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By Kang-In Rhee

A series of processes to recover the gold from electronic scrap which contains initially about 200-600 ppm Au have been developed. First, mechanical beneficiation including shredding, crushing and screening was employed. Results showed that 99 percent of gold component leaves in the fraction of under 1 mm of crushed scrap and its concentration was enriched to about 800 ppm without incineration. The scrap was leached in 50% aqua regia solution and gold was dissolved completely at 60°C within 2 hours. Other valuable metals such as silver, copper, nickel and iron were also dissolved. This resulting solution was boiled to remove nitrous compounds in the leachate. Finally, a newly designed electrolyzer was tested to recover the gold metal. More than 99% of gold and silver were recovered within an hour in electrowinning process.

Jan 1, 1995

By Pragna Bhakta

Newmont has investigated potential treatment options for low-grade refractory gold ores since 1988. After extensive R&D at Newmont?s laboratories, biooxidation pretreatment followed by ammonium thiosulfate leaching was selected for application to sulfidic preg robbing ores. A heap biooxidation and ammonium thiosulfate leaching demonstration facility was constructed in 1995 to conduct large-scale pilot tests at Newmont?s Carlin Operations. This paper presents Newmont?s experience with the recovery of gold from preg robbing ores using ammonium thiosulfate.

Jan 1, 2003

By Klara Kodrikova, Vera Kasparkova, Michaela Uhlirova, Karel Kolomaznik

"Potentially hazardous wastes from leather industry (blue shavings) are processed into various biostimulators within two steps. The first step takes place at high pH (11-12) and hydrolyzation is implemented with potassium alkali, in the second step the pH is lowered to 9 with phosphoric acid after enzymatic dechromation occurs. The resulting hydrolyzates were analyzed in the sense of molecular weight distribution and tested as biostimulators on rape (Brassica napus). The hydrolyzates can be also directly used as universal NPK fertilizers. It has been proved that the nitrate content in the edible parts of tested vegetables (radish, lettuce, and cucumber) was approximately 200 times lower compared to the vegetables fertilized with an inorganic nitrogen fertilizer. The harvests of vegetables fertilized with the hydrolyzate and the inorganic nitrogen fertilizer were almost the same.IntroductionDuring processing raw hide into leather (tanning processes), only 20% of the collagen material is used for the final product. The remaining 80% ends up as waste, both tanned and non-tanned. Non-tanned waste such as calcimine can be used for production of artificial collagen casings for sausages, gelatine and also in pharmaceutical industry as collagen capsulates. Further processing and recycling of tanned leather waste (especially chrome shavings) is more complicated. Although many technologies producing various quality collagen hydrolyzates have been developed and tested in laboratories, few have been implemented on industrial scale. A promising turn came in the works of ERRC USDA [1,2]. They worked out an enzymatic dechromation technology (hydrolysis) and achieved a considerable decrease of the amount of relatively expensive proteolytic enzyme, which solved the difference between the quality and price of the final product. The American experience of enzymic hydrolysis were applied on industrial scale in the Czech Republic, where a plant was built with daily processing capacity of 3 tons of chrome shavings. The experience of real operation was published in [3] and the cooperation between the Czech Republic and USA partners resulted in a patent [4]. The main asset of the patent was the use of volatile organic bases in the hydrolysis process giving high quality and cheap hydrolyzates with low ash content."

Jan 1, 2008

By Wenjie Zhu

Chromite ore processing residue (COPR) is a hazardous waste containing high concentration of chromium. We describe here a pioneer trial of detoxification of COPR in column reactor with an indigenous chromate reducing bacterium Leucobacter sp. Ch1, which showed high chromate reducing ability at high pH. Under the optimum conditions, at 30°C and pH 10.0, pH of leachate decreased from 10.3 to 8.3, and Cr(VI) concentration in solution decreased to zero mg L-1, and 76.4% of Cr(VI) was removed from COPR samples. The leaching toxicity of detoxified residue was 1.1 mg L-1 that was lower than national standard of China.

