BaSO4 Precipitation Research Articles

Laboratory Study on Precipitation of Barium Sulphate in Malaysia Sandstone Cores

Scale formation is one of the most serious oil field problems that inflict water injection systems primarily when two incompatible waters are involved. Two waters are incompatible if they interact chemically and precipitate minerals when mixed. Due to the lack of reaction kinetics data, the rate of barium sulphate deposition in porous rock was measured through flooding sandstone core samples of uniform properties with supersaturated brine. The brine was formulated at the core inlet by mixing of injected sea water and formation water that contained high concentration of barium ion at various temperatures (50 - 80°C) and differential pressures (100 - 200 psig). The rate of BaSO4 scale formation was estimated by monitoring the core effluent's barium ion concentration. The solubility of barium sulphate scale formed and how its solu- bility was affected by changes in salinity and temperatures (40 - 90°C) were also studied. Scanning Electron Microscopy analysis was also used to examine the nature of scale deposition throughout the core. The results indicated increased rate of BaSO4 precipitation at higher temperatures and greater brine super-saturation. The results were utilized to build a general reaction rate equation to predict BaSO4 deposition in sandstone cores for a given temperature, brine super-saturation and differential pressures.

Behaviour of the Alkaline Earth Elements (Beryllium to Radium) During the Precipitation of Jarosite-Type Compounds

The behaviour of the alkaline earth elements (beryllium, magnesium, calcium, strontium, barium and radium) during the precipitation of jarosite-type compounds was investigated over the range of conditions likely to be encountered in hydrometallurgical processes. Negligible amounts (< 0.05 wt%) of beryllium were incorporated in the structure of either potassium jarosite or sodium jarosite; this was a consequence of the small size of the divalent beryllium ion. In contrast, limited magnesium incorporation seemed to occur in the jarosite structure. Up to 0.20 wt% Mg was incorporated in sodium jarosite and up to 0.38 wt% Mg was detected in potassium jarosite; in both species, the amount increased as the magnesium concentration of the synthesis solution increased. Increasing temperatures, ferric ion concentrations and solution pH had only a minor effect on the extent of magnesium incorporation in the jarosite precipitates. In contrast, increasing concentrations of CuSO4 or ZnSO4 significantly reduced the level of Mg incorporation. Regardless of the calcium concentration of the solution, the calcium contents of the well-washed hydronium jarosite, sodium jarosite, potassium jarosite and lead jarosite precipitates were consistently less than 0.05 wt%Ca. The addition of soluble salts of strontiumand bariumto sulphate processing solutions resulted in the extensive precipitation of SrSO4 and BaSO4. However, electron microprobe analyses detected trace amounts of these elements in the potassium jarosite precipitates, suggesting a modest degree of Sr and Ba solid solubility. Picogram quantities of radium are soluble in sulphate media and 60-90% of the dissolved Ra precipitated with the jarosite-type compounds. However, it is not clear whether the radium was incorporated in the structure of the jarosite or whether it was adsorbed on the jarosite particles.

Convective micromixers — design and industrial applications

Convective static micromixers operate with high Reynolds numbers ( Re from 100 to 1000) in relatively large microchannels (100–1000 μm) for high flowrates and low risk of fouling and blocking. Typical flow characteristics of symmetrical mixing in T-shaped micromixers are presented with transient flow for Re number larger than 240. The simulation results are assisted by experimental data. Parallel mixing elements increase the mass flowrate up to 25 kg/h with 100 kPa pressure loss. The typical flow characteristics are described, which are essential for successful mixing devices. Three dimensionless parameters are introduced to describe the mixing performance and effectiveness of such devices. Particle generation are critical in microchannels due to fouling issues. The gas phase particle generation from homogeneous condensation of vitamin E acetate is described, reaching to particle diameters of 20 nm from temporal temperature gradients of about 1.6×106 K/s. In liquid phase, the reactive precipitation of BaSO4 is investigated, leading to particle diameters below 100 nm.

