Heat-treatment induced evolution of the morphology and microstructure of zirconia prepared from chloride solutions during

The properties of hydrous zirconia prepared from ZrOCl₂ solutions were studied as functions of precipitation pH and subsequent heat treatment. Precipitation at pH ≤ 6 yields hydrous zirconia containing excess sorbate anions (Cl^?), and at pH ≥ 7, ammonium ions. This difference considerably affects the thermolysis and morphology of the resulting samples. The samples prepared at pH ≥ 7 have far better developed surfaces. The morphological and structural evolution of hydrous zirconia samples during heat treatment is described. The involved processes are interpreted. At initial stages, the major process is the formation of metastable tetragonal ZrO₂, which transforms to the monoclinic phase during subsequent heating.     

Environmentally abundant anions influence the nucleation, growth, Ostwald ripening, and aggregation of hydrous Fe(III) oxides

The simultaneous homogeneous and heterogeneous precipitation of hydrous Fe(III) oxides was investigated in the presence of environmentally ubiquitous anions (nitrate, chloride, and sulfate). Experiments were conducted with 10(-4) M Fe(III) at acidic pH (pH = 3.7 ± 0.2), which often occurs at acid mine drainage sites or geologic CO(2) storage aquifers near injection wells. Quartz was used as a model substrate for heterogeneous precipitation. Small angle X-ray scattering (SAXS) and grazing incidence SAXS (GISAXS), atomic force microscopy (AFM), and dynamic light scattering (DLS) measurements were conducted. In situ SAXS/GISAXS quantified the size, total particle volume, number, and surface area evolutions of the primary nanoparticles formed in the nitrate and chloride systems. In both systems, the heterogeneously precipitated particles were smaller than the homogeneously precipitated particles. Compared with chloride, the volume of heterogeneously precipitated hydrous Fe(III) oxides on the quartz surface was 10 times more in the nitrate system. After initial fast heterogeneous nucleation in both nitrate and chloride systems, nucleation, growth, and aggregation occurred in the nitrate system, whereas Ostwald ripening was the dominant heterogeneous precipitation process in the chloride system. In the sulfate system, fast growth of the heterogeneously precipitated particles and fast aggregation of the homogeneously precipitated particles led to the formation of particles larger than the detection limit of GISAXS/SAXS. Thus, the sizes of the particles precipitated on quartz surface and in solution were analyzed with AFM and DLS, respectively. This study provides unique qualitative and quantitative information about the location (on quartz surfaces vs in solutions), size, volume, and number evolutions of the newly formed hydrous iron oxide particles in the presence of quartz substrate and ubiquitous anions, which can help in understanding the fate and transport of pollutants in the environment.     

The analysis of zirconium-thorium binary alloys

Thorium-zirconium binary alloys are analysed by complexometric procedures. For alloys containing more than 20% thorium or 5% zirconium by weight, the sum of the constituents is obtained by a back titration procedure at pH 2.6–2.8 with bismuth nitrate using xylenol orange as indicator. Thorium is then masked with sulphate and the liberated EDTA is titrated with bismuth at pH 1.2–1.3. For alloys containing less than 20% of thorium, thorium fluoride is precipitated on lanthanum fluoride to effect its separation before titration. For alloys containing less than 5% of zirconium, the zirconium is separated by precipitation with p-bromo-mandelic acid.     

The Effects of γ-Irradiation on the Electrokinetic and Thermal Behaviour of Zirconium Hydroxide

Zirconium hydroxide particles produced by rapid precipitation at pH 10.4, 7 or 2 were subjected toγ-irradiation up to a final dose of 20 MGy. The effects of the γ-irradiation were examined by X-ray powder diffraction, laser Raman spectroscopy, differential scanning calorimetry and microelectrophoretic measurements. It was found that γ-irradiation had no influence on the behaviour of zirconium hydroxide during calcination and subsequent cooling. The results of microelectrophoretic measurements showed that γ-irradiation influences the surface properties of zirconium hydroxide as a function of the precipitation pH. Zirconium hydroxide precipitated at pH 2 proved to be the most susceptible to γ-irradiation, while the sameγ-irradiation had very little (if any) effect on the surface properties of zirconium hydroxide precipitated at pH 10.5. After γ-irradiation, the electrophoretic mobility of zirconium hydroxide precipitated at pH 2 was increased at both low and high pH, thereby indicating an increase in its adsorption capacity. The analogy observed between the pH-dependence of the effects of γ-irradiation on the electrokinetic behaviour of zirconium hydroxide and the influence of ball-milling on the thermal behaviour of zirconium hydroxide [8] suggested that the susceptibility of amorphous zirconium hydroxide increases with decrease of the precipitation pH. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adsorption of univalent and bivalent metal nitrates on hydrous lead dioxide Adsorption behaviour of potassium, cupric, zinc, cadmium and nitrate ions

