Influence of iron/aluminium ratio on the retention of lead and copper by amorphous iron–aluminium oxides

Results are presented from a study on the influence of pH on the retention of Pb and Cu by amorphous iron, aluminium and mixed iron–aluminium oxides, plus kaolinite clay. The composition (Fe/Al molar ratio) of the oxides significantly affects their surface properties. Increasing the Fe/Al ratio generally enhances the surface area although the maximum surface area is found at Fe/Al=1. The cation exchange capacity (CEC) was dependent upon pH and Fe/Al ratio, decreasing in order Fe>3FeAl>Al>Fe3Al>FeAl≫kaolinite at pH 6.3–7. The oxide points of zero charge could be divided into two groups: Fe/Al≤1 (Al, Fe3Al, FeAl; pH_ZPC=6.2–6.4) and Fe/Al>1 (3FeAl, Fe; pH_ZPC=5.3–5.8). Batch equilibrium suspension tests were conducted with Pb and Cu (single metal solutions) to assess contaminant retention capability of each oxide and kaolinite. Pb retention by mixed oxides at a particular pH increases with Fe/Al ratio in the order Fe>3FeAl>FeAl>Fe3Al>Al. The same order is observed at low to medium Cu concentrations (0.5, 2.5, 5 mmol/l) but at higher metal loading (25 mmol/l), only Fe oxide has a clearly greater retention capacity. Oxides with Fe/Al<1 (Al, Fe3Al) retain more Cu than Pb in single contaminant tests at equal metal concentration. Bulk precipitation tests (no oxides or kaolinite) combined with surface charge measurements suggest that adsorption is the dominant retention mechanism, particularly at less than pH 6. Amorphous oxides demonstrate considerably greater heavy metal accumulation capacity, specific surface area, and surface charge than kaolinite.     

化学镀Ni-P-MoS_2复合镀层的制备与表征

在铁片上,采用化学镀的方法制备了Ni-P-MoS2复合镀层.讨论了表面活性剂PEG1500质量浓度及镀液pH对镀层形貌与沉积速率的影响.观察了镀层的表面及断面形貌,分析了镀层断面的元素分布,表征了镀层的成分,结构及相组成.结果表明,所得到的化学镀Ni-P-MoS2复合镀层为非晶态结构,颗粒分散均匀,尺寸约为0.2～3.0 μm.     

Effect of polymerization method on structure and properties of cationic polyacrylamide

Acrylamide and 2‐(methacryloyloxy)ethyltrimethylammonium chloride (AM/MADQUAT) copolymers were synthesized by solution and inverse microemulsion polymerization using (NH₄)₂S₂O₈/NaHSO₃ as redox initiator at the same feed mole ratio, and their microstructure, such as sequence distribution and composition distribution, was calculated from monomer reactivity ratios of different polymerization methods. The results show that charge distribution is more uniform for copolymer prepared in inverse microemulsion than that in solution, and copolymer composition distribution is close to unity, and maintains approximately at the feed ratio. Furthermore, the influence of the two structures of cationic polyacrylamides on kaolinite floc size and effective floc density, reduction of Zeta potential and floc compressive yield stress had been investigated at pH 7. The results show that the kaolinite floc size and effective floc density are strongly dependent upon copolymer microstructure, with greater floc size and lower effective floc density being observed for copolymer prepared in inverse microemulsion than for that in solution. Copolymer microstructure has a marked effect on the Zeta potential, whose reduction in the magnitude was much greater in the presence of copolymer prepared in inverse microemulsion than that in solution. Greater compressive yield stress was achieved for the strong flocs produced by copolymer prepared in inverse microemulsion than for the weak flocs produced by that in solution. The difference in flocs compressive yield stress may be attributed to flocs structure. Therefore, in this article, a correlation between the cationic polyacrylamide structure and flocculation property for kaolinite suspension was established. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The reaction of kaolin with fluorides: I. Effect of neutral and acid sodium fluoride solutions

