Vol.:(0123456789) 1 3 Journal of Sustainable Metallurgy https://doi.org/10.1007/s40831-019-00236-8 RESEARCH ARTICLE Chemical Composition Simplifcation of the Seydişehir (Konya, Turkey) Alumina Plant Waste Tuğba Selcen Atalay Kalsen 1  · Hakan Burak Karadağ 1  · Yasin Ramazan Eker 1  · Işıl Kerti 2 Received: 4 March 2019 / Revised: 26 June 2019 / Accepted: 28 June 2019 © The Minerals, Metals & Materials Society 2019 Abstract Red mud, a residue of alumina production from bauxite refning, contains oxides of valuable metals such as Fe, Al, Ti, Si, Na, Ca, etc. The presence of these numerous metal oxides does not allow introducing the highly basic raw red mud within any industrial process, which leads to its storage over a wide land area. In order to simplify the chemical composition of this waste, the efects of weak acid leaching (citric acid) and strong acid leaching (hydrochloric acid) are studied. The treatment efciency is discussed based on scanning electron microscope and X-ray difraction analysis of solid product and inductively coupled plasma spectrometry analysis of acidic solutions. The efects of temperature and acid concentration on metals dis- solution are estimated by rough kinetic considerations which present results comparable to those in the literature. More than 50% of Al and 50% of Ca detected by inductively coupled plasma mass spectrometry were separated via the organic acid process, while during leaching with HCl whole Ca, Fe, and more than 60% Ti and 80% of Al similarly determined were recovered. This confrms that within the red mud, metals behave diferently under several forms with diferent reactivity toward acidic medium. Therefore, an eventual combination of both acids can be an efcient way to prepare them ready and suitable for possible industrial applications. Keywords Metal leaching · Citric acid · Red mud · Hydrochloric acid Introduction Bauxite is the main raw material used for aluminum pro- duction in the Bayer chemical process. The frst step of this process is to digest the ore with sodium hydroxide (NaOH) under heat and pressure. At the end of this step, the produced red mud and aluminum hydroxide are separated. Depend- ing on the bauxite characteristics, about 1.5–2.5 tons of red mud per ton of produced alumina are continuously generated around the world [1, 2]. These alkaline (pH 10–12.5) wastes mainly consisting of stable oxides cause environmental dam- age and groundwater pollution. Unfortunately, industrialists are forced to dispose this waste in natural surrounding areas since no sustainable recovery solution has been developed [3, 4]. The red mud composition is afected by the origin of bauxite mineral, as well as the Bayer process parameters (temperature, pressure, time, etc.). The main solution sug- gested to valorize red mud is to directly integrate the wastes in diferent applications, such as ceramics additive, catalyst, or heavy metal adsorbent [5–7]. However, the complex con- tent of waste prevents optimization of the performance and implies the need for the extraction of the selected elements from the residue before their use. One of the suggested solutions is to recover metals and rare earths present in red muds by means of hydrometallurgical, pyrometallurgical, or hybrid techniques. Unfortunately, none of them are suf- fciently economically viable for an industrial application; moreover, these processes can originate extra contaminant produced during the recovery [8–11]. There are hydrometallurgical studies on the recovery of metals using red mud samples originating from the bauxite mine-rich regions in the world, such as Australia (24.4%), Greece (2.6%), China (1.7%), and Hungary (1.3%) [12]. The leaching process of Australian red mud with strong The contributing editor for this article was Brajendra Mishra. * Yasin Ramazan Eker yeker@erbakan.edu.tr 1 Metallurgical and Materials Engineering Department, Necmettin Erbakan University, Konya, Turkey 2 Metallurgical and Materials Engineering Department, Yıldız Technical University, Istanbul, Turkey