Malay K. Ghosh

Leaching of metals from Indian ocean nodules in SO2-H2O-H2SO4-(NH4)2SO4 medium

Abstract Studies have been carried out for extraction of Cu, Ni, Co, Zn and Mn with simultaneous avoidance of iron dissolution during leaching of manganese nodules in an aqueous SO2–H2SO4–(NH4)2SO4 system. The leaching parameters such as sulphuric acid concentration, ammonium sulphate concentration, time and pulp density were varied to study their effect on extraction of metals and precipitation of iron. It was observed that the presence of both sulphuric acid and SO2 was required for maximum recovery of Cu, Ni, Co, Zn and Mn. The iron in solution decreased with increase in ammonium sulphate concentration. The optimum conditions established for maximum metal extractions were: pulp density 20%, time 3 h, temperature 363 K, SO2 60 g l−1, sulphuric acid 3.0% (v/v) and ammonium sulphate 100 g l−1. Under these conditions the recoveries from a typical nodule sample were: 88.5% Cu, 99.8% Ni, 91.8% Co, 97.8% Zn, 99.6% Mn with iron extraction of 2.4%. Nodules containing different percentage of metal contents were also tested under the established conditions and it was observed that the dissolution of iron varied between 2.4 and 4.9% with no significant variations in recoveries of Cu, Ni, Co, Zn and Mn.

Effect of dissolved impurities during ammonia leaching of pure zinc sulphide

Abstract A systematic study on the effects of various minerals and metal ions during ammonia leaching of pure zinc sulphide is reported. The addition of chalcopyrite and sphalerite concentrate to pure zinc sulphide resulted in faster leaching. Various metal ions used for the study were: Cu (I), Cu (II), Pb (II), Ni (III), Fe (II) and Ag(I). Except Ni(II) and Co(II), all other ions displaced zinc from zinc sulfide; Cu (I), Cu (II), Ag(I) and Pb(II) increased the dissolution of zinc sulphide in the order Cu I ≈ Cu (II) > Ag (I) > Pb (II). Various chemical reactions taking place during exchange and oxidation of zinc sulphide in the presence of metal ions have been suggested.

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.

Heat treatment induced martensitic accommodation and adaptive anisotropy in melt spun Ni55Mn22Ga23 (at. %) ribbons

The effect of annealing on melt spun Ni55Mn22Ga23 (at. %) ribbon has been addressed in terms of structural, thermal, thermomagnetic, and magnetic field induced strain (MFIS) behaviour. In comparison to as-spun ribbons, the samples annealed within the L21 domain at 1073 K for 30 h with subsequent furnace cooling, showed a rise in martensitic transformation temperature. This was endorsed from electron microscopy studies revealing change in morphology of martensite plate and stacking of dislocations in a preferential orientation. The mechanism is associated to martensitic accommodation which enhanced ferro-elastic magnetic coupling and also lowered magnetic coercivity. Such accommodations and adaptive anisotropy improved the MFIS behavior in the annealed sample.

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%.

Mineralogical characterization and leaching behavior of Nigerian ilmenite ore

The characterization and H2SO4 leaching behavior of a Nigerian ilmenite ore following mechanical activation and alkali roasting were investigated. The effects of NaOH/ore ratio, H2SO4 concentration, leaching and roasting temperature on the Ti recovery from the milled ore were examined. The results show that mechanical activation significantly enhances the dissolution of ilmenite ore. Under the leaching conditions of 90 °C, 60% (v/v) H2SO4 and 4 h, about 72% Ti extraction was obtained from a milled ore roasted at 850 °C with 60% NaOH. X-ray diffraction (XRD) phase analysis of the roasted mass, water treated residue and leach residue supports the reaction mechanism and experimental results.

