Martín Reyes

Alkaline reactivity of arsenical natrojarosite

Jarosites are compounds that can undergo substitutions with several elements of environmental importance (such as As5+) during precipitation. Arsenic integrated in the structure could influence the solubility of the jarosite, potentially stabilizing the structure under a wide range of conditions that are tolerated by pure jarosite. Alkaline reactivity is characterized by the removal of sulfate and sodium ions from the lattice and by the formation of a gel consisting of iron hydroxides with adsorbed arsenate. The decomposition curves show an induction period, followed by a conversion period. The induction period is independent from the particle size and decreases exponentially as the temperature increases. The conversion period is characterized by the formation of a hydroxide halo around an unreacted arsenical natrojarosite core. The kinetic data are consistent with the chemical control of the process. The expression obtained in NaOH medium for [OH-] concentrations ranging from 3.84 × 10-3 to 1.08 × 10-1 mol L-1 is the following: r0/-v[1 - (1 - x)1/3] = 3.11 × 109 exp(-57.110/RT) [OH-]0.7 t. The expression in Ca(OH)2 medium for [OH-] concentrations ranging from 2.21 × 10-2 to 6.98 × 10-2 mol L-1 is the following: r0/-v[1 - (1 - x)1/3] = 9.22 × 1011 exp(-48.610/RT) [OH-]1.51 t.

Kinetic modeling of the decomposition of beudantite in NaOH medium

This piece of work presents a study on the reaction of beudantite in NaOH medium under a wide range of experimental conditions. The partial decomposition of solids indicates the presence of an unreacted beudantite core, a reaction front and a halo of amorphous decomposition gel made of iron hydroxides and lead, through which sulfate and arsenate ions diffuse from the beudantite into the medium, while hydroxide ions from the medium diffuse through the gel onto the core of spherical particles of beudantite. We studied the dependence of the reaction rate on (OH−1) concentration, temperature and particle size in order to determine the reaction order and activation energy of the decomposition process of beudantite. A comparative study on the experimental rate constants of the alkaline decomposition of beudantite and other arsenic jarosites was conducted.

Kinetic Analysis of the Decomposition of the KFe3(SO4)2-x(CrO4)x(OH)6 Jarosite Solid Solution in Ca(OH)2 Medium

The decomposition of the solid solution of potassium jarosite with chromium(VI) in Ca(OH)2 media was studied in the present work. According to experimental results, the incorporation of CrO42- into the crystal structure of jarosite resulted in a solid solution with the following approximate formula: [K0.86(H3O)0.14]Fe2.67[(SO4)1.23(CrO4)0.77][(OH)5.01(H2O)0.99]. The experimental data describe a reaction based on the shrinking core model with chemical control for spherical particles. A reaction order of n = 0.67 and an activation energy (Ea) of 63.75 kJ mol-1 were obtained in the induction period (tind). The progressive conversion period is characterized by the diffusion of K+, SO42- and CrO42- ions into the solution. In this stage, n = 1.99 with respect to OH-, and Ea = 51.56 kJ mol-1. The CrO42- diffusion is slower compared to that of sulfate, a slight amount of chromate is adsorbed in the layer of the solid residue consisting on Fe(OH)3. Finally, the equations that satisfactorily describe the reaction process were established from the data obtained.

Alkaline Reactivity of Solid Solution of NH4‐Na Jarosite with Arsenic

In this work, a kinetic analysis of the decomposition process of a solid solution of ammonium and sodium jarosite with arsenic incorporated into its structure in NaOH medium is presented. Atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectroscopy (ICP-OES), elemental analysis and X-ray diffraction (XRD) were used for the characterization of the solid solution and the decomposition products. According to the results, the approximate stoichiometry of the jarosite synthesized is as follows: [(NH4)0.72Na0.06(H3O)0.21]Fe3 2.52(SO4)1.85(AsO4)0.15[(OH)4.41(H2O)1.59].

Characterization of Mercury Jarosite

This paper presents the characterization of a sample of mercury jarosite that was synthesized by slowly adding Hg(NO3)2·H2O into a Fe2(SO4)3·nH2O solution. X-ray diffraction (XRD) analysis performed on the sample confirmed that the compound presents a crystal phase corresponding to mercury jarosite. Analysis through Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) determined that the precipitate is composed of mercury, sulfur, iron and oxygen. It is made up of spherical particles with an average size of 38 µm; these particles are made of rhombohedral micro-crystals with sizes ranging between 1 and 2 µm. Chemical characterization was performed through dichromatometry analysis, gravimetry and atomic absorption spectroscopy (AAS), thus obtaining the following composition: 27% Fe3+, 37% SO4 2− 14% Hg2+, 22% OH− + H3O+ + H2O. The following approximate formula of the compound was determined from chemical analysis: [Hg0.39(H3O)0.22]Fe2.71(SO4)2.17(OH)4.79(H2O)2.09.

