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Residual aeolian placers (RAPs) are formed by the wind, by preferential entrainment and removal of small and low-density detritusfrom a pre-existing, typically sedimentary sequence containing heavy minerals. Heavy minerals that are resistant to chemical alteration and either soft and malleable (gold), or extremely hard (diamond, sapphire, ruby, etc), are concentrated as a residual on the wind deflation surface, typically in the interstices between larger resistant clasts. RAPs form preferentially in arid or semi arid areas, where the vegetation is sparse or absent, and where topography and surface gradients are low, but may also form on beaches and in periglacial environments. RAPs consist of a continuous or discontinuous, planar or gently undulating horizon of heavy minerals in a single-clast-thick pavement of resistant pebbles, cobbles, or boulders, which mantles the present topography or palaeo-topography. Extreme wind erosion and surface deflation may condense the full pre-existing sequence into a layer of heavy minerals only. The grade of RAPs is substantially higher than in the precursor deposit, and commonly much higher than those typically found in most other placer types. Aside from their general occurrence as a thin pavement of resistant clasts, the best indicators of residual aeolian gold placers are the presence of wind-eroded stones (ventifacts) on the pavement, and the distinctive and unique shapes of aeolian gold grains themselves. The shape of the gold grains is progressively transformed by sand blasting during placer development, from grains with thickened rims, to toroidal grains on which the rims are æsplitÆ and peened inward toward the grain centre on one or both of the grain sides, to hemispherical or sub-spherical grains that are fully encapsulated by the in-turned rims. Gold that has undergone aeolian shape transformation is difficult to entrain and transport away from the site of aeolian concentration by anything other than mass movement or glacial processes. It is also easily retained by commercial recovery plants of any configuration.

Jan 1, 2004

By C R. Ferrari

Residual subsidence is generally accepted as being about 5% of the total subsidence occurring within 12 months of all mining finishing. This paper looks at five case studies from different parts of the country, in various mining settings within a depth range of 430m to 760m. From a single seam single panel working to working the eleventh seam, all are within the concealed coalfield, similar to today's mining. The monitoring of subsidence continued for many years once the mining had finished and the results obtained are at considerable variance from the accepted norm. Subsidence has been found to carry on for up to eleven years after mining has ended, within a range of 8% to 45% of total subsidence. A highly significant factor was that subsidence, as a whole, was generally much more than predicted. The residual subsidence aspect has to he viewed in this context and in order to debate the subject at length, the causes of residual subsidence have to be balanced against the apparent inability to accurately predict subsidence. The results from the case studies were similar, even though the mining settings differed considerably. Subsidence of around 10% to 20% continued for several years after mining had ceased.

Jan 7, 1997

By J. Morris, R. Sellaro

El petrodiesel es un colector común para la flotación de carbón, pero la partición de compuestos orgánicos de diesel (DRO por sus siglas en inglés) en corrientes de proceso no ha sido ampliamente estudiada. Investigaciones preliminares sugieren que bajo esquemas de dosificación normales los contenidos residuales totales de DRO en aguas de procesos deben estar limitados a la fracción soluble en agua (WSF por sus siglas en inglés) sub-ppm. Es más, los hidrocarburos aromáticos poli-cíclicos (PAH por sus siglas en inglés) debería segmentarse de manera proporcional con los compuestos orgánicos de diesel (DRO). El propósito de este estudio fue confirmar estos resultados en pruebas de flotación realizadas en laboratorio. Se midieron los contenidos totales de DRO Y PAH en aguas asociadas con los flujos o corrientes de concentrados y relaves. Los resultados muestran que las aguas con concentrados tenían de manera consistente mayores cantidades de DRO que las aguas de relaves. Es más, los contenidos de DRO en ambos flujos generalmente se incrementaban con el aumento de la dosis de diesel. De acuerdo con la investigación preliminar, los DRO parecían estar limitados a la fracción soluble en agua (WSF) y los PAH tendían a segmentarse proporcionalmente con los DRO. Bajo condiciones de operación típicas, los DRO residuales no deberían representar una preocupación medioambiental, pero deben evitarse situaciones que permitan una sobredosis significativa de diesel.

