Guide for Iron Ore Dressing

2019-03-25 13:52:38XinHai

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Generally, iron ore with a grade of less than 50% needs to go through a dressing process before it can be sent to smelting for utilization. After the mined ore goes through the processes of crushing and grinding, magnetic separation, flotation and gravity separation, the high-grade concentrate is obtained. At present, the iron ore resources are decreasing day by day. The characteristics of iron ore resources are more lean ore than rich ore, and the associated ore is more and the ore composition is complex.


Iron ore classification and component

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In nature, iron mainly exist in compounds, in which oxide of iron is the most part of them. There are more than 300 kinds of iron compounds in the nature. Among them, there are some important kind of iron are following:

1. Magnetite
2. Hematite
3. Limonite
4. Siderite


Magnetite


The main component of magnetite is Fe3O4, which is the compound of FeO and Fe2O3. The surface of magnetite is black grey. It is opacitas and with half-metal gloss. There are about 72.4% Fe and 27.6% O in the magnetite. The isometric system of a single crystal octahedron, and a small part of the diamond-shaped dodecahedron. Hardness 5.5~6.5, specific gravity 4.9~5.2, with strong magnetic.

Magnetite minerals also include titanium magnetite, vanadium magnetite, vanadium titanium magnetite, chromium magnetite, magnesium magnetite, etc. Magnetite oxidizes to hematite (pseudo hematite or limonite).

Hematite

The main component is Fe2O3, and the mass fraction of Fe is about 69.9%, showing trigonal crystal system. In nature, intact crystals of heavy hematite are relatively rare, crystalline hematite is steely gray, cryptocrystalline, earthen hematite is dark red, semi-metallic luster, hardness 5-6, specific gravity 5-5.3.

Hematite is often mixed with titanium, aluminum, manganese, calcium, magnesium and a small amount of gallium and cobalt. Hematite minerals also include pyrite, mica hematite, magnetite, clay hematite, etc., of which magnetite has strong magnetism.

Limonite

It is a mixture of goethite, pyrite, hydrogoethite, hydropyrite and siliceous clay containing water. Chemical composition and water content vary greatly. Goethite is an orthorhombic crystal system, which is acicular, columnar, lamellar or scaly. Limonite is rich in color, including light brown, reddish brown, black brown, tawny, dark red to black red. Goethite hardness 1~4, specific gravity 3.3~4, fibrinite hardness 4~5, specific gravity 4.01~4.1.

Siderite

Refers to the ore containing ferrous carbonate, the main component is FeCO3, in which the mass fraction of Fe is about 46.6%. It is a trigonal crystal system, usually rhedral, with curved crystal surface, yellow, light brown yellow to dark brown glass luster, hardness of 3.5~4.5, specific gravity of about 3.96. Siderite often contains magnesium and manganese. 

In addition to these four main iron ore, there are ilmenite, pyrite and so on in nature.

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Guide for iron ore dressing

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As one of the earliest, most widely used and most widely used metals in the world, iron ore is an important raw material for iron and steel production. Iron ore is an economic mineral aggregate containing iron elements or compounds.

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Magnetite processing technology and equipment

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Because of the strong magnetism of magnetite, the main processing technology of it is weak magnetic processing technology. The processing flow of magnetic includes:


1. Single weak magnetic separation process
2. Weak magnetic - reverse flotation separation process
3. Weak magnetic - strong magnetic -flotation separation process

Single weak magnetic separation process


It is suitable for simple single magnetite. It can be divided into successive-grinding weak magnetic separation process and stage-grinding weak magnetic separation process. Successive-grinding weak magnetic separation process is suitable for magnetite with coarse grain or high grade iron. Stage-grinding weak magnetic separation process is suitable for low grade magnetite with fine grain.

Weak magnetic-flotation separation process

It mainly points at iron ores which are difficult to increase its fineness or with many SiO2 impurities. It includes weak magnetic-cation anti-flotation separation process and magnetic-positive anion flotation separation process.

Weak magnetic-strong magnetic-flotation separation process

It mainly points at iron ores which are difficult to increase its fineness or with many SiO2 impurities. It includes weak magnetic-cation anti-flotation separation process and magnetic-positive anion flotation separation process.

We could choose weak magnetic equipment or flotation equipment.

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Hematite processing technology and equipment

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Hematite is weak magnetic ore, which can be easier separation by flotation than magnetite. In the old days, hematite was separated by gravity separation, however it was weed out for unreachable capacity. Now Hematite is separated by flows as follows:

1. Weak magnetic-strong magnetic separation
2. Flotation separation
3. Strong magnetic-flotation combined separation

Weak magnetic-strong magnetic separation

Commonly, weak magnetic separation can be added before strong magnetic separation to remove the strong magnetic ore or impurity in raw ore. Then strong magnetic separation is used to separating hematite, which is also the work flow of the mixture of magnetite and hematite.

