The roles of iron and manganese oxides in controlling trace element retention in soils across a range of parent materials

Hydrous manganese and iron oxides of soils and sediments are strong scavenging agents for heavy metal ions. Information on heavy metals extracted along with manganese and iron oxides has been used in mineral exploration. But currently used methods do not differentiate metal ions associated with manganese oxides and those associated with iron oxides. Manganese oxides differ from iron oxides in solubility in response to oxidation‐reduction conditions, charge characteristics, and the quantity and kind of metal ions scavenged. This paper reports the development of an extraction method for the selective dissolution of manganese oxides from soils and sediments with minimal attack on the coexisting iron oxides, based on the difference in behavior of manganese oxides and iron oxides toward reduction under various conditions. By dissolving manganese oxides and iron oxides separately and determining respective metal ions which are released in the process, the geochemical significance of interelement relationships may be established. Manganese oxides in soils and sediments are found to be readily dissolved by a hydroxylamine hydrochloride (NH 2 OH · HCl) solution, leaving the major part of iron oxides in the residue. Although dissolution of manganese oxides is relatively independent of pH (pH 1, 2, and 3) and concentration of the NH 2 OH · HCl solution (0.025 to 0.25 M ), and time of equilibration (15 to 60 min), progressively greater amounts of iron oxides are released with lower pH and higher concentration of NH 2 OH · HCl solution, and with longer time of equilibration. A 0.1 M NH 2 OH · HCl solution prepared in 0.01 M HNO 3 (pH 2) dissolves, on the average, 85% of manganese oxides and about 5% of iron oxides from various sediments after equilibrating for 30 min. Dissolution of manganese oxides and of iron oxides from four highly weathered soils by this solution amounts, respectively, to 50% and less than 1%. At pH 2, most heavy metal ions released during the dissolution of manganese oxides will be prevented from forming insoluble hydroxides or basic salts through hydrolysis, and then they can be determined in solution by appropriate analytical methods.

Remediation of cadmium-polluted weakly alkaline dryland soils using iron and manganese oxides for immobilized wheat uptake

The low rice production level in Africa is attributed to poor soil fertility despite the potential for rice cultivation in the inland valleys. This study was conducted to evaluate soil characteristics in some lowlands that have been continuously and intensively used for rice production for over two decades in southwestern Nigeria. Soil physical, chemical, and mineralogical properties, as well as phosphorus sorption characteristics, were assessed in soil samples collected from diagnostic horizons of profiles in six benchmark soils. The results show kaolinite, quartz, potassium(K)-feldspars, and mixed-layered smectite as the predominant minerals. The iron oxide fractions indicate that the soils are at varying degrees of development where the soils at the advanced stage of development are predominantly rich in kaolinite and quartz with a high concentration of total pedogenic iron oxide and generally low in soil fertility. Soil phosphorus buffering capacity is low and varies inversely with pH, confirming the deficiency of phosphorus at low pH. Short-range-order (SRO) iron (Fe) oxides show a strong affinity for phosphorus and this is stronger at lower soil horizons and mediated by some redoxomorphic reactions. The SRO iron oxide concentration has more influence on phosphorus retention in soils rather than the absolute concentration of iron oxides. The study concludes that SRO Fe oxides and soil pH are the major edaphic factors playing a prominent role in phosphorus retention and availability in the wetland soils rather than the clay minerals.

Natural surface coatings collected from natural substances (NSCsNS) were employed to study the roles of the main chemical components (iron oxides, manganese oxides, and other components) in controlling the adsorption of lead (Pb) and cadmium (Cd) in aquatic environments. The selective chemical extraction followed by the adsorption of Pb and Cd experiments and statistical analysis, were used to investigate the adsorption property of each component. Hydroxylamine hydrochloride was used to remove manganese oxides selectively, and sodium dithionite was used to extract iron oxides and manganese oxides. The result indicated that iron oxides and manganese oxides played an important role in the adsorption of Pb and Cd on NSCsNS, and the relative contribution was about two-thirds. The contribution of manganese oxides was the greatest, with a lesser role indicated for other components. The adsorption ability of manganese oxides for Pb and Cd was greater than that of iron oxides or other components for Pb and Cd. The Pb adsorption observed in each component was greater than Cd adsorption.

