Densification of iron(III) sludge in neutralization |
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| Institution: | 1. ARC Centre for Functional Nanomaterials, School of Chemical Engineering and Industrial Chemistry, The University of New South Wales, Sydney NSW 2052, Australia;2. Australian Nuclear Science and Technology Organisation, New Illawara Road, Lucas Heights, NSW 2234, Australia;1. School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, China;2. Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024, China;3. Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 200050, China;1. Department of Vascular Surgery, Academic Medical Center, Amsterdam, The Netherlands;2. Department of Vascular Surgery, Onze Lieve Vrouwe Gasthuis, Amsterdam, The Netherlands;3. Department of Vascular Surgery, VU University Medical Center, Amsterdam, The Netherlands;1. Research Group on Bioengineering, Membrane Technology and Energetics, University of Pannonia, Egyetem Ut 10, 8200, Veszprém, Hungary;2. Helmholtz-Centre for Environmental Research GmbH – UFZ, Department Environmental Microbiology, Permoserstrasse 15, Leipzig, 04318, Germany;3. Institute of Macromolecular Chemistry, AS CR, Heyrovsky Sq. 2, 162 06, Prague 6, Czech Republic;4. DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Biochemical Conversion Department, Torgauer Strasse 116, Leipzig, 04347, Germany;1. School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia;2. SA Water Corporation, 250 Victoria Square, Adelaide, SA, 5100, Australia;3. School of Natural and Built Environments, University of South Australia, SA, 5095, Australia;1. Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, PR China;2. Institute of Recycling Economy, Beijing University of Technology, Beijing 100124, PR China |
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| Abstract: | Acid mine drainage (AMD), of which iron is a substantial component, is a potential by-product in the mining industry. Conventional neutralization is a common approach to treat AMD, although it creates a major disposal problem due to the generation of voluminous sludge. Sludge recirculation improves solid density by slowing down the rate of neutralization and allowing the growth of precipitates, while existing solids act as seed particles by providing necessary surface area for precipitation. The mechanisms of iron sludge densification are not fully understood, mainly because of the complex nature of iron chemistry, and the variety of amorphous, polymeric oxides that could be formed. In this work, the effects of alkaline reagents, flocculant addition, and dosing sequence, on the precipitation of iron (III) hydroxide and densification of the recycled sludge were investigated. Slowly dissolving lime (Ca(OH)2) was found to be more effective than caustic (NaOH) in producing sludge with higher solid contents. Polymers addition created stronger aggregates that could withstand shearing without significant size reduction, but the overall sludge density was lower than those produced without flocculant. Conditioning the sludge at pH between 3.5 and 4.5 by adding fresh lime in a specific dosing manner appeared to be conducive to the growth of large agglomerates. The final sludge solid content of ～15 wt.% was considerably higher than others produced under different conditions. The plate-like structures of precipitates generated with more recycles in this instance, possibly helped ease the release of entrapped water between solids during shearing, thus producing sludge with higher solid density. |
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