Feasibility Study of Solidification for Low-Level Liquid Waste Generated by Sulfuric Acid Elution Treatment of Spent Ion Exchange Resin

We studied cement-like solidification process for low-level liquid waste with relatively high levels of radioactivity that contains a high concentration of sodium sulfate. For this type waste, it is important that the sulfate ion should not dissolve from the solid waste because it forms ettringite on reaction with minerals in the concrete of the planned repository, and this leads to cracking during repository storage. It is also preferable that the pH of the pore water of the solid waste be low, because the bentonite of the repository changes in quality on exposure to alkaline solution. Therefore, the present solidification process has two procedures: conversion into insoluble sulfate from sodium sulfate (CIS) and formation of low pH cement-like solid (FLS). In the CIS procedure, BaSO4 precipitation occurs with addition of Ba(OH)2•8H2O to the liquid waste. In the FLS procedure, silica fume and blast furnace slag are added to the liquid waste containing BaSO4 precipitate. We show the range of appropriate Ba/SO4 molar ratio is from 1.1 to 1.5 in the present solidification process by leaching tests for some kinds of solid waste samples. The CIS reaction yield is over 98% at a typical CIS condition, i.e. Ba/SO4 molar ratio=1.3, reaction temperature=60°C, and time=3 hr.

Micro-computed tomography of fatigue microdamage in cortical bone using a barium sulfate contrast agent

Accumulation of microdamage during fatigue can lead to increased fracture susceptibility in bone. Current techniques for imaging microdamage in bone are inherently destructive and two-dimensional. Therefore, the objective of this study was to image the accumulation of fatigue microdamage in cortical bone using micro-computed tomography (micro-CT) with a barium sulfate (BaSO 4) contrast agent. Two symmetric notches were machined on the tensile surface of bovine cortical bone beams in order to generate damage ahead of the stress concentrations during four-point bending fatigue. Specimens were loaded to a specified number of cycles or until one notch fractured, such that the other notch exhibited the accumulation of microdamage prior to fracture. Microdamage ahead of the notch was stained in vitro by precipitation of BaSO 4 and imaged using micro-CT. Reconstructed images showed a distinct region of bright voxels around the notch tip or along propagating cracks due to the presence of BaSO 4, which was verified by backscattered electron imaging and energy dispersive spectroscopy. The shape of the stained region ahead of the notch tip was consistent with principal strain contours calculated by finite element analysis. The relative volume of the stained region was correlated with the number of loading cycles by non-linear regression using a power law. This study demonstrates new methods for the non-destructive and three-dimensional detection of fatigue microdamage accumulation in cortical bone in vitro, which may be useful to gain further understanding into the role of microdamage in bone fragility.

CFD modelling of BaSO4 precipitation inside microemulsion droplets in a semi-batch reactor

Nanoparticle production using microemulsion droplets has become a very interesting technique in the recent years. It allows a controlled adjustment of the particle size, which is an essential task due to the highly size-dependent properties of nanoparticles. For numerical investigations of this configuration a population balance model (PBM) framework based on discrete coordinates has been derived. An appropriate reduction concept is applied to obtain an efficient numerical solution. Although the resulting zero-dimensional (spatially homogeneous) calculations show a qualitatively good agreement with the experimental data for stoichiometric conditions, larger deviations have been observed for cases with a high concentration excess of one reactant inside the microemulsion droplets. Such deviations might result from the fact that the precipitation rate strongly depends on the local supersaturation. High concentration differences, especially near the feed lead to large local variations of the supersaturation profile. Thus, computational fluid dynamics (CFD) simulations have been performed for a refined analysis. This has been managed by implementing the reduced PBM model in the commercial CFD code FLUENT® 6.2 via user-defined scalars and functions. By this way, it becomes possible to investigate the reaction process for various three-dimensional inhomogeneous hydrodynamic conditions with acceptable computational times. The obtained results are finally compared with the homogeneous calculation results and with the experiments. Moreover, local variations within the reactor are also examined.

