iron mining beneficiation plant process

Extraction, beneficiation, and processing of iron ore produces iron or steel. “Extraction” is defined as removing ore material from a deposit and encompasses all activities prior to beneficiation.

“Beneficiation” of iron includes concentration, generally by physical removal of unwanted gangue; also considered beneficiation is the regulation of product size, or other steps such as agglomeration to improve its chemical or physical characteristics prior to processing. Processing of the concentrated product into iron or steel typically involves the use of pyrometallurgical techniques (U.S. DOI, Bureau of Mines 1968; United States Steel 1973). As discussed in the introduction, processing operations are beyond the purview of this paper.

Historically, most iron ore was simply crushed and shipped directly to a blast furnace. Currently, some ores are high enough in iron content (greater than 50 percent) to be sent directly to furnaces without beneficiation activities other than crushing and washing. Most ores extracted today, however, must undergo a number of beneficiation procedures to upgrade the iron content and prepare the concentrate for the blast furnace. Technological advancements at blast furnace operations require ore feed of a specific size, structure, and chemical make-up for optimum efficiency (Weiss 1985).

Milling

Beneficiation begins with the milling of extracted ore in preparation for further activities to recover iron values. Milling operations are designed to produce uniform size particles by crushing, grinding, and wet or dry classification. The capital investment and operation costs of milling equipment are high. For this reason, economics plays a large part in determining the use of comminution equipment and the degree of crushing and grinding performed to prepare ore for further beneficiation. Other factors considered in determining the degree of milling include the value concentration of the ore, its mineralogy, hardness, and moisture content. Milling procedures vary widely both between mills and within individual mills depending on these variables.

Milling is a multistaged process and may use dry or wet ore feed. Typically, primary crushing and screening take place at the mine site. Primary crushing is accomplished by using gyratory and cone crushers (Weiss 1985). Primary crushing yields chunks of ore ranging in size from 6 to 10 inches. Oversize material is passed through additional crushers and classifiers to achieve the desired particle size. The ore is then crushed and sized at a secondary milling facility (Weiss 1985).

Secondary milling (comminution) further reduces particle size and prepares the ore for beneficiation processes that require finely ground ore feed. The product resulting from this additional crushing is usually less than 1 inch (1/2 to 3/4 inches). Secondary crushing, if necessary and economical, is accomplished by using standard cone crushers followed by short head cone crushers. Gyratory crushers may also be used (Weiss 1985).

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