Speciation major elements

Ball, J. W, E. A. Jenne and D. K. Nordstrom, 1979, WATEQ2 - a computerized chemical model for trace and major element speciation and mineral equilibria of natural waters. In E. A. Jenne (ed.), Chemical Modeling in Aqueous Systems, American Chemical Society, Washington DC, pp. 815-835. 

Direct methods for determining the combinational form of an element or its oxidation state include infrared absorption spectrometry, X-ray diffraction and, more recently, electron paramagnetic resonance - nuclear magnetic resonance -and Mossbauer spectrometry. With such techniques the combinational forms of major elements in soil components such as clay minerals, iron, manganese and aluminium oxyhydroxides and humic materials and the chemical structures of these soil components have been elucidated over the past 50 years. These direct, mainly non-destructive, methods for speciation are dealt with in some detail in Chapter 3 and are not further discussed here. 

WATEQ2—A Computerized Chemical Model for Trace and Major Element Speciation and Mineral Equilibria of Natural Waters... 

The focus of this research and other mass balance studies has been on trace elements (1,2,3). However, in future studies on speciation it will be necessary to know the concentrations of the elements present in amounts above 1%. Therefore, analyses of the oil shale and spent shale samples were performed for these elements. Atomic absorption and colorimetry were used for many of these analyses. Some major element results also were obtained by the broad-range instrumental analysis surveys. The comparison of the results obtained by the different techniques shows large discrepancies. 

In this chapter, we have tried to review the recent literature on trace elements in rivers, in particular by incorporating the results derived from recent ICP-MS measurements. We have favored a field approach by focusing on studies of natural hydrosystems. The basic questions which we want to address are the following What are the trace element levels in river waters What controls their abundance in rivers and fractionation in the weathering - - transport system Are trace elements, like major elements in rivers, essentially controlled by source-rock abundances What do we know about the chemical speciation of trace elements in water To what extent do colloids and interaction with solids regulate processes of trace elements in river waters Can we relate the geochemistry of trace elements in aquatic systems to the periodic table And finally, are we able to satisfactorily model and predict the behavior of most of the trace elements in hydrosystems ... 

Certainly, CO2 evolved during late diagenesis must ultimately return to the atmosphere/ocean. It also seems clear that transport of major components such as silicon and potassium between sandstones and shales at a scale of a few meters is required and can perhaps be accomplished by diffusion (Thyne et ai, 2001). New data, especially for shales, must be obtained before simultaneous quantitative balances can be proposed for the reactions in Table 1. The speciation of aluminum in pore fluids, the initial and final quantities of the reactants and products in both sandstones and shales, and the precise volumes of sandstones and shales in the sequences in question are key data needed to ascertain the scale of mobihty for the major elements in late diagenesis. Our abihty to answer basic questions about the rock cycle falls short, in large part, for lack of information about the major mineral components of shale, the most common type of sedimentary rock. 

This example illustrates the potential of TPR. Quantitative information is obtained on the speciation of a complex catalyst system. On the other hand, additional techniques are needed to get a molecular picture. Furthermore, from the results major elements are obtained for a recipe for calcination and reduction treatments. For instance, calcination should take place at conditions such that nitrates are completely removed the temperature should exceed 650 K. Furthermore, in general, Co ions should not diffuse into the support. As a consequence, a temperature of 900 K should not be exceeded (see Fig. 12.3 above a calcination temperature of 925 K the high temperature peak increases strongly due to the... 

Garrels and Thompson (1962) conducted speciation calculations for the major elements of seawater. They showed that the major cations (Na, K, Ca, Mg) and Cl are mostly (>90%) uncomplexed in seawater. The anions S04, COj, and HCO7 are tied up as complexes to a significant extent. When similar calculations are done for the minor elements in seawater, we find a different story. Most of the minor elements exist as complex ions or ion pairs. In particular, the metals form complexes with anions (ligands) such as CO , Cl , and especially OH . The best estimates of the speciation of the elements in seawater are given in Table 9-10. 

The method outlined is also applicable to trace metal data collected by ICP-MS and ICP-AES. Recently, Hassellov et al., demonstrated that it is possible to measure major elements as well as a range of trace metals, including Cs, Cd, Cu, Pb, Zn, and Further, they showed that it was possible to obtain speciation data across the size range. 

BaU, J.W., E.A. Jenne and D.K. Nordstrom, "WATEQ2 - A Computerized Chemical Model for Trace and Major Element Speciation and Mineral Equilibria of Natural Waters", Chemical Modeling in Aqueous Systems, E.A. Jenne, ed., ACS Symposium Series 93, pp 815-835, (1979)... 

SALI compares fiivorably with other major surface analytical techniques in terms of sensitivity and spatial resolution. Its major advantj e is the combination of analytical versatility, ease of quantification, and sensitivity. Table 1 compares the analytical characteristics of SALI to four major surfiice spectroscopic techniques.These techniques can also be categorized by the chemical information they provide. Both SALI and SIMS (static mode only) can provide molecular fingerprint information via mass spectra that give mass peaks corresponding to structural units of the molecule, while XPS provides only short-range chemical information. XPS and static SIMS are often used to complement each other since XPS chemical speciation information is semiquantitative however, SALI molecular information can potentially be quantified direedy without correlation with another surface spectroscopic technique. AES and Rutherford Backscattering (RBS) provide primarily elemental information, and therefore yield litde structural informadon. The common detection limit refers to the sensitivity for nearly all elements that these techniques enjoy. 

A major share of elemental analysis will eventually evolve into speciation analysis. 

New developments are, however, needed to make a major step forward in the field of speciation analysis. The first part, isolation and separation of species, may be the easiest one to tackle. For the second part, the measurement of the trace element, a major improvement in sensitivity is needed. As the concentration of the different species lies far below that of the total concentration (species often occur at a mere ng/1 level and below), it looks like existing methods will never be able to cope with the new demands. A new physical principle will have to be explored, away from absorption spectrometry, emission spectrometry, mass spectrometry, and/or more powerful excitation sources than flame, arc or plasma will have to be developed. The goal is to develop routine analytical set-ups with sensitivities that are three to six orders of magnitude lower than achieved hitherto. 

Various forms of off- and on-line AES/AAS can achieve element specific detection in IC. The majority of atomic emission techniques for detection in IC are based on ICP. In the field of speciation analysis both IC-ICP-AES and IC-ICP-MS play an important role. Besides the availability of the ICP ion source for elemental MS analysis, structural information can be provided by interfaces and ion sources like particle beam or electrospray. 

Reduction-oxidation is one of the most important processes controlling solubility and speciation of trace elements in soils, especially for those elements with changeable values, such as Cr, As and Se. Within normal ranges of redox potentials and pH commonly found in soils, the two most important oxidation states for Cr are Cr(III) and Cr(VI). Cr(III) is the most stable form of chromium and less soluble and nontoxic, but Cr(VI) is mobile, soluble and toxic. The main aqueous species of Cr(III) are Cr3+, Cr(OH)2+, Cr(OH)3° and Cr(OH)4" and the major aqueous species of Cr(VI)... 

Dyrssen D, Wedborg M (1980) Major and minor elements, chemical speciation in estuarine waters. In Olausson E, Cato I (eds) Chemistry and biogeochemistry of estuaries. Wiley, New York, pp 71-119... 

Ball, J. W. and D. K. Nordstrom, 1991, User s manual for WATEQ4F, with revised thermodynamic data base and test cases for calculating speciation of major, trace, and redox elements in natural waters. US Geological Survey Open File Report 91-183. 

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