S.C. Das

Leaching of manganese from low-grade manganese ore using oxalic acid as reductant in sulphuric acid solution

Abstract Leaching studies of low-grade Joda manganese ore containing 24.7% Mn and 28.4% Fe were carried out at high temperature and atmospheric pressure using oxalic acid as reductant in sulphuric acid medium. The experiments were designed according to 2 4 full factorial design, and regression equations for extraction of manganese, iron and aluminum were determined from the data. All the significant main and interaction effects on extraction of Mn, Fe and Al have positive effect, except oxalic acid concentration and time interaction for extraction of Al. Oxalic acid concentration has strongest effect on extraction of Mn, whereas temperature and time have strongest effect on extraction of Fe and Al, respectively. 98.4% Mn and 8.7% Fe were extracted from −150+105 μm ore with 30.6 g/l oxalic acid, 0.543 M sulphuric acid concentration at 85 °C in 105 min.

Aqueous SO2 leaching studies on Nishikhal manganese ore through factorial experiment

Abstract Aqueous SO 2 leaching studies of Nishikhal manganese ore containing 32.5% Mn and 16.5% Fe were carried out at atmospheric pressure and room temperature using H 2 SO 3 . The variables considered were SO 2 concentration, solid-to-liquid ratio, sulphuric acid concentration and duration of leaching. Regression equations for extraction of manganese and iron were determined from 2 4 full factorial design. The effect of variables on extraction of manganese were independent of each other within the range of variables chosen for experiment. It was found that 95% of manganese could be extracted in 15 min from −150 μm ore with twice the stoichiometric quantity of SO 2 required for dissolution of manganese. The quantity of SO 2 present in the solution is the controlling factor in the extraction of manganese.

MicroRNA-326 regulates profibrotic functions of transforming growth factor-β in pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a fatal disorder resulting from the progressive remodeling of lungs, with no known effective treatment. Although transforming growth factor (TGF)-β has a well-established role in lung fibrosis, clinical experience with neutralizing antibodies to TGF-β has been disappointing, and strategies to directly suppress TGF-β1 secretion are needed. In this study we used a combination of in silico, in vitro, and in vivo approaches to identify microRNAs involved in TGF-β1 regulation and to validate the role of miR-326 in pulmonary fibrosis.We show that hsa-miR-326 regulates TGF-β1 expression and that hsa-miR-326 levels are inversely correlated to TGF-β1 protein levels in multiple human cell lines. The increase in TGF-β1 expression during the progression of bleomycin-induced lung fibrosis in mice was associated with loss of mmu-miR-326. Restoration of mmu-miR-326 levels by intranasal delivery of miR-326 mimics was sufficient to inhibit TGF-β1 expression and attenuate the fibrotic response. Moreover, human IPF lung specimens had markedly diminished miR-326 expression as compared with nonfibrotic lungs. Additional targets of miR-326 controlling TGF-β signaling and fibrosis-related pathways were identified, and miR-326 was found to down-regulate profibrotic genes, such as Ets1, Smad3, and matrix metalloproteinase 9, whereas it up-regulates antifibrotic genes, such as Smad7. Our results suggest for the first time that miR-326 plays a key role in regulating TGF-β1 expression and other profibrotic genes and could be useful in developing better therapeutic strategies for alleviating lung fibrosis.

Leaching of manganese nodules in ammoniacal medium using glucose as reductant

Polymetallic Indian Ocean nodules can be leached in ammoniacal solution in the presence of glucose. The various parameters chosen for leaching studies were: amount of glucose, time, pH, temperature, concentrations of ammonia and ammonium salt, and particle size. The percentage extraction of copper, nickel and cobalt decreases when the glucose concentration is increased to more than 0.4 gramme per gramme of nodule at 338 K and 0.2 g/g at 358 K. The dissolution of copper has been found to be dependent more on the pH of the solution than on the total molarity of ammonia and the ammonium ion. Leaching temperatures above 373 K are disadvantageous for the extraction of copper and cobalt, whereas nickel extraction is about 95% even at 433 K. The rate of leaching for all three metals is independent of the particle size in the range studied. All the copper, about 90% of the nickel and 60% of the cobalt can be extracted under the following leaching conditions: temperature 358 K, time 4 h, initial ammonia concentration 2.5 M, ammonium chloride concentration 0.37 M and glucose 0.2 gramme per gramme of nodule.

Leaching of manganese nodules at elevated temperature and pressure in the presence of oxygen

Abstract Indian Ocean polymetallic nodules were leached with dilute sulphuric acid at elevated temperature and pressure in the presence of oxygen. Conditions were established for treating the nodules for the extraction of three metals, i.e. copper, nickel and cobalt, with minimum iron and manganese contamination of the leach solution. By leaching the nodules for 4 h at 423 K using 0.46 g of H 2 SO 4 per g of nodule and keeping the oxygen partial pressure at 0.55 MPs, almost all the copper and nickel and 88% of the cobalt could be extracted. Under these leaching conditions 28% manganese and 5.7% iron were also leached. To achieve the extraction of four metals, i.e. copper, nickel, cobalt and manganese, charcoal was used as the reductant for reducing the manganese dioxide and rendering it soluble as manganese sulphate. The extraction of copper, nickel, cobalt and manganese were 77, 99.8, 88 and 99.8% respectively under the following leaching conditions: time 4 h, temperature 423 K, H 2 SO 4 0.66 g of nodule and oxygen partial pressure 0.55 MPa. The studies showed that the conditions employed for leaching copper, nickel and cobalt could be extended to the extraction of manganese too, simply by increasing the acid concentration from 0.46 g to 0.66 g per g of nodule and with the addition of 0.05 g of charcoal per g of nodule to the initial slurry.

