Cd-Cl complexes

Hirsh and Banin (1990) reported that an increase in Cl concentration decreased Cd sorption due to formation of the CdCl+ ion pair. Enhanced sorption in the presence of HC03 was observed due to the formation of the CdHC03+ ion pair. Mahler et al. (1980) found that in calcareous soils treated with sewage sludge spiked with CdS04, Cd complexes were mainly Cd sulfate and carbonate complexes, and the formation of Cd-Cl complexes increased in both soils as total Cd increased. In sludge-amended California soils with pH 7-8, both Cd and Zn organic complexes and Cd phosphate complexes increase with P levels, but free Cd2+ and Zn2+ decrease with P levels (Fig. 3.4) (Villarroel et al., 1993). 

Calculate the concentration of all species present in a solution containing 1.00 M and 0.010 M Cd(N03)2 at 25°C. Because the solution is strongly acidic, Cd-OH complexing need not be considered. Solving the problem requires the simultaneous solution of equilibrium constant expressions and mass-balance equations involving the aqueous species. We are given stepwise formation (equilibrium) constant expressions for the Cd-Cl complexes that can be reformatted to give... 

It is useful to construct diagrams that show changes in the relative importance of complexes as a function of pH or the concentration of a metal or ligand. In such a problem, Butler (1964) describes how to calculate as a function of uncomplexed chloride ion, (Cl ), the fraction of Cd present as Cd ion and as the several Cd-Cl complexes. The general approach involves defining and solving simultaneously a series of equilibria, mass-balance, and charge-balance equations. 

First, Cd-Cl complexing is described in terms of the cumulative (overall) constant expressions. These are ... 

Similar expressions may be written for each of the Cd-Cl complexes, which, after substitution, are also seen to be functions of The simplest way to obtain these expressions is to divide both sides of Eqs. (3.36) to (3.39) by C, and then to substitute a C for (Cd " ) in each equation. Fractions of each complex then equal... 

In the text we hand calculated the speciation of a solution containing 1.00 M HCl and 0.010 M Cd(NO,)2 at 25°C and zero ionic strength. Enter the same information into MINTEQA2 and let the program calculate the speciation. Compare your MINTEQA2 result to the result given in the book. Results may differ because of a different choice of Cd-Cl complexes and/or the use of different stability constants for the complexes in the computer model (listed in the file thermo.dbs). Tabulate and compare the two sets of stability constants and explain differences between the results. 

The Cd sorption plot in Fig. 10.14 shows that a different isotherm is needed to describe Cd sorption at each NaCl concentration. This reflects weak adsorption of Cd-Cl complexes relative to free Cd + and increasing competition of Na for Cd sorption sites on the clay as the NaCl concentration increases. Obviously, such effects cannot be accounted for using an isotherm or model. 

Tl=Cs>Rb>K>NII4>Ag>Na>Ba>Sr>Ca>Mg Loizidou and Townsend [91] studied ferrierite from the same source with a view to its utility to scavenge NH4, Pb, and Cd from binary mixtures. They found that interpretation was hindered as the participation of K inherently present in the initial sample rendered the Pb systems ternary rather than binary. They were able to define thermodynamic parameters in the Cd/Na and Cd/NH4 systems that remained binary. They showed that Cd was not preferred over Na and NH4 The presence of Cl" altered Cd uptake due to Cd/Cl complex formation whereas presence of the nitrate anion improved uptake. 

The synthesis of [Ircp Cl(bpy-cd)]Cl, where bpy-cd is a /3-cyclo-dextrin attached at the 6 position to a bpy ligand, is detailed.138 The complexes [Ircp (diimine)X]+, X = C1, H, diimine = bpy, phen, are active catalysts for the light-driven water-gas-shift reaction.139 The hydride complexes luminesce at 77 K and room temperature, whereas the chloride complexes do not.140 The three-legged piano-stool arrangement of the ligands in [Ircp (bpy)Cl]+ and [Ircp (4,4 -COOFl-bpy)Cl]+ is confirmed by X-ray crystallography.141,142 Further mechanistic studies on the catalytic cycle shown in reaction Scheme 11 indicate that Cl- is substituted by CO and the rate-determining step involves loss of C02 and H+ to leave the Ir1 species, which readily binds Fl+ to yield the lrIH hydride species.143... 

