Speciation analysis of antimony in extracts of size-classified volcanic ash by HPLC-ICP-MS.

Although there is concern about the presence of toxic elements and their species in environmental matrices, for example water, sediment, and soil, speciation analysis of volcanic ash has received little attention. Antimony, in particular, an emerging element of environmental concern, has been less studied than other potentially toxic trace elements. In this context, a study was undertaken to assess the presence of inorganic Sb species in ash emitted from the Copahue volcano (Argentina). Antimony species were extracted from size-classified volcanic ash (<36 microm, 35-45 microm, 45-150 microm, and 150-300 microm) by use of 1 mol L(-1) citrate buffer at pH 5. Antimony(III) and (V) in the extracts were separated and quantified by high-performance liquid chromatography combined on-line with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Antimony species concentrations (microg g(-1)) in the four fractions varied from 0.14 to 0.67 for Sb(III) and from 0.02 to 0.03 for Sb(V). The results reveal, for the first time, the occurrence of both inorganic Sb species in the extractable portion of volcanic ash. Sb(III) was always the predominant species.

Optimization and empirical modeling of HG-ICP-AES analytical technique through artificial neural networks.

An artificial neural network technique has been applied to the optimization of a hydride generation-inductively coupled plasma-atomic emission spectrometry (HG-ICP-AES) coupling for the determination of Ge at trace levels. The back propagation of errors net architecture was used. Experimental parameters and their relationship have been studied, obtaining a surface response of the system. The results and optimization aspects achieved with the neural network approach have been compared to the "one variable at time" and SIMPLEX methods.

Sorption of antimony onto hydroxyapatite.

We prepared synthetic hydroxyapatite [HAP; Ca5(PO4)(3-x)(CO3)x(OH)(1+x) (x = 0.3)] and then investigated this material's ability to remove trivalent antimony [Sb(III)] from water. The HAP was characterized by X-ray diffraction analysis, scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. The sorption of Sb(III) to HAP was measured over an Sb(III) concentration range of 0.05-50 mg L(-1), at constant ionic strength (I = 0.01 mol dm(-3)) in equilibrated aqueous suspensions (34 g dm(-3)) for 5 < pH < 8 in vessels that were closed to the atmosphere. Under these conditions, we found that HAP particles were enriched in Ca after incongruent dissolution of the solid. More than 95% of the Sb(III) in solution adsorbed to the solid-phase HAP in <30 min. The equilibrium distribution of Sb(III) (solid vs liquid phase) was characterized by a Langmuir model with gamma(max) = 6.7 +/- 0.1 x 10(-8) mol m(-2) (1.4 +/- 0.2 x 10(-4) mol dm(-3) g(-1)) and K(ads) = 1.5 +/- 0.2 x 10(3) dm3 mol(-1). As Sb adsorption occurred, the pH of the isoelectric point (pH(iep)) of the HAP suspensions declined from 7.7 to 6.9. This finding supports the idea that the negative surface potential of the HAP increased due to the adsorption of Sb as a charged species. The decline in pH(iep) during Sb adsorption plus the thermodynamic description of the Sb(III)-HAP-H2O system suggest likely surface reactions for the interaction of Sb with HAP. We discuss the efficiency of Sb removal from water by HAP in the context of phosphate enrichment.