Electrowinning of copper from sulfate electrolyte in presence of sulfurous acid

Abstract The electrowinning of copper from acidic sulfate solution in the presence of sulfurous acid using a graphite anode was investigated. The effects of operating variables including sulfur dioxide concentration, copper concentration, sulfuric acid concentration, current density and temperature on the cell voltage, anode potential, power consumption, current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation characteristics were studied. Other anode materials such as Pb/Sb, Pb/Ag, Ti and Ti–IrO2 were also used to examine their effects on electrocatalytic activity for oxidation of SO2 and deposit quality. A rectangular stainless steel cathode of length 8 cm, width 5 cm and thickness 2 mm was used for copper electrowinning. Increases in SO2 concentration, copper concentration, sulfuric acid concentration and temperature lower the power consumption. These variables have no effect on the current efficiency of copper deposition. The presence of SO2 in the copper electrolyte affects both the cathodic and anodic polarisation curves. In addition, it causes shifting of preferred orientations from (220) (111) (200) (311) to (111) (200) (220) (311). Changes in crystallographic orientation are also seen in the surface morphology of deposited copper. It is found that minimum power consumption together with maximum current efficiency and improved surface morphology can be achieved using a graphite anode.

Effect of antimony(III) on the electrocrystallisation of zinc from sulphate solutions containing SLS

A detailed investigation has been carried out to determine the effect of antimony(III) on the electrocrystallisation of zinc from sulphate solutions containing sodium lauryl sulphate (SLS). The results indicated that addition of Sb(III) at trace level to the electrolysis bath without sodium lauryl sulphate decreased the current efficiency (CE) and deteriorated the quality of the zinc electrodeposits. However, its addition to the bath containing sodium lauryl sulphate increased the current efficiency and also improved the surface morphology of the zinc electrodeposits. There was no trace of antimony found in any of the deposits. Cathodic polarisation curves were traced and analysed to determine the kinetic parameters, exchange current density, Tafel slopes and transfer coefficients so as to elucidate the nature of the electrode reactions. Presence of Sb(III) alone in the electrolyte depolarised the cathode and SLS alone polarised it; however, presence of both gave a balanced condition suitable for zinc electrowinning.

Characterisation of fine polycrystals of metastable η-alumina obtained through a wet chemical precursor synthesis

Abstract An inexpensive and easy wet chemical synthesis is described which involves a mild base hydrolysis of an aqueous solution of aluminium sulfate with aqueous hydrazine hydrate solution as the hydrolysing precipitant, leading to the preparation of the basic aluminium sulfate (BAS) precursor. Heat treatment of the BAS precursor produces η-alumina (η-Al 2 O 3 ) when calcined at 900°C for 2 h; high temperature calcination at 1200°C of the precursor or of the above-mentioned calcined material leads to the formation of the thermodynamically stable α-alumina (α-Al 2 O 3 ). The alumina phases have been characterised by FTIR, X-ray diffraction, particle size measurements, electron micrography, weight-loss measurements and TGA-DTA analysis.

Factors controlling precipitation of finer size alumina trihydrate

Abstract The study was undertaken to produce superfine alumina trihydrate (ATH) from Bayer liquor. The specialty grade hydroxides suitable for nonmetallurgical applications should conform to certain qualities such as fineness, purity, brightness, etc. In the present paper, the effects of a number of parameters, such as precipitation, temperature, amount of seed, surface area of seed, precipitation time, soda content of pregnant liquor, addition of aluminium sulfate (modifier), etc., on the particle size of the precipitated ATH were examined. At higher temperatures, the particle size increases, whereas it is reduced at lower temperatures. The seed surface area and seed quantity are found to have marked effects on the particle size of the precipitated ATH. The higher seed specific surface area and the higher seed quantity favour the production of finer-sized particles. The increased soda content in the pregnant liquor also produces finer-sized particles. The most important parameter that influenced the precipitation process with respect to the particle size is the addition of a modifier namely, aluminium sulfate. The particle size is reduced to ∼1 μm even with the addition of a small quantity of aluminium sulfate. It is observed that the formation of finer-sized particles is associated with the degree of rate of nucleation, while the level of supersaturation controls the degree of rate of the nucleation. The seed dissolution in excess soda, available in Bayer liquor, enhances this supersaturation level. When aluminium sulfate is added, the alumina available in the modifier and excess dissolution of the seed due to the addition of a modifier further increases the supersaturation. The seed dissolution, thus, may be considered as a major factor that controls the nucleation rate. Therefore, the mechanism for the fine ATH precipitation from Bayer liquor may be modified to follow the steps: (I) seed dissolution, (II) nucleation, (III) agglomeration, and (IV) growth.

Adsorption of copper on manganese nodule residue obtained from NH3–SO2 leaching

Abstract Manganese nodules occurring in beds of many of the worlds oceans contain valuable metals such as Cu, Co, Ni, Mn, Zn, etc. in the form of oxides/oxy-hydroxides. Many processes have been developed worldwide to extract metal values from manganese nodules. A process based on NH 3 –SO 2 leaching has been developed at RRL, Bhubaneswar to recover Cu, Ni, Co and Zn. The process generates a large amount of residue. Studies were undertaken to examine the possibility of adsorption of heavy metal ions on this residue. Adsorption of copper on polymetallic nodule (PMN) leach residue was examined using synthetic copper sulfate solution. Adsorption was pH dependent and was maximum at pH between 4.0 and 5.0. The material was found to be a good adsorbent and its loading capacity was higher than activated charcoal.