iron ore beneficiation magnetic separation

dry iron ore beneficiation | iron ore separation - st equipment & technology

dry iron ore beneficiation | iron ore separation - st equipment & technology

Iron ore is the fourth most common element in earths crust. Iron is essential to steel manufacturing and therefore an essential material for global economic development. Iron is also widely used in construction and the manufacturing of vehicles. Most of iron ore resources are composed of metamorphosed banded iron formations (BIF) in which iron is commonly found in the form of oxides, hydroxides and to a lesser extent carbonates.

The chemical composition of iron ores has an apparent wide range in chemical composition especially for Fe content and associated gangue minerals. Major iron minerals associated with most of the iron ores are hematite, goethite, limonite and magnetite. The main contaminants in iron ores are SiO2 and Al2O3. The typical silica and alumina bearing minerals present in iron ores are quartz, kaolinite, gibbsite, diaspore and corundum. Of these it is often observed that quartz is the main silica bearing mineral and kaolinite and gibbsite are the two-main alumina bearing minerals.

Iron ore extraction is mainly performed through open pit mining operations, resulting in significant tailings generation. The iron ore production system usually involves three stages: mining, processing and pelletizing activities. Of these, processing ensures that an adequate iron grade and chemistry is achieved prior to the pelletizing stage. Processing includes crushing, classification, milling and concentration aiming at increasing the iron content while reducing the amount of gangue minerals. Each mineral deposit has its own unique characteristics with respect to iron and gangue bearing minerals, and therefore it requires a different concentration technique.

Magnetic separation is typically used in the beneficiation of high grade iron ores where the dominant iron minerals are ferro and paramagnetic. Wet and dry low-intensity magnetic separation (LIMS) techniques are used to process ores with strong magnetic properties such as magnetite while wet high-intensity magnetic separation is used to separate the Fe-bearing minerals with weak magnetic properties such as hematite from gangue minerals. Iron ores such goethite and limonite are commonly found in tailings and does not separate very well by either technique.

Flotation is used to reduce the content of impurities in low-grade iron ores. Iron ores can be concentrated either by direct anionic flotation of iron oxides or reverse cationic flotation of silica, however reverse cationic flotation remains the most popular flotation route used in the iron industry. The use of flotation its limited by the cost of reagents, the presence of silica and alumina-rich slimes and the presence of carbonate minerals. Moreover, flotation requires waste water treatment and the use of downstream dewatering for dry final applications.

The use of flotation for the concentration of iron also involves desliming as floating in the presence of fines results in decreased efficiency and high reagent costs. Desliming is particularly critical for the removal of alumina as the separation of gibbsite from hematite or goethite by any surface-active agents is quite difficult. Most of alumina bearing minerals occurs in the finer size range (<20um) allowing for its removal through desliming. Overall, a high concentration of fines (<20um) and alumina increases the required cationic collector dose and decreases selectivity dramatically. Therefore desliming increases flotation efficiency, but results in a large volume of tailings and in loss of iron to the tailings stream.

Dry processing of iron ore presents an opportunity to eliminate costs and wet tailings generation associated with flotation and wet magnetic separation circuits. STET has evaluated several iron ore tailings and run of mine ore samples at bench scale (pre-feasibility scale). Significant movement of iron and silicates was observed, with examples highlighted in the table below.

The results of this study demonstrated that low-grade iron ore fines can be upgraded by means of STET tribo-electrostatic belt separator. Based on STET experience, the product recovery and/or grade will significantly improve at pilot scale processing, as compared to the bench-scale test device utilized during these iron ore trials.

separation process of iron ore,iron ore magnetic separation machine,iron ore beneficiation design | prominer (shanghai) mining technology co.,ltd

separation process of iron ore,iron ore magnetic separation machine,iron ore beneficiation design | prominer (shanghai) mining technology co.,ltd

At present, there are about 300 kinds of iron-bearing minerals found in nature. According to their chemical composition, iron ore can be divided into magnetite, hematite, limonite and siderite; The specific magnetic susceptibility of the material is different, and iron ore is divided into strong magnetic and weak magnetic minerals, which also provides a basis for the selection. The beneficiation process of iron ore of different nature is also completely different.