Jan 1, 2014

By J. Morris, R. Sellaro

Petro-diesel is a common collector for coal flotation, but the partitioning of diesel range organics (DROs) in process streams has not been widely studied. Preliminary research suggested that under normal dosing schemes total residual DRO contents in process waters should be limited to the sub-ppm water-soluble fraction (WSF). Further, polycyclic aromatic hydrocarbons (PAHs) should partition proportionately with DROs. The purpose of this study was to confirm these findings in laboratory flotation tests. Total DRO and specific PAH contents were measured in the waters associated with the concentrate and tailings streams. The results show that concentrate waters consistently had higher amounts of DROs than tailing waters. Moreover, the DRO contents in both streams generally increased with increasing diesel dosage. In line with preliminary research, DROs appeared to be limited to the WSF, and PAHs tended to partition proportionately with DROs. Under typical operating conditions, it appears that residual DROs should not present an environmental concern, but conditions should be avoided that allow significant overdosing of diesel.

Jan 1, 2014

By J. Morris

Petro-diesel is a common collector for fine coal froth flotation but partitioning of diesel range organics (DROs) in process streams has not been widely studied. Preliminary research suggested that under normal dosing schemes total residual DRO in process waters should be limited to the sub-ppm water-soluble fraction (WSF). Further, polycyclic aromatic hydrocarbons (PAHs) should partition proportionately with DRO. The purpose of this study was to confirm these findings in laboratory flotation tests. Total DRO and specific PAHs were measured in tailings and concentrate streams, and coal recovery and ash rejection were tracked. Results show that concentrate waters consistently had higher DRO than tailing waters, and DRO in both streams generally increased with increasing diesel dosage. DRO again appeared to be limited to the WSF and PAHs tended to partition proportionately with DRO. Results indicate optimal flotation performance should generally coincide with minimal DRO partitioning to process waters. Under typical operating conditions residual DRO should not present an environmental concern; however, conditions should be avoided that allow significant overdosing of diesel.

Feb 23, 2014

By Norman O. Lotter, André R. Laplante

"The pursuit of concentrator surveying for purposes of metal accounting or process optimization has not yet connected with the well-published realm of geostatistics. The reality of lognormality in time has seldom been discussed. One publication by Krige, 1962, examined such effects for a gold concentrator in South Africa, towards an information system that would provide feedback to the mining and surveying teams on grade control of ore mined.During present studies which are designing and testing a new survey model, called statistical benchmark surveying, it was found that the distributions of feed, concentrate and tailings bear significant residual signs of the parent lognormality in space. The multiple hosting of paymetals in different mineral species complicates the understanding of these distributions. These features have to be recognized and treated in order to perform appropriate quality control on the diagnostic sampling performed in the pursuit of statistical benchmark surveying.It is shown in this paper that the above two features can actually be used to advantage in the diagnosis of continuous periods of operations data ahead of such surveying, including the estimation of recoverable paymetals in flotation tailings from a graphical method.INTRODUCTIONAssessment of Concentrator PerformanceMilling and flotation, sometimes accompanied by gravity separation, are well-established unit processes, which have traditionally been used to treat ore that has been mined. This is because these processes liberate, then separate, the valuable minerals, which contain paymetals, from host gangue. This is often done by a combination of crushing and grinding processes, or autogenous grinding, to liberate the paymetal minerals, followed by gravity separation and/or flotation, to separate these valuable minerals into a concentrate, or several concentrates. These concentrate(s) have a lower bulk than the parent ore from which they are derived. Further, they contain a high percentage of the valuable minerals. Accordingly, they are more economically treated in subsequent beneficiation processes than the ore from which they were produced."

Jan 1, 2005

By Packer M. L

Residual load development in driven precast piles has been widely researched in recent decades, however, cast-in-situ piles are often falsely assumed to be unaffected by this mechanism. In contrast to driven precast piles, driven cast-in-situ (DCIS) piles require adequate time prior to loading for the concrete hydration and curing processes to occur. The concrete-soil interaction is complex with several processes influencing the strains within the concrete pile after installation. DCIS piles are of particular interest given that residual loads can be developed during both the driving and casting phases. This paper present four instrumented end-bearing DCIS piles in which temperature and strains were monitored from installation, with the objective of identifying the processes contributing to the measured strains prior to testing. Strain gauges at all depths recorded a net compression and compressive strains continued to increase up to the commencement of load testing. Residual strains in the test piles were interpreted to be influenced by temperature (concrete and ambient soil and air temperature), consolidation of soils due to dissipation of excess pore water pressure, and swelling from absorption of groundwater. Several residual load interpretive methods are evaluated with the Siegel and McGillivray (2009) approach being consistent with the skin friction full mobilisation theory of the Unified Design method. The full-scale field tests presented herein provide a unique opportunity to examine DCIS pile behaviour, particularly given the lack of presently available published studies on these pile types.

