The mechanism of dissolution of minerals in acidic and alkaline solutions: Part IV equilibrium and near-equilibrium behaviour

Crundwell, Frank K.

doi:10.1016/j.hydromet.2015.01.012

Cited by 21 publications

(24 citation statements)

References 32 publications

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“…2 are close to neutral with pH values ranging from 5.5 -6.7. For the feldspars investigated in this study, steady-state dissolution rates are lowest for microcline with 4⋅10 -14 -8⋅10 -14 305 moles m -2 s -1 at pH ~ 6 (Crundwell, 2015) followed by sanidine with a rate of ~ 2⋅10 -13 moles m -2 s -1 at near neutral conditions (Crundwell, 2015), while dissolution of andesine occurs with a steady-state rate of 10 -12 -10 -11 moles m -2 s -1 at pH ~ 8 (Gudbrandsson et al, 2014). Hereby, initial dissolution rates of freshly suspended feldspar may be higher by up to three orders of magnitude than the rates at steady-state (Zhu et al, 2016).…”

Section: Aluminum Depletion and Surface Dissolutionmentioning

confidence: 78%

“…In addition to the exchange of surface ions discussed above (and in more detail in Kumar et al (2018a)), feldspars undergo slow 300 dissolution in water and aqueous solutions followed and accompanied by the precipitation of more stable phases like kaolinite, gibbsite or halloysite (Stillings and Brantley, 1995). Depending on the specific feldspar and solution pH, steady-state Si dissolution rates vary between 10 -10 and 10 -14 moles m -2 s -1 (Crundwell, 2015) with lowest values at near neutral conditions. The solution pH during the emulsion freezing experiments reported in Fig.…”

Section: Aluminum Depletion and Surface Dissolutionmentioning

confidence: 99%

See 1 more Smart Citation

Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 3 – Aluminosilicates

Kumar¹,

Marcolli²,

Peter³

2018

Preprint

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Abstract. Aluminosilicates (such as feldspars, clay minerals and micas) and quartz (a crystalline form of silica), constitute the majority of airborne mineral dust. Despite similarities in structures and surfaces they differ greatly in terms of their ice nucleation (IN) efficiency. Here, we show that determining factors for their IN activity include surface ion exchange, NH3 or NH4+ adsorption, as well as surface degradation due to the slow dissolution of the minerals. We performed immersion freezing experiments with the (Na-Ca)-feldspar andesine, the K-feldspar sanidine, the clay mineral kaolinite, the micas muscovite and biotite, and gibbsite (Al(OH)3, a mineral form of aluminum hydroxide) and compare their IN efficiencies with those of the previously characterized K-feldspar microcline and quartz. Samples were suspended in pure water as well as in aqueous solutions of NH3, (NH4)2SO4, NH4Cl and Na2SO4, with solute concentrations corresponding to water activities aw&#8201;=&#8201;0.88&#8211;1.0. Using differential scanning calorimetry (DSC) on emulsified micron-sized droplets, we derived onset temperatures of heterogeneous (Thet) and homogeneous (Thom) freezing as well as heterogeneously frozen water volume fractions (Fhet). Suspensions in pure water of andesine, sanidine and kaolinite yield Thet&#8201;=&#8201;242.8&#8201;K, 241.2&#8201;K and 240.3&#8201;K, respectively, while no discernable heterogeneous freezing signal is present in case of the micas or gibbsite (i.e. Thet &#8776; Thom &#8776; 237.0&#8201;K). The presence of NH3 and/or NH4+-salts as solutes has distinct effects on the IN efficiency of most of the investigated minerals. When feldspars and kaolinite are suspended in very dilute solutions of NH3 or NH4+-salts (<&#8201;0.1&#8201;molal, corresponding to aw&#8201;>&#8201;~&#8201;0.99), Thet shifts to higher temperatures (by 2.6&#8211;7.0&#8201;K compared to the pure water suspension). Even micas and gibbsite develop weak heterogeneous freezing activities in ammonia solutions. Conversely, suspensions containing Na2SO4 cause Thet of feldspars to clearly fall below the water-activity-based immersion freezing description (&#916;aw&#8201;=&#8201;const) even in very dilute Na2SO4 solutions, while Thet of kaolinite follows the &#916;aw&#8201;=&#8201;const curve. The water activity determines how the freezing temperature is affected by solute concentration alone, i.e. if the surface properties of the ice nucleating particles are not affected by the solute. Therefore, the complex behavior of the IN activities can only be explained in terms of solute-surface-specific processes. We suggest that the immediate exchange of the native cations (K+/Na+/Ca2+) with protons, when feldspars are immersed in water, is a prerequisite for their high IN efficiency. On the other hand, excess cations from dissolved alkali salts prevent surface protonation, thus explaining the decreased IN activity in such solutions. In kaolinite, the lack of exchangeable cations in the crystal lattice explains why the IN activity is insensitive to the presence of alkali salts (&#916;aw&#8201;=&#8201;const). We hypothesize that adsorption of NH3 and NH4+ on the feldspar surface rather than ion exchange is the main reason for the anomalous increased Thet in dilute solutions of NH3 or NH4+-salts. This is supported by the response of kaolinite to NH3 or NH4+, despite lacking exchangeable ions. Finally, on longer timescales (hours to days) the dissolution of the feldspars in water or solutions becomes an important process leading to depletion of Al and formation of an amorphous layer enriched in Si within less than an hour. This hampers the IN activity of andesine the most, followed by sanidine, then eventually microcline, the least soluble feldspar.

