High-Rate Fluidized-Bed Ferric Sulfate Generation for Hydrometallurgical Applications
Jaakko A. PuhakkaPäivi KinnunenT. van der MeerBestami ÖzkayaErkan ŞahinkayaAnna H. KaksonenPauliina Nurmi
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Abstract:
An overview is presented of a multi-year research effort on developing high-rate fluidized-bed bioprocesses for ferric sulfate production to be used as a unit process in various hydrometallurgical applications including indirect tank leaching of ore concentrates, regeneration of heap leach liquors and control of iron containing acidic mine wastewater. Iron oxidation rates of over 26 kg m-3 h-1 were achieved at hydraulic retention times of less than 1 h at 37 °C. Oxygen supply became the rate-limiting factor even with 99.5% dioxygen aeration. Fe2+ oxidation proceeded at pH below 1 even in the presence of 60 g Fe3+ L-1 allowing the regeneration of concentrated ferric sulphate solutions required in indirect tank leaching of sulfidic ore concentrate applications. Of several tested FBR carrier materials activated carbon was the most suitable based on its availability, long-term durability and the achieved high iron oxidation rates. Jarosite precipitates accumulating to the top of the inert carrier materials played an important role in the FBR biomass retainment. For regeneration of synthetic and actual sulfidic ore heap leaching liquors, a gravity settler was installed in the recycle line of the FBR. The system produced iron precipitates with good settling characteristics and settling tank effluent with low turbidity and suspended solids concentrations. These results revealed the potential of FBR process in both heap leach liquor regeneration and controlling the iron containing waste streams. The PCR-DGGE-partial seguencing of the 16S rRNA gene protocol revealed that the FBR culture at 25-37 °C remained dominated by Leptospirillum ferriphilum over a range of operational conditions studied over the years. A modeling approach for managing Fe3+ production by FBR in combination with heap leaching was based on an artificial neural network-back propagation algorithm (ANN-HEAP) and resulted in excellent match between the measured and the predicted concentrations. High-rate fluidized-bed iron oxidation is amenable to regeneration of tank and heap leaching solutions as well as controlling iron containing waste streams.Keywords:
Jarosite
Heap leaching
Settling
Aerated lagoon
本硏究는 Na₂SO₄를 添加한 Fe₂(SO₄)₃溶液에서, 溫度와 反應時間에 따라 鐵分이 Jarosite로 沈澱되는 반응을 實驗한 것이다. Jarosite (Natro-jarosite와 Hydronium-jarosite의 혼합물)는 pH 1. 7以下에서 生成되었으며, pH1.8以上에서는 水酸化第二鐵이 沈澱되었다. 이 수산화제2철은 여과하기 어려운 Colloid 상태로서, 피하여야만 한다. 따라서 여과하기 쉬운 Jarosite 沈澱物만 얻기 위해서는 pH값을 1.7以下로 조절하여야만 한다.
90℃에서 110℃까지 溫度를 다르게 하고 pH값을 1.2에서 2.2까지 變化시켰을 때. Jarosite 生成의 가장 좋은 條件은, 110℃에서 pH 1.7인 溶液을 反應시킨 것이다. Hydronium-jarosite에 대한 Natro-jarosite의 比率은 溫度上昇 따라 增加하였다.
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Jarosite (KFe3(SO4)2(OH)6) is a secondary mineral in acidic polluted environments such as mine tailing dump, but few investigations have evaluated arsenic removal by jarosite.This study investigated the role of jarosite in arsenic removal using flask shaking experiments in diluted sulfuric acid solutions (pH1-3). Jarosite was synthesized and the chemical composition of the jarosite was K0.54(H3O)0.46Fe2.38(SO4)2(OH)6. The shaking experiments found that As(V) was removed by the jarosite but As(III) was not removed. The mechanisms of As(V) removal were adsorption on the jarosite and co-precipitation with Fe(III) extracted from jarosite. The removal of As(V) from the liquid phase were increased with increasing pH, indicating that the adsorption of As(V) and SO42- is competitive or that ionic As species (H2AsO4-) is selectively adsorbed. The results suggest that jarosite is a sink for As(V) in acidic polluted environments.
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Jarosite is a common mineral in acidic, sulfate-rich environments where it can regulate acidity and capture toxic metals. This research examined jarosite-bearing outcrops in Victoria, Australia, to better understand jarosite formation and behaviour which is critical for its management. Geochemistry and crystal structure analysis showed that jarosite formation in acid-sulfate environments involves an interplay of chemical processes that, together with jarosite recrystallisation and environmental interactions, results in jarosite having chemical and structural complexity. Thorough characterisation of jarosite in acid-sulfate environments is therefore crucial to manage them in these environments successfully.
