Precipitation Of Hydrous Oxides Research Articles

Alumina Surface Treated TiO2 - From Process to Application

Titanium dioxide (TiO2) has found widespread use. Typically it is used in another matrix to impart certain properties. For example, it is widely used as a white pigment for paints and polymers. The aim of this research work was to achieve improvements in the sense of processability as well as the dispersion performance of alumina surface treated pigmentary TiO2in polymer matrix. Wet chemical method was used to modify the surface of the TiO2 pigment. Surface treatment included precipitation of hydrous oxides of aluminium on the surface of TiO2 particles. During controlled surface treatment, agglomeration has been avoided, which has been proved to improve applicative properties of TiO2 particles. In addition to that, organic additives were applied to enhance performance attributes of the pigmentary TiO2. The effectiveness of surface treatment was determined using scanning-transmission (STEM) and transmission (TEM) electron microscopy. Quantitative evaluation of quality and dispersion of the pigments has been performed using Filter pressure test. Lower pressure generated during filter pressure test when particles were well dispersed in a polymer matrix. Surface treatment also affected pigment processibility; i.e. filterability and settling, which is of high importance for process planning.

Plutonium sorption and precipitation in the presence of goethite at 25 and 80 ○C

Abstract We have examined the sorption of aqueous Pu(IV) and intrinsic Pu colloids to goethite across a Pu concentration range that spans the solubility of Pu(IV) hydrous oxide, at 25 and 80 ℃, and after equilibration for over 100 days. The strong affinity of aqueous Pu(IV) for the goethite surface is explained by the epitaxial growth of bcc Pu4O7 nano-particles on goethite. The 3–5 nm Pu4O7 nano-particles are strictly associated with goethite, widely dispersed across the goethite surface, and stable over the timescale of months at both 25 and 80 ℃. There is no indication that the sorbed Pu4O7 nano-particles alter to PuO2 over time. Intrinsic Pu colloids were identified by TEM as 3–5 nm PuO2 nano-particles. They exhibit a weaker association with the goethite surface. Aggregation of PuO2 nano-particles was observed. There is no indication that the PuO2 nano-particles, once formed, will alter to Pu4O7 on goethite. Based on supernatant Pu concentrations, PuO2 nano-particle aggregation behavior is consistent with Pu(IV) hydrous oxide precipitation.

Enhanced Phase Stability for Tetragonal Zirconia in Precipitation Synthesis

Tetragonal ZrO2 nanocrystallites—with or without yttria (3 mol%) doping—have been synthesized via a precipitation process in which the hydrous oxide precipitate reacts with hexamethyldisilazane (HMDS) vapor before calcination. The nanocrystallites are formed and retain a tetragonal structure for hours after calcination at temperatures of 300°–1100°C. The enhanced structural metastability has been attributed to the combined effect of suppressed grain growth and reduced surface energy that results from the HMDS treatment.

Hydrochemical characterization of acute acid mine drainage at Iron Duke mine, Mazowe, Zimbabwe

Acid mine drainage (AMD) with a minimum pH of 0.52 was recorded at Iron Duke mine near Mazowe, Zimbabwe during an investigation of the environmental geochemistry of mine waters in the Greenstone Belts of Zimbabwe. Hydrochemical data for waters emanating from the Iron Duke waste-rock pile indicate their super-saturation with respect to Fe and SO42–. Extremely high dissolved concentrations of Al, Zn, Cu, Co, Ni, V, Cr, Cd and As also prevail. Substantial losses of metals from solution occur within 400 m of the AMD source through the precipitation of crystalline sulphates, principally melanterite. Further downstream, hydrous oxide precipitation forms the dominant mechanism of metal attenuation in waters characteristically under-saturated with respect to Fe sulphates. Speciation and saturation index data generated using the equilibrium model WATEQ4F, suggest that such codes have broad utility for generic prediction of the mineralogical contraints on metal mobility in acute AMD systems. Major discrepancies between modelled and empirical hydrochemistries are, however, evident for super-saturated waters in which the kinetics of Fe precipitation are slow, and in which total ionic strengths markedly exceed their theoretical maximum.