Assessment of the significant parameters influencing the bio-oxidation and bio-precipitation of iron from industrial leach liquor

Abstract In the present study, iron oxidation and precipitation experiments were carried out using Acidithiobacillus ferrooxidans. Experiments were conducted in a specially designed bioreactor in batch as well as in continuous mode in order to evaluate the iron oxidation and precipitationparameters. The four basic parameters studied were pH, biomass, Fe(II) and Fe(III) concentration. Iron oxidation rate was observed to follow first order kinetics. The specific growth rate and dependence factorwere determined for each parameter. An Eh–pH diagram was developed to findout the theoretical conditions for iron precipitation. It was observed that by increasing the pH, the iron precipitation rate increased and at pH 2˙7 and 2˙9 precipitation was more than 90%. Iron oxidation and precipitation studies were carried out in a continuous mode and the processwas observed to be effective at a dilution rate of 35 ml/15 min. The technique was also tested using two different leach liquorsobtained from treating Zn tailings and lateritic nickel ore. Iron could be successfully precipitated in a crystalline form from the leach liquor using this process.

Construing the interactions between MnO2 nanoparticle and bovine serum albumin: insight into the structure and stability of a protein–nanoparticle complex

A systematic study of the interaction of bovine serum albumin (BSA) with MnO2 nanoparticles (NPs) was carried out. MnO2 nanoparticles were prepared via a low temperature (90 °C) single-step precipitation route in the absence of surfactant/template and characterized using XRD, TEM, FESEM, FTIR, XPS, and Raman spectroscopy. MnO2 particles were found to have a length of 900 nm and a diameter of 10 nm. The interaction of BSA with NP was investigated using various spectroscopic and biophysical techniques under physiological pH 7.4. MnO2 effectively quenches the intrinsic fluorescence of BSA through static quenching. The effect of MnO2 on the conformation of BSA was analyzed using circular dichroism (CD), Fourier transform infrared (FTIR), and Raman spectroscopy, and it was observed that the secondary structure of BSA altered after the interaction with MnO2. Thermal CD spectroscopy revealed insignificant variation in the melting temperature of BSA upon binding to MnO2. Additionally, the morphological changes of BSA upon interaction with MnO2 were characterized using a field emission scanning electron microscope (FESEM). Moreover, the increase in the size of the BSA–MnO2 complexes was analyzed using dynamic light scattering (DLS). This study shows that the adsorption of BSA on MnO2 is dependent on the concentration of the protein as well as the NP.

Aqueous processing of nickel spent catalyst for a value added product

Nickel was recovered from a fertilizer industry spent catalyst by leaching with nitric acid followed by nickel hydroxide precipitation. The optimization of temperature, initial acid concentration and particle size for leaching of the spent catalyst was done through 23 factorial design. A maximum extraction of 91.9% was achieved at 90 °C, 1.5M HNO3 and 62.5 μm particle size. Temperature and acid concentration showed positive effect, while particle size showed no effect. A regression equation was developed and employed to predict conditions for 100% extraction which were experimentally tested. Nickel hydroxide was electrochemically precipitated from the leach liquor and its maximum discharge capacity was found to be 155 mAh/g. A 3-stage counter current leaching circuit was designed to obtain a leach liquor of suitable pH. XRD characterization of the precipitated Ni(OH)2 shows to consist of both α- and β-forms.

Electrodeposition of γ-MnO 2 from Manganese Nodule Leach Liquor: Surface Modification and Electrochemical Applications

The electrolytic manganese dioxide (EMD) production through electrodeposition from manganese nodules by reduction leaching in H2SO4 medium using sucrose as reductant followed by purification through 2-stage precipitation methods is described. The purified leach liquor was the starting solution for electrodeposition. Influence of in situ addition of a cationic surfactant Cetyltri-methylammonium bromide (CTAB) (0–500 mg dm−3) on the surface morphology and electrochemical properties of the EMD was examined. The XRD patterns of the deposited material were indexed to the γ-MnO2 phase. FESEM results demonstrated that in the presence of CTAB uniform nano-fibrous type grains were formed. Higher concentration of CTAB in the electrolytic bath however, drastically decreased the current efficiency (CE) and increased the energy consumption (EC) during electrodeposition. Under the optimum CTAB concentration of 100 mg dm−3 the obtained CE and EC values were 87.64% and 1.70 kWh/Kg respectively.