Plutonium subsurface mobility is primarily controlled by its oxidation state, which in turn is loosely coupled to the oxidation state of iron in the system. Experiments were conducted to examine the effect of sediment iron mineral composition and oxidation state on plutonium sorption and reduction. A pH 6.3 vadose zone sediment containing iron oxides and iron-containing phyllosilicates was treated with various complexants (ammonium oxalate) and reductants (hydroxylamine hydrochloride and dithionite-citrate-bicarbonate (DCB)) to selectively leach and/or reduce iron oxide and phyllosilicate/clay Fe(III).57Fe-Mössbauer spectroscopy was used to identify initial iron mineral composition of the sediment and monitor dissolution and reduction of iron oxides and reduction of phyllosilicate Fe(III).57Fe-Mössbauer spectroscopy showed that the Fe-mineral composition of the untreated sediment is: 25–30% hematite, 60–65% small-particle/Al-goethite, and <10% Fe(III) in phyllosilicate; there was no detectable Fe(II). Upon reduction with a strong chemical reductant (dithionite-citrate-bicarbonate buffer), much of the hematite and goethite was removed. Partial reduction of phyllosilicate Fe(III) was evident in the sediments subjected to DCB treatment. Sorption of Pu(V) was monitored over one week for the untreated and each of five treated sediment fractions. Plutonium oxidation state speciation in the aqueous and solid phases was monitored using solvent extraction, coprecipitation, and XANES. The rate of sorption appears to correlate with the fraction of Fe(II) in the sediment (untreated or treated). Pu(V) was the only oxidation state measured in the aqueous phase, irrespective of treatment, whereas Pu(IV) and much smaller amounts of Pu(V) and Pu(VI) were measured in the solid phase. Surface-mediated reduction of Pu(V) to Pu(IV) occurred in treated and untreated sediment samples; Pu(V) remained on untreated sediment surface for two days before reducing to Pu(IV). Similar to the sorption kinetics, the reduction rate appears to be correlated with sediment Fe(II) concentration. The correlation between Fe(II) concentrations and Pu(V) reduction demonstrates the potential impact of changing iron mineralogy on plutonium subsurface transport through redox transition areas. These findings should influence the conceptual models of long-term stewardship of Pu contaminated sites that have fluctuating redox conditions, such as vadose zones or riparian zones.

Dithionite-citrate-bicarbonate (DCB) treatment is a classical method for removing iron oxides from soil. The DCB-induced dissolution effects on iron oxides are controversial. In this paper, samples from a typical loess-paleosol sequence in the Chinese Loess Plateau (CLP) and from other aeolian dust deposits in southern China were collected, and changes in the grain size composition and magnetic properties of the samples after DCB treatment were analyzed. The results show that the dissolution of iron oxides in loess-paleosol samples from the CLP is highly grain size dependent. In addition to completely dissolving nanometer-sized pedogenic iron oxides (< 0.2 μm), the standard DCB procedure can also dissolve submicron- and micron-sized aeolian iron oxides (0.2–6 μm). For these aeolian iron oxides, the submicron-sized (0.2–1 μm) iron oxides are sufficiently dissolved, and the solubility of the micron-sized (1–6 μm) iron oxides decreases with increasing particle size. The dissolution of > 6 μm aeolian iron oxides is negligible. DCB can neither separate pedogenic iron oxides from aeolian iron oxides nor selectively dissolve magnetite or maghemite. Although the total amount of dissolved iron oxides in the profiles from southern China is higher than that in the LC profile from northern China, the submicron- and micron-sized aeolian iron oxides in the latter are more easily dissolved.