May 1, 2022

By Reda M. Bakeer

"Measurements obtained during load testing of two steel H-piles driven at a site in Northeastern Mississippi are discussed. The general site conditions, equipment used, testing procedures and results of the pile load tests are presented. Both piles were tested in compression and one of the piles was subsequently tested in tension. The piles were instrumented with strain gauges and extensometers to measure the mobilized soil resistance and pile movement. Three different “zero strain” conditions were used to determine the mobilized soil resistance and residual loads due to driving or a load cycle. It was concluded that the effect of residual loads on driven piles could be significant. Driving residual loads influenced the magnitude and distribution of the load transfer curves more than those due to a load cycle. Results of the tension test were impacted by the residual loads from the previous compression test performed on the same pile.INTRODUCTIONSeveral factors affect the performance of a deep foundation system including the subsoil conditions, loading settings, pile type and installation method. Residual stresses develop in piles particularly due to pile driving, but they are typically not accounted for in the analysis (Fellenius 2002). Siegel and McGillivray (2009) presented an assessment of residual loads measured during load testing of instrumented auger-cast-in-place (ACIP) piles. The magnitude and distribution of residual stresses along the pile shaft and toe depend on the pile installation method, previous load cycles and time effects. Poulos (1987) reported that residual load due to driving at the pile toe is independent of pile driving equipment and may significantly affect the results of a pile load test. Hunter and Davisson (1969) reported results of pile load tests performed in compression on fully instrumented piles driven in cohesionless soils along with a discussion of the effects of residual loads. Tension loads of about 445 kN (100 kips) were measured at the pile toe after driving. Unloading residual compression load at the toe was detected as “apparent” tension since the instrumentation was zeroed prior to the test. The researchers suggested a graphical approach to obtain the “corrected” load distribution curves considering that residual load will dissipate following the tension test. Holloway et al. (1975) conducted a study on the effect of residual stresses due to pile driving and developed a computer software that accounts for residual loads. Briaud and Tucker (1984) suggested a method to account for residual loads based on the results of 33 pile load tests performed in mostly cohesionless soils."

Jan 1, 2017

In deposits in which the secondary zones are well defined a layer of rich oxidized ore is frequently found immediately to overlie the enriched sulphides, from which it is derived by direct oxidation in place. In deposits that contain oxidizing precipitants particles and masses of residual oxidized ore are likely to be scattered through the leached zone, having been precipitated during migration before reaching the zone of enrichment. This precipitation hinders secondary enrichment and in extreme cases prevents the formation of such concentrations. Residual ores are precipitated by various reagents. Carbonates are formed through the action of the carbonic acid contained in surface waters, and also directly through the replacement of calcite, especially where the containing rock is limestone. Native metals, such as copper, gold, and silver, are formed by the action of reducing agents, among which organic matter and ferrous sulphate are prominent. Kaolin, gouge, and certain shales occasionally act as powerful precipitants through adsorption. Silver is often found as residual chloride, formed through precipitation by the chlorine contained in surface waters. Residual ores are often the result of incomplete solution, the relatively insoluble minerals being left behind during the migration of associated metals; incomplete oxidation and solution often leave residual masses of unaltered, or partly altered, sulphides in the oxidized zone. Such residual particles or masses have commonly been enriched by additions from circulating, metal-bearing solutions. During oxidation under conditions that permit reprecipitation, such as the oxidation of sulphide deposits in limestone, a scat-

Jan 1, 1932

By C Gunther

In deposits in which the secondary zones are well defined a layer of rich oxidized ore is frequently found immediately to overlie the enriched sulphides, from which it is derived by direct oxidation in place. In deposits that contain oxidizing precipitants particles and masses of residual oxidized ore are likely to be scattered through the leached zone, having been precipitated during migration before reaching the zone of enrichment. This precipitation hinders secondary enrichment and in extreme cases prevents the formation of such concentrations. Residual ores are precipitated by various reagents. Carbonates are formed through the action of the carbonic acid contained in surface waters, and also directly through the replacement of calcite, especially where the containing rock is limestone. Native metals, such as copper, gold, and silver, are formed by the action of reducing agents, among which organic matter and ferrous sulphate are prominent. Kaolin, gouge, and certain shales occasionally act as powerful precipitants through adsorption. Silver is often found as residual chloride, formed through precipitation by the chlorine contained in surface waters. Residual ores are often the result of incomplete solution, the relatively insoluble minerals being left behind during the migration of associated metals; incomplete oxidation and solution often leave residual masses of unaltered, or partly altered, sulphides in the oxidized zone. Such residual particles or masses have commonly been enriched by additions from circulating, metal-bearing solutions. During oxidation under conditions that permit reprecipitation, such as the oxidation of sulphide deposits in limestone, a scab

Jan 1, 1932

By Chaoying Ni, Dimitry Sediako, Prashant Karandikar, Sean Fudger

Neutron diffraction measurements were performed on steel encapsulated metal matrix composites (MMCs) in order to quantify bulk residual stresses. A coefficient of thermal expansion (CTE) mismatch induced residual compressive stress method is utilized as a means of improving the ductility of the MMCs and overall efficiency of several macro hybridized materials systems. Systems consisting of an A36, 304 stainless steel, or Nitronic® 50 stainless steel shell filled with an Al-SiC or Al-Al2O3 metal matrix composite are evaluated in this work. Upon cooling from processing temperatures residual strains are generated due to a CTE mismatch between each of the phases: steel, aluminum, and reinforcement. The analysis shows variation in the measured strain and stress results due to outer steel thickness, difference in CTE between materials, and relative position within the composite.

Mar 1, 2017

By J. Mazia, H. Rosenthal

An investigation has been made of residual stress in the head and body of caliber 0.30 cartridge cases. The head was divided into four ring-lie sections which were cut off by a jeweler's saw. Spring-out was measured after a radial cut had relieved the circumferential bending moment. The residual stress corresponding to the observed spring-out was calculated by formulas in which the computed stress was a function of wall thickness. All rings sprang open, indicating compressive stress on the inner wall and tensile stress on the outer wall. The production stress-relief anneal of 475 F. for 45 min. reduced the stress to almost half. The priming and crimping operation, however, again raised the stress, especially in the flange section. The dect of stress-relief heat treatments on residual stresses in the body of caliber 0.30 cartridge cases was investigated by the split-ring method. Although this method did not reveal any large stresses in the body, the neck before mouth anneal was found to contain a computed stress of 30,000 psi. at the surface. This value was reduced to 15,000 psi. in 120, 30, and 15 min. at 400, 475, and 500 F., respectively.

Jan 1, 1945

By G. Sachs, G. Espey

IT is well known that high residual stresses are created in tubing by the sinking process, in which no internal tool or mandrel is used.1-4 In this process, the wall thickness is usually slightly increased.4,5 In tube drawing with a plug, the residual stresses are gradually reduced with increasing reduction of wall, and, by the conventional approximation methods of stress measurement, no stress is detected in tubing in which the wall reduction is over 50 per cent of the total reduction in cross-sectional area.1-6, It has also been observed that higher stresses are set up by the use of wide-angle dies than by the use of acute dies.2 The actual stress distribution in drawn .tubing has been investigated by a few workers,7-9 but has not been related to the conditions of the drawing process: Some attempts have been made to correlate accelerated cracking tests for stresses in brass products with the magnitude of the circumferential stresses and the condition of the metal.1-10 MATERIALS AND PREPARATION The material used in this experiment was commercial cartridge-brass (70 per cent Cu, 30 per cent Zn) tubing in the straightened and annealed condition.‡ This tubing was of various outside diameters and had a wall thickness of 0.032 in. It was sunk to 1/2-in. outside diameter by means of an experimental 10,000-lb. hydraulic draw-bench, with a maximum drawing speed of 8 ft. per minute. All dies were of 1/2 -in. diameter. Various die materials and contours were used in order to study the effect of die design on residual stresses in the tubing; the specifications for the dies are given in Fig. I. Castor oil was used throughout as lubricant. Chattering occurred in sinking some of the tubing, particularly when dies having the more acute angles were used, but the tubes showing chatter marks did not differ markedly from those with a smooth surface regarding the magnitude of residual stress. The source of the chattering has not yet been revealed. The wall of the tubing becomes thicker during sinking, as previously observed 4,5 The increases in wall thickness were 3, 7 and 9.5 per cent on the average for 6, 20 and 33 per cent reductions in diameter, no effect of the contour being noticeable. The reductions mentioned throughout this investigation do not consider this fact, but are reductions of the outside diameter. For the evaluation of the residual stress two fundamentally different methods were used. The approximation method1,11 of splitting a certain length of tubing was employed to obtain a bird's-eye view of the effect of various drawing conditions on the circumferential stress measured by the diameter change occurring on splitting. For the determination of the complete stress

