Misplaced Pages

#381618

65-461: Chanderiya Smelter Complex is the world's largest lead-zinc smelter complex in the Chittorgarh district of Rajasthan state of India . It is metallurgical type plant. The original complex was built from 1989 and commissioned in 1991. It refines lead-zinc ore from Rampura Agucha . It produces zinc , lead , cadmium and other precious metals . This article related to Rajasthan

130-565: A Bessemer converter or by other means including smelting reduction processes such as the Corex Process . Smelting has serious effects on the environment , producing wastewater and slag and releasing such toxic metals as copper , silver, iron, cobalt , and selenium into the atmosphere. Smelters also release gaseous sulfur dioxide , contributing to acid rain , which acidifies soil and water. The smelter in Flin Flon, Canada

195-415: A chemical reaction . Smelting, therefore, consists of using suitable reducing substances that combine with those oxidizing elements to free the metal. In the case of sulfides and carbonates, a process called " roasting " removes the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A few practical examples: Reduction

260-424: A hammer to produce wrought iron . Some of the earliest evidence to date for the bloomery smelting of iron is found at Tell Hammeh , Jordan, radiocarbon-dated to c.  930 BC . From the medieval period, an indirect process began to replace the direct reduction in bloomeries. This used a blast furnace to make pig iron , which then had to undergo a further process to make forgeable bar iron. Processes for

325-709: A low concentration of sulfur dioxide that was difficult to capture; a new generation of copper smelting technologies has supplanted them. More recent furnaces exploit bath smelting, top-jetting lance smelting, flash smelting , and blast furnaces. Some examples of bath smelters include the Noranda furnace, the Isasmelt furnace, the Teniente reactor, the Vunyukov smelter, and the SKS technology. Top-jetting lance smelters include

390-481: A range of more complex organic compounds known collectively as polycyclic aromatic hydrocarbons (PAH). Treatment technologies include recycling of wastewater; settling basins , clarifiers and filtration systems for solids removal; oil skimmers and filtration; chemical precipitation and filtration for dissolved metals; carbon adsorption and biological oxidation for organic pollutants; and evaporation. Pollutants generated by other types of smelters varies with

455-464: A rate of tens of nanometers per minute. The addition of hydrogen to the plasma augments the removal efficiency by chemical mechanisms. Mechanical agitation is another possibility for disrupting the oxide layer. Ultrasound can be used for assisting tinning and soldering; an ultrasonic transducer can be mounted on the soldering iron, in a solder bath, or in the wave for wave soldering . The oxide disruption and removal involves cavitation effects between

520-402: Is a stub . You can help Misplaced Pages by expanding it . Smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron , copper , silver , tin , lead and zinc . Smelting uses heat and a chemical reducing agent to decompose

585-526: Is burned at one end to melt the dry sulfide concentrates (usually after partial roasting) which are fed through openings in the roof of the furnace. The slag floats over the heavier matte and is removed and discarded or recycled. The sulfide matte is then sent to the converter . The precise details of the process vary from one furnace to another depending on the mineralogy of the ore body. While reverberatory furnaces produced slags containing very little copper, they were relatively energy inefficient and off-gassed

650-433: Is converted into steel . Plants for the electrolytic reduction of aluminium are referred to as aluminium smelters . Smelting involves more than just melting the metal out of its ore. Most ores are the chemical compound of the metal and other elements, such as oxygen (as an oxide ), sulfur (as a sulfide ), or carbon and oxygen together (as a carbonate ). To extract the metal, workers must make these compounds undergo

715-542: Is easily produced during the heating process, and as a gas comes into intimate contact with the ore. In the Old World , humans learned to smelt metals in prehistoric times, more than 8000 years ago. The discovery and use of the "useful" metals – copper and bronze at first, then iron a few millennia later – had an enormous impact on human society. The impact was so pervasive that scholars traditionally divide ancient history into Stone Age , Bronze Age , and Iron Age . In

SECTION 10

#1732798045382

780-436: Is known as diffusion soldering. Fluxless brazing of copper alloys can be done with self-fluxing filler metals. Such metals contain an element capable of reaction with oxygen, usually phosphorus . A good example is the family of copper-phosphorus alloys. Fluxes have several important properties: The composition of fluxes is tailored for the required properties - the base metals and their surface preparation (which determine

