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By Elsa Agante

Recycling of solid wastes, a common practice nowadays, requires the separation of the different materials in order to increase the products added value. The separation of one plastic from mixtures of different types of plastics is not easy due to their similar physical properties, but different techniques are available, from automatic sorting systems based on optical sensors to techniques adapted from mineral processing, namely gravity, froth flotation and electrostatic processes. In the last decade, many researchers have addressed the separation?s problem of different polymers, like Polyethylene Terephthalate (PET) and Polyvinyl Chloride (PVC), two polymers commonly used in packaging which have similar density. One proposed technique is the classical froth flotation performed in agitated cells. Froth flotation is a versatile and relatively cheap process widely used in mineral separation. It is based on the different behaviour of particles in the presence of an inter-phase air-water, which depends on the materials surfaces properties. Froth flotation can be affected by some variables such as impeller speed and air flow rate. Agitated cells, when used with low density materials, like plastics, can produce overstated turbulence that prevents the adhesion and collection of particles in the froths. In this case, separation is favoured by column flotation smoother hydrodynamics. This paper proposes the separation of PET from PVC by column flotation. The experimental work was carried out in a column of 9cm diameter and 1m high. The effects of some operating conditions, such as depressor and frother concentration, air flow rate and feed grain size on products grade and recovery were evaluated and the best flotation conditions for the separation of these plastics were established.

Jan 1, 2006

By Gaifeng Xue, Lei Zhang, Aimin Duan, J. Y. Hwang, Lina Wang

"The removal of chemical oxygen demand (COD) from coking wastewater was experimentally investigated using a three-dimensional electrode reactor. The experimental results showed that the refractory organics in coking wastewater can be effectively removed by this process, and COD removal efficiency was affected by the operating parameters, such as electrolytic retention time, particle electrode dosage, initial pH, current density, aeration amount and electrical conductivity. The experimental results show that the three-dimensional electrode could have a COD removal efficiency of more than 60% and a running cost of no more than 6 YUAN (RMB)/t. This indicates the great potential of a three-dimensional electrode reactor in engineering applications as an advanced treatment methods for coking wastewater.IntroductionCoking wastewater is generated from coal coking, coal gas purification, and by-product recovery processes of coking; it is composed of phenolic compounds, heterocyclic compounds, polycyclic aromatic hydrocarbons, ammonia, cyanide, polycyclic nitrogen-containing aromatics, acyclic compounds, etc. Most of these constituents are refractory, poorly biodegradabile, toxic and carcinogenic [1-3]. Currently, coking wastewater is usually treated by different forms of A/O biological nitrogen removal processes as the primary treatment means, but the aforementioned processes are not efficient enough to meet the requirements of the National Discharge Standard in China (GB13456-1992). According to the continuous requirement on improving environmental protection for the coking industry (revised 2008), increasing wastewater utilization ratios and reducing the discharge of effluent in the coke industry have to be implemented for cleaner production and sustainable development. Therefore, advanced technologies need to be developed to treat coking wastewater and reutilize the product as industrial cooling water, which would be one of the best choices to achieve zero discharge of wastewater and reduce water consumption per ton of steel produced. In this study, a three-dimensional fluidized bed electrode reactor was adopted for the advanced treatment of coking wastewater, and the effects of operating conditions, including particle dosage, initial pH, current density, supporting electrolyte, as well as aeration amount on the COD removal rate, were investigated. Its running costs were also estimated."

Jan 1, 2012

By N. Solak

CrN, TiN and Ti-B-N coatings were deposited onto H13 hot-working tool steel and alumina substrates by arc-PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Samples coated on H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coatings deposited on alumina substrates. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Oxide scale thickness change and TG data were used to calculate oxidation reaction activation energies. It was determined that boron addition into TiN coating improves not only mechanical properties but also oxidation resistance. Depending on the substrate material different oxidation activation energy values for the TiN and Ti-B-N coatings were determined revealing the importance of film morphology on oxidation resistance.

Jan 1, 2006

By Patrick R. Atkins

Energy issues will have increasing impacts on decision making in all facets of society over the next few decades. Industrial users of energy and producers of products that affect energy use must be fully aware of the implications of their processes and products on the energy situation. This paper describes a model that has been developed for the aluminum industry that allows scenarios to be evaluated to gain improved understanding of possible implications for our businesses. A brief overview of the model is provided.

