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By Zuomei Jin

The Mineralogical form of Silver in a Ag-rich complex ore was determined. In the complex sulfide ore, acidic thiourea leaching resulted in 35% extraction of silver directly. In the same complex sulfide ore, under the effect of ultrasonic treatment, 65% of silver can be ex¬tracted. After the above ore had been roasted and acidically leached of Zn and Cu, the silver extracted from this Pb-Ag residue was 96.8%. The effets of temperature, thiourea and ferric ion concentrations and partical size were examined. The leaching rate of silver from the Pb-Ag residue was diffusion controlled. The activation energy was calculated to be 10. 49%KJ/mole. The kinetic model for the thiourea leaching of silver from Pb-Ag residue was obtained and is given by, The kinetics of silver cementation by aluminium in thiourea solutions was also investigated. The activation energy was calculated to be 65. 13KJ/mole, which is reasonable fora rate-limiting surface reaction.

Jan 1, 1995

By Jewel Gomes

Produced water (PW) is salty water trapped in the reservoir rock and brought up along with oil or gas during production. It subsists under high pressures and temperatures, and usually contains hydrocarbons and metals. Therefore, it must be treated before being discharged to surface water. Different techniques are being used to treat PW through phase separations, system control and design, and chemical treatments. In this paper, we discuss our experimental results on treating PW through electrocoagulation (EC). The performance of EC was investigated for the reduction of chemical oxygen demand (COD) and metal ions. Effects of different electrodes, residence time, current density, and pH were also studied to optimize the treatment conditions. Different kinds of cleansing agents, such as lime and borax were used to break the buffering effect encountered during treatment. FTIR, SEM/EDS, and XRD were used to characterize the EC-floc and thus to elucidate removal mechanisms.

Jan 1, 2009

By S. P. Ball

A major limitation to maximising the rate of gold extraction in commercial operations occurs as a consequence of the limited solubility of oxygen in cyanide liquors. The use of additions of solid inorganic peroxides as an in-situ supply of oxygen to the lixiviant has been studied, in particular in its application to heap leaching. Experimental studies showed-that the release of oxygen into solution from these peroxides is very sensitive to solution pH. Agitated leaching tests showed that, when either Ba, Ca or Sr peroxides were used as the-sole source of oxygen, both the rate and extent of gold extraccion was enhanced. Column leach tests were used to simulate heap leach conditions. These showed that significant increases in the rate of gold extraction could be achieved by additions of calcium peroxide, made to the ore, prior to it being loaded into the columns.

Jan 1, 1989

By Gregor Kücher

Lack of basic knowledge on the semi-direct recycling methods for hard metals hinders the application on an industrial scale. However, advantages like reduced expenses and lower environmental impact draw interest at future potentials. Consequently, this report aims to offer insight into the influence of varying bulky hard metal substrates during their lixiviation in acidic media with an oxidant. The statistical software Modde 11 assisted in the development of a design of experiments (DOE) for evaluation of the impact of average grain size, binder and tantalum carbide (TaC) content on the leaching characteristics. The other experimental parameters were constant. Among them were temperature, solution concentration and quantity, duration and substrate surface exposed to liquid volume. Eventually, prediction plots and factors of the computed model equation describe the effects of varying substrate qualities on leached binder metal and selectivity.

By S. Gopalan, J. D. Milshtein, S. N. Basu

Production of syngas is proposed utilizing the W/W03 redox system and employing a solarpowered two-step thermochemical cycle. Three chemical reactions occur in two chambers. Assisted by a solar concentrator, a high temperature reaction reduces W03 powder to metallic tungsten in both chambers. Subsequently, the temperature in one of the chambers is lowered and H2(g) is produced via re-oxidation of the tungsten powder using steam. The temperature in the other chamber is simultaneously lowered to an intermediate temperature and CO(g) is produced via oxidation of the tungsten powder using C02(g)· The gas streams coming out of the two chambers result in the syngas production. A complete thermodynamic analysis of the system is described. The W/W03 redox cycle offers greater gravimetric fuel productivity compared to previously proposed systems, and the entire cycle can be operated below 1273K.