Jan 1, 2008

By Gerhard Bayer

X-ray and thermoanalytical studies were carried out on the formation and stability of Ca-, Mg-and Mn-tungstate, and of the corresponding minerals scheelite and wolframite. The tungstates were synthesized by different methods: precipitation from solution, solid state reactions, displacement reactions with solutions and in the solid state. The reactivity of natural scheelite and wolframite with different salt solutions and in mixtures with other minerals was investigated.

Jan 1, 1989

By Ruirui Wei, Mingrui Yang, Xuewei Lv

Calcium ferrite, as the main bonding phase in the sintering process, greatly influences the property of sintered ore. Ultrasonic vibration has been widely applied to the treatment of metals to improve the properties of metals. In this work, ultrasonic vibration was introduced into the calcium ferrite and numerical simulation was carried out by solving the Rayleigh-Plesset equation to investigate the influence of ultrasonic conditions, including frequency, power and initial radii of cavitation bubbles on the cavitation bubbling behavior in calcium ferrite melt. The results indicated that lower ultrasonic frequency, higher power, and an appropriate initial radius of bubble promotes ultrasonic cavitation.

Mar 1, 2018

By Shengli Wu, Wei Huang, Xinliang Liu, Kaifa Zhang

The slagging behavior, the phase of primary blast furnace slag and its transformation law of structure for the single furnace burden were studied in this paper. The results showed that the formation of primary slag was controlled by CaO/SiO2, Al2O3 content, MgO content, reducibility, iron content and porosity of the furnace burden. Fayalite (2FeO•SiO2) was easily formed from acid ferrous furnace burden while kirschsteinite (2(Fe,Ca)O•SiO2) was produced from alkaline ferrous furnace burden

Jan 1, 2015

By S. P. Vanka, B. G. Thomas, S. Sivaramakrishnan

"During the continuous casting of steel, transient 'flow events can be very important to the generation of quality problems, such as shear entrainment, surface level fluctuations and bubble entrainment. These phenomena can be better predicted using Large Eddy Simulation (LES) models than the K-E models, which have been extensively studied. In this work the turbulent transient flow in a water model of a continuous caster has been both simulated using LES models and measured using Particle Image Velocimetry (PIV). The results of PIV and LES have been compared to validate the LES model and also to enhance the understanding of the prominent transient features of the flow field. The flow near the top surface in PIV was found to contain periods of 5-1 Os when the velocities were three to four times their mean values, which is of importance to the shear entrainment of the liquid flux. In both simulation and PIV the upper roll structure is found to change chaotically from a single large recirculation structure to a set of distinct vortices. The inlet swirl in PIV is seen to persist more than halfway across the mold, causing a characteristic staircase velocity vector pattern when viewed in a plane parallel to the wide faces. The lower rolls in PIV are significantly asymmetric for very long periods of time (- I-hour) and go through a repeating sequence of features. One of these features involving a short circuit between the upward and downward flow in the lower roll is also seen in the simulation and is of significance to bubble entrapment.IntroductionThe turbulent flow through the nozzle and in the mold of the continuous caster has been studied extensively using computational Reynolds Averaged Navier Stokes (RANS) models of turbulent flow [1,2]. Defects, such as internal inclusion of liquid fl4x through surface shear, pencil pipe defects due to bubble entrapment, surface defects due to level fluctuations are caused by transient flow phenomena oc'curring in the mold. These phenomena can be better predicted using transient Large Eddy Simulation [3] or ""LES"" models."

