Given that the mobility, bioavailability, and toxicity of arsenate in natural systems is often controlled by the strong binding capacity of iron oxyhydroxides, the objective of this study was to document the interactions of Dowex M4195 Fe3+-substituted chelating resins (a potential fieldbased tool for the quantification of potential arsenate bioavailability) and arsenic-bearing ferrihydrite (AFH) as a function of suspension pH, suspension concentration, and background electrolyte concentration. In 0.5 g AFH/L (0.001 M NaNO3) suspensions, arsenate sorption to the resins was proportional to the degree of acidification of the AFH suspensions by the resins. H+-enhanced dissolution of ferrihydrite artificially increased the arsenate in solution, causing a consistent overestimation of potential arsenate bioavailability. Resin-induced acidification was decreased with increasing suspension concentration. Arsenate sorption to the resins in 0.5 g/L suspensions at pH 8 decreased with increasing NaNO3 concentrations, reflecting the decreasing activity of arsenate under these conditions. The results of this study indicate that the high buffer capacity of natural soils would prevent acidification as a result of resin introduction. Thus, Dowex M4195 Fe3+-substituted chelating resins should provide a reasonable assessment of potential arsenate bioavailability from poorly-crystalline iron oxide minerals. Possibly more importantly, Dowex M4195 Fe3+-substituted chelating resins appear to be a new choice of passive equilibrium sampling device that should work well for the determination of bioavailable arsenate concentrations in the field.

Si la République Centrafricaine, ne manque pas d’eau, de nombreux forages sont abandonnés, en raison de teneurs en fer trop élevées. Parmi les techniques d’élimination des polluants métalliques utilisables en vue de rendre l’eau propre à la consommation humaine, l’adsorption par l’hydroxyde de fer déposé sur un support semble être une méthode bien adaptée, en raison de son faible coût d’utilisation et de la non génération d’autres polluants. En vue d’optimiser cette technique et de la rendre exploitable dans les pays en voie de développement, nous avons remplacé le support sable par un matériau naturel présent dans la plupart des pays, la brique, et nous avons choisi parmi les oxyhydroxydes de fer, la ferrihydrite qui possède l’aire spécifique la plus élevée. Deux méthodes d’activation du support constitué par des grains de brique ont été optimisées : HCl 1M durant 24h et HCl 6M 6h à 90°C. La composition de la brique et son état de surface ont été étudiés par les techniques FTIR, ESEM/EDS, RX, RMN du solide (27Al et 28Si), ATG /MS, ATG/ATD, mesure d’aire spécifique, ICP-AES. Des études cinétiques sur l’adsorption des ions ferreux ont été réalisées sur la ferrihydrite déposée sur la brique modifiée par les deux traitements chimiques. Le traitement des données cinétiques expérimentales nous a permis d’estimer l’énergie d’activation des systèmes étudiés et les paramètres thermodynamiques résultants. La gamme optimale du pH des eaux à traiter a été établie par la mesure du point de charge nulle (PZNPC). Une approche théorique des phénomènes mis en jeu a été abordée par des expériences sur colonne. La possibilité de régénérer l’adsorbant par l’utilisation d’eau de Javel, comme éluant, a été examinée, en vue de rendre le système opérationnel sur le terrain. / In developing countries, freshwaters contain frequently undesirable and naturally occurring inorganic, microbial contaminants. Thus, ground waters in Bangui regions (Central Africa Republic) _ that serve as sole source of drinking water in the rural communities of the country _ are known to contain elevated amounts of soluble iron (up to 10 mg/liter). This metal precipitates easily in the presence of air oxygen, this becoming undrinkable and even inappropriate to be used for washing / … the laundry. To eliminate this pollutant, there is evidence in the literature that ….with iron oxides / hydroxides can be used as an adsorbent for cations / anions removal from waters. In the present work, we are poured our attention on the use of a new low-cost material, brick _ that is commonly made by local craftsmen in Central African Republic_ which is mainly composed of sand and metakaolinite. To enhance the efficiency of water purification process with the brick, this adsorbent had however to be improved in its chemical nature, crystalline surface properties and preparation methods thermal and acid treatments by using several techniques: FTIR, ESEM/EDS, RX, Solid- RMN (27Al et 28Si), ATG /MS, ATG/ATD, Specific surface, ICP-AES. In this thesis, we have poured our attention on the determination of the chemical composition and crystalline / morphological characteristics of the raw brick and its various modified forms obtained by acid activation. Some kinetic aspects of Fe (II) adsorption onto FeOOH coated brick were further … in this work and activated energy and thermodynamic parameters were evaluated and discussed. Finally, the adsorption of iron (II) onto brick pellets from aqueous solutions was investigate by using a …glass column and performances when filling of the various composites prepared in this work were compared each other : Thomas model was applied to our experimental data to assess the characteristic parameters of the column. Furthermore the possibility to regenerate the adsorbent by the use of bleach as an elute and to use it directly in the field was raised.

