River water cations

The resulting species distribution (Table 6.7), as would be expected, differs sharply from that in seawater (Table 6.4). Species approach millimolal instead of molal concentrations and activity coefficients differ less from unity. In the Amazon River water, the most abundant cation and anion are Ca++ and HCOJ in seawater, in contrast, Na+ and Cl- predominate. Seawater, clearly, is not simply concentrated river water. 

In the river water, as opposed to seawater, the neutral species C>2(aq), CC>2(aq), and Si02(aq) are among the species present in greatest concentration. Complexing among species is of little consequence in the river water, so the major cations and anions are present almost entirely as free ions. 

The extraction of an anionic surfactant from river water has been performed by ion-pair LLE with the methylene blue cation [15—17] a recovery in river water of 96.7% and a detection limit of 0.05 mg L-1 have been reported. 

An analytical procedure that quantifies the total AE concentration resolved by alkyl chain length for various environmental matrices (influent, effluent, and river water) was developed by Di Corcia et al. [41]. The method utilises a reverse-phase column to extract and concentrate AE from surface waters and wastewaters and utilises strong anionic and cationic exchange columns to remove potential interferences. Samples are passed through the RP extraction column (Ci). AE and potential anionic and cationic interferences are eluted from the Ci column and passed directly through the SAX and SCX. The SAX and SCX columns retain anionic and cationic materials while non-ionic AE are not retained. Recovery of AE from influent, treatment plant effluent, and river water is quantitative (65—102%) over a range of concentrations for all matrices. 

We have been able, however, on occasions to use a very simple model to help understand specific plant problems where river water analyses were available and on one occasion to show that at different times the boiler water had (as corrosion evidence suggested) alternated between acidic and alkaline conditions. The model assumes that by 350 C any normally dissociated multi-charged ions will be sufficiently unstable that they will undergo whatever appropriate hydrolysis reactions can reduce their charge to unity. Whether the water goes acid or alkaline then simply depends on whether the total (equivalent) concentration of multiply charged cations exceeds or is smaller than the concentration of multiply charged anions. 

The cations become a component of river water and are eventually transported to the sea. About 45% of the dissolved solids entering the ocean are derived from the weathering of detrital silicates. Feldspars are the most important somce rock for terrigenous clays as illustrated by the following reaction... 

Most cation exchange occurs in estuaries and the coastal ocean due to the large difference in cation concentrations between river and seawater. As riverborne clay minerals enter seawater, exchangeable potassium and calcium are displaced by sodium and magnesium because the Na /K and Mg /Ca ratios are higher in seawater than in river water. Trace metals are similarly displaced. 

The overall effect of the terrestrial weathering reactions has been the addition of the major ions, DSi, and alkalinity to river water and the removal of O2, and CO2 from the atmosphere. Because the major ions are present in high concentrations in crustal rocks and are relatively soluble, they have become the most abimdant solutes in seawater. Mass-wise, the annual flux of solids from river runoff (1.55 x 10 g/y) in the pre-Anthropocene was about three times greater than that of the solutes (0.42 x 10 g/y). The aeolian dust flux (0.045 X 10 g/y) to the ocean is about 30 times less than the river solids input. Although most of the riverine solids are deposited on the continental margin, their input has a significant impact on seawater chemistry because most of these particles are clay minerals that have cations adsorbed to their surfaces. Some of these cations are desorbed... 

Also called vapour-phase interferences or cation enhancement. In the air-acetylene flame, the intensity of rubidium absorption can be doubled by the addition of potassium. This is caused by ionization suppression (see Section 2.2.3), but if uncorrected will lead to substantial positive errors when the samples contain easily ionized elements and the standards do not. An example is when river water containing varying levels of sodium is to be analysed for a lithium tracer, and the standards, containing pure lithium chloride solutions, do not contain any ionization suppressor. 

The comparison of CMC data in distilled vs. hard river water shows that the decrease in CMC with hardness has the order anionics cationics nonionics (Rosen et al., 1996). Hardness increases the dependence of the CMC on alkyl carbon chain length of CnE0mS04, indicating that in hard water the influence of additional carbon atoms is the same for CnE0mS04 as for CnEOm surfactants (Rosen et al., 1996). The influence of ionic strength on micellization of nonionic surfactants is due to a salting out effect of the hydro-phobic moiety of the surfactant molecule (Carala et al., 1994). 

Ruiz-Cruz, J., and M.C. Dobarganas-Garcia. 1979. Relation between structure and biodegradation of cationic surfactants in river water. Grasas Aceites 30, 67-74. 

Figure 9. Analysis of anions and cations in river water using tartaric acid/18-crown-6/methanol-water eluent with a carboxylated polyacylate stationary phase in the protonated form. Ions 1) sulfate 2) chloride 3) nitrate 4) eluent dip 5) unknown 6) sodium 7) ammonium 8) potassium 9) magnesium 10) calcium (from ref. 80)...

