Mode of action of ferric and ferrous iron salts in activated sludge

BACKGROUND: Both ferric iron Fe(III) and ferrous iron Fe(II) salts are commonly used for chemical phosphorus removal (CPR) in the activated sludge (AS) process but only a few studies have compared Fe(III) and Fe(II) salts regarding their effect on the physical and biological properties of AS. In this research, the units of a continuous flow laboratory‐scale AS plant were dosed with Fe(III) and Fe(II) salts at a concentration of 25 mg Fe dm^?3 feed and changes in the AS properties were measured as Fe accumulated or washed out during startup, normal operation and withdrawal of dosing. RESULTS: The morphological characteristics of the flocs showed marked differences depending on the type of ion used. Fe(II) dosed flocs were more compact, less filamentous and smaller in size than Fe(III) dosed flocs. The settleability index of the Fe(II) dosed sludge was lower than that of the Fe(III) dosed sludge. The activity of ammonium (NH₄⁺‐N) and nitrite (NO₂^?‐N) oxidizing bacteria was found to be affected by the accumulation of Fe relating products into the sludge. CONCLUSIONS: Fe(II) was a more effective flocculent than Fe(III) and this was attributed to its ability to form stronger ionic bonds with the flocs prior to its oxidation to Fe(III). A hypothesis explaining the mode of action of Fe(II) is proposed. Floc surface properties were enhanced, this being beneficial to the morphological characteristics and settleability with further implications for the operation of AS. However, the effect may be reversed at high Fe contents. Copyright © 2010 Society of Chemical Industry     

Electrochemical behaviour of pure iron in the aluminium refining electrolyte

The reduction of iron dissolved in the aluminum refining industrial melt was studied using cyclic voltammetry and chronopotentiometry. The required solutions were obtained by adding ferrous or ferric fluoride to the Gadeau electrolyte. The experimental arrangement permitted molten fluoride electrolysis as well as the introduction of additional salts under an inert argon atmosphere. Platinum, iron and graphite electrodes were used. Chemical analysis proved that the stable ionic valency of iron in the melt at 750° wasII. The reduction reaction of the Fe(II) ions was reversible and involved two electrons. The diffusion coefficient of the Fe(II) ions was calculated.     

Effect of operating conditions on iron corrosion rates in zero-valent iron systems for arsenic removal

Owing to newly established water quality standards, the use of the zero-valent iron (ZVI) method for arsenic removal is gaining attention. The spontaneous chemical oxidation of ZVI by dissolved oxygen, a complex process involving a variety of metastable ferrous–ferric intermediate species, was studied in short-term batch experiments using two different commercially available ZVI materials. Differences in corrosion rates may be attributed to the different specific reactivity of these materials. The effects of pH, ZVI loading, initial conductivity and dissolved oxygen concentration on both Fe(II) and Fe(III) kinetic profiles were investigated. ZVI corrosion rates in the presence of As(III) and As(V) were also studied. Depending on the pH, the concentrations of Fe(II) and Fe(III) are significantly influenced by the presence of As(III) and As(V). Our results may be important from a technological point of view, since it is well known that iron corrosion rates govern the generation of sites for arsenic removal.     

Effect of ferrous and ferric iron impurities on the crystallization of gypsum and sludge formation in wet-process phosphoric acid

The effect of ferrous and ferric iron on the crystallization of calcium sulfate dihydrate, the rate of filtration, and the precipitation of sludge in concentrated acid were investigated. A bench scale unit was used to simulate dihydrate plant conditions. It was found that ferrous iron was oxidized to ferric, and the behavior of the two impurities in the acid was therefore very similar. At low levels of impurities, ferrous and ferric iron improved filtration, but further additions decreased it. Sludge collected from the concentrated acid after five weeks was mainly calcium sulfate hemihydrate and anhydrate. With the addition on 0.5% and 0.75% iron impurities however, the presence of (Fe,Al) 3 KH 14 (PO 4 ) 8 ·4H 2 O was evident in electron micrographs.     

