Precipitation of sodium silicofluoride (Na2SiF6) and cryolite (Na3AlF6) from HF/HCl leach liquors of alumino-silicates

The HF + HCl leach liquor generated from the dissolution of silica, alumina and silicate gangue minerals in a low-grade molybdenite concentrate contains H2SiF6 and H3AlF6. Studies were conducted to recover the two valuable fluorides as Na2SiF6 and Na3AlF6 (synthetic cryolite) by precipitation with Na2CO3 from the leach liquor. An initial investigation was carried out to determine the precipitation conditions for Na2SiF6 and Na3AlF6 from their individual acid solutions. Subsequently, the conditions were determined for the selective precipitation of the two fluorides from a synthetic mixed acid solution similar to the leach liquor. When the acid solution was neutralized with 3 mol/L Na2CO3, Na2SiF6 precipitated first at pH 1.35 whilst Na3AlF6 required an increase in pH above 2.2 before it precipitated. Maximum recovery of the two fluorides was best achieved at about 50 °C. A similar trend was observed for the precipitation of Na2SiF6 and Na3AlF6 from the leach liquor of molybdenite upgrading. Phases of precipitated fluorides were identified by XRD and surface morphology by SEM. The purity of the Na2SiF6 precipitate was 99.5% whereas Na3AlF6 was contaminated with Na3FeF6

Extraction of trivalent chromium from tannery effluent by ion exchange with indion 790 resin

Extraction of chromium(III) from a model tanning effluent has been studied by ion exchange using Indion 790 resin. The resin has been found to be selective for the sorption of chromium(III) in the pH range 0.5-3.5 from a model solution containing 500 ppm chromium(III). Beyond pH 3.5 extraction of chromium(III) drastically decreases from 92% to 76.5%. Sorption of chromium(III) on Indion 790 follows Freundlich isotherm indicating strong chemical interaction of the metal ion with the resin. Desorption of chromium(III) from the loaded resin increases with the increase in concentration of eluant (5-20% H2SO4). With 20% sulfuric acid solution 89% chromium(III) was eluted in two stages. The bench scale results are also validated in continuous mode in a fixed bed column for the recovery of chromium(III) from tannery effluent

Biomineral Processing for Extraction of Copper Metal from Lean Ore of Malanjkhand Copper Project

Bioprocessing for metal recovery from different oxidic and sulphidic ores and concentrates is considered very attractive in view of low energy consumption and enviro-nmentally benign option.The present work is carried out to recover copper from lean grade copper ore (0.3% Cu) of Malanjkhand Copper Project (MCP). In Malanjkhand Copper mine rich ore containing 0.9 to 1.0% Cu is currently beneficiated. Lean grade ore with 0.3-0.4% copper, which is adjacent to the rich grade ore, may be utilized to meet the growing demand of the country. The conventional processes are not suitable to treat this low grade ore as the desired grade with acceptable yield can not be achieved. Therefore bioleaching may be opted for recovery of copper along with some other valuable metals from the lean ore. Different parameters such as pH, temperature, pulp density,particle size, etc; were studied to optimise the process

Microbial dissolution of a low grade Indian chalcopyrite ore using mixed culture of Mesophiles

An enriched culture of mesophiles namely, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans derived from mine water of Malanjhkhand Copper Project (MCP), India in the ratio of 4:1, and adapted on 5%(w/v) ore at 35oC was used for the bioleaching of a low grade chalcopyrite ore (0.27% Cu). Optimum copper recovery of 91% was achieved at 1.5pH and 10% (w/v) pulp density in 30days using <50μm particles. Copper recovery decreased to 82% when pH was raised to 2.5 under similar conditions. Higher copper recovery at pH 1.5 may be attributed to the improved bacterial activity (7.0x108 cells/mL), higher redox potential (666mV) and formation of minimum amount of hydronium jarosite, which was prominent at higher pH. Copper recovery was 41.2% in sterile control leaching conditions at 1.5pH. However, unadapted bacterial consortium yielded copper recovery of 69.4% only in 30 days at pH 1.5 under the above conditions. Higher metal recovery with adapted mixed culture may be attributed to increased rate of iron bio-oxidation. The biorecovery of copper from the MCP lean grade ore appeared to follow direct as well as indirect mechanism

Recovery of Molybdenum from Spent HDs Catalyst Leach Liquor by Solvent Extraction using Aliquat 336