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The formation conditions of jarosite in the system Fe_2(SO_4)_3-K_2SO_4-H_2O were studied. The results show that jarosite can be formed rapidly under normal temperature and pressure by controlling suitable pH value and Fe_2(SO_4)_3 and K_2SO_4 concentrations. The pH value, temperature and concentration of Fe_2(SO_4)_3 media are key factors affecting the formation of jarosite. At normal temperature, the precipitation of jarosite can be seen within 24 hours when the pH value is between 2.60 and 3.10, and a great quantity of jarosite is formed within 48 hours. At about 90℃, the pH value range forming jarosite extends to 1.20～3.10, and within this range, the rising pH value is advantageous to the formation of jarosite. High Fe_2(SO_4)_3 concentration is also favorable for the formation of jarosite. Relative pure jarosite can be synthesized when Fe_2(SO_4)_3 concentration is high (0.05 M) and jarosite containing melanterite and colloid amorphous hydroxide vitriol iron can be formed when Fe_2(SO_4)_3 concentration is low. The depositing process of jarosite can be used to tackle waste water from mines and other industries and remove S, Fe and other toxic and harmful elements such as As, Cr, Hg and Pb in water. The achievement of rapid formation of jarosite under normal temperature and pressure presents a potential good application prospect in using the precipitation of jarosite colloid and its analogues as isolation mantle layers of mine tailing producing acid mine drainage
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The hydrothermal conversion of K jarosite, Pb jarosite, Na jarosite, Na–Ag jarosite, AsO4 containing Na jarosite and in situ formed K jarosite and Na jarosite to hematite was investigated. Potassium jarosite is the most stable jarosite species. Its conversion to hematite in the absence of Fe2O3 seed occurred only partially after 5 h reaction at >240°C. In the presence of Fe2O3 seed, the conversion to hematite was nearly complete within 2 h at 225°C and was complete at 240°C. The rate of K jarosite precipitation, in situ at 225°C in the presence of 50 g L−1 Fe2O3 seed, is faster than its rate of hydrothermal conversion to hematite. In contrast, complete conversion of either Pb jarosite or Na–Pb jarosite to hematite and insoluble PbSO4 occurs within 0·75 h at 225°C in the presence of 20 g L−1 Fe2O3 seed. Dissolved Fe(SO4)1·5 either inhibits the conversion of Pb jarosite or forms Pb jarosite from any PbSO4 generated. The hydrothermal conversion of Na–Ag jarosite to hematite was complete within 0·75 h at 225°C in the presence of 20 g L−1 Fe2O3 seed. The Ag dissolved during hydrothermal conversion and reported to the final solution. However, the presence of sulphur or sulphide minerals caused the reprecipitation of the dissolved Ag. The conversion of AsO4 containing Na jarosite at 225°C in the presence of 20 g L−1 Fe2O3 seed was complete within 2 h, for H2SO4 concentrations <0·4M. Increasing AsO4 contents in the Na jarosite resulted in a linear increase in the AsO4 content of the hematite, and ∼95% of the AsO4 remained in the conversion product. Increasing temperatures and Fe2O3 seed additions significantly promote the hydrothermal conversion of in situ formed Na jarosite at 200–240°C. However, the conversion of previously synthesised Na jarosite seems to proceed to a greater degree than that of in situ formed Na jarosite.
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The study of jarosite produced under diverse conditions is essential to gain insight into its diverse formation mechanisms on earth. Such investigations can even pave ways to better understanding of the genesis of jarosite discovered in extra-terrestrial bodies such as Mars. Jarosite samples from two costal locations in central Norway are investigated through the application of multiple analytical techniques. The jarosite-rich encrustations on seaward cliff walls were studied with a focus on the characterization of their micromorphology and geochemistry. Light and electron microscopic analyses revealed distinct laminations and microlaminations in the samples. These layered laminations likely imply the existence of favorable periods in a cyclic manner for mineralization/biomineralization of jarosite in tandem with gypsum formation and dissolution. The pH level measured is not low similar to that usually described as conducive for jarosite formations. Different viable jarosite formation mechanisms are explored. Though some indicators are implied from microstructural and compositional analyses, further investigations are required for establishing the biogenic nature of the mechanism involved. Signs of the possible formation of jarosite in the Mid-Pleistocene Transition, 1.1–1.3 million years B.P., are acquired from Ar39/Ar40 geochronological determinations. Useful paleoenvironmental and paleobiological information could be found preserved in the microstructures of such jarosite formations.
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