采用草酸和紫外光催化法处理赤泥(英文)

利用草酸作为浸出剂以除去拜耳法残渣赤泥中的氧化铁,从而提高赤泥的工业应用价值,同时对草酸浸出液进行紫外光照射,将草酸铁还原成草酸亚铁沉淀,实现草酸溶液循环再利用。实验结果表明,在75°C下,赤泥在1mol/L草酸溶液中浸出2h,氧化铁的浸出率可达到96%,浸出后赤泥中氧化铁的含量由17.6%降低至小于1%。在紫外光照催化作用下,1h内浸出液中90%以上的草酸铁转变成草酸亚铁沉淀,剩余草酸可循环再利用。该草酸亚铁为β-FeC2O4.2H2O。对UV催化沉淀的机理进行讨论分析。     

Adsorption behavior of Sb(III) in single and binary Sb(III)—Fe(II) systems on cationic ion exchange resin: Adsorption equilibrium,kinetic and thermodynamic aspects

The present study dealt with the mechanism of competitive adsorption of Sb(III) and Fe(II) ions from a copper-containing aqueous solution on Purolite S957, a commercially available cationic ion-exchange adsorbent. Experiments were conducted using aqueous copper sulfate solutions containing either single or conjoint ions, using both sedentary and batch adsorption techniques to ascertain the sensitivity of the adsorption process to variation in pH, mass of resin, contact time, and temperature as well as establishing the optimal range of variables for maximum ion removal. The data from single ion adsorption tests were fitted by non-linear regression techniques to Henry, Langmuir, Freundlich, Temkin, and Dubinin—Radushkevich isotherm models. Freundlich isotherm for Sb(III) and Freundlich and Henry models for Fe(II) solutions best express the adsorption equilibrium data; while for binary ion electrolytes, the extended Freundlich model fitted the data satisfactorily. The kinetic model adequately describing adsorption was shown to be the pseudo-first-order, underscoring the dominant role of physical adsorption playing in the process. Thermodynamic parameters for the adsorption process reveal differences in the Sb(III) adsorption mechanism from single ion and Sb(III)—Fe(II) containing electrolytes. The adsorption of Sb(III) alone is endothermic, whereas the process becomes exothermic in the Sb(III)—Fe(II) system.     

Coprecipitation thermodynamics of iron(II-III) hydroxysulphate green rust from Fe(II) and Fe(III) salts

Iron(II-III) hydroxysulphate GR(SO₄²⁻) was prepared by precipitating a mixture of Fe(II) and Fe(III) sulphate solutions with NaOH, accompanied in most cases by iron(II) hydroxide, spinel iron oxide(s) or goethite. Its [Fe(II)]/[Fe(III)] ratio determined by transmission Mössbauer spectroscopy was 2±0.2, whatever the initial [Fe(II)]/[Fe(III)] ratio in solution. Proportion of Fe(OH)₂ increased when the initial [Fe(II)]/[Fe(III)] ratio increased, whereas proportion of α-FeOOH or spinel oxide(s) increased when this ratio decreased. GR(SO₄²⁻) is metastable vs. Fe₃O₄ except in a limited domain around neutral pH. Precipitation from solutions containing both Fe(II) and Fe(III) dissolved species seems to favour GRs formation with respect to stable systems involving iron (oxyhydr)oxides.     

Kinetics of Pit Initiation at the Alloy Fe5Cr

Pit initiation at the passive alloy Fe5 Cr was studied and compared to the results obtained with pure iron. At constant electrode potential the addition of chloride to the solution increases the dissolution rate of Fe(III). Above the critical pitting potential the first pits develop during a time of incubation after addition of chloride. The total current density and the dissolution rate of Fe(II) rise simultaneously and suddenly. The logarithm of the times of incubation increase linearly with the reciprocal of the difference between the actual electrode potential and the pitting potential. Galvanostatic experiments show that, with Fe 5 Cr as with iron, chloride catalyzes the transfer reaction of oxygen ions at the interface between oxide and electrolyte more strongly than the dissolution of Fe(III). Addition of chloride. The total current density and the dissolution rate of Fe(II) rise simultaneously and suddenly. The logarithm of the times of incubation increase linearly with the actual electrode potential and the pitting potential. Galvanostatic experiments show that, with Fe5Cr as with iron, chloride catalyzers the transfer reaction of oxygen ions at the interface between oxide and electrolyte more strongly than the dissolution of Fe(III). Addition of Chromium lowers the current efficiency of Fe(III) dissolution and favors oxide growth. The ionic conductivity of the passivating oxide is not significantly changed by chloride but is lowered by chromium. Fluctuations connected to the onset of pitting are slower with Fe 5 Cr than with iron.     

