The influence of hydrating agents on the hydration of industrial magnesium oxide

BACKGROUND: The influence of different hydrating agents on the pH of the hydrating solutions, rate of hydration of MgO to Mg(OH)₂ and product surface area was studied as a function of temperature of hydration. Hydrating agents used were aqueous solutions of ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, magnesium chloride, sodium acetate and hydrochloric acid and distilled water as control. These were chosen to determine either the effect of addition of a common ion, the effect of changing the solution pH or due to the presence of an acetate ion, found earlier to have a beneficial effect on the hydration of MgO. RESULTS: There was no significant difference in the hydration behaviour of the hydrating agents up to 50 °C, where less than 10% of magnesium hydroxide was formed. The amount of hydroxide increased at temperatures above 60 °C. When compared with the hydration in water, all the hydrating agents, with the exception of sodium acetate, showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2% magnesium hydroxide. The largest percentage (56.7%) of magnesium hydroxide was formed from hydration in magnesium acetate. CONCLUSION: It seems that MgO hydration is a dissolution‐precipitation process controlled by the dissolution of MgO. The increased degree of hydration in magnesium acetate is possibly due to the presence of acetate and Mg²⁺ ions. Copyright © 2010 Society of Chemical Industry     

Formation of a high polymer of acrylamide by utilizing Kolbe's electrolysis

During the electro-initiated polymerization of acrylamide by utilizing Kolbe's electrolysis as a source of free radicals in an aqueous solution of acetic acid and potassium acetate, only an oligomer with a molecular weight of 4000–6000 was obtained. However, by the addition of ferric ion, a high-polymer with a molecular weight of a few millions was obtained. The effective action of ferric ions was retarded by the presence of ferrous ion and a large amount of chloride ion. The optimum amount of ferric ion for the formation of high-polymer and the effects and roles of various ions on the process of polymerization are discussed.     

Electrochemical studies of magnetite coating on carbon steel in ascorbic and picolinic acid

Electrochemical impedance and cyclic voltammetric measurements of magnetite coating formed on carbon steel substrates were carried out in deaerated solutions of 1.0 × 10^–2 M ascorbic acid and 3.5 × 10^–2 M picolinic acid at 28 °C. Impedance data showed that the interaction between magnetite and ascorbic acid is associated with an incubation period, after which reductive dissolution takes place accompanied by oxidation of ascorbic acid. Once the magnetite film loses its thickness and protective properties on prolonged exposure to ascorbic acid, the charge transfer resistance and the capacitance is reduced. Initial dissolution of magnetite in picolinic acid is due to congruent chemical dissolution with little contribution from reduction by the electrons arising from the corrosive attack of acid on the carbon steel. With time the contribution of the latter process increases as more and more of the substrate opens up. Cyclic voltammetric studies showed that there is an adsorption phenomenon leading to the formation of a surface ferric complex that undergoes reduction to the ferrous species and transfers to the bulk solution. The accumulation of the ferrous ion accelerates the dissolution resulting in an increase in current. Dissolution of magnetite in picolinic acid is slow. The better complexing capability of picolinic acid compared to ascorbic acid does not permit the accumulation of the ferrous ion as indicated by the absence of a peak in the voltammogram.     

Preparation and formation mechanism of nano-iron oxide black pigment from blast furnace flue dust

A mixed solution of ferrous and ferric sulfate leached from blast furnace (BF) flue dust was used to prepare nanometer-sized iron oxide black pigment (Fe₃O₄, magnetite) by the co-precipitation method. The pH value played a very important role in affecting the color and particle size of Fe₃O₄ and the evolution of green rust in to Fe₃O₄ or FeOOH. The experimental conditions including the solution pH, the way of adding precipitant, volume of air and reaction time for the formation of nano-iron oxide black pigment were investigated carefully in order to determine the optimal ones. The color, morphology and particle size of as-prepared Fe₃O₄ pigment were characterized by means of a color measurement instrument, X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively. The results showed that the obtained pigment had low average spectral reflectance (<4%), good oil absorption (～23%), high black intensity and narrow size distribution of 60–70 nm. Furthermore, the formation mechanism of Fe₃O₄ from the mixed solution of ferrous and ferric sulfate was discussed.     