Selective removal of iron from aqueous solution using ion imprinted thiocyanato-functionalized silica gel sorbents

We combined surface imprinting technique with sol-gel process for preparing a new iron(III)-imprinted thiocyanato-functionalized silica gel sorbent using 3-thiocyanatopropyltriethoxysilane as the functional monomer, and epichlorohydrin as the cross-linking agent for the selective removal of iron(III) from aqueous solution. The iron(III)-imprinted thiocyanato-functionalized silica gel was characterized by FT-IR spectra, SEM, and the static adsorptiondesorption method. Maximum binding capacity, optimum pH, and equilibrium binding time were found to be 20.31 mg·g^?1, pH 4.2, and 20min, respectively. The relative selectivity coefficients of Fe(III)-imprinted thiocyanato-functionalized silica gel sorbents for Fe(III)/Ni(II), Fe(III)/Co(II), Fe(III)/Cd(II) and Fe(III)/Pb(II) were 11.8, 10.6, 8.2 and 9.1 times greater than the non-imprinted silica gel, respectively. The iron(III)-imprinted thiocyanato-functionalized silica gel sorbents could be used repeatedly without decreasing in their adsorption capacities significantly.     

Complementary use of IR and EPR spectroscopies for characterization of iron species in thermally treated MFI-type zeolites

Iron species formed by thermal treatment of iron- and aluminium-based ion exchanged MFI-type zeolites were investigated by IR and EPR spectroscopies and by the adsorption of NO as a probe molecule. The parallel investigation of the residual acidity by adsorption of pyridine allowed to calculate the number of acidic sites and the number of Lewis centres both in iron- and aluminium-based MFI zeolites. It was confirmed that the activation process could be divided into two regions, depending on temperature. At lower temperatures the main process is hydrolysis and thermal decomposition of precursors such as iron aquacomplexes and/or hydroxides, but at higher temperatures dehydroxylation and subsequent redox reaction, balancing the amounts of Fe(II) and Fe(III) ions, takes place. Combined EPR and IR studies showed that the process of thermal activation can be tracked over wide temperature range (from ambient temperature to 1020 K) by following the properties of both ferrous and ferric sites and implied that at least the part of Fe cations cannot be observed by neither method, suggesting they adopt a form of bulk oxide-like species.     

Application of crosslinked carboxymethyl konjac glucomannan in speciation of dissolved Fe(II) and Fe(III) in water samples

A new solid‐phase extraction technique has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in environmental water samples with a microcolumn packed with crosslinked carboxymethyl konjac glucomannan (CCMKGM) prior to its determination by flame atomic absorption spectrometry (FAAS). Various influencing factors on the separation and preconcentration of Fe(II) and Fe(III), such as the acidity of the aqueous solution, sample flow rate and volume, and eluent concentration and volume, have been investigated systematically and optimized. Fe(III) could be quantitatively retained by CCMKGM in the pH range of 3.0–7.0, then the retained Fe(III) on the CCMKGM was eluted with 5.0 mol L^?1 HCl after cleaning with 0.01 mol L^?1 HCl to eliminate Fe(II) and determined by FAAS. Total Fe was determined after the oxidation of Fe(II) to Fe(III) by H₂O₂, and Fe(II) concentration was calculated by subtracting Fe(III) from total iron. The adsorption capacity of CCMKGM for Fe(III) was found to be as high as 162.3 mg g^?1. The detection limit (3σ) for Fe(III) was 1.5 μg L^?1 and the RSD was 3.5% (n = 11, c = 20 μg L^?1) with an enrichment factor of 50. The proposed method has been applied to the speciation of iron in water samples with satisfactory results. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

还原钛铁矿中亚铁的测定

拟定了一种快速简便的差减法来测定还原钛铁矿中的亚铁,即一份试样用三氯化钛－钨蓝重铬酸钾法测出全铁的百分含量Ａ;另一份试样用ＦｅＣｌ３溶液浸取,重铬酸钾滴定法测出金属铁的含量Ｂ。实验证明,还原钛铁矿中几乎不含高价铁,故（Ａ－Ｂ）即为亚铁的百分含量     

A rapid spectrophotometric method for the determination of peroxide value in food lipids with high carotenoid content

A rapid and sensitive ultraviolet-visible spectrophotometric method for determination of peroxide value (PV) in foods with high carotenoid content (e.g., paprika oleoresin, paprika powder, red palm oil) has been developed. The proposed protocol [modified International Dairy Federation (IDF) method] was established from the IDF Fe(II)-oxidation-based spectrophotometric method, and the main one of the introduced modifications consisted of a clean-up extraction step of pigments before determining the PV by complexing Fe(III) ions with thiocyanate. Fe(II) oxidation time, reaction medium, and Fe(III)-thiocyanate complex formation time were optimized. The modified IDF method was compared with and was validated by iodometric AOAC official method with a good correlation (R ²=0.957) between data obtained by both analytical methods. The high sensitivity of the method allows the use of only about 0.010–0.015 g of sample, with a detection limit of 0.044 mequiv peroxide/kg of sample. Therefore, an improved spectrophotometric method for assessing PV in food lipids with high carotenoid content is now available and can be applied to any kind of sample, independent of oil and pigment content.     