Hafnia ceramic nanofiltration membranes. Part I: Preparation and characterization

We have used a sol–gel process as an efficient method for the preparation of hafnia nanofiltration membranes. A stable colloidal sol was obtained after hydrolysis of an alkoxide and peptization of the hydrous oxide precipitate. After the drying of the sol, the hafnia powder was characterized using several methods, such as X-ray diffraction, dilatometry, thermal analysis, electrophoretic, and BET measurements. The hafnia membrane was obtained by coating the colloidal sol on a mesoporous ceramic support, followed by a drying and sintering of the gelled layer. The membrane was characterized by SEM and nitrogen adsorption–desorption to determine the pore size. The filtration properties of a hafnia membrane sintered at 450°C were determined using water permeability and rejection of solutions containing sucrose, polyethylene glycols of different molecular weights (400, 600, 1000) and salt solutions. This membrane is characterized by a MWCO of 420 Da and pore size near 1 nm.

Behavior of plutonium(V) in alkaline media

In alkaline solutions with NaOH concentration below 8 M, Pu(V) has been found to be unstable, disproportionating to form Pu(IV) hydrous oxide precipitate and dissolved Pu(VI). Sorption of Pu(V) on the freshly precipitating Pu(IV) hydrous oxide and partial reduction of Pu(VI) by water α-radiolysis products complicate disproportionation of Pu(V). Disproportionation and reproportionation equilibrium constants were measured in the range 4–8 M NaOH. The yield of disproportionation and reproportionation reaction products increase with temperature and sharply fall with NaOH concentration.

Reactive Solute Transport in an Acidic Stream: Experimental pH Increase and Simulation of Controls on pH, Aluminum, and Iron

Solute transport simulations quantitatively constrained hydrologic and geochemical hypotheses about field observations of a pH modification in an acid mine drainage stream. Carbonate chemistry, the formation of solid phases, and buffering interactions with the stream bed were important factors in explaining the behavior of pH, aluminum, and iron. The precipitation of microcrystalline gibbsite accounted for the behavior of aluminum; precipitation of Fe(OH)3 explained the general pattern of iron solubility. The dynamic experi ment revealed limitations on assumptions that reac tions were controlled only by equilibrium chemistry. Temporal variation in relative rates of photoreduction and oxidation influenced iron behavior. Kinetic limita tions on ferrous iron oxidation and hydrous oxide precipitation and the effects of these limitations on field filtration were evident. Kinetic restraints also characterized interaction between the water column and the stream bed, including sorption and desorption of protons f...

Trace characterisation of lithium niobate by neutron activation analysis

Coprecipitation behaviour of As, Au, Co, Cr, Cu, Eu, Fe, Ir, La, Lu, Mn, Mo, Nb, Ni, Pd, Pt, Sb, Sc, Ta, W, Zn and Zr during precipitation of hydrous oxide of niobium from lithium niobate was investigated. The matrix was dissolved in HF-HNO3, evaporated to dryness and niobium was precipitated from HNO3-H2O2 medium. The recovery studies were made using radiotracers. A radiochemical separation scheme based on group precipitation has been developed for the determination of Au, Co, Cr, Cu, Fe, Mn, Ni, Pd, Pt, Zn, Zr and rare earth elements. The method was applied to the analysis of lithium niobate. This analysis has provided fruitful information for improving the quality of the crystal.

The influence of a smectite clay on the hydrolysis of iron(III)

The hydrolysis and precipitation of Fe(III) in simple inorganic electrolyte solutions and in aqueous dispersions of the clay mineral montmorillonite have been investigated by UV-absorption spectrophotometry, pH-titration, chemical analysis, electron microscopy, electron-probe microanalysis and microelectrophoresis. Experimental evidence indicates that during the neutralization of acid-Fe(III) solutions in perchlorate, nitrate, chloride and sulphate media, Fe(III) speciation is essentially confined to the simple hexa-aquo ion Fe 3+, the first hydrolysis product, FeOH 2+, and the 1:1 complex species FeCl 2+ and FeSO + 4. Thermodynamically irreversible precipitation appears to occur in these systems under well-defined solution conditions, yielding compounds which conform to the stoichiometry Fe(OH) x A (3- x)/ n where the value of x depends on the identity of the anion species A n− . The presence of sulphate at SO 2− 4/Fe(III) mole ratios > 1 increases the pH value required for the onset of precipitation owing to formation of the relatively stable complex FeSO + 4. Formation function data have been compared with previously proposed hydrolysis/precipitation mechanisms. In the presence of montmorillonite, hydrolysis of Fe(III) is promoted, prior to precipitation, owing to preferential adsorption of FeOH 2+ at the clay surface. Whilst the presence of the clay appears to have no significant influence on the conditions required for hydrous oxide precipitation, experimental evidence shows a marked effect of the clay are the stoichiometry and growth of the initially precipitated Fe(III) phase.