Although the impacts of foreign species on aqueous transformations and arsenic adsorption by 2-line ferrihydrite (FH2) have been extensively studied, much less is known about the impact of transformation inhibitors on solid-state transformation of FH2 and arsenic adsorption. In this study, the influence of inhibitors (Si(IV), Mg(II), Al(III), Ti(IV), and Ci(citrate)), aging time, and heat treatment on FH2 transformation and arsenic adsorption was investigated. The FH2s were synthesized by mixing Fe(III) salts with an inhibitor at pH 7.5 and air drying for 2 d. With increases in Al/Fe molar ratio, FH2, poorly crystalline Al hydroxide, gibbsite, and bayerite were formed in the FH2-Al series, whereas FH2 was formed in the other FH2s. Heat treatment had a more considerable impact on the transformation, structure, and PZC of FH2 than aging at RT for 235 d. Upon heating the FH2s at 360 oC, most of the amorphous Fe oxide was transformed into hematite, whereas Si and Al had stronger retarding effects on transformation than the other inhibitors. Hematite and FH2 were identified with increases in Si/Fe molar ratio, whereas with increasing Al/Fe molar ratio, FH2 remained, gibbsite and bayerite were decomposed, and boehmite appeared as a trace component. However, the effect of Si was much more pronounced than that of Al in retarding the transformation. The adsorption density for As(III) on the FH2s (at pH 7) decreased in the order: FH2-Mg-2 > FH2 > FH2-Al-1, whereas As(V) followed the order: FH2-Al-1 > FH2-Mg-2 > FH2. Compared to aging at RT for 235 d, heat treatment at 360 oC resulted in significantly reduced arsenic adsorption. The heated FH2 showed a smaller adsorption capacity for arsenic compare to that of the other FH2s. In contrast, the heated FH2-Al and FH2-Si series showed much higher adsorption capacities for As(V) than any other FH2, whereas the heated FH2-Mg series exhibited the largest adsorption capacity of As(III) among the heated FH2s. It is concluded that the use of the FH2-Al, FH2-Mg, or FH2-Si series instead of pure FH2 as filter media in water treatment might achieve more efficient arsenic removal and enhance arsenic retention at waste-disposal sites.

