Metal distribution coefficient

Fig. 6.4 Calculated, estimated, or apparent salting out constants for various chemicals (a) selected aromatic compounds, (b) selected aliphatic compounds, (c) natural or surrogate hgands, (d) anthropogenic ligands, (e) sediment organic matter (SOM), (f) transition metal complexes, (g) trace metal complexes in the Mersey Estuary. Reprinted with permission from Turner A, Martino M, Le Roux SM (2002) Trace metal distribution coefficients in the Mersey Estuary UK Evidence for salting out of metal complexes. Environ Sci Technol 36 4578-4584. Copyright 2002 American Chemical Society...

The sampling and analytical conditions are described in detail in Section 8.2.1. For estimation of a medium water influence on the sediments the mean values of the water components over the investigation period of two years were used as the first (independent) data matrix the metal distribution coefficients were taken as the dependent data matrix. For description of deposition-remobilization effects a heavy metal distribution coefficient, DCh was defined as ... 

Tab. 8-16. Error in the prediction of metal distribution coefficients from the water components...

The mean error for all the elements studied is 20.1%, which means that the influence of water components on the variation of the metal distribution coefficients can be predicted with an error of approximately 20%. The errors can be explained by sediment transport processes, inhomogeneities in the water phase during the sampling process, and biochemical processes in the complex river system. Otherwise, it is possible to describe the distribution of heavy metals between the water phase and the sediment in the... 

Fig. 8-18. PLS modeling of the effect of pH variation on heavy metal distribution coefficients...

Turner, A., Martino, M., and Le Roux, S.M. (2002) Trace metal distribution coefficients in the Mersey Estuary, UK evidence for salting out of metal complexes. Environ. Sci. Technol. 36, 4578- 1584. 

The quantity of interest here is the metal distribution coefficient (cf. Eq. 2.31) ... 

Note CEC = cation exchange capacity HISM = hydroxyinterlayered smectite HIV = hydroxyinterlayered vermiculite Kf = Freundlich metal distribution coefficients LSB = lime stabilized biosolids = total aluminosilicates. 

The degree of the metal extractions depends on its concentration. Por example, with increasing europium concentration the distribution coefficients in the alkali-DOBTA system decrease, while in the alkali-tartaric acid system a maximum at 7x10 4 M Eu concentration is observed. As we suggested the enhancement in the metal distribution coefficient is evidently due to the metal polymerization in the organic phase, and the decrease is caused by polymerization in the aqueous phase, which eventually results in low extractable polymer form. The latter assumption is supported by the fact that as the alkali concentration increases the maximum on extraction curves undergoes a shift towards lower concentration of the metal. 

The capacity factors of SN-SiO, for metal ions were determined under a range of different conditions of pH, metal ions concentrations and time of interaction. Preconcentration of Cd ", Pb ", Zn " and CvS were used for their preliminary determination by flame atomic absorption spectroscopy. The optimum pH values for quantitative soi ption ai e 5.8, 6.2, 6.5, 7.0 for Pb, Cu, Cd and Zn, respectively. The sorption ability of SN-SiO, to metal ions decrease in line Pb>Cu> >Zn>Cd. The soi ption capacity of the sorbent is 2.7,7.19,11.12,28.49 mg-g Hor Cd, Zn, Pb, andCu, respectively. The sorbent distribution coefficient calculated from soi ption isotherms was 10 ml-g for studied cations. All these metal ions can be desorbed with 5 ml of O.lmole-k HCl (sorbent recovery average out 96-100%). 

On the basis of data obtained the possibility of substrates distribution and their D-values prediction using the regressions which consider the hydrophobicity and stmcture of amines was investigated. The hydrophobicity of amines was estimated by the distribution coefficient value in the water-octanole system (Ig P). The molecular structure of aromatic amines was characterized by the first-order molecular connectivity indexes ( x)- H was shown the independent and cooperative influence of the Ig P and parameters of amines on their distribution. Evidently, this fact demonstrates the host-guest phenomenon which is inherent to the organized media. The obtained in the research data were used for optimization of the conditions of micellar-extraction preconcentrating of metal ions with amines into the NS-rich phase with the following determination by atomic-absorption method. 

