『Abstract
The montmorillonite dissolution in saline solutions that mimic
synthetic lung fluids (SLF) was investigated to gain knowledge
on the clearance mechanisms of inhaled clay particles. Dissolution
rates were measured at pH 4 (macrophages) and 7.5 (interstitial
fluids) at 37℃ in flow-through reactors. The effect of organic
acids was investigated through the addition of lactate, citrate,
and glycine (0.15, 1.5, and 15 mmol/L). Lactate or glycine does
not markedly affect the montmorillonite dissolution rates at pH
4, but at pH 7.5 there exists a slight inhibitory effect of lactate
on the dissolution, probably due to a reduction in the number
of reactive surface sites caused by lactate adsorption. Citrate
enhances the dissolution rates by 0.5 order of magnitude at pH
4 and more than 1 order of magnitude at pH 7.5, thus indicating
the prevalence of the ligand-promoted over the proton-promoted
dissolution mechanism under these experimental conditions. The
kinetic data were used to estimate the reduction in size of an
inhaled clay particle. at pH 7.5, a particle 500 nm in diameter
could be reduced 25％ in the presence of citrate, whereas the reduction
in saline solution would only be 10％ after 10 years.
Ligand adsorption was measured in batch experiments at pH 2-11
and EQ3NR was used to model the capacity of the ligands to form
soluble species of Al. Citrate, glycine, and lactate adsorb onto
montmorillonite under acidic conditions, up to 23, 26, and 60μmol/g,
respectively. However, only citrate can complex the released aqueous
Al at pH 4 and 7.5, which contributes to enhance dissolution rate
and prevents precipitation of gibbsite at pH 7.5.
The enhancement of the dissolution rate in acidic citrate solution
very likely comes from the formation of surface complexes between
the ligand and the edge surface of montmorillonite. In neutral
conditions the effect may be also due to the decrease of the activity
of Al3+ by formation of aqueous al-citrate complexes.
Keywords: Montmorillonite; dissolution rate; organic ligands;
adsorption』
Introduction
Materials and methods
Montmorillonite characterization and pretreatment
Experimental setting
Dissolution experiments
Adsorption experiments
Kinetic calculations
Results
Dissolution experiments
Experiments without organic ligands
Experiments with organic ligands
Adsorption experiments
Saturation and aqueous speciation
Discussion
Dissolution experiments
Lactate and glycine solutions
Citrate
Montmorillonite biodurability
Adsorption experiments
Lactate
Citrate
Glycine
Dissolution mechanism
Lactate and glycine
Citrate
Acknowledgments
References cited