Although the impacts of foreign species on aqueous transformations and arsenic adsorption by 2-line ferrihydrite (FH2) have been extensively studied, much less is known about the impact of transformation inhibitors on solid-state transformation of FH2 and arsenic adsorption. In this study, the influence of inhibitors (Si(IV), Mg(II), Al(III), Ti(IV), and Ci(citrate)), aging time, and heat treatment on FH2 transformation and arsenic adsorption was investigated. The FH2s were synthesized by mixing Fe(III) salts with an inhibitor at pH 7.5 and air drying for 2 d. With increases in Al/Fe molar ratio, FH2, poorly crystalline Al hydroxide, gibbsite, and bayerite were formed in the FH2-Al series, whereas FH2 was formed in the other FH2s. Heat treatment had a more considerable impact on the transformation, structure, and PZC of FH2 than aging at RT for 235 d. Upon heating the FH2s at 360 oC, most of the amorphous Fe oxide was transformed into hematite, whereas Si and Al had stronger retarding effects on transformation than the other inhibitors. Hematite and FH2 were identified with increases in Si/Fe molar ratio, whereas with increasing Al/Fe molar ratio, FH2 remained, gibbsite and bayerite were decomposed, and boehmite appeared as a trace component. However, the effect of Si was much more pronounced than that of Al in retarding the transformation. The adsorption density for As(III) on the FH2s (at pH 7) decreased in the order: FH2-Mg-2 > FH2 > FH2-Al-1, whereas As(V) followed the order: FH2-Al-1 > FH2-Mg-2 > FH2. Compared to aging at RT for 235 d, heat treatment at 360 oC resulted in significantly reduced arsenic adsorption. The heated FH2 showed a smaller adsorption capacity for arsenic compare to that of the other FH2s. In contrast, the heated FH2-Al and FH2-Si series showed much higher adsorption capacities for As(V) than any other FH2, whereas the heated FH2-Mg series exhibited the largest adsorption capacity of As(III) among the heated FH2s. It is concluded that the use of the FH2-Al, FH2-Mg, or FH2-Si series instead of pure FH2 as filter media in water treatment might achieve more efficient arsenic removal and enhance arsenic retention at waste-disposal sites.

Arsenic in drinking water is a problem in many developing nations such as Taiwan and Bangladesh. Currently, no oral binding agent exists for the mitigation of arsenic toxicity. The goals of this research were to 1) screen a variety of sorbents for their ability to sorb As from water and screen for potential nutrient interactions with vitamin A (VA) and riboflavin (RF) isotherms; 2) further describe the sorption of As to ferrihydrite using isothermal analysis and a simulated gastrointestinal model (GI), and by testing ferrihydrite’s ability to protect Hydra from As toxicity; 3) verify ferrihydrite’s safety and efficacy in a short term rodent model. Ferrihydrite was found to be the most effective sorbent for both As(III) and As(V). Exchanging SWy-2 with sulfur containing organic groups increased the sorption of both As(V) and As(III) compared to the parent clay, though the total As sorbed was much less than As sorption by ferrihydrite. Ferrihydrite and an industrially produced ferrihydrite (IPF) both sorbed As(V) and As(III) with high capacity. Both ferrihydrites also sorbed As(V) and As(III) at high capacity in the simulated GI model. Fe measured in the simulated GI tract was below tolerable daily limits for both ferrihydrite and IPF. Ferrihydrite at 0.25 percent w/w was found to protect Hydra up to 200 times the minimal effective concentration (MEC) for As(III) and over 2.5 times the MEC for As(V), while IPF at 0.25 percent w/w protected Hydra up to 200 times the MEC for As(III) and just over 2 times the MEC for As(V). IPF was apparently safe and well tolerated by the rats in our study over a period of 2 weeks. No statistically significant differences were seen in serum biochemistry, serum Fe, serum VA, or serum vitamin E between rats fed control diet versus those fed 0.5 percent w/w IPF. Ferrihydrite was found to reduce urinary As after a single gavage of 0.5 mL of 500 ppm As(III) or As(V). These results verify in vitro findings and suggest that ferrihydrite is apparently safe and effective as an enterosorbent for As.

