Process for biological oxidation and control of dissolved iron in bioleach liquors

Iron has a central role in bioleaching and biooxidation processes. Fe²⁺ produced in the dissolution of sulfidic minerals is re-oxidized to Fe³⁺ mostly by biological action in acid bioleaching processes. To control the concentration of iron in solution, it is important to precipitate the excess as part of the process circuit. In this study, a bioprocess was developed based on a fluidized-bed reactor (FBR) for Fe²⁺ oxidation coupled with a gravity settler for precipitative removal of ferric iron. Biological iron oxidation and partial removal of iron by precipitation from a barren heap leaching solution was optimized in relation to the performance and retention time (τ_FBR) of the FBR. The biofilm in the FBR was dominated by Leptospirillum ferriphilum and “Ferromicrobium acidiphilum.” The FBR was operated at pH 2.0 ± 0.2 and at 37 °C. The feed was a barren leach solution following metal recovery, with all iron in the ferrous form. 98–99% of the Fe²⁺ in the barren heap leaching solution was oxidized in the FBR at loading rates below 10 g Fe²⁺/L h (τ_FBR of 1 h). The optimal performance with the oxidation rate of 8.2 g Fe²⁺/L h was achieved at τ_FBR of 1 h. Below the τ_FBR of 1 h the oxygen mass transfer from air to liquid limited the iron oxidation rate. The precipitation of ferric iron ranged from 5% to 40%. The concurrent Fe²⁺ oxidation and partial precipitative iron removal was maximized at τ_FBR of 1.5 h, with Fe²⁺ oxidation rate of 5.1 g Fe²⁺/L h and Fe³⁺ precipitation rate of 25 mg Fe³⁺/L h, which corresponded to 37% iron removal. The precipitates had good settling properties as indicated by the sludge volume indices of 3–15 mL/g but this step needs additional characterization of the properties of the solids and optimization to maximize the precipitation and to manage sludge disposal.     

Ferrous iron oxidation and uranium extraction by Thiobacillus ferrooxidans

The microbiological oxidation of ferrous iron in batch and continuous systems has been investigated in relation to uranium extraction from a low-grade ore by Thiobacillus ferrooxidans. The influence of the parameters, agitation, and aeration on oxygen saturation concentration, rate of oxygen mass transfer, and rate of ferrous iron oxidation was demonstrated. The kinetic values, V_max and K were determined using an adapted Monod equation for different dilution rates and initial concentrations of ferrous iron. The power requirements for initial leaching conditions were also calculated. Uranium extraction as high as 68% has been realized during nine days of treatment. Regrinding the leach residue and its subsequent leaching yielded 87% uranium solubilization.     

Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1–1.3

The extreme acid conditions required for scorodite (FeAsO₄·2H₂O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO₂ in air were added as sole energy and carbon source. The highest growth rate (0.066 h⁻¹) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO₂ concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the maximum specific growth rate of the mixed culture was 0.022 h⁻¹, with ferrous iron oxidation rates of 1.5 g L⁻¹ d⁻¹. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent ferrous iron concentrations above 6 g L⁻¹ caused instability of Fe²⁺ oxidation, probably due to product (Fe³⁺) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible at the extreme conditions required for continuous biomineral formation.     

The effect of pH on the kinetics of iron release from human transferrin

The rate of iron release from the N-terminal and C-terminal monoferrictransferrins (Fe_N-transferrin and Fe_C-transferrin, respectively) has been studied at 37°C over the pH range 3.5–10.6 using EDTA as the accepting chelate. Fe_N-transferrin is the more facile except above pH 8.2. Plots of log₁₀k_obs against pH showed a deviation for both monoferrictransferrins between pH 5.6 and 6.0 and studies above and below this transition point indicated that iron release occures by different mechanisms. At low pH (< 5.6) the rate of release from Fe_N-transferrin is independent of the presence of EDTA or NaClO₄, whereas Fe_c-transferrin shows a small but significant increase with increasing EDTA concentration. Rapid protonation of both monoferrictransferrins is followed by relatively slow release of Fe³⁺ which is subsequently chelated by EDTA. The slower release from Fe_c-transferrin is probably due to its greater binding strength for iron and the greater conformational stability of the C-terminal domain. Above pH 6.0 iron release from both monoferrictransferrins increases as the concentration of EDTA is increased. Direct attacks of EDTA probably occurs giving Fe-transferrin (HCO₃). EDTA as a transition state or intermediate. The factors which may lead to the observed pH dependence of the rate include (i) protonation of groups directly bound to the iron, (ii) conformers which differ in degree of protonation and (iii) the degree of protonation of the attacking chelating agent. It is suggested that an increase in conformational fluctuations as the pH is lowered may play a very important role. Studies with differrictransferrin at pH 4.53 and 7.40 showed that when iron is released to EDTA the rate is independent of the occupancy of the other site; that is, the two sites are exhibiting non-co-operativity.     