Generation of Gas-Phase VO2+, VOOH+, and VO2+−Nitrile Complex Ions by Electrospray Ionization and Collision-Induced Dissociation

Cationic metal species normally function as Lewis acids, accepting electron density from bound electron-donating ligands, but they can be induced to function as electron donors relative to dioxygen by careful control of the oxidation state and ligand field. In this study, cationic vanadium(IV) oxohydroxy complexes were induced to function as Lewis bases, as demonstrated by addition of O2 to an undercoordinated metal center. Gas-phase complex ions containing the vanadyl (VO2+), vanadyl hydroxide (VOOH+), or vanadium(V) dioxo (VO2+) cation and nitrile (acetonitrile, propionitrile, butyronitrile, or benzonitrile) ligands were generated by electrospray ionization (ESI) for study by multiple-stage tandem mass spectrometry. The principal species generated by ESI were complexes with the formula [VO(L)n]2+, where L represents the respective nitrile ligands and n=4 and 5. Collision-induced dissociation (CID) of [VO(L)5]2+ eliminated a single nitrile ligand to produce [VO(L)4]2+. Two distinct fragmentation pathways were observed for the subsequent dissociation of [VO(L)4]2+. The first involved the elimination of a second nitrile ligand to generate [VO(L)3]2+, which then added neutral H2O via an association reaction that occurred for all undercoordinated vanadium complexes. The second [UO(L)4]2+ fragmentation pathway led instead to the formation of [VOOH(L)2]+ through collisions with gas-phase H2O and concomitant losses of L and [L+H]+. CID of [VOOH(L)2]+ caused the elimination of a single nitrile ligand to generate [VOOH(L)]+, which rapidly added O2 (in addition to H2O) by a gas-phase association reaction. CID of [VONO3(L)2]+, generated from spray solutions created by mixing VOSO4 and Ba(NO3)2 (and precipitation of BaSO4), caused elimination of NO2 to produce [VO2(L)2]+. CID of [VO2(L)2]+ produced elimination of a single nitrile ligand to form [VO2(L)]+, a V(V) analogue to the O2-reactive V(IV) species [VOOH(L)]+; however, this V(V) complex was unreactive with O2, which indicates the requirement for an unpaired electron in the metal valence shell for O2 addition. In general, the [VO2(L)2]+ species required higher collisions energies to liberate the nitrile ligand, suggesting that they are more strongly bound than the [VOOH(L)2]+ counterparts.

Experimental approaches for understanding mixing performance of a minireactor

AbstractThree experimental approaches are presented to determine the mixing characteristics of a new kind of high‐efficiency membrane dispersion minireactor in which microfiltration membranes are applied as the dispersion media. Residence time distribution (RTD) curves were measured for determining the macromixing characteristics. A typical Dushman reaction (iodide–iodate) coupled with a neutralization and precipitation reaction of BaSO4 were introduced to characterize the micromixing performance of a single‐phase mixing process. A dye extraction method was also applied to study the micromixing performance of a two‐liquid phase‐mixing system. The RTD result showed that the flow performance in the minireactor was almost in the plug flow condition. The micromixing performance was expressed with a segregation index, which could be &lt;0.002. The single‐phase micromixing performance reached the desired level. The result of precipitation of BaSO4 showed that the mixing performance had a substantial influence on the particle size and size distribution. It was found that in the single‐phase mixing process the mixing performance was mainly influenced by the phase flux and the membrane pore size. With decreasing dispersed fluid flux or the membrane pore size, or with increasing continuous fluid flux, the micromixing performance was enhanced. The dye extraction method can correctly determine the mixing performance of a two‐liquid phase‐mixing system. Unlike the single‐phase mixing process, in the two‐liquid phase‐mixing process there was a minimum value for the mixing efficiency with the change of the continuous‐ or dispersed‐phase flux, when the membrane pore size was &gt;0.9 μm. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Numerical study on particle size distribution in the process of preparing ultrafine particles by reactive precipitation