Ces travaux s’inscrivent dans le cadre du contrat d’objectifs AQUAL dont le but est la lutte contre les pollutions diffuses en milieu rural. Ils portent sur la compréhension des mécanismes de rétention du cuivre dans les sols viticoles. Afin de s’affranchir de la complexité des sols, sept constituants ont été sélectionnés (quartz,calcite, kaolinite, matière organique, goethite, ferrihydrite et birnessite). Le comportement du cuivre a été étudié sur les constituants seuls puis dans des mélanges de complexité croissante, afin d’évaluer l’implication de chacun d’entre eux, en fonction du pH et de la concentration en cuivre. L’influence du vieillissement et de la concentration sur la répartition géochimique du cuivre a ensuite été évaluée dans des sols synthétiques et naturels contaminés. L’ensemble des résultats a été obtenu grâce à la combinaison de plusieurs techniques permettant d’obtenir des informations complémentaires aux échelles macroscopique, microscopique (STEM-EDX et μ-XRF) et moléculaire (XANES).Les résultats montrent d’une part, que les principaux constituants responsables de la rétention du cuivre sont la matière organique et les oxydes de fer et de manganèse et d’autre part, que l’existence d’interactions organo-minérales influe significativement sur la rétention du cuivre. Lacombinaison d’expériences de sorption et d’extractions séquentielles a permis de mettre en évidence que les processus de rétention du cuivre se produisant dans le sol naturel peuvent être mimés dans un sol synthétique, ce dernier pouvant ainsi être utilisé comme modèle. / This work is a part of the AQUAL research program which aims to strive against diffuse pollution in rural environment. It deals with the understanding of copper retention mechanisms in vineyard soils.To overcome the soil complexity, seven constituents were selected (quartz, calcite, kaolinite,organic matter, goethite, ferrihydrite and birnessite). The copper behavior was firstly studied on the single constituents, then on increasing complexity constituents mixtures in order to assess their implication as a function of pH and copper concentration. The influence of aging time and copper concentration was evaluated on the copper geochemical partitioning in synthetic and natural soils.Conclusion could be drawn by combination of several techniques providing complementary information at macroscopic, microscopic (STEM-EDX, μ-XRF) and molecular (XANES) scales.The results showed on the one hand, that organic matter and iron and manganese oxides are the main constituents involved in copper retention and on the other hand, that the presence of organo-mineral interactions also significantly influences the copper retention. Sorption experiments combined with sequential extractions emphasized that copper retention processes occurring in a natural soil can be mimicked in a synthetic soil which could then be used as a model.

Dans les sédiments de rivière à l’aval des drainages miniers acides (DMA), l’arsenic est souvent présent sous les formes As(III) et As(V) associées à des minéraux de type (oxy)hydroxydes de fer et d’aluminium. La structure et la réactivité de ces minéraux qui piègent l’arsenic dans les particules en suspension et dans les sédiments de fond n’ont pour l’instant été que très peu étudiés sur le terrain. Pourtant ces pièges représentent probablement un des facteurs majeurs de contrôle de ce type de contamination dans les eaux à pH proche de la neutralité, impactées par les DMA. Au cours de ce travail de thèse, nous avons étudié la cristallochimie d’une série d’échantillons de ferrihydrites (Fh) riches en aluminium prélevées dans les sédiments de la rivière Amous (Gard, France – pH 6-7), laquelle est affectée par le DMA du site de Carnoulès, contaminé par l’arsenic. Ces Fh ont été caractérisées et comparées à une série de Fh alumineuses synthétiques analogues, qui présentent différents rapports molaires Al/Fe. Des expériences d’adsorption de As(III) et As(V) ont été réalisées sur ces Fh alumineuses et non-alumineuses à pH 6, afin d’évaluer l’influence de l’aluminium sur le piégeage de l’arsenic. Cette étude a combiné l’analyses chimique des solutions avec la caractérisation des solides par Diffraction des Rayons X (DRX), la Microscopie Electronique en Transmission (MET) et la Spectroscopie d’Absorption des Rayons X (XAS). Nous constatons que la ferrihydrite est la phase majoritaire qui se forme au cours de la neutralisation des DMA, et que jusqu'à 25-30 ± 10 mol% Al est substitué à Fe dans la structure de ces Fh. Les Fh alumineuses synthétisées sont moins substituées en aluminium (14 à 20 ± 5 mol% Al). Les résultats obtenus montrent que l’efficacité du piégeage de l’arsenic dépend fortement de la présence d’aluminium dans la ferrihydrite et de l’état d’oxydation de l’arsenic. En effet, à pH 6, l’adsorption de As(III) diminue fortement avec le rapport Al/Fe, tandis que l’adsorption de As(V) augmente avec le rapport Al/Fe. La spectroscopie EXAFS suggère que, à pH6, As(III) forme des