Concentration Of Iron In Solution Research Articles

Pyrophosphate and orthophosphate addition to soils: sorption, cation concentrations, and dissolved organic carbon

Liquid polyphosphate fertilisers contain both orthophosphate and pyrophosphate, and have shown significant yield increases compared to granular orthophosphate fertiliser on highly phosphorus (P) fixing soils. The P sorption chemistry of the dominant P species in a polyphosphate fertiliser (pyrophosphate and orthophosphate) was compared on a range of Australian soils, and the effect of these P species on equilibrium solution chemistry was also examined. Phosphorus supplied as pyrophosphate had a stronger sorption affinity than orthophosphate in all soils. The greater efficiency of pyrophosphate-based fertiliser on some soil types is therefore not due to reduced sorption of this P supplied as pyrophosphate compared to P supplied as orthophosphate fertiliser. In general, the addition of pyrophosphate to soil resulted in a larger decrease in calcium concentration in solution compared to orthophosphate. In contrast, there was an increase in iron concentration in solution with pyrophosphate addition, indicating sequestration reactions associated with the dissolution of dissolved organic carbon into soil solution. The pyrophosphate ion generally mobilised more Fe into solution than orthophosphate in several soils, likely through complexation reactions leading to Fe desorption/dissolution from the soil solid phase. These findings highlight the differences in soil chemical reactions that occur with the addition of polyphosphate fertilisers, which may contribute to their yield advantage in some soil types.

Particle growth parameters in the precipitation of metastable iron phases from zinc-rich solutions

Agglomeration of metastable iron phases was studied at constant supersaturation in a continuous crystallizer. Specific attention was given to the influence of operating parameters such as pH, temperature, hot iron solution iron concentration, mass of seed, size of seed, stirring rate and viscosity of the iron solution on the agglomeration and quality of ferrihydrite and schwertmannite precipitates. The relative importance of the operating parameters was expressed in terms of the filterability of the solids formed, the change in the particle population density and iron removal efficiency using the so-called Hadamard matrix. The effect of seed addition on the purity of agglomerates was also evaluated.

A Fenton-like Oxidation Process Using Corrosion of Iron Metal Sheet Surfaces in the Presence of Hydrogen Peroxide: A Batch Process Study Using Model Pollutants

This study evaluates a new method for chemically destroying organic pollutants in wastewater using spontaneous corrosion of iron metal sheet surfaces in the presence of hydrogen peroxide. Model pollutants (phenol and benzoic acid) were degraded in batch experiments to investigate which parameters affected the process performance. Iron metal sheet surfaces spontaneously corrode under acidic conditions producing iron species (mainly ferrous ions) dissolved in aqueous solution, which react with hydrogen peroxide via the Fenton reaction. In order to optimise the oxidation system, several factors (pH, H2O2 dosage, initial concentration of organic substances) affecting corrosion of the iron metal sheet surface were investigated. Total iron concentration in solution was investigated with different dosages of H2O2 (100 mg l−1, 1000 mg l−1 and 1900 mg l−1) at different pH values (1.5, 2.5 and 3.0). Iron corrosion increased with the decrease of pH. The addition of H2O2 resulted in a significant increase of iron corrosion. Organic substances also had a marked effect with, for instance, the presence of phenol or benzoic acid resulting in a considerable increase of iron corrosion. In contrast, the absence of either hydrogen peroxide or iron metal brought no change in total organic carbon (TOC). In order to obtain the most effective combination of parameters for TOC removal of phenol solution, experiments were conducted under varied conditions. The experimental results showed that there is an optimum pH requirement (in this work, 2.5). The factors affecting the TOC removal are discussed and the oxidation mechanisms leading to mineralization of organic substances are proposed.