Multimetal-containing magnetite gangue minerals often contain silicate and carbonate minerals, cobalt pyrite, chalcopyrite or apatite, etc. It is recommended to use a combined weak magnetic separation-flotation process, that is, use weak magnetic separation The process first recovers iron, and then uses the flotation process to recover sulfide or apatite, which is conducive to obtaining higher beneficiation indexes.

Generally, the combined process of weak magnetic separation and flotation is also divided into two types: weak magnetic separation-flotation and flotation-weak magnetic separation. The difference between these two processes lies in the destination of the conjoined magnetite and sulfide.

This shows that under the same grinding particle size, the combined process of flotation and magnetic separation can obtain iron concentrates with low sulfide content and sulfide concentrates with high recovery rate.

Single weakly magnetic iron ore mainly includes hematite, siderite, limonite, and hematite (spiegelite)-siderite ore. Due to the variety of minerals involved in this kind of minerals and a wide range of particle sizes, the beneficiation method will be more complicated, often using gravity separation, flotation, strong magnetic separation or their combined processes.

The flotation process is mainly used for the separation of fine-grained and particulate weakly magnetic iron ore, including two process flows of positive flotation and reverse flotation. Among them, the positive flotation process is suitable for quartz hematite ore without easy pumice gangue, and the reverse flotation process is suitable for ore with easy flotation gangue.

However, due to the low grade of strong magnetic separation concentrates of most weak magnetic iron ore, and the low processing capacity of the gravity separation process unit, the combined process of strong magnetic separation and gravity separation is often used, that is, the strong magnetic separation process is first used to discard a large amount of waste. Qualified tailings, and then use the gravity separation process to further process the strong magnetic concentrate to improve the grade of the concentrate.

Polymetallic weakly magnetic iron ore refers to phosphorus-containing hematite and siderite ore. Most concentrators will first use gravity separation, flotation, strong magnetic separation or a combined process to recover iron minerals, and then use the flotation process to recover phosphorus or sulfide.

It is not difficult to see that due to the large variety and complex nature, most iron ore will use multiple combined beneficiation processes to obtain ideal beneficiation indicators. It is recommended that mine owners must do a good job of beneficiation tests, and rationally choose the appropriate iron ore beneficiation process based on the final report results.

Prominer has been devoted to mineral processing industry for decades and specializes in mineral upgrading and deep processing. With expertise in the fields of mineral project development, mining, test study, engineering, technological processing.

beneficiation of an iron ore fines by magnetization roasting and magnetic separation - sciencedirect

beneficiation of an iron ore fines by magnetization roasting and magnetic separation - sciencedirect

The beneficiation of a hematite ore fines with magnetization roasting and magnetic separation was proposed and studied.The magnetic properties of ore can be enhanced due to the selective conversion of hematite and siderite into magnetite.Magnetization roasting can be applied effectively for the processing of carbonate-containing hematite ore.

The utilization of abundant low-grade iron ores is potentially important to many countries in the word, especially to China. These iron ores contain many detrimental impurities and are difficult to upgrade to make suitable concentrates for the blast furnace. In this paper, the beneficiation of a low-grade hematite ore fines containing carbonates with magnetization roasting and magnetic separation was proposed and studied. The hematite and siderite are almost completely converted into magnetite by 8wt% coal at roasting temperature of 800C for 8min. Under the optimized conditions, a high grade magnetic concentrate containing 65.4wt% iron with an iron recovery of 92.7% was achieved. Meanwhile, the effects of roasting temperature, reaction time and coal to ore ratio on the magnetic properties of roasted materials were investigated using a vibration sample magnetometer (VSM). The results show that the magnetic susceptibility and magnetism saturation of hematite ore can be highly increased due to the selective conversion of hematite and siderite into magnetite caused by magnetization roasting which facilitates their separation from non-magnetic minerals.

iron ore beneficiation technology and process,gravity and magnetic separation | prominer (shanghai) mining technology co.,ltd

iron ore beneficiation technology and process,gravity and magnetic separation | prominer (shanghai) mining technology co.,ltd

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.

