Alafara A. Baba

Development of a combined pyro- and hydro-metallurgical route to treat spent zinc–carbon batteries

The potential of solvent extraction using Cynanex272 for the recovery of zinc from spent zinc carbon batteries after a prior leaching in hydrochloric acid has been investigated. The elemental analysis of the spent material was carried out by ICP-MS. The major metallic elements are: ZnO (41.30%), Fe(2)O(3) (4.38%), MnO(2) (2.69%), Al(2)O(3) (1.01%), CaO (0.36%) and PbO (0.11%). The quantitative leaching by hydrochloric acid showed that the dissolution rates are significantly influenced by temperature and concentration of the acid solutions. The experimental data for the dissolution rates have been analyzed and were found to follow the shrinking core model for mixed control reaction with surface chemical reaction as the rate-determining step. About 90.3% dissolution was achieved with 4M HCl solution at 80 degrees C with 0.050-0.063 mm particle size within 120 min at 360 rpm. Activation energy value of 22.78 kJ/mol and a reaction order of 0.74 with respect to H(+) ion concentration were obtained for the dissolution process. An extraction yield of 94.23% zinc by 0.032M Cyanex272 in kerosene was obtained from initial 10 g/L spent battery leach liquor at 25+/-2 degrees C and at optimal stirring time of 25 min. Iron has been effectively separated by precipitation prior to extraction using ammoniacal solution at pH 3.5, while lead and other trace elements were firstly separated from Zn and Fe by cementation prior to iron removal and zinc extraction. Finally, the stripping study showed that 0.1M HCl led to the stripping of about 95% of zinc from the organic phase.

Bioleaching of Zn(II) and Pb(II) from Nigerian sphalerite and galena ores by mixed culture of acidophilic bacteria

Zn(II) and Pb(II) from Nigerian sphalerite and galena ores were bioleached by a mixed culture of acidophilic bacteria. The influences of pH and ferric ion on the bioleaching rates of sphalerite and galena were examined. The result shows that pH 2.1 and 2.7 are favourable for the leaching of Zn(II) and Pb(II) from sphalerite and galena, respectively. It was observed that the use of agarose-simulated media caused cells to excrete exopolymers containing ferric ions which enhanced oxidation. The oxidation equilibrium for sphalerite and galena took 3 and 4 d, respectively. About 38.3% sphalerite and 34.2% galena were leached within 1 d and approximately 92.0% Zn(II) and 89.0% Pb(II) were recovered in 5 d, respectively. The unleached residual products were examined by X-ray diffraction for sphalerite, revealing the presence of elemental sulphur(S), zinc sulphate (ZnSO4) and few traces of calcium aluminate (Ca3Al2O6). The XRD pattern also indicates the presence of elemental sulphur (S), lead sulphate (PbSO4) and few traces of itoite (Pb(S,Ge)(O,OH)4) and cobalt lead silicate (Pb8Co(Si2O7)3) in the unleached galena ore.

Characterization and kinetic study on ammonia leaching of complex copper ore

Abstract Ammonia leaching kinetics of a complex Cu-ore assaying 8.8% Cu and 36.1% Fe was examined. Mineralogical characterization indicated that the major phase of the ore was siderite with chalcopyrite as the major sulfide mineral. The effects of parameters such as agitation, temperature, NH 3 concentration, particle size and oxygen partial pressure ( p O2 ) were investigated. Under the standard leaching conditions of 125–212 µm particle size, 120 °C, 1.29 mol/L NH 3 and 202 kPa of p O2 , about 83% Cu could be selectively extracted in 2.5 h. However, when using higher NH 3 concentration and lower particle size, more than 95% extraction was achieved. The leaching process was found to be surface reaction controlling. The estimated activation energy was (37.6±1.9) kJ/mol and empirical orders of reaction with respect to p O2 and [NH 3 ] were about 0.2 and 1, respectively.

Application of Cyanex® extractant in cobalt/nickel separation process by solvent extraction

This study presents a detailed review on the advanced hydrometallurgical treatment involving the extraction and separation of Cobalt (Co) and Nickel (Ni) by Cyanex® extractants. The structures, properties and applications of various Cyanex® extractants such as Cyanex®272, Cyanex®301, Cyanex®921, Cyanex®923 and Cyanex®421X were discussed and compared. Cyanex®272 thus proved to be the most appropriate solvent extractant for the separation of Co and Nickel from sulphate and chloride media due to its stability to common oxidant, better physicochemical properties and its ability to avoid gypsum crystallization in stripping-electrowinning circuit. Finally, various solvent extraction (SX) techniques for the extraction and separation of Co and Ni using Cyanex® extractants were discussed as well as newer processes of extraction and separation.

Use of mobile phones and cancer risk.

Mobile phones work by transmitting and receiving radio frequency microwave radiation. The radio frequency (RF) emitted by mobile phones is stronger than FM radio signal which are known to cause cancer. Though research and evidence available on the risk of cancer by mobile phones does not provide a clear and direct support that mobile phones cause cancers. Evidence does not also support an association between exposure to radio frequency and microwave radiation from mobile phones and direct effects on health. It is however clear that lack of available evidence of cancer as regards the use of mobile phone should not be interpreted as proof of absence of cancer risk, so that excessive use of mobile phones should be taken very seriously and with caution to prevent cancer.