Geological record of an acidic environment driven by iron hydrochemistry: The Tinto River system

The existence of possible hematitic strata on the surface of Mars demands a search for terrestrial analogues formed in unusual environments. This will help us to recognize and interpret environmental and, perhaps, biological signatures preserved in Mars' hematites. Such an analogue would allow us to establish valid reference systems based on geomicrobial and biogeochemical signatures. Two different aspects place the Tinto River inside the boundaries of a natural extreme system: its high level of biological diversity and the presence of fluvial rocks formed in the same acidic conditions as in the modern system, which could predate the Tertiary. Study of both the modern system and the ancient system is necessary to understand the formation of biosignatures. A chemolithotrophic community that biooxidizes the Iberian Pyritic Belt, acidifying water (pH between 0.9 and 3.0) and favoring high concentrations of ferric iron in solution (up to 20 g·L−1), maintains this iron‐driven system. In spite of these extreme conditions, high microbial diversity was found. Its acidic bacteria, archaea, and eukarya constitute a complex community supported by algal biomass in highly stable hydrochemical conditions, which are achieved through iron buffering. The pH is maintained at constant low levels even at very high water dilution. In these conditions, iron minerals as oxyhydroxides, hydroxides, and sulfates are formed. The modern and recent parageneses contrast with the ancient Tinto River terrace mineral associations, which show dehydrated and desulfated iron oxides. If this dehydration process is considered, these Tinto River ironstones may be a key for knowing some aquatic habitats, which may have hosted a part of the early Mars biosphere.

Nutrient application reduces iron toxicity in lowland rice in West Africa

Iron toxicity is a widespread nutrient disorder that affects rice growing in inland swamps and on irrigated lowland soils throughout the humid forest and savanna zones of West Africa. It has been reported to reduce lowland rice yields in West Africa by 12-100%, depending on the intensity of the toxicity and the tolerance of the rice cultivar (Sahrawat et al 1996). The disorder occurs when large amounts of iron are mobilized in situ or when an inflow of iron occurs from adjacent upper slopes, especially in the inland valley systems of West and Central Africa. In mineral soils, the occurrence of iron toxicity is associated with a range of concentration of ferrous ions in the soil solution. Light-textured soils high in extractable acidity are especially prone to iron toxicity (Moormann and van Breemen 1978). It is also known that a high concentration of iron in solution decreases the absorption of other nutrients, especially phosphorus (P), potassium (K), and zinc (Zn) (Yoshida 1981).

Idle time in the washing and iron concentration in leachate removed: two basic parameters in the desulphurization of coal in a packed column

Column biodesulphurization of coal is at the experimental stage and is influenced by many variables including temperature, pH, particle size, concentration of iron in solution, among others. Idle time in the washing process and the concentration of dissolved iron in the purged leachate are two variables with a definite effect on the yield of the desulphurization system. In the laboratory, several trials were run with columns packed with coal for different idle times: 1, 2, 3, 5, 6 and 7 days, and for different concentrations of iron in the purged leachate: 500 to 4,000 mg/l. The optimal values for the two variables; that is, those allowing for the highest desulphurization yields, were idle times of 3 and 5 days, which give an elimination of 56% and 49% of pyritic sulphur, respectively, and 3,000 mg/l of iron concentration in the purged leachate, giving a decrease in pyritic sulphur in coal of 57%.

Uptake and removal of iron by immobilised persimmon tannin

Persimmon tannin was immobilised with formaldehyde (the aldehyde gel) and potassium peroxodisulfate (the persulfate gel). The resulting gels have high abilities to adsorb iron. The persulfate gel can adsorb iron from both iron(II) and iron(III) solutions with high efficiency. The adsorption of iron(III) by the persulfate gel was rapid and was affected by the solution pH, the concentration of iron in solution, and the mass of adsorbent. Adsorbed iron was easily desorbed with 0.1 mol dm−3 HCl solution. The gel can be repeatedly re-used for iron recovery using the adsorption–desorption cycle. The persulfate gel could remove trace amounts of iron in a sake-brewing water to facilitate the production of high quality sake. © 2000 Society of Chemical Industry

Uptake and removal of iron by immobilised persimmon tannin

Persimmon tannin was immobilised with formaldehyde (the aldehyde gel) and potassium peroxodisulfate (the persulfate gel). The resulting gels have high abilities to adsorb iron. The persulfate gel can adsorb iron from both iron(II) and iron(III) solutions with high efficiency. The adsorption of iron(III) by the persulfate gel was rapid and was affected by the solution pH, the concentration of iron in solution, and the mass of adsorbent. Adsorbed iron was easily desorbed with 0.1 mol dm−3 HCl solution. The gel can be repeatedly re-used for iron recovery using the adsorption–desorption cycle. The persulfate gel could remove trace amounts of iron in a sake-brewing water to facilitate the production of high quality sake. © 2000 Society of Chemical Industry

