No description available.

No description available.

Masters Research - Master of Science / The jarosite group of compounds are yellow/brown clay like substances, both naturally occurring and synthetically produced in metallurgical processes. Jarosites have the structure MFe3(SO4)2(OH)6, where M can be numerous elements or compounds, most often potassium or sodium. The term jarosite refers specifically to the potassium form of the compound, but is synonymous with the whole group of compounds, often leading to confusion. In nature, jarosites can be associated with acid mine drainage and acid sulphate soils as an intermediate product of the oxidation of pyrite and other iron/sulphur bearing minerals. In industry, jarosites are used in metallurgical processes, synthetically produced to precipitate an easily filterable form of solid iron. Jarosites have properties that make them a chemically unstable solid. Upon decomposition the jarosite group of compounds will generate sulphuric acid. A literature review found many references to jarosites, their stability, methods of conversion to iron oxides, methods to extract reusable materials and environmental concerns. Most methods of recycling were unsuccessful. Accelerated conversion of jarosites to a form of iron oxide was a successful method of mitigating the risk of future acid generation. There were numerous specific ways of completing this task. The BHP Billiton patented nickel atmospheric leach process generates natrojarosite (sodium form of the compound) as a by-product, when extracting nickel from lateritic ores. The by-product of this process was tested for stability to understand the decomposition process. Accelerated decomposition of natrojarosite was attempted using limestone and hydrated lime at 90OC. Limestone did not react with the natrojarosite. Hydrated lime caused extensive dissolution of sodium and sulphur from the solid. However XRD analysis still reported natrojarosite as the solid material, suggesting incomplete decomposition and the formation an amorphous form of iron oxide not detected by XRD. Further decomposition tests were completed using elevated temperatures and pressures in an autoclave. Natrojarosite was not detectable in the solid phase after treatment at a temperature of 212OC, converting to haematite at temperature above 150OC. The stability of natrojarosite was measured using a number of methods on two natrojarosite samples sourced from the atmospheric leach process. The methods used were batch agitation, column testing and permeability testing. The aim was to provide a holistic result for the stability of natrojarosite if stored in a waste facility. Results obtained were compared against the standard TCLP test and found to be a more accurate method for measuring the stability of natrojarosite. The tests are more time consuming than TCLP testing but showed that natrojarosite was capable of decomposing to form sulphuric acid with time. This result was not obtained from TCLP tests, which suggested the solid material was stable. It was also found that salt water stabilised natrojarosite. Decomposition occurred in 40 and 80 days respectively, for two natrojarosite samples tested in deionised water. There was no evidence of decomposition after 150 and 280 days respectively for the same two samples. The common ion theory is thought to stabilise the natrojarosite which decomposes in an equilibrium reaction. Excess ions present in solution decrease the propensity for the solid to decompose. The two natrojarosite samples tested varied in calcium concentration. Limestone and hydrated lime were added to the natrojarosite during the nickel extraction process. Gypsum is theorised to form an impermeable layer around the natrojarosite, increasing the stability of the compound. Gypsum is sourced from the neutralisation reaction between limestone or hydrated lime and the acid generated from natrojarosite decomposition.

Undergraduate honors paper--Mount Holyoke College, 2006. Dept. of Astronomy. / Includes bibliographical references (leaves 80-87).

Thesis (PHD)--University of Montana, 2009. / Contents viewed on December 18, 2009. Title from author supplied metadata. Includes bibliographical references.

The crystallization kinetics of hydronium jarosite have been studied in the area of the Fe₂O₃-SO₃-H₂O phase diagram where hematite is the stable phase. Hydronium jarosite has been shown to be a kinetically favored intermediate to hematite over a wide range of chemical and thermal conditions. A model useful for predicting the crystal size distribution as a function of temperature, free acid and iron concentrations, and residence time has been developed. Hydronium, sodium, and potassium jarosite have been shown to convert, via a solid phase reaction, to hematite. A model useful for predicting the conversion rate as a function of temperature, free acid concentration, and particle size has been developed. A predictive model, the growing core model, has been developed. It is useful for predicting the crystal size distribution and the product split between hydronium jarosite and hematite when both crystallization and conversion are occurring simultaneously. The cardinal assumption in this model is that crystal growth and conversion occur at separate cites on the crystal surface simultaneously. The model, with only one adjustable constant, has been verified with experimental results. The effect of double draw off (DDO) operation in this system has been demonstrated. It has been shown, via the growing core model and experimental results, that DDO operation can produce a high iron, low sulfur product. Without DDO operation, this high product quality can only be achieved through higher operating temperature, high neutralization rates, or very large vessel size.

No description available.