complexes de surface bidentate similaires sur les Fh alumineuses ou non-alumineuses, sans évidence de complexation sur les sites aluminols de la surface. En revanche, l’adsorption de As(V), connue par ailleurs pour impliquer des liaisons hydrogène avec la surface de la Fh, apparaît être moins affectée, voire favorisée par la présence d’aluminium. Les données EXAFS montre cependant qu’une fraction de As(V) forme des complexes d’adsorption bidentate sur la Fh alumineuse et sur les Fh non-alumineuses naturelles et synthétiques. Ces résultats constituent une preuve directe du piégeage de l’arsenic par les Fh alumineuses, ce qui souligne l’importance possible du rôle de ces phases minérales dans le piégeage de polluants dans les systèmes naturels ou anthropisés et que la présence d’aluminium peut fortement modifier la réactivité de surface de ce nanomatériau naturel. / In the river system downstream of acid mine drainage (AMD) where the pH of water declined to near neutral, arsenic is usually present as As (III) and As (V) associated to iron and aluminum oxyhydroxydes. Structure and reactivity of these arsenic scavangers have so far been little investigated in the field. However, these traps are probably one of the major factors controlling this type of contamination in water at pH close to neutral, impacted by the DMA.In this thesis, a series of aluminum-rich ferrihydrite (Fh), was removed from the sediments of the river Amous (Gard, France- pH 6-7), which is affected by the AMD Carnoulès contaminated with arsenic. These Fh samples were characterized and compared with a series of Al-bearing Fh, which have different molar ratio of Al/Fe. As(III) and As(V) adsorption experiments were carried out on Al-free ferrihydrite and Al-bearing ferrihydrite at pH 6 to evaluate the influence of aluminum on the arsenic scavenging. This study combined water chemistry analysis with characterization of solide : X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Absorption Spectroscopy of X-rays (XAS).We note that Fh is the predominant phase forming during the neutralization of the AMD, and that up to 25–30 ± 10 mol% Al substitutes for Fe in the structure of Fh naturelle. Synthetic aluminous Fh are found to be less Al-substituted (14–20 ± 5 mol %Al) regardless of the molar ratio Al/Fe we used. The results obtained show that the trapping efficiency of arsenic strongly depends on the presence of aluminum in the ferrihydrite and the oxidation state of the arsenic. Indeed, at pH 6, the adsorption of As (III) greatly decreases with the Al / Fe ratio, whereas the adsorption of As (V) slightly increases with the Al / Fe ratio. The EXAFS analysis suggest that, at pH 6, As(III) forms similar surface complexes (type bidentate) on both Al-free and Al-bearing Fh without evidence of complexation on aluminols sites of the surface. However, the adsorption of As (V), is known to involve hydrogen bonds with the surface of the Fh, appears to be less affected by the presence of aluminum. EXAFS spectroscopy shows however a fraction of As (V) forms adsorption complexes of bidentate on the surface of Al-free and Al-bearing Fh natural and synthetic.These results provide direct evidence of arsenic sequestration by aluminous Fh, underscoring the potential importance of the role of these mineral phases in the trapping of pollutants in natural and engineered systems, and the presence of aluminum can greatly modify the surface reactivity of this natural nanomaterial.

At Cameco mine sites in northern Saskatchewan, naturally occurring elements of concern (EOC) such as As, Ni, Mo, and Se are present in uranium ore bodies. Ferrihydrite (Fh) is found in tailings management facilities (TMF) and is known to sequester arsenates and arsenites. Fh is known to be metastable and undergo phase transformations to goethite (α-FeOOH) and hematite (α-Fe2O3). Reductive conditions are known to be a driving force in Fh transformation and the release of adsorbed As species from the surface. This study uses electrochemistry to control reductive potentials applied to Fh adsorbed As species. Electrochemistry was coupled with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to determine the behaviour of adsorbed arsenate and arsenite on the Fh surface. The potentials required to desorb As(III) and As(V) from the Fh surface were negative enough to cause the reduction of water, thus increasing the pH of the solution through the generation of OH-. In order to measure the extent of the pH change a miniature palladium/palladium oxide pH sensor was fabricated in order to make in-situ pH measurements during spectroelectrochemical studies. Additionally, in-situ solution potential (Eh) measurements were made during potential control. It was found that potential induced pH and Eh changes were significant enough to release arsenite from the Fh surface. Arsenate was also found to desorb from Fh during the application of reductive potentials though successive deprotonation leading to a totally deprotonated As(V) species.

