How do smelters work

Particulate emissions are commonly controlled by fabric filters and electrostatic precipitators. Large amounts of water are used in flotation processes such as copper concentration.

Most of this water is recycled back into the process. Tailings from the flotation process are pumped as slurry into sedimentation ponds. Water is recycled in the process. Metal-containing process water and rainwater are cleaned in water-treatment plants before discharging or recycling. Solid-phase wastes include slags from smelting, blowdown slurries from sulphur dioxide conversion to sulphuric acid and sludges from surface impoundments e. Some slags can be reconcentrated and returned to smelters for reprocessing or recovery of other metals present.

Many of these solid-phase wastes are hazardous wastes that must be stored according to environmental regulations. Copper is mined in both open pits and underground mines, depending upon the ore grade and the nature of the ore deposit. Once the ore is delivered above the ground, it is crushed and ground to a powdery fineness and then concentrated for further processing.

In the concentration process, ground ore is slurried with water, chemical reagents are added and air is blown through the slurry. The air bubbles attach themselves to the copper minerals and are then skimmed off the top of the flotation cells. The tailings, or gangue minerals, from the ore fall to the bottom of the cells and are removed, dewatered by thickeners and transported as a slurry to a tailings pond for disposal.

All water used in this operation, from dewatering thickeners and the tailings pond, is recovered and recycled back into the process. Copper can be produced either pyrometallurgically or hydrometallurgically depending upon the ore-type used as a charge.

The ore concentrates, which contain copper sulphide and iron sulphide minerals, are treated by pyrometallurgical processes to yield high purity copper products. Oxide ores, which contain copper oxide minerals that may occur in other parts of the mine, together with other oxidized waste materials, are treated by hydrometallurgical processes to yield high purity copper products. Copper conversion from the ore to metal is accomplished by smelting. During smelting the concentrates are dried and fed into one of several different types of furnaces.

There the sulphide minerals are partially oxidized and melted to yield a layer of matte, a mixed copper-iron sulphide and slag, an upper layer of waste. The matte is further processed by converting. The slag is tapped from the furnace and stored or discarded in slag piles onsite. A small amount of slag is sold for railroad ballast and for sand blasting grit. A third product of the smelting process is sulphur dioxide, a gas which is collected, purified and made into sulphuric acid for sale or for use in hydrometallurgical leaching operations.

Following smelting, the copper matte is fed into a converter. Lime and silica are added to the copper matte to react with the iron oxide produced in the process to form slag. Scrap copper may also be added to the converter. Then the converter is rotated to pour off the iron silicate slag.

Once all of the iron is removed, the converter is rotated back and given a second blow of air during which the remainder of the sulphur is oxidized and removed from the copper sulphide. The converter is then rotated to pour off the molten copper, which at this point is called blister copper so named because if allowed to solidify at this point, it will have a bumpy surface due to the presence of gaseous oxygen and sulphur. Sulphur dioxide from the converters is collected and fed into the gas purification system together with that from the smelting furnace and made into sulphuric acid.

Due to its residual copper content, slag is recycled back to the smelting furnace. Blister copper, containing a minimum of The first step is fire refining, in which the molten blister copper is poured into a cylindrical furnace, similar in appearance to a converter, where first air and then natural gas or propane are blown through the melt to remove the last of the sulphur and any residual oxygen from the copper.

The molten copper is then poured into a casting wheel to form anodes pure enough for electrorefining. In electrorefining, the copper anodes are loaded into electrolytic cells and interspaced with copper starting sheets, or cathodes, in a bath of copper sulphate solution.

When a direct current is passed through the cell the copper is dissolved from the anode, transported through the electrolyte and re-deposited on the cathode starting sheets.

When the cathodes have built-up to sufficient thickness they are removed from the electrolytic cell and a new set of starting sheets is put in their place.

Solid impurities in the anodes fall to the bottom of the cell as a sludge where they are ultimately collected and processed for the recovery of precious metals such as gold and silver. This material is known as anode slime. The cathodes removed from the electrolytic cell are the primary product of the copper producer and contain These may be sold to wire-rod mills as cathodes or processed further to a product called rod.

This rod product is shipped to wire mills where it is extruded into various sizes of copper wire. In the hydrometallurgical process, the oxidized ores and waste materials are leached with sulphuric acid from the smelting process. Leaching is performed in situ , or in specially prepared piles by distributing acid across the top and allowing it to percolate down through the material where it is collected. The ground under the leach pads is lined with an acid-proof, impermeable plastic material to prevent leach liquor from contaminating groundwater.

In the cementation process which is rarely used today , the copper in the acidic solution is deposited on the surface of scrap iron in exchange for the iron.

When sufficient copper has been cemented out, the copper-rich iron is put into the smelter together with the ore concentrates for copper recovery via the pyrometallurgical route.

In the SXEW process, the pregnant leach solution PLS is concentrated by solvent extraction, which extracts copper but not impurity metals iron and other impurities. The copper-laden organic solution is then separated from the leachate in a settling tank. Sulphuric acid is added to the pregnant organic mixture, which strips the copper into an electrolytic solution. The leachate, containing the iron and other impurities, is returned to the leaching operation where its acid is used for further leaching.

The copper-rich strip solution is passed into an electrolytic cell known as an electrowinning cell. An electrowinning cell differs from an electrorefining cell in that it uses a permanent, insoluble anode. The copper in solution is then plated onto a starting sheet cathode in much the same manner as it is on the cathode in an electrorefining cell. The copper-depleted electrolyte is returned to the solvent extraction process where it is used to strip more copper from the organic solution.

The cathodes produced from the electrowinning process are then sold or made into rods in the same manner as those produced from the electrorefining process. Electrowinning cells are used also for the preparation of starting sheets for both the electrorefining and electrowinning processes by plating the copper onto either stainless steel or titanium cathodes and then stripping off the plated copper.

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.

Precautions include: LEV for dusts during transfer operations; local exhaust and dilution ventilation for sulphur dioxide and carbon monoxide; a noise control and hearing protection programme; protective clothing and shields, rest breaks and fluids for heat stress; and LEV, PPE and electrical precautions for electrolytic processes.

Respiratory protection is commonly worn to protect against dusts, fumes and sulphur dioxide. Table 1 lists environmental pollutants for various steps in copper smelting and refining. Sulphur dioxide, particulate matter containing arsenic, antimony, cadmium, lead, mercury and zinc.

Slimes containing impurities such as gold, silver, antimony, arsenic, bismuth, iron, lead, nickel, selenium, sulphur and zinc. The primary lead production process consists of four steps: sintering, smelting, drossing and pyrometallurgical refining. To begin, a feedstock comprising mainly of lead concentrate in the form of lead sulphide is fed into a sintering machine.

Other raw materials may be added including iron, silica, limestone flux, coke, soda, ash, pyrite, zinc, caustic and particulates gathered from pollution control devices. In the sintering machine the lead feedstock is subjected to blasts of hot air which burn off the sulphur, creating sulphur dioxide. The sinter is then fed along with coke, various recycled and cleanup materials, limestone and other fluxing agents into a blast furnace for reducing, where the carbon acts as a fuel and smelts or melts the lead material.

All layers are then drained off. The speiss and matte are sold to copper smelters for recovery of copper and precious metals. The blast furnace slag which contains zinc, iron, silica and lime is stored in piles and partially recycled.

Sulphur oxide emissions are generated in blast furnaces from small quantities of residual lead sulphide and lead sulphates in the sinter feed. Rough lead bullion from the blast furnace usually requires preliminary treatment in kettles before undergoing refining operations.

A dross, which is composed of lead oxide, along with copper, antimony and other elements, floats to the top and solidifies above the molten lead. The dross is removed and fed into a dross furnace for recovery of the non-lead useful metals.

During the fourth step, the lead bullion is refined using pyrometallurgical methods to remove any remaining non-lead saleable materials e. The lead is refined in a cast iron kettle by five stages.

Antimony, tin and arsenic are removed first. Then zinc is added and gold and silver are removed in the zinc slag. Next, the lead is refined by vacuum removal distillation of zinc. Refining continues with the addition of calcium and magnesium. These two materials combine with bismuth to form an insoluble compound that is skimmed from the kettle.

The refined lead will have a purity of The major hazards are exposure to ore dusts during ore processing and smelting, metal fumes including lead, arsenic and antimony during smelting, sulphur dioxide and carbon monoxide during most smelting operations, noise from grinding and crushing operations and from furnaces, and heat stress from the furnaces.

Precautions include: LEV for dusts during transfer operations; local exhaust and dilution ventilation for sulphur dioxide and carbon monoxide; a noise control and hearing protection programme; and protective clothing and shields, rest breaks and fluids for heat stress.

Biological monitoring for lead is essential. Table 2 lists environmental pollutants for various steps in lead smelting and refining. The zinc concentrate is then reduced to zinc metal in one of two ways: either pyrometallurgically by distillation retorting in a furnace or hydrometallurgically by electrowinning. Four processing stages are generally used in hydrometallurgic zinc refining: calcining, leaching, purification and electrowinning. Roaster types include multiple-hearth, suspension or fluidized-bed.