Characterization of suspended solids in a stream receiving acid mine effluents, Bersbo, Sweden

Suspended particulate matter was recovered by filtration (0.40 μm) of water from a stream receiving acidic effluents from a mine tailings deposit. This solid phase formed rapidly as pH increased from 3.5 at the release point to 6.5, approximately 2 km downstream. The suspended solid was present in concentrations that ranged from 10–20 mg/l for anoxic conditions (winter) to 30–120 mg/l for oxic conditions (early spring). The solid consisted of FeOOH + Fe(OH) 3(am) and AlOOH + Al(OH) 3(am), as well as silicates. The organic content (of natural origin) was up to 30% (dry wt). Most of the Fe and Al from the leachate was precipitated in the particulate phase, approximately 98% of total metal content in the aqueous phase, as well as ∼50% of Mn, Cu, Zn, Cd and Pb. These elements were predominantly adsorbed on the hydrous oxide precipitate, or to some extent (Mn and Pb) coprecipitated, as indicated from a sequential leaching procedure and powder X-ray diffractometry. All the elements, particularly Cu, were to a significant degree associated with organic matter.

Electroprecipitation treatment of acid mine wastewater

The utilization of electroprecipitation for the treatment of acid solutions associated with the non-ferrous mining industry on a laboratory scale is explored. The electrolytic couple involved in the active process includes a consumable metal anode and an inert cathode. Mechanistically, oxidation of the anode is matched by the reduction of dissolved hydrogen ion to H 2 gas resulting in a pH increase in solution. Heavy metal removal is accomplished by either precipitation of hydrous oxides or by adsorption. Reduction of the solution metal content of from 100% for Al 3+ to 25% for Mn 2− is accomplished using a stainless steel rod anode; final solution pH stabilizes at a value of 4.9. Stabilization of solution pH reflects the attainment of kinetic equilibrium with respect to the rates of oxidation at the anode and diffusion of the oxidized products to the cathode where they precipitate as the hydroxide. Zinc and lead sacrificial anodes are also studied.

Determination of bismuth in ores, concentrates and non-ferrous alloys by atomic-absorption spectrophotometry after separation by diethyldithiocarbamate extraction or iron collection

Two simple, reliable and moderately rapid atomic-absorption methods for determining trace and minor amounts of bismuth in copper, nickel, molybdenum, lead and zinc concentrates and ores, and in non-ferrous alloys, are described. These methods involve the separation of bismuth from matrix elements either by chloroform extraction of its diethyldithiocarbamate (DDTC) complex, at pH 11.5–12.0, from a sodium hydroxide medium containing citric acid, tartaric acid, EDTA and potassium cyanide as complexing agents, or by co-precipitation with hydrous ferric oxide from an ammoniacal medium. Bismuth is ultimately determined, at 223.1 nm after evaporation of the extract to dryness in the presence of nitric and petchloric acids and dissolution of the salts in 20% v/v hydrochloric acid, or by dissolution of the hydrous oxide precipitate with the same acid solution, respectively. Results obtained by both methods are compared with those obtained spectrophotometrically by the iodide method after the separation of bismuth by DDTC and xanthate extractions.

Stability of polyvinyl chloride latex and of silica sols in the presence of copper (II) sulfate

The stability of polyvinyl chloride (PVC) latex and of Ludox HS-40 silica dispersions in the presence of copper(II) sulfate in varying concentrations has been studied over a broad pH range. The results are presented graphically in the form of the stability domains. The initial precipitation boundary for copper hydrous oxides was found to be affected by the presence of either PVC or silica particles but in each case the direction of the shift was different; for the PVC the boundary was moved to a some-what lower pH region whereas silica caused a shift toward higher pH. Entrapment in the copper hydrous oxide precipitate was found to be a major factor in the removal of PVC particles from suspension but this was not the case for the silica sols.

Electrometric Studies on the Precipitation of Hydrous Oxides of Some Quadrivalent Cations. Part II. Precipitation of Thorium Hydroxide from Solutions of Thorium Salts

Electrometric Studies on the Precipitation of Hydrous Oxides of Some Quadrivalent Cations. Part II. Precipitation of Thorium Hydroxide from Solutions of Thorium Salts

Spectrophotometric determination of rhenium with 4-methylnioxime

A simple method applicable to the spectrophotometric determination of less than 0.001% to more than 1.0% of rhenium in molybdenite concentrate and in “molybdenite roaster flue dust” has been developed. Interfering elements commonly found in these materials are removed in three operations: evaporation with hydrochloric acid, precipitation of hydrous oxides with ammonia, and formation of organometallic compounds with ethyl xanthate and chloroform extraction. The method is based on the formation of a soluble, stable, yellow-green rhenium-4-methylnioxime chelate where rhenium VII is reduced by tin II chloride in a dilute hydrochloric acid solution in the presence of 4- methylnioxime (4-methyl-1:2-cyclohexanedionedioxime). The colour develops in less than 5 min and the chloroform extract shows a maximum absorption at 436 mμ. The calibration curve conforms to Beer's law. The molar extinction coefficient for rhenium-4-methylnioxime is about 6.89 × 10 4 as compared to less than 4.5 × 10 4 reported for other methods for rhenium.

Spectrophotometric determination of copper, nickel, cobalt, iron and manganese as their pyridine thiocyanates: Simultaneous determination in mixtures

Spectrophotometric determinations of copper, nickel, cobalt, iron, and manganese, based on the chloroform extraction of the metal pyridine thiocyanates, have been investigated. Optimum conditions require the pH of the aqueous solution to be in the range about 5–8; tartaric acid is used to prevent precipitation of hydrous oxides. An excess of pyridine must be used because chloroform readily extracts pyridine from the aqueous solution. Results are improved by making the extraction from a solution of high ionic strength (2 or above), which is provided by magnesium nitrate. Perchlorate decreases the absorbance, but the effect is essentially constant over a perchlorate concentration range of 0.8 to 2 M. Although the metal pyridine thiocyanates are extracted by benzene, substituted benzenes, and halogenated hydrocarbons, chloroform is superior to other solvents in extraction efficiency and in colour stability of the extracted species. An example is given of the simultaneous determination of copper, nickel, cobalt, and iron in the same solution. Anions that also form metal pyridine compounds must be absent.

Separation of niobium and tantalum by N-benzoyl-N-phenylhydroxylamine

The pH range 3.5 to 6.5 for the complete precipitation of niobium and a pH below 1.5 for the precipitation of tantalum in separation and gravimetric analysis using N-benzoyl-N-phenylhydroxylamine are examined. Theyare verified to be correct. There is no possibility of the precipitation of hydrous oxide, even when the niobium or the tantalum solution is made ammonical in these pH ranges. (N.W.R.)

Radiochemical Separations of Indium

The radiochemical separation of indium by sulfide precipitation, solvent extraction of the bromide with diethyl ether, extraction with thenoyl trifluoroacetone and anion exchange in hydrochloric acid solution has been critically evaluated. Comparison of the efficiency of separation from 15 representative radioactive tracers showed that the sulfide precipitation lacked specificity as a decontamination step. Its primary utility is for the final preparation of counting plates or as a step preliminary to the determination of carrier yield by hydrous oxide precipitation. Ether extraction of the bromide gave decontamination factors as high as lO/sup 4/ for many dissimilar elements when conditions were well standardized. Thenoyltrifluoroacetone extractions gave decontaminations of 100 to 1000 for most elements. The anion exchange technique, when operated far from equtlibrium with a short column, gave decontamination factors of about 10/sup 3/ for many elements with a procedure that requires 1 hour.

Observations on the Rare Earths. LXI. Precipitation of Hydrous Oxides or Hydroxides from Perchlorate Solutions1

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTObservations on the Rare Earths. LXI. Precipitation of Hydrous Oxides or Hydroxides from Perchlorate Solutions1Therald Moeller and Norman FogelCite this: J. Am. Chem. Soc. 1951, 73, 9, 4481Publication Date (Print):September 1, 1951Publication History Published online1 May 2002Published inissue 1 September 1951https://doi.org/10.1021/ja01153a530RIGHTS & PERMISSIONSArticle Views112Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (155 KB) Get e-Alerts Get e-Alerts