845-426: Is much more reactive than molecular hydrogen. In contact with surface oxides it forms hydroxides, water, or hydrogenated complexes, which are volatile at soldering temperatures. A practical dissociation method is an electrical discharge. Argon-hydrogen gas compositions with hydrogen concentration below the low flammable limit can be used, eliminating the safety issues. The operation has to be performed at low pressure, as

910-414: Is not known which component of the fumes causes the problem. While molten solder has low tendency to adhere to organic materials, molten fluxes, especially of the resin/rosin type, adhere well to fingers. A mass of hot sticky flux can transfer more heat to skin and cause more serious burns than a comparable particle of non-adhering molten metal, which can be quickly shaken off. In this regard, molten flux

975-408: Is occasionally found in commercially significant quantities. These minerals are primarily carbonates , sulfides , or oxides of the metal, mixed with other components such as silica and alumina . Roasting the carbonate and sulfide minerals in the air converts them to oxides. The oxides, in turn, are smelted into the metal. Carbon monoxide was (and is) the reducing agent of choice for smelting. It

1040-490: Is often necessary to use flux , such as limestone (or dolomite ), to remove the accompanying rock gangue as slag. This calcination reaction emits carbon dioxide. The required temperature varies both in absolute terms and in terms of the melting point of the base metal. Examples: Fluxes are materials added to the ore during smelting to catalyze the desired reactions and to chemically bind to unwanted impurities or reaction products. Calcium carbonate or calcium oxide in

1105-597: Is only marginally harder, and had even less impact by itself. The earliest evidence for iron-making is a small number of iron fragments with the appropriate amounts of carbon admixture found in the Proto-Hittite layers at Kaman-Kalehöyük and dated to 2200–2000 BC. Souckova-Siegolová (2001) shows that iron implements were made in Central Anatolia in very limited quantities around 1800 BC and were in general use by elites, though not by commoners, during

1170-430: Is oxidized in two stages. First, carbon (C) combusts with oxygen (O 2 ) in the air to produce carbon monoxide (CO). Second, the carbon monoxide reacts with the ore (e.g. Fe 2 O 3 ) and removes one of its oxygen atoms, releasing carbon dioxide (CO 2 ). After successive interactions with carbon monoxide, all of the oxygen in the ore will be removed, leaving the raw metal element (e.g. Fe). As most ores are impure, it

1235-401: Is similar to molten hot glue . In some cases the presence of flux is undesirable; flux traces interfere with e.g. precision optics or MEMS assemblies. Flux residues also tend to outgas in vacuum and space applications, and traces of water, ions and organic compounds may adversely affect long-term reliability of non-hermetic packages. Trapped flux residues are also the cause of most voids in

1300-934: Is soluble in molten rosin. Some activators may also contain metal ions, capable of exchange reaction with the underlying metal; such fluxes aid soldering by chemically depositing a thin layer of easier solderable metal on the exposed base metal. An example is the group of fluxes containing zinc , tin or cadmium compounds, usually chlorides, sometimes fluorides or fluoroborates. Common high-activity activators are mineral acids , often together with halides, amines, water or alcohols: Inorganic acids are highly corrosive to metals even at room temperature, which causes issues during storage, handling and applications. As soldering involves high temperatures, compounds that decompose or react, with acids as products, are frequently used: The terms resin flux and rosin flux are ambiguous and somewhat interchangeable, with different vendors using different assignments. Generally, fluxes are labeled as rosin if

1365-412: Is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide, made by incomplete combustion in an air-starved furnace) pulls the final oxygen atoms from the raw metal. The carbon source acts as a chemical reactant to remove oxygen from the ore, yielding the purified metal element as a product. The carbon source

SECTION 20

#1732798045382

1430-422: Is typically dual: dissolving the oxides already present on the metal surface to facilitate wetting by molten metal, and acting as an oxygen barrier by coating the hot surface, preventing oxidation. For example, tin-lead solder attaches very well to copper metal, but poorly to its oxides, which form quickly at soldering temperatures. By preventing the formation of metal oxides, flux enables the solder to adhere to