Sodium trimetaphosphate was used as an eluting agent for the removal of heavy metals such as Pb, Cd, Co, Cu, Fe, Ni, Zn and Cr from aqueous solutions. Distribution coefficients of these elements have been determined regarding five different concentrations of sodium trimeta phosphate (3T0 M 5T0 M 0.01 M 0.05 M 0.1 M) on this resin. By considering these distribution coefficients, the separation of heavy metals has been performed using a concentration gradient of 3T0 - 5T0 M sodium trimetaphosphate. Qualitative and quantitative determinations were realized by ICP-AES. 

Stability constants of metal complexes of 9-hydroxy-4//-pyrido[l,2-n]pyrimidin-4-one [Ni(II), Co(II), Zn(II), and Cd(II)] were determined by potentiometric and polarographic investigations (93JCC283). The distribution coefficient of risperidone (11) in H20- -octanol at pH 7.4 (log D — 2.04) was determined by an RP-HPLC method (01JMC2490). 

Kd = distribution coefficient (as defined above) s/m = salt to metal ratio by weight F = fraction of equilibrium attained B = effects of side reactions... 

Atmospheric sensitivity renders the preparation of ultrapure samples difficult. Nevertheless, vacuum distillation ", ultra-high-vacuum reactive distillation " and crystal growth purification methods " are described zone-refining methods have been applied on a limited scale only - , presumably because of the high volatility of the metals and the unfavorable distribution coefficients. 

When a melt-zone is moved through a long crystal, an impurity concentration builds up in the melt zone due to rejection by the crystal as it resolidifies. We can also say that the distribution coefficient favors a purification process, i.e.- k 1. Another reason (at least where metals are concerned) is that a solid-solution between impurity and host ions exists. It has been observed that the following situation, as shown in the following diagram, occurs ... 

Alexander WR, McKinley IG (1994) Constraints on the use of in situ distribution coefficients (Kd) values in contaminant transport modeling. Eclogae Geol Helv 87 321-324 Andrews JN, Wood DF (1972) Mechanism of radon release in rock matrices and entry into groundwaters. Inst Min Metall Trans B81 198-209... 

A comprehensive survey is available in literature on the sorption behavior of elements over a range of hydrochloric acid concentrations. The compiled data show the following (i) a number of elements exhibit no sorption tendency at all (ii) many exhibit a change of behavior with hydrochloric acid concentration and (iii) several cases exhibit high distribution coefficients over at least some part of the concentration range. It can be found out that there is a possibility of separating certain metal combinations not easily obtainable by conventional chemical means. 

In closing, recovery of technetium from waste solution should be touched upon. Studies of the base hydrolysis of technetium P-diketone complexes revealed that all of the complexes studied decompose in an alkaline solution even at room temperature, until technetium is finally oxidized to pertechnetate. These phenomena are very important for the management of technetium in waste solutions. Since most metal ions precipitate in alkaline solution, only technetium and some amphoteric metal ions can be present in the filtrate [29]. A further favorable property of pertechnetate is its high distribution coefficient to anion exchangers. Consequently, it is possible to concentrate and separate technetium with anion exchangers from a large volume of waste solution this is especially effective using an alkaline solution [54],... 

These results differ sharply from the behavior predicted by the distribution coefficient (K( ) approach. This approach, despite being broadly acknowledged as too simplistic to describe the behavior of heavy metals, is nonetheless the sorption model most commonly applied in studying aquifer remediation. 

Indium, cadmium and silver can be extracted into chloroform as their 8-hydroxyquinoline complexes, and the pH1/2 values for these metals are 2.1, 6.3 and 8.8 respectively. Plot a graph of theoretical percent extraction against pH over the range 0 to 9 for each metal. Deduce the pH of incipient extraction (0.01%) and complete extraction (99.99%) for each metal, and comment on the feasibility of separating each from the other assuming that all the distribution coefficients are sufficiently high. 

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