盐酸法钛白粉新工艺副产氯化亚铁制备四氧化三铁

探索了一种以盐酸法钛白粉新工艺副产氯化亚铁为原料制备四氧化三铁磁粉的放大试验工艺,把副产危废氯化亚铁制备成用途广泛的四氧化三铁磁粉,实现资源的综合利用。研究结果表明：选用氧化钙为沉淀剂与氯化亚铁反应得到氢氧化亚铁,在分散剂辅助作用下通入空气使氢氧化亚铁被氧化成三价氢氧化铁,控制氧化钙及分散剂加料时间间隔为1.5 h、氧化温度为80℃、氧化时间为8.5 h,将氢氧化铁与氢氧化亚铁以物质的量比为2∶1均匀混合,通过正压分离得到固体,控制分离前pH为6.5,最后通过烘干、研磨等后处理得到四氧化三铁磁粉。进行50 kg级别放大试验得到四氧化三铁产品,收率达到97%。该工艺将副产危废转化为有一定经济效益的产品,进一步完善了盐酸法钛白粉新工艺。     

铬铁矿酸浸过程强化及铬铁分离研究进展

铬铁矿是铬盐生产的主要原料来源,铬铁矿酸浸工艺因无Cr（Ⅵ）污染且资源利用率高而备受关注。综述了近年来铬铁矿酸浸过程强化以及铬铁分离方法的研究进展。铬铁矿酸浸工艺是以硫酸为强酸浸出,通过机械活化处理、氧化剂的加入以及微波加热等辅助强化方法,使得铬铁矿能够被高效、快速地浸出。浸出液中的铬铁分离方法主要有针铁矿法、黄铁矾法、萃取法、草酸法、铁蓝沉淀法和莫尔盐法等。多种强化手段与反应过程相结合已成为铬铁矿硫酸浸出工艺的重要研究方向。     

Patterning of Lithium Niobate Thin Films Derived from Aqueous Solution

The micropatterning of lithium niobate (LiNbO₃) thin films was conducted by applying a photolithographic technique to an aqueous precursor solution that was derived from a double alkoxide. The neutralization process of the alkaline lithium niobium hydroxide solution was essential to avoid the dissolution of the aluminum masking pattern on the sapphire substrate. The acetic acid was a suitable neutralizer to form the stoichiometric and transparent gel film. The gel film that was prepared from a neutralized precursor solution at pH 6.4 gave high-quality crystalline LiNbO₃ films after heat treatment at 500°C.     

Effect of the preparation condition on the properties of titania-silica derived from tetraisopropyl titanate(IV) and tetraethyl orthosilicate

Titania-silica mixed oxide was prepared by hydrolyzing tetraethyl orthosilicate and tetraisopropyl titanate(IV) with a mixture of ethanol and 0.01 N aqueous acetic acid. Surface Ti content, BET surface area, and the number of acid sites increased with an increase in 0.01 N aqueous acetic acid. Thus hydrolysis of both alkoxides occurred simultaneously with a large amount of the acetic acid solution, and there was extensive interaction between TiO₂ and SiO₂ phases. With small amount of 0.01 N aqueous acetic acid, however, titanium hydroxide was first formed and, then, it was covered with the silica phase produced in a later stage of the hydrolysis. Increase in the acetic acid solution also led to the formation of a large amount of tetrahedral Ti species, which were active for the epoxidation of oct-1-ene usingt-butyl hydroperoxide as an oxidant.     

Low-Temperature Synthesis of Fully Crystallized Spherical BaTiO3 Particles by the Gel–Sol Method

The synthesis of spherical BaTiO₃ particles was attempted by a new technique, the "gel–sol method," at 45°C. The (Ba–Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with a barium acetate aqueous solution ([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] = 4, [barium acetate]/[TIP] = 1) at 45°C for 48 h. Potassium hydroxide (KOH) was used as a catalyst for the formation of BaTiO₃. Powder X-ray diffractometry (XRD) results and Fourier-transform infrared (FT-IR) measurements for the (Ba–Ti) gel showed that the gel was amorphous, but the spatial arrangement of barium and titanium in the (Ba–Ti) gel is similar to that in crystalline BaTiO₃ particles. Fully crystallized spherical BaTiO₃ powder with a particle size of 40–250 nm formed at the very low reaction temperature of 45°C. Scanning electron microscopy images showed that the final particles formed via aggregation of the fine particles that seem to be the primary particles of bulk (Ba–Ti) gel. From the XRD, FT-IR, and Raman spectroscopy analysis, it was found that the crystal structure of the as-prepared particles continuously transformed from cubic to tetragonal as the calcination temperature increased, and high crystalline tetragonal BaTiO₃ phase was obtained at 1000°C after 1 h of heat treatment.     