1495-562: Is unknown. The first such bronzes may have been a lucky accident from tin-contaminated copper ores. However, by 2000 BC, people were mining tin on purpose to produce bronze—which is remarkable as tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. The discovery of copper and bronze manufacture had a significant impact on the history of the Old World . Metals were hard enough to make weapons that were heavier, stronger, and more resistant to impact damage than wood, bone, or stone equivalents. For several millennia, bronze

1560-517: The Americas , pre- Inca civilizations of the central Andes in Peru had mastered the smelting of copper and silver at least six centuries before the first Europeans arrived in the 16th century, while never mastering the smelting of metals such as iron for use with weapon craft. Copper was the first metal to be smelted. How the discovery came about is debated. Campfires are about 200 °C short of

1625-619: The New Hittite Empire (~1400–1200 BC). Archaeologists have found indications of iron working in Ancient Egypt , somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BC). Significantly though, they have found no evidence of iron ore smelting in any (pre-modern) period. In addition, very early instances of carbon steel were in production around 2000 years ago (around

1690-546: The Mitsubishi smelting reactor. Flash smelters account for over 50% of the world's copper smelters. There are many more varieties of smelting processes, including the Kivset, Ausmelt, Tamano, EAF, and BF. Of the seven metals known in antiquity , only gold regularly occurs in nature as a native metal . The others – copper , lead , silver , tin , iron , and mercury – occur primarily as minerals, although native copper

1755-678: The Sn-Sb 5 requires as little as 10 °C, but the Sn-Pb 37 alloy requires 77 °C above its melting point to dissolve its surface oxide. The self-dissolved oxide degrades the solder's properties and increases its viscosity in molten state, however, so this approach is not optimal. Solder preforms are preferred to be with high volume-to-surface ratio, as that limits the amount of oxide being formed. Pastes have to contain smooth spherical particles, preforms are ideally made of round wire. Problems with preforms can be also sidestepped by depositing

1820-415: The activator generally increases with temperature, up to a certain value where activity ceases, either due to thermal decomposition or excessive volatilization. However the oxidation rate of the metals also increases with temperature. At high temperatures, copper oxide reacts with hydrogen chloride to water-soluble and mechanically weak copper chloride, and with rosin to salts of copper and abietic acid which

1885-655: The activators is primarily disruption and removal of the oxide layer on the metal surface (and also the molten solder), to facilitate direct contact between the molten solder and metal. The reaction product is usually soluble or at least dispersible in the molten vehicle. The activators are usually either acids, or compounds that release acids at elevated temperature. The general reaction of oxide removal is: Salts are ionic in nature and can cause problems from metallic leaching or dendrite growth, with possible product failure. In some cases, particularly in high- reliability applications, flux residues must be removed. The activity of

1950-418: The ancient world. It is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for sling projectiles. However, since it was easy to cast and shape, workers in the classical world of Ancient Greece and Ancient Rome used it extensively to pipe and store water. They also used it as a mortar in stone buildings. Tin was much less common than lead,

2015-461: The base metal ore. For example, aluminum smelters typically generate fluoride , benzo(a)pyrene , antimony and nickel, as well as aluminum. Copper smelters typically discharge cadmium, lead, zinc , arsenic and nickel, in addition to copper. Lead smelters may discharge antimony , asbestos, cadmium, copper and zinc, in addition to lead. Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform

Chanderiya Smelter Complex - Misplaced Pages Continue

2080-434: The bonds in the ore. Sulfide ores such as those commonly used to obtain copper, zinc or lead, are roasted before smelting in order to convert the sulfides to oxides, which are more readily reduced to the metal. Roasting heats the ore in the presence of oxygen from air, oxidizing the ore and liberating the sulfur as sulfur dioxide gas. Smelting most prominently takes place in a blast furnace to produce pig iron , which

2145-553: The clean metal surface, rather than forming beads, as it would on an oxidized surface. In soldering metals, flux serves a threefold purpose: it removes any oxidized metal from the surfaces to be soldered, seals out air thus preventing further oxidation, and improves the wetting characteristics of the liquid solder. Some fluxes are corrosive , so the parts have to be cleaned with a damp sponge or other absorbent material after soldering to prevent damage. Several types of flux are used in electronics. A number of standards exist to define

