Abstract
Due to its alkalinity, red mud produced by the Bayer process may affect both the environment and human health. For this reason, its further utilization instead of disposal is of great importance. Numerous methods have already been studied for hydrometallurgical treatment of red mud, especially for the recovery of various metallic components such as iron, aluminum, titanium or rare earth elements. This study focuses on the extraction of titanium from red mud and in particular the mineralogical changes, induced by leaching. Sulfuric acid, hydrochloric acid and their combination have been utilized as leaching agents with the same leaching parameters. It has been determined that sulfuric acid is the best candidate for the red mud treatment in terms of titanium leaching efficiency at the end of 2 h with a value of 67.3%. Moreover, samples from intermediate times of reaction revealed that leaching of Ti exhibit various reaction rates at different times of reaction depending on acid type. In order to explain differences, X-ray Diffraction (XRD), scanning electron microscope (SEM) and QEMSCAN techniques were utilized. Beside titanium oxide (TiO2) with available free surface area, a certain amount of the TiO2 was detected as entrapped in Fe dominating oxide. These associations between Ti and Fe phases were used to explain different leaching reaction rates and a reaction mechanism was proposed to open a process window.
Highlights
There are growing efforts in industry to promote the sustainability and implementation of zero-waste production; the use of waste products from industrial processes is becoming increasingly important
The cumulative amount of red mud by 2015 is estimated to be close to 4 × 109 tons. These higher production rates and precious mineral content such as Fe2 O3, Al2 O3, SiO2, TiO2, Na2 O and CaO and rare earth elements induced the utilization of red mud as a secondary resource [4,5]
A new leaching model was proposed for HCl and H2 SO4 and difficulties of titanium dissolution from red mud were explained in detail
Summary
There are growing efforts in industry to promote the sustainability and implementation of zero-waste production; the use of waste products from industrial processes is becoming increasingly important. Reduced process costs with respect to primary metal production routes favors red mud usage in economic aspects. Valorization of such a highly alkaline product stored in the environment provides ecological benefits [4]. There have been many studies conducted on titanium recovery from red mud by hydrometallurgical methods [6]. There is not a systematic study to explain the differences in leaching mechanisms and kinetics depending on acid type. This lack of knowledge leads to the detailed phase and mineralogical investigation on red mud and leach residue to open a process window. A new leaching model was proposed for HCl and H2 SO4 and difficulties of titanium dissolution from red mud were explained in detail
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