Assessing the performance of phosphorus-saturated ochre as a fertilizer and its environmental acceptability

Abstract. Flooding of abandoned coal mines often causes discharges of iron-rich drainage water into the environment. Treatment of these discharges results in the formation of ochre (hydrous iron oxides) for which no end-use has been identified. Ochre effectively adsorbs phosphate from solution and thus could be used for remediation of waste waters. The resulting P-enriched ochre could then potentially be recycled as a P fertilizer. Pot and field experiments were set up to assess performance and environmental acceptability of ochre in this role, using grass and barley as test crops, as well as birch and spruce tree seedlings. Soils and plant materials were analysed for total and available P, total metals and pH. Results showed that P-saturated ochre functioned as a slow-release P fertilizer, and in the short term was as effective as conventional P fertilizer in maintaining crop yields. It also raised soil pH, and did not pose any significant problem through introduction of potentially toxic trace metals into the soil.     

Ochre deposits and associated bacteria in some field drains in Scotland

Drainage systems installed in highly organic soils, with the ground water pH near to neutral and affected by iron ochre deposition, were studied at six sites in Scotland. The iron ochre was composed of iron–encrusted filamentous bacteria entrapping amorphous material. The filamentous bacteria were identified as Gallionella spp., Sphaerotilus natans, Leptothrix ochracea and Leptothrix pseudo–ochracea . Heterotrophic iron–oxidizing bacteria were also present in the iron ochre, but Thiobacillus ferroxidans was not isolated. Differences in the proportion of species could not be correlated with peat type or the age of the drainage system. Sulphate reducing bacteria and bacteria capable of reducing Fe³⁺ were also isolated from the drainage water.
A preliminary investigation of the importance of biotic factors in the kinetics of Fe²⁺ oxidation showed that the rate of Fe²⁺ oxidation in unfiltered drainage water, was about twice the rate in filtered water, at 10°C. Incubations over a range of temperatures showed that the differences in rates were greatest at low temperatures.     

OCHRE FORMATION IN FIELD DRAINS IN PYRITIC SOILS

Two distinct forms of ochre are known to occur in field drains. One form, which is most common in wet peaty areas, is caused by the growth of filamentous iron bacteria. The second form is associated with Thiobacillus ferrooxidans, and occurs where the soil contains pyrite. Contrary to previous reports, liming decreases the rate at which pyrite is oxidized in soil and, by decreasing the amount of iron entering the drains in a given period, should significantly increase the active life of the drainage system. Regular liming is probably preferable to a single large initial dressing.     

Characteristics of ferrous iron forms in paddy soil with reference to development of the soil profile

It is considered that transformation of iron compounds owing to alternation of submergence and drainage exert a complicated influence on physico-chemical properties of paddy soils and that subsequent changes in physicochemical properties play an important role in the development of paddy soil profile, for example gley formation, occurrence of iron mottling etc. Ferrous iron in waterlogged condition, however, exists in many complex forms, and is under physico-chemical equilibrium in conjunction with the environmental soil condition. In the previous paper, the authors have suggested that ferrous iron status in submerged condition is closely related to the characteristics of genetic soil types from their experiment on fractionation of inorganic ferrous iron (8).     

Distribution of acidophilic iron- and sulphur-oxidizing bacteria in a sulphur and iron sulphide mine

Abstract

The numbers of acidophilic iron- and sulphur-oxidizing chemolithotrophic bacteria, as well as certain physical and chemical environmental factors, were examined in weathered iron sulphide ores and acid mine drainage waters at the abandoned Matsuo sulphur and iron sulphide mine in Japan. In the ores, the population of iron-oxidizing bacteria was smaller than that of sulphur-oxidizing bacteria. On the other hand, an inverse relationship between iron- and sulphur-oxidizing bacteria was observed in the acid mine waters. The marked differences between the ores and acid mine waters in their numbers of iron- and sulphur-oxidizing bacteria, may reflect the availability and content of the respective energy sources: ferrous iron and elemental sulphur.     