Jan 1, 2013

By R. Padilla

The reaction of chalcopyrite with gaseous sulfur has been investigated in the range 350-450 °C in order to transform this mineral into a more acid soluble copper sulfide and insoluble iron sulfide. The results of thermodynamic analysis of this system as well as the X-ray diffraction analysis of the reaction products showed that in the temperature range 350 400°C the sulfidation reaction proceeded without formation of intermediate copper-iron sulfides according to: The effects of temperature and time on the conversion of chalcopyrite were studied. Conversion of chalcopyrite reached about 80% very rapidly with increase in temperature up to about 400°C. The recovery of copper from the sulfidized samples was determined by leaching in oxygenated 1.2M H2S04, 2M NaCI solution. Copper recoveries over 90 % were obtained from samples sulfidized for 30 min at temperatures lower than 400°C.

Jan 1, 2001

By A. R. Udupa

The reduction roasting behavior of chalcopyrite has been investigated using various combinations of a desulfurizing agent, i.e., CaO or Na2CO3, and a reductant, i.e., CO, H2 or C. Using these, combinations the sulfur is removed from the mineral as CaS or Na2S rather than SO2 as is the case with conventional copper smelting and converting. The laboratory reduction ex¬periments were conducted using thermogravimetric analysis (TGA) and boat tests of mixed combinations of fine particulate reactants subjected to a continuous gas stream. The degrees of metallization were determined by both weight loss and chemical analysis methods and the products examined using optical and scanning electron microscopy and electron probe microanalysis. The percent reduction after one hour at 900°C ranged from 60% to 94%. From these data It was possible to provide postulations as to the controlling reduction mechanisms.

Jan 1, 1983

By Gus Van Weert

Hydrometallurgical oxidation of sulphides is capital and energy intensive, with autoclave and bio-technology competing for lowest overall cost status. The use of surface aerators instead of stirred tank reactors could provide lower costs for bio-oxidation of concentrates. With this in mind, the Delft Inclined Plate reactor was designed with inclined plates above a settler shaped reactor to continuously return slurry from the lowest point in the settler to the surface of the liquid. The multiplate superstructure overcomes the scale-up restriction of the standard circular surface aeration patterns. DIP aerator energy and volume requirements for oxygen transfer from air will be presented in terms of kg O2/kWh and kg O2/m3/h transferred as a function of wt % sand in the slurry and compared to stirred tank performance. Scale up from the 4 m3 pilot unit will be discussed.

Jan 1, 1996

By T. T. Chen

Canadian Electrolytic Zinc has developed the "cement-stabilization of jarosite residue" Garofix) process to stabilize zinc plant jarosite residues for disposal. The cement-jarosite mixtures cure quickly, have good mechanical strength and low hydraulic permeability; they possess good neutralizing capability and chemical stability. In the jarofix process, Portland cement partly decomposes jarosite to form (SO4MOH)12.nH2O, ferric hydroxide and an alkali sulphate. Approximately 40% of the jarosite reacts in mixtures containing 30% cement. The jarofix product also contains various Ca-Al-Fesilicate-sulphate-hydrate phases and gypsum, which bond the individual particles together imparting mechanical strength and reducing the permeability. Most of the reactions take place in the first few hours of curing. Ammonium jarosite is slightly more reactive than sodium jarosite but releases NH3 gas; water-soluble Zn in the jarosite residue is stabilized in the cement reaction products.

Jan 1, 1996

By Batric Pesic

Reactions of metallic iron were studied in several different aqueous solution systems: water, medium salt solution used for the growth of T ferrooxidans, ferric iron solution and solution containing T ferrooxidans. Each system was studied under abiotic and biotic conditions in the presence of T ferrooxidans and as a function of pH, particle size of iron powder, temperature, ferrous and ferric iron concentrations. It was found that metallic iron reacts with water differently than does with ferric iron in water. Surprisingly, T ferrooxidans were non-functional in the dissolution of metallic iron. Also, the reactions of metallic iron with pure water were indistinguishable from the reactions with water containing medium salts for bacterial growth. The reactions with ferric iron were also independent of medium culture compounds. The mechanisms of metallic iron reactions with ferric ions are different from the mechanisms of metallic iron reactions with water.