Based on the population balance and mass balance in a reactive precipitation process, a numerical simulation model was developed to predict the particle size distribution (PSD) in the reactive precipitation process. The precipitation system of BaCl2 with Na2SO4 to prepare BaSO4 in aqueous solution was adopted to obtain ultrafine particles in a stirred precipitation reactor and the particle size distribution and the morphology of the particle were observed under transmission electron microscope. It was illustrated by the experimental observation of the micrographs of BaSO4 particles obtained that apparent agglomeration occurred between the particles, which phenomenon must be taken into consideration in PSD modeling. The population balance equation was calculated by discretization method to obtain particle number and particle size distribution. By implementing the model, the reactive precipitation process in a batch reactor including reaction, nucleation, growth and agglomeration was simulated. The simulation results were validated by the experimental data of BaSO4 precipitation. Further analysis was endeavored to explore the effects of some important factors such as the supersaturation degree and agglomeration on the evolution of the volume-based characteristic particle size and the variance of volume-based characteristic size of the particles. It was depicted that particle size and particle size distribution are controlled by the supersaturation degree and agglomeration between the particles. Stemming from the analysis in the context, the disciplinarian of the influences of these factors and the method for controlling particle size distribution were presented for the reactive precipitation process.

Fatigue Microdamage in Bovine Cortical Bone Imaged by Micro-Computed Tomography Using a Barium Sulfate Contrast Agent

AbstractAccumulation of microdamage during fatigue can lead to increased fracture susceptibility in bone. Current techniques for imaging microdamage in bone are inherently destructive and two-dimensional. A non-destructive, three-dimensional technique is needed to measure the spatial density of microdamage accumulation. Therefore, the objective of this study was to image microdamage accumulation in cortical bone during fatigue using micro-computed tomography (micro-CT) with a barium sulfate (BaSO4) contrast agent. Bovine cortical bone beams were loaded under four-point bending fatigue. Two symmetric notches were machined on the tensile surface in order to generate damage at the stress concentrations during loading. Specimens were loaded to a specified number of cycles or until one notch fractured, such that the other notch exhibited accumulated microdamage just prior to fracture. Microdamage ahead of the notch was stained by precipitation of BaSO4 and imaged using micro-CT. Reconstructed images showed a distinct region of bright voxels around the notch tip or along propagating cracks due to the presence of BaSO4, which was verified by backscattered electron imaging and energy dispersive spectroscopy. The stained region exhibited a characteristic kidney shape perpendicular to the notch tip, which was correlated to principal strain contours calculated by finite element analysis. The area of stained regions was positively correlated with the number of loading cycles.

Improvement of the sample preparation method for AMS measurement of 36Cl in natural environment

The isobaric interference, 36S, is a main problem in AMS measurement of 36Cl. The SO42− ion exists in the natural environment with an amount compared with the chlorine concentration. The chemical procedure should have a powerful capacity to remove sulfur from samples. Traditionally, precipitation of BaSO4 is used to separate S from the sample material. The sulfur reduction process should be repeated more than two times for measurement of the sample with a36Cl/Cl ratio down to 10−13. The multi-reduction processes take a long time and chlorine recovery is low. In the present work, a new cation-exchange-column method is used. The Ba column is used for separation of S. When the sample solution is passed through the Ba Column, SO42− are absorbed. After removal of SO42− the sample solution is passed through the H column to absorb metal ions and transfer Cl− to HCl. Then the HCl solution is passed through the Na column to convert HCl to NaCl. Finally, excess AgNO3 is added to the NaCl solution and AgCl is precipitated for AMS measurement. The chemical process only takes ∼6 h, the time much shorter than the traditional method, and the chlorine recovery is higher than ∼90%. The rainwater, groundwater and seawater samples were prepared with this method. The 36Cl/Cl ratios in those samples were measured in range of 10−13– 10−14. The method can also be used for soil, sediment and rock samples after extraction of chlorine (36Cl) from the sample materials. Some sediment and rock samples were prepared and 36Cl was measured.