The Indirect Mechanism of Bacterial Leaching

Mathematical models of the chemical leaching of a sulphide mineral and the bacterial oxidation of ferrous ions are combined in a mathematical model of bacterial leaching. It is shown that the models of the chemical leaching of sphalerite and the bacterial oxidation of ferrous ions are in excellent agreement with the experimental results. The indirect mechanism of bacterial leaching, which is a combination of these two sub-processes, is able to account for the shape of the reaction curve obtained from bacterial leaching experiments. It is also shown that even at very low concentrations of iron in solution the indirect mechanism may be the dominant pathway in bacterial leaching or sulphidic minerals.

An Exploration of the Removal of Iron (Fe3+) from Aqueous Solutions Using β-Dicalcium Silicate and α-Monocalcium Silicate as Alternative Precipitants to Calcium Hydroxide

The present work has studied the removal of iron (Fe3+) ions from solution using β-dicalcium silicate (C2S), α-monocalcium silicate (CS) and calcium hydroxide. The merits of these precipitants were analyzed by studying their effectiveness for removing iron (Fe3+) from solutions of ferric chloride and the properties of the flocs formed. The initial concentration of iron in solution was varied between 10 and 1000 mg l−1 Fe3+ for different additions of precipitant. The residual silicate particles upon hydrolysis appear to enhance the overall removal process in a manner different from the coagulating effect of calcium ions. Considerable enhancement in the rate of removal of iron resulted from use of more finely ground silicates. It is suggested that the reaction can proceed either by the specific adsorption of polynuclear ferric hydroxo complexes on to the surface of negatively charged silica rich layers of C2S, formed by loss of Ca2+ upon hydrolysis or by direct exchange of Fe3+ with Ca2+ in the charged layer. At the end of the second minutes of the settling period, remaining iron concentrations were 12.0 mg l−1 and 525.0 mg l−1, respectively when 3.90 g l−1 of C2S and 2.10 g l−1 of calcium hydroxide were applied to solutions containing 1000 mg l−1 Fe3+. By the end of second minutes of settling period, the remaining iron concentrations were 40 mg l−1 and 78 mg l−1, respectively when 0.39 g l−1 of C2S and 0.21 g l−1 of calcium hydroxide were applied to solutions containing 100 mg l−1Fe3+ in a sedimentation tank designed on the basis of a surface loading rate of 48 m3m−2d−1. In the case of C2S, the specific resistance to filtration and the Capillary Suction Time (CST) values of the sludge produced were lower than that when calcium hydroxide was used thus indicating better dewaterability characteristics. The filter yields of the sludges from C2S and calcium hydroxide treatment of 10, 100 and 1000 mg l−1 iron solutions were estimated as 27.0, 15.8, 23.2 kg m−2h−1 and 12.8, 6.5, 7.8 kg m−2h−1, respectively.

An Exploration of the Removal of Iron (Fe3+) from Aqueous Solutions Using β-Dicalcium Silicate and α-Monocalcium Silicate as Alternative Precipitants to Calcium Hydroxide