Recycling spent catalysts is very important due to its generation in large amount, enormous economic values and environmental concerns if disposed off directly. This work describes the recovery of Mo from spent hydro-desulph-urization (HDS) catalysts (NiMo/A1204). Catalyst was roa-sted at 500°C to eliminate volatile impurities and leached. The leach solution was subjected to solvent extra-ction to recover Molybdenum. Several solvents such as D2EHPA-TBP, LIX 84-IC and Aliquot 336 were tried and aliquat was finally used for further studies. Conditions for maximum extraction of Mo were optimized by varying different parameters such as pH of the feed solution, sol-vent concentration, aqueous / organic phase ratio etc. Under optimized condition the stage requirement for complete extraction of molybdenum was determined and with 1:2 phase ratio, more than 98% extraction of molybdenum was achieved at pH of 1.5. The molybdenum from loaded organic was stripped with 0.4MNaOH

Copper biodissolution from a low grade chalcopyrite ore by unadapted/adapted acidithiobacillus ferrooxidans

The depletion of high-grade deposit of copper around the world has drawn attention for the utilisation of low-grade reserves . Malanjkhand Copper Project (MCP) in India is a low-grade ore containing -0.3% Cu in which copper metal is found to be present as chalcopyrite associated with pyrite in quartz veins and granitic rocks. In order to extract copper from this material , an alternate processing option such as bioleaching has been followed. Bench scale bioleaching experiments were carried out using Acidithiobacillus ferrooxidans (Ac. Ti) isolated from mine water. On using unadapted Ac. Tf isolate directly at pH 2.0 and 35°C, the optimum leaching conditions in shake flask were found to be 5% pulp density (PD), 2.OpH , 35°C temperature for <50p .m particles , yielding 72% Cu biorecovery in 35days. The Tf isolate when adapted to the ore and employed for the bioleaching of the ore at 5% PD (w/v), 2.OpH and 25 °C with three particle sizes viz.150 -76μm, 76-5011m and <50μm, resulted in recovery of 38 .31%, 29.68% and 47.5% Cu respectively with a rise in Eh from 530 to 654 mV in 35 days. Under similar conditions , the unadapted strain gave maximum recovery of 44.0 % for <50pm ore size with rise in Eh from 525 to 650mV . Copper biorecovery increased to 75.3% with the adapted isolates at 35°C for the finer particles of <50gm at 2.OpH with a rise in cell count from lx l 07 cells/mL to 1.13x109 cells/mL in 35 days. The biodissolution of copper from chalcopyrite with the involvement of adapted Ac. Tf species resulted in the improvement of iron oxidation rate (Fe2+ to Fe'`) and consequently higher redox potential

An overview on different processes for recovery of valuable metals from tungsten carbide scrap.

Cemented tungsten carbide material has been widely used in the hard metal industry for the manufacture of cutting tools, drilling tools, mining and machining tools and high wear resistant parts. When these tool bits and components are scrapped, they are collected and processed for recycling following appropriate methods. Tungsten and cobalt both are strategic rare metals and the cost of these metals entrapped in these scraps is estimated to be very high. Therefore, WC scraps have been considered as an important secondary resource of cobalt and tungsten metals. Recycling of hard materials like tungsten carbide scrap require specialised techniques. This paper presents a review of the different processes reported so far to recover valuable metals (W, Co) from cemented tungsten carbide scrap materials. Recycling techniques following either hydro or pyrometallurgical or a combination of them to recover the valuable metals (W, Co) are discussed. Thermal oxidation in presence of air/oxygen generates friable oxides of metals contained in tungsten carbide hard material, which is either leached in acid/alkali to produce tungsten oxide or subjected to reduction by hydrogen to produce tungsten powder. Direct leaching of tungsten scrap in concentrated acid/alkali solutions has also been investigated and different value added materials like ammonium para tungstate, tungstic acid etc are produced in the subsequent processing of leach liquor. The electrochemical route has emerged as an attractive method as it is a single step dissolution process consuming very low energy. However, passivation has been reported to slow down the dissolution rate and hence, some additives have also been tried for continuous dissolution. The environmental and economical aspects of some of the important processes have also been highlighted in this paper

Anodic dissolution behaviour of tungsten carbide scraps in ammoniacal media

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 for their recycling to recover metal values. However, it has been seen that anodic passivation retards the dissolution of the scrap and adversely affects the recovery of metals. To minimise 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, 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, 2% NH4Cl was found suitable to obtain maximum anodic dissolution (current) in the ammoniacal (1N) 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 were recovered as tungsten oxide and metallic chips, respectively

