Advanced Materials Research Vol. 828

Abstract: The gold-sulfide deposit Southern Ashaly is localized in carbonaceous terrigenous formation (black shale strata) of the middle carboniferous (Bukon suite, which is the ore-hosting for super large deposit Bakyrchik). The Southern Ashaly is at the exploration stage and according to preliminary estimates of the expected resources belongs to a large deposit in scale. Ore gold mineralization of such level as Southern Ashaly in southwestern Kalba is found for the first time and gives hope for the discovery of such objects in the Boko Vassilyevskoye ore field. Ore-hosting at the field Southern Ashaly is carbonaceous terrigenous formation of the middle carboniferous, with no visible signs of volcanic formations. But, it was revealed, at microscopic research by us, paragenetic relation of the gold mineralization with small intrusions of plagiogranites and zones of plagiogranite porphyry dykes and found volcano-sedimentary rocks (aleuritic tuffsandstone, tuff breccia) which have undergone hydrothermal-metasomatic changes. The vein-disseminated gold-sulfide mineralization is associated with beresitizated plagiogranites and plagigranite-porphyries and hydrothermally altered tuff sandstones, tuff breccia and carbonaceous shales. Southern Ashaly unlike Bakyrchik deposit which contains invisible gold in sulfides, all the gold is concentrated in the pyrite mainly in the form of micro-sized (1-5 µm or less) in arsenopyrite is noted rarely.

Abstract: In the present paper, potentiodynamic studies of WC scrap have been carried out as these studies give better idea about the anodic dissolution behaviour of the scrap material to recover the metal values. However, it has been seen that anodic passivation retards the dissolution of the scrap and adversely affects the recovery of metals. To minimize the passivity and to increase the anodic dissolution, some chemicals are often used as additives. Two different electrolytes namely hydrochloric acid and aqueous ammonia at varying concentrations had been employed for the above studies. The additives citric acid and oxalic acid were added to the acidic electrolyte whereas ammonium chloride, ammonium carbonate and ammonium sulphate were added in different concentration to the ammoniacal electrolyte. The studies revealed that 2% citric acid in 1N HCl was the optimum to achieve maximum anodic dissolution (current) of WC scrap. On the other hand, 5% NH₄Cl was found suitable to obtain maximum anodic dissolution (current) in the ammoniacal (150 g/L) medium. The potentiodynamic studies were followed by the actual electrodissolution experiments in an electrolytic cell with the help of a rectifier. The W and Co recoveries were encouraging.

Abstract: This paper discusses filtration behavior of very-fine grained alkaline leach slurry containing dissolved uranyl carbonate using commercial flocculants and dewatering surfactants. Evaluation of the best combination of flocculant and surfactant was made on the basis of capillary suction time (CST) data. Addition of INDFLOC 477 and CTAB to the alkaline leach slurry reduced the CST to 17 seconds from a very high level of 177 seconds obtained without the addition of any filtration aids. Detailed optimization of critical parameters like dosages and temperature of filtration were carried out on INDFLOC 477 and CTAB reagent combine adopting central composite rotatable design of experimentation to obtain maximum rate of filtration with minimum cake moisture. The studies indicated scope of achieving filtration rate of about 695 kg/h.m² with 23% cake moisture upon addition of 167 g/t of INDFLOC 477 and CTAB at filtration temperature of 60⁰ C.

Abstract: Out of the industrial waste streams/effluents entering in the aquatic system containing metallic species, tanneries release high amounts of chromium, an anthropogenic pollutant because of use of basic chromium sulphate in the tanning processes. Trivalent chromium, Cr (III) is the targeted ionic species for removal by biosorption on a fungal species in this work, as the technique has inherent merit of easy adsorbent regeneration and lower capital costs. The study involves the use of Aspergillus niger (A. niger), to remediate chromium from a model tanning bath with Cr (III) concentration of 500 mg L^-1. The fungal species was grown in Czapek Dox media at pH 2.5 and 35°C temperature and its biomass was used in various forms such as live, autoclaved and alkali treated. With 1% (w/v) alkali treated biomass, the biosorption of chromium reached a maximum of 91% for a feed concentration of 500 mg L^-1 in 2 h time at pH 2.5, temp 35°C and A/R (adsorbent : solution volume) ratio of 1/100. The lower biosorption of metal (42 - 44%) was observed with live and autoclaved biomass. The biosorption of chromium (III) on the fungal biomass was explained with various isotherms and fitted to the kinetic model involving first order expression. The study focuses on establishing the mechanism of bioremediation of chromium on A. niger.