The present work has studied the removal of iron (Fe3+) ions from solution using β-dicalcium silicate (C2S), α-monocalcium silicate (CS) and calcium hydroxide. The merits of these precipitants were analyzed by studying their effectiveness for removing iron (Fe3+) from solutions of ferric chloride and the properties of the flocs formed. The initial concentration of iron in solution was varied between 10 and 1000 mg l−1 Fe3+ for different additions of precipitant. The residual silicate particles upon hydrolysis appear to enhance the overall removal process in a manner different from the coagulating effect of calcium ions. Considerable enhancement in the rate of removal of iron resulted from use of more finely ground silicates. It is suggested that the reaction can proceed either by the specific adsorption of polynuclear ferric hydroxo complexes on to the surface of negatively charged silica rich layers of C2S, formed by loss of Ca2+ upon hydrolysis or by direct exchange of Fe3+ with Ca2+ in the charged layer. At the end of the second minutes of the settling period, remaining iron concentrations were 12.0 mg l−1 and 525.0 mg l−1, respectively when 3.90 g l−1 of C2S and 2.10 g l−1 of calcium hydroxide were applied to solutions containing 1000 mg l−1 Fe3+. By the end of second minutes of settling period, the remaining iron concentrations were 40 mg l−1 and 78 mg l−1, respectively when 0.39 g l−1 of C2S and 0.21 g l−1 of calcium hydroxide were applied to solutions containing 100 mg l−1Fe3+ in a sedimentation tank designed on the basis of a surface loading rate of 48 m3m−2d−1. In the case of C2S, the specific resistance to filtration and the Capillary Suction Time (CST) values of the sludge produced were lower than that when calcium hydroxide was used thus indicating better dewaterability characteristics. The filter yields of the sludges from C2S and calcium hydroxide treatment of 10, 100 and 1000 mg l−1 iron solutions were estimated as 27.0, 15.8, 23.2 kg m−2h−1 and 12.8, 6.5, 7.8 kg m−2h−1, respectively.

Bacterial leaching of complex sulfide ore samples in bench-scale column reactors

Several variables were examined in column bioleaching of a complex sulfide ore material which contained chalcopyrite, pentlandite, pyrite, pyrrhotite and sphalerite as the main sulfide minerals. Samples were used with varying proportions of pyrrhotite, pyrite, quartzite (low acid consumption) and skarn (high acid consumption). The experiments were carried out using bench-scale column leaching reactors which were inoculated with acidophilic, Fe- and S-oxidizing bacteria, initially derived from the source mine water. Leaching rates in sterile controls were negligible. In inoculated columns new solid phases (covellite, jarosite, Fe (III) oxide and elemental sulfur) were formed. Acid consumption was highest under low pH and low redox potential conditions. The solubility of ferric iron was controlled by jarosite and an Fe (III) hydroxide (initially amorphous). The leaching rates of Co (from pyrite and pentlandite), Cu (chalcopyrite), and Zn (sphalerite) showed a tendency to increase with dissolved ferric iron concentration. The leaching of Ni (from pyrrhotite and pentlandite) did not correlate with the concentration of ferric iron in solution. Microscopic counts of bacteria in solution, deemed insufficient to represent total bacterial counts, showed a tendency to be higher at the lower pH and intermediate redox potential ranges. Trickle-leaching conditions yielded higher acid production and redox-potential values compared with flood leaching. The leaching rates of Co, Cu, Ni and Zn each responded differently to redox potential and pH regimes. The accelerating effect of a decreasing particle size on the metal leaching rates was amplified by low pH values.

Bacterial oxidation conditions for gold extraction from Olympias refractory arsenical pyrite concentrate

The arsenical pyrite concentrate produced at the Olympias mine, Macedonia, Greece, assays approximately Fe: 40%, S: 40%, As: 12% and Au: 26g/t. Mineralogically, it consists mainly of pyrite (68–70%) and arsenopyrite (23–26%), the former includes both arsenic-free and arsenian pyrite. Gold is mainly associated with the arsenopyrite and arsenian pyrite. The concentrate is highly refractory in nature, as direct cyanidation yields gold recovery lower than 10%. An oxidative pretreatment step is, therefore, necessary before cyanidation, in order to break up the sulphide lattice and liberate gold. The present paper aims at elucidating the effect of the leaching conditions on the bacterial oxidation of the Olympias concentrate. This research subject is of particular interest because selective oxidation of the arsenopyrite and arsenical pyrite fractions may result in high gold recoveries without the need for total sulphur oxidation. Based on the above, this study is focused on the factors that enhance preferential arsenopyrite oxidation. It has shown that preferential oxidation of arsenopyrite is observed especially at short retention times and pulp densities in excess of 10% solids. Arsenopyrite oxidation is complete at EMF values of 480–550 mV, while the oxidation of pyrite is observed to commence at higher EMF values, where the oxidation of arsenopyrite is almost complete. High ferric iron concentrations in solution enhance arsenopyrite but have an adverse affect on pyrite oxidation rates. When operating at constant pH values in the range 1.0–1.2, selective oxidation of arsenopyrite is observed, while pyrite oxidation proceeds at higher pH values, around 1.5. The indirect mechanism is deduced to play a significant role in the bio-oxidation of arsenopyrite, while pyrite oxidation is mainly attributed to direct bacterial attack.