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrate at 45–47°C and pH 1.8–2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the microorganisms from the experimental and aboriginal communities during the oxidation of sulfide ore flotation concentrate at 47°C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus (the most active sulfur oxidize) and Sulfobacillus thermotolerans (active oxidizer of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrate at high pulp density (S : L = 1 : 4).     

Arsenic Release from a Natural Rock under Near‐natural Oxidizing Conditions

The effects of carbonate concentration and the presence of iron hydroxide phases on the process of arsenic release from an ore material were investigated under experimental oxic conditions and in the pH range from 6.0 to 9.0. These experimental conditions are pertinent to arsenic leaching from tailings and mining wastes. The leaching tests lasted for ≤ 99 days and were performed with materials of five different particle sizes (≤ 2 mm). Carbonate ions were produced in‐situ by dolomite dissolution or were contained in used waters (0 to 30 mM as HCO₃^–). Iron hydroxide phases were formed in situ by oxidative dissolution of metallic iron (Fe⁰) or pyrite (FeS₂). Non‐disturbed batch experiments and air‐homogenized experiments were conducted with a constant amount (10 g/L) of an arsenic‐bearing rock (ore material) of a given particle size and different types of water (deionized, tap and mineral water). For comparison, experiments were conducted with 0.1 M EDTA, 0.1 M Na₂CO₃, and 0.1 M H₂SO₄. Neither the use of dolomite nor the use of water containing various carbonate (HCO₃^–) concentrations could confirm the recent results on the favorable role of As^III‐carbonate complexes on the arsenic transport in the environment. On the other hand, iron hydroxide phases (from Fe⁰ and FeS₂) univocally delayed the As release in both experimental procedures. Furthermore, the theoretically expected effects of the particle size of the ore material was observed. If one takes into consideration that the used HCO₃^– concentrations were up to six times larger then those of natural surface waters (≤ 5.5 mM) but up to five times lower than those currently used in the literature (≥ 100 mM), it is concluded that the reported conflicting results for As leaching from sediments may be a misinterpretation of processes occurring in the sediment and yielding increased As release with increasing HCO₃^–/CO₃^2– concentration.     

Alterations in surfaces and textures of minerals during the bacterial leaching of a complex sulfide ore

Abstract

The purpose of the work was to characterize changes in surface textures of minerals during the biological leaching of a complex sulfide ore. The ore contained pyrrhotite (Fe_I__xS), pyrite (FeS₂), sphalerite (ZnS), pentlandite [(Ni,Fe,Co)₉S₈], and chalcopyrite (CuFeS₂). Several mixed cultures were initially screened using the ore material as the sole substrate. Shake flask leaching experiments showed no major differences among test cultures, which were all derived by enrichment techniques using environmental samples collected from a mine site. Leached pyrrhotite surfaces were invariably surrounded by a dark rim of elemental S. A reaction zone was also associated with leached sphalerite grains. Chemical analyses of leach solutions indicated that the relative ranking of biological leaching of the sulfide minerals was Zn > Ni > Co > Cu. Microscopic observations were in keeping with this rankin     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Magnetite formation from ferrihydrite by hyperthermophilic archaea from Endeavour Segment,Juan de Fuca Ridge hydrothermal vent chimneys