含H2S的硫酸溶液中Cl^—对铁阳极溶解的影响

应用电化学动电位扫描方法研究了在含低浓度Ｈ２Ｓ的硫酸溶液中Ｃｌ＾－对铁阳极溶解的影响。采用量子化学计算方法,得到了Ｃｌ＾－与ＨＳ＾－在电极表面吸附的稳定形态,优化计算了阳极电位下Ｃｌ＾－与ＨＳ＾－竞争吸附的总能量,结合能和Ｆｅ原子净电荷分布。     

Synthesis and Properties of Dispersed Systems Based on Elemental Iron and Tungsten Obtained through Precipitation on Aluminum in the Presence of Citric Acid

The process of coprecipitation of iron and tungsten from aqueous solution containing Fe(III) and tungstate ions in the presence of citric acid has been investigated. The element and phase composition of precipitates in the Fe–Al–W system has been evaluated. The synthesized precipitate particles were shown to repeat the shape and size of the initial aluminum matrix, have a developed surface, and comprised solid tungsten solutions in iron in the presence of the elemental aluminum phase.     

嗜酸氧化亚铁硫杆菌浸出黄铜矿中氧化还原电位、黄铁钾钒和胞外聚合物的关系和影响(英文)

在合成的胞外聚合物(EPS)溶液中,研究不同起始总铁量、不同Fe(III)与Fe(II)摩尔比条件下嗜酸氧化亚铁硫杆菌浸出黄铜矿过程中pH、电位、可溶性铁离子和Cu2+浓度随浸出时间的变化。结果表明:当溶液电位低于650mV(vsSHE)时,因细菌产生的EPS可通过絮凝黄铁钾钒延缓污染,即使铁离子浓度达到20g/L,黄铁钾钒对细菌浸出黄铜矿的阻碍作用也不是致命的,但随着铁离子浓度的增加而增加;细菌氧化的铁离子容易吸附在黄铜矿表面的EPS表层,有黄铁钾钒的EPS层是弱离子扩散壁垒,细菌通过把EPS空间内外的Fe2+氧化成Fe3+,进一步创造高于650mV的电位,导致EPS层离子扩散性能的快速恶化,严重地和不可逆地阻碍生物浸出黄铜矿。     

The retentiveness of ceramic microfiltration membranes with respect to ferric iron ions

The retentiveness of microfiltration membranes based on crystalline silicon dioxide with an average pore size of 3 μm with respect to ferric iron ions Fe(III) is studied. A correlation between the state of Fe(III) in water solutions and the degree of retention, as well as the membrane surface origin and structural properties, is found. A comparative assessment of the retentiveness of the microfiltration ceramic and ultrafiltration polyamide membranes—with an average pore size of 7.8 nm—with respect to Fe(III) ions is made.     

Acidithiobacillus ferrooxidans enhanced heavy metals immobilization efficiency in acidic aqueous system through bio-mediated coprecipitation

This study investigated the promotion effect of A. ferrooxidans on complex heavy metals coprecipitation process. A. ferrooxidans significantly enhanced the ferrous oxidation, which also promoted the formation of iron-oxyhydroxysulphate. Cu(II) concentration reduced to 0.058 mmol/L in A. ferrooxidans inoculated system, and Cd also reduced to the lowest concentration (0.085 mmol/L). Pb was mainly immobilized as anglesite and iron-oxyhydroxysulphate promoted the removal of remanent Pb in solution. The precipitates are characterized by XRD, SEM, and FTIR analysis. The main component of the iron-oxyhydroxysulphate was well crystallized jarosite. A. ferrooxidans contributed to the formation of schwertmannite in later monovalent cation lack stage. Higher ferrous iron oxidation rate and Fe(III) supply rate in A. ferrooxidans inoculated system facilitated polyhedron crystal formation and the increase of particle diameter. Complex heavy metals could be incorporated into iron oxyhydroxysulphate crystal, and efficiently removed from acidic wastewater through A. ferrooxidans mediated coprecipitation.     