Transport into sediments of the trace elements Cu, Zn, Pb, Cd, Cr, and Sr by settling particles was investigated in Lake Zurich; the concentrations of these elements in settling particles collected in sediment traps and in the water column were determined at different times of year. Correlations of trace element concentrations with the various main components of the settling particles (biological material, calcium carbonate, manganese and iron oxides, silicate minerals) and examination of seasonal variations both of these concentrations in particles and of particle fluxes to the sediments show that biological material is an important carrier phase (especially for Cu and Zn). Iron and manganese oxides also contribute to trace element transport; calcium carbonate is inefficient as a carrier material.

Behaviors of trace elements in Neoarchean and Paleoproterozoic paleosols: Implications for atmospheric oxygen evolution and continental oxidative weathering

An experiment was carried out in the Grain Technology Laboratory, Department of Crops, Faculty of Agriculture - Omar Al-Mukhtar University, during the 2023 AD season, with a completely random design, to study the effect of soaking seeds and spraying seedlings with some Nanoparticles) NPs( (iron, manganese, and copper Nano oxides), Nano-Phosphorus, and Biota agro, and their reflection in some plant growth indicators. Mung beans (Vigna radiata L.) at a concentration of 1 cm/L of one M solution for 10 minutes, then planted in pots with a capacity of 3 kg, with 10 seeds per pot through 3 observations of each treatment. The data showed: • A significant response of mung bean plants to the application of nanoparticles (iron, manganese and copper oxides), nano phosphorus and beta agro was observed in some growth indicators (plant weight, plant height, leaf area, crop growth rate and leaf specific gravity). • Nano phosphorus outperformed by giving the plant the highest weight and leaf area. The crop growth rate reached (3.780 g, 19.2 cm2, 0.506 g/day, respectively) compared to the control treatment. Also, both iron oxide and nano phosphorus outperformed the rest of the treatments under study by giving the highest leaf specific weight. (0.1493, (0.0993) respectively. • Biota Agro excelled in giving the highest plant height, reaching 23 cm, followed by manganese oxide, which reached 21 cm, compared to the control treatment, which decreased to 8.50 cm Keywords: soaking seeds, mung bean growth, Nano-fine fertilizers, Biota agro, Nanoparticles(NPs)

Consolidation of the ferruginous manganese ore fines is of vital importance for manganese extraction in the smelting process. The main impurities in the Fe–Mn ores are Ca and Si constituents and they have a significant effect on the consolidation of iron and manganese oxides. In this study, characterization on the behaviors of Ca and Si constituents during the roasting process of Fe–Mn ores were investigated by thermodynamic, fusion temperatures, and phase identification analyses. The results showed that the Ca and Si constituents can decrease the fusion temperature of the MnO2–Fe2O3 binary system dramatically due to the formation of low-melting complicate silicates from the CaO, SiO2, and partial manganese and iron oxides. The high-melting solid manganese ferrites phase generated from the remaining manganese and iron oxides were bonded and solidified by the liquid phase. This provided favorable mineralization conditions for the consolidation of Fe–Mn ore.

Background. An experiment was conducted at the Grain Technology Laboratory, Crop Department, Faculty of Agriculture, Omar Al-Mukhtar University, during the 2023 season. The experiment utilized a completely randomized design to study the response of barley to foliar application of fine nanoscale iron, manganese, and copper fertilizers. The application was carried out as foliar spray at two different doses, two weeks and one month after sowing, using 3 kg capacity pots with 20 seeds per pot. The experiment included three observations for each treatment, with the nanoscale iron, manganese, and copper oxides applied at a concentration of 1 cmol/L. The data revealed the following: Significant positive response of barley shoots to foliar application of nanoscale iron, manganese, and copper fertilizers in various growth indicators, including shoot weight, shoot length, leaf area, crop growth rate, and specific leaf weight. High significant differences were observed in the effect of nanoscale iron, manganese, and copper oxides on the average shoot weight, crop growth rate, and leaf area. Copper oxide and manganese oxide showed the highest means, followed by iron oxide, compared to the control. Iron oxide exhibited the highest specific leaf weight for barley shoots, followed by copper oxide and then manganese oxide, compared to the control treatment.