Jan 1, 2000

By Lei Wang, Jianjun Wang, Lingen Luo, Zhengbang Li

Dearsenication in molten steel was studied by adding Ca-Fe Alloy-based arsenic removal agent. In order to improve the utilization rate of Calcium Iron Alloy and improve arsenic removal ratio, [O] is less than 0.0005% and [S] is less than 0.0035%, Al is added into the molten steel. In the processes of adding CaO-Al2O3 based alkalinity slag for arsenic removing in molten steel (initial arsenic content is 0.0080%), arsenic removal ratio reaches 50% when Ca-Fe Alloy addition amount is 18%. During the arsenic removal experiment, adding Rare Earth promotes the arsenic removal reaction and makes the arsenic removal more effectively.

Jan 1, 2015

By V. I. Lakshmanan

"Historically flowsheets are developed for efficient separation of metals for economic recovery. With increasing emphasis on reduction, reuse and recycle (3Rs) efficient methods are sought to recover values from a variety of feeds where cost of collection, transportation, local consumer behaviour and regulatory guidelines dictate the development of economically viable flowsheets. Innovative understanding of potential market applications can provide means to develop value added end products. The paper with examples will discuss the use of innovative-separation technologies to obtain value added end use materials from secondary sources.IntroductionFlowsheets are developed for the efficient separation of materials of value for economic recovery. However with increasing societal pressures and regulatory initiatives for stricter environmental guidelines, there is strong need to provide focus to recover materials efficiently and economically in an environmentally accepted manner. North American industries are increasingly caught between demands for high technology value added products and responsibility for environment. An aspect that is receiving increasing attention is Design for Environment'. This incorporates a system wide approach for product design and incorporates environmentally preferable features such as recyclability, disassembly, maintainability, reusability and use of safe materials as part of a product's design objectives.The present paper with case histories will address innovative flowsheet development to convert wastes into recyclables value added products or for minimising generation of waste materials. Case HistoriesProcess for Separating Fibres from Composite Materials 1In the automotive industry, sheet molded compound (SMC) is used to produce panels, bumpers and the like. During the manufacture and at the end of life, considerable waste materials are generated which are potentially recyclable. Fibre reinforced plastics where fibre substrate impregnated with thermosetting resin, find applications in several manufacturing processes and are potentially recyclable at the end of life."

Jan 1, 1996

By C. Hakan Gür

Optimization and control of the microstructure is important for improving the properties of steel components. Development of non-destructive techniques for microstructure characterization is a critical task. Magnetic Barkhausen Noise (MBN) technique is a promising and challenging non-destructive technique fo automated evaluation of microstructures in steel components in a fast and reliable manner. This paper presents the results of MBN measurements for microstructure characterization of the quenched and tempered steels.

Mar 1, 2017

By Theo Lehner

The Rönnskär smelter has wide experience in the field of recycling of non-ferrous metals. Today, smelting and refining from primary and secondary raw materials are integrated in a complex flow sheet. Boliden operates a lead flash smelter, a lead refinery, a copper smelter and refinery, a sulphuric acid and sulphur dioxide plant, a slag fuming plant and precious metal plant at its Rönnskär smelter in the North of Sweden. The Business Area Smelter Operations also incorporates Boliden Bergsöe, Sweden's lead-acid battery recycler, and Norzink, Norway, where recycled zinc accounts for more than 20% of it's production. Raw materials for the Rönnskär smelter include concentrates, ashes, slags, metallic scrap, electronic scrap and electric arc furnace (EAF) steel-making dust. This paper briefly describes current operations and illustrates current measures to improve productivity. Limits to recycling as experienced by a non-ferrous smelter are, illustrated. The deportment of critical elements contained in raw materials is also discussed.

Jan 1, 1998

By Michael K. Rhodes

A 120 tonne per day BacTech bacterial oxidation plant treating refractory gold concentrates for Gold Mines of Australia's Youanmi project in Western Australia commenced operation September 1994. This was the first commercial application of the BacTech process. A pilot plant trial on concentrates produced from Youanmi ore was carried out at BacTech's laboratory in Perth. Results and measurements from this trial were used by Signet Engineering Pty Ltd to design the commercial plant. This paper cover the results obtained from the piloting, their implementation in the plant design and the initial commissioning of the full scale plant.

