Further details of this will be found in the article on the blast furnace. Processes for the second stage include fining in a finery forge and from the Industrial Revolution puddling. However both processes are now obsolete, and wrought iron is now hardly made. Instead, mild steel is produced from a bessemer converter or by other means. The ores of base metals are often sulphides.
In recent centuries, reverberatory smelters sometimes called cupolas have been used. These keep the fuel and the charge being smelted separate. Traditionally these were used for carrying out the first step: formation of two liquids, one an oxide slag containing most of the impurity elements, and the other a sulfide matte containing the valuable metal sulfide and some impurities.
Such "reverb" furnaces are today about 40 m long, 3 m high and 10 m wide. Fuel is burned at one end and the heat melts the dry sulfide concentrates usually after partial roasting , which is fed through the openings in the roof of the furnace.
The slag floats on top of the heavier matte, and is removed and discarded or recycled. The sulfide matte is then sent to the converter. However the precise details of the process will vary for one metal to another. Pleiner, R. Veldhuijzen, H. Dias, I. Categories: Metallurgy Metals processes Steelmaking. Read what you need to know about our industry portal chemeurope.
My watch list my. My watch list My saved searches My saved topics My newsletter Register free of charge. Keep logged in. Cookies deactivated. To use all functions of this page, please activate cookies in your browser. Login Register. Home Encyclopedia Smelting Smelting. Additional recommended knowledge. Main article: History of ferrous metallurgy. Retrieved on Topics A-Z. All topics. Among smelter workers prior to , or where inadequate control of fluoride effluents continued, variable degrees of bony fluorosis have been seen.
The first stage of this condition consists of a simple increase in bone density, particularly marked in the vertebral bodies and pelvis. As fluoride is further absorbed into bone, calcification of the ligaments of the pelvis is next seen. Finally, in the event of extreme and protracted exposure to fluoride, calcification of the paraspinal and other ligamentous structures as well as joints are noted. While this last stage has been seen in its severe form in cryolite processing plants, such advanced stages have rarely if ever been seen in aluminium smelter workers.
Apparently the less severe x-ray changes in bony and ligamentous structures are not associated with alterations of the architectural or metabolic function of bone. By proper work practices and adequate ventilatory control, workers in such reduction operations can be readily prevented from developing any of the foregoing x-ray changes, despite 25 to 40 years of such work.
Finally, mechanization of potroom operations should minimize if not totally eliminate any fluoride associated hazards. Fluoride—both gaseous and particulates, carbon dioxide, sulphur dioxide, carbon monoxide, C 2 F 6 ,CF 4 and perfluorinated carbons PFC. Since the early s an asthma-like condition has been definitively demonstrated among workers in aluminium reduction potrooms.
This aberration, referred to as occupational asthma associated with aluminium smelting OAAAS , is characterized by variable airflow resistance, bronchial hyperresponsiveness, or both, and is not precipitated by stimuli outside the workplace.
Its clinical symptoms consist of wheezing, chest tightness and breathlessness and non-productive cough which are usually delayed some several hours following work exposures. The latent period between commencement of work exposure and the onset of OAAAS is highly variable, ranging from 1 week to 10 years, depending upon the intensity and character of the exposure.
The condition usually is ameliorated with removal from the workplace following vacations and so on, but will become more frequent and severe with continued work exposures. While the occurrence of this condition has been correlated with potroom concentrations of fluoride, it is not clear that the aetiology of the disorder arises specifically from exposure to this chemical agent. Given the complex mixture of dusts and fumes e. It presently appears that this condition is one of an increasingly important group of occupational diseases: occupational asthma.
The causal process which results in this disorder is determined with difficulty in an individual case. Signs and symptoms of OAAAS may result from: pre-existing allergy-based asthma, non-specific bronchial hyperresponsiveness, the reactive airway dysfunction syndrome RADS , or true occupational asthma.