Ferrihydrite in a suspension has been studied as a solution for purification of arsenic contaminated water. Many development countries, amongst them Burkina Faso, have arsenic in their groundwater and the current methods for purification are too expensive. Measurements have shown extremely high levels of arsenic in the groundwater in several places in Burkina Faso. Since the availability of surface water is limited, the groundwater is still used as drinking water.   A suspension of ferrihydrite has capacity to adsorb arsenic in water due to its chemical characteristics. Small-scale laboratory work with ferrihydrite suspensions has been performed in parallel in Uppsala, Sweden, and Ouagadougou, Burkina Faso. To purify the water with regard to the economical and practical circumstances in Burkina Faso, a column with safety filter was made out of simple materials such as plastic bottles, plastic tubes and glass wool. The contaminated water was flowing upwards through the column to prevent the filter from clogging.   In Uppsala it was discovered that a 1 L ferrihydrite suspension containing 10 g ferrihydrite can adsorb 0.7 g arsenic while it was shaken and centrifuged well. In Ouagadougou it was possible, in the setup, to clean 2 L arsenic contaminated water with the concentration of 100 µg/L. The conclusions from the experiments in this project are that ferrihydrite can adsorb arsenic in contaminated water but that the setup used needs to be further evaluated and developed

A novel phosphorus (P) adsorbent, ferrihydrite-modified diatomite (FHMD) was developed and characterized in this study. The FHMD was made through surface modification treatments, including NaOH treatment and ferrihydrite deposition on raw diatomite. In the NaOH treatment, surface SiO2 was partially dissolved in the NaOH solution. The dissolved Si contributed to form stable 2-line ferrihydrite, which deposited into the larger mesopores and macropores of the diatomite. The 2-line ferrihydrite not only deposited into the pores of the diatomite but also aggregated on the surface. Filling the larger mesopores and macropores of the diatomite and aggregation on the diatomite surface with 0.24 g Fe/g of 2-line ferrihydrite resulted in a specific surface area of 211.1 m2/g for the FHMD, which is an 8.5-fold increase over the raw diatomite (24.77 m2/g). The surface modification also increased the point of zero charge (pHPZC) values to 10 for the FHMD from 5.8 for the raw diatomite.<p> Effects of the formation process parameters such as concentrations of FeCl2, NaOH, and drying temperature on the formation mechanism and crystalline characteristics of FHMD were studied by using X-ray absorption near-edge structure (XANES) spectroscopy. The spectra were recorded in both the total electron yield (TEY) and the fluorescence yield (FY) modes to investigate the chemical nature of Fe and Si on the surface and in the bulk of ferrihydrite-modified diatomite, respectively. It was found that only the surface SiO2 was partially dissolved in the NaOH solution with stirring and heating, whereas the bulk of diatomite seemed to be preserved. The dissolved Si was incorporated into the structure of ferrihydrite to form the 2-line Si-containing ferrihydrite. The crystalline degree of ferrihydrite increased with the increasing FeCl2 concentration and the Brunauer-Emmett-Teller (BET) specific surface area of FHMD decreased with the increasing FeCl2 concentration. The NaOH solution of higher concentration partially dissolved more surface SiO2 and the crystalline degree of ferrihydrite decreased with the increase in NaOH concentration. The dehydroxylation on the surface of FHMD occurred in the high temperature calcination, causing an energy shift in the Si L-edge spectra to the high energy side and an increase in the crystalline degree of ferrihydrite. In this study, the optimal synthesis conditions for the FHMD with the least crystalline degree and the highest surface area were found to be as the follows: 100 mL of 0.5M FeCl2 solution, 6M NaOH solution and the drying temperature of 50 ºC.