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By C. P. Broadbent

Due to growing .public awareness of environmental issues and greater sensitivity towards waste management, many countries around the world are implementing more stringent legislation governing the storage and disposal of hazardous wastes containing heavy metals such as As, Sb, Pb, Cd or Hg. These wastes can no longer be dumped without providing clear guarantees that the material concerned is environmentally safe and will not leach toxic elements to the surroundings. In the Netherlands the current dumping charge for chemical waste (i.e. worst category) is $280/t, and for industrial waste this cost reduces to $75/t. If the material can be reused there may be a small positive credit for selling it, for example discard slag as an aggregate to the construction industry. A number of (pyre)-metallurgical operations, mostly associated with the extraction of metals from sulphidic ores, produce arsenic residues in the form of As2O3 containing flue dusts and speises. If the flue dust is of high purity it can be sold, though many traditional uses are being substituted by other materials. In many cases upgrading the quality of the arsenical dusts is not possible for either technical or economic reasons. Traditional practice is to dissolve these dusts in acid prior to precipitation as ferric arsenate, which is at present classified by many countries as industrial waste and can be dumped. Recent work, however, has cast doubt on the stability of arsenates for disposal and alternative disposal routes have been investigated. Tests have shown that up to 10% (dm) As can be incorporated into "glassy" silicate slags with very low levels of arsenic leaching in the cooled product. Calcium arsenate was added to a range of synthetic and industrial slags from the system SiO2-FexOy-CaO-A12O3-AsmOn, under mildly oxidising conditions and quenched subsequently in water. It would appear that this represents an environmentally acceptable method for the disposal of many arsenical residues and there is some optimism that this method will be equally applicable to the disposal of other toxic metal residues.

Jan 1, 1994

By S. Aguayo-Salinas, J. L. Valenzuela-García, A. L. Leal-Cruz, M. I. Pech-Canul, M. T. Certucha-Barragán

"The aim of this research was to carry out a comparative and systematic study of the degradation of cyanide by hybrid natural/biodegradation and biodegradation methods using a mixture of Pseudomonas sp and Bacillus megaterium native bacteria. Bioreactors consist of filled columns with contaminated ore containing 100 ppm of total cyanide. In the biodegradation tests a mixture of bacteria was inoculated into the biodegrading solution. Results of cyanide degradation show a similar asymptotic behavior in both the hybrid (opened system) and biodegradation (closed system) methods; however, for the same period of time (72 h) the permissible maximum levels (1-2 ppm of cyanide) are only attained in the closed system. While in the closed system the cyanide levels are reduced from 100 to 1.5 ppm, in the open system, cyanide decreases from 100 to 2.4 ppm.IntroductionOne of the most important tasks of mining industry is the treatment of the wastes generated in mining operations. Accordingly, industrial waste waters and ores represent a complex problem and a great challenge. In addition to ethic and communitarian considerations, there are laws that prohibit or regulate the contamination of water and air. Moreover, they establish that the restoration of wastes must be considered as a necessary operation cost [1]. Currently this important problem is being addressed by the mining and metallurgical industries using different approaches; mainly they are focusing on the treatment of waste waters and ores generated by the leaching process in which cyanide is used as a leaching agent for the recovery of precious metals as gold and silver. Cyanides have toxic characteristics and thus negatively impact the environment when they are discharged to the ground without previous treatment. While there are some processes in current use there are others that have only been proposed and that allow cyanide degradation, transformation to less toxic compounds and/or the complete elimination of cyanide. The second group includes a variety of techniques that use natural, chemical and biological treatments. Natural treatments consist of the passive abandoning of the heap and of its washing with water. Since these processes are slow and generate great volumes of water partially contaminated, then other alternatives should be considered."

Jan 1, 2008

By F. J. Tavera

A study on the electro kinetics of lead carbonate, silica, and alumina, in aqueous media was carried out at different pH values. The behavior of potential was determined for these species in the pH range between 3 and 12. Homocoagulation of lead carbonate in aqueous media is analyzed at its isoelectrical point. Lead carbonate heterocoagulation is analyzed with silica, alumina, and silica ? alumina mixtures at low pH values. The experimental results are considered for their possible application to treat residual water polluted with lead.