The individual adsorption behaviour of potassium, cupric, zinc, cadmium and nitrate ions on hydrous lead dioxide (HLD) was investigated. HLD was found to be an amphoteric ion-exchanger with an equi-adsorption point in the vicinity of pH 4.6. For bivalent metal ions, the amount of adsorption increased with pH (at pH > 3) and there was almost 100% adsorption at pH > 6. Both the adsorption capacity and the adsorption affinity on HLD were in the order copper(II) > zinc(II) > cadmium(II).     

Quinolinium and lutidinium molybdates as reagents for the precipitation of phosphate

The precipitation of phosphate with quinolinium molybdate was studied by means of radioactive tracers, in relation to the excess of reagent, temperature of precipitation, etc. Precipitation is almost quantitative (99.3%) even with a stoichiometric amount of reagent added but an excess helps to minimise the inhibitory effects of certain ions, notably Fe³⁺ ; inhibitory effects are eliminated by digesting the solution for 2 h. Chromium(III) nitrate, nickel(II) nitrate and manganese(II) nitrate have relatively little effect on the precipitation of quinolinium molybdophosphate. Under the conditions required for the quantitative precipitation of phosphorus, arsenic is also quantitatively precipitated.Phosphate can be precipitated as lutidinium molybdophosphate using 2,4-, 2,5- or 2,6-lutidinium molybdate; the reagents are less efficient than quinolinium molybdate but can be used to precipitate phosphate under conditions which leave arsenate in solution.     

Separation of niobium and tantalum with n-benzoyl-n-phenylhydroxylamine

The use of N-benzoyl-N-phenylhydroxylamine for the separation of niobium and tantalum, allows a satisfactory estimation of niobium from a tartrate solution at an acidity of 2.0N. The pH range for complete precipitation can be extended to 6.5. For tantalum precipitation, the pH of the solution should be below 1.5 and the acidity may even be above 2.0N. At pH 3.5–6.5, niobium is completely precipitated and tantalum remains in solution; the latter is precipitated by lowering the pH. Niobium and tantalum in ratios of 1:16 to 100:1 can be separated by a single precipitation, in the case of a ratio of 1:100 precipitation must be carried out twice. Titanium, zirconium, vanadate and molybdate interfere with the determination of niobium though other ions have no effect in the presence of complexone III and tartaric acid. The precipitates are granular and easy to filter and wash. The time taken for a complete analysis is much less than that of other methods     

The determination of zirconium in fluoride-containing solutions

In the recommended procedure the zirconium is first precipitated from solution as the insoluble barium fluozirconate. After separation, the precipitate is dissolved in a mixture of nitric and boric acids and the zirconium is then precipitated as its hydroxide. This precipitate is separated, dissolved in hydrochloric acid and this solution is evaporated to fumes of perchloric acid to remove completely fluoride ions. The zirconium content is then determined volumetrically by adding a slight excess of a standard solution of ethylenediaminetetra-acetic acid and back titrating with a standard iron solution at pH 2.3 using potassium benzohydroxamate as indicator and the photometric technique for end-point detection. This method is applicable to the determination of milligram amounts of zirconium in fluoride-containing nitric or hydrochloric acid solutions provided that the concentration of these acids is below 3N. It is also suitable for the determination of zirconium in the presence of any of the following elements - uranium, titanium, niobium, tantalum, molybdenum, tungsten, lead, iron, copper and tin.     

The use of continuous extraction for the removal of interfering elements in the determination of calcium and magnesium

Solvent extraction with a continuous extractor has been used to separate Al, Be, Bi, Cd, Ce, Cr, Co, Cu, Ga, In, Fe, Pb, Hg, Mo, Ni, Tl, Th, Sn, Ti, W, U, V, Zn and Zr, from calcium and magnesium, before titration of the latter with ethanediaminotetraacetic acid. Most of these elements arc extracted at ca, pH 5.0 as their chelates with 8-hydroxyquinoline using chloroform. Be, Ce and Cr are not extracted under these conditions and are converted into their acetylacetonates, before extraction with chloroform. Manganese is not quantitatively removed by any of these processes and is precipitated as its hydrated dioxide by boiling the extracted solution with sodium chlorite. Phosphate, arsenate and selenate can be removed by precipitating them in acid solution with excess zirconium nitrate, and removing the latter with 8-hydroxyquinoline.     