Chemical and Mineralogical Characterization of a Mixed Sulphide Ore at Zimapan, Hidalgo, Mexico

Chemical and mineralogical characterization of a sulphide ore from the mining district of Zimapan, Hidalgo, Mexico, was performed in order to obtain accurate information on the composition of the ore to optimize the subsequent flotation process. A combination of techniques was used: Scanning Electron Microscopy (SEM) with Energy Dispersive Spectrometer (EDS), X-ray diffractometry (XRD), Inductively Coupled Plasma (ICP) and Fourier transform infrared spectroscopy (FTIR). The SEM mapping confirmed the presence of the elements: Ca, Si, Fe, K, S, Al, Zn, Mg and Mn. The XRD analysis suggests that the ore matrix is calcite; additional species found were wollastonite, johannsenite, and pyrite, among other impurities. The FTIR analysis performed for the aqua regia insoluble showed the presence of calcium oxide, copper oxide and silicon oxide. The results for the ICP analysis were:13.31% S, 2.55% Fe, 0.46% Zn, 0.03% Cu, 0.06% Pb, 0.07% Mn, 0.09% As, 0.01% Sb and 0.08 grton-1 Ag.

Characterization and Stoichiometry of the Cyanidation Reaction in NaOH of Argentian Waste Tailings of Pachuca, Hidalgo, México

The argentian resources of Pachuca, Hidalgo, Mexico have suffered an extensive exploitation, resulting in more than 100 million tons of waste tailings located in several sites around the city of Pachuca and surrounding municipalities. Chemical, mineralogical and granulometric characterization of the waste tailings of Pachuca, Hidalgo, Mexico, was carried out in this work. Characterization results indicate that these argentian wastes contain 56 g Ag ton–1, and the silver is present in the forms of metal, argentite and argentian jarosite in a quartz matrix. Stoichiometry of the cyanidation reaction in NaOH media was analyzed, and the following conclusions were obtained: 1) both metal silver and silver present in the form of argentite can be quickly cyanidation, 2) Alkaline decomposition of argentian jarosite is the rate-control step in the cyanidation reaction.

Study of Behavioral about the Decomposition Reaction of the Solid Solution KFe3(SO4)2‐x(CrO4)x(OH)6 in Ca(OH)2 Media

The decomposition of the solid solution KFe3(SO4)2-x(CrO4)x(OH)6 and its capacity to detain CrO 4 2- under alkaline conditions were studied. A solution of Ca(OH)2 was the media used. The incorporation of CrO 4 2- in crystalline structure of jarosite, resulted in a solid solution with the following approximate formula: [K0.86(H3O)0.14]Fe2.67[(SO4)1.23(CrO4)0.77][(OH)5.01(H2O)0.99]. The experimental data describe a reaction based in the model of decreasing core with chemical control. Decomposition curve shows an induction period, characterized by the formation of active centers where is initiated and established a reaction front, that is the beginning of the progressive conversion period, during which is formed a layer of inert products of Fe(OH)3 and is characterized for the massive diffusion of K+, SO 4 2- and CrO 4 2- toward the solution. However, the mappings by SEM-EDS from a particle decomposed partially, shows that the SO 4 2- is released preferentially, meanwhile, an important quantity of the CrO 4 2- is adsorbed in the layer of Fe(OH)3.

Influence of Cu2+ and Zn2+ on the Dissolution of Ag IN S2O32- Medium

The dissolution of Ag contained in metallurgical tailings was studied by adding ions Cu2+ and Zn2+ in S2O32- medium. Chemical analysis of mine tailings by cupellation revealed a Ag concentration of 71 g/ton. The XRF and XRD analysis confirmed the preponderance of SiO2 in the mineral matrix. The experimental dissolution process was conducted in alkaline solution using six concentrations of NaOH and five of S2O32-, at different temperatures, also using five concentrations of Cu2+ and Zn2+ as a catalyst. The results showed similar values for both systems (96.8% and 97.13%). The ion Cu2+ and Zn2+ increases the dissolution of Ag, and decrease the reaction time of dissolution. Under the conditions used, pH and stirring rate did not affect the dissolution of Ag.