Jan 1, 2006

By Jackson Jenkins

The second survey of world copper SXEW plants has been completed. Solvent extraction and electrowinning data published in 1996 has been updated and leach data from seventeen plants is now included. The following pages list the results of the thirty- two plants that responded to the survey. Selected information is summarized in graphical form.

Jan 1, 1999

By Ahmad Umar

A variety of ZnO nanostructures such as sea-urchin-like structures composed of nanowires and nanorods, nanocombs, nano/micro spheres and cages, star-shaped ZnO nanostructures, flower-shaped nanostructures, needle-like nanostructures etc. have been synthesized applying two different fabrication techniques i.e. thermal evaporation and cyclic feeding chemical vapor deposition techniques at different reaction parameters such as reaction temperature, growth period, reactant concentrations, types of source material and substrates etc. It was observed from the experiments that the morphologies of the grown structures were highly influenced by the reaction parameters and fabrication techniques and specific morphology can be obtained at particular reaction parameters in a specific synthetic procedure. Extensive morphological investigations of the obtained products demonstrate that the grown structures are single crystalline and having a wurtzite hexagonal phase. Room-temperature photoluminescence spectra of all the deposited products exhibited good optical properties. Finally, the growth process of the fabricated structures were proposed and discussed in detail.

Jan 1, 2006

By Matthew Jeffrey

Leaching, cementation, electroplating and flotation are all electrochemical phenomenon. They are also key processes in the hydrometallurgical treatment of metals. Unfortunately electrochemical methods tend to be under-utilized when studying these processes and one possible reason for this is the confusion surrounding the large number of electrochemical techniques available. In this paper four former PhD students of Professor Ian Ritchie present an insight into how one electrochemical technique can be used to compliment rate/kinetic studies. The paper details how to perform the experiments, interpret data, and recognize complications with the results. Examples where this approach has been highly successful are presented, and include: cementation of zinc by aluminium, cementation of copper by nickel, cyanide leaching of gold and the cementation of gold thiourea by mild steel. The examples illustrate that this universal approach adopted by Ian Ritchie provides the key to understanding the mechanism of many hydrometallurgical reactions.

Jan 1, 2003

By Guozhu Ye, Mikael Lindvall

"Swedish iron ore contains about 0.1 %V. The vanadium is reduced to the hot metal in a blast furnace and oxidised to the slag in a converter. The high V-content, up to 5 % V, leads to a very limited external application of the steel slag in Sweden. Since 2004, MISTRA - the Swedish Foundation for Strategic Environmental Research has together with the steel and mining industry in Sweden and Finland initiated and supported a long term project aiming at efficient recovery of vanadium in the slag, and at the same time a useful slag product with low V-content. The proposed concept consists of a reduction step and a phosphorus removal step. This paper will highlight some of the results with focus on the various metallurgical reactors used for slag reduction, including results from recently performed pilot trials using a DC furnace for cotreatment of metallurgical slags and other wastes.IntroductionToday, less than half of the produced LD-slag in Sweden is recycled to the blast furnace as a lime source and the rest is temporarily stored inside the steel plant. The steel slags cannot be used externally due to its content of vanadium and free lime. As the slag storage area is limited, this has become a problem for Swedish steel producers. The disposition of the slag is also a great waste of a valuable vanadium resource. The current potential value of vanadium in the discharged steel slag annually amounts to roughly US$ 100 million. Currently, Swerea MEFOS is conducting an 8-year vanadium recovery project called VILD (Vanadium in LD-slag) aiming at efficient recovery of vanadium and at the same time producing a useful slag product with low V-content. The project is financed by MISTRA - the Swedish Foundation for Strategic Environmental Research and the steel and mining industry in Sweden and Finland. Various reactors and process options have been tested in the past 7 years, from 3 kg laboratory scale, 150 kg induction furnace, 3 MVA pilot DC furnace, 5 MVA pilot AC furnace, 5 tons Kaldo furnace, to full scale direct hot slag reduction in the industrial site (12 tons of slag). This paper will introduce the VILD-concept and review the experiences gained from these trials. The advantages and disadvantages of the different options will be discussed and concluded."