Diagnosis of this condition is presently problematic, requiring a compatible history, the presence of variable airflow limitation, or in its absence, production of pharmacologically induced bronchial hyperresponsivity. But if the latter is not demonstrable, this diagnosis is unlikely. However, this phenomenon can eventually disappear after the disorder subsides with removal from work exposures.
Since this disorder tends to become progressively more severe with continued exposure, affected individuals most usually need be removed from continued work exposures. While individuals with pre-existent atopic asthma should initially be restricted from aluminium reduction cell rooms, the absence of atopy cannot predict whether this condition will occur subsequent to work exposures.
There are presently reports suggesting that aluminium may be associated with neurotoxicity among workers engaged in smelting and welding this metal. It has been clearly shown that aluminium is absorbed via the lungs and excreted in the urine at levels greater than normal, particularly in reduction cell room workers. However, much of the literature regarding neurological effects in such workers derives from the presumption that aluminium absorption results in human neurotoxicity.
Accordingly, until such associations are more reproducibly demonstrable, the connection between aluminium and occupational neurotoxicity must be considered speculative at this time. Such episodes are most likely to occur when the weather initially changes from the moderate to hot, humid conditions of summer.
In addition, work practices which result in accelerated anode changing or employment over two successive work shifts during hot weather will also predispose workers to such heat disorders.
Heat stroke has occurred but rarely among aluminium smelter workers except among those with known predisposing health alterations e. Exposure to the polycyclic aromatics associated with breathing of pitch fume and particulates have been demonstrated to place Soderberg-type reduction cell personnel in particular at an excessive risk of developing urinary bladder cancer; the excess cancer risk is less well-established.
Workers in carbon electrode plants where mixtures of heated coke and tar are heated are assumed to also be at such risk. Hence the reduction cells utilizing prebaked electrodes have not been as clearly shown to present an undue risk of development of these malignant disorders. Other neoplasia e. In the vicinity of the electrolytic cells, the use of pneumatic crust breakers in the potrooms produce noise levels of the order of dBA.
The electrolytic reduction cells are run in series from a low-voltage high-amperage current supply and, consequently, cases of electric shock are not usually severe.
However, in the power house at the point where the high-voltage supply joins the series-connection network of the potroom, severe electrical shock accidents may occur particularly as the electrical supply is an alternating, high voltage current. Because health concerns have been raised regarding exposures associated with electromagnetic power fields, the exposure of workers in this industry has been brought into question.
It must be recognized that the power supplied to electrolytic reduction cells is direct current; accordingly, the electromagnetic fields generated in the potrooms are mainly of the static or standing field type. Such fields, in contrast to low frequency electromagnetic fields, are even less readily shown to exert consistent or reproducible biological effects, either experimentally or clinically.
In addition, the flux levels of the magnetic fields measured in present day cell rooms are commonly found to be within presently proposed, tentative threshold limit values for static magnetic fields, sub-radio frequency and static electric fields.
Exposure to ultra-low frequency electromagnetic fields also occur in reduction plants, especially at the far-ends of these rooms adjacent to rectifier rooms. However, the flux levels found in the nearby potrooms are minimal, well below present standards.
Finally, coherent or reproducible epidemiological evidence of adverse health effects due to electromagnetic fields in aluminium reduction plants have not been convincingly demonstrated. Workers in contact with pitch fumes may develop erythema; exposure to sunlight induces photosensitization with increased irritation. Cases of localized skin tumours have occurred among carbon electrode workers where inadequate personal hygiene was practised; after excision and change of job no further spread or recurrence is usually noted.
During electrode manufacture, considerable quantities of carbon and pitch dust can be generated. Where such dust exposures have been severe and inadequately controlled, there have been occasional reports that carbon electrode makers may develop simple pneumoconiosis with focal emphysema, complicated by the development of massive fibrotic lesions.
The grinding of coke in ball mills produces noise levels of up to dBA. A variety of exposures have been associated with other diseases e. Gold mining is carried out on a small scale by individual prospectors e. The simplest method of gold mining is panning, which involves filling a circular dish with gold-bearing sand or gravel, holding it under a stream of water and swirling it. The lighter sand and gravel are gradually washed off, leaving the gold particles near the centre of the pan.
