The surface of labradorite feldspar after acid hydrolysis

in particular the leached layer theory. Most importantly, our data provide critical evidence for 51 a single mechanism based on interfacial dissolution-reprecipitation. This concept not only 52 unifies weathering processes for the first time, but we also suggest that nanoscale-surface 53 processes can have a potentially negative impact on CO 2 uptake associated with chemical 54 weathering. The results in this study, when combined with recently published research on 55 fluid-assisted mineral replacement reactions, supports the idea that dissolution-reprecipitation 56 is a universal mechanism controlling fluid-mineral interactions . 57Based on this we propose the existence of a chemical weathering continuum based solely on 58 the interfacial dissolution-reprecipitation mechanism. 59 3

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“…819 layers has also been reported (e.g. Casey et al, 1989Casey et al, , 1993Weissbart and Rimstidt, 2000). 829…”

Section: Properties Of Thin Fluid Films and Precipitates 657mentioning

confidence: 93%

Unifying natural and laboratory chemical weathering with interfacial dissolution–reprecipitation: A study based on the nanometer-scale chemistry of fluid–silicate interfaces

et al. 2012

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“…Plagioclase dissolution have been long known to be incongruent, with Al, Na and Ca being preferably dissolved at the surface (e.g. Blum and Stillings 1995;Carroll and Knauss 2005;Casey et al 1989;Inskeep et al 1991;Muir et al 1989Muir et al , 1990aSchweda et al 1997). This dissolution generates an Al-Na-Ca-poor thin layer (which is consequently enriched in Si) at the plagioclase surface (Blum and Stillings 1995).…”

Section: Plagioclase Reactivitymentioning

confidence: 94%

“…Dilute acidic conditions produce relatively thick Si-rich layers, up to several thousands of Å (e.g. Blum and Stillings 1995;Casey et al 1989;Hellmann et al 2003;Muir andNesbitt 1992, 1997), whereas dissolution at near-neutral pH produces only thin leached layers of tens of Å between pH 5 and 8 (Blake and Walter 1999;Blum and Stillings 1995;Muir and Nesbitt 1997). The circumneutral environments prevailing in the Tio mine waste rock kinetic tests should promote the formation of such thin leached layers (tens of Å ) on the plagioclase feldspar surfaces.…”

Section: Plagioclase Reactivitymentioning

confidence: 98%

Predicting Geochemical Behaviour of Waste Rock with Low Acid Generating Potential Using Laboratory Kinetic Tests

2010

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Prediction of contaminated neutral drainage using laboratory kinetic tests designed for acid mine drainage prediction is challenging because of the low metal concentrations generated by low sulfide oxidation rates. Fresh and weathered samples from the Tio mine waste rock piles were submitted to humidity cell tests. The waste rocks were demonstrated to be non-acid generating in the long term, as interpreted by conservative oxidation-neutralization curves. The results demonstrate that even though the main neutralizing minerals react differently after 25 years of natural weathering (with regard to Ca, Mg, Al, and Si release), the response of the fresh waste rocks during humidity cell leaching was very similar to those of the weathered waste rocks, when considering all the elements related to silicate dissolution, including those implicated in secondary phase precipitation. However, Ni generation was greater in the weathered waste rocks even though sulfide oxidation rates were similar, as Ni sorption properties reach saturation. Although the Ni concentrations from the leachates of humidity cell tests remain below regulated values, they are bound to increase with continued weathering if no preventive or control measures are undertaken at the site.

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“…Leached layers are a characteristic by-product of feldspar dissolution under acid laboratory conditions whereby selective removal of Al and Na/K/Ca relative to Si, renders the outermost <0.1 mm of grains amorphous and non-stoichiometric (e.g. Casey et al, 1989;Muir et al, 1989;Hellmann et al, 1990). Kawano and Tomita (1994) found that a tens of nm thick leached layer on albite grains hydrothermally reacted with distilled water had subsequently crystallized to Na-smectite and mica via a non-crystalline and fibrous material.…”

Section: Discussionmentioning

confidence: 99%

Weathering microenvironments on feldspar surfaces: implications for understanding fluid-mineral reactions in soils

Lee¹,

Brown²,

Hodson³

et al. 2008

Mineral. mag.

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The mechanisms by which coatings develop on weathered grain surfaces, and their potential impact on rates of fluid-mineral interaction, have been investigated by examining feldspars from a 1.1 ky old soil in the Glen Feshie chronosequence, Scottish highlands. Using the focused ion beam technique, electron-transparent foils for characterization by transmission electron microscopy were cut from selected parts of grain surfaces. Some parts were bare whereas others had accumulations, a few micrometres thick, of weathering products, often mixed with mineral and microbial debris. Feldspar exposed at bare grain surfaces is crystalline throughout and so there is no evidence for the presence of the amorphous 'leached layers' that typically form in acid-dissolution experiments and have been described from some natural weathering contexts. The weathering products comprise sub-mm thick crystallites of an Fe-K aluminosilicate, probably smectite, that have grown within an amorphous and probably organic-rich matrix. There is also evidence for crystallization of clays having been mediated by fungal hyphae. Coatings formed within Glen Feshie soils after~1.1 ky are insufficiently continuous or impermeable to slow rates of fluid-feldspar reactions, but provide valuable insights into the complex weathering microenvironments on debris and microbe-covered mineral surfaces.

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The surface of labradorite feldspar after acid hydrolysis

Cited by 94 publications

References 25 publications

Unifying natural and laboratory chemical weathering with interfacial dissolution–reprecipitation: A study based on the nanometer-scale chemistry of fluid–silicate interfaces

Unifying natural and laboratory chemical weathering with interfacial dissolution–reprecipitation: A study based on the nanometer-scale chemistry of fluid–silicate interfaces

Predicting Geochemical Behaviour of Waste Rock with Low Acid Generating Potential Using Laboratory Kinetic Tests

Weathering microenvironments on feldspar surfaces: implications for understanding fluid-mineral reactions in soils

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