M.T. Dorado

Transport of chromium (VI) through a Cyanex 923–xylene flat-sheet supported liquid membrane

Abstract The present investigation deals with carrier-facilitated membrane transport of chromium (VI) from chloride media across a flat-sheet supported liquid membrane (FSSLM) using as organic reagent the phosphine oxide, Cyanex 923. The permeation of Cr (VI) has been studied under various experimental conditions: stirring speed of the source phase, initial metal and carrier concentrations, organic phase diluent, HCl concentration in the source phase, composition of the stripping phase and support characteristics. The mass transfer coefficient was calculated as 67 μm/s and the thickness of the aqueous boundary layer was calculated to be 15 μm. Chromium permeation and thus speciation across the membrane was also investigated, and the order found was: CrO 4 2− =Cr 2 O 7 2− >Cr 3+ .

Preconcentration and matrix separation of precious metals in geological and related materials using metalfix-chelamine resin prior to inductively coupled plasma mass spectrometry

Abstract A method for determining Au, Pt, Pd, Ir and Rh in ores and silicates and Fe-formation rocks is described. Sample decomposition was carried out with aqua regia and HF, followed by fusion of any insoluble residue with Na22O2 in a glassycarbon crucible. The precious metals were separated, in 1.2 mol dm−3 HCl media, from the matrix elements by ion-exchange, using a mini-column with tetraethylenepentamine (metalfix-chelamine) resin. The resin was destroyed with HNO3 and H2O2 in a high-pressure vessel assisted by microwave heating, and the precious elements were determined by flow-injection inductively coupled plasma mass spectrometry. The sample treatment, optimization of analytical variables and measurable concentration levels are discussed. The limits of quantification (10 sdn − 1) calculated from a procedural blank sample solution were 4.0, 2.0, 1.5, 0.8 and 0.5 ng g−1 for Au, Pt, Pd, Ir and Rh, respectively. The accuracy of the proposed method was tested by determining these elements in SARM 7 platinum-ore reference material. For all the analytes, the relative standard deviation of the combined dissolution, separation and determination methods was below 3.5% (n = 6).

Extraction of platinum(IV) from hydrochloric acid solutions by amine alamine 304 in xylene. Estimation of the interaction coefficient between PtCl62− and H+

Abstract The extraction of Pt(IV) by Alamine 304 has been studied measuring the percentage of metal extraction as a function of different amine and metal concentrations and aqueous ionic strengths. Results indicated the formation of the species (R 3 NH + ) 2 PtCl 6 2− in the organic phase, the extraction reaction is exothermic (ΔH° = −1.9 kJ/mol). The formation constants vary linearly with the ionic strength; the interaction coefficient between PtCl 6 2− and H + was estimated using the Specific Interaction Theory. Further studies on the extraction of hydrochloric acid by the amine Alamine 304 are also presented.

Uphill permeation of chromium (VI) using Cyanex 921 as ionophore across an immobilized liquid membrane

The transport of chromium (VI) through an immobilized liquid membrane (ILM) containing Cyanex 921 (phosphine oxide) as a carrier has been studied. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentrations of chromium (VI) and HCl in the source phase, carrier concentration and diluent in the membrane, strippant in the receiving phase and support characteristics. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921-based ILM towards different metal ions and the behaviour of the system against other carriers are presented.

Phosphine oxide mediate transport: modelling of mass transfer in supported liquid membrane transport of gold (III) using Cyanex 923

The permeation of gold (III) through a supported liquid membrane impregnated with the phosphine oxide Cyanex 923 in n-decane has been investigated. A model is reported describing the transport mechanism which consists of: di6usion process through the feed aqueous di6usion layer, fast interfacial chemical reaction and di6usion through the membrane. The experimental data are quantitatively explained by mathematical equations describing the rate of transport. Di6erent rate-controlling processes take place as long as the metal transport occurs. High selectivity in the separation of gold (III) with respect to the platinum group metals is achieved. ? 2001 Elsevier Science Ltd. All rights reserved.

Determination of minor elements in steelmaking flue dusts using laser ablation inductively coupled plasma mass spectrometry.

Element determination in solid waste products from the steel industry usually involves the time-consuming step of preparing a solution of the solid. Laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the analysis of Cr, Ni, Cu, As, Cd and Sn, elements of importance from the point of view of their impact on the environment, in electric arc furnace flue dust (EAFD). A simple method of sample preparation as pressed pellets using a mixture of cellulose and paraffin as binder material was applied. Calibration standards were prepared spiking multielement solution standards to a 1:1 ZnO+Fe(2)O(3) synthetic matrix. The wet powder was dried and mechanically homogenised. Quantitative analysis were based on external calibration using a set of matrix matched calibration standards with Rh as a internal standard. Results obtained using only one-point for calibration without matrix matched, needing less time for standardization and data processing, are also presented. Data are calculated for flue dust reference materials: CRM 876-1 (EAFD), AG-6203 (EAFD), AG-6201 (cupola dust) and AG-SX3705 (coke ashes), and for two representative electrical arc furnace flue dusts samples from Spanish steelmaking companies: MS-1 and MS-2. For the reference materials, an acceptable agreement with certificate values was achieved, and the results for the MS samples matched with those obtained from conventional nebulization solutions (CN). The analytical precision was found to be better than 7% R.S.D. both within a single pellet and between several pellets of the same sample for all the elements.

