determine the adsorption performance of lead (II) ions onto nanocomposites that were synthesized, using a batch adsorption technique in an aqueous medium. The investigation analyzed the influence of different issues on the adsorption capability of the nanocomposite. Further, the lead (II) concentration, medium pH, contact time & adsorbent use were taken into account. Adsorption process order was determined with the help of kinetics. Kinetics data of pseudo 1st and 2nd order models were analyzed. There was a strong correlation between the data and the second-order kinetic model. Based on our research, we conclude that the nanocomposite showed good agreement with the Langmuir model of Pb(II) ions. The nanocomposite underwent a desorption procedure utilizing solutions of CaCl2, NaCl and 0.01 M HNO3 to attain complete elimination of Pb(II) ions. This process are revealed that CS/OMMT demonstrated remarkable efficacy as an absorbent for heavy metal ions, suggesting its potential as a viable method for purifying heavy metal-contaminated water.

A Review on the Removal of Heavy Metals from Water by Phosphorus-Enriched Biochar

In recent years, the utilization of phosphorus-enriched biochar (PBC) has attracted significant attention due to its exceptional stability and surface reactivity. This review systematically summarizes the advancements in research related to the application of PBC as an adsorbent for remediating water contaminated with heavy metals. Initially, the precursors utilized in the production of PBC, encompassing biomass and phosphorus sources, are introduced. Subsequently, the distinct physicochemical properties and adsorption characteristics resulting from phosphorus doping on the biochar surface through various carbonization processes and parameters are elucidated. Additionally, the diverse adsorption mechanisms employed by PBC in removing heavy metals from water are analyzed. Lastly, future research prospects and associated challenges concerning PBC are presented. This paper aims to furnish comprehensive background information for the practical implementation of PBC in the purification of heavy metal-contaminated water environments.

Adsorption of lead ions from wastewater using electrospun zeolite/MWCNT nanofibers: kinetics, thermodynamics and modeling study.

Heavy metal contamination in water is a serious environmental issue due to the toxicity of metals like lead. This study developed zeolite and multi-walled carbon nanotube (MWCNT) incorporated polyacrylonitrile (PAN) nanofibers via needleless electrospinning and examined their potential for lead ion adsorption from aqueous solutions. The adsorption process was optimized using response surface methodology (RSM) and artificial neural network (ANN) modeling approaches. The adsorbent displayed efficient lead removal of 84.75% under optimum conditions (adsorbent dose (2.21 g), adsorption time (207 min), temperature (48 °C), and initial concentration (62 ppm)). Kinetic studies revealed that the adsorption followed pseudo-first-order kinetics governed by interparticle diffusion. Isotherm analysis indicated Langmuir monolayer adsorption with improved 5.90 mg g-1 capacity compared to pristine PAN nanofibers. Thermodynamic parameters suggested the adsorption was spontaneous and endothermic. This work demonstrates the promise of electrospun zeolite/MWCNT nanofibers as adsorbents for removing lead from wastewater.

EDTA functionalized Mg/Al hydroxides modified biochar for Pb(II) and Cd(II) removal: Adsorption performance and mechanism

This study has successfully synthesized layered double hydroxide (LDH) biochar (E-Mg/Al-LDH BC) with ethylenediaminetetraacetic acid (EDTA) and examined its adsorption capabilities towards Pb(II) and Cd(II). The results demonstrate that the kinetics of heavy metal removal can be well described by the pseudo-second-order model. The intraparticle diffusion model indicates that the controlling steps for Pb(II) and Cd(II) are not uniform. The adsorption isotherm for Cd(II) conforms to the Langmuir model, while for Pb(II), it adheres to the Freundlich model. The distribution coefficient (Kd) shows that Pb has a significantly higher competitive adsorption capacity than Cd(II). Therefore, in comparison to single adsorption, the maximum adsorption capacity of Cd(II) in competitive adsorption decreased by 58.86%, while Pb(II) only decreased by 13.54%. Surface complexation, cation exchange, chemical precipitation, electrostatic interaction, and cation-π bonding are the inherent mechanisms by which E-Mg/Al-LDH BC removes heavy metal ions. E-Mg/Al-LDH BC has the potential to remediate heavy metal-contaminated water, and it also provides insights for the application of modified biochar in the treatment of multi-metal water pollution.