Synthesis of controlled-structure sulfate-based copolymers via atom transfer radical polymerisation and their use as crystal habit modifiers for BaSO4

Atom Transfer Radical Polymerisation (ATRP) has been used to polymerise ammonium 2-sulfatoethyl methacrylate (SEM) in aqueous media using various poly(ethylene glycol) (PEG) macro-initiators to give a range of controlled-structure, sulfate-based block copolymers. Such PEG–SEM diblock copolymers are effective crystal habit modifiers for the in situ precipitation of BaSO4 in dilute aqueous solution. In the presence of the PEG–SEM copolymer, near-monodisperse, lozenge-shaped BaSO4 particles were obtained, depending on the relative block lengths. X-Ray diffraction and thermogravimetric analysis of these particles demonstrated that they are polycrystalline in nature and contain around 8% copolymer by mass. This compares with the characteristic polydisperse rectangular platelets of single crystal BaSO4 obtained in the absence of the copolymer. Control experiments suggest that, while only the SEM block interacts directly with the particle surface, the PEG block also plays an important role in controlling the crystal growth. Independent variation of the PEG and SEM block lengths therefore provides a subtle mechanism for controlling the morphology, size distribution and crystalline structure of the inorganic phase.

Computational Fluid Dynamics Modeling of the Precipitation Process in a Semibatch Crystallizer

To better understand the complicated phenomena in a precipitation process, computational fluid dynamics (CFD) is utilized to account for reactions, crystallization, mixing, and their interactions. The moment transformations of the population balances taking into account the chemical and crystallization kinetics are integrated into a CFD solver to describe the generation and transportation of the crystal phase. The current work applies this CFD tool to simulate the reactive precipitation process in a semibatch crystallizer, which is widely used in chemical and pharmaceutical industries. BaSO4 precipitation is employed as an example system. The influence of hydrodynamics in the stirred tank, as characterized by the impeller speed and feed location, on the distribution of supersaturation and the subsequent crystal size distribution is investigated. The numerical predictions are validated with measurements and can be used as an aid in the optimization of semibatch precipitator design.

Effect of ion excess on particle size and morphology during barium sulphate precipitation: an experimental study

Precipitation of BaSO 4 has been studied in a vessel of ∼8 l stirred by a Rushton turbine. Either BaCl 2 or Na 2SO 4 as a limiting reactant of concentration 0.1 M was added to the tank containing the opposite component at a concentration from 0.0018 to 0.027 M , thereby giving total molar ratios from 1/15 to 1 or 1 to 15/1, respectively. The results were generally not symmetrical. Molar ratios closest to 1 with BaCl 2 as the feed gave the largest d 43 (∼20 – 30 μm) whilst for Na 2SO 4 feed, the mean size d 43 was ∼10– 15 μm . At the ratios 1/15 ( BaCl 2 feed) and 15/1 ( Na 2 SO 4 feed), the mean sizes were much smaller and very similar (∼3– 5 μm) . In all cases, the CoV was ∼0.4 –∼0.5. The impact of agitation speed was generally rather small. It is suggested that varying ionic ratios might be an effective and rather simple way of achieving a degree of particle size control.

Catalytic Desulfurization of Carbon Black on a Platinum Oxide Electrode

Organically bound sulfur is a common impurity in carbon blacks, such as vulcanized carbon and coal. Whereas this organosulfur is usually removed by heating to high temperatures, we describe a low-temperature method to desulfurize solid carbon via oxidation (ultimately to SO42-) on a Pt catalyst in oxygenated aqueous media. The reaction is monitored on Vulcan carbon, which is the favored support for the Pt catalysts used in fuel-cell electrodes but which has a high concentration (nominally 5000 ppm) of organosulfur. Vulcan carbon is electrodesulfurized by dispersing it in a heated, dilute HNO3 electrolyte where it can physically contact a Pt mesh anode that is maintained as Pt oxide. After 40−180 min of electrolysis in oxygenated solution at +1.0 V versus Pd/H, sulfate is present in the electrolyte (as measured by precipitation of BaSO4). X-ray photoelectron spectroscopy of the dried, electrodesulfurized carbon shows that ∼30% of the near-surface organosulfur is removed. The remaining sulfur presumably doe...

