On the influence of carbonate in mineral dissolution: I. The thermodynamics and kinetics of hematite dissolution in bicarbonate solutions at T = 25° C

Details On the influence of carbonate in mineral dissolution: I. The thermodynamics and kinetics of hematite dissolution in bicarbonate solutions at T = 25° C On the influence of carbonate in mineral dissolution: I. The thermodynamics and kinetics of hematite dissolution in bicarbonate solutions at T = 25° C

Mar 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.1139b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 56, Issue 3, pp.1139-1147

Computer Science

6

Scientific paper

We have studied the thermodynamics and kinetics of hematite dissolution in bicarbonate solutions under constant pCO 2 . The solubility of hematite is increased in the presence of bicarbonate. We have established that the complexes responsible for this increase are FeOHCO 3 (aq) and Fe ( CO 3 ) 2 - . The stability constants of these complexes at the infinite dilution standard state are log 11 = -3.83 ± 0.21 and log 2 = 7.40 ± 0.11, respectively (all errors are given at 2 confidence level through this work). The rate of dissolution of hematite is enhanced in bicarbonate solutions. This rate of dissolution can be expressed as R diss = k 1 [ HCO 3 - ] 0.23 (mol m -2 h -1 ), with k 1 = 1.42 10 -7 h -1 . The combination of the study of the surface complexation and kinetics of dissolution of hematite in bicarbonate solutions indicate that the dissolution of hematite is surface controlled and bicarbonate promoted. The rate of dissolution follows the expression R diss = k HCO 3 - =FeOH -- HCO 3 - }, where k HCO 3 - = 1.1 10 -3 h -1 . The implications of these findings in the oxic cycle of iron in natural waters are discussed, most importantly in order to explain the high-Fe(III) concentrations measured in groundwaters from the Poços de Caldas complex in Brazil.

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