Refining of Precious Metal Bearing Materials from Secondary Sources-Methanesulfonic Acid Leaching of Raw Silver Granules as a Promising Approach towards a Green Way of Silver Refining

The state-of-the-art technology of raw silver refining in a silver nitrate-based electrorefining process (Moebius-electrolysis) is accompanied by several disadvantages, both from a technological and from an ecological point of view. In addition, increasing concentrations of critical impurities from secondary sources, like palladium, in raw silver are a further challenge for the future of silver refining. Thus, there is strong motivation for the development of an adequate, alternative process of raw silver refining to substitute the existing Moebius-electrolysis. Due to its less environmentally toxic character and the high aqueous solubility of its silver salt, methanesulfonic acid (MSA) is a possible base chemical for the design of an efficient refining method based on leaching of raw silver followed by electrowinning, with less ecological and technological complications. In this paper the results of some fundamental investigations on the leaching of raw silver granules, containing approx. 94% silver, with methanesulfonic acid and hydrogen peroxide as an oxidation agent are presented. Agitation leaching experiments were conducted on a laboratory scale and the effects of the solid concentration, the hydrogen peroxide dosage and the temperature as leaching parameters were studied. The obtained results indicate that silver leaching yields of more than 90% are achievable with leaching at elevated temperatures of 65 °C or 80 °C, solid concentrations of 500 g/L and at a stoichiometric H2O2:Ag-ratio of 3:1. Increased solid concentrations greater than 500 g/L and elevated temperatures of 65 °C or 80 °C additionally improved the selectivity of the process regarding the leaching of Pd.

Preliminary Study on the Reductive Leaching of Manganese Ores using FeSO₄/Iron Powder as Reducing Agents under Room Temperature

The leaching of manganese (Mn) ore in sulphuric acid (H2SO4) under reductive conditions has been studied. The effects of leaching parameters such as ore/reductant mass ratio, acid concentration, ore particle size, solid/liquid ratio, leaching time and different reductant potential on the maximum recovery of manganese have been investigated. The optimal leaching conditions were ore/reductant mass ratio of 1:3.4, acid concentration of 10% v/v H2SO4, ore particle size of 63-200 µm, particle size of iron powder of –150 µm, solid/liquid ratio of 1:20, and leaching time of 1.5 hours at room temperature. A comparative analysis on the recovery of manganese ore was also investigated under the optimal leaching conditions for two different reductants, iron sulphate (FeSO4) and iron powder. The maximum manganese recoveries at the optimal leaching conditions in the presence of FeSO4 and iron powder are 80.6% and 95%, respectively. The results indicate that manganese can readily be leached during short time at room temperature. Furthermore, iron powder has a stronger reducing power compared to FeSO4 with respect to manganese ore recovery.

Adaptive process for improving leaching efficiency of germanium from secondary zinc oxide

Adaptive process was used to treat germanium-containing secondary zinc oxide. The leaching parameters were determined by batch experiment, and continuous experiment was conducted and the stability of the process was verified. The leaching efficiency of Zn and Ge in the batch experiments were 92.51 and 90.67%, respectively, while the leaching efficiencies of Zn and Ge in the continuous experiment were 93.53 and 88.47%, respectively. In the neutralization process, the Fe3+ concentration in the neutralized solution is within 0.025 g/L. The Fe2+in the leaching solution increased gradually, as the neutralized residue was returned to the leaching process, the Zn in leaching residue reduce and the leaching efficiency of Zn increased. The residue mainly contained zinc sulfide and lead sulfate, with some fluffy structures on the surface. The process is promising for industrial application from indicators, economy, and applicability.

Influence of leaching parameters on the vanadium extraction from petroleum coke

More than 60 trace elements, including rare metals, can be found in heavy oils. The most valuable component of oils and petroleum products is vanadium. It is used as an alloying agent to create extra strong steel, as a cathode for lithium-ion batteries, and also as a catalyst in the chemical industry. Nowadays studies of various methods for extracting vanadium from heavy oils and petroleum products are actively carried out. This work presents the method of alkaline and acid leaching of vanadium from petroleum coke and also results of the examination of influence of factors such as the duration of the process (0.5, 1.5 and 2.5 h) and the ratio of solid and liquid phases (1:2, 1:3 and 1:4). The highest yield of vanadium 80% is observed using sulfuric acid with the process duration is 1.5 hours and the ratio S/L = 1:4