Effect of pH on the Oxidation of Ferrous Ion and Immobilization Technology of Iron Hydr(oxide) in Fluidized Bed Reactor

Abstract

New, efficient, and a cheap method for the removal of ferrous ion from aqueous in a fluidized bed reactor was developed. Different from the adsorption process in the treatment of iron species, the immobilization of iron oxide on support media in a fluidized bed never reaches saturation. Furthermore, the immobilized iron oxide is reusable in catalysis and adsorption. Silica sand (Si) and iron oxide (SiG) were employed as support media to remove Fe(II) from aqueous in a fluidized bed reactor. The oxidation rate of Fe(II) and the immobilization rate of iron oxide are strongly depend on pH value so the variation of solution pH is considered to be the major parameter. Furthermore, the aeration effect on iron removal efficiency is investigated. 97% of total iron was removed at pH 8 in the presence of SiG and 87% of total iron was removed at pH 6 in the presence of Si. When the initial pH was adjusted to 6 and was not adjusted during the reactions, the optimum total iron removal efficiency (97%) was found. The air aeration was provided to keep the dissolved oxygen in constant. Aeration air accelerates the oxidation of ferrous ion, but does not improve the total iron removal efficiency.     

Adsorption of Fe(II) and Fe(III) from aqueous solution by using sepiolite: speciation studies with MINEQL+ computer program

ABSTRACT

As a low-cost adsorbent, sepiolite has been used for the adsorption of Fe(II) and Fe(III) from aqueous solutions. The proposed method was applied to the determination of iron in tap water, employing standard addition. The results reported with a confidence interval for the 95% confidence level show the applicability of the proposed method to water analysis. Speciation studies are very important for understanding of the toxicity, bio-availability, bio-accumulation, and transport of an element in different environmental media. In this study, Fe(II) and Fe(III) speciation was investigated for optimum concentration and pH in aqueous solutions with MINEQL+ computer program.     

自酸洗废液制磁性铁泥的氧化共沉淀工艺研究

采用氧化共沉淀方法处理总铁质量分数为3.0%~15.0%的酸洗废液,制备可用作炼铁原料的高含铁 磁性铁泥。以磁性铁泥中干基铁含量为评价指标,研究了中和温度、氧化稀释比、氧化温度、氧化pH、氧化铁比 ［n（铁3+）/n（铁2+）］、氧化气速、脱水合成pH、脱水合成稀释比、脱水合成温度等主要影响因素,得出最佳工艺条件。在中和温度为45 ℃、氧化稀释比为10.0、氧化温度为45 ℃、氧化pH为8.0、氧化铁比为1.7、氧化气速为1.2 L/min、脱水合成pH为8.0、脱水合成稀释比为10.0、脱水合成温度为107 ℃条件下,可制得铁质量分数为57.4%的磁性铁泥。该方法实用价值高,具有较好的经济和社会效益。     

用钛白副产硫酸亚铁生产氧化铁系列颜料

介绍了用钛白副产硫酸亚铁为原料，采用液相氧化法生产铁红和铁黄，氢氧化亚铁凝胶氧化法生产铁黑，氯酸钠氧化-转化法生产透明氧化铁等生产工艺的化学原理及技术要点，同时也对锌铁黄和复合铁绿这两个特殊品种作了简单介绍。     

An improved leaping detector for flow analysis applied to iron speciation in drugs