Relationship between formation conditions, properties, and crystallite size of boehmite

Boehmites (gamma-AlOOH) with a variety of crystallite sizes were prepared under various precipitation conditions from solutions of aluminum nitrate and sodium aluminate and also by hydrothermal treatment of a commercial boehmite powder. The relationships between the crystallite size and other properties of the boehmites were investigated. Crystalline boehmite was formed in the pH range 7 to 10 while gels precipitated below pH 7 and bayerite (Al(OH)3) formed at pH 11. The crystallite size of the boehmite increased at higher pH, higher temperature of the precursor solution, and longer aging time. As the crystallite size of the boehmite increased, the specific surface area, pore volume, and excess water decreased. Boehmites of small crystallite size, called pseudoboehmite, showed broadened X-ray peak widths and increased d-spacing of the 020 reflection. These changes are attributed to the small crystallite size (smaller numbers of stacking layers) and also to excess water in the interlayers of the boehmite structure.     

Rapid analysis of fertilizers by the direct-reading thermometric method

The authors have developed rapid methods for the determination of the main components of fertilizers, namely phosphate, potassium and nitrogen fixed in various forms. In the absence of magnesium ions phosphate is precipitated with magnesia mixture; in the presence of magnesium ions ammonium phosphomolybdate is precipitated and the excess of molybdate is reacted with hydrogen peroxide. Potassium is determined by precipitation with silico-fluoride. For nitrogen fixed as ammonium salts the ammonium ions are condensed in a basic solution with formalin to hexamethylenetetramine; for nitrogen fixed as carbamide the latter is decomposed with sodium nitrite; for nitrogen fixed as nitrate the latter is reduced with titanium(III). In each case the temperature change of the test solution is measured. Practically all essential components of fertilizers may be determined by direct-reading thermometry; with this method and special apparatus the time of analysis is reduced to at most about 15 min for any determination.     

Determination of zirconium in zirconium metal and zirconium powder by use of mandelic acid

An accurate gravimetric method is proposed for the determination of zirconium in zirconium metal and zirconium powder by use of mandelic acid. The sample is dissolved in a mixture of hydrofluoric, nitric, perchloric and sulfuric acids, the solution is evaporated to dryness, and the salts are dissolved in dilute hydrochloric acid. Zirconium mandelate is precipitated at 80°. The residual zirconium in the filtrate is recovered by heating at 80° overnight and the combined precipitates are ignited to Zirconium dioxide. An investigation was made of the factors involved in the dissolution of the sample, precipitation with mandelic acid, ignition of the precipitate, and size of sample. The effect of hafnium is discussed.     

Sorption studies of strontium on hydrous zirconium dioxide

Summary Hydrous zirconium dioxide was prepared to study the sorption behavior and the removal of strontium from radioactive waste solutions. The hydrous zirconium dioxide were identified and characterized. The parameters affecting the strontium adsorption were investigated. Sorption data have been interpreted in terms of Langmuir equations. Thermodynamic parameters for the sorption system have been determined at 303, 313, 323 and 333 K temperatures. The values ofDH°=102.30 kJ/mol andDG°=-26.03 kJ/mol at 313 K prove that the sorption of strontium on hydrous zirconium oxide is an endothermic and a spontaneous process.     

The effect of arsenate,and of transitioń-metal ions,on the precipitation of phosphate as ammonium 12-molybdophosphate

The radionuclides phosphorus-32, arsenic-74, iron-59 and molybdenum-99 were used to determine the effect-of arsenate and some transition-metal ions on the precipitation of phosphorus as ammonium 12-molybdophosphate. Under the conditions necessary for the quantitative precipitation of phosphorus, arsenic is also precipitated by ammonium molybdate. The presence of iron(III) nitrate inhibits the precipitation of phosphorus and, particularly, arsenic, although the precipitates contain more molybdenum, and are heavier, than when iron is absent. Chromium (111) nitrate, nickel(II) nitrate and manganese(II) nitrate do not inhibit the precipitation of phosphorus and arsenic to the same extent as iron (III) nitrate.     