Jan 1, 2001

By Xiang Ma, Halvor Dalaker, Kai Tang, Stefan Andersson

Silicon carbide (SiC) is one of the most important non-oxide ceramic materials for many industrial applications and is mainly synthesized by carbothermic reduction of silicon oxide by coke above 2200°C. Replacing natural gas (mostly methane, CH4) for coke in SiC synthesis could considerably reduce energy consumption and CO2-emissions owing to higher carbon activity of CH4 at lower temperature. The generally accepted reaction mechanism is that SiC is synthesized through gaseous intermediate silicon monoxide, SiO. In the present study, the reaction mechanism for the SiO and CH4 gaseous mixture has been examined using atomic scale modelling. Molecular dynamics (MD) using a reactive force field (ReaxFF) has been utilized to examine the initial stages of reactions involving a gas mixture of SiO and CH4 and surfaces of SiC. The MD results revealed some interesting SiC formation mechanisms. The reaction energies of the critical intermediate species were also estimated by density functional theory (DFT) calculations and the implications for the force field parameters used in ReaxFF was discussed.

Jan 1, 2015

By R. Cameron

The growing use and acceptance of electric vehicles (EV), as evidenced by the record sales of over 750 thousand vehicles in 2016 and a current global EV stock of 2 million vehicles, is putting pressure on sourcing raw materials such as cobalt, and to a lesser extent, nickel. Global supply is poorly diversified, with 50– 60% of global cobalt production sourced solely from the Democratic Republic of Congo (DRC). One potential source for cobalt and nickel are low-grade nickeliferous pyrrhotite tailings, of which 50–100 million tonnes are present in the Sudbury area alone. This paper presents the extraction of cobalt and nickel from this material using a combination of flotation and bioleaching technologies. The findings of a high-level techno-economic analysis of the proposed processing flowsheet are presented.

By A. Haxhiaj, Mitovica, E. Haxhiaj

"The paper discusses problems encountered during the release and possibility of using the thermal gas quantity Mathematical models are used to calculate the positive thermal effects of the gases and losses of thermal quantity with gases in the melting process of electric furnaces. The paper discusses in details the percentages of CO, CO2, H2S, O2 and the humidity in gases and their impact on the technological process in electrical furnaces in Drenas. The paper also confers the quantity and temperature of gases, the transfer of thermal quantity and dust with gases in the environment. The paper presents the percentage of humidity in the load which is added in electric furnace for melting and its impact on thermal and environmental balance in the technological process of melting in electric furnaces. Key words: Furnace, load, temperature, humidity, gases.IntroductionNickel easily reacts with gases in the atmosphere of the furnace in which the nickel ore is processed. Such reactions can explain challenges in producing high quality nickel. Reductive atmosphere with the surrounding gases composed of sulphurous anhydrite has harmful effects on the production of nickel. This is mainly due to solubility of hydrogen as well as nickel oxide in the melted metal. Nickel reacts with carbon monoxide and forms carbide of nickel and nickel oxide which dissolve in the melted metal. Carbon monoxide also dissolves in the melted metal. The presence of carbon dioxide and water vapor in the atmosphere of the furnace impact the decrease of acidity in reductive atmosphere of the furnace. The carbon dioxide reacts with nickel and forms nickel oxide and carbon monoxide. Water vapor reacts with nickel and forms hydrogen and nickel oxide that have negative impact on the structure of nickel and its alloys. In this paper the analytical and experimental analyses are proposed that lead to minimization of the negative effects of gasses and humidity in the melting process. As the practical example, the electrical furnace in Drenas is analyzed.1. The Load and Its CompositionThe basic function of the rotational furnace is drying and reductive roasting of the ore which directly is loaded into the electrical furnace for melting. It is important to mention that the degree of roasting and pre-reduction of iron-nickel oxides is reached if the roasting process of the load in the rotational furnace is done at the temperature of 900°C to 1000°C, with the reductive atmosphere in the furnace and with minimal amount of oxygen in the processing gas. The optimal process of roasting and pre-reduction of the load in its mass is around 13 wt%. With the removal of the humidity and the sterile pare of the ore, with the positive impacts in utilization of the thermal and electrical energy in the melting process in electrical furnaces."

