Minerals melanterite

Alternately, on roasting FeS in the presence of limited air, the first product is ferrous sulfate. (Ferrous sulfate occurs as the mineral melanterite or copperas, from the atmospheric oxidation of native pyrites.) However, on roasting with fnrther air, it converts to ferric oxide pins sulfur dioxide and sulfur trioxide, depending npon the reaction conditions. 

White and yellow evaporite minerals form thin crusts on the surface of and within fissures in the tailings. XRD analyses identified the hydrated iron sulphates, melanterite (FeS04-7H20), Zn-melanterite ((Zn,Fe)S04-7H20),... 

In this case study, the selected phases are pyrite, amorphous FeS, calcite (present in limestones in the roof strata Fig. 5), dolomite (possibly also present in the limestones), siderite (which occurs as nodules in roof-strata mudstones), ankerite (present on coal cleats in the Shilbottle Seam), melanterite and potassium-jarosite (representing the hydroxysulphate minerals see Table 3), amorphous ferric hydroxide (i.e., the ochre commonly observed in these workings, forming by precipitation from ferruginous mine waters), and gypsum (a mineral known to precipitate subaqueously from mine waters with SO4 contents in excess of about 2500 mg/L at ambient groundwater temperatures in this region, and with which most of the mine waters in the district are known to be in equilibrium). In addition, sorption reactions were included in some of the simulations, to contribute to the mole transfer balances for Ca, Na, and Fe. 

An indication of the degree of exothermicity of sulphide oxidation reactions can be gained by comparing the enthalpy of formation (A//f), that is, a measure of the energy locked up in each chemical species, relative to native elements. The difference in enthalpies of formation of all reactants and all products defines the enthalpy (heat released or absorbed) of the reaction. Thermodynamic data on sulphide minerals, such as pyrite, are notoriously varied and disputed, and the values in Table 4 must be treated with caution. Nevertheless, depending on whether one defines the reaction as ending in an aqueous solution (equation 5), an intermediate secondary sulphate (e.g., melanterite - equation 6) or in complete oxidation to an oxyhydroxide (equation 7), the calculated reaction enthalpy (AH°) released is of the order of at least 1000 kJ/mol. 

Most mineral collections contain potentially harmful species or forms. Toxic species may be the primary components in a specimen, but they may also occur as deterioration products. An example of this is melanterite, which is a common by-product of the decomposition of pyrite and marcasite. This highly poisonous sulfate of iron occurs as a white powder or crust on decomposed specimens. 

When oxidised by weathering, the final product of pyrites is hydrated ferric oxide or rust, as stated above, but the method of oxidation depends upon circumstances. In the absence of carbon dioxide or carbonates, it is usual for oxidation to ferrous sulphate to first take place whence the mineral copperas or melanterite (see below). This, in course of time, oxidises to limonite. In the presence of carbon dioxide, however, it appears that the sulphate is not first formed, but the readily oxidisable carbonate, which is then converted into limonite.3... 

As mentioned earlier, large amounts of copiapite have been found accumulating on ore surfaces in areas protected for direct rainfall. The mechanism of its formation is not at all clear but from field observations it appears that acid mine water is being drawn by capillary forces to an exposed surface where it quickly evaporates to melanterite and/or copiapite. Coquimbite is intimately associated with copiapite and these two minerals appear to be very stable as long as they are protected from rainfall or running water. No thermodynamic data... 

Mineral saturation indices for melanterite and amorphous iron hydroxide agree quite well with field occurrences of the same minerals. Jarosite, however, appears to be supersaturated for nearly all of the samples regardless of the presence or absence of the mineral in these streams. Field observations indicate that jarosite precipitation occurs in the microenvironment of bacterial colonies where the chemical conditions may be quite different from the bulk solution. These considerations lead us to suggest that there is a kinetic barrier which hinders jarosite precipitation but does not hinder ferric hydroxide precipitation and that this barrier is overcome by the surfaces of bacterial colonies (both iron-oxidizers and unidentified nonoxidizers ). ... 

We have observed melanterite, FeSOi 7H2O, to be one of the coimnon sulfate minerals produced by the oxidation of pyrite during weathering. Unfortunately, its solubility and related thermodynamic properties are not well established. The log K for melanterite dissolution has been derived from the free energies of... 

The standard technique used for detection of sulfates is X-ray diffraction of the LTA. Nevertheless, we have observed that in some cases sulfates are present in the coal, but the X-ray does not show any line attributable to them (44). The most abundant divalent iron sulfate observed in the coals studied is FeS04 H20 (szomolnokite), a monoclinic crystal with a tetramolecular unit cell (45). This compound orders antiferromagnetically around 10 K with an effective internal field of 359 kOe (22, 23). Other sulfate minerals found less frequently are FeS04 -4H20 (rozenite) and FeS04 7H20 (melanterite) anhydrous ferrous sulfate was detected when the coal was stored under vacuum. The ferric sulfates commonly observed in several coals are coquimbite and jarosites (16). 

Helz et al. (1987) found that the 40-day leachate from Coal A in Table A 12.4 was at samration with respect to gypsum, melanterite, and goethite. Input the analysis into MINTEQA2, adjusting values for sulfates as necessary (Table 12.7), and compute SI values for these minerals. Are other sulfates near saturation in the leachate Based upon your calculations, if the minerals reported by Helz et al. (1987) are not at saturation, discuss possible reasons. 

Field or laboratory observations of miscibility gaps, spinodal gaps, critical mixing points or distribution coefficients can be used to estimate solid-solution excess-free-energies, when experimental measurements of thermodynamic equilibrium or stoichiometric saturation states are not available. As an example, a database of excess-free-energy parameters is presented for the calcite, aragonite, barite, anhydrite, melanterite and epsomite mineral groups, based on their reported compositions in natural environments. 

Caswell No. 460 CCRIS 7331 ERA Pesticide Chemical Code 050502 Ferrous sulfate, heptahydrate Fesofbr Fesotyme Haemofort Iron protosulfate Iron sulfate heptahydrate lron(2- ) sulfate heptahydrate Iron(ll) sulfate heptahydrate Iron vitriol Ironate Irosul Melanterite mineral Presfersul Sal Martis Salt of steel Shoemaker s Black Siderotil mineral Sulfuric acid, iron(2+) salt (1 1), heptahydrate Szomolnikite mineral Tauriscite mineral. As a chemical intermediate, in electroplating, as a pesticide and medicinally as a hematinic. Registered by EPA as a herbicide (cancelled). Blue-green monoclinic crystals d n 1.897 loses H2O to form the tetrahydrate at 56.6", and the monohydrate at 65" soluble in H2O, insoluble in EtOH LDso (mus iv) n 65 mg/kg, (mus orl) = 1520 mg/kg. Generic Sigma-Aldrich Co. 

Iron(II) sulfate hydrate (and its mineral analogue melanterite) does not appear to have been used directly as a pigment, but found widespread employment historically as a precursor compound calcination of so-called copperas leads to a loss of water and sulfur trioxide - that is, sulfuric acid - to give synthetic iron oxide compounds. 

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