Coupled diffusion and oxidation of ferrous iron in soils. I. Kinetics of oxygenation of ferrous iron in soil suspension

The kinetics of oxidation of iron in an aqueous suspension of a thoroughly reduced low-humus tropical rice paddy soil were followed by measuring the extractable ferrous iron in the whole suspension and in the solution. Three-quarters of the initial ferrous iron was oxidized rapidly (first-order rate constant = 9.2 × 10^?5 s^?1). The subsequent reaction was slow (first-order rate constant = 9.4 × 10^?7 S^?1) and was not studied in detail. The pH fell from 6.6 to 4.9 over the course of the fast reaction. In further experiments the rate of oxidation was followed at constant pH values in the range 6.5 to 4.5. It was concluded that the oxidation of adsorbed iron was much faster than solution iron, and that the adsorbed iron was oxidized at a rate that was nearly independent of the pH. During the reaction some ferrous iron is adsorbed on the ferric hydroxide formed. The proportion of the remaining ferrous iron adsorbed on ferric hydroxide rather than the original exchange surfaces was high at pH > 6.0 and low at pH < 5.0. The rate of oxidation of the ferrous iron was similar whether it was adsorbed on exchange sites or on the ferric hydroxide formed. Since the rate of oxidation of the iron adsorbed on ferric hydroxide was very much slower than that on ferric hydroxide formed in the absence of soil, it is suggested that the rate in soil may be controlled by diffusion of oxygen to the adsorption sites.     

The Effectiveness and Feasibility of Using Ochre as a Soil Amendment to Sequester Dissolved Reactive Phosphorus in Runoff

Incidental losses of dissolved reactive phosphorus (DRP) to a surface waterbody originate from direct losses during land application of fertilizer, or where a rainfall event occurs immediately thereafter. Another source is the soil. One way of immobilising DRP in runoff before discharge to a surface waterbody, is to amend soil within the edge of field area with a high phosphorus (P) sequestration material. One such amendment is iron ochre, a by-product of acid mine drainage. Batch experiments utilising two grassland soils at two depths (topsoil and sub-soil), six ochre amendment rates (0, 0.15, 1.5, 7.5, 15 and 30 g kg⁻¹ mass per dry weight of soil) and five P concentrations (0, 5, 10, 20 and 40 mg L⁻¹) were carried out. A proportional equation, which incorporated P sources and losses, was developed and used to form a statistical model. Back calculation identified optimal rates of ochre amendment to soil to ameliorate a specific DRP concentration in runoff. Ochre amendment of soils (with no further P inputs) was effective at decreasing DRP concentrations to acceptable levels. A rate of 30 g ochre kg⁻¹ soil was needed to decrease DRP concentrations to acceptable levels for P inputs of ≤10 mg L⁻¹, which represents the vast majority of cases in grassland runoff experiments. However, although very quick and sustained metal release above environmental limits occurred, which makes it unfeasible for use as a soil amendment to control P release to a waterbody, the methodology developed within this paper may be used to test the effectiveness and feasibility of other amendments.     

Aufnahme und Sorption von zwei- und dreiwertigem Eisen durch Sonnenblumenpflanzen (Heliantus annuus L.)

Uptake and adsorption of ferrous and ferric iron by sunflower plants The uptake of iron by 13 day-old sunflower seedlings in water culture experiments was studied using FeCl₃, Fe-citrate and ferroammoniumsulfat (Mohr'sches Salz) in the-nutrient solution. By raising the N-, K- and Ca-content and lowering the P-content of the nutrient solution at the same time the iron content of the exudate in the FeCl₃-treatment was increased up to 200 %. In the case of Fe-citrate, similar values were obtained only under aeration conditions of the nutrient medium. Application of iron as ferrous sulfate led to an increase of the iron content in the exudate and in the aerial plant parts amounting to about 200 and 400 %. respectively over that of the FeCl₃ treatment. After 15 hr-uptake, most of the iron, taken up by the seedlings was in an unexchangeable form in the root system. The results give a further evidence for the peferential uptake of iron in the ferrous form.     

THE OXIDATION OF IRON SULPHIDES IN SOILS IN RELATION TO THE FORMATION OF ACID SULPHATE SOILS, AND OF OCHRE DEPOSITS IN FIELD DRAINS

Aerating pyritic soils causes acidification and the forrnation of acid sulphate soils, or cat-clay. The Oxidation of pyrite in soils is associated with the deposition in tile drains of a form of ochre quite distinct from that formed by the action of filamentous iron bacteria. Pyrite-derived ochre results from the action of Thiobacillus ferrooxidans, which, below pH 3.5–4.0, catalyses the Oxidation of Fe²⁺ and pyrite. In soils less acid than c. pH 4, pyrite oxidizes relatively slowly by chemical reactions to Fe²⁺ and SO²₄^?. Under these conditions iron enters the drains as Fe²⁺ and is there oxidized by T. ferrooicidans and deposited as hydrated ferric oxide. Once the soil becomes acid enough for T. ferrooxidans to multiply, the rate at which pyrite oxidizes increases several-fold, and at c. pH 3 iron appears in the drainage water in the ferric form. Liming seems to decrease the rate of Oxidation.     