More advanced hydraulic gold mining consists of directing a powerful stream of water against the gold-bearing gravel or sand. This crumbles the material and washes it away through special sluices in which the gold settles, while the lighter gravel is floated off. For river mining, elevator dredges are used, consisting of flat-bottomed boats which use a chain of small buckets to scoop up material from the river bottom and empty it into a screening container trommel.
The material is rotated in the trommel as water is directed on it. The gold-bearing sand sinks through perforations in the trommel and drops onto shaking tables for further concentration. There are two main methods for the extraction of gold from ore.
These are the processes of amalgamation and cyanidation. The process of amalgamation is based on the ability of gold to alloy with metallic mercury to form amalgams of varying consistencies, from solid to liquid.
The gold can be fairly easily removed from the amalgam by distilling off the mercury. In internal amalgamation, the gold is separated inside the crushing apparatus at the same time as the ore is crushed.
The amalgam removed from the apparatus is washed free of any admixtures by water in special bowls. Then the remaining mercury is pressed out of the amalgam. In external amalgamation, the gold is separated outside the crushing apparatus, in amalgamators or sluices an inclined table covered with copper sheets. Before the amalgam is removed, fresh mercury is added. The purified and washed amalgam is then pressed.
In both processes the mercury is removed from the amalgam by distillation. The amalgamation process is rare today, except in small scale mining, because of environmental concerns. Extraction of gold by means of cyanidation is based on the ability of gold to form a stable water-soluble double salt KAu CN 2 when combined with potassium cyanide in association with oxygen. The pulp resulting from the crushing of gold ore consists of larger crystalline particles, known as sands, and smaller amorphous particles, known as silt.
The sand, being heavier, is deposited at the bottom of the apparatus and allows solutions including silt to pass through. The gold extraction process consists of feeding finely ground ore into a leaching tub and filtering a solution of potassium or sodium cyanide through it. The silt is separated from the gold cyanide solutions by adding thickeners and by vacuum filtration.
Heap leaching, in which the cyanide solution is poured over a levelled heap of coarsely crushed ore, is becoming more popular, especially with low grade ores and mine tailings. In both instances, the gold is recovered from the gold cyanide solution by adding aluminium or zinc dust. In a separate operation, concentrated acid is added in a digest reactor to dissolve the zinc or aluminium, leaving behind the solid gold.
Under the influence of carbonic acid, water and air, as well as the acids present in the ore, the cyanide solutions decompose and give off hydrogen cyanide gas. In order to prevent this, alkali is added lime or caustic soda. Hydrogen cyanide is also produced when the acid is added to dissolve the aluminium or zinc. Another cyanidation technique involves the use of activated charcoal to remove the gold.
Thickeners are added to the gold cyanide solution before slurrying with activated charcoal in order to keep the charcoal in suspension. The gold-containing charcoal is removed by screening, and the gold extracted using concentrated alkaline cyanide in alcoholic solution. The gold is then recovered by electrolysis. The charcoal can be reactivated by roasting, and the cyanide can be recovered and reused.
Both amalgamation and cyanidation produce metal that contains a considerable quantity of impurities, the pure gold content rarely exceeding per mil fineness, unless it is further electrolytically refined in order to produce a degree of fineness of up to Gold ore occurring in great depths is extracted by underground mining.
This necessitates measures to prevent the formation and spread of dust in mine workings. The separation of gold from arsenical ores gives rise to arsenic exposure of mine workers and to pollution of air and soil with arsenic-containing dust. In the mercury extraction of gold, workers may be exposed to high airborne mercury concentrations when mercury is placed in or removed from the sluices, when the amalgam is purified or pressed and when the mercury is distilled off; mercury poisoning has been reported amongst amalgamation and distilling workers.
The risk of mercury exposure in amalgamation has become a serious problem in several countries in the Far East and South America.
