Jarosite [KFe₃(SO₄)₂(OH)₆] minerals are effective scavengers of potentially toxic elements (PTEs) and are abundant, for example, in acid rock/mine drainage scenarios. The retention process is highly relevant for environmental attenuation of heavy metals and metalloids since these are usually highly soluble and thus mobile under acidic conditions. We investigated both macroscopically and at the molecular scale the extent and the effects of concomitant incorporation of As(V) and Pb(II) into synthetic jarosite at different As/Pb starting molar ratios, using XRD-Rietveld, SEM, ATR-FTIR spectroscopy and wet chemistry. The amount of arsenate substituted in the jarosite structure was larger when Pb(II) was also incorporated, the former filling up to approximately 33% of the tetrahedral sites normally occupied by SO₄ ²⁻, as compared to 21% when Pb(II) was absent. Similarly, the amount of Pb(II) incorporated in the structure was larger when As(V) was also taken up. The jarosite unit cell volume increased as higher amounts of As(V) incorporated into its structure, but simultaneous Pb(II) incorporation seemed to limit this increase due to its smaller size as compared to K⁺. The extent to which As and Pb can accommodate in the jarosite structure was found to be limited by concentration maxima under the imposed synthesis conditions. At As/Pb ratios up to 1, Pb–As-jarosites were the only crystalline products. Above this ratio, a mixture of Pb–As-jarosite, anglesite (PbSO₄) and poorly-crystalline ferric arsenate (AFA) phases was observed. At the highest As/Pb ratio investigated of 1.80 Pb–As-jarosite was no longer formed. Infrared spectroscopy analysis was applied for the first time here to substituted jarosites with both cations and anions, showing spectral changes in the solids as the As/Pb ratio increased: a characteristic As–O doublet at ∼810 and ∼855 cm⁻¹ was observed upon Pb incorporation, showing an indirect effect of Pb(II) on the As–O bonds in the jarosite structure. Thus, structural incorporation of Pb plays a pivotal role in the unit cell environment of jarosite to balance the distortion caused by AsO₄-for-SO₄ substitution. The retention processes found in this work have important environmental implications and impacts: through the synergistic incorporation encountered, remediation enhancement of cationic pollutants such as Pb(II) is possible in a concomitant fashion with As(V) attenuation in acidic mining and metallurgical environments.

The detailed mineralogical, physical and chemical characterization of nine samples of imported cosmetic talc and of two samples of talc from currently non-productive Mexican ore deposits (Oaxaca and Puebla States) is presented. The imported cosmetic talc was classified into two groups, considering whether they are packed in the country of origin or in Mexico and considering their price. X-ray diffraction, infrared short wave, thermogravimetric analysis and scanning electron microscopy were used for mineralogical characterization. For the physical characterization, colorimetry and laser granulometry were used. The chemical composition (major, trace elements) was studied by ICP-MS. It was concluded that only the highest priced and imported in packaged form talcs meet the specific purity requirements for a talc of cosmetic type. The talcs that are packed in Mexico and the talc of the studied Mexican deposits present mineralogical and chemical impurities that make their use difficult in the manufacture of high-quality cosmetic talc. The low-price talc should not be sold as cosmetic talc, and the regulations in Mexico on this subject should be reviewed and updated.

The mineralogy of surface crusts and efflorescent salts of two old abandoned tailings (Xochula and Remedios) of the mining district of Taxco, Guerrero, was studied by short-wave infrared spectroscopy (SWIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The chemistry of the selected samples was studied with induced coupled plasma mass spectrometry (ICP–MS). Principal mineralogy is composed of hydrated sulfates of iron (di-trivalent), other less-soluble sulfates such as gypsum and jarosite, and oxides–hydroxides of iron, all of which are the result of the weathering of sulfides (mainly pyrite) accumulated in mining waste. Using quantitative X-ray diffraction (Rietveld method) and the spatial distribution of secondary minerals, two main zones (lateral and central) have been established in both tailings. The genetic model for their formation shows that the secondary iron minerals (sulfates, oxides, and hydroxides) in these deposits have been formed at least in three different stages, mainly by oxidation, dissolution, and precipitation processes in combination with dehydration and primary sulfides neutralization reactions. The chemical analyses of some salts confirm the presence of potentially toxic elements (PTE) in their structure and therefore indicate that the dissolution of the efflorescences in these deposits is a potential source of contamination during the wet season.