Jan 1, 2012

By O. C. Rojas

Improvements and modifications on lay out and process, from 1997 till 1998, are presented. Based on a Teniente Converter, started up 1993, a Strategic Development Plan was structured to increase the production efficiency and comply with the enviromental regulations, too. It considered the oxygen supplies to the Teniente Converter and Peirce Smith converters; reverberatory furnace shut down as a smelting unit; and the Teniente converter slag treatment through a combined process between a Slag Settler furnace and flotation. Also it included the off-gas handling and treatment.

Jan 1, 1999

By Pedro Morales C.

From its beginning in the 1970s, the Teniente Converter has consistently achieved continuous improvement, and has contributed to the competitiveness and sustainability of Codelco's copper operations. The later introduction of the Slag Cleaning Furnace technology has helped to create a full technology package, referred to as the Teniente Technology. This paper outlines the features of a new research and innovation program designed to bring the Teniente Technology as a modem, competitive technology into the 21st century. The overall objectives and features of the program are described and discussed. It is fully anticipated that these activities will help position the Teniente Technology as a world-class modem technology, well-integrated and operating in a fully continuous mode in conjunction with the other units at the plant, a competitive technology which operates in harmony with respect to environmental regulations.

Jan 1, 1999

By P. Barrios

Over a period of one year, an in-depth investigation was carried out in a conventional copper refinery to understand the behaviour of silver in copper electrolysis. The increase in silver content in the cathodes increases almost linearly with the duration of electrolysis, and the silver content of the electrolyte between the electrodes shows similar behaviour. The silver content of the cathode deposited daily depends directly on the silver concentration of the electrolyte and this, in turn, is strongly influenced by its internal temperature. The average temperature between the electrodes rises from the first to the second and to the third crop, because of the increase in the distance between the electrodes and the heat generated by the passage of the current. The mechanism of dissolution of silver from the anode, and its passage to the cathode, are discussed. Following the change to the Isa system, it was proved that the results and conclusions are analogous. Based on these results, a reduction of more than 20% in silver losses in the cathodes was achieved.

Jan 1, 1999

By T. Goda, H. Kiuchi, M. Iguchi

"IntroductionThe utilization of silver in the electronic industry has been increasing in recent years. It is desirable that valuable metals are recovered from the used scraps of these industrial goods. Condensor chips, for example, contain silver, palladium, and Ag-Pd alloy. The dissolution behavior of silver was studied assuming that scraps such as used condensor chips in which Ag-Pd paste is used are subjected to wet treatment.ExperimentalIn this study the powder, granules, and flakes of silver were used in these nitric acid leaching experiments. The nitric acid solution was agitated in a glass reactor with a magnetic stirrer and heated to the required temperature. The experiment was started by putting the silver sample in the solution. After the leaching, the solution was filtered and the concentration of silver in the filtrate was analyzed by ICP.ResultsIn dilute nitric acid of less than 5 N, silver powder dissolved easily with increase in the concentration of nitric acid and temperature. However, the more intensive the stirring of the solution was, the lower the dissolution quantity became. Fig. 1"

Jan 1, 2000

By J. Murphy

The economics of microbial coal desulfurization are affected significantly by the proper selection of the plant site and by maintenance of variables at suitable levels. High sulfur coal particles below 200 mesh show sulfate production rates triple those with 150 mesh coal but grinding costs are greater. Slurry solids density increases from 5% to 20% reduced the rate constant by a factor of 10. Coal added to a batch reactor in the stationary phase resulted in a sudden second exponential sulfate production phase indicating feasibility of lower cost continuous operation. Successful operation in the absence of beef broth, yeast or added nutrients at non-sterile conditions enhanced projected economics. Finally, the need for adequate agitation and aeration was well established.

Jan 1, 1985

By Helena Byrdziak

KGHM Polska Miedz S.A. is a significant European copper producer with production of 447,000 mtpy, operating three underground mines and three smelters. The company has been involved for years in environmental activity, which was stimulated not only by the company itself, but by the development of environmental regulations as well. The first set of regulations, concerning water protection, was' established in Poland' in 1974, while a comprehensive environmental law was passed in 1980. This law in general requires industry to submit all data of environmental significance to the local authorities. Based on this data, they establish limits concerning emissions into the air, water and ground, the amount of wastes produced and the means of their disposal. A company has to pay fees for each tonne of emitted substances and stored wastes. When the emission of a substance exceeds the limit, the company has to pay a penalty which is about ten times higher than the fees. This approach in general is effective because it forces companies toward: reduction of their emissions. The problem is that the law is constantly subject to change and is becoming not only more restrictive but is involving more and more bureaucracy.