In amalgamation processes the mercury must be placed on the sluices and the amalgam removed in such a manner as to ensure that the mercury does not come in contact with the skin of the hands by using shovels with long handles, protective clothing impervious to mercury and so on. The processing of the amalgam and the removal or pressing of mercury must also be as fully mechanized as possible, with no possibility of the hands being touched by mercury; the processing of amalgam and the distilling off of mercury must be carried out in separate isolated premises in which the walls, ceilings, floors, apparatus and work surfaces are covered with material which will not absorb mercury or its vapours; all surfaces must be regularly cleaned so as to remove all mercury deposits.
All premises intended for operations involving the use of mercury must be equipped with general and local exhaust ventilation. These ventilation systems must be particularly efficient in premises where mercury is distilled off. Stocks of mercury must be kept in hermetically sealed metal containers under a special exhaust hood; workers must be provided with the PPE necessary for work with mercury; and the air must be monitored systematically in premises used for amalgamation and distilling.
There should also be medical monitoring. Contamination of the air by hydrogen cyanide in cyanidation plants is dependent on air temperature, ventilation, the volume of material being processed, the concentration of the cyanide solutions in use, the quality of the reagents and the number of open installations.
Medical examination of workers in gold-extracting factories has revealed symptoms of chronic hydrogen cyanide poisoning, in addition to a high frequency of allergic dermatitis, eczema and pyoderma an acute inflammatory skin disease with pus formation.
Proper organization of the preparation of cyanide solutions is particularly important. If the opening of drums containing cyanide salts and the feeding of these salts into dissolving tubs is not mechanized, there can be substantial contamination by cyanide dust and hydrogen cyanide gas.
Cyanide solutions should be fed in through closed systems by automatic proportioning pumps. In gold cyanidation plants, the correct degree of alkalinity must be maintained in all cyanidation apparatus; in addition, cyanidation apparatus must be hermetically sealed and equipped with LEV backed up by adequate general ventilation and leak monitoring.
All cyanidation apparatus and the walls, floors, open areas and stairs of the premises must be covered with non-porous materials and regularly cleaned with weak alkaline solutions. The use of acids to break down zinc in the processing of gold slime may give off hydrogen cyanide and arsine. These operations must therefore be performed in specially equipped and separated premises, with the use of local exhaust hoods.
Smoking should be prohibited and workers should be provided with separate facilities for eating and drinking. Workers must be supplied with personal protective clothing impervious to cyanide compounds. There is evidence of exposure to metallic mercury vapour and methylation of mercury in nature, particularly where the gold is processed.
In one study of water, settlements and fish from gold mining areas of Brazil, the mercury concentrations in edible parts of locally consumed fish surpassed by almost 6 times the Brazilian advisory level for human consumption Palheta and Taylor In a contaminated area of Venezuela, gold prospectors have been using mercury to separate gold from auriferous sand and rock powders for many years.
The high level of mercury in the surface soil and rubber sediments of the contaminated area constitutes a serious occupational and public health risk.
Cyanide contamination of wastewater is also a great concern. Cyanide solutions should be treated before being released or should be recovered and reused. Emissions of hydrogen cyanide gas, for example, in the digest reactor, are treated with a scrubber before being exhausted out the stack.
Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia Air Pollution Engineering Manual. Profile of the Nonferrous Metals Industry. Monographs on the Evaluation of Carcinogenic Risks to Humans. Lyon: IARC.
Respiratory abnormalities amongst workers in iron and steel industry. Brit J Ind Med — Asbestos-related disease in employees of a steel mill and a glass bottle manufacturing plant. Ann NY Acad Sci — Silicosis in a grey iron foundry. The persistence of an ancient disease. Scand J Work Environ Health — Palheta, D and A Taylor.
Mercury in environmental and biological samples from a gold mining area in the Amazon Region of Brazil. Science of the Total Environment Thomas, PR and D Clarke. Occup Med 42 3 — Smelting and Refining Operations.