Inhibitoren der Korrosion (14). pH-Wert-Änderungen in Suspensionen von Eisen in 0, 2 m NaCl-Lösungen unter den Bedingungen der Sauerstoffkorrosion

Corrosion inhibitors (14) pH variations in suspensions of iron in 0.2 m NaCl solutions under conditions of oxygen corrosion The pH of iron suspensions is deter-mined in a suitable apparatus under varying reaction conditions. The results are as follows:

• 1 In a suspension of 25 grs of carbonyl iron powder in 100 ml of pure water there is no pH variation, neither under nitrogen nor under oxygen.
• 2 When 25 g of carbonyl iron powder are introduced under 100ml 0.2 m NaCl solution, the pH value rises from 6.60 to 9.4-9.5 within three to eight minutes.
• 3 Determination of the dissolved Fe(OH)₂ quantity and conversion of the latter to pH units reveals, that the pH rise is due to (a) an exchange of OH^?-ions for CL^?-ions at the boun.

     

Film Growth and Dissolution of Iron Ions at passive iron in neutral solutions containing chloride

The passivating oxide layer on iron grows by transfer of oxygen ions from the solution into the oxide. As expected theoretically, the dissolution rate of iron ions increases with the growth rate of the layer. In neutral solution the current efficiency for oxide growth is larger than in acid solutions. By addition of chloride to the solution the current efficiency is further enhanced, because chloride catalyzes the transfer of oxygen ions more strongly than the transfer of iron ions. Chloride in the solution does not change the ionic conductivity of the oxide to a measurable extent. During galvanostatic polarization in solutions containing chloride, fluctuations of the potential and of the dissolution rate of Fe(II) are observed. The frequency of the fluctuations increases with current density and chloride concentration.     

Untersuchung des Passivierungsmechanismus von Eisen in Phosphatelektrolyten an erosiv beanspruchten Oberflächen

Investigation into the passivation mechanism of iron in phosphate electrolytes on surfaces exposed to erosive attack On iron electrodes in neutral phosphate electrolytes by continuous solid particle impingement a reaction layer is formed within the transition potential region under anodic polarization. XPS and AES investigations show that the reaction layer formed under impingement will be replaced by an oxide layer during the transition into the passive state under simultaneous decrease of the layer thickness. The active/passive transition in phosphate electrolytes may be attached to the equilibrium potential of the reaction . According to this thermodynamic interpretation of both the active/passive transition and the passive/active transition, respectively on iron in presence of phosphate ions may be described as the Fe(II)/Fe(III)-redox reaction with two solid phases, the iron(II)-phosphate phase and the iron(III)-oxide phase. The increase of the interfacial dynamic processes at the solid/liquid interface causes in consequence of the solid particle impingement that thermodynamic laws govern the course of reactions.     

Untersuchungen zum Aktiv/Passiv-Übergang von nichtrostenden Chromnickelstählen in organisch wäßrigen Medien. Teil 3. Resultate der Impedanzmessungen und Passivierungsmodell einer Legierung