Abstract: The Hall-Heroult process for the production of aluminium is based on the electrochemical reduction of alumina (Al₂O₃) dissolved in a cryolite (Na₃AlF₆) based electrolyte. Instability in cell voltage is referred to as noise. Normal voltage noise is inevitable due to bubble evolution and it has little effect on performance parameters such as, current efficiency and power consumption. Metal rolling noise (wavy noise) is caused by the disturbances in cell magnetic field and it affects the cell current efficiency adversely. Investigating the causes of the cell instability in the aluminium smelting cells can lead to better cell performance. Understanding the variation in cell voltage is critical for cells, because magnitude of voltage determines the energy consumption pattern in the process and hence, any saving on voltage can save energy. Voltage affects the current efficiency of the cell and an optimum cell voltage leads to higher current efficiency without compromising on energy consumption. Magnetic, current distribution, heat loss and voltage at zero current measurements along with online current and voltage signal can help to identify the problems and their combined effects on the performance of the cells. In order to estimate the loss in current efficiency of the aluminum electrolysis cells due to metal instabilities, measurements were performed and data analyzed. The present paper analyses the effect of voltage fluctuations (noise) during metal instability along with cause of instability and its effect on current efficiency of the cell. Measurements carried out to estimate the deviations from the normal cell operations are also discussed.

Abstract: During production of ammonium meta-vanadate from vanadium sludge an arsenic containing (~2.2g/L) spent liquor is generated. Safe disposal of such liquor without arsenic contamination to the environment is essential. Therefore, various methods such as ion-exchange, adsorption, solvent extraction and precipitation were applied for recovery of arsenic from the spent liquor. Based on the Eh-pH diagram of As-H₂O, the arsenic based species were delineated. For ion exchange Lewatit FO 36 and Amberlite IRA 400 Cl^- resins were used to extract arsenic from the spent liquor. With Lewatit FO 36 a maximum of 20% arsenic was recovered at A/R ratio of 50. Amberlite IRA 400 Cl^- on the other hand didnt extract arsenic at all. A two stage solvent extraction process using TBP as an extractant, with a recovery of 97% arsenic from the spent liquor was developed. From the loaded TBP almost complete stripping of arsenic was obtained with 0.1-0.5M NaOH solution. Precipitation of arsenic from the spent liquor as copper arsenate or iron arsenate was also examined. During the fixation of arsenic with iron, 70% arsenic was recovered in the precipitate. This process needs to be evaluated further with the aim of using the iron hydroxide containing arsenic for different applications.

Abstract: Studies based on electrocrystallization of antimony were carried out to evaluate the effects of current density and antimony concentration in the electrolytic bath on cathodic current efficiency, energy consumption, and quality of the deposits during electrowinning of antimony from Sb₂O₃-HCl and Sb₂S₃-NaOH systems. In acidic bath, current efficiency for electrodeposition of antimony increases with the increase in current density till 150 A/m², beyond which it follows a trend of gradual diminution. On varying antimony concentration in the bath, current efficiency was found to improve significantly and the optimum antimony concentration in Sb₂O₃-HCl system was evaluated to be about 60 g/L. In alkaline bath, current efficiency was observed to be maximum at 50 A/m² and further, with the increase in current density it progressively decreases. However, energy consumption for electrowinning of antimony in both of the baths gradually increases with the increase in current density. At a current density less than 150 A/m², alkaline bath was found to be more current efficient in comparison to the acidic bath. Crystallographic studies by XRD, imaging by optical microscopic technique and morphological studies by SEM were also carried out to differentiate antimony deposits obtained from acidic and alkaline baths.

Abstract: The heat treatable 7xxx series Al alloys (Al-Zn-Mg) show good combination of tensile properties through precipitation hardening. Similar to Al-Cu alloy minor addition of Sn in this alloy also influences its structure and properties. The hardness improves after natural ageing and further improves after duplex ageing. Duplex ageing refines the grains also. SEM-EDX results indicate that β-Sn is present in the form of precipitates. DSC results indicate that Sn suppresses the formation of GP zone and the stability of intermediate η phase is higher.

Abstract: The presence of soluble Cr(VI) particularly in the overburden soil samples of the chromite mines area is about 300-500mg Cr(VI)/kg. The level of Cr(VI) in final effluents needs to be reduced to the permissible limit <0.05mg/L (USEPA) using appropriate technology before it is discharged into the soil. Out of 12 bacterial isolates from the mine samples, CSB-9 was proven effective in reducing hexavalent chromium to its trivalent form with its inherent ability to survive proficiently in 200ppm Cr(VI). The isolate, confirmed to be Bacillus cereus, was characterised as gram-positive and capsule forming with the optimum growth at pH 7.0 and 35°C. The process of bioreduction of Cr(VI) using B. cereus was optimized with various parameters, viz., pH, initial concentration, dosage of adsorbent, temperature. The bacterium gave 90% reduction from 100ppm Cr(VI) aqueous feed in 120h at pH 7.0, 35°C using 1% (v/v) cells/mL.