Simultaneous precipitation kinetics of kaolinite and gibbsite at 80[degrees]C and pH 3

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(93)90333-R· OSTI ID:5067705

Nagy, K L; Lasaga, A C ^[1]

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1. Yale Univ., New Haven, CT (United States)

Precipitation rates of kaolinite and gibbsite were measured in stirred-flow reactors with a mixed seed substrate of kaolinite plus gibbsite at 80[degrees]C and pH 3. Input solutions were supersaturated simultaneously to different degrees with respect to both kaolinite and gibbsite. Rates were determined by assuming that each mineral precipitated only on its own seed. The calculated precipitation rates for each mineral are in good agreement with published data on the saturation state dependence of precipitation rates for each mineral alone. One rate for kaolinite was determined at a saturation state given by [delta]G[sub r] = +1.11 kcal mol[sup [minus]1]. This value doubles the range of saturation states at which kaolinite precipitation rates had been measured in the single-phase experiments. The new precipitation rates (mol m[sup [minus]2]s[sup [minus]1]) for kaolinite support either a linear dependence of precipitation rate on solution saturation state for 0 [le] [delta]G[sub r] [le] 1.11 kcal mol[sup [minus]1] given by Rate[sub ppt] = (5.0 [+-] 1.3) [times] 10[sup [minus]13][[delta]G[sub r]/RT], or a dependence derived from Transition State Theory given by Rate[sub ppt] = (3.4 [+-] 0.91) [times] 10[sup [minus]13][1 [minus] exp (([minus]1.9 [+-] 1.4)[delta]G[sub r]/RT)]. The experimental technique shows promise for measuring precipitation rates of minerals in solutions supersaturated with respect to more than one phase. The results also indicate that a mineral preferentially will grow on itself. The gibbsite-like surface of kaolinite does not appear to serve as a nucleation site for gibbsite when gibbsite is also available for growth in solutions near equilibrium with respect to both minerals.

• OSTI ID: 5067705
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 57:17; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM HYDROXIDES
ALUMINIUM SILICATES
DISPERSIONS
GIBBSITE
HYDROGEN COMPOUNDS
HYDROXIDES
KAOLINITE
KINETICS
MINERALS
MIXTURES
OXIDE MINERALS
OXYGEN COMPOUNDS
PRECIPITATION
REACTION KINETICS
SATURATION
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOLUTIONS