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Ferrous Metals Waste Production and Recycling
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
The high content of zinc as well as the complex chemical and morphological composition of the steelmaking dusts and sludges has been cited as one of the key challenges affecting the recycling potential of such materials in the steel plant. As a result, the chemical and morphological form in which the zinc exists in steelmaking dusts is an essential indicator of the efficiency of the dust processing method (Havlík et al., 2012). As discussed in Section 4.5.1.3, it is difficult to correctly predict the form in which the zinc compounds are present due to the complexity in the chemical and mineralogical characteristics of steelmaking dusts. According to Leclerc et al. (2003), most of the zinc speciates as franklinite (ZnFe2O4) in steelmaking dusts, and these compounds tend to be stable and insoluble in most acidic, alkaline and chelating media under mild conditions, thereby creating problems for zinc recovery based on conventional hydrometallurgical processes.
Recycling of Metal Production Wastes
Published in Hong Hocheng, Mital Chakankar, Umesh Jadhav, Biohydrometallurgical Recycling of Metals from Industrial Wastes, 2017
Hong Hocheng, Mital Chakankar, Umesh Jadhav
Flotation tailings contained 0.56% Cu and 4.74% Zn. Copper was present mostly as digenite, bornite, and free metal. Zinc was present as a ferrite (franklinite) ZnFe2O4 and, to a lesser degree, as silicate. Biooxidation of ferrous iron (FeSO4·7H2O) was carried out in a 5.0 L vessel with 4.0 L of the liquid at 40°C and aeration rate 4/min using a consortium of moderately thermophilic acidophilic chemolithotrophic microorganisms, including Sulfobacillus species. The obtained solution was used as lixiviant in the chemical leaching process.
Effects of coexisting zinc and nickel ions on crystallization behaviour and properties of spinel synthesised in chromium-containing wastewater
Published in Canadian Metallurgical Quarterly, 2023
Min Wei, Jin-fang Lv, Ying-cong Quan, Xian Xie
To investigate the crystal evolution of the synthetic products, the experiments were conducted at an initial concentration of nickel ion of 10 mg/L and zinc ion of 10 mg/L. Under that condition, it made the saturation magnetisation sharply increases. The obtained products at different times were detected by XRD, as charted in Figure 4. It can be found that the synthetic products may be one or more of spinel, including chromite, nichromite, zincochromite, franklinite, trevorite, magnetite and maghemite. However, due to the similar diffraction peak of spinel minerals, they were indistinguishable just by XRD. In addition, within 2–15 min, as the reaction time increased, the peak intensity of synthetic products gradually enhanced, suggesting that the product’s crystal size was improved. Further, the diffraction peak moved from high diffraction angle area to a low diffraction angle area, indicating that zinc ions and nickel ions with more enormous radii gradually replaced the ferric ions and chromium ions with a smaller radius in the structures of spinel, resulting to enlargement of the united cell [22–24]. However, when the reaction time reached more than 20 min, the intensity of the characteristic peak of the synthetic products decreased step by step and even disappeared. This can be interpreted as the crystal’s destruction by prolonged stirring [25].
Comparison of mechanical and leaching behaviours of pulverised fuel ash/low-grade magnesium oxide-cement blended stabilised/solidified baghouse dust
Published in European Journal of Environmental and Civil Engineering, 2019
PFA is a well-established binding agent so XRD results for PFA-blended samples are not presented in this paper. On the other hand, the XRD analysis and micrograph of a selected mix combination (CEMI:MgO:EAFD 1:2:2) is presented to provide an overall idea on the phases identified when waste is incorporated into a cement-MgO blended mix matrix. Crystalline phases identified in the S/S product are presented in Figure 6(a) with a micrograph and sum spectrum in Figure 6(b) and (c), respectively. SEM- EDX analysis reveals the presence of O, C, Fe, Ca, Mg and Zn, which are attributed to periclase, calcite, ettringite, franklinite, larnite (β-C2S); with periclase, quartz and vaterite as the dominant phases in the sample. In addition, a γ-C2S phase was detected with dolomite. The existence of those phases was also confirmed by XRD analysis. The reflection peaks observed in the XRD patterns are in agreement with the Rietveld refinement results. Accordingly, periclase, franklinite and C2S-β are the dominant phases present in this sample while periclase and franklinite phases were also found in the as-received EAFD. Franklinite had reflection peaks at 30°, 35.5°, 43° and 62°, periclase at 43° and 62.2°. The content of the crystalline phases is directly proportional to the reflection peak intensity. Results show that when MgO is blended with cement and EAFD, periclase and dolomite are the major crystalline phases dominating the XRD pattern of the paste. As a result of EAFD addition, a hydration retardation of cementitious materials was expected. This would cause the appearance of the un-reacted di- and tri-calcium silicate phases as reported by Asavapisit, Naksrichum, and Harnwajanawong (2005). The formation of franklinite was expected and reported during the Portland cement hydration in the presence of Zn. It is well known that Zn is present as ZnFe2O4 (franklinite) and ZnO (zincite) in EAFD while Fe is present mostly as Fe3O4 (magnetite). Zincite is considered as a problematic phase when it comes to leaching. When Zn is present in the form of zincite, it is easily leached/dissolved into the solution whereas zinc ferrite is less likely to cause leaching problems (Oustadakis, Tsakiridis, Katsiapi, & Agatzini-Leonardou, 2010). The XRD analysis revealed the presence of zinc ferrite in the S/S of EAFD; this explains the excellent immobilisation of Zn as illustrated in the leaching test results.