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Section: Aluminum Depletion and Surface Dissolutionmentioning

confidence: 78%

Section: Aluminum Depletion and Surface Dissolutionmentioning

confidence: 99%

Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 3 – Aluminosilicates

Kumar¹,

Marcolli²,

Peter³

2018

Preprint

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“…However, even the TLM model cannot adequately capture the shape of the adsorption edges and it underestimates the Cr(VI) adsorption mainly at higher Cr concentrations and above pH 5. One of the causes of this trend might be the failure to include the effect of clay minerals dissolution ( Figure S4), which is pronounced under both acidic and alkaline conditions [61][62][63]. In addition, the partial dissolution of birnessite releasing Mn 2+ ions in systems with lower ionic strengths at pH > 7…”

Section: Modeling Approach For Kaolinite and Illitementioning

confidence: 99%

Chromate adsorption on selected soil minerals: Surface complexation modeling coupled with spectroscopic investigation

Veselská

Fajgаr

Číhalová

et al. 2016

Journal of Hazardous Materials

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“…This approach has been applied to the dissolution of silicates 20 and oxides, hydroxides, and sulfides. 22 The dissolution of forsterite 26 and feldspar 27,28 has been analyzed in detail in terms of this approach.…”

Section: Introductionmentioning

confidence: 99%

On the Mechanism of the Dissolution of Quartz and Silica in Aqueous Solutions

2017

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Quartz and silica are common materials, and their dissolution is of significant interest to a wide range of scientists. The kinetics of the dissolution of quartz and silica have been measured extensively, yet no clear theory of dissolution is available. A novel theory of dissolution and crystallization has recently been proposed that envisages the removal of material from the surface to form ions in solution leaving behind a charged surface vacancy. These vacancies create a potential difference across the Stern layer that accelerates or retards the removal of ions. In this way, the surface potential difference is caused by and influences the rate of the removal of ions. From this theory, a model of quartz dissolution is derived that predicts the observed orders of reaction. This prediction of the orders of reaction fits a data set consisting of 285 experiments. The model also describes the effect of Na + , K + , and Li + ions, as well as the effect of heavy water. A significant component of the model is its ability to describe the zeta potential of the quartz–water interface. The model successfully predicts a transient period at the beginning of the reaction when the rate could either increase or decrease.

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The mechanism of dissolution of minerals in acidic and alkaline solutions: Part IV equilibrium and near-equilibrium behaviour

Cited by 21 publications

References 32 publications

Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 3 – Aluminosilicates

Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 3 – Aluminosilicates

Chromate adsorption on selected soil minerals: Surface complexation modeling coupled with spectroscopic investigation

On the Mechanism of the Dissolution of Quartz and Silica in Aqueous Solutions

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