Jan 1, 2006

By V. G. Papangelakis

The implementation of a flow-through yttria-stabilized zirconia (YSZ) sensor for pH measurements in high temperature and concentrated electrolyte systems relevant to hydrometallurgical processing of nickeliferous laterites is discussed. Instrumentation involved the use of a custom made flow-through titanium electrochemical cell. Accuracy and validity of the pH measurements at temperatures up to 250C were assessed using concentrated sulphate process solutions ranging from synthetic binary sulphuric acid ? water solutions to progressively multicomponent metal ? sulphate solutions simulating laterite Pressure Acid Leach conditions. The measurements were also compared with theoretical models using recently obtained thermodynamic data. A difference of ±0.25 pH units was observed between measured and calculated pH values at temperatures. This is an acceptable difference given that these are the first direct high temperature pH measurements ever on the concentrated acidic sulphate solutions. This result is encouraging more research for the development of industrial electrochemical systems for direct pH measurements in autoclaves.

Jan 1, 2003

By Paul B. Queneau

U.S. plants solely devoted to recovering values from metal-rich wastes have established market niches based on one or more competitive advantages: superior process technology, access to key feedstocks, unique equipment, special knowledge of markets, and an appropriate exit for outfall water. Plant methodology, competitiveness, environmental factors, and economics are examined, with particular attention to feedstocks, technologies, products, and outputs.

Jan 1, 2003

By L. B. Tsymbulov

At present data on thermodynamic properties of metallic melts, containing copper and ?iron family? metals, is rather limited. Determination of the activity of metallic melts components under high temperature by experimental methods requires high level of labour inputs. With this it is not always possible to obtain the results with high level of accuracy. Due to that in a number of cases it is more appropriate to apply different methods of analysis, with the help of which there can be calculated thermodynamic properties of ternary and even more complicated systems, prominent thermodynamic properties of binary systems being used as a basis for these calculations. This work presents the results of calculations of different components activity and activity ratio in such ternary system melts as Ni-Cu-Fe, Ni-Cu-Co, Fe-Cu-Co and Fe-Co-Ni. Good compliance of calculations results with those obtained in the course of reliable experimental investigations fulfilment is demonstrated. There are presented the results of activity and activity ration analysis for some compositions of Cu-Ni-Co-Fe system.

Jan 1, 2006

By John A. Gisby

Phase equilibria for multi-component systems can be calculated reliably from critically assessed thermodynamic data for sub-systems using software packages like MTDATA, developed by the National Physical Laboratory, UK (NPL). Models and data resulting from an ongoing Mineral Industry Research Organisation (MIRO) project make such calculations possible for the complex systems encountered during sulphide smelting, involving interactions between matte, slag, metal, and gas phases. Predictive calculations can be made that are directly relevant to industrial processes, covering composition and temperature ranges beyond the scope of hard- copy phase diagram compilations, allowing the feasibility of more economic and environmentally sound routes to be explored, better choice of materials to be made, and pilot plant studies to ,be directed more efficiently. Current applications include the selection of suitable fluxing practices in copper and nickel smelting, analysing the operation of the Kennecott copper smelter, optimising the recovery of precious metals and investigating refractory wear.

Jan 1, 2002

By M. D. Bishop

Loss of organic solvent extraction circuits occurs through several accepted methods. Losses are commonly attributed to entrainment of the plant organic and evaporative loss of diluent. Evaporative losses of diluent have been estimated using various models or by considering all losses over and above entrainment to be due to evaporation. Other possible loss mechanisms are discussed and data on losses during weather conditions are presented. Accurate estimation of evaporative loss is vitally important to the industry due to both cost factors and environmental concerns. Data for and description of the Diffusive Flux Model are presented as an improved-method of estimating evaporative losses:

Jan 1, 1999

By Barry T. Kilbourn

There is a continuous quest for better-performing materials, for example, to withstand higher temperatures, to resist more efficiently degradation or to be electrically conductive under extreme conditions. The oxides, and similar compounds, of the lanthanides and yttrium can, in some cases, help provide such behavior. Other advanced materials, such as hydrocarbon catalysts, optical ceramics or sensitive phosphors, may also require these oxides for some essential function. The role of the oxides in a wide variety of technologies, some novel and developing, will be reviewed and the underlying physico-chemical principles, the common threads, between several less well-known and apparently unrelated uses discussed.