Characterization of iron(III) oxide nanoparticles prepared by using ammonium acetate as precipitating agent

The effect of precipitating agent on the preparation of iron(III) oxide particles was investigated. Iron(III) oxide particles were prepared by precipitation of aqueous ferric nitrate solution by using ammonium acetate and ammonium hydroxide as precipitating agents. Particle size, shape, chemical composition, crystalline formation rate, crystallinity and magnetic property were measured for Fe₂O₃ particles obtained by precipitating with ammonium acetate, and compared with those of particles formed by using ammonium hydroxide. TGA, DTA, IR, XRD, TEM and VSM were used to characterize the particles. The nanoparticles synthesized with ammonium acetate showed a narrow size distribution, spherical shape, fast crystalline formation rate, high crystallinity and complete hysteresis loop. The better properties of particles formed by using ammonium acetate were originated from the chelating effect of carboxylate ions and higher crystallinity than those synthesized with ammonium hydroxide.     

Electrode reaction of tris(1,10-phenanthroline)iron(II) complex in aqueous and non-aqueous solvents

The electrode reaction of tris(1,10-phenanthroline)iron(II) complex was studied in aqueous and non-aqueous solvents. The experimental results were compared with the diagnostic criteria derived by Nicholson and Shain. It was found that the oxidation of Fe(phen)²⁺₃ was the simple reversible reaction at low pH; however, at high pH, the reversible process was followed by the irreversible formation reaction of ferric hydroxide ion. In acetonitrile, the reversible oxidation of Fe(phen)²⁺₃ was coupled with the catalytic reduction of Fe(phen)³⁺₃ to reproduce the ferrous complex. The major cause of solvent effect on the electrode reaction could be attributed to the labile nature of ferric complex of 1,10-phenanthroline.     

Adsorption of Uranium from Dilute Aqueous Solution on Inorganic Adsorbents

Abstract

The adsorption of uranium from a dilute aqueous solution by a large number of inorganic adsorbents has been investigated. A mixture of aluminum hydroxide, ferric hydroxide, and activated carbon in the weight ratio 1:3:4 has shown a high adsorbability for uranium. The separation of uranium from a dilute aqueous solution by this mixed adsorbent under various temperatures and pH values has been studied. The adsorbability was found to exhibit a maximum at pH 4.0 to 5.5 and to decrease with increasing temperature. A number of eluting solutions for the desorption of uranium from the mixed adsorbent were also tested; 1 N (NH₄)₂ CO ₃ was found to be the most suitable eluting solution (93% recovery of uranium).     

Characteristics of phosphate adsorption on ferric hydroxide synthesized from a Fe<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript> aqueous solution discharged from a hydrometallurgical process

Ferric hydroxide adsorbent was prepared by a chemical treatment process with H₂O₂, NaOH, and aeration from a Fe₂(SO₄)₃ aqueous solution as a side product discharged from the hydrometallurgical process used to extract neodymium. The ferric hydroxide was used as an adsorbent to prevent eutrophication in water. At the time of synthesis, the most important process variable is the pH condition, which, in this experiment, was changed from pH 3 to 13. The cost of synthesizing ferric hydroxide was sharply reduced by using ferric sulfate, which is considered a side product of the aforementioned hydrometallurgical process, as a starting material, and an adsorbent with high adsorption ability was prepared by controlling the pH level. Microstructural characterization of the synthesized ferric hydroxide revealed particles with a specific surface area of 194.2 m²/g and an average pore diameter of 2.66 nm at pH 6 and 298 K. A column-type packed-bed adsorption experiment was conducted under the following conditions: a flow rate of 0.567 BV/min (3.2 mL/min), 298 K, and atmospheric pressure. The results of the adsorption performance test indicated that the adsorption efficiency of phosphate at concentrations of 10 ppm was 100% at a flow rate of 0.567 BV/min within a contact time of 2 min, and the maximum adsorption capacity for phosphate ions was 65 mg/g.     