Modeling of filtration processes of technological solutions in block underground leaching

PAO “Priargunsky Production Mining and Chemical Association” has been working on reserves of uranium deposits of the Streltsovsky ore field for more than 50 years. During this period, most of the rich ores have been worked out by traditional mining and physical technology. The share of poor and ordinary ores remains significant, but traditional technology does not provide the necessary level of profitability. Therefore, the widespread introduction of physicochemical technology: underground block (BPV) and heap leaching (KV) can be a decisive moment in the continuation of the operation of these deposits. The applied technology of underground block leaching has one significant drawback – a low rate of uranium recovery into a productive solution, which significantly reduces the effectiveness of this technology in the development of poor uranium deposits. To increase the yield of uranium into the productive solution, it is necessary to analyze the entire preparation and leaching process and establish the main reasons for the low rates of transition of uranium to a mobile state. For this purpose, it is proposed to simulate the underground leaching process by building visual models of halos spreading of solutions along shrinked ore mining mass accumulated in an underground chamber. During the simulation, it was found that the distribution of the size classes of the broken ore pieces in the chamber can be predicted at the stage of drilling and blasting operations, and when determining the line of least resistance W and the distance between the ends of the wells, take into account the diameter of the controlled crushing zone R_p. At the same time, 3 zones of granulometric compositions are formed: a re-grinding zone, an optimum zone and a non-carbarite exit zone. The flow of solutions through these zones will differ the more significantly, the higher the height of the chamber. In a zone with larger crushing, an almost steep distribution of the solution spreading front is expected. Accordingly, the smaller the fraction, the lower the front to the horizontal is. The following functions are offered to simulate filtering processes: – it is possible to control the flow of working solutions to the fan of irrigation wells in order to achieve optimal leaching parameters, i.e. to quickly control the process; – knowledge of the law of distribution of irrigation flares makes it possible to select the optimal grid of location of single sprinklers

The application of citric acid solutions for selective removal of zinc from steelmaking dust

Steelmaking dust is one of the wastes which are produced by ironworks. This kind of waste is a byproduct made mainly in electric arc furnace. Zinc content in dust is different and depends on the charge processed in the furnace. The basic technology used for recycling steelmaking dust is Waelz process however it requires a large amount of reducer and generates a lot of waste which need to be stored. First stage in this study was to analyze if steelmaking dust is safe to be exposed for atmospheric conditions. To verify this subject the dust exposed for two kinds of leaching, in standards of TCLP and EN-12457-2. The amount of extracted elements was too large that's why steelmaking dust must be treated as dangerous waste. Leaching in citric acid solutions was divided in four series. The first one was set to determine the time and temperature for most selective zinc leaching. Next series optimized three leaching parameters which were: citric acid concentration, liquid to solid phase ratio (l/s), and the stirring speed. Performed experiments showed the optimal conditions for selective leaching: temperature of 50 ?C, leaching time of 60 minutes, citric acid concentration of 0.5 mol/dm3, l/s ratio of 10, and stirring speed of 250 rpm.

Studying the impact of alkaline sulfide leaching parameters upon the efficiency of arsenic recovery from copper skimmings of lead production

The article is concerned with the problem of arsenic circulation as copper skimmings of lead production — the product of the lead bullion decopperization process at a metallurgical complex, uniting copper and lead plants. A brief overview of the methods of processing arsenic-containing middling products for the purpose of arsenic removal is given; the main advantages and disadvantages are indicated. The possibility of processing copper skimmings by the method of alkaline sulfide leaching with separation into arseniccontaining solution and lead-copper precipitate is studied. The results of the researches into the influence of temperature, process duration, solids content in the pulp, particle size, and the ratio of sodium hydroxide to elemental sulfur in the alkaline sulfide reagent on the process of alkaline sulfide leaching of copper skimmings af lead production are provided. Within the studied range of varied factors, the highest indexes of arsenic extraction into solution (85.04%) were achieved under the following conditions: temperature — 85 °C, duration — 4 hours, solids content in the pulp — 350 g/dm3, fraction (–0.08 mm), NaOH/S ratio = 100 g/100 g in 1 dm3 of the solution. The proposed method for processing copper skimmings will allow one to selectively isolate arsenic into the dump waste product during subsequent precipitation and separate contaminant from lead-copper cake, into which precious metals also pass. Such an approach provides the reduction of arsenic circulation between the lead and copper manufacturing facilities.