2210-463: The composition and thickness of surface oxides), the solder (which determines the wetting properties and the soldering temperature), the corrosion resistance and ease of removal, and others. Fluxes for soft soldering are typically of organic nature, though inorganic fluxes, usually based on halogenides or acids, are also used in non-electronics applications. Fluxes for brazing operate at significantly higher temperatures and are therefore mostly inorganic;

2275-408: The discovery happened several millennia before the invention of writing, there is no written record of how it was made. However, tin and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident. Recent scholarship however has called this find into question. Lead is a common metal, but its discovery had relatively little impact in

2340-513: The establishment of trade networks that spanned large areas of Europe and Asia and had a major effect on the distribution of wealth among individuals and nations. The earliest known cast lead beads were thought to be in the Çatalhöyük site in Anatolia ( Turkey ), and dated from about 6500 BC. However, recent research has discovered that this was not lead, but rather cerussite and galena, minerals rich in, but distinct from, lead. Since

2405-454: The first-century .) in northwest Tanzania , based on complex preheating principles. These discoveries are significant for the history of metallurgy. Most early processes in Europe and Africa involved smelting iron ore in a bloomery , where the temperature is kept low enough so that the iron does not melt. This produces a spongy mass of iron called a bloom, which then must be consolidated with

2470-787: The flow of slag in smelting, is the origin of the word flux in metallurgy. The flux most commonly used in iron and steel furnaces is limestone , which is charged in the proper proportions with the iron and fuel . Fluxes have several serious drawbacks: In special cases the drawbacks are sufficiently serious to warrant using fluxless techniques. Acid flux types (not used in electronics) may contain hydrochloric acid , zinc chloride or ammonium chloride , which are harmful to humans. Therefore, flux should be handled with gloves and goggles, and used with adequate ventilation. Prolonged exposure to rosin fumes released during soldering can cause occupational asthma (formerly called colophony disease in this context) in sensitive individuals, although it

2535-416: The fluxes for use at lower temperatures. At higher temperatures even relatively mild chemicals have sufficient oxide-disrupting activity, but the metal oxidation rates become fairly high; the barrier function of the vehicle therefore becomes more important than the fluxing activity. High molecular weight hydrocarbons are often used for this application; a diluent with a lower molecular weight, boiling off during

2600-520: The form of lime are often used for this purpose, since they react with sulfur, phosphorus, and silicon impurities to allow them to be readily separated and discarded, in the form of slag. Fluxes may also serve to control the viscosity and neutralize unwanted acids. Flux and slag can provide a secondary service after the reduction step is complete; they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to readily oxidize. This prevents impurities from forming in

2665-453: The joint. Thicker gold coatings are usually limited to use with indium-based solders and solders with high gold content. Removal of the oxides from the solder preform is also troublesome. Fortunately some alloys are able to dissolve the surface oxides in their bulk when superheated by several degrees above their melting point; the Sn-Cu 1 and Sn-Ag 4 require superheating by 18–19 °C,

Chanderiya Smelter Complex - Misplaced Pages Continue

2730-422: The joints. Flux-less techniques are therefore desirable there. For successful soldering and brazing, the oxide layer has to be removed from both the surfaces of the materials and the surface of the filler metal preform; the exposed surfaces also have to be protected against oxidation during heating. Flux-coated preforms can also be used to eliminate flux residue entirely from the soldering process. Protection of

2795-411: The metal at the elevated temperatures has to be avoided. This means that fluxes need to be more aggressive and to provide a physical barrier. Traditionally borax was used as a flux for brazing, but there are now many different fluxes available, often using active chemicals such as fluorides as well as wetting agents. Many of these chemicals are toxic and due care should be taken during their use. In

2860-515: The metal. The ores of base metals are often sulfides. In recent centuries, reverberatory furnaces have been used to keep the charge being smelted separately from the fuel. Traditionally, they were used for the first step of smelting: forming two liquids, one an oxide slag containing most of the impurities, and the other a sulfide matte containing the valuable metal sulfide and some impurities. Such "reverb" furnaces are today about 40 meters long, 3 meters high, and 10 meters wide. Fuel

2925-413: The metals to be joined. In some applications molten flux also serves as a heat-transfer medium, facilitating heating of the joint by the soldering tool. In high-temperature metal joining processes ( welding , brazing and soldering ), fluxes are nearly inert at room temperature, but become strongly reducing at elevated temperatures, preventing oxidation of the base and filler materials. The role of flux