Prominer has been devoted to mineral processing industry for decades and specializes in mineral upgrading and deep processing. With expertise in the fields of mineral project development, mining, test study, engineering, technological processing.

limonite siderite iron ore beneficiation

limonite siderite iron ore beneficiation

A laboratory mineral-dressing investigation was conducted by the Federal Bureau of Mines on four limonitic and four sideritic iron ores from the North Basin of the east Texas iron-ore district. The samples, composited from drill cores, were considered representative of the iron-ore reserves of the area. The objectives of this research were twofold: (1) To devise a mineral-dressing method whereby the yield from currently mined east Texas iron ores might be increased and the grade improved, and (2) to extend such treatment to include the lower grade ferruginous materials that are not amenable to beneficiation by simple washing and, therefore, are not being exploited. Of the mineral-dressing methods used in this investigation, magnetic separation of roasted ore was shown to be the most effective. Results show that, by this method, a laboratory recovery of 82 percent of the iron is attainable at a grade surpassing that obtained by current plant practice and that both limonite and siderite are amenable to concentration by the process.

The existence of large deposits of iron ore in eastern Texas has been recognized for over 100 years. These ores were first exploited during the Civil War and were mined intermittently until about 1911. From that time until 1944 when the Defense Plant Corporation financed the erection of three blast furnaces to use these east Texas ores, production was almost at a standstill.

The Sheffield Steel Co. concentrator uses a comparatively high-grade feed, containing 35 percent or more of Fe, and produces concentrates averaging more than 44 percent Fe by a comparatively simple washing operation.

The Lone Star Steel Co. concentrator feed averages about 23 percent Fe. This feed is one of the lowest grade iron ores currently being used in this country. The process, in brief, involves stage crushing, with intervening scrubbing and sizing to remove fine gangue and recover coarse iron minerals.

The low recovery obtained by the commercial concentrators, together with the large reserves of low-grade ore in the east Texas field, prompted the Bureau of Mines to undertake research to develop methods for increasing the recovery of iron from the ores of plant-feed grade and for extending the methods to those ores not amenable to existing plant practice.

In the North Basin area of the east Texas iron-ore district, the ore occurs principally as horizontal ledges and lenses in weathered greensand. The oxide zone is 45 feet thick or more, while the carbonate zone is as much as 65 feet. Recent figures released by the Bureau of Mines show a reserve of 160 million long dry tons of ore in the North Basin that could be washed to a grade of 40 percent Fe.

To obtain the large representative ore samples required for this investigation, the Bureau of Mines drilled 56 holes 7 inches in diameter on 4 properties in the North Basin. These properties are held by the Lone Star Steel Co. through either warranty or iron-ore deeds and consist of the Connors, Pouns, and Lattimer properties in eastern Morris County and the Pynson property in western Cass County. The total footage drilled amounted to 2,145 feet, of which 840 feet was in brown iron ore, 806 feet in carbonate ore, and 499 feet in waste. Selected drill cuttings were combined for metallurgical samples.

The samples consisted of brown iron ore (limonite) and carbonate ore (siderite). The limonite was composed of both amorphous and crystalline oxides; the siderite was dense and crystalline. Principal impurities were siliceous, free silica as quartz sand, siliceous clay, and residual grains of the hydrous silicate, glauconite. Partial chemical analyses of the individual ores are given in table 1.

Previous work by the Bureau of Mines showed that limonitic ores from the North Basin could be upgraded to an acceptable, but low-grade, concentrate by a simple washing-sizing treatment. Current plant practice in the east Texas field results in a grade concentrate similar to that obtained by washing and sizing the limonitic and sideritic ores investigated. For this study, all samples were crushed to minus 1-inch and blunged at 50 percent solids for 1 hour in a 12-inch-diameter mill equipped with four equispaced lifters. The iron minerals in the scrubbed ores were separated by screening on 10-mesh and 48-mesh sieves; the minus 48-mesh fraction was further classified in a hydrocyclone.

Comparative test runs of blunging in water only and blunging in water containing 1 pound per ton each of sodium silicate and sodium hydroxide showed almost identical recoveries and grade of concentrate. Therefore, the results of blunging with water containing sodium silicate and sodium hydroxide are not tabulated in this report.

With the laboratory washing-sizing process, limonite ores from the Connors, Pouns, and Pynson properties yielded concentrates averaging 41.0 percent Fe and 24.7 percent acid insoluble material and representing a recovery as high as 46.0 percent of the total iron (tables 2, 3, and 4). The overall concentrate grade and iron recovery approached commercial plant results in the east Texas field. Experiments on the Lattimer limonite (table 5) failed to produce the 40 percent iron concentrate that was considered the minimum acceptable grade. The siderite ores also failed to yield a 40 percent iron concentrate (tables 2, 3, 4, and 5).