Jan 1, 2013

By J. D. Budai, D. H. Lowndes, D. P. Norton, D. K. Christen, B. C. Chakoumakos, J. R. Thompson, B. C. Sales

"Artificially-layered structures, consisting of (Sr,Ba,Ca)CuO2 layers in the tetragonal, ""infinite layer"" crystal structure, have been grown by pulsed-laser deposition. Superlattice chemical modulation is observed for structures with SrCuO2 and (Sr,Ca)CuO2 layers as thin as a single unit cell (~3.4 Å). In addition, novel thin film superconductors were formed by using the constraint of epitaxy to stabilize SrCuO2/BaCuO2 superlattices in the infinite layer structure. Using this approach, two new structural families, Ba2Srn-1CUn+l O2n+2+ d) and Ba4Srn-1CUn+3O2n+6+ d, have been synthesized which superconduct at temperatures as high as 70 K. These results represent not only the synthesis of new structural families of superconductors, but also demonstrate that pulsed-laser deposition and epitaxial stabilization can be effectively used to engineer artificially-layered thin-film materials.Advances in the understanding of epitaxial thin-film growth of the cuprates have heightened interest in creating artificially layered superconductors.(1-3) The layered structure of the copper oxide superconductors opens the possibility of forming novel materials by carefully controlling the epitaxial growth of sub-units of the crystal structures. Thin-film growth methods offer unique opportunities for the atomic engineering of new high-temperature superconducting (HTSc) materials through the ability to form artificially layered crystal structures.(4,S) Moreover, the surfaces of single-crystal substrates provide an ""atomic template"" that can be used to stabilize epitaxial films in metastable crystal structures.An important development in forming new HTSc compounds by artificially-layered epitaxy has been the epitaxial growth of (Sr,Ca)CuO2 films in the so-called infinite layer structure.(6-17) This material, which can be considered the parent compound of all of the copper oxide superconductors, has a relatively simple, layered structure consisting of CUO2 planes separated by planes of alkaline earth elements.(18) Bulk synthesis of (Sr,Ca)CuO2 with the tetragonal, infinite layer structure generally requires the use of high pressure and high temperature bulk processing techniques.(19-24) However, recent experiments show that this metastable compound can be epitaxially stabilized at less than atmospheric pressure, resulting in the growth of tetragonal (Sr,Ca)CuO2 single crystal thin films of the infinite layer defect perovskite structure by pulsed-laser deposition (PLD) over a wide range of growth conditions.(6-17)"

Jan 1, 1994

By Wanderson Silva Rodrigues, Paulo Adão Marinho dos Santos, José Antonio Silva Souza, Luis Alves Venancio, Emanuel Negrão Macedo

"1 AbstractThe production of alumina from bauxite using the Bayer process generates 0.7 to 2.0 ton of the residue known as red mud per ton of alumina. This material has no large scale current use and is usually stored. This paper shows that it can be used in a suspension with water as a gas effluent cleaner with high efficiency to remove SO2. It can substitute other materials currently used reducing the overall environmental impact and potentially reducing the cost of gas treatment.2 IntroductionThe production of millions of tons per year of alumina around the world generates from 0.7 to 2.0 ton of the residue known as red mud per ton of alumina. The vast majority of the red mud is stored in large sealed lakes. Due to the high reactivity this material is considered dangerous and currently there is no operating process capable of reuse all the material produced at any refinery. These lakes after filled of solid material eventually have the surface revegetated. In any cases they will remain as an environmental passive and need monitoring for decades. The search of industrial processes that combine the cleaning of gas effluents emission and reuse of these residues can contribute to the reduction of the overall impact of the alumina production process.The main objective of this work is to study the efficiency of the red mud as alternative raw material for the control of emissions of SO2 in combustion gases. Usually this is made through alkaline solutions of CaCO3 or NaOH in absorbing equipments like spray towers or packed column. This project main objective is to study the reaction of the SO2 with a suspension of red mud and water in order to obtain the basic parameters to design equipment capable of process this reaction on a pilot scale. With that goal compositions of red mud on spray were processed with flow of gas containing SO2 with concentration similar to the exhaust gases of the combustion process of the refineries."