In general, calcining begins with the mixing of zinc-containing materials with coal. This mixture is then heated, or roasted, to vaporize the zinc oxide which is then moved out of the reaction chamber with the resulting gas stream. The gas stream is directed to the baghouse filter area where the zinc oxide is captured in baghouse dust.

All of the calcining processes generate sulphur dioxide, which is controlled and converted to sulphuric acid as a marketable process by-product. Electrolytic processing of desulphurized calcine consists of three basic steps: leaching, purification and electrolysis. Leaching refers to the dissolving of the captured calcine in a solution of sulphuric acid to form a zinc sulphate solution.

The calcine may be leached once or twice. In the double-leach method, the calcine is dissolved in a slightly acidic solution to remove the sulphates. The calcine is then leached a second time in a stronger solution which dissolves the zinc. This second leaching step is actually the beginning of the third step of purification because many of the iron impurities drop out of the solution as well as the zinc.

After leaching, the solution is purified in two or more stages by adding zinc dust. The solution is purified as the dust forces deleterious elements to precipitate so that they can be filtered out. Purification is usually conducted in large agitation tanks. The elements recovered during purification include copper as a cake and cadmium as a metal. After purification the solution is ready for the final step, electrowinning.

Zinc electrowinning takes place in an electrolytic cell and involves running an electric current from a lead-silver alloy anode through the aqueous zinc solution. This process charges the suspended zinc and forces it to deposit onto an aluminium cathode which is immersed in the solution.

Every 24 to 48 hours, each cell is shut down, the zinc-coated cathodes removed and rinsed, and the zinc mechanically stripped from the aluminium plates. The zinc concentrate is then melted and cast into ingots and is often as high as Electrolytic zinc smelters contain as many as several hundred cells. A portion of the electrical energy is converted into heat, which increases the temperature of the electrolyte.

During electrowinning a portion of the electrolyte passes through cooling towers to decrease its temperature and to evaporate the water it collects during the process. The major hazards are exposure to ore dusts during ore processing and smelting, metal fumes including zinc and lead during refining and roasting, 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.

Precautions include: LEV for dusts during transfer operations; local exhaust and dilution ventilation for sulphur dioxide and carbon monoxide; a noise control and hearing protection programme; protective clothing and shields, rest breaks and fluids for heat stress; and LEV, PPE, and electrical precautions for electrolytic processes. Table 3 lists environmental pollutants for various steps in zinc smelting and refining. Bauxite is extracted by open-pit mining. The richer ores are used as mined.

The lower grade ores may be beneficiated by crushing and washing to remove clay and silica waste. The production of the metal comprises two basic steps:. Experimental development suggests that in the future aluminium may be reduced to the metal by direct reduction from the ore. There are presently two major types of Hall-Heroult electrolytic cells in use.

In such smelters exposure to polycyclic hydrocarbons normally occurs in the electrode manufacturing facilities, especially during mixing mills and forming presses. Smelters utilizing the Soderberg-type cell do not require facilities for the manufacture of baked carbon anodes. Rather, the mixture of coke and pitch binder is put into hoppers whose lower ends are immersed in the molten cryolite-alumina bath mixture.

As the mixture of pitch and coke is heated by the molten metal-cryolite bath within the cell, this mixture bakes into a hard graphitic mass in situ.

Metal rods are inserted into the anodic mass as conductors for a direct current electric flow. These rods must be replaced periodically; in extracting these, considerable amounts of coal tar pitch volatiles are evolved into the cell room environment. To this exposure is added those pitch volatiles generated as the baking of the pitch-coke mass proceeds.

Within the last decade the industry has tended to either not replace or to modify existent Soderberg type reduction facilities as a consequence of the demonstrated carcinogenic hazard they present. In addition, with the increasing automation of reduction cell operations—particularly the changing of anodes, tasks are more commonly performed from enclosed mechanical cranes.

Consequently worker exposures and the risk of developing those disorders associated with aluminium smelting are gradually decreasing in modern facilities. By contrast, in those economies wherein adequate capital investment is not readily available, the persistence of older, manually operated reduction processes will continue to present the risks of those occupational disorders see below previously associated with aluminium reduction plants.

Indeed, this tendency will tend to become more aggravated in such older, unimproved operations, especially as they age. The electrodes required by pre-bake electrolytic reduction to pure metal are normally made by a facility associated with this type of aluminium smelting plant. The anodes and cathodes are most frequently made from a mixture of ground petroleum-derived coke and pitch.