Comparison of Laser Ablation and Dried Solution Aerosol as Sampling Systems in Inductively Coupled Plasma Mass Spectrometry

This paper describes a study designed to determine the possibility of using a dried aerosol solution for calibration in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The relative sensitivities of tested materials mobilized by laser ablation and by aqueous nebulization were established, and the experimentally determined relative sensitivity factors (RSFs) were used in conjunction with aqueous calibration for the analysis of solid steel samples. To such a purpose a set of CRM carbon steel samples (SS-451/1 to SS-460/1) were sampled into an ICP-MS instrument by solution nebulization using a microconcentric nebulizer with membrane desolvating (D-MCN) and by laser ablation (LA). Both systems were applied with the same ICP-MS operating parameters and the analyte signals were compared. The RSF (desolvated aerosol response/ablated solid response) values were close to 1 for the analytes Cr, Ni, Co, V, and W, about 1.3 for Mo, and 1.7 for As, P, and Mn. Complementary tests were carried out using CRM SS-455/1 as a solid standard for one-point calibration, applying LAMTRACE software for data reduction and quantification. The analytical results are in good agreement with the certified values in all cases, showing that the applicability of dried aerosol solutions is a good alternative calibration system for laser ablation sampling.

Preconcentration and analysis of gold from cyanide solutions with the use of a microcolumn packed with the phosphine oxide Cyanex 921

The phosphine oxide Cyanex 921 (tri-n-octylphosphine oxide) was found to be a very efficient extradant for gold from aurocyanide aqueous solutions. A system comprising a microcolumn packed with this new reagent was developed for the separation and enrichment of gold. Because of the high selectivity of the developed system it is possible to analyze gold in the presence of an excess of other metals and/or in high ionic strengh solutions.

Study of the application of air-water flow injection inductively coupled plasma mass spectrometry for the determination of calcium in steels

This paper describes a methodology for the determination of Ca, an important element in the process of steel making. Determination of Ca is typically problematic when using ICP-MS because of the 40Ar interference on the most abundant Ca isotope. In the present study the use of the 44Ca isotope for ICP-MS measurement was considered. To dissolve the samples, a microwave digestion system was applied to guarantee the total dissolution of the Ca compounds, thus minimizing the sample preparation time, the amounts of reagents used and the risk of contamination. Carbon and Si, normally present in steel samples, were eliminated by treatment with H2SO4 and HF to avoid 12C16O2 and 28Si16O isobaric interferences on the 44Ca isotope. After matrix removal by the use of mercury cathode electrolysis, air–water FI-ICP-MS was used for the determination of Ca. Scandium, with an ionization potential and mass number close to those of Ca, was used as an internal standard for quantitative measurements. The operating parameters for air-water FI-ICP-MS were optimized with respect to signal peak height intensities, stability and matrix effect. The detection limit obtained was 0.6 µg g–1 and the RSD value, calculated from ten replicates of a 200 µl injection of a 50 µg l–1 Ca solution spiked with 2 µg l–1 of Sc, was 0.7%. Data are presented for four certified reference steel materials: JSS 169–5 and 171–5, from Japanese Standards of Iron and Steel; and ECRMs 195–1 (Cr–Ni–steel) and 096 (low-S, low-Ca steel), from the Bureau of Analysed Samples.

Analysis of electrical arc furnace flue dusts by spark ablation inductively coupled plasma atomic emission spectrometry

A medium-voltage spark was used for the direct nebulization of electric arc furnace (EAF) flue dust. In order to attain the necessary sample conductivity, powder pellets are briquetted after mixing the sample 1 + 1 with graphite. The elutriated material was excited in an argon inductively coupled plasma (ICP). The use of cellulose as binder provides better results in terms of reproducibility. After optimization of the spark parameters (voltage, 500 V; repetition rate, 400 s–1; and resistance, 2.2 Ω), the carrier gas flow rate (2.1 l min–1 of argon) and the operating power of the ICP (1.2 kW), precisions (relative standard deviation) for zinc, lead, cadmium and iron range from 0.8 to 2.0%. The stability of the spark sampling, during a complete spark ablation (SA) ICP process (≈90 s) was tested by plotting emission intensity versus time profiles. The similarity between the amounts of analyte obtained from different pellets was proven by collecting the spark-eroded particles and analysing their carbon contents. Five steelmaking EAF flue dusts were selected for this study, using the two samples with extreme contents of the elements considered, for calibration. The results obtained by SA-ICP matched the results obtained by ICP from nebulized solutions.