Hyperthermophilic iron reducers are common in hydrothermal chimneys found along the Endeavour Segment in the northeastern Pacific Ocean based on culture‐dependent estimates. However, information on the availability of Fe(III) (oxyhydr) oxides within these chimneys, the types of Fe(III) (oxyhydr) oxides utilized by the organisms, rates and environmental constraints of hyperthermophilic iron reduction, and mineral end products is needed to determine their biogeochemical significance and are addressed in this study. Thin‐section petrography on the interior of a hydrothermal chimney from the Dante edifice at Endeavour showed a thin coat of Fe(III) (oxyhydr) oxide associated with amorphous silica on the exposed outer surfaces of pyrrhotite, sphalerite, and chalcopyrite in pore spaces, along with anhydrite precipitation in the pores that is indicative of seawater ingress. The iron sulfide minerals were likely oxidized to Fe(III) (oxyhydr) oxide with increasing pH and E_h due to cooling and seawater exposure, providing reactants for bioreduction. Culture‐dependent estimates of hyperthermophilic iron reducer abundances in this sample were 1740 and 10 cells per gram (dry weight) of material from the outer surface and the marcasite‐sphalerite‐rich interior, respectively. Two hyperthermophilic iron reducers, Hyperthermus sp. Ro04 and Pyrodictium sp. Su06, were isolated from other active hydrothermal chimneys on the Endeavour Segment. Strain Ro04 is a neutrophilic (pH_opt 7–8) heterotroph, while strain Su06 is a mildly acidophilic (pH_opt 5), hydrogenotrophic autotroph, both with optimal growth temperatures of 90–92 °C. Mössbauer spectroscopy of the iron oxides before and after growth demonstrated that both organisms form nanophase (<12 nm) magnetite [Fe₃O₄] from laboratory‐synthesized ferrihydrite [Fe₁₀O₁₄(OH)₂] with no detectable mineral intermediates. They produced up to 40 mm Fe²⁺ in a growth‐dependent manner, while all abiotic and biotic controls produced <3 mm Fe²⁺. Hyperthermophilic iron reducers may have a growth advantage over other hyperthermophiles in hydrothermal systems that are mildly acidic where mineral weathering at increased temperatures occurs.     

纳米铁氧化物对Pelotomaculum schinkii培养系丙酸厌氧降解产甲烷的影响

微生物能利用导电材料进行电子传递,提高种间电子传递效率。铁基纳米导电物质可以加速土壤及厌氧消化系统中微生物间的种间电子传递,促进有机废弃物的产甲烷过程。前期获得了厌氧丙酸富集培养系,互营丙酸氧化菌（Pelotomaculum schinkii）在培养系中占优势,本研究考察了10~4 000 mg/L 纳米铁氧化物对丙酸降解产甲烷过程的作用及微生物的影响。结果表明,低浓度的铁基纳米材料对丙酸降解有一定的促进作用,而高浓度会抑制产甲烷：10~1 000 mg/L纳米Fe₃O₄对产甲烷无明显影响,1 500~4 000 mg/L最大产甲烷速率抑制了26%~80%,延滞期增加了174%~222%;10~200 mg/L纳米Fe₂O₃使最大产甲烷速率提高了21%~29%,1 500~4 000 mg/L最大产甲烷速率抑制了48%~58%,延滞期增加了29%~85%。微生物群落解析结果表明,与对照相比,10~1 000 mg/L纳米Fe₂O₃使P. schinkii相对丰度略有增加,而4 000 mg/L纳米₃O₄/Fe₂O₃使P. schinkii的相对丰度下降了70.7%和55.9%,说明高浓度纳米铁氧化物会抑制P. schinkii的活性,导致丙酸降解及产甲烷速率降低。     

Direct zinc sulphide bioleaching by Thiobacillus ferrooxidans and Thiobacillus thiooxidans

Summary Direct bioleaching (no iron(II) present) by Thiobacillus ferrooxidans mainly occurs on the surface of the very insoluble sulphides but is more important in solution when the sulphides are more soluble. In this case, Thiobacillus thiooxidans, normally not able to leach directly insoluble sulphides, has an effective leaching action.     

Effect of Water Potential on Growth and Iron Oxidation by Thiobacillus ferrooxidans

The effect of water potential on the growth of two strains of Thiobacillus ferroxidans was determined by adding defined amounts of sodium chloride or glycerol to the culture medium. The two strains differed slightly, and the most tolerant strain had a minimum water potential for growth of -15 to -32 bars when sodium chloride was used and -6 bars when glycerol was used. In another approach, the limiting water potential was determined by equilibrating small amounts of culture medium with atmospheres of relative humidities equivalent to specific water potentials, and the ability of the organism to grow and oxidize ferrous iron was determined. Under these conditions, which are analogous to those which might control water potential in a coal refuse pile or copper leaching dump, the lower limit at which iron oxidation occurred was -23 bars. The water potential of some coal refuse materials in which T. ferrooxidans was present were determined, and it was found that the water potentials at which the organism was active in these habitats were similar to those at which it was able to grow in culture. However, marked variation in water potential of coal refuse materials was found, presumably due to differences in clays and organic materials, and some coal refuse materials would probably never have water potentials at which the organism could grow. Some literature on the water potentials in copper leach dumps is reviewed, and it is concluded that control of water potential is essential to maximize the success of leaching operations. Because adequate drainage is necessary in a leach dump to ensure sufficient aeration, in many cases water availability in leach dumps may restrict the development of the bacterium necessary for the process.     