Jan 1, 1941

By D. Sediako

Excessive residual stress in Al engine blocks may result in cylinder distortion which reduces engine operating efficiency. As such, neutron diffraction was used to measure residual strain along the Fe liners and Al, in the hoop, radial and axial orientations with respect to the cylinder axis, at the cylinder interbore region. Residual stresses were subsequently calculated using generalized Hooke's law and related to the microstructure along the cylinder bridge. The results suggest that the residual stresses in the Al interbore region are tensile and increased with depth in the axial direction of the cylinder. The increase in residual stress at the bottom of the cylinder coincides with a finer and more uniform microstructure in this region of the cylinder. The refinement in microstructure at the bottom of the cylinder likely increased alloy strength, thereby decreasing this section's susceptibility to distortion. This study successfully quantified the residual stress profiles in a heat treated engine block and related the stress profiles to an as-cast engine block.

Jan 1, 2011

By G. Vouille, P. Bérest

Residual stresses observed in rocks often result from non-compatible initial strains. These stresses can be determined when the incompatibility tensor associated with the initial strain tensor is known. The residual stresses in a cylindrical rock sample can be computed the sample is considered small enough for its incompatibility tensor to be constant. Les contraintes résiduelles, dont on observe couramment les manifestations dans les roches, résultent souvent de l’existence de déformations initiales non-compatibles. Ces contraintes peuvent être calculées lorsque le tenseur d’incompatibilité associé aux déformations initiales est connu. Les contraintes résiduelles dans une éprouvette cylindrique sont données dans le cas où le tenseur d’incompatibilité est constant. Eigenspannungen, die man haeufig in Steinen beobachtet, sind oft Ergebnis einer inkompatiblen Deformation des Anfangszustandes. Diese Spannungen koennen berechnet werden, wenn der Inkompatibilitaets-Tensor der Anfangsdeformation bekannt ist. Die Eigenspannungen einer zylindrischen Probe werden fuer Fall eines konstanten Inkompatibilitaets-Tensor bestimmt.

Jan 1, 2003

By L. Hacini, N. Van L ê, P. Bacher, D. Thibault

Manufacturer welded components may suffer from high level of residual stresses which can cause premature cracking and decrease the life of the components if they reach values close to the yield strength of the material. In the present work, a robotized hammer peening technique is simulated by an impact machine and the residual stresses generated by the indentation are measured. To better understand phenomena behind residual stresses relaxation by hammer peening, the impact energy level was changed. 304L steel plates were hammer peened with 10 impacts. The contact between the hammer and sample surface was always at the same location. The strains on the surface close to the impact location were recorded during the test using strain gauges to follow residual stresses variations. At the end of the test residual stresses were measured indepth using hole drilling technique at 8mm from the impact center. The micro-hardness was monitored to evaluate the affected zone by the hammer peening. This approach gave a good estimation of the energy and number of blows to be used for efficient relaxation of the manufactured parts.

Jan 1, 2006

By D Langberg, R Taylor

Many metallurgical operations produce fine residues and dusts as by-products which can be difficult to handle and offer little direct financial incentive to treat. There is a growing imperative to deal with these materials particularly since land fill is fast becoming an uncertain long term solution. One possible means of treatment is to extract the valuable metals while fusing the remainder into a slag. In this way valuable metal components of the material can be recovered and the less valuable components be converted into useful products, eg cements and inorganic polymers which have a high environmental stability and a growing market. The aim of this project is to establish solids injection and fusion in a slag bath as a viable method of treating industrial wastes and residues. The benefits of this approach are expected to be: the ability to treat a wide range of organic and inorganic residue materials, ease of recovery of volatile and valuable elements and the production of final materials which could be used in other industries. In ongoing experimental work at the CSIRO Minerals a 250 kg slag bath reactor has been used to test the injection of Paragoethite residue into an iron silicate based slag. An experimental apparatus has been designed and commissioned to pneumatically inject solid material at feed rates of up to 80 kg/hour. The capture efficiency of injected solids by the slag bath was calculated by monitoring the composition of the slag. Using this method of treatment, the zinc contained in the residue can be recovered as a fume by varying the oxidation state of the slag. Other valuable elements could be recovered by creating a matte or metal phase in the reactor with the final material being used in the production of cement. A capture efficiency of injected solid paragoethite particles in the slag bath of up to 97 per cent was achieved. Under the conditions of the experimental work capture efficiency was found to be independent of injection velocity and slag depth. The rate of fuming during injection was found to increase slightly with injection velocity and was independent of slag depth.