Jan 1, 1989

By Michael J. Virnig

The formation of crud is a normal part of operating a solvent extraction circuit for the recovery of copper. It periodically must be removed from the circuit. This results in significant costs in terms of manpower, downtime, and loss of circuit organic. Field studies have been carried out that show that the presence of a thermodynamic modifier in the organic phase contributes to crud formation. In an effort to better understand what factors contribute to crud formation, laboratory studies involving competitive adsorption studies with model solids have been carried out. The results of these laboratory studies will be integrated with the results of the field studies to present a better understanding of crud formation.

Jan 1, 1999

By C. K. Gupta

Electrometallurgical processes have a definite place in the extraction technology of rare earth metals and alloys. Some of the advantages of the molten-salt electrometallurgical processes include fast electrode reaction, providing accurately controlled large amount of energy to a relatively small reactor volume, negligible over voltage, simplicity of operation, and possibility of accomplishing continuous or semicontinuoue operations. This paper provides a vivid account of the theoretical and practical aspects of electrometallurgical processes for the production and processing of some of the rare earth metals and alloys. Reference has been drawn to the work reported on electrometallurgical processes as applied to the preparation of lanthanum, cerium and misch metal from author's laboratory.

Jan 1, 1992

By A. Robles

The main goal of the present work is to propose a viable alternative for selective arsenic elimination from copper smelter flue dust without the need of a global leaching scheme for all the individual components of the flue dust. Using this alternative, the inherent copper recovery problems are avoided. Arsenic precipitation is also considered for regenerating the solution and completing the process cycle. The experimental results for arsenic extraction and precipitation are satisfactory. Concentration of NaOH used was relatively low. The main reason for succeeding in high arsenic extraction and low NaOH consumption is due to the previous water washing of the flue dust. Water washing dissolves much of the iron and copper that are present in certain percentage as sulphate.

Jan 1, 1999

By E. R. Vance, D. R. M. Brew

"Historically, Ordinary Portland cement has been the preferred medium to immobilise arsenic. However, arsenic in cement gives rise to calcium-arsenic phases and their known decomposition to calcium carbonate and arsenic trioxide via atmospheric carbonation raises serious questions about the long-term suitability of cement for arsenic immobilisation. Alternative matrices such as low-temperature ceramics (LTCs) potentially offer superior resistance towards carbonation owing to the absence of calcium. Consequently, the potential for arsenic immobilisation using LTCs has been investigated. Both AsIII and AsV have been incorporated and samples assessed according to a standard leaching protocol. AsIII persists in the porewater of alkali-bonded LTCs as sodium arsenite rendering them unsuitable for immobilisation. Thermal treatment of these LTCs to consolidate the microstructure and reduce open porosity resulted in sodium-rich cryptocrystalline matrices that leached arsenic and sodium readily. The omission of sodium in acid-bonded LTC formulations resulted in leach data that were close to the target value of 5 µg/ml in Toxicity Characterisation Leaching Protocol tests.IntroductionArsenic is a carcinogenic substance and its adverse effects of on humans, flora and fauna have been well documented [1-5]. As a consequence, many papers have been written on the prospective handling of arsenic-bearing waste. These can largely be divided into: (a) cleanup of arsenic-contaminated water using bacteria, precipitation, and/or UV irradiation to generate arsenic-rich sludges for subsequent immobilisation; (b) cleanup of arsenic-contaminated soil via chemical extraction for immobilisation of the As concentrate; and (c) immobilisation of industrial waste contaminated with As."

Jan 1, 2008

By Eliezer Martinez-Jimenez, Gretchen T. Lapidus

"Electro-assisted reduction is an effective pretreatment to render chalcopyrite less refractory towards oxidative leaching. In this process, chalcopyrite is selectively converted to chalcocite or copper metal in an electrolytic cell under ambient conditions, while ferrous ion is leached into solution. However, the reaction velocity is hampered by the formation of a ferrous sulfide passivating layer on the solid surface, especially at elevated solid to liquid ratios. In the present work, several strategies for overcoming this problem were evaluated. On one hand, specific ligands for ferrous ion were added in order to increase its solubility and, on the other, an anode material which promotes the oxidation of the sulfide ion was chosen. Leaching tests showed citric acid to be an effective ligand for both ferrous and ferric ions and, in combination with a lead-silver anode, significantly increased the kinetics of chalcopyrite reduction and subsequent copper leaching.IntroductionAttempts to oxidize chalcopyrite at a rapid rate in aqueous solutions, below their normal boiling point, have met with difficulties because of passivation by some of its own components. An alternative line of research explores reductive pretreatment, transforming the chalcopyrite into less refractory copper phases, which can later be oxidized. A recompilation of these efforts up until 2000 was published by Dreisinger and Abed [1]. However, this practice usually requires large excesses of reducing agents, such as copper, lead, aluminum or iron, and in this last case at near-boiling temperatures, in highly"