Jan 1, 1995

By John E. Litz

The Denver Process is a chemical/metallurgical process for treating radioactive or mixed wastes by extraction and concentration of the radioactive and/or hazardous component(s). The process was developed at bench scale, evaluated at pilot scale, and will be implemented at full scale to remediate a low-level radioactive sludge. Six unit operations comprise the process: feed handling, leaching, solvent extraction, electrodeposition, precipitation, and tailing preparation. Unit operation design may be modified to tailor the process for varying feed stock composition. Radioactive or mixed waste is reacted with aggressive reagents in an aqueous phase, solubilizing targeted components. These components are then selectively extracted and concentrated in subsequent steps. Waste solids and solution exit the process as non-hazardous non¬radioactive waste. Dehydration of aqueous waste by submerged combustion eliminates aqueous discharge.

Jan 1, 1994

By HeeDong Lee, Owen Reedy, Lawrence Matson, Naidu Seetala, Thomas Key

Spark Plasma Sintering (SPS) consolidated ZrB2+SiC composites using nano-powders (around 40 nm) showed smaller grains compared to those using micron size powders and segregation of SiC into islands is minimal but with higher oxidation of ZrB2 to form ZrO2 in nano-composites. Argon-gas purging prior to SPS consolidation at around 2000 °C and 40 MPa of ZrB2+20vol.%SiC nano-powders was used to minimize the oxidation and obtain fine granules with high densification. The densification of the Argon-gas purged nano-composites is higher compared to those consolidated without Argon gas purging. The EDX analysis showed a strong reduction in the oxygen peak for the Argon gas purged composites. The XRD spectra also support this observation with less ZrO2 phase composition in Argon gas purged composites. The Vickers micro-hardness showed slightly lower values for Argon gas purged composites though they have higher densification.

Mar 1, 2017

By Du Sichen, S. Seetharaman, Wei Liu

"The viscosities of two-phase mixtures are of great importance in the modelling of the fluid flow in metallurgical processes. For example, in steel making and refining, the intimate mixing of metal droplets in the slag phase requires a consideration of the effective viscosities for the mixture. The present work was aimed at an understanding the phenomena underlying the viscous flow in a two-phase mixture with widely differing viscosities.Emulsions of silicone oils of known viscosities (345mPa.S and 1010mPa.S at 293K) with small amounts of water evenly distributed in the same were prepared by subjecting the mixture to uniform stirring using a magnetic stirrer. The viscosities of these emulsions were measured at constant temperature by rotating cylinder method using Brookfield Digital Rheometer. The uniformity of the preparation of the emulsions was confirmed by the reproducibility of the results. Th7 measured viscosities were generally found to be independent of the torque under the experimental conditions so that the two-phase mixture could be considered as a Newtonian liquid. The variation of viscosities with temperature and the effect of addition of a surface-active substance were also studied in this work.The measured viscosities were found to be· higher than those of both pure water and silicone oil. The experimental viscosities were found to increase with increasing concentration of water. The influence of surface tension on the viscosities was examined by adding surfaceactive agent to the mixtures. The result is discussed and compared with theoretical models developed by Einstein, Taylor and Oldroyd."