Flotation Separation

Hematite is easier to floated than magnetic, which could be separated by positive flotation. As the density of iron ore is much higher than that of gangue mineral, gangue mineral is more likely to attach to the foam than iron ore. Therefore, for iron ore, reverse flotation is more advantageous than positive flotation. When the magnetite content mixed in hematite is higher, reverse flotation is a more convenient method for separation.

Strong magnetic-flotation combined separation

In the process of high intensity magnetic-flotation, a part of gangue mineral in the ore is firstly removed by high intensity magnetic separation, and then the coarse concentration of high intensity magnetic separation is sent to the flotation to obtain the final qualified concentrate.


Combined with the above beneficiation process, in the hematite beneficiation process, strong magnetic separation equipment and flotation equipment can be selected.

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Limonite processing technology and equipment

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Limonite is one of the main iron ores, but its iron content is lower than magnetite and hematite, and it is a secondary iron ore. At present, the industrial application of limonite processing process includes:


1. Single concentration process
2. Combined dressing process

Single concentration process

The single separation process of lignite is mainly used for the lignite with high iron content and good selectivity, which can be divided into a single magnetic separation process and a single gravity separation process. The single gravity separation process is used to deal with the ore with coarser grain size, and the equipment is selected according to the grain size of the ore. Single magnetic separation process generally refers to a single strong magnetic separation process, this process has a strong adaptability to the ore, the concentrate is easy to concentrate and filter, but it is not suitable for fine grade slime.

Combined dressing process

The combined separation process only used for limonite includes magnetization - magnetic separation process, flotation - strong magnetic separation process, heavy separation - strong magnetic separation process, etc., which are used for the treatment of limonite with relatively complex composition. The specific technological process shall be determined after the ore separation test has proved the ore properties.Lignite ore dressing equipment should be determined according to the determined technological process.


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Siderite processing technology and equipment

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Like limonite, siderite is a low-grade iron ore that is unstable. The technological processes used in siderite concentrator are gravity separation and strong magnetic separation. Different siderite has different separation methods. Single siderite with coarse grain size is suitable to be treated with single gravity separation, single strong magnetic separation and combined process including the two. For siderite with fine grain size, effective technological processes include roasting magnetic separation, strong magnetic separation, flotation or magnetic flotation combined process. 

Siderite containing magnetite can be separated by a combined process of weak magnetic separation and gravity separation, strong magnetic separation, or flotation in series, or a more complex process.

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Treatment of iron ore tailings

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Iron ore processing capacity is huge, iron ore tailings account for about half of the total metal tailings, in recent years due to the increasing awareness of environmental protection and tailings accidents, whether from the perspective of comprehensive utilization of resources or from the perspective of environmental protection and safety, iron ore tailings treatment is a problem that needs attention.

To avoid resource waste and tailings accidents at the source, the main treatment methods of iron ore tailings at present are: tailings reprocessing, tailings dry drainage and full tailings consolidation and filling method.

Reprocessing of iron ore tailings

Tailings reelection is a kind of valuable elements in recycling and comprehensive utilization of tailings overall measures, including the old tailings reelection new tailings reelection, use, and can effectively reduce the tailings dam dam and maintenance cost, save the broken mill, mining, and new process development, iron ore tailings reelection so far have achieved obvious economic benefits, can effectively improve production rate and recovery rate.

Iron ore tailings dry stacking

Tailings dry discharge is a new treatment technology for tailings that has emerged in recent years. It refers to the process of multistage concentration of tailings followed by dehydration to form slag with low water content and easy to be precipitated, solidified and utilized, which is convenient for transportation and dry storage. For iron tailings with large number, fine particle size, various types and complex properties, tailings dry discharge can reduce the area occupied by tailings pond and reduce the hidden danger of tailings dam break.

Full tailings consolidation and filling method

In this tailings treatment process, the whole tailings obtained after the tailings slurry is dehydrated and treated as the filling aggregate, and the stable homogeneous structure of the backfill is made by adding slag and other materials, which can not only reduce the production cost, but also benefit the mine environmental protection.

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Distribution of iron ore resources

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The world is rich in iron ore resources, the distribution of high-grade iron ore concentration, geological reserves of more than 800 billion tons, the proven reserves of about 400 billion tons, the world's large iron ore distribution in China, Australia, Brazil, Bolivia, India, Canada, the United States, Russia, Ukraine, France, Sweden and other countries and regions.

At present, the world's major iron ore export state-owned Brazil, Australia, India and so on. The biggest producers include China, Brazil, Australia and India.

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