<p> Phosphorus adsorption behavior and adsorption mechanism of FHMD were investigated in the research. The Langmuir model best described the P adsorption data for FHMD. Because of increased surface area and surface charge, the maximum adsorption capacity of FHMD at pH 4 and pH 8.5 was increased from 10.2 mg P/g and 1.7 mg P/g of raw diatomite to 37.3 mg P/g and 13.6 mg P/g, respectively. Phosphorus showed the best affinity of adsorption onto FHMD among common anions. K-edge P XANES spectra demonstrate that P is not precipitated with Fe (III) of FHMD, but adsorbed on the surface layer of FHMD.<p> Phosphorus removal from lake water and limiting phosphorus release from sediment by FHMD was examined. Phosphorus removal from lake water proceeded primarily through P adsorption onto the surface of FHMD. When a dose of FHMD of 250 mg/L was applied to lake water, a total phosphorus (TP) removal efficiency of 88% was achieved and a residual TP concentration was 17.0 µg/L which falls within the oligotrophic TP range (3.0-17.7 µg/L). FHMD settled down to the bottom of the 43 cm high cylinder within 6 hours, which suggested that retention time of FHMD in the 5.5 m of Jackfish lake water column was close to the equilibrium time of P adsorption onto FHMD (72 hours). During the 30-day anoxic incubation period, TP concentrations in lake water treated by 400, 500 and 600 mg/L of FHMD showed a slight decrease and maximum TP concentrations remained at levels lower than 15 µg/L. The addition of FHMD resulted in a marked increase in Fe-P fraction, a pronounced decrease in labile-P and organic-P fractions, and stable Al-P, Ca-P and residual-P fractions. The effect of FHMD on limiting P release was comparable with those of the combination of FHMD and alum solutions with logarithmic ratios of Al to mobile P of 0.5 and 0.8. FHMD not only can effectively remove P from lake water but also keep a strong P-binding capacity under anoxic conditions and competition for P with alum at high amounts.<p> The role of gypsum on stabilizing sediment and the optimum dose of gypsum were investigated. The effectiveness of gypsum in stabilizing sediment was proved by the fact that at the same agitation speed, turbidities and soluble reactive P (SRP) concentrations of samples treated with gypsum were much lower than those of sample without gypsum. The optimal thickness of the gypsum layer was found to be 0.8 cm.<p> Combined application of FHMD and gypsum to P control was investigated in the research. It was found in the 30-day incubation of lake water and sediment treated by FHMD and gypsum that no P release seemed to occur regardless of oxic or anoxic conditions. In order to investigate the 120-day effects of FHMD and gypsum on the P control under anoxic and agitation conditions a lab-scale artificial aquarium was established in an environmental chamber. Daily oscillation of a metal grid did not yield the sediment resuspension due to the gypsum stabilization. The combined application of FHMD and gypsum resulted in a 1 g/L increase in the SO42- concentration in the 120-day aquarium compared with that in the control aquarium; however it did not affect the total kjeldahl nitrogen (TKN) concentrations in both the control aquarium and the 120-day aquarium. The addition of FHMD and gypsum enhanced total alkalinity in the 120-day aquarium, thereby improving buffering capacity of lake water. Under anoxic conditions and sediment resuspension conditions, relative to a large increase in total P (TP) concentrations in the control aquarium, TP concentrations in the 120-day aquarium stayed relatively stable, fluctuating within the range of 9.1-13.3 µg/L. Relative to control sediment, Fe-P was significantly enhanced during the 60-day incubation; however, Fe-P did not appear to increase significantly in the second 60-day incubation. Labile-P and organic-P decreased with sediment depths in both control aquarium and test aquariums; however, Al-P, Ca-P and residue-P increased with sediment depth. Lower Al-P is observed in treatment aquariums than in control sediment.<p> As an effective P adsorbent, FHMD showed a high adsorption capacity as well as a significantly higher affinity for P than other anions. A combined application of FHMD and gypsum effectively reduced sediment resuspension and maintained TP levels within the oligotrophic range under anoxic conditions in the laboratory-scale artificial aquarium.