A Mossbauer study of early precipitation in Cu-Fe alloy

Mossbauer spectroscopy was used to study the early stages of precipitation in Cu-0.6 at.% Fe alloy. A set of data for the concentration of iron in solution was obtained for annealing times from 1 to 105 s at 400 degrees C. The results were interpreted in terms of quenched monovacancies and divacancies. A proposed analytical expression describes the annealing fairly well. The application of the Mossbauer spectroscopy in short-time-scale annealing experiments seems to promise new possibilities for investigation of the diffusion properties.

Lupinus species differ in their requirements for iron

The effect of iron supply on the growth and nodulation of Lupinus angustifolius L. (Gungurru), Lupinus luteus L. (R-1171) and Lupinus pilosus Murr. (P20957) was studied in acid solutions. Plants of the three species were grown together in the same solution and inoculated with Bradyrhizobium (Lupinus) WU 425. Plants were then grown with or without applied NH4NO3. The lupin species differed greatly in their sensitivity to low iron concentrations in solution with L. pilosus being most tolerant and L. luteus most sensitive. L. pilosus had the highest iron concentration in tissues and had a higher ratio of iron concentration in the youngest fully expanded leaf blades (YEB) to that in roots than the other two species. L. luteus had higher iron concentrations in roots but lower iron concentration in YEB and shoots than did L. angustifolius. The requirements of internal iron for the maximal chlorophyll synthesis in YEB were 65 μg g-1 for L. angustifolius and L. luteus, and 52 μg g-1 for L. pilosus. In contrast to effects on growth, the three species had similar external iron requirements for nodule formation in roots and for maximal nitrogen concentrations in shoots. The results indicate that iron tolerant lupin species require lower internal and external iron supply and have a greater ability than sensitive species to translocate iron from roots to shoots.

Experimental study of iron-chloride complexing in hydrothermal fluids

Mineral assemblage solubilities were measured in cold-seal pressure vessels as a function of pressure, temperature, and potassium chloride concentration in order to determine the nature and thermodynamic properties of iron-chloride complexes under hydrothermal conditions. The assemblage pyritepyrrhotite-magnetite was used to buffer ƒS 2 and ƒO 2 , and K + H + ratios were buffered at reasonable geologic values using the assemblage potassium feldspar-muscovite (or andalusite)-quartz. The pressure-temperature ranges were 0.5-2.0 kbar and 300–600°C, and initial fluid compositions ranged from 0.01–2.0 molal KCl. With all other factors constant, the concentration of iron in solution increases with increasing temperature, with decreasing pressure, and with increasing total potassium chloride concentration. Changes in iron concentrations as a function of KCl concentration, in conjunction with charge balance, mass action, and mass balance constraints on the system, place constraints on the stoichiometry of the important iron-chloride complexes under each of the experimental conditions. Using least-squared linear regression fits to determine these slopes, the calculations yield values for the average ligand numbers that are in the range 1.2-1.9, with uncertainties ranging from ±0.1-0.6 at the several PT conditions considered. The slopes of the regressed fits to the data suggest that both FeCl + and FeCl 2 0 are important in the experimental fluids, with FeCl 2 0 becoming dominant at the higher temperatures. Theoretical calculations, however, indicate that FeCl + does not contribute significantly to the solubility. Because of the large uncertainties associated with some of the calculated average ligand numbers, we base our data analysis on the theoretical calculations. A statistical analysis is applied to the solubility data in order to determine the values and uncertainties of the dissociation constant for FeCl 2 0 that best fit the data at each of the experimental pressures and temperatures. The calculated stability of FeCl 2 0 increases with increasing temperature and total chloride concentration, and with decreasing pressure. The values of the dissociation constant of FeCl 2 0that are calculated in this study are in moderately good agreement with FeCl 2 0dissociation constants from other studies of iron-chloride complexing in supercritical fluids. Differences are likely due to different assumptions made concerning activity coefficients of aqueous species. Log k d values for full dissociation of FeCl 2 0 at 0.5 kbar—300°C—and at 1 kbar—400, 500, and 600°C, respectively—are −3.75 ± 0.40, −6.25 ± 0.10, −9.19 ± 0.44, and −13.29 ± 0.09.

