What do dissolution experiments tell us about natural weathering?

Casey, William H.; Banfield, Jillian F.; Westrich, Henry R.; McLaughlin, L.

doi:10.1016/0009-2541(93)90115-y

Cited by 120 publications

(62 citation statements)

References 28 publications

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“…Nanometre scale observations carried out on mica surfaces indicate that the density of etch pits decreases when pH increases from 1.1 to 5.7. This shows that as pH increases, the available reactive surface decreases confirming previous studies where it was postulated that mica dissolution depends on H + activity (Bales and Morgan, 1985;Carrol-Webb and Walther, 1988;Acker and Bricker, 1992;Casey et al, 1993;Kalinowski and Schweda, 1996;Oelkers et al, 2008). According to the Transition State Theory, when a mica crystal is in contact with solutions, H + may exchange with K + to form an activated complex with surface cations leading to polarisation and instability of cationic bonds with the mineral surface (Stumm and Wollast, 1990).…”

Section: Discussionsupporting

confidence: 73%

Influence of pH and temperature on the early stage of mica alteration

Pachana¹,

Zuddas²,

Censi³

2012

Applied Geochemistry

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a b s t r a c tMineral dissolution and precipitation reactions actively participate in controlling fluid chemistry during water-rock interaction. In this study, the changes in the biotite and muscovite basal surface nano-morphology were evaluated during interaction with fluids of different pH (pH = 1.1, 3.3 and 5.7) at different temperatures (T = 25°, 120°, and 200°C). Results show that at the nanometre scale resolution of the atomic force microscope (AFM), dissolution generates etch pits with a stair-shaped pattern over the (0 0 1) surface. The flux of dissolved elements decreases when pH increases. However, at pH 5.7, a change was found in the flux after 42 h of reaction when abundant gibbsite and kaolinite coat the dissolving mineral surface. This phenomenon was widely observed at edges of the etch pits by AFM. It was also found that an increase in temperature produces an enhancement in the elemental flux in both micas. Dissolution regime changes after less than one day of interaction at high temperature because of abundant coating formation over the etch pits and edges. The results demonstrate the key role of nanometre size neogenic phases in the control of elemental flux from mica surfaces to solution. The formation of nanometre size coatings, blocking the sites active for dissolution, appears to control the alteration of phyllosilicates even at the early stage of the interaction.

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Section: Discussionsupporting

confidence: 73%

Influence of pH and temperature on the early stage of mica alteration

Pachana¹,

Zuddas²,

Censi³

2012

Applied Geochemistry

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“…Finally, ligand exchange rates of cations correlate well with the reactivity of both divalent metal oxides (Casey et al, 1993) and sulphides (Morse and Luther, 1999) at the solidwater interface. Casey et al (1993) reported that the water exchange rate of the hydrated ion is particularly low for Ni 2+ (10 4.4 s -1 ) compared to that for Fe 2+ (10 6.5 s -1 ) and that this difference may explain the lower dissolution rate of Ni-oxides and orthosilicates compared to their Fe analogues.…”

Section: Resultsmentioning

confidence: 88%

“…Casey et al (1993) reported that the water exchange rate of the hydrated ion is particularly low for Ni 2+ (10 4.4 s -1 ) compared to that for Fe 2+ (10 6.5 s -1 ) and that this difference may explain the lower dissolution rate of Ni-oxides and orthosilicates compared to their Fe analogues. In addition, Morse and Luther (1999) proposed that, since Ni 2+ has lower kinetics of water exchange than Fe 2+ , incorporation of Ni 2+ into FeS 2 should be kinetically favoured over precipitation of pure NiS 2 , as we demonstrate here.…”

Section: Resultsmentioning

confidence: 99%

Nickel accelerates pyrite nucleation at ambient temperature

Morin¹,

Noël²,

Menguy³

et al. 2017

Geochem. Persp. Let.