Influence of the conditions of manufacture of nanomeric zirconium dioxide,stabilized with yttrium oxide,on its catalytic properties in the oxidation of CO

The morphological and catalytic properties of samples of nanomeric zirconium dioxide, stabilized with yttrium oxide, manufactured via the effect of a UHF field during the process of drying precipitated zirconium hydroxide and calcination at temperatures from 300 to 1000 °C, were studied. It was shown that the highest activity in the oxidation of CO occurred with 40 nm particles of zirconium dioxide prepared at 1000 °C. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 96–101, March–April, 2007.     

Trägerfreie Abtrennung von Rhenium-Isotopen aus einer deuteronenbestrahlten Wolfram-Matrix

A method is described for the carrier-free separation of rheniumisotopes from deuteron-irradiated tungsten. After being irradiated, metallic tungsten is first treated with a mixture of hydrofluoric acid and nitric acid, and the residue is then dissolved in ammonia and hydrogen peroxide. Ammonium nitrate is added to the solution, and thepH is adjusted to 4.5–5. The separation is performed on a column of hydrous zirconium dioxide using 2% ammonium nitrate solution; ≥99.9 of the tungsten is retained on the ion exchanger. The solution containing the rheniumisotopes is evaporated to dryness, and the ammonium nitrate removed by heating to about 160°C.      

Use of organic reagents in inorganic analysis

Summary Thorium and zirconium have been determined gravimetrically with phenylglycine-p-carboxylic acid and zirconium alone with phenylglycine-o-carboxylic acid, almost within the same pH range. Better results are obtained when zirconium is precipitated in acetic acid solution in presence of a little ammonium acetate. A number of foreign ions may be separated from thorium and zirconium with these reagents. Iron and titanium cause heavy interference. The interference caused by iron, may however, be eliminated by adding a little ascorbic acid, before precipitation of the metals. The para acid can also extract thorium from a mixture of cerite earths and from monazite sands.Part V: See Z. anal. Chem. 158, 347 (1957).The author likes to thank Dr. B. N. Bose, Principal of the College and Dr. S. K. Sinha, the Head of the Department of Chemistry for their kind advice and encouragements.     

Ion-exchange selectivities of amorphous and anatase-types hydrous titanium dioxides and the possible separation of bivalent transition metal ions

Summary Amorphous and anatase-type hydrous titanium dioxides showed typical amphoteric ion-exchange properties. The ion-exchange selectivity for bivalent transition metal ions was studied as a function of both pH and metal ion concentration in ammonium nitrate media. The selectivity series was Co<Ni<Mn<Zn<Cd<Cu for the amorphous and Ni<Co<Mn<Zn<Cd<Cu for the anatase-type material. The separation factor on the anatase-type material is larger than on the amorphous material. Effective group separation of Co–Ni and Zn–Cd–Cu could be achieved on an ion-exchange column containing the anatase-type hydrous titanium dioxide.Part XXIV in a series on synthetic inorganic ion-exchange materials.     

Precipitation of molybdenum(V) as the hydroxide and its separation from rhenium

A study of the conditions for precipitation of molybdenum(V) hydroxide shows that for Mo concentration 1 mg ml about 97.5% of the Mo can be precipitated between pH 5 and 5.8. Lower concentrations of molybdenum(V) or molybdenum(VI) can be precipitated quantitatively by using 20 times the amount of zirconium as collector, at the same pH. On this basis, a simple method is given for quantitative separation of rhenium from large amounts of molybdenum and is attested by analysis of synthetic and molybdenite samples.     

Empirical investigation of precipitation of hexadecanoic acid from toluene/brine system: Implication to naphthenic acid precipitation from crude oils

Naphthenic acids, due to their tendency to precipitate out of solution when in contact with formation water, present a formidable challenge for the petroleum industry. In this study, precipitation of hexadecanoic acid from an idealized oil-water (toluene/brine) system was investigated. The FTIR results revealed that the acid was mainly precipitated as calcium hexadecanoate. Experiments designed to study the effect of water cut, acid concentration, brine concentration, and pH of the brine on the amount of the precipitate formed revealed that the amount of precipitate formed increased with increase in brine pH, concentration of the acid and calcium ions. Similar effect was observed with respect to water cut but with maximum amount of the precipitate formed at water cut of about 40%, below and above which relatively lower amount of the acid was precipitated irrespective of the levels of the other factors. In general, the observed effects of the factors suggest that precipitation of the naphthenic acid can be minimized with acidic formation water that contains relatively low concentration of calcium ions particularly when the concentration of the acid in the oil is as low as possible.