Jan 1, 1999

By A. Raraz

The optimization of the plutonium electrorefining process has been studied on the basis of modeling and model materials. The plutonium electrorefining process has been reviewed and the basics of the electrorefining process with molten salts as electrolytes and under forced convection has been presented. The definition of the problem in plutonium electrorefining has been related to three factors and this research has addressed these three factors to provide an insight to this process. The hydrodynamic factor gives information on the behavior of the mechanically stirred system. The chemical stability and solidification factor shows the interactions among the components of the electrorefining cell. The electrochemical factor is oriented to study the efficiency of the electrorefining process on the basis of limiting current density, stirring rate and configuration cell. As a result of this study the optimization of plutonium electrorefining implies mainly a re-design of the cell.

Jan 1, 1995

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 Yongxiang Yang, Yanping Xiao, Robert G. Harskamp

"Stricter environmental regulations demand for safer treatment and disposal of incineratior fly ashes. So far no sound technology and processes are available for a sustainable and ecological treatment of the waste incineration ashes, and only partial treatment is practised for temporary and short-term solutions. New processes and technology need to be developed for comprehensive utilization and detoxification of the MSW (Municipal Solid Waste) incinerator residues. The objective of the current research is to better understand the behaviour of the environmental harmful elements during low or high temperature treatment, and to find an optimum route for an efficient processing of the incineration fly ash. In the present study, the fly ashes including boiler ash and ESP (Electrostatic Precipitator) ash sampled from a MSW incinerator were washed with warm water, and the residues were dried and sintered or vitrified at high temperatures. The solutions from ash washing were analysed, and will be treated for salt extraction and purification. The ash residues before and after thermal treatment were also analysed. The results of vitrification and thermal behaviour were compared with those from the ashes without pre-washing. It was found that water pre-washing is an efficient way to remove certain water-dissolvable volatile salts such as chlorides, and thus the secondary emissions during vitrification could be reduced. INTRODUCTION The air pollution control residues from MSW incineration are classified as harzardous waste, including boiler ash, ESP ash and filter cake. The boiler ash is the firstly settled flue dust in the dust-collecting equipment under the boiler, the ESP ash is collected by an electrostatic precipitator in the second step, finally the flue-gas is further cleaned by the wet-scrubbers and residues are accumulated in the filter cake. Both the boiler ash and ESP ash are classified as hazardous materials, harmful to the environment due to the high concentrations of environmental hazardous elements. However, due to the different locations of the ash collection, the boiler ash has different compositions compared to the ESP ash, and is considered less toxic. Fly ash is generally toxic and with low bulk density, and has to be treated before final disposal. The current industrial practice is normally the landfilling after partial detoxification such as cement solidification."

Jan 1, 2008

By H. J. Thevik, A. K. Dahle

"A mathematical model that calculates the stress development in a coherent and stationary dendritic network due to interdendritic flow is proposed. The fluid flow is assumed to be related to the solidification shrinkage, and under the assumption of no porosity formation and unidirectional solidification, the shrinkage-induced flow within the mushy zone is calculated analytically. The interdendritic melt flow exerts a force on the solid network and an analytical expression for the stress build-up in the network is developed. Parameter studies illustrating the influence of cooling conditions, mushy zone length, dendrite coherency, fraction solid, volume fraction of eutectic, and solidification shrinkage upon the stress development within the solid network are presented. Comparing the magnitude of the calculated stresses to measurements of the strength in equiaxed mushy zones shows that it is possible for the stresses to exceed the strength, thereby resulting in reorientation or collapse of the dendritic network.IntroductionInterdendritic fluid flow is at present regarded as a very important mechanism for feeding of shrinkage during solidification of metal alloys. Solidification of many alloys is often characterised by heterogeneous nucleation of the primary phase on substrates in the melt with subsequent evolution of equiaxed dendrites. These equiaxed dendrites can initially grow freely, but impinge on each other and form a continuous dendritic network, ie. dendrite coherency, quite early in the solidification process. Measurements of the dendrite coherency point have shown that the dendritic network is established at solid fractions ranging between 0.1 and 0.5, and most often around about 0.2 [l]. Depending on the alloy composition this means that as much as 70 to 80% of the volumetric shrinkage has to be compensated by flow of liquid through the interdendritic network. Interdendritic flow occurs with a much larger resistance compared to free flow of the liquid and flow of a liquid with dispersed crystals. The pressure drop associated with the interdendritic flow increases rapidly with decreasing fraction ofliquid."