The reaction between kaolinite and neutral and acid sodium fluoride solutions was investigated at different temperatures and over the acid pH range. The stoicheiometric replacement of hydroxyls in the kaolinite crystal lattice by fluoride ions, as reported by earlier workers, was not confirmed. The release of hydroxyl ions into solution was due predominantly to the disruption of the kaolinite crystal lattice. In the presence of sodium ions and at pH < 7, sodium fluoro-silicate and cryolite were found as solid phases. At pH > 7, only cryolite was found as a solid phase. Small, spherical, particles were observed in all cases. These particles were believed to be amorphous silica, formed as an intermediate phase in the disruption process.     

Précipitations sélectives des métaux solubilisés biologiquement de boues aérobies d'épuration

The selective and successive precipitation resulting from the biological solubilization (Thiobacillus ferrooxidans) of sewage sludge metals was studied. At the same time, theoretical diagrams representing the solubility of hydroxides and metal carbonates (Ca, Mg, Fe, Al, Cu, Zn, Ni, Cd, Mn) and their complexes are compared to the experimental values. The pH was progressively increased by means of Ca(OH)₂- The iron hydroxide precipitate, which was the least contaminated, was obtained at pH of 3.5. The theoretical pH's for acceptable metal precipitation were identified as: Fe⁺³ at pH 3.2, Al⁺³ at pH 4.7, Cu⁺² at pH 6.9, Zn⁺² at pH 8.15, Ni⁺² at pH 8.4 and Mn⁺² at pH 9.1, and were closed to theoretical values. The hydroxide ion controls Ca, Mg and Cu solubilities. A precipitate with about 20% of Cu can be obtained at a pH of 7 after iron hydroxide was precipitated. Recovery of other metals than iron is thus possible.     

New Preparation Method for PZT Films Using Electrochemical Reduction

PZT perovskite films on stainless steel were prepared by electrochemical reduction in solutions containing TiO²⁺, ZrO²⁺, and Pb²⁺ ions. Heat treatment at temperatures higher than about 500°C was necessary for crystallization, because the as-deposited oxide films were amorphous. The deposited oxides consisted of a mixture of hydroxides and oxide produced by an increase of pH due to some electrochemical reduction reactions of NO₃⁻, H⁺, and H₂O on the electrode surface. The composition of the PZT films was easily controlled by the composition in solution during the electrolysis. The mechanism of the PZT precursor deposition is discussed.     

硫铁矿废水制备铁黑颜料的工艺

采用湿法氧化沉淀法,通过调节反应溶液初始pH值(7～12)、反应温度(70～95℃)、反应时间(1～4.5h)和搅拌速度(50～250r/min),探索了硫铁矿废水制备铁黑颜料的工艺条件。结果表明:在pH值为9.5、反应温度为85℃、反应时间为2.5h、搅拌速度为150r/min的条件下,能制备得到较优的铁黑颜料。其经XRD、SEM及铁黑颜料技术指标检测分析,表明该铁黑颜料粒径在60nm左右,Fe3O4含量在95%以上,各项指标均能达到氧化铁黑颜料行业标准中一级品的要求。     

Finite element analysis of dip coating with bingham fluids

A finite element analysis of the dip coating process with Bingham fluids is presented. The solution method for the viscoplastic flow problem was based on the augmented Lagrangian method allowing a rigorous treatment of the stress discontinuity. To compute the location of the free surface at equilibrium, an iterative method was used based on the arbitrary Eulerian-Lagrangian approach in conjunction with mesh smoothing. Numerical predictions were validated against experimental data for the Newtonian limit case. Computations were then performed with Bingham fluids. The influence of yield stress on the meniscus flow Is discussed.     