The jarosite group of minerals is part of the alunite supergroup, which consists of more than 40 different mineral species that have the general formula AB3(TO4)2(OH, H2O)6. There is extensive solid-solution in the A, B and T sites within the alunite supergroup. Jarosite group minerals are common in acid mine waste and there is evidence of jarosite existing on Mars. Members of the jarosite - natrojarosite – hydronium jarosite (K,Na, H3O)Fe3(SO4)2(OH)6 solid-solution series were synthesized and investigated by Rietveld analysis of X-ray powder diffraction data. The synthesized samples have full iron occupancy, where in many previous studies there was significant vacancies in the B site. Well-defined trends can be seen in the unit cell parameters, bond lengths A – O and Fe - O across the solid-solution series in the synthetic samples. Based on unit cell parameters many natural samples appear to have full iron occupancy and correlate well with the synthetic samples from this study. In addition, the infrared spectra of the samples were analyzed. The atomic structure of ammoniojarosite, (NH4)Fe3(SO4)2(OH)6, has been solved using single-crystal X-ray diffraction to wR 3.64% and R 1.4%. The atomic coordinates of the hydrogen atoms of the NH4 group have been located and it was found that the ammonium group has two different orientations with equal probability. Samples in the ammoniojarosite – hydronium jarosite solid-solution series were synthesized and analyzed using powder X-ray diffraction and Rietveld refinement. It was found that an incomplete solid-solution series exists between jarosite and plumbojarosite, Pb[Fe3(SO4)2(OH)6]2, based on experimental and mineralogical data. At the studied synthesis conditions, lead solubility in jarosite is extremely limited with occupancy of 2% in the potassium site. Increased Pb in the iv starting solution resulted in no increased substitution of Pb into jarosite, but an increased substitution of H3O+. The stable isotope (H) geochemistry of hydronium jarosite, (H3O,K)Fe3(SO4)2(O,OH)6, and the effect that the presence of hydronium in the crystal structure has on exchange rates of stable isotope values of jarosite with hydronium substitution has been investigated in this study. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2008-05-07 18:21:45.136

L'objectif de cette thèse est de bâtir un modèle prédictif d'une unité industrielle continue de dissolution de minerai de nickel/ et précipitation de fer simultanées. La méthodologie adoptée consiste dans un premier temps à réaliser des expériences en réacteur fermé ou semi-fermé pour identifier et modéliser séparément les différents phénomènes en jeu, puis dans un second temps à construire un modèle d'unité continu les rassemblant tous. Ce travail a permis certaines avancées tant sur le système retenu que sur les méthodes et modèles adoptés. Tout d'abord la thermodynamique des solutions Na-Fe(III)-H2SO4 aux alentours de 100°C a été clarifiée et la constante de solubilité de la natrojarosite Na0,84H0,16Fe2,90(SO4)2(OH)5,7 a été déduite. Ensuite les paramètres influant sur les précipitations des jarosite de sodium et potassium ont été mis en évidence et leur cinétiques de croissance ont pu être déterminées grâce à l'utilisation originale de la méthode des caractéristiques. Puis les cinétiques de dissolution des minerais ont été obtenues, en prenant en compte différentes phases du minerai et leurs granulométries. Après avoir déduit tous les paramètres nécessaires, un modèle original, permettant de simuler une cascade de réacteur de dissolution/précipitation avec recyclage a été construit puis validé. Cet outil de conception, couplé à une étude technico-économique peut permettre d'optimiser le procédé. / The goal of this thesis is to build a predictive model for a continuous industrial unit combining simultaneously nickel ore dissolution and iron precipitation. A two steps method was used. First experiments in batch or semi-batch reactors were done in order to understand and model separately the different phenomenon that take place. Then all the equations and associated constants were used to build a model. This work allowed some advances both on the system studied and on the methods used. First thermodynamics of Na-Fe(III)-H2SO4 solutions in the 70-100°C temperature range was clarified and natrojarosite solubility constant Na0,84H0,16Fe2,90(SO4)2(OH)5,7 was deduced. Secondly parameters acting on sodium and potassium jarosite precipitation were highlighted and their growth kinetics were deduced through an original use of caracterisctics method. Then ore dissolution kinetics were found, taking into account different ores phases and their granulometry. After deducing all the necessary parameters, an original model allowing to simulate a cascade of dissolution/precipitation reactors with recyling loop was build and validated. This conception tool, coupled with a technico-economic study allows the optimisation of such a process.

This study investigates jarosite formation and stability patterns at the abandoned Davis Pyrite Mine in Rowe, Massachusetts. Jarosite, an iron-sulfate hydroxide, is found in acid mine drainage (AMD) environments, in acid sulfate soils, and on Mars. Jarosite and the iron oxides goethite and hematite are present at the site. Soil samples from the site were examined by XRD, SEM, and EDS. Five mineralogical areas were found, based on mineral abundance patterns. Jarosite exists in four of these areas. Two jarosite morphologies were identified. “Variable” jarosite, with partly-dissolved crystals of about 0.5 to 5 micrometers diameter, exists in spoil pile samples. “Donut” jarosite, with tightly-packed, sharp-edged crystals less than 0.5 micrometers that form a thin mantle on the surface of a second mineral, exists in native soil samples. Donut jarosite has not been previously characterized. These jarosite morphologies are controlled by the presence and relative mobility of pyrite oxidation products Fe and SO4, which in turn are controlled by water saturation levels. Three pathways are possible. On Path 1, both ions are mobile, go into solution, and variable jarosite forms at a distance from the pyrite source. On Path 2, only sulfur ions are mobile, an iron-oxide gossan develops. No jarosite forms. On Path 3, neither ion is mobile, and donut jarosite forms. On this path, Fe and SO4 ions are trapped in a thin film of stagnant water covering the pyrite. When sufficient ions are present, donut jarosite precipitates.