Iron ore is one of the important raw materials for the production of pig iron and steel in the iron and steel industry. There are many types of iron ore. According to the magnetic properties of the ore, it is mainly divided into strong magnetism and weak magnetism. In order to improve the efficiency and production capacity of ore dressing and meet the smelting production requirements of iron and steel plants, appropriate and technology should be selected according to the different properties of different iron ore during beneficiation to achieve better beneficiation effects.
The composition of iron ore of a single magnetite type is simple, and the proportion of iron minerals is very large. Gangue minerals are mostly quartz and silicate minerals. According to production practice research, weak magnetic separation methods are often used to separate them. In a medium-sized magnetic separation plant, the ore is demagnetized and then enters the crushing and screening workshop to be crushed to a qualified particle size, and then fed to the grinding workshop for grinding operations. If the ore size after grinding is greater than 0.2 mm, one stage of grinding and magnetic separation process is adopted; if it is less than 0.2 mm, two stages of grinding and magnetic separation process are adopted. In order to increase the recovery rate of iron ore as much as possible, the qualified tailings may be scavenged and further recovered. In areas lacking water resources, a magnetic separator can be used for grinding and magnetic separation operations.
Because magnetite is easily depleted under the effect of weathering, such ores are generally sorted by dry magnetic separator to remove part of gangue minerals, and then subjected to grinding and magnetic separation to obtain concentrate.
The magnetite in the polymetallic magnetite is sulfide magnetite, and the gangue mineral contains silicate or carbonate, and is accompanied by cobalt pyrite, chalcopyrite and apatite. This kind of ore generally adopts the combined process of weak magnetic separation and flotation to recover iron and sulfur respectively.
Process flow: the ore is fed into the magnetic separator for weak magnetic separation to obtain magnetite concentrate and weak magnetic separation tailings, and the tailings enter the flotation process to obtain iron and sulfur.
The common process flow in actual production is: the raw ore is fed into the shaft furnace for roasting and magnetization, and after magnetization, it is fed into the magnetic separator for magnetic separation.
Gravity separation and magnetic separation are mainly used to separate coarse-grained and medium-grained weakly magnetic iron ore (20~2 mm). During gravity separation, heavy medium or jigging methods are commonly used for the gravity separation of coarse and very coarse (>20 mm) ores; spiral chutes, shakers and centrifugal concentrators for medium to fine (2~0.2mm) ores, etc. Reselect method.
In magnetic separation, the strong magnetic separator of coarse and medium-grained ore is usually dry-type strong magnetic separator; the fine-grained ore is usually wet-type strong magnetic separator. Because the grade of concentrate obtained by using one beneficiation method alone is not high, a combined process is often used:
Combination of flotation and magnetic separation: the magnetite-hematite ore of qualified particle size is fed into the magnetic separator for weak magnetic separation to obtain strong magnetic iron ore and weak magnetic tailings, and the tailings are fed into the magnetic separator for weak magnetic separation. In strong magnetic separation, strong magnetic separation tailings and concentrate are obtained, and the concentrate is fed to the flotation machine for flotation to obtain flotation iron concentrate tailings.
Combined gravity separation and magnetic separation: similar to the combined flow of flotation and magnetic separation, only the flotation is replaced by gravity separation, and the products are gravity separation concentrate and tailings. These two combined methods can improve the concentrate grade.
The above are mainly the common separation methods and technological processes of strong and weak magnetic iron ore. The composition of natural iron ore is often not so simple, so in actual production, it is necessary to clarify the mineral composition, and use a single sorting method or a joint sorting method according to the corresponding mineral properties. Only in this way can the beneficiation effect be improved.
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Iron ore beneficiation is a multi-stage process that raw iron ore undergoes to purify it prior to the process of smelting, which involves melting the ore to remove the metal content. The process of iron ore beneficiation has two complementary goals and these define the methods used to refine it. The iron content of the ore needs to be increased and gangue, which is native rock and minerals of lesser value within the ore itself, must be separated out. Methods such as screening, crushing, and grinding of iron ore are often used in various ways to purify it, along with several stages of magnetic separation.
The iron ore industry classifies the material by the concentration of the metal that is present after iron ore beneficiation has been completed. High-grade iron ore must have a concentration of 65% iron or higher, and medium grade of 62% to 65%. Low-grade iron ore includes all mixtures below 62% iron concentration, which are not considered to be viable types of ore for use in metallurgy. Several different types of natural iron ore exist, but the two most common types used for metal refining are hematite, Fe2O3, which is usually 70% iron, and magnetite, Fe3O4, which is 72% iron. Low-grade iron ores also exist, such as limonite, which is hematite bonded to water molecules at 50% to 66% iron, and siderite, FeCO3, that is 48% iron.
One of the approaches to iron ore beneficiation first involves a basic screening or filtering of the ore and then crushing it using equipment like a jaw crusher to break up the rock from its natural state down to individual block or rock sizes with dimensions of length or height no greater than 3.3 feet (1 meter). This rock is then further pulverized in medium and fine level cone crushers or fine jaw crushers, and screened down to particle sizes of 0.5 inches (12 millimeters) or less, and is then passed on to a flotation process for separation. Separation involves using low-power magnetic fields to pull the ore with high-metal content away from lower-grade metal particles. The lower-grade ore at this point is cycled back into the rough flotation stage for further refining.
The end product that emerges from crushing and magnetic separation equipment is then ground into a powder-like consistency in a ball mill. This material is then further refined through iron ore beneficiation by using a dehydration tank to remove water content and by applying high-intensity magnetic fields generated by a disc magnetic separator. At this stage, low-grade ore that still contains metal value is placed back at the start of the cycle, and tailings, which are even lower-grade residues, are removed as waste.
Iron ore mining often focuses on looking for hematite deposits known as red iron ore, and magnetite, as they have naturally weak magnetic fields that aid in their purification. Hematite, however, responds better to the flotation process in iron ore beneficiation than magnetite, so it is the preferred type of ore. It responds best to what is known as gravity separation as well and several types of gravity equipment can be used to refine it, including jiggers, centrifugal separators, and shaking tables.
The global industry for iron purification has perfected the methodology for refining hematite as of 2011 more than other types of iron ore, and it therefore offers the highest yield in net iron content of any ore mined to date. Deposits of hematite around the world are considered to be the best form of iron ore available, though it is not clearly understood how such deposits were formed. The deposits are a diminishing natural resource that are believed to have formed on Earth approximately 1,800,000,000 to 1,600,000,000 years ago.
A biomining approach to process low-grade iron ores has the potential to turn closed mines or uneconomic mineral deposits into economic resources. Microorganisms and their metabolites have been commercially applied in the leaching of metals from medium- and low-grade sulfide minerals for many years. Efforts are now being directed to the application of biomining to oxide ore systems as high-grade ore becomes scarce. This chapter discusses the potential exploitation of microorganisms and their metabolites for the bioleaching of phosphorus from iron ore and as bioreagents for the selective flotation and flocculation of iron ore minerals.