The role of anion additives in the electrodeposition of nickel-cobalt alloys from sulfamate electrolyte

Nickel-cobalt alloys have been deposited from sulfamate electrolyte with acetate and citrate-anion additives and evaluated for structure and properties, such as microhardness, tensile strength, internal stress and high-temperature oxidation. XRD data show that at low Co content, the alloys exhibit face-centered cubic (fcc) growth orientations. Above 60% Co, the deposit is completely hexagonal close packed (hcp) with pronounced (100) and (110) lines. It seems likely that the Ni-Co deposits from typical sulfamate electrolyte at pH 5, as well as at current density higher than 5 A/dm², include metal hydroxides. This is followed by the formation of a more strained structure. The high-temperature oxidation rate of the Ni-Co coating from sulfamate electrolyte at pH 5 is twice that of the alloy deposited from the electrolyte with anion additives. We believe that, citrate complexes of Ni and Co, which are assumed to be involved in alloy deposition, eliminate the incorporation of hydroxides into the deposits and enable low-internal-stress coating. The anion-modified bath offers stability of structure and properties of the alloy over a wide range of acidity and current density.     

The structure and strength of depletion force induced particle aggregates

Aggregating fine particulate matter is common practice in many industrial solid-liquid separation processes. Data obtained in this work on dilute aqueous dispersions of model colloidal polystyrene latex spheres indicate that depletion flocculation, which uses non-adsorbing polymer, can yield very compact aggregates. Flocculation of the negatively charged latex particles was induced by the addition of a poly(acrylic acid) at pH 10. The structural compactness of the latex flocs formed in the dilute dispersions was characterised using small-angle static light scattering in terms of mass fractal dimensions. Rheological measurements on the concentrated latex dispersions in the presence of the non-adsorbing polyacid showed Bingham yield stress behaviour. Both the compactness and strength of the latex flocs were found to be significantly dependent upon the level of the polyacid, as well as the concentration of the initial particles. In particular, as the level of the polyacid was raised the floc compactness decreased, whereas its strength increased. They were both seen to level off at high polymer concentrations. Atomic force microscopy measurements were made at varying concentrations of the polyacid to provide a qualitative explanation of the observed floc structural behaviour of the dilute dispersions. By combining the fractal dimension and the Bingham yield stress we were also able to estimate the energy required to separate the flocs into single units in the concentrated dispersions. It was concluded that the interparticle interaction energy is the key to understanding the dependence of both the floc structure and strength on the polymer concentration.     

Direct simulations of spherical particle motion in Bingham liquids

The present work deals with the development of a direct simulation strategy for solving the motion of spherical particles in a Bingham liquid. The simulating strategy is based on a lattice-Boltzmann flow solver and the dual-viscosity Bingham model. Validation of the strategy is first performed for single phase (lid-driven cavity flow) and then for two phase flows. Lid-driven cavity flow results illustrate the flow's response to an increase of the yield stress. We show how the settling velocity of a single sphere sedimenting in a Bingham liquid is influenced by the yield stress of the liquid. The hydrodynamic interactions between two spheres are studied at low and moderate Reynolds number. At low Reynolds number, two spheres settle with equal velocity. At moderate Reynolds number, the yield effects are softened and the trailing sphere approaches the leading sphere until collision occurs.     

Characteristics of Yttrium Iron Garnet Ultrafine Particles Prepared by the Alkoxide Method

Hydrolysis of a mixture of iron ethoxide and yttrium butoxide produced amorphous yttrium iron garnet (YIG) ultrafine particles with a mean diameter of 9 nm. The particles prepared by hot water vapor hydrolysis were less agglomerated than those prepared by plain hot water. DTA revealed that a broad phase transition temperature T _o from amorphous YIG to crystalline YIG ultrafine particles is 691°C with heat discharge of 118 kJ/mol which is attributed to the entropy decrease accompanying the crystallization, whereas magnetic experiments gave a value of T _o= 650°C. The particles calcined at 700°C were single-crystalline ones while those calcined at higher temperatures (at least higher than 800°C) were multicrystalline ones.     