A low inner volume (ca. 64 ml) probe was built up in an injector-commutator in order to behave as a photometric leaping detector in flow analysis. It comprises a bicolour light-emitting diode (BLED), as a source of pulsed radiation in the red and green visible region, and two phototransistors as transducers. Sample injection, detector relocation, analytical signal recording, data treatment and definition of the spectral working range were computer-controlled. The feasibility of the system was initially demonstrated in the flow-injection speciation of iron, and the overall standard deviation of results was estimated as +/- 1.6 and +/- 1.4% for 1.6-4.0 mg l(-1) Fe(II) or total iron after eightfold processing of synthetic samples. The system was further applied to drug analysis: the mean deviations of results for typical samples were estimated as +/- 5.2 and +/- 3.3%, and the relative standard deviation as +/- 1.6 and +/- 1.3% for Fe(II) and total iron, respectively. Results were compared with those obtained by a conventional spectrophotometric procedure and no statistic differences at the 95% confidence level were found. In relation to an earlier system with multi-site detection, the proposed system is more stable, presenting low drift with a relative standard deviation of 0.026% and 0.039% for measurements (n=120 during 4 h of observation) with green and red emission. It is also faster with a sampling rate of 133 h(-1) and carryover problems are not found. The possibility of compensating the Schlieren noise by dual-wavelength spectrophotometry is discussed.     

Determination of mumol l level of iron (III) in natural waters and total iron in drugs by flow injection spectrophotometry

The equilibrium problems, characterized by recurring end-points, involved in the reaction of iron (III) with iodide make the batch iodometric determination of iron (III) unsuitable. Since the flow injection determination does not require attainment of steady state either for mixing of reagents or for the chemical reaction, the iodometric determination has been accurately and precisely performed using this technique in the present work. This method does not require any special reagent, including chelating agents or those which are loxic, and has a limit of detection of 0.2 mumol l(-1) (11 mug l(-1)) of iron (III). The interference of fluoride has been avoided by adding zirconyl nitrate to the test sample solution, and of copper (II) by complex formation with 2-mercaptobenzoxazole. The method has been applied to determine iron (III) in natural waters, and total iron in drugs.     

氧化铁黑中铅、镉含量检测的影响因素研究

氧化铁广泛应用于化妆品中。研究了使用原子吸收分光光度仪测定氧化铁黑中微量元素铅和镉的试验条件。试验发现甲基异丁基酮对三价铁有较高的萃取率,通过氧化过程将氧化铁黑中的两价铁转化为三价铁后,再对样品进行萃取,可消除高浓度铁离子在原子吸收分光光谱测试中对铅和镉含量的干扰。具有较高的准确度和精密度。     

Cathodic dissolution of the passive film on iron—I. Kinetics and mechanism

The cathodic reduction of passive film on iron has been investigated by the potentiodynamic and galvanostatic techniques in phosphate—borate buffer solutions of various pH values. The reduction was completed through two processes occurring at different potentials. One of them was the simultaneous reduction of ferric oxide to ferrous ion and metallic iron. This process consisted of a number of reaction steps, and the rate-determining step was the charge transfer reaction from FeOH²⁺ to (FeOH)_ads.As another process, it was unreasonable to consider the reduction of magnetite to iron which had been proposed previously; however, the reaction was possibly the reduction of Fe²⁺ to Fe.     

EFFECT OF FERROUS AND FERRIC IRON IMPURITIES ON THE CRYSTALLIZATION OF GYPSUM AND SLUDGE FORMATION IN WET-PROCESS PHOSPHORIC ACID

The effect of ferrous and ferric iron on the crystallization of calcium sulfate dihydrate, the rate of filtration, and the precipitation of sludge in concentrated acid were investigated. A bench scale unit was used to simulate dihydrate plant conditions. It was found that ferrous iron was oxidized to ferric, and the behavior of the two impurities in the acid was therefore very similar. At low levels of impurities, ferrous and ferric iron improved filtration, but further additions decreased it. Sludge collected from the concentrated acid after five weeks was mainly calcium sulfate hemihydrate and anhydrate. With the addition on 0.5% and 0.75% iron impurities however, the presence of (Fe,Al) 3 KH 14 (PO 4 ) 8 ·4H 2 O was evident in electron micrographs.     

浊点萃取分光光度法测定水样中痕量铁

建立了浊点萃取-分光光度法测定痕量铁的新方法。详细考察了溶液的pH值、螯合剂和表面活性剂浓度、平衡温度和时间等条件对浊点萃取效果的影响。该方法的线性范围为6.0~500μg/L(r=0.9996),检出限为1.58μg/L,加标回收率为98.7%~101.6%,相对标准偏差为1.3%~2.2%。该方法已成功应用于实际水样分析。