Jr. Ferreira et al., CHEMISTRY OF RIVERINE AND ESTUARINE SUSPENDED PARTICLES FROM THE OUSE-TRENT SYSTEM, UK, Colloids and surfaces. A, Physicochemical and engineering aspects, 120(1-3), 1997, pp. 183-198
Three samples of suspended particulate matter (SPM), two riverine and
one estuarine, were characterised by bulk chemical analysis, electron
microscopy, chemical extraction, electrophoresis and acid-base titrati
on. The river samples contained both mineral and biological material a
nd were rich in organic matter (R. Ouse sample 24%, R. Trent sample 54
%), while the estuarine sample consisted mostly of clay minerals, with
only 9% of organic matter. The river particles had higher contents of
base-extractable carbon and phosphate and acid-extractable trace meta
ls than the estuarine sample. The electrophoretic mobilities of all th
ree samples were negative, but acid-base titrations revealed differenc
es in their proton-dissociating characteristics, the R. Ouse sample ha
ving approximate to 2 meg g(-1) of pH-dependent charge titrating betwe
en pH 4 and 9, approximately twice the content of the R. Trent sample,
and four times that of the estuarine sample. However, the estuarine s
ample had a relatively large fixed (negative) charge (approximate to-0
.7 meq g(-1)). Centrifugation-depletion experiments showed that for al
l three samples, phosphate adsorbed most strongly at pH 6-7, the parti
cles releasing phosphate to solution at both low and high pH values. T
race metal adsorption experiments, carried out by centrifugation-deple
tion and, in the case of Cu, with an ion-specific electrode, showed th
at adsorption increases with pH, except in some cases at pH > 7, where
solution complexation reverses the trend. A simple metal-proton excha
nge model provided an approximate description of the observations, and
allowed comparison amongst metals and particle samples. The three sam
ples adsorbed trace amounts of metals with the same selectivity: Cs <
Sr < Co similar or equal to Ni similar or equal to Cd < Zn < Cu < Pb <
Eu. The strengths of adsorption of a given metal by the three samples
varied over an order of magnitude, increasing in the order Ouse estua
ry < R. Trent less than or equal to R. Ouse. These results, and other
published data, show that natural SPM varies appreciably in its (surfa
ce) chemical properties. The possibilities of accounting for the varia
bility in terms of the properties of constituent particles are discuss
ed.