The use of different types of seeding material to cause the layer deposition of desired iron phases is an attractive technique for the treatment of industrial waste waters, synthesis of iron products and the study of adsorption and dissolution reactions involving iron oxides. In this study, recycled solids (consisting of mainly ferrihydrite), goethite and haematite seeds were used during batch oxidation and precipitation of iron from ferrous sulphate solutions. A 4L standard stirred tank reactor was used. Air was used as the oxidising agent. High ferrous iron concentrations typical of acid mine drainage associated with South African coal and gold mining were used. All the three oxides of iron catalysed the oxidation reaction rate in the order, recycled solids < goethite < haematite. The products formed were mainly the same as the seed material with varying amounts of ferrihydrite in lesser proportions. The product formation process involved two mechanisms; the direct formation of precipitate on the seed material and formation of small particles in the bulk which later adhered onto the seed material. The latter mechanism appeared to be the dominant one due to the high supersaturation levels induced by the catalytic effect of the seeds on the oxidation rate.
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