Molybdenum extraction process: An overview

An ever-increasing quantity of low-grade molybdenite concentrates are being produced from secondary sources especially as by-products of copper and uranium mining. Such low-grade MoS, concentrates are nor amenable for the extraction of Mo metal by traditional methods. A critical survey indicates that over the past three decades significant research efforts have been directed not only to improve and modify the conventional methods, but also to develop new methods for the extraction of molybdenum satisfying indigenous needs and environmental considerations. In this paper, the various methods of extracting molybdenum from its primary and secondary sources are critically reviewed. Ten distinct new approaches have been considered as potentially useful methods and a critical appraisal has been made of the new routes investigated during the past two decades. At the end, the Indian status on this subject is critically reviewed and potentially useful processes have been identified

STATUS OF WILD BOAR (Sus scrofa L.) ON THE ISLAND KRK

Divlja svinja u Republici Hrvatskoj autohtona je vrsta. Zakonski spada u krupnu, lovostajem zaštićenu vrstu divljači. Krajem prošlog stoljeća tjerana nagonom za širenjem svoje vrste plivanjem dolazi na otok. Krk je danas veoma kvalitetno stanište za život krupne divljači. Obilje hrane, vode, gusta vegetacija, raznolikost staništa, mir u lovištu, kvalitetno tlo, zapuštanje poljoprivrednih površina koje se pretvaraju u šikaru, rezultira stalnim prirastom postojeće divljači kao i zauzimanje prostora od nove pristigle divljači. Nekada je otok izgledao bitno drugačije nego kako izgleda danas. Obrađivao se svaki komadić zemlje, a danas se većina prepušta sukcesiji. Nova situacija u staništu uvjetuje i pojavu novih životinjskih vrsta. Upravo ovakva situacija pogoduje krupnoj, a ne odgovara sitnoj divljači. Divlje svinje nalaze se i u nelovnim površinama, gdje dolaze zbog hrane i mira, budući se tu zbog zakonskih propisa ne vrši lov. Nelovne površine služe kao rezervat iz kojeg nastanjuju najkvalitetnija staništa. «Crna divljač» na otoku Krku smatra se nepoželjnom vrstom divljači, te se sukladno naredbama ministarstva lovi cijele godine, bez obzira na spol i dob. Zbog odstrjela krmača vodilja, kvalitetnog staništa i velikog odstrjela bucanje i prašenje traje tijekom cijele lovne godine. Divljač pokušava opstati koristeći svoje prirodne mehanizme za očuvanje svoje vrste. U devet lovnih godina s otoka je izlučeno 3.602 grla divljih svinja. Kvalitetu staništa potvrđuje i snaga trofeja odstreljenih veprova, koja zbog nepravilnog odstrjela opada. Želja za potpunim izlučenjem divlje svinje s otoka Krka borba je sa prirodom, a za sada priroda uvijek pobjeđuje. Da li će tako biti i ovoga puta pokazati će budućnostThe wild boar is a native species in the Republic of Croatia. This large game animal is protected by law in closed season. At the end of the last century, driven by instinct to expand its species, it swam from the mainland to the island of Krk. Today Krk provides an excellent habitat for large game animals. Due to an abundance of food, water, dense vegetation, habitat diversity, peaceful hunting ground, fertile ground, abandoned farming areas which have been turning into thick underbrush, the existing game is on a constant increase while new arrivals crowd the existing habitat. The island has changed much and the landscape is not what it was once. Each parcel of land was once cultivated, while today it is left to succession. The new situation in the habitat has caused the emergence of new animal species. It is exactly this type of situation that suits the large and not the small game animals. Wild boars are found in areas not designated for hunting where they come to feed in a peaceful environment since by law hunting is prohibited there. Areas not designated for hunting serve as a game refuge and as such are considered to be habitats of the highest quality. The “black game” on the island of Krk is considered an undesirable type of game animal and pursuant to regulations may be hunted throughout the year, regardless of its sex or age. Due to the eradication of dominant female wild boars, excellent habitat and the large number of killings, mating lasts throughout the entire hunting season. The wild boar tries to survive using its natural mechanisms to preserve its species. In the nine years of hunting 3,602 head of wild boars were eradicated. The quality of the habitat is measured by the number of male boars that were killed as trophies, this being on the decline due to irregular killings. The desire to completely eradicate the wild boar from the island of Krk is a battle against nature and nature is winning, for now. Will this be the case now, only the future will tell