四川盆地西部漂洗土壤区水体铁元素的分布特征

铁是水质监测的重要指标。为了弄清四川盆地西部漂洗土壤区不同水环境中铁的形态和含量、浅层潜水的季节动态及其形成原因,为该区土、水资源合理利用提供一定参考,于不同时期在四川省名山县漂洗土壤区采集潜水、池塘水、稻田和茶园沟渠地表水、土壤孔隙水及相应的土壤样品,分析了其铁的形态和含量及相应的理化性质。结果表明,从潜水和土壤孔隙水来看,潜水总铁和亚铁含量（分别为0.30、0.08mg·L^-1）均为最低,稻田孔隙水总铁和亚铁含量（分别为2.92、1.13mg·L^-1）均为最高,茶园孔隙水总铁和亚铁含量（3a生以下茶园分别为1.25、0.92mg·L^-1,6a生以上茶园分别为2.66、0.65mg·L^-1）居中;就稻田和茶园的土壤孔隙水与沟渠地表水比较而言,孔隙水总铁和亚铁含量总体上高于沟渠地表水相应的总铁和亚铁含量;潜水总铁和亚铁含量分别变动在0~0.86mg·L^-1和0~0.36mg·L^-1之间,其季节动态在不同区域间存在一定差异,与其所处地形部位及地表径流条件、离居民房屋和畜禽圈舍远近、土壤pH、有机质和铁元素的形态和含量、土地利用方式及作物种植年限、天气状况及水井自身氧化还原电位等条件有关。     

A new method for determining ferrous iron in paddy soils

Introduction

To make clear the chemical behavior of free iron compounds in paddy soils, it is necessary to find an accurate and rapid method for determining ferrous iron in waterlogged paddy soils. Several methods^1,2,3) have been proposed for this purpose, most of which use dilute acids, such as sulfuric and hydrochloric acid, as extracting reagents. According to the writers' experience, however, these methods seem to be inadequate. The reason is that the acid solutions extract not only ferrous iron, but also ferric iron and reducing substances from soils, and the latter two react immediately in the extract to produce ferrous iron, thus we obtain larger value for ferrous iron than the one actually existing in soils. The writers have found that acetate buffer of pH 2.8 is a very suitable extractant for ferrous iron, and they have been able to establish a new method for the determination of ferrous iron in soils using this buffer. The experimental details will be given in this paper.     

Nitrite stability influenced by iron compounds

The decomposition of nitrite was studied in the presence of (1) different amounts of ferrous iron and (2) an amorphous and a crystalline (haematite) iron product at different pH and Eh conditions. It was found that ferrous iron positively influenced the nitrite decomposition. Even at pH 6, where self-decomposition is excluded, some nitrite was decomposed. It was shown that at all studied pH values the second order decomposition rate increased as the amount of ferrous iron increased. From the calculation of the activation energy it was found that the dependence of the rate constant on temperature increased when the medium was more acid, or when the amount of Fe²⁺ increased at the same pH. The nitrite half-life was longest at pH 6, 25°C and 200 mg Fe²⁺ l^?1; it was shortest at pH 4, 30°C and 800 mg Fe²⁺ l^?1. The experiments with Fe²⁺ derived from solid iron compounds showed that all conditions favouring a high amount of ferrous iron in solution, such as low redox potential, low pH, amorphous or less crystalline material, enhanced nitrite decomposition.     