草酸-酸亚硅钼蓝光度法检测钢铁及合金中硅的含量

试样用稀酸溶解,在微酸性溶液中,硅酸与钼酸铵生成硅钼杂多酸,在草酸存在下,用硫酸亚铁铵还原成硅钼蓝,测其吸光度.与钼酸盐形成杂多酸的硅必须以正硅酸状态存在,所以在试样溶解过程中必须避免硅酸的聚合.在溶液中硅酸较易于聚合,其聚合程度与溶液的酸度、溶解时加热的程度和时间以及最终溶液中正硅酸离子的浓度有关     

An SECM observation of dissolution distribution of ferrous or ferric ion from a polycrystalline iron electrode

The dissolution of iron as ferrous or ferric ion from a polycrystalline iron electrode during anodic polarization in pH 2.3 sulfate solution was evaluated by using scanning electrochemical microscopy (SECM). A graphite reinforcement carbon (GRC) microelectrode was employed as a probe electrode of SECM to detect ferrous or ferric ions dissolved from the iron electrode in the active-dissolution, passive or trans-passive region. The probe current above the iron electrode surface subjected to active-dissolution showed the dissolution distribution of ferrous ion, depending on the substrate grains. It was found that the active-dissolution rate of iron as ferrous ions from the grain on which the thicker film was formed in the passive region, was lower than that from the grain on which the thinner film was formed in the passive region.     

ABSORPTION OF OXYGEN INTO AQUEOUS ALKALINE SUSPENSIONS OF FERROUS HYDROXIDE LEADING TO FORMATION OF EXTREMELY FINE GOETHITE AND MAGNETITE PARTICLES

The absorption of oxygen into aqueous alkaline suspensions of ferrous hydroxide leading to formation of extremely fine goethite and magnetite particles was performed using a bubble column with draft tube. The overall oxidation rates in both the systems were found to be promoted by the solid dissolution in the liquid film around a gas bubble even in this gas dispersed equipment, and were compared with prediction on the basis of a film-theory model incorporating the diffusion, the chemical reaction and the solid dissolution as the parallel steps. The trend of augmentation of the enhancement factor due to the solid dissolution could be represented by this modified model.     

新型绿锈制备方法

采用半间歇式滴加合成法成功制取了绿锈。此方法的特点是在pH值接近中性的条件下,将三价铁溶液滴加到亚铁溶液中,同时通过调节NaOH溶液的滴加速度,维持体系pH值恒定。TEM图片显示该制备工艺所得绿锈只有六边形晶貌,没有三价铁氢氧化物针状晶体形成。该方法制备的绿锈可较长时间存在,并且达到纳米级,对纳米级铁氧体产品的制备有十分重要的研究意义。     

Fe3O4磁粉的合成与结构表征

采用化学共沉淀法制备纳米磁性Fe3O4粒子。选用NH3.H2O作为沉淀剂,加入到Fe2+和Fe3+的混合盐溶液中,制得了纳米磁性Fe3O4粒子。考察了影响产物粒径的一些实验因素。通过X-Ray谱图证实了产物结构特征,平均粒径在37 nm左右,平均晶粒度只有28 nm左右的均分散。     

草酸溶液处理对SAPO-34分子筛物性和催化性能的影响

用XRD、SEM、N₂物理吸附、XRF、ICP-AES以及NH₃-TPD、FT-IR、固体NMR和固定床甲醇制烯烃技术（MTO）反应评价等表征手段,研究了草酸溶液处理对SAPO-34分子筛的改性作用。结果表明,用草酸溶液对SAPO-34分子筛进行后处理可以通过刻蚀骨架在晶体中产生大孔,调变孔道结构,改善微孔扩散性能;选择性地降低分子筛的骨架硅含量,从而降低分子筛的酸强度和酸中心密度。将改性前后的分子筛应用于MTO反应中。评价结果表明,适度的酸处理能够在保证分子筛收率和乙烯、丙烯选择性的前提下,明显提高催化剂的单程寿命。草酸溶液处理是一种值得研究的SAPO-34分子筛后处理改性方法和MTO催化剂制备手段。     

Separation and recovery of vanadium from leached solution of spent residuehydrodesulfurization (RHDS) catalyst using solvent extraction

Leached solution, generated by oxalic acid washing of spent residue hydrodesulfurization (RHDS) catalyst, was used for separation and recovery of vanadium. First of all, solvent extraction, using mixture of 20% (v/v) Alamine-336 and 5% (v/v) tri-butyl phosphate (TBP) as a phase modifier, was conducted to extract molybdenum completely at pH 0.50. Then molybdenum-free solution was used for vanadium extraction at pH 1.25 with 20% Alamine-336 and 5% TBP. Stripping of vanadium from loaded organic solution was performed with 1.5 M H₂SO₄ at O/A phase ratio of 5:1 where more than 99% of vanadium was stripped in two stages. The stripped vanadium solution was further processed by precipitating with ammonium hydroxide to recover ammonium-meta-vanadate which was calcined to obtain vanadium pentoxide. Finally a conceptual process was established for recovery of high purity vanadium pentoxide from oxalic acid leached solution of spent residue hydrodesulfurization (RHDS) catalyst.