Jan 1, 2000

By Ali S. Al-Watban

"In this paper, the room temperature friction and deformation properties of various polycrystalline diamonds; i.e. aggregates of diamond crystals with a ""binder"" phase of cobalt and a polycrystalline coating produced by a chemical vapour deposition processes (CVD) were studied when softer metallic and ceramic sliders were used. The experiments were conducted· at relatively low sliding speeds (10 mm/min), in a vacuum of 10-5 mbr after having cleaned the specimen surfaces by out-gassing them for about 30 min at 800 °C. As a result of increasing the number of traversals significant wear of the coated diamond by softer metallic sliders (aluminium and mild steel) was observed. With ceramic sliders, it is shown that the multiple traversals result in the formation of wear groove. With diamond silicon carbide, high friction and adhesion lead to significant metal transfer which then pre-empts cumulative deformation of the harder materials. With the diamond-cobalt composite, the friction is surprisingly low, there accumulation of wear debris on the tip of the slider but no permanent transfer of metal and the harder specimen is not damaged even after 5000 traversal.IntroductionPolycrystalline diamond is mainly produced as tool materials for the machining of hard metals and composites. Thus, the sliding friction and wear resistance are amongst the most important properties relevant to those applications.During cutting by PCD the wear mechanism is mostly influenced by the chemical affinity between the tool material and the workpiece. For example, diamond based materials are not recommended for machining ferrous materials because carbon is highly solubie in iron: This leads to the graphitisation of diamond particles and hence a high rate of diffusion wear is observed (Brookes and Lambert, 1982)."

Jan 1, 2000

By B. S. Terry

Experiments have been conducted to assess the feasibility of capturing bearing emissions arsenic with CaO during the roasting of enargite (Cu3AsS4). Enargite/CaO mixtures have been heat treated in air, nitrogen or oxygen for various times and the products of reaction analysed by X-ray diffraction and cleaned analysis. The results show that substantial capture of arsenic can be achieved via the formation of calcium arsenates and/or calcium arsenides. In addition significant capture of sulphur is achieved by the formation of calcium sulphate andlor sulphide. Complete conversion to copper sulphide with total removal of arsenic can be achieved within 30 minutes at 700°C. Further heat treatment in air or oxygen leads to the formation of copper oxide and copper oxysulphate. Without optimisation of reaction conditions, it has proved possible to achieve retention of in excess of 85% of the arsenic content of enargite in the form of calcium arsenates.

Jan 1, 1994

By Michael E. Stout

M.A. Industries, Inc. has developed and is now offering on a commercially available basis, complete systems to recover and recycle lead from spent SLI batteries. The system begins with the breaking and separation of the component parts of the batteries and subsequent treatment of the effluent water produced by this operation. The recyclable materials recovered from this process are metallic lead, lead paste and polypropylene. The lead paste is introduced into a process to convert it from a lead sulfate to a lead carbonate. The process also regenerates the salt solutions into reusable carbonate. The lead carbonate is then leached into an acid bath where it is later recovered by a proprietary electrolytic process. The metallic lead is recovered in a short rotary furnace producing metal for further refining and alloying. The polypropylene is further washed and then introduced to a reclaim extruder along with the proper modifiers and additives. The resulting resin can then be sold on the open market to injection molding processors. This complete system greatly reduces the amount of waste to be disposed of and completely complies with all applicable EPA guidelines.

Jan 1, 1993

By Jun Deng, Daohong Wu, Zhicheng Cao, Jingkun Tang, Luxing Feng, Xun Xue

The effect of reducing temperature, H2/CO mole ratio, and reduction gas flow rate on the metallization rate of oxide pellets were investigated at laboratory scale, with ludwigite iron concentrate used as raw materials. The reducing temperature varied from 850 to 950 °C, the H2/CO mole ratio changed from 1.5 to 4.5, the range of reduction gas flow rate was from 2 to 5 L/min. The results indicate that the metallization degree of pellets increase with increase of the temperature, H2/CO mole ratio, and gas flow rate. However, after temperature rises to 850 °C, metallization degree increases slowly. The effect of H2/CO on the metallization degree is not very obviously with the ratio of H2/CO increasing from 1.5 to 4.5. When the gas flow rate was increased from 2 to 3 L/min, the metallization degree increased greatly from 72.2 to 92.1%. In the flow range from 3 to 5 L/min, the metallization degree was increased slowly. The results obtained could be useful for comprehensive utilization of ludwigite iron concentrate by gas-based direct reduction method.

Mar 1, 2017