Magnetic separation is a simple, yet often effective, method of ore concentration usually considered in investigations concerned with the separation and recovery of iron minerals. Iron-hearing minerals that can be beneficiated by this means are (1) naturally occurring magnetite and (2) the paramagnetic products of the roasting of iron-bearing minerals.

Iron carbonate changes to a magnetic oxide by thermal decomposition. Carbon dioxide begins to evolve endothermically at about 300 C. to form FeO; an exothermic reaction follows, if oxygen is available for reaction with ferrous oxide. When iron carbonate is roasted in an inert atmosphere, some nonmagnetic ferrous oxide results; when it is roasted with full access to air, the nonmagnetic ferric oxide is formed. Best results are obtained under the weakly oxidizing conditions that exist when the furnace vents are open to the air but with no forced draft.

The ores investigated included limonite and siderite. Roasting research covered the individual ore types as well as composites of the two. Although the individual samples were considered as either limonite or siderite, they were in reality contaminated, one with the other, with the siderite containing a large amount of ferric iron and the limonite a lesser amount of ferrous iron (table 1, p. 3).

As preliminary work revealed that both the limonite and siderite could be roasted effectively at 1-inch size, all roasting tests were made on ore sized to minus 1-inch, unless otherwise specified. Except for a brief investigation of flash roasting, all roasts were made in an externally fired drum roaster, with provision for close control of both roaster temperature and atmosphere. This roaster is shown in figure 1.

The optimum conditions of roasting the limonite ores, as determined by controlled time, temperature, and furnace atmosphere variables, were found to be a 30-minute roast at 600 C. in carbon monoxide. These conditions were established by varying the temperature of the roast from 400 to 700 C. at 50 intervals; time of roast from 15 to 40 minutes; and atmospheres from carbon monoxide to hydrogen, propane, and mixtures of propane and air.

The optimum roasting conditions for the siderite ore were a 15-minute roast at 500 C. in the gases resulting from the decomposition of the ore. Temperatures of roast studied varied from 400 to 600 C. and roasting time from 5 to 30 minutes; furnace atmospheres used were atmospheric air, helium, and gases resulting from the decomposition of the ore.

Mixed limonite-siderite ores were subjected to an oxidizing roast before the reduction. Controlled variables of reduction were the same as for the limonite ore. Optimum conditions determined were a 20-minute roast at 550 C. in carbon monoxide.

Magnetic separations were made with a Wetherill high-intensity crossbelt separator, used as a rougher, and with a Davis-tube magnetic separator, used as a cleaner or finisher for the Wetherill magnetic concentrate. Other separators used were a Jeffrey wet drum, a high-intensity induced roll, and an a.-c., traveling-field, experimental unit made in the local laboratories.

The limonite ore of this deposit was of low grade; the metallurgical sample contained 23.3 percent Fe and 50.2 percent acid insoluble matter. Most of the iron was present as limonite, with only 3 percent of the total iron as the carbonate.

In a typical roasting test on this ore, magnetic ferroso-ferric oxide was formed by roasting for 30 minutes at 600 C. in an atmosphere of carbon monoxide. Magnetic separation in a Davis tube recovered 84.1 percent of the total iron in a concentrate containing 49.4 percent Fe and 17.9 percent acid insoluble material.

Siderite ore from the Connors Brothers deposit was higher in iron content than the limonite ore. It contained 30.6 percent iron and 26.4 percent acid insoluble material. Of this total iron, however, only 71 percent was present as the carbonate.

When the ore was roasted for 15 minutes at 500 C. in the atmosphere resulting from the thermal decomposition of the carbonate (mostly CO2), only the siderite was converted to the magnetic ferroso-ferric oxide owing to insufficient reductant present in the furnace atmosphere to reduce a large portion of the limonite. Separation of the ore roasted under these conditions recovered 71.9 percent of the total iron in a concentrate containing 53.9 percent Fe and 13.3 percent acid insoluble material.

Roasting of a composite of equal weights of two ore types for 20 minutes at 550 C. in an atmosphere of carbon monoxide, followed by magnetic separation in a Davis tube, recovered 79.0 percent of the total iron in a concentrate containing 49.9 percent Fe and 17.2 percent acid insoluble matter.

Limonite ore from the Pouns deposit with an iron content of 30.7 percent and 35.4 percent acid insoluble was the highest grade ore used in this investigation. Of the total iron in this ore, 8.0 percent was in the carbonate form.