Assessing the Environmental Impact of Heavy Metal Contamination in Water, Sediments, and Aquatic Vegetation of River Yamuna in Delhi

Assessing the Environmental Impact of Heavy Metal Contamination in Water, Sediments, and Aquatic Vegetation of River Yamuna in Delhi

Efficient remediation of heavy metal-contaminated water using a magnetically collectible nanoscale Cu/Fe/rGO primary battery

The removal of highly toxic heavy metal ions is essentially the migration of heavy metal ions from water to materials through adsorption, complexation, exchange, and other forms. However, heavy metals still exist as highly toxic ions on the surface of materials, easily desorbed, and cause secondary pollution. In this study, a novel primary battery of graphene-supported zero-valent copper/iron bimetallic composites (Cu/Fe/rGO) was first prepared with copper as the positive electrode, iron as the negative electrode, and graphene as the "wire". The network-like nanoscale primary battery was fabricated for the reduction and removal of typical highly toxic heavy metal ions (Pb2+) from the water environment. The removal rate of Pb2+ within 20 min was 95.28%. The Pb-immobilized Cu/Fe/rGO primary battery after treatment can be easily separated via a weak magnetic field and maintained an excellent removal rate of Pb2+ during 6 cycles of use. The great potential of Cu/Fe/rGO primary battery in Pb2+ reduction removal was due to its high reduction ability, large surface area, and magnetic separability. This study provides an important foundation for the rapid and stable removal of heavy metals from water, which may have a tremendous application prospect in environmental fields.

Tackling Heavy Metal Pollution: Evaluating Governance Models and Frameworks

Water pollution by heavy metals represents a significant threat to both the environment and public health, with a pronounced risk of stomach cancer and fatalities linked to the consumption of heavy metal-contaminated water. Consequently, the need for effective governance in heavy metal remediation is paramount. Employing a comprehensive review of the existing literature, this study delves into prevalent governance models, including state-centric governance, market governance, network governance, and voluntary governance. The primary objective of this research is to pinpoint the optimal framework for heavy metal remediation and the most efficient governance model. Through an analysis informed by the simplified Multi-Criteria Decision Analysis (MCDA) method, this study presents key findings, offering valuable insights for policymakers, environmental agencies, and industries seeking holistic strategies to combat heavy metal pollution and alleviate its detrimental consequences. These findings significantly contribute to the ongoing global efforts to safeguard the environment, enhance public health, and mitigate the adverse impacts of heavy metal contamination.

Mechanisms of Zn removal from water by amorphous geopolymer: Molecular-level insights from X-ray absorption spectroscopy, isotope fractionation, and surface complexation modeling

Porous geopolymers have attracted widespread attention as promising heavy metal adsorbents that can be synthesized from aluminosilicate solid wastes. However, the precise microstructural evidence for adsorbed heavy metals on geopolymers remains unclear due to the insensitivity of conventional characterization techniques on minerals with amorphous structure and surface disorder. Batch adsorption and column experiments coupled with X-ray absorption spectroscopy (XAS), Zn stable isotope, and surface complexation model (SCM) were employed to reveal the Zn removal mechanisms with coal fly ash porous geopolymer (CFAPG) at a molecular scale. The macroscopic kinetic and isothermal adsorption of Zn on CFAPG were well described by the pseudo-second-order model and Bi_Langmuir equation, respectively, indicating the presence of abundant heterogeneous active sites on the CFAPG surface. Two types of active sites on the CFAPG surface were identified by XAS coupled with Zn isotopes in batch experiments at pH ≤ 6.0: one is pH-dependent and associated with tetrahedral zinc coordination, and the other is pH-insensitive and associated with octahedral zinc coordination; these sites were confirmed by the bidentate SCM as the variable charge site (surface complexation, >S-OH) and the permanent negative charge site (cation exchange, >X–), respectively. Furthermore, the important contribution of surface co-precipitation besides surface complexation and cation exchange to the Zn adsorption on CFAPG was identified by XAS coupled with SCM in a flow-through column experiment at pH >6.0. These investigations provide a systemic understanding of the Zn adsorption mechanisms on CFAPG and an SCM reference for the application and prediction of geopolymers in heavy metal-contaminated water remediations.