Micromixing in a single‐feed semi‐batch precipitation process

AbstractA mixing‐precipitation model (based on engulfment, the E‐model by Baldyga and Rohani, 1987) is applied to a single‐feed semi‐batch precipitation process to describe the mixing effects on the final particle‐size distribution (PSD) and particle morphology. The model describes mixing on two scales: the microscale (at which the flow directly affects nucleation and growth phenomena in the mixed‐precipitation (MP) zone) and a macroscale (which controls the environment for the MP‐zone). Application of the model is limited to 1≪Sc&lt;4,000 and slow feed addition rates. When the model was applied to experimental results of BaSO4 precipitation, satisfactory agreement between predicted and observed results was obtained. Experiments were carried out in a single‐feed 18‐L Rushton reactor, whereby the effects of various operating conditions such as feed rate, intensity of mixing, mean initial reactant concentration and reactant volume ratio on barium sulfate precipitation process were investigated.

A reaction cell for in situ studies of hydrothermal titration

A reaction cell for in situ studies of both ion-exchange and hydrothermal titration reactions has been designed and built. This cell allows the injection of reagents into a reaction mixture over time during X-ray data collection. A demonstration experiment followed the injection of Na2SO4(aq) into BaClz(aq) to yield a time-resolved X-ray powder diffraction pattern of the precipitation of BaSO4(s). Time-resolved synchrotron X-ray powder diffraction has provided information on the crystallization kinetics and the identity of intermediate phases during hydrothermal synthesis experiments. In particular, the formation of zeolites, microporous phosphates, mesoporous silicates, mieroporous sulfides and Sorel cements have been investigated extensively (Barnes et al., 1996; Francis et al., 1996; Gualtieri et aL, 1997; Norby, 1996, 1997a,b; N~rlund Christensen et aL, 1997). We have previously developed a reaction cell for these in situ studies (Norby, 1996) in which reactions take place in a 0.5-1 mm quartz glass capillary mounted in a Swagelock fitting and held in place using a ferrule. Pressure applied from a nitrogen cylinder and heating using a hot air stream allow hydrothermal conditions to be achieved. This method permits the study of a reaction mixture under static or noninteractive conditions. Some syntheses however require the addition of reactants over time. Such hydrothermal titration techniques have been used in syntheses of microporous sulfides (Parise et aL, 1996) as well as to study the formation of iron sulfide phases via precipitation/transformation reactions (Schoonen & Barnes, 1991). These studies were performed using steel autoclaves where injection of reactants without loss of pressure could be performed. Typically, a reaction mixture is kept at temperature and pressure for some time to allow formation of precursor species. Later, additional reactants are injected into the solution to induce precipitation of the materials of interest. These investigations are important for gaining mechanistic information, but are restricted in that reactions must be quenched before analysis. By performing time-resolved in situ experiments, it is possible to obtain detailed information about the system under actual reaction conditions. We describe here the development of a microreaction cell for in situ powder diffraction studies which can be used for hydrothermal titration, ion exchange, hydrothermal precipitation reactions and to investigate solid/gas phase interactions in real time. The design of the reaction cell is shown in Fig. 1. Reactions take place in a 1 mm quartz glass capillary (A) which is mounted in a Swagelock tee (B) using a Vespel ferrule. Through the connected tube (C), a pressure can be applied to the surface of the reaction mixture in the capillary. Injection takes place through a 0.3 mm quartz glass capillary (D), which goes through the tee and into the 1 mm capillary. This 0.3 mm capillary is mounted between a Swagelock elbow and the tee with Vespel ferrules, all of which are mounted on a modified goniometer head (F). Injection under pressure through the elbow (E) is possible via a gas chromatography syringe (not shown) mounted in an aluminium holder. A screw connected to the piston of the syringe ensures pressurization. By turning the screw, the piston is depressed and a controlled volume can be injected into the 1 mm capillary through the 0.3 mm capillary. Alternatively, the position of the sample capillary (A) can be plugged and the assembly extended to expose the injection capillary location to the X-ray beam. Ports (G) and (C) then become supply and exhaust lines, respectively, for flowthrough ion-exchange experiments or solid/gas phase reac

Reduction of nitrate to ammonium by sulphate green rust: activation energy and reaction mechanism

