wAbstract
@Far from equilibrium enstatite dissolution rates both open to
atmospheric CO2 and CO2
purged were measured as a function of solution pH from 8 to 13
in batch reactors at room temperature. Congruent dissolution was
observed after an initial period of inconguent dissolution with
preferential Si release from the enstatite. Steady-state dissolution
rates in open to atmospheric CO2 conditions
decrease with increase in solution pH from 8 to 12 similar to
the behavior reported by other investigators. Judging from the
pH 13 dissolution rate, rates increase with pH above pH 12. This
is thought to occur because of the increase in overall negative
surface changes on enstatite as Mg surface sites become negative
above pH 12.4, the pH of zero surface charge of MgO.
@Steady-state dissolution rates of enstatite increase above pH
10 when CO2 was purged by performing the
experiments in a N2 atmosphere. This suggests
inhibition of dissolution rates above pH 10 when experiments were
open to the atmosphere. The dissolved carbonate in these solutions
becomes dominantly CO32- above
pH 10.33. It is argued that CO32-
forms a Mg2-CO3 complex
at positively charged Mg surface sites on enstatite, resulting
in stabilization of the surface Si-O bonds. Therefore, removal
of solution carbonate results in an increase in dissolution rates
of enstatite above pH 10. The log rate of CO2-purged
enstatite dissolution in moles per cm2 per s as a function
of increasing pH above pH 10 is equal to 0.35. This is consistent
with the model of silicate mineral dissolution in the absence
of surface carbonation in alkaline solutions proposed earlier
in the literature.x
1. Introduction
2. Materials and methods
3. Experimental results
4. Discussion
@4.1. Relative rate of element release
@4.2. Effect of dissolved CO2
5. Concluding remarks
Acknowledgments
References