We investigated the extractability of manganese (Mn) and iron (Fe) oxides from typical Japanese soils (Entisols, Inceptisols, and Andisols) by 0.5 mol L−1 hydroxylamine hydrochloride (NH2OH-HCl) extraction (pH 1.5; 16 h shaking at 25°C; soil:solution ratio 1:40), referred as to HHmBCR, which is Step 2 (used for the reducible fraction) of the modified BCR (Community Bureau of Reference) sequential extraction procedure. The HHmBCR procedure extracted almost all Mn oxides from the non-Andisol samples, but failed to extract a part of the Mn oxides from some Andisol samples. The procedure extracted most short-range ordered Fe oxides from non-Andisol samples, but it extracted only 7.5% and 13% of the short-range ordered Fe oxides from allophanic and non-allophanic Andisol samples, respectively. This remarkably low extractability of Fe oxides suggests that the HHmBCR method is not suitable for extracting oxide-occluded heavy metals from Andisols. Since the extraction rate of short-range ordered Fe oxides from various soils with the extractant was negatively correlated with the amounts of oxalate- and pyrophosphate-extractable Al even when the variability of the extraction pH was reduced by increasing the soil:solution ratio from 1:40 to 1:500, the extractability of Fe oxides would be negatively affected by the presence of active Al, including allophane/imogolite, amorphous Al, and Al-humus complexes. Because these Al constituents are abundant in Andisols, they would be at least partially responsible for the lower extractability of Fe oxides by HHmBCR from Andisols.

The morphological properties (colour, structure, texture, consistence, miscellaneous features and horizon boundary conditions) of inland valley soils in central Cross River State were described. The soils were sampled from pedogenic horizons and analyzed for physico-chemical properties. They were specially analyzed for pedogenic forms of iron (Fe) and manganese (Mn), namely, acid (pH 3) oxalate extractible and citrate-bicarbonate-dithionite (CBD) extractable forms The soils were deep, gleyed/mottled acid loams and clays, with low (3%) orgaic matter contents. The contents of CBD extractible Fe (FeD) in the surface horizons of soils range from 6255.00 mg kg-1 to 8131 mg kg-1 with a mean of 7100.0 mg kg-1 while the subsoil horizon values range from 5421.0 mg kg-1 to 8131 mg kg-1 with a mean of 6500 mg kg-1. Amorphous iron (Feox) in the surface soil ranged between 959.0 mg kg-1 and 5838 mg kg-1 with a mean of 4000.00 mg kg-1; and the subsoil horizon values ranged from 1084 mg kg-1 to 5838.0 mg kg-1 with a mean of 3500 mg kg-1. Active iron ratio of the surface horizons was in the range of 0.15 and 0.85 with a mean of 0.55. The extractable manganese oxides for the surface horizons ranged between 83.3 mg kg-1 and 550.0 mg kg-1 with a mean of 250.0 mg kg-1 while the subsoil values ranged from 25.0 mg kg-1 to 3392.7 mg kg-1 with a mean of 570.0 mg kg-1. The surface amorphous manganese oxide values ranged from 41.70 mg kg-1 to 325.0 mg kg-1 with a mean of 261.0 mg kg-1. The subsoil results ranged between 20.8 mg kg-1 and 1583.3 mg kg-1 to give a mean of 378.0 mg kg-1. With these concentrations of manganese and iron oxides in these soils, supplemental phosphorus especially after liming during cultivation is recommended for optimum crop yield. Nigerian Journal of Soil Science Vol.4 2003: 41-49

Selective chemical extraction and separation of Mn, Fe oxides and organic material in natural surface coatings: application to the study of trace metal adsorption mechanism in aquatic environments

Mn-Fe binary oxide adsorbents are prepared by co-precipitation method for removal of arsenic from contaminated drinking water. Arsenic adsorption ability is influenced by pH of reaction solution and Mn/Fe mole ratio. Adsorbent M/F4/6-12 with amorphous phase shows higher arsenic removal of 99.9 %. The adsorption isotherm followed Langmuir equation, indicating that it could effectively remove arsenic even from contaminated drinking water in which arsenic concentration is markedly low. The maximal adsorption capacity of As(III) and As(V) are 54.1 mg/g and 49.5 mg/g, respectively.