2990-487: The molten solder and the base metal surface. A common application of ultrasound fluxing is in tinning of passive parts (active parts do not cope well with the mechanical stresses involved); even aluminium can be tinned this way. The parts can then be soldered or brazed conventionally. Mechanical rubbing of a heated surface with molten solder can be used for coating the surface. Both surfaces to be joined can be prepared this way, then placed together and reheated. This technique

3055-722: The oldest evidence, now appears to be hammered, native copper. Combining copper with tin and/or arsenic in the right proportions produces bronze , an alloy that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 BC from Asia Minor . The Inca bronze alloys were also of this type. Arsenic is often an impurity in copper ores, so the discovery could have been made by accident. Eventually, arsenic-bearing minerals were intentionally added during smelting. Copper–tin bronzes, harder and more durable, were developed around 3500 BC, also in Asia Minor. How smiths learned to produce copper/tin bronzes

3120-412: The ore, driving off other elements as gases or slag and leaving the metal behind. The reducing agent is commonly a fossil-fuel source of carbon , such as carbon monoxide from incomplete combustion of coke —or, in earlier times, of charcoal . The oxygen in the ore binds to carbon at high temperatures, as the chemical potential energy of the bonds in carbon dioxide (CO 2 ) is lower than that of

3185-483: The organic compounds tend to be of supplementary nature, e.g. to make the flux sticky at low temperature so it can be easily applied. The surface of the tin-based solder is coated predominantly with tin oxides; even in alloys the surface layer tends to become relatively enriched by tin. Fluxes for indium and zinc based solders have different compositions than fluxes for ordinary tin-lead and tin-based solders, due to different soldering temperatures and different chemistry of

3250-464: The oxides involved. Organic fluxes are unsuitable for flame soldering and flame brazing, as they tend to char and impair solder flow. Some metals are classified as "unsolderable" in air, and have to be either coated with another metal before soldering or special fluxes or protective atmospheres have to be used. Such metals are beryllium , chromium , magnesium , titanium , and some aluminium alloys . Fluxes for high-temperature soldering differ from

3315-612: The physical tasks demanded by their jobs. In the United States, the Environmental Protection Agency has published pollution control regulations for smelters. Flux (metallurgy) Some of the earliest known fluxes were sodium carbonate , potash , charcoal , coke , borax , lime , lead sulfide and certain minerals containing phosphorus . Iron ore was also used as a flux in the smelting of copper. These agents served various functions,

SECTION 50

#1732798045382

3380-461: The preheat phase, is usually used to aid application. Common fluxes are ammonium chloride or resin acids (contained in rosin ) for soldering copper and tin ; hydrochloric acid and zinc chloride for soldering galvanized iron (and other zinc surfaces); and borax for brazing , braze-welding ferrous metals, and forge welding . Organic fluxes typically consist of four major components: Inorganic fluxes contain components playing

3445-469: The process of smelting , inorganic chlorides, fluorides (see fluorite ), limestone and other materials are designated as "fluxes" when added to the contents of a smelting furnace or a cupola for the purpose of purging the metal of chemical impurities such as phosphorus, and of rendering slag more liquid at the smelting temperature. Slag is a liquid mixture of ash , flux, and other impurities. This reduction of slag viscosity with temperature, increasing

3510-493: The reaction speed is too slow for practical applications.) Very low partial pressures of oxygen and water vapor have to be achieved for the reaction to proceed. Other reactive atmospheres are also in use. Vapors of formic acid and acetic acid are the most commonly used. Carbon monoxide and halogen gases (for example carbon tetrafluoride , sulfur hexafluoride , or dichlorodifluoromethane ) require fairly high temperatures for several minutes to be effective. Atomic hydrogen

3575-512: The same role as in organic fluxes. They are more often used in brazing and other high-temperature applications, where organic fluxes have insufficient thermal stability. The chemicals used often simultaneously act as both vehicles and activators; typical examples are borax , borates , fluoroborates , fluorides and chlorides . Halogenides are active at lower temperatures than borates, and are therefore used for brazing of aluminium and magnesium alloys; they are however highly corrosive. The role of

