Decomposition Of Jarosite Research Articles

Stability relations of jarosite and natrojarosite at 150–250°C

The jarosite decomposition reaction KFe 3( SO 4) 2( OH) 6 = 1.5 Fe 2 O 3 + K + + 2 SO 4 2− + 3 H + + 1.5 H 2 O and the analogous natrojarosite reaction have been studied in hydrothermal experiments of 1 to 1 1 weeks duration at 150–250°C. For a log mK 2 SO 4 in the coexisting aqueous phase of between −0.4 and −1.2, the log mH 2 SO 4 required to stabilize jarosite decreases from −0.35 ± 0.05 at 250° to −0.58 ± 0.12 at 200°C. At higher K 2SO 4 concentrations the H 2SO 4 concentration required to stabilize jarosite increases at both temperatures, consistent with the position of the jarosite-hematite boundary predicted with PHRQPITZ. Natrojarosite could not be produced from hematite at 250°C. At 200°C, the natrojarositehematite boundary occurs at log mH 2 SO 4 of −0.17 ± 0.08 at log mNa 2 SO 4 of −0.2 to −1.0. At log mNa 2 SO 4 below about −1.0, natrojarosite is unstable with respect to the assemblage hematite +Fe(SO 4)(OH). Apparent standard molal Gibbs free energies computed from the experimental data are ΔG 0 jarosite,200°,100 bars = −3416.3 ± 1.7 kJ/mol and ΔG 0 natrojarosite, 200°, 100 bars = −3371.9 ± 2.0 kJ/mol. The estimated errors reflect a lack of complete reversibility in the experiments, but do not consider other, potentially greater, sources of uncertainty such as those associated with calculation of aqueous activity coefficients. Additional experiments were used to study the exchange reaction KFe 3( SO 4) 2( OH) 6 + Na + = NaFe 3( SO 4) 2( OH) 6 + K +. Ln K D for this reaction is −3.1 ± 0.5 at 250°C, −3.7 ± 0.4 at 200°C, and −4.9 ± 0.2 at 150°C. Ln K D does not show a systematic variation with X Na at either 250 or 200°C, which suggests that jarosite and natrojarosite may be modeled as an ideal solid solution at these temperatures. At 150°C In K D does not vary from X Na = 0.1 to 0.6, but good constraints on its value could not be obtained outside this compositional range. The experimental data therefore do not rule out a significant departure from ideality at higher X Na at 150°C.

Solid-state reactivity and mechanisms in oxide systems: I. Reaction of small amounts of zinc oxide with α-iron(III) oxide prepared by different methods

Deposition of small amounts of ZnO formed by thermal decomposition of Zn(NO 3) 2 on the surface of α-Fe 2O 3 powders prepared by different reactions is reported as a useful method for characterizing the reactivity of the α-Fe 2O 3 specimens. The fraction reacted, α, is measured as a function of time at 810°C for ZnO-α-Fe 2O 3 mixtures with a molar ratio of 1:2000 using α-Fe 2O 3, prepared from goethite, calcination of FeCO 3 decomposition of jarosite and hydrothermal precipitation from Fe(NO 3) 3 solution. The different forms of α-Fe 2O 3 have been investigated by electron microscopy, and their wetting behaviour and morphological parameters were determined

Precious metals recovery from pressure oxidized Porgera concentrates

Preconcentration of Porgera ore results in high recoveries of gold into gravity and flotation concentrates. The bulk of the gold is contained in auriferous pyrite flotation concentrate and is not readily recoverable by direct cyanidation. Oxidation in autoclaves at high pressure and temperature produces a residue that contains the gold in recoverable form. Pilot plant treatment of the autoclave residue is described, through washing and jarosite decomposition stages, to cyanide leaching and recovery of gold and silver by carbon-in-pulp techniques. The concerns associated with disposal of plant effluents are also addressed.

Decomposition of jarosite

Precipitation of iron as a jarosite is used in various hydrometallurgical processes. There are several advantages to this route, for example excellent liquid-solid separation characteristics, selective precipitation of iron in environmentally more stable form, recovery of sulfur as sulfuric acid and higher zinc extraction. However, jarosite precipitation also has disadvantages, the major being the high cost of reagents. A laboratory study was therefore carried out on the conversion of ammonium jarosite to iron oxide with recovery of reagents as byproducts. The investigation resulted in the development of three process possibilities: 1) thermal decomposition with separate recovery of hematite, ammonia and sulfur dioxide, 2) decomposition of jarosite in an aqueous slurry to hematite and ammonium sulfate, or 3) decomposition in an aqueous slurry to magnetite and ammonium sulfate. The conditions affecting the decomposition of jarosite by all three methods have been defined and the chemical, mineralogical and physical characteristics of the iron products are identified.

Transformation of ferric compounds into iron oxides

Ferrihydrite (2.5 Fe2O2-4.5 H2O) is an unstable colloidal mineral. It dissolves in highly alkaline solutions and is precipitated from them in the form of goethite. Jarosite is stable at very low pH but is decomposed at higher values of pH with separation of iron oxides. Experiments show that in rapid decomposition of jarosite a protohematite substance, ferrihydrite, is formed. This transformation occurs at moderate pH values when solutions percolate through the aggregates of jarosite. Ferrihydrite, an unstable colloidal hydrated oxide of ferric iron, changes spontaneously to stable hematite with time. Very slow decomposition of jarosite results in its replacement by iron hydroxide, goethite. Under laboratory conditions in alkaline solutions lepidocrocite may be obtained from jarosite. The synthesis of this iron hydroxide passes through a stage of intermediate products: ferrihydrite and hydrated ferric oxide - ferriprotolepidocrocite, formed by solution of ferrihydrite in strongly alkaline solutions. The t...