S. Agatzini-Leonardou

Titanium leaching from red mud by diluted sulfuric acid at atmospheric pressure

Laboratory-scale research has focused on the recovery of titanium from red mud, which is obtained from bauxite during the Bayer process for alumina production. The leaching process is based on the extraction of this element with diluted sulfuric acid from red mud under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The titanium recovery efficiency on the basis of red mud weight reached 64.5%. The characterization of the initial red mud, as well as this of the leached residues was carried out by X-ray diffraction, TG-DTA and scanning electron microscopy.

Hydrometallurgical process for zinc recovery from electric arc furnace dust (EAFD). Part I: Characterization and leaching by diluted sulphuric acid

The present paper is the first of a series of two articles dealing with the development of an integrated process for the recovery of zinc from electric arc furnace dust (EAFD), a hazardous industrial waste generated in the collection of particulate material during steelmaking process via electric arc furnace. Part I presents the EAFD characterization and its leaching process by diluted sulphuric acid, whereas Part II deals with the purification of the leach liquor and the recovery of zinc by solvent extraction/electrowinning. The characterization of the examined electric arc furnace dust was carried out by using granulometry analysis, chemical analysis, X-ray diffraction (XRD), thermogravimetric/differential thermal analysis (TG/DTA) and scanning electron microscopy (SEM). The leaching process was based on the Zn extraction with diluted sulphuric acid from EAFD under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The zinc recovery efficiency on the basis of EAFD weight reached 80%. X-ray diffraction and scanning electron microscopy were used for the characterization of the leached residues.

Leaching of nickel and iron from Greek non-sulphide nickeliferous ores by organic acids

Abstract Several organic acids were tested and compared for their ability to solubilise nickel and iron from Greek laterite ores. The results were also compared with sulphuric acid leaching under the same conditions. Citric acid proved to be the most effective organic acid for nickel extraction, achieving recoveries up to 60%. In some instances, citric acid gave as high nickel yields as equimolar sulphuric acid under the same leaching conditions but with slower kinetics. It was, however, found that at specific low pH values, adjusted by the addition of sulphuric acid, the citric acid resulted in higher nickel recoveries than sulphuric acid of the same free acid concentration; the better performance was attributed to its strong chelating action under those conditions. Oxalic acid displayed remarkable selectivity in iron extraction, releasing more than 60% of it, but it could hardly dissolve any nickel. Lactic, formic, acetic and salicylic acids were relatively ineffective compared with sulphuric acid. Considerable variability in nickel and iron recoveries was observed when leaching with different laterite ores, due to their different mineralogical analyses.

Hydrometallurgical process for zinc recovery from electric arc furnace dust (EAFD). Part II: Downstream processing and zinc recovery by electrowinning

The characterization and the agitation leaching of electric arc furnace dust (EAFD) by diluted sulphuric acid have been studied in Part I, as a separate article. The aim of the present research work (Part II) is the development of a purification process of the leach liquor for the recovery of high-purity zinc by electrowinning. The proposed hydrometallurgical process consists of the following four (4) unit operations: (1) Removal of iron as easily filterable crystalline basic sulphate salt of the jarosite type, at atmospheric pressure, by chemical precipitation at pH: 3.5 and 95 degrees C. (2) Zinc solvent extraction by Cyanex 272 at pH: 3.5, T: 40 degrees C, with 25% extractant concentration. (3) Stripping of the loaded organic phase by zinc spent electrolyte (62.5 g/L Zn(2+)) at T: 40 degrees C with diluted H(2)SO(4) (3 mol/L). (4) Zinc electrowinning from sulphate solutions (at 38 degrees C) using Al as cathode and Pb as anode. The acidity of the electrolyte was fixed at 180 g/L H(2)SO(4), while the current density was kept constant at 500 A/m(2).

Synthesis of TiO2 nano-powders prepared from purified sulphate leach liquor of red mud

The research work presented in this paper is focused on the development of a purification process of red mud sulphate leach liquor for the recovery of titanium oxide (TiO(2)) nano-powders in the form of anatase. Initially, titanium was extracted over iron and aluminium from the leach liquor by solvent extraction using Cyanex 272 in toluene, at pH: 0.3 and T: 25°C, with 40% extractant concentration. Stripping of the loaded, with titanium, organic phase was carried out by diluted HCl (3 mol/L) at ambient temperature. Finally, the recovery of titanium nano-powder, in the form of anatase, was performed by chemical precipitation at pH: 6 and T: 95°C, using 10 wt% MgO pulp as neutralizing agent. The produced precipitates were characterized by X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric/differential thermal analysis (TGA/DTA). Their morphological characteristics and microstructure were studied by scanning electron microscopy (SEM). High grade titanium white precipitate, in the form of anatase, was obtained. Iron concentration in the precipitate did not exceed 0.3%, whereas no aluminium was detected.

Heap leaching of poor nickel laterites by sulphuric acid at ambient temperature

Column leach tests were conducted to evaluate the amenability of poor Greek nickel laterites to heap leaching with dilute sulphuric acid at ambient temperature. The ore tested was limonitic laterite with less than 1% nickel and it was subjected to a suitable pretreatment with water prior to it being loaded into columns, following findings of preliminary research work. The acid solution was recycled after suitable pH adjustment. Factorial designs were used to determine the effects and interactions of the following factors: sulphuric acid concentration, ore column height, ore grain size and ratio of the solution volume to the ore quantity. The responses which were investigated included nickel and cobalt recoveries, co-dissolution of iron, calcium, magnesium, aluminium, chromium and silica and also sulphuric acid consumption. Experimental error was also determined. The tests showed that nickel recovery of 86% could be achieved in 80 days.

Bulk precipitation of nickel and cobalt from sulphate leach liquor by CaO pulp

Abstract The research work in the present paper determined the conditions at which nickel and cobalt can be recovered, as easily filterable precipitates, from leach liquors, which are produced by sulphuric acid leaching of nickel oxide ores at atmospheric pressure. Nickel and cobalt were precipitated as hydroxides at pH = 8·7, using CaO pulp as a neutralising agent, by 99·9 and 99·8% respectively. At this pH value manganese and magnesium, which were contained in the leach liquor, were precipitated, having a concentration of about 2·6 and 4·7% respectively in the final mixed precipitate. Statistical design and analysis of experiments were used in order to determine the main effects and interactions of the precipitation factors, which were the pH value at equilibrium and temperature. The characterisation of the produced mixed precipitate was carried out by X-ray diffraction, thermogravimetric/differential thermal analysis (TG/DTA), scanning electron microscopy and particle size distribution analyser. The main mineralogical phases of the precipitate after drying at 110°C were nickel hydroxide and bassanite (CaSO4.0·5H2O).