Merged with duplicate record 10026.1/1768 on 14.02.2017 by CS (TIS)A systematic study of the microstructures of particulate
material from the Tamar Estuary using a BET nitrogen adsorption
technique has been carried out. The results showed that suspended
material had a higher BET surface area (approximately 20m² / g )
than the associated sediments (approximately 13m² / g) . Also the
BET surface areas (8-20m² / g) of suspended material collected
during axial transects (S = 0-30°/oo) of the Tamar Estuary indicated
relatively higher BET surface areas in the turbidity maximum zone as
compared to material from up or down estuary. The BET surface areas
were inversely related to the carbon content of the particles and
although the role of Fe and Mn coatings was examined no definitive
relationship to BET surface area was evident. Analysis of nitrogen
adsorption-desorption hysteresis loops indicated the pores to be of
the parallel plate or slit type in the size range <2-50 nm. The shape
and dimensions of these pores would accomodate the penetration of
metal ions, like Zn and Cu, into the pore spaces in the particle
matrix.
A method was designed to enable the analysis of natural Zn
and Cu concentrations in small volumes extracted from a reactor on a
timescale suitable for kinetic analysis. Dissolved Cu and Zn
adsorption-desorption experiments were carried out under controlled
conditions using Tamar suspended solids as the adsorbents. The uptake
and release profiles were interpreted in terms of a two stage reaction
mechanism which involved both surface adsorption and solid state
diffusion into the pores. Rate constants were derived from a kinetic
analysis to enable evaluation of the chemical timescales of the
sorption reactions. When compared to field data of Zn distributions
in the Tamar Estuary the time constants allowed a reasoned explanation
of the observations. They also pointed to a strong coupling between
the physical and chemical timescales within estuaries.
This work has indicated an association between trace metal
sorption reaction rates and estuarine particle microstructure. These
rate constants are of value in the refinement of hydrodynamic models
and this study has implications for the availability of trace metals
for biological or chemical remobilisation.Institute for Marine
Environmental Research,
Prospect Place, The Hoe
PLYMOUT