Ore smelting involves heating rock containing metals to separate the native metal for further use. Early smelting involved introducing carbon into the furnace. Modern smelting tools reduce emissions and recycle wastewater. The flash furnace is a newer, closed environmental system that generates heat through chemical reactions. Pollution remains a significant problem in the industry.
Ore smelting is a process in which rock containing metals in ore form is heated, often with the addition of other chemicals or gases, to separate the native metal for further use and processing. Copper and silver are believed to have been the first metals ever smelted by mankind, and the origins of the process can be traced back many thousands of years before the dawn of civilization. Early smelting of oxide minerals such as iron involved introducing carbon into the smelting furnace in the form of charcoal, where the carbon bonded with the oxygen in the ore at high temperatures and liberated the base metal. Many early eras of civilization’s progress are named after the period’s common smelting technology, or lack thereof, such as the Stone Age, Bronze Age, and Iron Age.
A contemporary smelting furnace is typically a large heat-treated steel reactor chamber lined with carbon and often known as a reduction cell. The chamber is heated to the metal’s melting point and is reacted with chemicals that bind to its oxidizing agents. The metal is drained and the solid waste material, known as slag, is stored for safe disposal. Smelting techniques are known to be heavy environmental pollutants, as they can create wastewater and heavy metal contaminants such as arsenic, cadmium and mercury, which pollute local waterways.
A common complaint about ore smelting has been that the equipment also creates dangerous air pollution that leads to acid rain. Potentially causing damage to the atmosphere in the form of sulfuric acid mist, the result of melting metal sulfides is the emission of sulfur dioxide gas which reacts with the atmosphere. An example of this is copper sulfide, CuFeS2, which is smelted in much the same way as it was centuries ago. Acid rain is not only harmful to human and animal populations, it can also increase the level of acidity in the soil, as most plants cannot thrive in highly acidic environments. Modern smelting tools now involve the use of electrostatic precipitators that act as air scrubbers to reduce emissions and the recycling of melted wastewater in the process instead of releasing it into the environment.
A newer method of ore smelting involves what’s known as a flash furnace, which is used to smelt anything from copper to tin or aluminum. It is more of a closed environmental system than traditional and largely exothermic smelters, where the smelter generates heat through chemical reactions rather than primarily external sources. Smelting alumina ore is thus processed into aluminum in a reaction cell operating at temperatures from 1.778° to 2.102° Fahrenheit (970° to 1.150° Celsius). The reaction cell is also electrically charged, which helps remove impurities and causes alumina to react with carbon to form aluminum and carbon dioxide.
The flash furnace gets its name from the ore smelting process in which the sulfur oxides in the ore are instantly converted into sulfur dioxide gas. This gas is diverted by new types of smelting tools into the furnace, stored and sold for other industrial uses. While this increases smelting safety, conversion to flash furnaces from older-style sinter and ore smelting blast furnace designs only began to occur in the mid-1990s. Pollution is still a significant problem in the smelting industry and the land around smelters has traditionally been a wasteland, where nothing natural could thrive.
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