Selective Leaching of Molybdenum from Bulk Concentrate by Electro-Oxidation

This paper proposes selective leaching of molybdenum from Mo/Cu complex bulk concentrates in a 5 M NaCl solution using the electro-oxidation method. Here, the effects of several factors such as pH, pulp density, current density, and temperatures were investigated. A higher leaching yield of Mo increased with increasing pH from 5 to 9 and decreased with increasing pulp density from 1 to 10%. A rise in current density did not help enhance Mo, and the elevating temperature did not always result in a higher leaching yield. Application of ultrasonic led to higher leaching yield of Mo. Ninety-two percent of leaching yield was obtained upon leaching of Mo in 5 M NaCl at 25 °C, pulp density of 5%, and the current density of 0.292 A/g under ultrasonic irradiation with a power of 27 kW. The resultant residue mainly consisted of chalcopyrite.

Leaching of Copper from Waste-Printed Circuit Boards (PCBs) in Sulfate Medium Using Cupric Ion and Oxygen

In the present paper, the leaching of copper from printed circuit boards (PCBs) using sulfuric acid with Cu2+ and O2 is proposed. The effects of various process parameters such as agitation speed, temperature, the type and the flow rate of gas, initial Cu2+ concentration, and pulp density were investigated to examine the dissolution behavior of Cu from PCBs in 1 mol/L sulfuric acid. The kinetic studies were performed using the obtained leaching data. The leaching rate of Cu from PCBs was found to be higher on addition of Cu2+ and O2 to the leachant in comparison with the addition of O2 or both Cu2+ and N2 in the leachant. The leaching efficiency of Cu was found to be increased with increasing agitation speed, temperature, O2 flow rate, and initial Cu2+ concentration and decreasing pulp density. The 96% of Cu leaching efficiency was obtained under the following conditions: sulfuric acid concentration, 1 mol/L; temperature, 90 °C; agitation speed, 600 rpm; pulp density, 1%; initial Cu2+ concentration, 10,000 mg/L; and O2 flow rate, 1000 cc/min. The leaching data and analyses indicate that the Cu leaching from PCBs followed the reaction-controlled model satisfactorily and determined that the activation energy was found to be 23.8 kJ/mol. Therefore, these results indicate that the sulfuric acid solution with Cu2+ and O2 as a mild leach medium without strong oxidants such as HNO3, H2O2, and Fe3+ is valid for Cu leaching from PCBs.

Effect of Initial Cell Concentration on Bio-Oxidation of Pyrite before Gold Cyanidation

Bio-oxidation of refractory sulfidic gold minerals has been applied at the commercial scale as a pre-treatment to improve gold yields and reduce chemical consumption during gold cyanidation. In this study, the effect of initial cell concentration on the oxidation of pyritic gold ore was evaluated with four aerated bioreactors at 30 °C with 10% pulp density and pH maintained at 1.4 with NaOH. Results of NaOH consumption and changes in soluble Fe and S concentrations indicated that increasing the initial cell concentration from 2.3 × 107 to 2.3 × 1010 cells mL−1 enhanced pyrite oxidation during the first week. However, by day 18 the reactor with the lowest initial cell concentration showed profound performance enhancement based on soluble Fe and S concentrations, sulfide-S and pyrite contents in the residues, and subsequent gold leaching of the bio-oxidation residues by cyanidation. Overall, the results showed that the cell concentration was clearly beneficial during the initial stages of oxidation (first 7–8 days).

Recovery of Coal Values from Middling and Rejects by Froth Flotation and Mozley Mineral Separation

The recovery of coals values from Middling and Rejects carries out by using Froth flotation and Mozley Mineral Separation. The middling and rejects are the waste products from gravity beneficiation process, it has been noted that most of washery plants are selling this product at low cost because they have less values.The independent variables selected for Mozley Mineral Separator and their ranges were indicated in the parentheses as follow, water flow rates (400, 600, 800ml/s), amplitude (1.25, 1.5, 1.75inch) and collection time (30, 40, 60 s) while the independent variables for froth flotation were; Pulp density (10, 12.5, 15 %), collector dosage (39.3, 44.4, 49.5 g/t) and frother dosage (61.8, 65.3, 68.8 g/t). The number of experimental runs and regression equation determined by using Design Expert softwareThe d80 for middling and rejects samples were 10.5mm and 12.89mm respectively. The ash contents for the middling sample treated by froth flotation decrease from 37% to 15.85% at the reagent concentration of 49.5g/t collector, 65.3g/t frother and pulp density of 10%. The froth flotation results of middling sample shown to have a great reduction of ash contents. The overall optimum middling recovery and yield for washery grade I and II attain at reagent concentration and pulp density of 47.703g/t, 68.568g/t and 13.2% for collector, frother and pulp density respectively. The feed of reject coal was 71% and the ash contents reduced to 28.87% with the recovery of 0.85%. The analysis through Mozley mineral separator did not show significant changes in the reduction of ash from both middling and rejects. The ash contents achieved were above the scope of the studies for recovering of coal values. The experiments for middling and reject by froth flotation and Mozley mineral separator may be carried out by varying other parameters as well as the type of methods.