Roasting this ore for 30 minutes at 600 C. in an atmosphere of carbon monoxide, followed by magnetic separation at minus 100-mesh, resulted in the recovery of 81.9 percent of the total iron in a magnetic concentrate containing 49.9 percent Fe and 18.3 percent acid insoluble.

This ore was roasted under the previously determined optimum conditions of 500 C. for 15 minutes in an atmosphere composed of the gases produced by the decomposition of the ore. Magnetic separation recovered 52.8 percent of the total iron in a magnetic concentrate containing 50.8 percent Fe and 13.5 percent acid insoluble. The low recovery is due, in part, to the small percentage of total iron present in the ferrous state for the transformation to the paramagnetic form under roasting conditions employed and to the high content of iron-bearing clay in this ore.

Roasting of a composite of equal weights of limonite and siderite ores at 500 C. for 20 minutes in an atmosphere of carbon monoxide, followed by magnetic separation in a Davis tube, resulted in the recovery of 64.8 percent of the total iron in a magnetic concentrate containing 51.9 percent Fe and 15.8 percent acid insoluble. Table 7 gives the results of these tests.

The limonite ore from the Pynson property was also of very low grade, containing 21.3 percent Fe and 51.4 percent acid insoluble. It consisted almost entirely of ferric iron, with only 3 percent of the total being in the ferrous state.

The ferroso-ferric oxide formed by roasting at 600 C. for 30 minutes in an atmosphere of carbon monoxide was recovered by magnetic concentration in a Davis tube. This concentrate, containing 49.4 percent Fe and 17.5 percent acid insoluble, represented a recovery of 78.3 percent of the total iron in the crude ore.

This carbonate ore was of even lower grade than the limonitic ore, with only 19.7 percent iron content and 45.3 percent acid insoluble. Of the total iron present, 64.5 percent was in the ferrous state.

Roasting for 15 minutes at 500 C. in an atmosphere consisting mainly of the gases resulting from thermal decomposition of the ore (carbon dioxide and water vapor), followed by magnetic separation, resulted in the recovery of 58.9 percent of the total iron in a concentrate containing 49.9 percent Fe and 12.7 percent acid insoluble.

A sample containing equal weights of the two ore types was roasted for 20 minutes at 550 C. in an atmosphere of carbon monoxide and then magnetically separated. This treatment produced a magnetic concentrate containing 52.6 percent Fe and 15.2 percent acid insoluble, representing a recovery of 65.7 percent of the total iron. Results are tabulated in table 8.

The limonite ore was the lowest in grade of all the limonitic ores investigated, with an iron content of 21.0 percent and an acid insoluble content of 53.5 percent. Like the other limonitic ores, it contained little ferrous iron,with only 3 percent of the total being in this reduced state.

Reduction roasting at 600 C. for 30 minutes in an atmosphere of carbon monoxide, followed by magnetic separation in the Davis tube, recovered 70.5 percent of the total iron in a magnetic concentrate containing 48.4 percent Fe and 19.4 percent acid insoluble.

When roasted for 15 minutes at 500 C. in an atmosphere of decomposition gases and separated in a Davis tube, this ore responded, as other siderites in previous tests, with a low recovery of iron. The magnetic concentrates contained 49.2 percent Fe and 15.4 percent acid insoluble and represented 60.2 percent of the total iron.

A composite of equal weights of the two Lattimer ores, when roasted at 550 C. for 20 minutes in an atmosphere of carbon monoxide, followed by magnetic separation, resulted in the recovery of 64.1 percent of the total iron in a magnetic concentrate containing 49.1 percent Fe and 17.3 percent acid insoluble. Summation of results is given in table 9.

The investigation of roasting and magnetic separation, as applied to the several individual ores and to composites of both ore types from each property, considered only the variables of roasting time, roasting temperature, and furnace atmosphere. Further research to study other techniques, such as oxidizing the ore before reduction, wet versus dry magnetic separations, and the relative magnetic susceptibilities of magnetite and gamma-hematite, was conducted on a composite of equal weights of all eight of the ores.