Jan 1, 2012

By Peter Schwartz

This paper presents GBN's "Global Scenarios" for the first decade of the 21st century. We describe a set of key scenario actors and develop 6 driving forces in demography, technology, climate change, macroeconomic change, globalization, and geopolitics. We argue that a set of majorchallenges to world systems of commerce and politics will coalesce in the next several years. We develop four scenarios which differ according to how these challenges are handled, and which scenario actors play the key roles in managing the transition.

Jan 1, 1999

By M. W. Wadsley

Despite the convenient subdivision of extractive metallurgy into hydro- and pyro- divisions, many flowsheets contain both types of process. When complex materials are used as feed, combinations of hydro- and pyro-metallurgical processes are even more common. Hydrometallurgy is used to treat many by-products and waste-products. (Bio-metallurgical processes may be considered to be a sub-set of hydro-metallurgical processes.) Combinations of the different processes in the Australian metallurgical industry are described. Selected international examples demonstrate that the use of combked processes is not a unique. Antipodean phenomenon. The motives for selection of combined pyre- and hydro-metallurgical processes in a flowsheet are examined.

Jan 1, 1994

By Michael S. Moats

As commercial copper electrorefineries look to expand their capacities by increasing their operating current density, the likelihood of anode passivation intensifies. To improve the industry?s understanding of the passivation phenomena, the role of anode composition was evaluated. While previous studies have focused on studying one impurity element at a time, this study was conducted using forty-four commercial electrorefining anode samples supplied by ten copper companies The passivation response of each sample was evaluated under accelerated galvanostatic conditions in synthetic copper electrowinning electrolyte at 65°C. This information allows for correlations between composition and passivation tendencies over a wide range of impurity elements and concentrations. It was found that selenium, tellurium, silver, lead and nickel accelerated passivation. It appeared that oxygen accelerated passivation when increased from 500 to 1500 ppm, but further increases did not have an effect. Arsenic was the only impurity found that inhibited passivation.

Jan 1, 2006

By R. D. Prengaman

Wrought lead-calcium-tin anodes developed by RSR Corporation have improved the performance compared with the other lead alloy anodes. These anodes have been in continuous service at various locations around the world for as long as fourteen years. Calcium provides mechanical strength to the anode to prevent the deformation while tin increases the mechanical strength, reduces the rate of corrosion, prevents the formation of non-conducting layers on the anode surface, and dramatically improves the conductivity of the anode. Tin is also instrumental in developing the unique rolled structure of the anode which leads to the reduced rates of corrosion, longer life, and improved oxygen evolution. Cobalt additions to the electrolyte further enhance the oxygen evolution and improve the anode life. Higher current densities and higher operating temperatures reduce the anode life. The unique patented method of attaching the rolled anode sheet to the bus bar substantially reduces the resistance of this important joint and offers the substantial savings in power over the life of anode.

Jan 1, 1999

By Ron H. Schonewille

Experiments were conducted by injecting air-oxygen gas mixtures through a ceramic lance into molten copper matte and measuring the sulphur dioxide content of the offgas. The injection conditions were characterized by measuring pressure fluctuations immediately upstream of the lance and capturing the information on an oscilloscope screen. The parameters investigated were gas flowrate, lance geometry, lance immersion, orifice diameter and melt composition. An overhead nitrogen lance was used in specific tests to create an inert gas blanket directly above the bath surface to inhibit reaction in this region. The extent of oxidation was modeled by separating the gas-liquid contact into three stages; bubble growth, bubble rise and bubble rupture. The contribution of each stage to oxygen utilization was determined by varying the lance immersion and by performing tests both with and without an inert gas blanket. Bubble rise was found to be relatively unimportant, accounting for less than 5% of the total oxygen utilization. Bubble rupture and bubble growth were found to contribute approximately equally, with bubble rupture becoming more important with increasing gas flow rate. This study highlights the importance of reactions taking place above the bath surface in a copper converter.

Jan 1, 1999