Preliminary heats of solution of C0CI2 and CuCl2 have been measured up to 300 C by Cobble and Murray (50). Hydrolysis was suppressed by HC1 addition so that when the work is completed and when the extent of Cl complexing (and Cu + reduction) can be allowed for the data will prove extremely valuable. Preliminary concentration cell studies on the Cl complexing of Cd + and Ni + up to 170 C (51) support the conclusions given earlier that such complexing with first row transition metal ions is likely to be significant by 300°C. 

Information about the stoichiometry of selector-selectand complex is difficult to gain from CE. However, this knowledge is useful in order to characterize the structure of intermolecular complexes as well as for the calculation of the binding constants. Previous research and review papers (3, 4,62,65) summarize the application of this technique to the problems related to chiral CE. As shown in Fig. 4, despite the involvement of different parts of the CL molecule in complex formation, the stoichiometry of CL complexes most likely is the same (1 1) with /3-CD and HDAS-/3-CD (65). 

Et2NCH2CH2PPh2596 and HMPA597 have been described. The complex [CdL Cy (L = HMPA) is tetrahedral (Cd—Cl, 2.399 A Cd—O, 2.179 A) with monodentate O-donor ligands 597 [ClLCd(jU-Cl)]2 (L = Et2NCH2CH2PPh2) is a chloro-bridged dimer (86)596 while [Zn(PhMeP02)(dioxane)] is polymeric, with a repeat distance (Zn—Zn) of 4.614 A.594... 

Inorganic speciation in solution can also affect the mobility of metal ions (Doner, 1978). The formation of an ion-pair with Cl can more than double the mobility of Cd in the presence of 200molm 3NaCl. At the same chloride concentration, however, the mobilities of Cu2+ and Ni2+ are only increased slightly (5-10%), presumably because of very weak complexation with Cl. This mechanism could increase the leaching of Cd from saline soils but it may not be effective in non-saline soils because the ratio of the total concentrations of Cd Cl must be >1 106 before >50% of total Cd is complexed by Cl (estimated using the computer model TITRATOR (Cabaniss, 1987), which considered the chloro and hydroxy complexes of Cd at pH 5.0 and a total Cd concentration of 0.1 mmolm-3 equilibrium constants were taken from Lindsay (1979)). 

The authors also studied pset/do-rotaxane formation of CDs with aliphatic polyesters, polydiene, polysiloxane, and polysilane, as summarized in Table 2. CDs were found to form inclusion complexes with aliphatic polyesters, such as PTA, PBA, PEA [107], and P(e-CL) [108,109]. a- and y-CDs formed complexes with these polyesters in high yields, although p CD gave complexes in moderate yields. Although the yields of the complexes of a-CD with PTA and... 

PBA decreased with increasing molecular weight, a-CD formed complexes with PEA in high yields even at higher molecular weights. a-CD-P(g-CL) complexes were stoichiometric one-to-one (CD monomer unit) compounds, and y-CD-P(e-CL) complexes were one-to-two compoimds when the molecular weights of P(fi-CL) are low. 

Spadini L, Manceau A, Schindler PW, Charlet L (1994) Structure and Stability of Cd Surface Complexes on Ferric Oxides. 1. Results from EXAFS Spectroscopy. J Colloid Interface Sci 168 73-86 Steefel Cl, van Cappellen P (1990) A new kinetic approach to modehng water-rock interaction Role of nucleation, precursors, and Ostwald ripening. Geochim Cosmochim Acta 54 2657-2677 Stem LA, Durham WB, Kirby SH (1997) Grain-size-induced weakening of H2O ices I and II and associated anisotropic recrystallization. J Geophys Res-Solid Earth 102 5313-5325 Suzuki A, Kotera Y (1962) The kinetics of the transition of titanium dioxide. Bull Chem Soc Japan 35 1353-1357... 

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