Inhibition of iron uptake from iron salts and chelates by divalent metal cations in intestinal epithelial cells

Iron chelates, namely, ferrous bisglycinate and ferric EDTA, are promising alternatives to iron salts for food fortification. The objectives of this study were to compare iron uptake from radiolabeled ferrous sulfate, ferrous ascorbate, ferrous bisglycinate, ferric chloride, ferric citrate, and ferric EDTA by Caco-2 cells with different iron status and in the presence of divalent metal cations. Iron-loaded Caco-2 cells, with reduced DMT-1 and elevated HFE mRNA levels, down-regulated uptake from ferrous ascorbate and bisglycinate but not from ferric compounds. Nevertheless, iron uptake from all compounds was markedly inhibited in the presence of 100-fold molar excess of Co2+ and Mn2+ cations, with ferrous compounds showing a greater percent reduction. Our results suggest that ferrous iron is the predominant form of iron taken up by intestinal epithelial cells and the DMT-1 pathway is the major pathway for uptake. Iron uptake from chelates appears to follow the same pathway as uptake from salts.     

海绵铁缓解污水厌氧氨氧化反应器中硝酸盐积累的效果

该文旨在通过向厌氧氨氧化反应器中投加海绵铁来减轻厌氧SBR(sequencingbatchreactoractivatedsludge process)反应器中的硝酸盐积累,试验研究了海绵铁与硝酸盐和亚硝酸盐在静态条件下的反应。在静态条件下,部分硝酸盐和亚硝酸盐被海绵铁还原成了氨。对比动态试验表明投加海绵铁可以将SBR出水硝酸盐质量浓度控制在25～30 mg/L左右。相同条件下不投加海绵铁出水硝酸盐质量浓度不断累积,直至超过55 mg/L。这可能是由于铁将硝酸盐还原为亚硝酸盐并与厌氧氨氧化进行了耦合。采用高通量测序发现投加海绵铁的反应器中厌氧氨氧化菌在微生物群落中所占的比例(22.55%)约为不投加反应器(8.85%)的3倍,表明投加海绵铁有利于反应器中厌氧氨氧化(ANAMMOX)菌的生长和厌氧氨氧化反应器的启动。     

A MÖSSBAUER SPECTROSCOPIC STUDY OF THE EFFECT OF pH ON THE REACTION BETWEEN IRON AND HUMIC ACID IN AQUEOUS MEDIA

Mössbauer specttoscopy has been used to provide information on the effect of pH on the nature of the complexes formed between iron and humic acid. At an initial suspension pH greater than 3 the iron occurs in the ferric form, although it is difficult to assess to what extent it is in combination with organic matter. On lowering the pH, iron is reduced with a considerable proportion of the ferrous iron entering solution, partly as a solvated ion and partly as complex forms. Raising the pH leads to re-oxidation and the precipitation of a considerable proportion of the iron in an inorganic form with Mossbauer parameters similar to those of β-FeOOH. No evidence was obtained for Fe(III) in solution or for Fe(II) in any form at pH values greater than 4.     

水稻土中氧化还原过程的研究——Ⅷ.水溶态亚铁的区分

在上一工作(保学明等,1964)中,已证明当土壤中加入大量有机质并溃水时,水溶态亚铁可以高达每100克土数十毫克,占亚铁总量的10-25%,水溶液中的亚铁浓度达百万分之一二百甚至更高.由于水溶态亚铁是亚铁中最活泼的部分,对于土壤性质和水稻生长具有直接影响,所以关于水溶态亚铁的性质的研究,应该具有重要意义.     

Visualisation of oxidizing power of rice roots and of possible participation of bacteria in iron deposition

The oxidizing power of rice roots was observed in narrow transparent root boxes containing different media. Plants precultivated in nutrient solution were embedded in semisolid agar medium to observe oxidation of ferrous iron cations and leuco methylene blue as well as solubilization of ferrous sulfide. In the presence of ferrous sulfate reddish brown coloration due to formation of ferric oxide/hydroxide was observed around the roots and on the root surface during one day of incubation. When agar medium blackened by ferrous sulfide was used, the root zone became transparent. Within a few hours leuco methylene blue was oxidized to methylene blue on and near the roots. Furthermore, seedlings were grown in agar medium containing ferrous sulfide inoculated with soil filtrate. Besides diffuse ferric iron precipitation, iron was also deposited on spherically shaped structures in the rhizosphere and near the agar surface as well as in slimy layers appearing on the root surface. The spherical structures and slimy layers were obviously bacterial colonies extending with time. As the roots grew old, parts of them turned black. In the rhizosphere, black spots occurred resembling colonies of sulfate-reducing bacteria. Rice was also grown in sand supplemented with nutrients and iron sulfide. While root growth was straight in agar, it was twisted in the sand medium. Again, heavy ferric iron deposition occurred on the root surface. On older root parts the lateral roots became blackish. The results suggest participation of bacteria in ferric iron deposition in the rhizosphere of rice.     