Coke first is ground in ball mills, then conveyed and mixed mechanically with the pitch and finally cast into blocks in a moulding presses. These anode or cathode blocks are next heated in a gas-fired furnace for several days until they form hard graphitic masses with essentially all volatiles having been driven off. Finally they are attached to anode rods or saw-grooved to receive the cathode bars. It should be noted that the pitch used to form such electrodes represents a distillate which is derived from coal or petroleum tar.

In the conversion of this tar to pitch by heating, the final pitch product has boiled off essentially all of its low-boiling point inorganics, e. Thus, such pitch should not present the same hazards in its use as coal or petroleum tars since these classes of compounds ought not to be present.

There are some indications that the carcinogenic potential of such pitch products may not be as great as the more complex mixture of tars and other volatiles associated with the incomplete combustion of coal.

The hazards and preventive measures for aluminium smelting and refining processes are basically the same as those found in smelting and refining in general; however, the individual processes present certain specific hazards. However, the possibility of the presence of crystalline silica in bauxite ores should be considered.

The extensive use of caustic soda in the Bayer process presents frequent risks of chemical burns of the skin and eyes. Descaling of tanks by pneumatic hammers is responsible for severe noise exposure. The potential hazards associated with the inhalation of excessive doses of aluminium oxide produced in this process are discussed below.

All workers involved in the Bayer process should be well informed of the hazards associated with handling caustic soda. In all sites at risk, eyewash fountains and basins with running water and deluge showers should be provided, with notices explaining their use. PPE e. Showers and double locker accommodations one locker for work clothing, the other for personal clothing should be provided and all employees encouraged to wash thoroughly at the end of the shift.

All workers handling molten metal should be supplied with visors, respirators, gauntlets, aprons, armlets and spats to protect them against burns, dust and fumes. Workers employed on the Gadeau low-temperature process should be supplied with special gloves and suits to protect them from hydrochloric acid fumes given off when the cells start up; wool has proved to have a good resistance to these fumes.

Respirators with charcoal cartridges or alumina-impregnated masks give adequate protection against pitch and fluorine fumes; efficient dust masks are necessary for protection against carbon dust. Workers with more severe dust and fume exposure, particularly in Soderberg operations, should be provided with air-supplied respiratory protective equipment.

As mechanized potroom work is remotely performed from enclosed cabins, these protective measures will become less necessary. Electrolytic reduction exposes workers to the potential for skin burns and accidents due to molten metal splashes, heat stress disorders, noise, electrical hazards, cryolite and hydrofluoric acid fumes.

Electrolytic reduction cells may emit large quantities of dusts of fluoride and alumina. In carbon-electrode manufacturing shops, exhaust ventilation equipment with bag filters should be installed; enclosure of pitch and carbon grinding equipment further effectively minimizes exposures to heated pitches and carbon dusts. Regular checks on atmospheric dust concentrations should be made with a suitable sampling device. Periodic x-ray examinations should be carried out on workers exposed to dust, and these should be followed up by clinical examinations when necessary.

In order to reduce the risk of handling pitch, transport of this material should be mechanized as far as possible e. Regular skin examinations to detect erythema, epitheliomata or dermatitis are also prudent, and extra protection can be provided by alginate-base barrier creams. Workers doing hot work should be instructed prior to the onset of hot weather to increase fluid intake and heavily salt their food. They and their supervisors should also be trained to recognise incipient heat-induced disorders in themselves and their co-workers.

All those working here should be trained to take the proper measure necessary to prevent the occurrence or progression of the heat disorders. Workers exposed to high noise levels should be supplied with hearing protection equipment such as earplugs which allow the passage of low-frequency noise to allow perception of orders but reduce the transmission of intense, high-frequency noise.

Moreover, workers should undergo regular audiometric examination to detect hearing loss. Finally, personnel should also be trained to give cardiopulmonary resuscitation to victims of electric shock accidents. The potential for molten metal splashes and severe burns are widespread at many sites in reduction plants and associated operations.

In addition to protective clothing e. Individuals using cardiac pacemakers should be excluded from reduction operations because of the risk of magnetic field induced dysrhythmias. The hazards to workers, the general population and the environment resulting from the emission of fluoride-containing gases, smokes and dusts due to the use of cryolite flux have been widely reported see table 1.

In children living in the vicinity of poorly controlled aluminium smelters, variable degrees of mottling of permanent teeth have been reported if exposure occurred during the developmental phase of permanent teeth growth.

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 metal itself is often oxidized. 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.

At every stage of the process, there is no guidance and no guarantee of success. Does this dirt contain iron ore?