Inadequate iron supply and high bicarbonate impair the symbiosis of peanuts (Arachis hypogaea L.) with different Bradyrhizobium strains

In the present study, we examined the effects of iron deficiency in an acid solution and in an alkaline solution containing bicarbonate on the growth and nodulation of peanuts inoculated with different bradyrhizobial strains or supplied with fertilizer nitrogen. Inadequate iron supply in acid solution decreased the number of nodule initials, nodule number and nodule mass. Alleviating the iron deficiency increased acetylene reduction but not bacteroid numbers in nodules. Nitrogen concentrations in shoots of inoculated plants increased as iron concentrations in solution increased when determined at day 30 but not at day 50. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic nitrogen fixation than for those receiving fertilizer nitrogen. Adding bicarbonate to the solution with 7.5 μM Fe markedly depressed nodule formation. This effect was much more severe than that of inadequate iron supply alone. Bicarbonate also decreased nitrogenase activity but did not decrease bacteroid concentrations in nodules. Both NC92 and TAL1000 nodulated peanuts poorly when bicarbonate was present. However, an interaction between iron concentrations in acid solutions and Bradyrhizobium strains on nodulation of peanuts was observed. Alleviating iron deficiency increased the number of nodule initials and nodules to a much greater extent for plants inoculated with TAL1000 than for plants inoculated with NC92.

The role of iron in nodulation and nitrogen fixation in Lupinus angustifolius L

SUMMARYThe effects of iron concentration in solution on nodulation and symbiotic N2 fixation in lupins (Lupinus angustifolius L. ev. Yandee) were studied in solution culture in the glasshouse by comparing plants supplied with NH4NO3 with those reliant on N2 fixation.At very low iron supply, adding NH4NO2 did not increase shoot growth. Under moderate iron deficiency, where plants were pale green, adding NH4NO3 increased shoot growth, implying that moderate iron deficiency was, operationally, nitrogen deficiency. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic N2 fixation than for those supplied with NH4NO3Iron deficiency depressed nodule initiation earlier than host plant growth, resulting in decreased nodule number and mass. Alleviating iron deficiency enhanced leghaemoglobin production in nodules and increased nitrogen concentrations in the shoots. Iron concentration in the youngest fully expanded leaves provided a good indication of the severity of iron deficiency‐caused chlorosis.The results suggest that iron is involved in symbiotic N2 fixation through effects on both nodule initiation and nodule function, and that the symbiosis has a higher iron requirement than that needed for host plant growth.

Mechanisms controlling zinc solubility in soils

SUMMARYThe removal of zinc from solution has been studied for seven soils of varying properties. The presence of a background electrolyte as an ionic strength buffer and the nature of the anions and cations in solution have also been examined. This process has been considered as both a surface adsorption and a precipitation mechanism. Evidence presented suggests a role for a precipitation mechanism involving zinc and iron, which is independent of pH. Iron concentration in solution decreased with increasing zinc concentration; the ion product pZn+2pFe was constant (15.00, SD 1.00) over all seven soils. A further indicator of a precipitation mechanism was the shape of the Langmuir plot at low equilibrium concentrations of zinc in solution.

Changes in the roots of sunflower under iron stress

Abstract Growth and physiological changes in sunflower (Helianthus annus L. cv. Northrup King 265) were observed when plants were grown at selected concentrations of iron in solution. Plant roots were tested for reduction capacity with tetrazolium (2,3,5‐triphenyl‐tetrazolium chloride). Iron stressed roots indicated very high capacities for reduction. The amount of reduction was quantified and expressed as amount of tetrazolium reduced per gram of root fresh weight. Root respiration levels were monitored using an oxygen electrode. Iron stressed roots consumed more oxygen than nonstressed roots.