Heavy Metal Accumulation in Plant Species Indigenous to a Contaminated Portuguese Site: Prospects for Phytoremediation

Acid rock drainage (ARD) often contains ferrous iron, sulphate and high concentrations of trace elements detrimental to the environment. Future costs will be enormous if the problem is not treated today. Simple and cost-effective methods for remediation of historical mine sites are therefore desired. In this study, three mine waters were mixed with alkaline ash leachates, and the fate of trace elements from both the mine waters (Cd, Cu, Pb, Zn, Ni and Co) and the ash leachates (Cr and Mo) was studied. Addition of ash water precipitates hydrous ferric oxides (HFO) and hydrous aluminium oxides (HAO) induced trace element sorption and coprecipitation. Composition of the formed HFO/HAO mix determines efficiency of the sorption and the relative order of sorption for different trace elements. Sorption occurred much earlier (often one pH unit or more) in a system with high iron concentrations compared to systems with lower iron concentrations. Removal of cadmium and zinc was low, below pH 8, if the amount of precipitates was low. Using ash for generation of alkaline water may be a problem with regard to chromium and molybdenum. This study shows that it is possible to avoid problems with molybdenum by keeping the final pH around 7, and chromium(VI) from the ash water will be reduced into chromium(III) and precipitated as the hydroxide in the presence of iron(II). Results imply that it is possible to also use fly ashes in alkaline leach beds in order to neutralize ARD followed by precipitation and sorption of trace elements.     

In vitro iron availability from iron-fortified whole-grain wheat flour

Iron deficiency is the most common nutritional disorder worldwide. Iron fortification of foods is considered to be the most cost-effective long-term approach to reduce iron deficiency. However, for fortified foods to be effective in reducing iron deficiency, the added iron must be sufficiently bioavailable. In this study, fortification of whole-grain wheat flour with different sources of iron was evaluated in vitro by measuring the amount of dialyzable iron after simulated gastrointestinal digestion of flour baked into chapatis and subsequent intestinal absorption of the released iron using Caco-2 cell layers. The dialyzability of iron from iron-fortified wheat flour was extremely low. Additions of 50 mg/kg iron to the flour in the form of ferrous sulfate, Ferrochel amino acid chelate, ferric amino acid chelate taste free (TF), Lipofer, ferrous lactate, ferrous fumarate, ferric pyrophosphate, carbonyl iron, or electrolytic iron did not significantly increase the amount of in vitro dialyzable iron after simulated gastrointestinal digestion. In contrast, fortification of flour with SunActive Fe or NaFeEDTA resulted in a significant increase in the amount of in vitro dialyzable iron. Relative to iron from ferrous sulfate, iron from SunActive Fe and NaFeEDTA appeared to be 2 and 7 times more available in the in vitro assay, respectively. Caco-2 cell iron absorption from digested chapatis fortified with NaFeEDTA, but not from those fortified with SunActive Fe, was significantly higher than from digested chapatis fortified with ferrous sulfate. On the basis of these results it appears that fortification with NaFeEDTA may result in whole-grain wheat flour that effectively improves the iron status.     

亚铁对水平潜流人工湿地污染物去除能力的分层效应影响

通过模拟试验,考察并探讨不同浓度亚铁添加对水平潜流人工湿地中氮和COD去除能力的影响以及作用机理。结果表明:添加亚铁有利于水平潜流人工湿地各层中总氮、硝态氮和铵态氮的去除效果,而且添加亚铁浓度为50mg/L的人工湿地系统优于其他各处理组,但是过高的亚铁添加又限制了氮的去除效果,尤其是对下层铵态氮的去除能力有抑制作用,但是均高于对照组,而且亚铁添加影响了湿地系统这3种无机形态的氮分层效应。亚铁的添加促进试验初期人工湿地对COD的去除能力,在一定程度上影响了各层COD的去除效果。亚铁离子进入人工湿地后,系统中各层铁元素浓度迅速下降,但是由于铁元素的变价结构及其易水解特性,使得各处理系统出水pH先增加后趋于平稳,且下层pH低于上层和中层,同时也使得系统各层氧化还原电位(ORP)发生变化。亚铁添加促进了湿地系统中ORP的分层,却减缓了ORP的下降。