Keller (1964) reported that Ca is the dominant exchangeable cation on mont-morillonite in equilibrium with river water. In sea water Ca and also Na (Carroll and Starkey, 1960) tend to be replaced by Mg which becomes the dominant exchangeable cation. In many ancient clays, Na is the most abundant exchangeable cation therefore, this abundance of Na appears to be inconsistent with the above data. Recently Hanshaw (1964) conducted exchange experiments with compacted clays and found that the order of cation selectivity is dependent upon whether a clay is dispersed or compacted. He found that compacted montmorillonite preferred cations in the following order K+> Na+>H+>Ca2 +>Mg2 +. It may be that in dispersed marine mont-morillonites Mg is the predominant exchange cation, but as the mud is compacted by burial, Na replaces a portion of the Mg. This has been confirmed by Weaver and Beck (1971a). 

Chakrabarti, C.L., Lu, Y., Gregoire, D.C., Back, M.H. and Schroeder, W.H. (1994) Kinetic studies of metal speciation using Che lex cation exchange resin application to cadmium, copper, and lead speciation in river water and snow. Environ. Sci. Technol, 28, 1957-1967. 

Flowing FS-MMLLE with on-line hyphenation to FtPLC has also been investigated. Sandahl et al. were the first to interface FS-MMLLE with reversed-phase HPLC for the on-line extraction of methyl-thiophanate in natural water, obtaining an LOD of 0.5 pg L-1.89 Also, a parallel FS-SLM and FS-MMLLE design was coupled on-line to reverse-phase HPLC for the extraction of methyl-thiophanate (by MMLLE) and its metabolites (by SLM) in natural water.90 In addition, on-line coupling of FS-MMLLE and normal-phase HPLC has been successfully applied in the determination of vinclozolin (Ee =118 and LOD = 1 pg I. ) in surface water91 and of in-sample ion-paired cationic surfactants (Ee > 250 and LOD = 0.7-5 ug L-1) in river water and wastewater samples.92... 

All cations and anions are included in the summation term of this equation. The typical /for river water is 0.0021 m compared to 0.7 m in seawater (Libes, 1992). 

Table 3 lists examples of more than a dozen different chemical types of river water. Although Ca and HCO j" are generally dominant, Mg dominance over Ca + can be found in rivers draining various lithologies such as basalt, peridotite, serpentinite, dolomite, coal, or where hydro-thermal influence is important (Semliki). Sodium may dominate in sandstone basins, in black shales (Powder, Redwater in Montana), in evaporitic sedimentary basins (Salt), in evaporated basins (Saoura), and where hydrothermal and volcanic influence is important (Semliki, Tokaanu). rarely exceeds 4% of cations, except in some clayey sands, mica schists, and trachyandesite it exceeds 15% in extremely dilute waters of Central Amazonia and in highly mineralized waters of rift lake outlets (Semliki, Ruzizi). 

Not only are accurate data for trace metals in rivers sparse, there are complications that exist at the river-sea interface. The increase in salinity occurring at the river-sea water interface, with its concomitant increase in the concentrations of the major seawater cations, can lead to flocculation and sedimentation of trace metals such as iron (Boyle et al., 1978 Sholkovitz and Copeland, 1983) or to desorption from suspended riverine particles of trace metals such as barium (Edmond et al., 1978). In organic-rich rivers a major fraction of dissolved trace metals can exist in physiochemical association with colloidal humic acids. Sholkovitz and Copeland (1983) used product-mode mixing experiments on filtered Scottish river water, and observed that iron removal was almost complete due to the flocculation of strongly associated iron-humic acid colloids in the presence of the increased... 

The mean concentrations of constituents of seawater are determined not by simple distillation of river water but by their various mechanisms of removal from the ocean. The dominant cation in river water, e.g., is calcium from weathering of carbonate and silicate rocks, whereas the dominant cation in the ocean is sodium, because there are no efficient loss mechanisms for sodium analogous to the formation of CaC03 as a loss... 

Based on chemical measurements for river water and atmospheric particles, it is clear that river inflow is by far the most important mechanism for the delivery of dissolved major ions and elements to the ocean. This is not the case for all elements some of the trace metals such as iron and lead have important sources from atmospheric dust, but our discussion will focus on the flux of major elements to the ocean. The concentration and origin of the major ions to river water is presented in Table 2.1. Weathering of rocks on land is the origin of the cations, Na+, Mg ", Ca " and K", whereas the source of the anions Cl, SO4 and HCOj is partly from rock weathering and partly from the gases CO2, SO2 and HCl that are delivered to the atmosphere via volcanic emissions over geologic time. 

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