3640-585: The second stage include fining in a finery forge . In the 13th century during the High Middle Ages the blast furnace was introduced by China who had been using it since as early as 200 b.c during the Qin dynasty . [1] Puddling was also introduced in the Industrial Revolution . Both processes are now obsolete, and wrought iron is now rarely made. Instead, mild steel is produced from

3705-481: The simplest being a reducing agent, which prevented oxides from forming on the surface of the molten metal, while others absorbed impurities into slag , which could be scraped off molten metal. Fluxes are also used in foundries for removing impurities from molten nonferrous metals such as aluminium , or for adding desirable trace elements such as titanium . As reducing agents, fluxes facilitate soldering , brazing , and welding by removing oxidation from

3770-449: The solder alloy directly on the surfaces of the parts or substrates, by chemical or electrochemical means for example. A protective atmosphere with chemically reducing properties can be beneficial in some cases. Molecular hydrogen can be used to reduce surface oxides of tin and indium at temperatures above 430 and 470 °C; for zinc the temperature is above 500 °C, where zinc is already becoming volatilized. (At lower temperatures

3835-542: The stability of atomic hydrogen at atmospheric pressure is insufficient. Such hydrogen plasma can be used for fluxless reflow soldering. Active atmospheres are relatively common in furnace brazing; due to the high process temperatures the reactions are reasonably fast. The active ingredients are usually carbon monoxide (possibly in the form of combusted fuel gas) and hydrogen. Thermal dissociation of ammonia yields an inexpensive mixture of hydrogen and nitrogen. Bombardment with atomic particle beams can remove surface layers at

3900-523: The surfaces against further oxidation is relatively simple, by using vacuum or inert atmosphere. Removal of the native oxide layer is more troublesome; physical or chemical cleaning methods have to be employed and the surfaces can be protected by e.g. gold plating. The gold layer has to be sufficiently thick and non-porous to provide protection for reasonable storage time. Thick gold metallization also limits choice of soldering alloys, as tin-based solders dissolve gold and form brittle intermetallics , embrittling

3965-651: The temperature needed, so some propose that the first smelting of copper may have occurred in pottery kilns . (The development of copper smelting in the Andes, which is believed to have occurred independently of the Old World , may have occurred in the same way. ) The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia. A mace head found in Turkey and dated to 5000 BC, once thought to be

SECTION 60

#1732798045382

4030-483: The various flux types. The principal standard is J-STD-004. Various tests, including the ROSE test , may be used after soldering to check for the presence of ionic or other contaminants that could cause short circuits or other problems. Brazing (sometimes known as silver soldering or hard soldering ) requires a higher temperature than soft soldering (> 450 °C). As well as removing existing oxides, rapid oxidation of

4095-426: Was formerly used to repair small damages on aluminium aircraft skins. A very thin layer of zinc can be used for joining aluminium parts. The parts have to be perfectly machined, or pressed together, due to the small volume of filler metal. At high temperature applied for long time, the zinc diffuses away from the joint. The resulting joint does not present a mechanical weakness and is corrosion-resistant. The technique

4160-1041: Was one of the largest point sources of mercury in North America in the 20th century. Even after smelter releases were drastically reduced, landscape re-emission continued to be a major regional source of mercury. Lakes will likely receive mercury contamination from the smelter for decades, from both re-emissions returning as rainwater and leaching of metals from the soil. Air pollutants generated by aluminium smelters include carbonyl sulfide , hydrogen fluoride , polycyclic compounds , lead, nickel , manganese , polychlorinated biphenyls , and mercury . Copper smelter emissions include arsenic, beryllium , cadmium , chromium , lead, manganese, and nickel. Lead smelters typically emit arsenic, antimony , cadmium and various lead compounds. Wastewater pollutants discharged by iron and steel mills includes gasification products such as benzene , naphthalene , anthracene , cyanide , ammonia , phenols and cresols , together with

4225-526: Was the material of choice for weapons such as swords , daggers , battle axes , and spear and arrow points, as well as protective gear such as shields , helmets , greaves (metal shin guards), and other body armor . Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as chisels , saws , adzes , nails , blade shears , knives , sewing needles and pins , jugs , cooking pots and cauldrons , mirrors , and horse harnesses . Tin and copper also contributed to

#381618