Role of Magnesium Salts in Coal De-Ashing by Flotation

The most frequently investigated salts in coal flotation are chlorides. However, seawater contains additional salts such as sulfates. In coal flotation, magnesium chlorides showed the best results in terms of higher yield and lower ash content compared to the other magnesium salts studied. Therefore, two magnesium salts were tested in this investigation, namely magnesium chloride and magnesium sulfate. The effect of the magnesium salts as well as the optimization of coal flotation were investigated by statistical design of experiments in terms of pulp density, particle size, conditioning time and different dosages of MgCl2 and MgSO4. The flotation results obtained by statistical design show that the ash content was lowest at 8.2% when a mixture of 2 kg/t MgSO4 and 2 kg/t MgCl2 has been used, with pulp density 20%, particle size 400 lm and conditioning time 15 min. The particle size plays an important role in reducing the ash content when the conditioning time has been extended and pulp density has been reduced. The strong interaction between the salts hinders the reduction of the ash content to less than 8.2%.

Bioleaching of Iron, Copper, Lead, and Zinc from the Sludge Mining Sediment at Different Particle Sizes, pH, and Pulp Density Using Acidithiobacillus ferrooxidans

Globally, the amounts of metal ore deposits have been declining, so the research directions investigating the extraction of metals from materials that are classified as waste are gaining more importance every year. High concentrations of Cu, Pb, Zn, and Fe were analyzed in the sludge sediment (Zlaté Hory, Czech Republic), which is a waste product of the mining industry. In the bioleaching process, bacterial cells have been established as being able to convert metals from solid to liquid phase. However, the most important parameters of bioleaching are particle size, pH, and pulp density, thus our research focused on their optimization. The acidophilic and mesophilic bacteria Acidithiobacillus ferrooxidans were applied due to the high Fe content in the sample. The recovery of metals in the leachate was determined by F-AAS and the residual metal concentrations in the waste fraction were analyzed by XRF. The grain size fractions <40 µm –200 µm were investigated. The atomic absorption spectrometry (AAS) results show that the highest Fe (76.48%), Cu (82.01%), and Pb (88.90%) recoveries were obtained at particle size of 71–100 μm. Zn was dissolved for all fractions above 90%. Experiments with different pH values were performed at a pH of 1.6–2.0. The highest dissolution rates of Zn, Fe, and Cu were achieved with a suspension pH of 1.8, where 98.73% of Zn, 85.42% of Fe, and 96.44% of Cu were recovered. Due to the high percentage dissolution of metals, experiments were performed under pilot conditions in a bioreactor at a pulp density of 2.5% and 4.2% (w/v). From an economic point of view, the leaching time of 28 days was evaluated as sufficient.

Flotation Performance Analysis on Coal Washery Rejects

Coal washery rejected coals and coal slurries have better options in froth flotation as a separation process. In this study, coal slurry received from Sudamdih coal washery, Jharkhand, India, examined for cleaning through fixed cell flotation. The Petrography study of the feed sample showed the presence of vitrinite, semi vitrinite and liptinite and inertinite as major minerals. General full factorial statistical design package (Minitab V17) was used to develop the regression models for the responses like froth height, froth density, recovery and ash content of clean coal. Results showed that experimental responses like froth height, froth density, recovery and ash content were found to be more sensitive to the frother dosage. The coefficient of correlation (R2) values between the experimental and the predicted values of the flotation responses was found to be >0.98 for all the models. Further, flotation tests were conducted for varying pulp density and its effect on recovery, froth height, ash content, tests with five levels of pulp density (8, 9, 10, 11, 12 and 13%solids by weight). It found that the coal slurry sample from the study area could be cleaned with sufficient efficiency. The cleaned coal is suitable for powder coal consuming industries.