The first approach to the problem of mixed-ore types, with their varied requirements for magnetic roasting, was by roasting in an atmosphere of ore-decomposition products. According to Mellor, it is probable that ferrous carbonate first splits into ferrous oxide and carbon dioxide and that these react on one another to give ferric oxide and carbon monoxide. The intent of this roasting was to use the carbon monoxide released from the thermal decomposition of siderite to reduce the limonitic iron oxides. This technique was not successful, as the amount of magnetic iron oxide produced was barely sufficient to account for the iron originally contained in the siderite. Analysis of the exit gases disclosed no carbon monoxide. The presence of 0.2 to 0.4 percent of free carbon in the roasted ore suggests that carbon monoxide was combining to produce carbon dioxide and free carbon instead of reducing the iron oxides in the ore.

The second approach to this problem was through an oxidizing roast before the reduction roast. When roasted in air, both ferrous carbonate (siderite) and the hydrated iron oxides (limonite) are converted to ferric oxide, which is readily reduced to the magnetic iron oxide, magnetite.

Reduction roasting and magnetic separation of this uniformly oxidized material showed improvement in both grade of concentrate and recovery over that obtained when the different ore types were treated without a prior oxidizing roast.

In a typical test, the ore was first roasted in air at 600 C., then reduced at the same temperature by passing a stream of carbon monoxide through the roaster. The reduced ore was cooled in an inert atmosphere to prevent reoxidation. The temperature of the oxidizing step was shown to have a decided influence on both grade and recovery of the concentrate derived from the reduced ore (tables 10, 11, and 12). Processing at 600 C. resulted in the highest grade concentrate and lowest recovery (50.9 percent Fe and 15.2 percent acid insoluble with a recovery of 75.7 percent), while the ore roasted at 800 C. showed the lowest grade and highest recovery (49.4 percent Fe and 21.9 percent acid insoluble with a recovery of 82.4 percent). The higher recovery results from the recovery of altered glauconite (hydrous silicate of iron and potassium) grains that have become susceptible, in part, to reduction to magnetic iron oxide after a preoxidation treatment at 800 C. The galuconite was, in effect, magnetic but of low iron content. The micrographs of roasted glauconite grains (figs. 2 and 3) show the magnetic iron oxide as white coatings and stringers in a grey matrix of glauconite, thus emphasizing the impracticality of grinding to the degree necessary to liberate this iron oxide.

A series of magnetic oxides of iron may be formed from iron-bearing minerals by roasting under proper conditions of temperature and atmosphere. Magnetite (Fe3O4) and maghemite (Fe2O3) are the end members of what appears to be a continuous series of solid solutions. 14/ Reduction roasting of iron-bearing minerals in hydrogen from 400 to 570 C. results in the formation of a product with, or similar to, the composition of magnetite; above 570 C. ferrous oxide is likely to form. When magnetite is heated in air between 200 and 400 C., it takes in oxygen, the rate and extent being functions of temperature, and the composition approaches that of gamma-hematite (maghemite). This change is accompanied by a substantial increase in volume (7.76 percent), if the final product is maghemite.

In this research, magnetite was oxidized to maghemite to determine which form of the oxide would exhibit the greatest magnetic susceptibility when very finely divided and (2) whether the large expansion accompanying gamma oxidation would tend to loosen the locked magnetite-gangue particles. Results of the study were inconclusive as to magnetic susceptibility. Increased liberation of the gangue particles by the oxidation expansion was not significant, but the oxidation did improve the grindability of the roasted ore.

Effective magnetic separation of iron-bearing minerals does not require that the mineral grain be completely reduced (or oxidized) to a ferromagnetic form. The formation of a relatively thin surface layer of material with high magnetic susceptibility will make the entire grain magnetically separable.

A brief study of this concept of incomplete magnetic roasting was made to determine if the process was technically feasible for the east Texas iron ores. Roasting was accomplished in a vertically mounted electric tube furnace equipped with baffles to control the retention time of the ore and a water seal at the base to permit control of the roasting atmosphere.