Jan 1, 2011

By Xiaoming Huaa

The effect of the anodic polarization on the composition and morphology of the surface layer formed on chalcopyrite during ammonia–ammonium chloride leaching was investigated. The anodic polarization on the chalcopyrite electrode was used for oxidation and dissolution of chalcopyrite, and the resulting oxidized layers were characterized by XPS, SEM and optical microscopy. The results show that oxide layers exist on the chalcopyrite surface with or without any anodic polarization in the leaching solution at ambient atmosphere. However, the composition and morphology of the layers are strongly depended on the extent of polarization. The distribution of FeOOH and Fe2O3 within the oxidized layer was inhomogeneous for the sample at the open circuit potential (OCP). The composition and morphology of the oxidized layers which were formed at anodic potentials lower than 0.3 V versus SCE were similar to those of the chalcopyrite at the OCP. At anodic potentials above 0.4 V, the oxidized layers contained many cracks, and they were fragile and exfoliated. Furthermore, the sulfide had been oxidized to sulfur species with higher oxidation states. The oxidation of the chalcopyrite seemed to undergo a cyclically oxidative process that suggested growth and spallation of oxidation layers on chalcopyrite in a layer-by-layer sequence.

By Ruiling DU, Xiao YUAN, Keng Wu, Daan XU, Changyao CHAO

To utilize low grade coals to produce high quality semi-coke which can be used in blast furnaces, the pyrolysis of low grade coals was studied in this paper. According to the characteristics of coal pyrolysis process, the temperature range was divided into three parts. The interfacial chemical reaction model, random pore model and the internal diffusion model with the shrinking volume of resultant were established to describe the different ranges of pyrolysis process respectively. The results showed that the experimental data was fitted well, and all the correlation coefficients (r2) exceeded 0.97. Finally, the kinetic parameters for each temperature range have been calculated, which laid a necessary foundation for the simulation and expanded production.

Jan 1, 2016

By Sanaz Mosadeghsedghi

The feasibility of the application of electrodialysis in separation of light and heavy rare earth elements (REE) in synthetic solutions was investigated. The experiments were carried out using single and binary solutions of a light (cerium) and heavy (ytterbium) REE. The effects of electrical voltage, electrical current, and the addition of complexing agent (EDTA) to increase the separation selectivity were investigated. Separation of Ce and Yb was achieved in binary solutions with and without the addition of EDTA. Higher degrees of separation were seen at higher voltages. Ce–Yb separation was more significant in the presence of EDTA. The separation factor of Ce–Yb and Ce–Yb-EDTA were 1.44 and 2.60, respectively.

By Georgios Kolliopoulos

Water is a critical commodity of our generation and a key compound for the chemical and mining industries. Sustainable industrial development is directly associated with the ability to recover clean water from contaminated sources. Forward Osmosis (FO) is a low-energy footprint membrane process allowing the recovery of clean water from high salinity effluent streams. In FO, water is recovered spontaneously into a concentrated draw solution (CDS). Energy is required to separate the recovered water from the resulting dilute draw solution (DDS). In the current work, the fundamentals of the FO process and the most important aspects affecting its performance are discussed. An energy comparison of FO and conventional water recovery technologies is presented. Finally, the opportunities FO presents in the field of hydrometallurgy are analyzed.

By Hannu Johto

Boliden Harjavalta has operated a flash smelter for nickel sulphide concentrates in Finland since late 1959. The original nickel flash smelting process was modified in 1995 to a novel nickel matte smelting (DON) with semi-low iron where the batchwise operated converting became obsolete. Since that, the process has been applied to multiple chemically variable nickel sulphide concentrates with high environmental performance. In this paper, the status of the current smelter operations is described together with the recent modernizations of the nickel flash smelting furnace and the slag cleaning furnaces.