Investigations into the active/passive transition of 304 stainless steel in organic media containing water and hydrogen chloride Part 3. Results of the impedance measurements and passivation model of an alloy Steady state polarization curves and electrode impedances were measured during the active/passive transition of type 304 stainless steel in dearated ethanolic solution containing hydrogen chloride and different amounts of water. The passivation potential and the critical current density for passivation strongly depend on the water content of the solution. The impedance measurements in the active/passive transition show the same sequence of diagrams independent of the water content of the solution. They indicate the onset of passivation before the maximum current density and show two time constants related to two different passivating species on the alloy surface. The experimental results were interpreted on the basis of a reaction model with parallel dissolution and passivation mechanism of the iron and the chromium compound of the alloy. The resulting total surface composition (related to the steady-state polarization curves) can be described with a reaction model of iron–the alloy behaviour is that of pure metal. The fundamental passivation reaction is described as a potential dependent equilibrium between adsorbed Me(II)- and passivating Me(III)-hydroxide, water molecules being directly involved in the formation of this primary passivating film. In the case of stainless steel this primary passivating film mainly consists of chromium (III) adsorbates. Finally, a general model for the passivation is proposed: The passivation of a pure metal or of an alloy can be understood as the coupling of the stepwise deprotonation of the water molecules at the interface metal/solution and the formation of a high cation charge density in this adsorbed hydroxide/oxide film to build up the passive layer. The effect of water content, pH, adding of passivating species to the solution or the alloying with chromium on the passivation potential and the critical current density thus can be explained.     

The role of oxygen in the interaction of emeraldine base polyaniline with Cu(II) or Fe(III) ions in NMP solution

The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV–vis–NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role of O₂ and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0 mmol L⁻¹ EB-PANI with 0.8, 2.0 and 20 mmol L⁻¹ Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence of O₂, PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N₂ atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O₂, and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N₂ and, further, the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O₂ and, so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs.     

The separation and concentration of iron from zinc process solutions

In order for solvent-extraction technology to be acceptable in the zinc industry as an alternative to existing jarosite precipitation circuits, iron must be cleanly separated and concentrated into a feed stream suitable for downstream iron by-product recovery. In this article, the use of OPAP, a mixed extractant consisting of mono- and di-octylphenyl phosphoric acids, is described as a potentially suitable extractant to selectively extract Fe(III) from concentrated ZnSO₄(90 g/l zinc)/H₂SO₄(50 g/l) solutions, followed by stripping of Fe(III) with 4–6 N HCl. OPAP was found to exhibit very low solubility/degradation characteristics (similar to D2EHPA) and excellent loading characteristics with minimal zinc and sulfate co-extraction. OPAP seems to have the lowest sulfate carryover than any other extractant previously proposed for iron extraction from strong acidic solutions. In terms of stripping, a 70 g/l Fe(II) (as FeCl₂)/6 N HCl solution was found to be effective in producting 100 g/l total iron in the strip solution. For more information, contact G.P. Demopoulos, McGill University, Department of Mining and Metallurgical Engineering, 3610 University Street, Montreal, QC, Canada H3A 2B2; (514) 398-2046; fax (514) 398-4492; e-mail george@minmet.lan.mcgill.ca.     

Transformation of green rust (Cl−) into different oxyhydroxides in aqueous solution containing molybdenum ions

To investigate the influence of the addition of molybdenum ions on the transformation of green rust GR(Cl^?) comprising Fe(II) and Fe(III) into different oxyhydroxides, suspensions of GR(Cl^?) containing molybdenum ions were oxidized by passing nitrogen gas containing oxygen through the suspensions. X‐ray diffraction (XRD) was used for identifying the solid particles formed by oxidation. The results showed that in the presence of molybdenum ions, the formation of β‐FeOOH and α‐FeOOH was enhanced as compared to that of γ‐FeOOH in the GR(Cl^?) suspensions. This implied that the molybdenum ions interacted with the chloride ions obtained from GR(Cl^?) and induced the formation of β‐FeOOH that contained chloride ions. Transmission electron micrographs of the solid particles showed that the particle size of the resulting oxyhydroxides was considerably reduced because of the addition of the molybdenum ions. The pH and oxidation–reduction potential (ORP) of the aqueous solution were also measured during the oxidation. The addition of molybdenum ions was found to cause characteristic changes in the pH and ORP in the initial stage of the oxidation.     