Structure of iron saturated C‐lobe of bovine lactoferrin at pH 6.8 indicates a weakening of iron coordination

The bilobal lactoferrin is an approximately 76 kDa glycoprotein. It sequesters two Fe³⁺ ions together with two ions. The C‐terminal half (residues, Tyr342–Arg689, C‐lobe) of bovine lactoferrin (BLF) (residues Ala1–Arg689) was prepared by limited proteolysis using trypsin. Both C‐lobe and intact BLF were saturated to 100%. Both of them retained up to nearly 85% of iron at pH 6.5. At pH 5.0, C‐lobe retained 75% of iron whereas intact protein could retain only slightly more than 60%. At pH 4.0 both contained 25% iron and at pH 2.0 they were left with iron concentration of only 10%. The structure of iron saturated C‐lobe was determined at 2.79 Å resolution and refined to R_cryst and R_free factors of 0.205 and 0.273, respectively. The structure contains two crystallographically independent molecules, A and B. They were found to have identical structures with an r.m.s. shift of 0.5 Å for their C^α atoms. A high solvent content of 66% was observed in the crystals. The average value of an overall B‐factor was 68.0 Ų. The distance of 2.9 Å observed for the coordination bond between Fe³⁺ ion and N^e2 of His595 appeared to be considerably longer than the normally observed values of 1.9–2.2 Å. This indicated that the coordination bond involving His595 may be absent. Other coordination distances were observed in the range of 2.1–2.3 Å. Based on the present structure of iron saturated C‐lobe, it may be stated that His595 is the first residue to dissociate from ferric ion when the pH is lowered. Proteins 2016; 84:591–599. © 2016 Wiley Periodicals, Inc.     

Oxidation of gold-antimony ores by a thermoacidophilic microbial consortium

Antimony leaching from sulfide ore samples by an experimental consortium of thermoacidophilic microorganisms, including Sulfobacillus, Leptospirillum, and Ferroplasma strains was studied. The ores differed significantly in the content of the major metal sulfides (%): Sb_S, 0.84 to 29.95; Fe_S, 0.47 to 2.5, and As_S, 0.01 to 0.4. Independent of the Sb_S concentration in the experimental sample, after adaptation to a specific ore and pulp compaction, the microorganisms grew actively and leached/oxidized all gold-antimony ores at 39 ± 1°C. The lower was the content of iron and arsenic sulfides, the higher was antimony leaching. For the first time the investigations conducted with the use of X-ray microanalysis made it possible to conclude that, in a natural high-antimony ore, Sb inhibits growth of only a part of the cell population and that Ca, Fe, and Sb may compete for the binding centers of the cell.     

Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum‐dominated chemostat culture

Biomining is the use of microorganisms to catalyze metal extraction from sulfide ores. However, the available water in some biomining environments has high chloride concentrations and therefore, chloride toxicity to ferrous oxidizing microorganisms has been investigated. Batch biooxidation of Fe²⁺ by a Leptospirillum ferriphilum‐dominated culture was completely inhibited by 12 g L^?1 chloride. In addition, the effects of chloride on oxidation kinetics in a Fe²⁺ limited chemostat were studied. Results from the chemostat modeling suggest that the chloride toxicity was attributed to affects on the Fe²⁺ oxidation system, pH homeostasis, and lowering of the proton motive force. Modeling showed a decrease in the maximum specific growth rate (µ_max) and an increase in the substrate constant (K_s) with increasing chloride concentrations, indicating an effect on the Fe²⁺ oxidation system. The model proposes a lowered maintenance activity when the media was fed with 2–3 g L^?1 chloride with a concomitant drastic decrease in the true yield (Y_true). This model helps to understand the influence of chloride on Fe²⁺ biooxidation kinetics. Biotechnol. Bioeng. 2010; 106: 422–431. © 2010 Wiley Periodicals, Inc.     