不同方法制备羟基氧化铁的脱硫活性研究

羟基氧化铁的制备受到制备条件或环境的强烈影响,不同的制备方法将得到不同结构和特性的产物,如不同晶型不同形貌或相同晶型不同形貌的同质异构体．为了制备高活性的常温煤气脱硫剂,采用两步法、快速氧化法、强制水解法和中和法分别合成多个羟基氧化铁,并对所制得的样品进行了物性表征和脱硫活性研究．研究表明,添加H2O2快速氧化制成的无定形FeOOH,有较好的脱硫活性,饱和硫化增重率为66．0％,100min模拟德士古煤气热重硫化转化率达69．03％．     

Microemulsion polymerization of styrene using developed redox initiation system and study of rheological properties of obtained latices

Microemulsion polymerization of styrene was kinetically studied using a potassium persulfate (KPS)/P‐methyl benzaldehyde sodium bisulfite (MeBSBS) adduct as the developed redox pair initiation system. The rate of microemulsion polymerization of styrene was found to be dependent on the initiator, emulsifier, and monomer to the powers of 1.4, −0.77, and 0.83, respectively. The apparent Arrhenius activation energy (E_a) estimated for the microemulsion polymerization system was 6.5 × 10⁴ J/mol. Also, the morphological parameters were studied at different initiator concentrations. The rheological measurements for the prepared microemulsions were carried out to investigate the effect of the preparation parameters on the rheological behavior of the polystyrene microemulsions. The rheological flow curves of the polystyrene microemulsion latices prepared at different temperatures were carried out, and we found that the plastic viscosity and Bingham yield values of the flow curves increased with an increasing reaction temperature. That may be due to the cage effect of the prepared polymer particles, which trapped the medium molecules. The plastic viscosity increased with increasing emulsifier concentration while the Bingham yield value decreased. For the polystyrene microemulsion prepared in the presence of different initiator concentrations, the plastic viscosity and Bingham yield increased with increasing initiator concentration. This trend was found to be the same for the microemulsion latices prepared in the presence of different monomer concentrations. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1240–1249, 2000     

Adsorbing Colloid Flotation of Pb(II). Feasibility of Utilizing Streaming Current Detector

Abstract

A feasibility study was conducted to assess the application of a streaming current detector (SCD) in the flotation of dissolved heavy metals. The adsorbing colloid flotation of Pb(II) with iron oxide and sodium dodecylsulfate was injvestigated. Both zeta potential and streaming current (SC) readings of each colloidal system were measured. For colloids of goethite or of amorphous iron oxide, the results show SC changed with pH values and can be well correlated to the zeta potential. The removal of Pb(II) increased with increasing pH. Judging from the experimental results, it is proposed that when pH is at 3.0 or lower, Pb(II) is mainly removed by foam fractionation. When pH values are between 4.0 and 7.0, Pb(II) removal can be attributed to both foam fractionation and adsorbing colloid flotation. When pH values are higher than 7.0, Pb(II) is mainly removed by precipitate flotation in the form of Pb(OH)₂(s) or Pb-Fe coprecipitate. Advantages and limits of utilizing SCD in flotation processes are discussed. Preliminary results show it is feasible for SCD to be utilized in the flotation of Pb(II).     

Influence of iron on kaolin whiteness: An electron paramagnetic resonance study

Well characterized kaolin samples from different deposits of Brazil were studied by electron paramagnetic resonance. Three paramagnetic species attributed to iron in different chemical environments were identified in raw samples. A very intense and broad line with 0.2 mT linewidth was typical of large particles of iron oxides/hydroxides. A species at g = 2.0 with 0.04 mT line width was associated with superparamagnetic particles adsorbed to kaolinite surfaces or trapped between its lamellae. An isotropic and/or orthorhombic species in the g = 4.2 region belongs to structural Fe³⁺ replacing Al³⁺ in sites with different crystal-field symmetries. It was verified that large iron oxide particles were responsible for keeping the kaolin whiteness at levels below 50%. Superparamagnetic iron particles mainly affect whiteness in the range of 50%< whiteness < 86%. They may be totally removed by magnetic separation followed by chemical treatment using sodium dithionite. The kaolin high whiteness levels (whiteness > 86%) were determined by Fe³⁺ iron content in the kaolinite structure. However, only a small part of this species can be removed from the kaolinite structure by traditional industrial processing techniques. These results showed that EPR is a powerful technique to assist in controlling kaolin quality in industrial processes.     

