Title: Olivine dissolution kinetics at near-surface conditions
Abstract: Fluidized bed dissolution experiments have been conducted as a function of pH at 25°C with fayalitic olivine (Fo6) in HCl solutions and with forsteritic olivine (Fo91) in solutions containing the organic ligand potassium hydrogen phthalate (KHP). At 25°C the dissolution rate (R) of fayalite as a function of pH is: R(mol cm −2s−))=1.1·10−10aH+0.69 +3.2·10−14+1.2·10−16aH+−0.31 where aH+ is the activity of H+ in solution. The dissolution rate at 25°C of Fo6 at a given pH is a factor of 6 greater than that of forsteritic olivine. The assumption that the rates increase on a molar basis with Fe content allows calculation of dissolution rates of Fe-Mg solid solution olivines of intermediate compositions. Batch-type dissolution experiments were completed with Fo91 at 65°C in solutions at pH 1.8, 6.0 and 9.8. The rate equation obtained from these experiments is: R (mol cm−2s−1)=3.5·10−10aH+0.5+1.0·10−13aH+0.5 When combined with previously published data for Fo91 at 25°C, the 65°C experiments indicate that the activation energy of the olivine dissolution reaction in acidic, organic-free solutions is ∼19 ± 2.5 kcal. mol−1. Dissolution experiments with forsteritic olivine in solutions containing KHP at 25°C demonstrate that the rate of dissolution is increased in these solutions relative to rates measured in KHP-absent HCl-H2O solutions. Apparently, the increase in rate is caused by Mg complexation at the olivine surface. Ligand-promoted dissolution is thought to occur in parallel with proton-promoted dissolution. Therefore, the net rate, Rnet, is the sum of the two rates: Rnet (mol cm−2s−1)=0.8·10−12[LP]0.45+RH+ where [LP] denotes the concentration of KHP; and RH+ denotes the proton-promoted dissolution rate.
Publication Year: 1992
Publication Date: 1992-05-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 216
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