The role of solvent on the doping of polyaniline with Fe(III) ions

The products formed from the reaction of emeraldine base polyaniline (EB-PANI) with Fe(III) ions in N-methyl-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol media have been investigated using UV–VIS–NIR and resonance Raman (λ₀ = 632.8 and 1064 nm) spectroscopies. Through these results it was verified that the different PANI forms in solution can be formed by the suitable choice of the solvent. The behavior of Fe(III)/EB-PANI in different solvents was rationalized in terms of the interactions among Fe(III) ions, EB-PANI and solvent. In basic NMP, DMA and DMF media, the reaction of Fe(III) with EB-PANI yields EB-PANI doping giving ES-PANI and/or the EB-PANI oxidation to PB-PANI. The formation of ES-PANI is favored in DMF while PB-PANI is formed in a greater extension in NMP and DMA. In acidic m-cresol, only ES-PANI is produced in Fe(III)/EB-PANI solutions indicating the important role played by the solvent in the nature of the product.     

SOLVENT EXTRACTION OF Fe(Ⅲ) FROM SULFATE SOLUTIONS WITH TERTIARY AMINE

The tertiary amine can be used to extract Fe(Ⅲ) very effectively in the pH range resulting inpartial hydrolysis of Fe~(3+) ions.The iron extracted into the organic phase can be strippedrather easily with dilute H_2SO_4 or even with H_2O.Fe(Ⅲ) is extracted into the tertiary aminesulfate solution in the form of[(R_3NH)_2Fe(OH)(SO_4)_2]_2 complex by adduct formation.Equa-tion was derived to represent the chemical reactions involved during extraction.From theinfrared spectrum studies on the extraction species in waxy solid form separated from the so-lution,sulfate group is a bidentate ligand to the iron atom.The extraction species has beenconsidered to contain (FeOH)_2 unit based on the ultra violet spectra.The possible structure ofthe extraction species has been proposed.     

The effects of added impurities upon the electrochemical behaviour of iron in liquid ammonia solutions

Polarization data are presented for an iron electrode in liquid ammonia solutions containing ammonium salts and small amounts of the impurities: water, oxygen, nitrogen, ammonium carbamate, urea and boron trifluoride at 40°C. Additions of water up to a limiting concentration increase the iron dissolution currents in the active region. Additions of oxygen have a similar effect. The presence of either oxygen or water assists the onset of passivation and gives the phenomenon a more irreversible character.In ammonia, one mole of oxygen with two moles of Fe(II) forms a complex which can be cathodically reduced on vitreous carbon (1.0F per mol of Fe(II) or on iron (2.0F per mol of Fe(II)). On an iron cathode molecular oxygen is reduced at a rate determined by the mass transfer of oxygen, except at values of electrode potential more positive than the iron passivation potential.Nitrogen and urea do not affect the polarization behaviour of iron. Ammonium carbamate increases the iron dissolution currents obtained with nitrate or fluoroborate electrolytes but considerably inhibits the process in chloride electrolytes. Boron trifluoride profoundly increases the activity of iron towards dissolution.     

The effects of added impurities upon the electrochemical behaviour of iron in liquid ammonia solutions

Polarization data are presented for an iron electrode in liquid ammonia solutions containing ammonium salts and small amounts of the impurities: water, oxygen, nitrogen, ammonium carbamate, urea and boron trifluoride at — 40°C. Additions of water up to a limiting concentration increase the iron dissolution currents in the active region. Additions of oxygen have a similar effect. The presence of either oxygen or water assists the onset of passivation and gives the phenomenon a more irreversible character.In ammonia, one mole of oxygen with two moles of Fe(II) forms a complex which can be cathodically reduced on vitreous carbon (1.0F per mol of Fe(II)) or on iron (2.0F per mol of Fe(II)). On an iron cathode molecular oxygen is reduced at a rate determined by the mass transfer of oxygen, except at values of electrode potential more positive than the iron passivation potential.Nitrogen and urea do not affect the polarization behaviour of iron. Ammonium carbamate increases the iron dissolution currents obtained with nitrate or fluoroborate electrolytes but considerably inhibits the process in chloride electrolytes. Boron trifluoride profoundly increases the activity of iron towards dissolution.