Adapted from the 3rd edition, Encyclopaedia of Occupational Health and Safety. Overview of Processes Two metal recovery technologies are generally used to produce refined metals, pyrometallurgical and hydrometallurgical. Pyrometallurgy During pyrometallic processing, an ore, after being beneficiated concentrated by crushing, grinding, floating and drying , is sintered or roasted calcined with other materials such as baghouse dust and flux.
Hydrometallurgy Examples of hydrometallurgical processes are leaching, precipitation, electrolytic reduction, ion exchange, membrane separation and solvent extraction.
Hazards and Their Prevention Prevention of health risks and accidents in the metallurgical industry is primarily an educational and technical question. In planning of new production facilities, the following aspects should be taken into account as a minimum: The potential sources of air contaminants should be enclosed and isolated.
The design and placement of the process equipment should allow easy access for maintenance purposes. Areas in which a sudden and unexpected hazard may occur should be monitored continuously. Adequate warning notices should be included. For example, areas in which arsine or hydrogen cyanide exposure might be possible should be under continuous monitoring. Addition and handling of poisonous process chemicals should be planned so that manual handling can be avoided.
Personal occupational hygiene sampling devices should be used in order to evaluate the real exposure of the individual worker, whenever possible. Regular fixed monitoring of gases, dusts and noise gives an overview of exposure but has only a complementary role in the evaluation of exposure dose. In space planning, the requirements of future changes or extensions of the process should be taken into account so that the occupational hygiene standards of the plant will not worsen.
There should be a continuous system of training and education for safety and health personnel, as well as for foremen and workers. New workers in particular should be thoroughly informed about potential health risks and how to prevent them in their own working environments.
In addition, training should be done whenever a new process is introduced. Work practices are important. For example, poor personal hygiene by eating and smoking in the worksite may considerably increase personal exposure.
The management should have a health and safety monitoring system which produces adequate data for technical and economic decision making. Injuries The smelting and refining industry has a higher rate of injuries than most other industries. Heat Heat stress illnesses such as heat stroke are a common hazard, primarily due to infrared radiation from furnaces and molten metal.
Chemical hazards Exposure to a wide variety of hazardous dusts, fumes, gases and other chemicals can occur during smelting and refining operations. Other hazards Glare and infrared radiation from furnaces and molten metal can cause eye damage including cataracts.
Pollution and Environmental Protection Emissions of irritant and corrosive gases like sulphur dioxide, hydrogen sulphide and hydrogen chloride may contribute to air pollution and cause corrosion of metals and concrete within the plant and in the surrounding environment.
Published in Smelting and Refining Operations. Read more Adapted from EPA Copper Copper is mined in both open pits and underground mines, depending upon the ore grade and the nature of the ore deposit.
Hazards and their prevention The major hazards are exposure to ore dusts during ore processing and smelting, metal fumes including copper, lead and arsenic during smelting, sulphur dioxide and carbon monoxide during most smelting operations, noise from crushing and grinding operations and from furnaces, heat stress from the furnaces and sulphuric acid and electrical hazards during electrolytic processes.
Table 1. Process Material input Air emissions Process wastes Other wastes Lead sintering Lead ore, iron, silica, limestone flux, coke, soda, ash, pyrite, zinc, caustic, baghouse dust Sulphur dioxide, particulate matter contain-ing cadmium and lead Lead smelting Lead sinter, coke Sulphur dioxide, particulate matter contain-ing cadmium and lead Plant washdown wastewater, slag granulation water Slag containing impurities such as zinc, iron, silica and lime, surface impoundment solids Lead drossing Lead bullion, soda ash, sulphur, baghouse dust, coke Slag containing such impurities as copper, surface impoundment solids Lead refining Lead drossing bullion.
You actually dump the ore and the fuel together into the furnace and ignite the entire mess. The molten metal drips down. In other furnaces hotter ones, I presume , liquid metal runs out and down channels into molds.
All this stuff is a lot of work. The videos only show snippets, but you can tell that each process takes hours and hours of hard physical labor. And the result in the end is unimpressive by modern standards.
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