Solutions, chemistry strength

The effect of solution chemistry on the speciation of the organic contaminant 1-naphtol (1-hydroxynaphthalene) and its complexatiom with humic acid is reported by Karthikeyan and Chorover (2000). The complexation of 1-naphtol with humic acid (HA) was studied during seven days of contact, as a function of pH (4 to 11), ionic strength (0.001 and 0.1 M LiCl), and dissolved concentration (DO of 0 and 8 mg L ) using fluorescence, UV absorbance, and equilibrium dialysis techniques. In a LiCl solution, even in the absence of HA, oxidative transformation of 1-naphtol mediated by was observed. In addition, the presence of humic acid in solution, in the absence of DO, was found to promote 1-naphtol oxidation. These reactions are affected by the solution chemistry (pH, ionic strength, and cation composition). 

Fig. 16.20 Fluorescence quenching (FQ) of 1-naphthol in the presence of HA as a function of pH and reaction time (1-naphthol = 8pmol LHA = 11 ppm C ionic strength of O.IM LiQ) F and F denote fluorescence intensities in the absence and in the presence of the quencher (HA), respectively. Reprinted with permission from Karthikeyan KG, Chorover J (2000) Effects of solution chemistry on the oxidative transformation of 1-naphtol and its complexation with humic acid. Environ Sci Technol 34 2939-2946. Copyright 2000 American Chemical Society...

In considering an organic-rich slurry wall additive, the governing sorption mechanism is often considered to be hydrophobic partitioning and the effects of solution chemistry (pH, ionic strength, etc.) are considered secondary. The specification ofthe appropriate sorption model requires several choices ... 

Kosa, S., D. Shreiber (1994), The Enthalpy of Mixing Aqueous Solutions of CdCl 2, CuCl 2, MnCl 2 and ZnCl 2 with HC1 at Varying Ionic Strength at 25°C , Journal of Solution Chemistry, Vol. 4, p. 511. 

Worked example 5.7 — soil solution chemistry ionic strength and activity coefficients... 

Electrostatic interactions appear when the adsorptive is an electrolyte that is dissociated or protonated in aqueous solution under the experimental conditions used. These interactions, which can be either attractive or repulsive, strongly depend on the charge densities of both the carbon surface and the adsorptive molecule and on the ionic strength of the solution. The nonelectrostatic interactions are always attractive and can include van der Waals forces and hydrophobic interactions. The factors that influence the adsorption process are the characteristics of the adsorbent and the adsorptive, the solution chemistry, and the adsorption temperature. 

Among the characteristics of the adsorbent are its pore texture, surface chemistry, and mineral matter content. The characteristics of the adsorptive are its molecular size, solubility, polarity, pIC, (for electrolytes), and nature of the substituents if it is aromatic. Finally, the solution chemistry factors are the pH and the ionic strength [5]. I shall focus in this section only on the role of the characteristics of the adsorbent, especially its carbon surface chemistry, on the adsorption processes, because although its importance has long been recognized [6, 7], the exact nature of this importance has often been controversial and misunderstood [1]. 

Magny B, Iliopoulos I, Audebert R. Aggregation of hydrophobically modified polyelectrolytes in dilute solutions ionic strength effects. In Dubin P, Bock J, Davies RM, Schulz DN, Thies C, eds. Macromolecular Complexes in Chemistry and Biology. Berlin Springer Verlag, 1994 51-62. 

We have already discussed the structure of the stable adduct of 41 and THF in Section III.A.l. The addition of anions to 1,1-dimethylsilene in the gas phase is mentioned in Section III.B.3.h. Also, the solution chemistry of the adducts of 1,1-dimethyl-2,2-bis(trimethylsilyl)silene 54 has been investigated266. This silene dimerizes rapidly even at —100 °C when free but forms an isolable silenate with trimethylamine, stable up to 0°C. Even at room temperature it decomposes only over a period of weeks and yields the dimer of 54. Since excess NMe3 slows down the formation of the dimer, the free silene 54 is clearly involved in this reaction, but it is not yet known whether it attacks a molecule of silenate or whether it dimerizes. The existence of an equilibrium between the silenate and its constituents is also supported by the mass spectrometric detection of the constituents in the vapor of this sublimable material (equation 115). It is possible to replace a weaker donor in a silenate by a stronger one, and the order of strength is F" >NMe3>NEt3>Br >THF (with 12-crown-4 complexed Li+ as the counterion). 

While this method is commonly used (De Nobih and Fornasier (1994), Kiichler et al. (1994), Mazid (1988), BeUn et al. (1993), Shaw et al (1994), Burba et al (1998), Buffle et al (1978), Crum et al (1996), Aiken (1984), Amy et al (1987), Reinhard (1984), Amy et al (1992), Hepplewhite (1995)), most authors have used different filtration protocols for their fractionation experiments. Cells can be operated in series (cascade) or in parallel, volumes and concentrations are varied, and some authors refill the cell with pure water to keep the cell concentration constant. All these factors influence the results obtained, and solution chemistry, pH, and ionic strength may also influence results. Generally reported size results are above the expected sizes of FA and FIA. UF MWCOs used are usually 0.5-1, 3, 5, 10, 30 kDa. 

Experiments were carried out in a background buffer solution that was chosen as a simple model of natural surface waters, with a monovalent and divalent cation and a background electrolyte to allow pH adjustment without changing ionic strength. The concentration of the cation calcium, was selected after the analysis of the Mooney Mooney Dam surface water. The composition of this water is shown in Appendix 1. The composition of the model system is summarised in Table 4.1. This background solution was used in all experiments, if not otherwise indicated. The species in solution as a function of solution chemistry is described in Appendix 5. 

---