Jan 1, 1999

By Kazuki Morita, Ye Wang

In order to optimize the B removal during slag-refining process for solar-grade silicon production, a new process for the removal of B in molten Si was proposed based on the principle of oxidized chlorination and evaporation. B can be generated and evaporated in the form of B-containing gas (BOCl) from molten Si using CaO–SiO2–CaCl2 slag system. Compared with the binary systems of CaO–CaCl2 and SiO2–CaCl2 slag, the ternary slag system CaO–SiO2–CaCl2 showed a better potential (90 pct) for B removal at 1723 K for 2 h. Moreover, the diffusion coefficient (D) of B in the slag was also determined using tube-molten pool method. Through this, it was found that the rate-limiting step of B-removal in the slag refining process is controlled by B transfer in the slag interface and surface.

Mar 1, 2017

By Tetsuro Sakai

Home appliance recycling law was put into force in April 2001 in Japan. Specified kinds of home appliances, such as air conditioners, television sets, refrigerators and washing machines, should be recycled according to the law. Mitsubishi Materials Corporation (MMC) in cooperation with home appliance manufacturers is operating five home appliance recycling plants in Japan. MMC established complete treatment system of recyclable materials generating from home appliance recycling plants, which is formed by unique collaboration among home appliance recycling plants, copper smelter and refinery, and cement plants. Recyclable materials containing copper and precious metals are only handled and treated within the MMC group. By using this lock-in system, safe treatment and traceability of materials are guaranteed as 100% materials recycle.

Jan 1, 2008

By J. N. Kondo, M. Hara, T. Smida, N. Ooto, K. Domen

"A porous material composed of two-dimensional anionic sheets of a layered perovskite, KSrNb30 10, was studied as photocatalyst for the production of Hz in the presence of alcohol sacrificial donors. Colloidal single and multi-layered HSr2Nb30 10 sheets were formed by intercalating ietra(n-buthylammonium) cations into the interlayeres of H+-exchanged KSr2Nb30 10 (HSr2Nb30 10), and addition of HN03 solution to the colloidal suspension precipitated the porous materials in which HSrNb30 10 sh~ets rand~mly stuck together. Original HSr2Nb30 10 before exfoliation had a BET surface area of 1 m2 g-1, whereas the surface area of a porous material prepared under optimal conditions exceeded 100 m2 g-1. The porous HSr2Nb30 10 had considerably higher photocatalytic'activitie8 for oxidation of 1-propanol and 1-buthanol than HSr2Nb39io, indicating that in the porous materials many niobate sheets are available for decomposition of these large alcohols.IntroductionQuite a research effort has gone into the design and study of porous materials. Such materials with large surface areas would have applications in highly efficient adsorbents or catalytic reactions.We have been studying photocatalytic reaction by cation-exchangeable layered metal oxides, where alkali metal cations are intercalated into the interlayers of inorganic sheets.[1,2] There are several advantages to using layered compounds rather than bulk powders for photocatalysis. Layered compound is rich in variety, in addition, modifications of them are easily performed by exchanging alkali metal cations in the inter layers for H + or other metal cations. The most important advantage is that some layered compounds have considerably high photocatalytic activities than bulk catalysts because the electrons and holes generated in each thin inorganic sheet readily reach interlayer spaces as reaction sites at the illterlayer spaces. It should be very important for further improvements· of layered photocatalysts to utilize two-dimensional inorganic sheets effectively."

Jan 1, 2000