Hydrometallurgical application for treating a Nigerian chalcopyrite ore in chloride medium: Part I. Dissolution kinetics assessment

The dissolution kinetics of a Nigerian chalcopyrite ore in hydrochloric acid was studied in this article. Acid concentration, reaction temperature, and ore particle size were chosen as experimental parameters. The chemical and morphological studies of the ore before and after leaching at optimal conditions were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is revealed that increasing the acid concentration and system temperature and decreasing the ore particle size greatly enhances the dissolution rate. The dissolution kinetics was found to follow the shrinking core model for the diffusion control mechanism where the activation energy (Ea) of 32.92 kJ·mol−1 was obtained for the process and supported by morphological changes at a higher dissolution of 91.33%.

Treatment of a Nigerian covellite ore. Part I: Dissolution kinetics study by ammonia solution

In the present work, the leaching kinetics of covellite ore in ammonia solution was studied and the following variables, the solution concentration, reaction temperature and particle size were considered. A kinetics model representing the effects of these variables on the leaching rate was developed and it was ascertained that the leaching rate increases with increasing solution concentration, reaction temperature and decreasing particle size. At optimal conditions, 75.1% of covellite ore was reacted within 120 min and the leaching reaction was diffusion controlled by surface chemical mechanism. The calculated activation energy of 56.98 kJ/mol supported the proposed dissolution process.

Purification of a Nigerian Wolframite Ore for Improved Industrial Applications

Increasing demands for pure wolframite ore in the form of ammonium paratungstate (APT), tungsten oxide cannot be over emphasized. Thus, treatment of a Nigerian wolframite ore containing admixtures of scheelite (CaWO4: 96-900-9631) and stolzite (PbWO4: 96-900-9813) by hydrometallurgical route was investigated in hydrochloric acid chelated with phosphoric acid to extract tungsten via solvent extraction. During leaching, parameters such as leachant concentration, chelate dosage and reaction temperature on ore dissolution were examined. At optimal conditions (1.5 mol/L HCl + 2.0 mol/L H3PO4 solution; 75 °C), 95.0% of the initial 10 g/L ore reacted within 120 min. The derived activation energy of 56.80 kJ/mol supported the proposed dissolution mechanism. The unreacted product analyzed by XRD was found to contain siliceous impurities. Tungsten recovery from leachate was carried out by solvent extraction with Aliquat 336 in kerosene. Pure tungsten was recovered as APT and beneficiated to produce high grade industrial tungsten oxide of industrial values.

Characterisation and treatment of spent deposited sludge of transformer oil (DSTO) by acid leaching and solvent extraction

ABSTRACT The characterisation of spent transformer oil to determine its fitness for re-refining as well as the recovery of metals by hydrometallurgical treatment in chloride medium has been investigated. The leaching experiments on the spent material showed that its dissolution increases with leachant concentration performed at 75°C. Leaching studies showed that at optimal conditions, the dissolution reached 93% by 1.0 mol L−1 HCl solution within 120 min at 75°C. The solvent extraction of copper by bis(2,2,4-trimethylpentyl) phosphinic acid (CYANEX®272) in kerosene from a pregnant solution of aqueous spent deposited sludge of transformer oil containing 1243.4 mg L−1 Cu++, 389.2 mg L−1 Fe++/+++, 110.7 mg L−1 Ca++ and 235 mg L−1 Al+++ was studied. The results for the solvent extraction give an extraction efficiency of 91.77% total copper acquired via 0.2 mol L−1 CYANEX®272 in kerosene at 27 ± 2°C within 25 min at pH 4.0. A 0.1 mol L−1 HCl solution was found to be sufficient for the stripping of about 94.77% copper from the loaded organic phase. The Fourier transform–infrared spectroscopic analysis of the loaded organic phase supports the stripping experiment as there was no Cu metal ion present in the separated organic phase.

Dissolution behaviour of a beryl ore for optimal industrial beryllium compound production

ABSTRACT This study involves the leaching of the beryl ore with sulphuric acid (H2SO4) solution for predicting optimal beryllium extraction conditions with the aim of assessing the importance of leachant concentration, reaction temperature and particle size on the extent of dissolution. A kinetic model to represent the effects of these variables on the leaching rate was developed. It was observed that the dissolution of beryl ore increases with increasing H2SO4 concentration, temperature, decreasing particle size and solid to liquid ratio. At optimal leaching conditions, 89.3% of the ore was reacted by 1.25 mol/L at 75°C temperature and 120 minutes with moderate stirring, where 1612.0 mg/L Be2+, 786.7 mg/L Al3+, 98.1 mg/L Fe3+ and 63.4 mg/L Ag+ were found as major species in the leach liquor. The unleached products constituting about 10.7% were examined by X-ray diffraction (XRD) and found to contain primarily, siliceous compounds such as Xonotlite, Antigorite, Chrysolite and Kaolinite.