Optimization of bioleaching and oxidation of gold-bearing pyrite-arsnopyrite ore concentrate in batch mode

Biooxidation of refractory gold-bearing pyrite-arsenopyrite flotation concentrate was optimized and the abundance of predominant groups in the community of thermophilic acidophilic chemolithotrophic microorganisms at various stages of bioleaching was determined. The optimal parameters for growth and leaching/oxidation of the mineral components of the concentrate were pH 1.4–1.8; 47.5°C; and the following salt concentrations in the liquid phase (g/L): K₂HPO₄ · 3H₂O ? 0.53, (NH₄)₂SO₄, 1.6 and MgSO₄ · 7H₂O, 2.5 (or (NH₄)₂SO₄, 1.23; ammophos, 0.41; KOH, 0.1) with 0.03% yeast extract. The optimal conditions resulted in high growth rate, high levels of iron and arsenic leaching, of Fe²⁺ and S^2?/S⁰ oxidation, and predominance of Acidithiobacillus caldus, Sulfobacillus spp., and Ferroplasma spp. in the community.     

Mineral Products of Pyrrhotite Oxidation by Thiobacillus ferrooxidans

The biological leaching of pyrrhotite (Fe_1-xS) by Thiobacillus ferrooxidans was studied to characterize the oxidation process and to identify the mineral weathering products. The process was biphasic in that an initial phase of acid consumption and decrease in redox potential was followed by an acid-producing phase and an increase in redox potential. Elemental S was one of the first products of pyrrhotite degradation detected by X-ray diffraction. Pyrrhotite oxidation also yielded K-jarosite [KFe₃(SO₄)₂(OH)₆], goethite (α-FeOOH), and schwertmannite [Fe₈O₈(OH)₆SO₄] as solid-phase products. Pyrrhotite was mostly depleted after 14 days, whereas impurities in the form of pyrite (cubic FeS₂) and marcasite (orthorhombic FeS₂) accumulated in the leach residue.     

Controlled microbiological in-situ stope leaching of a sulphidic ore

A mixed culture of Thiobacillus ferrooxidans, T. thiooxidans, and Leptospirillum ferrooxidans was used for inoculation of a sulphidic ore body for a bacterial in-situ stope-leaching experiment in the Ilba mine in Romania. The ore body was inoculated with 10⁷ cells/g ore. Measurements at six main sites of the ore body indicated that microbial leaching was started by the inoculation. After about 8 weeks, sufficient microbial activity was measurable only in the upper third of the ore body. Due to the angle of incidence of the ore (75°), the leach liquor percolated only through the upper part leaving two-thirds humidified unsatisfactorily. The leach results, metal mobilization, indicated that by inoculation with the indigenous microorganisms efficient leaching was achieved. Metal output after 18 months of operation amounted to 10% of Cu and 78% of Zn. In the winter months energy for aeration and circulation was not available and this was reflected by reduced values for microbial activity, temperature, and daily metal output. The biological metal mobilisation after 18 months of operation was as active as at the beginning. Cu was mobilised predominantly by microbial leaching whereas Zn was leached mainly by chemical reactions. Both mechanisms contributed equally to iron output. Correspondence to: W. Sand     

Synthesis and characterization of glucosyl-curcuminoids as Fe3+ suppliers in the treatment of iron deficiency

The Fe³⁺ chelating ability of some curcumin glucosyl derivatives (Glc-H; Glc-OH; Glc-OCH₃) is tested by means of UV and NMR study. The pK _a values of the ligands and the overall stability constants of Fe³⁺ and Ga³⁺ complexes are evaluated from UV spectra. The only metal binding site of the ligand is the β-diketo moiety in the keto-enolic form; the glucosyl moiety does not interact with metal ion but it contributes to the stability of metal/ligand 1:2 complexes by means of hydrophilic interactions. These glucosyl derivatives are able to bind Fe³⁺ in a wide pH rage, forming complex species thermodynamically more stable than those of other ligands commonly used in the treatment of iron deficiency. In addition they demonstrate to have a poor affinity for competitive biological metal ions such as Ca²⁺. All ligands and their iron complexes have a good lypophilicity (log P > −0.7) suggesting an efficient gastrointestinal absorption in view of their possible use as iron supplements in oral therapy. The ligand molecules are also tested for their antioxidant properties in “ex vivo” biological system.