At 700 C. in an atmosphere of carbon monoxide, minus 65-mesh ore was reduced in approximately 2 seconds. The reduction appeared to be complete throughout the grains. On minus 6- plus 65-mesh ore, under the same roasting conditions, 7 seconds were required to reduce a surface film. This reduction

made the particles magnetically separable, but further grinding destroyed the film, leaving a core that was not recoverable by magnetic means. Concentrates obtained from this flash-roasted material were of acceptable grade (46 percent Fe and 20 percent acid insoluble), but recovery was limited to 51 percent. One of the chief deterrents to flash roasting is the difficulty of grinding the crude ore to the necessary degree of fineness. On ore fractions, such as washer tailings, that would not require grinding, this roasting may prove valuable. As applied to washer tailings obtained in this research, a magnetic concentrate containing 39.9 percent Fe and 27.6 percent acid insoluble was recoverable. Recovery at this grade was only 16 percent of the total iron, but the feed contained only 15.8 percent Fe, most of which was present as slimes.

magnetite ore mining solution - mineral processing

magnetite ore mining solution - mineral processing

Most of the iron minerals in a single magnetite are magnetite. Because the single magnetite is simple in composition, strong in magnetism, and easy to grind and sort, the weak magnetic separation method is often used for selection.

When the particle size of grinding is greater than 0.2mm, most iron ore magnetic separation plants often adopt a process of grinding and magnetic separation; When the grinding particle size is less than 0.2mm, the two-stage grinding-magnetic separation process is used; If qualified tailings are separated in the rough grinding stage, the magnetite magnetic separation plant should adopt the stage grinding-magnetic separation process; For dry and water-scarce areas, the magnetite ore dressing plant may consider using dry grinding-dry magnetic separation process; For the depleted magnetite-rich ore or magnetite-rich ore, the gangue can generally be removed by dry magnetic separation process, and then the lump-rich ore is obtained, and then the concentrate is obtained through the grinding-magnetic separation process.In order to obtain high-grade concentrate, magnetite concentrate can be treated by reverse flotation or high-frequency fine screen. In addition, in order to further improve the recovery rate, processes such as tailings gravity separation may also be considered to further recover magnetic minerals.

The gangue containing polymetallic magnetite often contains silicate or carbonate minerals, associated with cobalt pyrite, chalcopyrite and apatite, etc. Generally, the combined process of weak magnetic separation-flotation is used, that is, weak magnetic separation process recovers iron, and flotation process recovers sulfide or apatite.In general, the combined processes of weak magnetic separation-flotation process of polymetallic magnetite can be divided into weak magnetic separation-flotation and flotation-weak magnetic separation, the difference of which lies in the different direction of the continuum of magnetite and sulfide.For the weak magnetic separation-flotation process flow, the contiguous body mainly enters the iron concentrate; for the flotation-weak magnetic separation process flow, the conjoined body mainly enters the sulfide concentrate. Therefore, under the same grinding particle size, the first float and then magnetic process process can obtain iron concentrate with lower sulfide content and sulfide concentrate with higher recovery rate.

According to the types of iron-bearing minerals, common iron ore can be divided into magnetite, hematite, vanadium-titanium magnetite, limonite, siderite and mixed ore consisting of two or more of these iron bearing minerals. Among them, magnetite-hematite is a common mixed ore, and its beneficiation usually adopts a combined process flow composed of multiple beneficiation methods.

The single magnet-hematite is mostly fine-grained; the gangue mineral is mainly quartz, and some of it contains iron silicate. The proportion of magnets in the ore is gradually increases from the surface of the deposit to the deep part. The following two beneficiation methods are commonly used for selection:Weak magnetic separation, gravity separation/flotation/strong magnetic separationThe combined process of using weak magnetic separation to recover magnetite and then gravity separation, flotation or strong magnetic separation process to recover weak magnetic iron mineral.Production practice shows that for the weak magnetic separation-flotation process, the flotation method can be placed after the weak magnetic separation according to the nature of the ore and the actual conditions of the beneficiation plant, so as to ensure stable production indicators and save costs.

The iron minerals in polymetallic magnetite are mainly magnetite and hematite or siderite, medium and fine-grained; gangue minerals are mainly silicate and carbonate minerals or fluorite, etc., and the accompanying components include apatite , pyrite, chalcopyrite and rare earth minerals.The sorting of polymetallic magnetite is relatively complicated. Generally, the combined process consisting of weak magnetic separation and other mineral separation methods is used, that is, the weak magnetic separation method is used to recover the magnetite first, and then the gravity separation, flotation or strong magnetic separation method is used to recover weak magnetic iron minerals, and the associated components are final recovered by flotation.The above is the common magnetite beneficiation method. For magnetite beneficiation, it is recommended to tailor the process to suit your own through the beneficiation test, and rationally select the appropriate magnetite beneficiation method according to the final beneficiation test report.

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