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Smelting

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction (for the production of steel) from iron ore, and copper extraction and other base metals from their ores. Smelting uses heat and a chemical reducing agent, commonly a fuel that is a source of carbon such as coke, or in earlier times charcoal, to change the oxidation state of the metal ore. The carbon or carbon monoxide derived from it removes oxygen from the ore to leave the metal. The carbon is thus oxidized, producing carbon dioxide and carbon monoxide. As most ores are impure, it is often necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag.

Plants for the electrolytic reduction of aluminium, while not using carbon, are also generally referred to as smelters.

Iron smelting

Early iron smelting
The earliest evidence to date for the bloomery smelting of iron is found at Tell Hammeh, Jordan (see also external link), and dates to 930 BC (C14 dating). However, based on the archaeological record of iron artifacts, it is clear that intentional reduction of iron metal from terrestrial ores (in the case of Hammeh a Haematite ore), must have started near the end of the Late Bronze Age (ca. 1600–1150 BC). Where and how iron smelting was discovered is widely debated, and remains uncertain due to the significant lack of production finds. Nevertheless, there is some consensus[citation needed] that iron technology originated in the Near East, perhaps in Eastern Anatolia.

In Ancient Egypt, somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BC), there are indications of iron working. Significantly though, no evidence for the smelting of iron from ore has been attested to Egypt in any period. There is a further possibility of iron smelting and working in West Africa by 1200 BC[1]. In addition, very early instances of carbon steel were found to be in production around 2000 years before the present in northwest Tanzania, based on complex preheating principles. These discoveries are significant for the history of metallurgy.[2]

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 has to be consolidated with a hammer.

Later iron smelting
From the medieval period, the process of direct reduction in bloomeries began to be replaced by an indirect process. In this, a blast furnace was used to make pig iron, which then had to undergo a further process to make forgeable bar iron. (Further details of this can 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.

Base metals

The ores of base metals are often sulfides. 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.

冶炼
　　词义:用焙烧、熔炼、电解以及使用化学药剂等方法把矿石中的金属提取出来;减少金属中所含的杂质或增加金属中某种成分,炼成所需要的金属.
　　英文:smelting
　　冶炼分为火法冶炼、湿法提取或电化学沉积
　　火法冶炼（Pyrometallurgy）
　　又称为干式冶金，把矿石和必要的添加物一起在炉中加热至高温，熔化为液体，生成所需的化学反应，从而分离出粗金属，然后再将粗金属精炼。
　　湿式冶金（Hydrometallurgy）
　　湿法冶金这种冶金过程是用酸、碱、盐类的水溶液，以化学方法从矿石中提取所需金属组分，然后用水溶液电解等各种方法制取金属。此法主要应用在低本位、难熔化或微粉状的矿石。现在世界上有75％的锌和镉是采用焙烧-浸取-水溶液电解法制成的。这种方法已大部分代替了过去的火法炼锌。其他难于分离的金属如镍-钴，锆-铪，钽-铌及稀土金属都采用湿法冶金的技术如溶剂萃取或离子交换等新方法进行分离，取得显著的效果。
　　利用某种溶剂，借助化学反应（包括氧化、还原、中和、水解及络合等反应），对原料中的金属进行提取和分离的冶金过程。湿法冶金包括4个主要步骤：①用溶剂将原料中有用成分转入溶液，即浸取。②浸取溶液与残渣分离，同时将夹带于残渣中的冶金溶剂和金属离子回收。③浸取溶液的净化和富集，常用离子交换和溶剂萃取技术或其他化学沉淀方法。④从净化液中提取金属或化合物。
　　湿法冶金在锌、铝、铜、铀等工业中占有重要地位，世界上全部的氧化铝、氧化铀，大部分锌和部分铜都是用湿法生产的。湿法冶金的优点在于对非常低品位矿石（金、铀）的适用性，对相似金属（铪与锆）难分离情况的适用性；以及和火法冶金相比，材料的周转比较简单，原料中有价金属综合回收程度高，有利于环境保护，并且生产过程较易实现连续化和自动化。