Particle concentration effect

Particle Concentration Effect. Experimental data often show a "particle concentration effect", i.e., the Kq decreases with the concentration of particles. Such observations are in contradiction with thermodynamics. Various "artefacts" could account for this observation (Morel and Gschwend, 1987) ... 

Mackay D, Powers B (1987) Sorption of hydrophobic chemicals from water a hypothesis for the mechanism of the particle concentration effect. Chemosphere 16 745-757... 

Several investigators have reported a particle concentration effect associated with the sorption of hydrophobic solutes. The decrease in the amount sorbed with increasing particle concentration is most pronounced for compounds characterized by large partitioning (Kd > 1000 mL/g). O Conner and Connolly (1980) reported observations that linear partition coefficients are inversely dependent upon the concentration of the solids in the system. Voice et al. (1983) also observed a significant increase in sorption as the solids concentration decreased and attributed it to the presence of microparticles contributed by the solids and not removed from suspension in the separation procedure. This suggests that sorption coefficients produced in studies using different techniques are not necessarily comparable. 

While several explanations for the particle concentration effect have been presented, VanHoof and Andren (1990) suggested a kinetic explanation rather than a thermodynamic one. Equilibrium sorption is independent of particle size, but kinetics is not, with small particles reaching equilibrium faster. A solids concentration effect on 4-chlorobi-phenyl was observed in an aqueous suspension of polystyrene microspheres. The apparent inverse relationship of 4-chlorobiphenyl partitioning with particle concentration diminished with time, demonstrating that nonattainment of equilibrium results in the observed phenomenon. 

Figure 14.5 Particle concentration effect showing negative relationship between particle/solution partition coefficient (X,j) of selected trace metal ions and suspended particulate matter (SPM). Data are from six Texas estuaries (USA). (Modified from Benoit et al., 1994.)...

The particle concentration effect has been defined as the physical effects which lead to a decreasing overall partition coefficient with increasing particle concentration the effect is documented for both organic and inorganic species. ... 

Benoit G. (1995) Evidence of the particle concentration effect for lead and other metals in fresh waters based on ultrafiltration technique analyses. Geochim. Cosmochim. Acta 59(13), 2677-2687. 

Benoit G. and Rozan T. F. (1998) The influence of size distribution on the particle concentration effect and trace metal partitioning in rivers. Geochim. Cosmochim. Acta 63(1), 113-127. 

If the analytically determined dissolved phase contains colloids, artifacts in distribution coefficients, such as a so-called particle concentration effect... 

Figure 13. Raw water particle concentration effects of flocculation and settling on particle size distribution function (A = 419 mgjL B = 13.2...

Particle Concentration Effect on the Multi-Wavelength Backscattering Spectra... 

Even if the study by Honeyman and Santschi clearly showed the problems associated with solid-liquid separation, the solid-concentration effect still circulates in the recent literature [25]. In these latter studies, the authors studied metal ion sorption onto goethite in the presence of a phosphate buffer to control the pH phosphate strongly sorbs onto goethite itself, so that observed particle concentration effects should not be interpreted without considering the action of phosphate. It is highly probable that the metal ions were sorbed on a (more or less) phosphated goethite and not to a pure goethite. 

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