Jan 1, 2002

By Garrigan J. S, Oakes I

Current operating practice in a plant commissioned some five years ago to treat ferritic zinc plant residue by the "Jarosite" process is described. Major problems overcome include obtaining reliable pH measurements at 100¦C, prevention of scale build up in spent electrolyte heaters, blinding of jarosite filter cloths and the deposition of gypsum in filter presses.

Jan 1, 1977

By Juergen Antrekowitsch, Stefan Steinlechner

"Within the last decades, mainly the base metals, like zinc, copper and lead were recycled from different industrial residues without taking into account that accompanied minor side-elements are often also present. A high supply risk for critical raw materials derives mainly due to the high share of the worldwide production in a limited number of countries. Examples include indium and germanium in China, PGM in South Africa and Russia or cobalt and tungsten in the Democratic Republic of Congo. By taking the market of critical metals into account, the recycling of potential residues does not only contribute to an economic treatment but also to the European strategy to decrease the supply risk of certain metals. Depending on the metal discussed, political unrest, decreasing primary resources leading to supply risks in different countries or also simply economic interests moved these mentioned side elements and with this the residues where they are present in, into the focus of the recycling industry.Because of this, the typical routes of lead, zinc and copper production are evaluated concerning generated residues and their typical contents of contained minor elements. Finally, the paper tries to answer the questions how a possible treatment of these wastes could contribute to the overall supply of for example silver but also other minor elements."

Jan 1, 2016

By S. Steinlechner, S. Wegscheider

"In the past, the metallurgical industry was most of the time dedicated on their main commodity, recovering base metals like zinc, copper or lead but leaving other valuable side elements in the generated residues. As a result, these accompanying minor elements, like gold, silver, indium or also PGMs can be found in the dumps of the corresponding industry. Because of political unrest, strikes, economic reasons or decreasing primary resources leading to a high supply risk, also those mentioned minor elements moved into the focus of the recycling industry. Therefore, beside the base metals, first of all the recovery of those minor metals would be of high interest contributing to the economic viability of recycling processes, although they occur in much smaller quantities in materials. In this context, residues from zinc industry, like leaching residues or precipitation residues show high potential to carry silver as well as indium next to lead and zinc. Therefore, the paper summarizes carried out thermochemical calculations investigating a possible recovery of silver as well as indium by volatilization and the influence of zinc and lead on this process. Based on these theoretical investigations with HSC, trials in lab scale were done verifying the obtained results.INTRODUCTIONHuge amounts of iron precipitate, mainly jarosite get landfilled every year although there is a high content of valuable metals in this residue beside iron. Nevertheless, jarosite has to be dumped due to the presence of contaminating heavy metals. The accumulation of these residues takes up massive land on the one hand but also causes a series of environmental problems in ecosystems on the other. Moreover, some toxic ingredients such as arsenic and cadmium can be dissolved in rain water and are therefore harmful to the health of the aquatic systems. (Erdem & Özverdi, 2011; ÖzverdI & Erdem, 2010) Approximately 0.5 t of dry jarosite accumulate in the production of 1 t of zinc by the hydrometallurgical zinc-winning route (Svens, 2010). Jarosite is a precipitation residue formed during the iron removal. In general, the iron already exists in the zinc ore which is why zinc ferrite builds up during the roasting step of the zinc ore. Zinc ferrite is only soluble in strongly acidic solutions and during the hot acid leaching step it gets dissolved while zinc and iron enter the solution. It is necessary to get rid of the iron because otherwise it would deposit on the cathode first due to its precious character which would be harmful in the zinc-winning electrolysis. Nevertheless successful investigations were done by adding chlorine to the jarosite to recover silver. These findings leads to another residue which occurs in huge amounts – electric arc furnace dust (abbreviated with EAFD) from the iron and steel industry. In 2013 the annual electric steel production reached about 451 million tons. Around 15-20 kg of EAFD is produced per ton of steel in an electric arc furnace (EAF), creating approximately up to 9 million tons of dust per year. (Grabda, Oleszek, Shibata, & Nakamura, 2014; World Steel Association) Next to elements like zinc, lead and iron, chlorine and fluorine are present in this dust. While galvanized steel plates in the scrap act as a source for zinc, casting powders, flame retardants and synthetic coatings are responsible for the chlorine and fluorine contents in the dust."

Jan 1, 2016