Effect of some water‐soluble melamine formaldehyde‐free polycondensates on the rheological properties of cement pastes

Water‐soluble melamine formaldehyde‐free polycondensate products were prepared. The chemical structure of these polymers was confirmed with different spectroscopic techniques. The effects of these polymers on the rheological properties of the cement pastes were investigated. The rheological parameters (shear stress, yield stress, and plastic viscosity) were calculated with the Bingham model. The minislump of superplasticized cement pastes at different interval times (5, 30, 60, 90, and 120 min) was determined. The results showed that the new superplasticizers increased the fluidity and minislump of the cement pastes and reduced the minislump loss of the cement pastes not only at early ages (30 min) but also at later early ages (120 min). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2212–2218, 2005     

Activation of Ground Blast-Furnace Slag by Alkali-Metal and Alkaline-Earth Hydroxides

The effects of pH, time, valence, and radius of the activator cation on the reaction products and microstructure of ground granulated iron blast-furnace slag were studied by thermogravimetry and derivative thermogravimetry, X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray microanalysis. Blast-furnace slag was activated by alkali-metal hydroxides of Li, Na, and K (12.34 pH 14.71) and alkaline-earth hydroxides of Ca, Sr, and Ba(12.47 pH 13.53) using a water/slag ratio of 0.4 and curing for 1 day to 26 months. Reactivity of the slag was more strongly dependent on pH than on time. The reaction products were mainly varieties of C─S─H, (C,M)₄AH₁₃, and minor amounts of Ca(OH)₂ and C₂ASH₈ (strätlingite). The nature of C─S─H was dependent on pH. A 1.2-nm peak appeared in X-ray diffractograms only when the activation pH was ⌣14.7. Water was present in the C─S─H in a way similar to water in tobermorite and synthetic C─S─H. Leached Ca from unreacted blast-furnace slag was present around the glass particles as an amorphous layer which crystallized into Ca(OH)₂ with time; Mg behaved similarly. The effect of the charge or ionic radius of the activator cation was insignificant.     

A pigment based on coprecipitated iron(III) and nickel(II) hydroxides

The formation of precipitates of iron(III) and nickel(II) hydroxides by coprecipitation is considered. It is established that by changing the pH a hydroxide precipitate that contains Fe and Ni with a ferrite proportion of 2:1 can be prepared. The methods of IR spectroscopy, DTA, and x-ray phase analysis are used to show the possibility of formation of nickel ferrites that are suitable as overglaze paints for decorating porcelain and faience.     

Graphene-supported carbonaceous dielectric sheets and their electrorheology

Two-dimensional dielectric sheets composed of graphene-supported amorphous carbon were prepared by annealing polyaniline-coated graphene oxide sheets in vacuum. The morphology and structure were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy. This showed that annealing the polyaniline-coated graphene oxide had little influence on its plate-like morphology but transformed the graphene oxide core into conducting graphene and the polyaniline shell into insulating nitrogen-enriched amorphous carbon. An electrorheological suspension was prepared by dispersing the graphene-supported carbonaceous sheets in silicone oil and its electrorheological property was investigated by rhelogical tests under electric fields. The suspension demonstrated a strong electrorheological effect. Its yield stress and shear stress were about three times as large as those of a suspension of pure carbonaceous particles at equal electric field strengths. The storage modulus of the suspension was also higher than that of a suspension of pure carbonaceous particles, indicating stronger electrorheological activity. Dielectric measurements indicated that the presence of the graphene core had increased the polarization property, and this is responsible for the increased electrorheological activity.