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Chemical and isotopic compositions of pyrites are used as biogeochemical tracers in Archean to modern sediments. Moreover, pyrite formation from monosulphide precursors has been proposed to be involved in prebiotic chemistry. However, the factors controlling pyrite formation and distribution in the sedimentary record are incompletely understood. Here, we show that Ni 2+ ions accelerate ~5 times the nucleation of pyrite at ambient temperature. Using Fe and Ni K-edge EXAFS and TEM-EDXS we demonstrate that Ni(II) is directly involved in the nucleation of pyrite synthesised by reacting Fe(III) with Na 2 S in the presence of aqueous Ni(II) impurity. Initial formation of a Ni-enriched pyrite core is followed by overgrowth of a Ni-depleted pyrite shell, leading to compositional zoning of the Fe 1-x Ni x S 2 nanocrystals (x = 0.05 to 0.0004). The molar Ni/Fe ratio in the final aqueous solution was then 2000 times lower than the starting ratio of 0.01. This enhanced and accelerated trapping of Ni by pyrite could be of prime importance in controlling Ni concentration in the ocean during early diagenesis of marine sediments, and could thus have important implications for interpreting abundances of Ni and pyrite in the sedimentary record. In addition, acceleration of pyrite nucleation in the presence of nickel could help understanding the role of Fe-Ni sulphides in catalysing potential prebiotic reactions.

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“…b Density of hornblende [32]. c Rate constant for dissolution of FeO as a function of pH (k(pH)) was estimated from dissolution rate constants at pH 2 for metal oxides assuming that n (log k(pH) = log k o + n pH) equals -0.7 and k o = 1.4 x 10 -5 mol m -2 s -1 as per [45]. Porefluid pH was assumed = 7 (more alkaline than the pH 5.1 measured at bedrock-saprolite interface [16] due to the low water-rock ratio).…”

Section: Weathering and Denudationmentioning

confidence: 99%

A spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady-state denudation

Fletcher

Buss

Brantley

2006

Earth and Planetary Science Letters

211

229

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Spheroidal weathering, a common mechanism that initiates the transformation of bedrock to saprolite, creates concentric fractures demarcating relatively unaltered corestones and progressively more altered rindlets. In the spheroidally weathering Rio Blanco quartz diorite (Puerto Rico), diffusion of oxygen into corestones initiates oxidation of ferrous minerals and precipitation of ferric oxides. A positive ∆V of reaction results in the buildup of elastic strain energy in the rock. Formation of each fracture is postulated to occur when the strain energy in a layer equals the fracture surface energy. The rate of spheroidal weathering is thus a function of the concentration of reactants, the reaction rate, the rate of transport, and the mechanical properties of the rock. Substitution of reasonable values for the parameters involved in the model produces results consistent with the observed thickness of rindlets in the Rio Icacos bedrock (≈ 2-3 cm) and a time interval between fractures (≈ 200-300 a) based on an assumption of steady-state denudation at the measured rate of 0.01 cm/a. Averaged over times longer than this interval, the rate of advance of the bedrock-saprolite interface during spheroidal weathering (the weathering advance rate) is constant with time. Assuming that the oxygen concentration at the bedrock-saprolite interface varies with the thickness of soil/saprolite yields predictive equations for how weathering advance rate and steadystate saprolite/soil thickness depend upon atmospheric oxygen levels and upon denudation rate. The denudation and weathering advance rates at steady state are therefore related through a condition on the concentration of porewater oxygen at the base of the saprolite. In our model for spheroidal weathering of the Rio Blanco quartz diorite, fractures occur every ~ 250 years, ferric oxide is fully depleted over a four rindlet set in ~ 1000 years, and saprolitization is completed in ~ 5000 years in the zone 2 containing ~ 20 rindlets. Spheroidal weathering thus allows weathering to keep up with the high rate of denudation by enhancing access of bedrock to reactants by fracturing.Coupling of denudation and weathering advance rates can also occur for the case that weathering occurs without spheroidal fractures, but for the same kinetics and transport parameters, the maximum rate of saprolitization achieved would be far smaller than the rate of denudation for the Rio Blanco system. The spheroidal weathering model provides a quantitative picture of how physical and chemical processes can be coupled explicitly during bedrock alteration to soil to explain weathering advance rates that are constant in time.

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What do dissolution experiments tell us about natural weathering?

Cited by 120 publications

References 28 publications

Influence of pH and temperature on the early stage of mica alteration

Influence of pH and temperature on the early stage of mica alteration

Nickel accelerates pyrite nucleation at ambient temperature

A spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady-state denudation

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