AbstractIron(II)-containing minerals are potential inorganic nitrate reductants in soils and sediments. Specifically, synthetic green rust (Fe4IIFeIII2(OH)12SO4.yH2O, GR) reduces nitrate to ammonium. The reaction of GR with two different nitrate salts, NaNO3and Ba(NO3)2, has been compared. The reaction stoichiometry and the reaction order with respect to Fe(II) in GR does not change in the examined temperature range (15-50°C) irrespective of the nitrate salt used. Activation energies of 83.9±7.6 kJ mol-1and 90.5±6.9 kJ mol-1have been determined for the reaction of GR with NaNO3and Ba(NO3)2, respectively. However, for the latter reaction the rate of reaction is increased 40 times. Based on X-ray and M6ssbauer investigations, this acceleration of the reaction rates is attributed to the forced exchange of sulphate with nitrate in GR interlayers caused by precipitation of BaSO4outside the GR particles, a reaction which does not occur in the presence of NaNO3. This difference in anion exchange behaviour is confirmed by anion exchange experiments with the redox-inactive GR-analogue, pyroaurite. A reaction model initiated by nitrate electrostatically bound at positively charged sites of GR is proposed.

Assessment of Dowex 1-X8-based Anion-exchange Procedures for the Separation and Determination of Ruthenium, Rhodium, Palladium, Iridium, Platinum and Gold in Geological Samples by Inductively Coupled Plasma Mass Spectrometry

Synthetic multielement solutions of the platinum group metals (PGE: Ru; Rh; Pd; Ir; Pt) and gold, with analysis by ICP-AES and ICP-MS, have been used to study the behaviour of the precious metals on Dowex 1-X8 resin. Simple solutions of precious-metal chlorocomplexes showed near-complete adsorption (>99%) of most elements, and only minor breakthrough of Ru and Ru (≈5%). Solutions pre-treated with acid mixtures typically used to decompose geological samples, demonstrated that perchloric acid adversely affects the adsorption of the PGEs on the resin. Solutions treated with HF–HNO 3 –HCl maintained good retention of Ir, Pt, Au (>99%), Pd (>94%) and Ru (>90%), but displayed significant loss (up to 40%) of Rh. A two-step procedure was necessary to elute the precious metals from the resin: 0.3 mol l - 1 thiourea prepared in 0.1 mol - 1 HCl removed Ru, Pd, Pt, Au, and some Rh: 12 mol l - 1 HCl eluted remaining Rh and all Ir. Recoveries ranged from 50 to 100%. At low levels, the determination of PGE and Au in the thiourea fraction by ICP-MS was compromised by high levels of total dissolved solids (TDS), which necessitated dilution of the eluate prior to analysis. The TDS was reduced by decomposing thiourea with HNO 3 and removing SO 4 2 - by precipitation of BaSO 4 , but this led to lower and more erratic results, and increased contamination. An assessment of the optimised procedure employing geological reference materials PTM-1, PTC-1 and SARM7, indicated that acceptable results should be attainable for ICP-MS determination of most elements in geological samples containing high concentrations (>1 µg g - 1 ) of the PGE, for which decomposition of thiourea is unneccessary. The addition of a decomposition step led to low recovery of all elements except Ir, which was present entirely in the HCl eluate. The method is viable for the determination of Ir in a range of geological materials, but modifications will be required if it is to be extended to the other precious metals.

Three-zone approach for precipitation of barium sulphate

The three-zone approach, introduced by Gösele and Kind [1] [Chem. Ing. Tech. 63 (1991) 59], has been used to investigate BaSO4 precipitation. Experimental relations for the growth and nucleation of BaSO4 are found that show good agreement with those of Angerhöfer [2] [Thesis, TU München, 1994] and Van der Leeden [3] [Thesis, TU Delft, 1991]. The parameters studied in the three-zone approach are the feed concentration, circulation time and volume of the zones. Preliminary results show that the model used correctly predicts the influence of the above-mentioned parameters on the mean particle size and the conversion. Experiments conducted at various mixing conditions in the 3 zones show that the influence of the parameters becomes stronger when the mixing in the 3 zones becomes less intensive. This influence cannot be explained by the present model, which assumes that the zones are ideally mixed.