『Abstract
Iron-complexes on the surface of minerals may play an important
role in Fe dissolution in acidic cloud water containing certain
organic ligands, and dissolved Fe serves as a critical nutrient
in biogeochemical cycles in certain aquatic systems. As the first
step to explore this issue, laboratory experiments were conducted
to investigate the effects of oxalate on the dissolution of hematite,
with leaching of Fe from oxalate-coated hematite in comparison
with pure hematite in oxalate solution. The dissolution of oxalate-coated
hematite was measured as a function of dissolution time, loading
amount of oxalate and pH. The amount of oxalate adsorbed on hematite
at pH 2.4 is greater than that at pH 5, while the amount of adsorption
increases with increasing oxalate equilibrium concentration in
solution. Adsorption of oxalate on hematite follows the Freundlich
adsorption model. The amount of Fe dissolved at pH 2.4 is much
more than that at pH 5. In low concentration oxalate solution,
the amount of Fe dissolution from hematite is independent of oxalate
loading on the surface of hematite. In high concentration oxalate
solution, however, a relatively high oxalate loading on the hematite
surface releases more Fe relative to low oxalate adsorption density
on the surface of hematite when the system reaches equilibrium,
suggesting that the high content of Fe(III)-oxalate
complexation promotes Fe dissolution. Ferric ion dissolution and
adsorbed oxalate leaching in solution as a function of pH are
two co-existing processes, and pH 〜2.5 is a critical turning point
relating the two processes that occur simultaneously. The fitting
of the experimental data from this work to a model indicates that
Fe-(oxalate)+ and Fe-(oxalate)2-
are predominant species in solution in the pH range of 1.5-4.5
during oxalate-coated hematite dissolution in background electrolyte.』
1.Introduction
2. Experimental methods
2.1. Preparation of the experiments
2.2. Batch experimental tests
2.2.1. Oxalate-coating
2.2.2. Dissolution kinetics of coated hematite
2.2.3. Dissolution kinetics of non-coated hematite
2.2.4. pH effect
3. Results and discussion
3.1. Adsorption isotherm
3.2. Dissolution kinetics in 25μM oxalate solution
3.3. Dissolution kinetics in 220μM oxalate solution
3.4. Effect of pH on dissolution of oxalate coated hematite
4. Conclusions
Acknowledgements
References