medium magnetite agitation tank in phuket

assessment project of magnetite powder with heavy medium - xinhai

assessment project of magnetite powder with heavy medium - xinhai

Heavy medium means the density of water medium is larger than that of water, which including heavy liquid and heavy suspension. Minerals been beneficiated in heavy medium called heavly medium beneficiation, such as magnetite mineral processing,and its density should between that of heavy minerals and light minerals, only in this way can promise the light minerals floating as well as the heavy minerals falling down. As heavy liquid has higher price, heavy floating liquid can be the optimized material in industry producing. Heavy medium and water composed of heavy floating liquid, which magnetite powder belongs to.

Due to Heavy medium magnetite powder has characterized by inertia, higher relative density and easy to recycle, thus can meet the need of coal separation. Magnetite in natural usually exists with other elements which will reduce the density of magnetite powder and affect the magnetic property. Iron ion can be replaced by elements which has close radius such as Ti4+, Mg2+ and Mn2+, which distributes to reduce the magnetic property of magnetite powder, and influences the characteristics of floating liquid as well as increases the consumption of heavy medium.

Content, particle size and density of magnetic materials are the main elements when choosing heavy medium magnetite powder for coal separation. Daily inspection should be made to the magnetic material content and moisture of -325 mesh, other inspection elements can slack when this index completed.

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two factors affect the magnetic separation process - xinhai

two factors affect the magnetic separation process - xinhai

As one of the common mineral processing technologies, magnetic separation method is widely used in the separation of magnetite, manganese, ilmenite and other magnetic minerals by virtue of the advantages of simple equipment and good separation effect. But do you know how many factors affecting the magnetic separation process? And How does each factor affect the effect of the magnetic separation process?

According to the working principle of the magnetic separation process, we can know that the magnetic separation process mainly uses the magnetic differences among various minerals to realize mineral separation in the uneven magnetic field of various magnetic separation equipment. Thus, we can find two key factors that affect the magnetic separation process: one is the magnetic difference of minerals, another is the magnetic field distribution of magnetic separation equipment.

According to the magnetic differences, the minerals can be classified into strong magnetic minerals, weak magnetic minerals and non-magnetic minerals. It is because of the magnetism of the minerals that we can use the magnetic separation method to separate the different minerals. In other words, the magnetic differences in minerals are the basis of magnetic separation technology.

For strong magnetic minerals, such as magnetite, pyrrhotite, magnetite hematite, etc., the specific susceptibility is more than 3.810-5m3/kg. The low-intensity magnetic separator (magnetic field intensity is 0.1-0.3T) is usually applied;

For weak magnetic minerals, such as chromite, ilmenite, manganese ore, etc., the specific susceptibility is between 7.510-6 to 1.2610-7m3/kg. The strong intensity magnetic separator (magnetic field intensity is 1-2T) is usually applied.

There are many factors that affect the magnetic properties of minerals, and the magnetic properties of minerals in different regions and deposits are not the same, and some of them are quite different. Therefore, when conducting the magnetic separation for the specific minerals in a certain region, we should judge the magnetic properties by the magnetic determination results of minerals, and then select the strong magnetic separation process or the weak magnetic separation process.

In order to enlarge the magnetic difference of minerals in the actual production, some magnetic separation plants usually change the magnetic properties of minerals with the help of some methods, such as magnetization roasting, alkali dipping magnetization, magnetization of magnetic species, etc., so as to change the magnetic properties of minerals and facilitate the magnetic separation.

The magnetic field is a special state in the space around a magnet. The magnet placed in a magnetic field is subjected to the magnetic force. The magnetic field intensity, gradient and direction (that is, whether the magnetic field is evenly distributed) in the separation space of the magnetic separation equipment often affect the effect of the magnetic separation process.

In the uniform magnetic field, the mineral particles are only affected by the steering force, the diversion of the mineral particle sizes is parallel to the field direction. In the heterogeneous magnetic field, the mineral particles are subject to the steering force and magnetic force. The minerals rotate and move towards the increasing magnetic gradients, which forms the rollover phenomenon, so the magnetically different grains are separated.

Magnetic separation equipment can be divided into weak magnetic field separator (magnetic field intensity is 0.1t-0.2t), medium magnetic field separator (magnetic field intensity is 0.2t-0.5t) and strong magnetic field separator (magnetic field intensity is 0.5t-2.0t).

The common strong magnetic field separators include dry magnetic separator, continuous high gradient magnetic separator, electromagnetic pulsating high gradient magnetic separator, etc. Most of them have a more complex magnetic field design.

Take dry magnetic separator as an example, the magnetic separator has few types, such as single row single roll type, double row double roll type, double row multiple roll type. After the coil is energized, the magnetic field is generated between the induction roller and the magnetic pole. The material is separated by the magnetic field that passes.

In summary, it is not difficult to find that although the magnetic separation process is a kind of relatively simple mineral processing technology, it is not simple in the process design and selection. It is very necessary to understand the mineral properties, magnetic separation process and magnetic separation equipment in advance.

It is suggested to entrust the mineral processing equipment suppliers with qualification of mineral processing test to seek technical support, and choose the scientific and reasonable magnetic separation process and equipment according to the recommended results of ore dressing test, so as to ensure the perfect matching of technological process and ore properties, and the win-win situation of production indexes and economic benefit.

The selected grade was 23.15%, the concentrate grade was 65.95% and the tailings grade was 10.05%, which greatly improved the technical index of mineral processing. At the same time, the new mineral processing equipment and high-efficient mineral processing agents played a very good role, greatly promoting the progress of hematite ore processing technology, which was highly praised by the project customer.

heavy media separation process

heavy media separation process

The Sink and Float separation process is part of what is also known as aHeavy Media Separation Process(HMS) and are commercial adaptations of the common laboratory procedure used for separating a mixture of two products having differentials in specific gravity by immersing the sample in a heavy liquid having a gravity intermediate to those of the products to be separated. The lighter fraction of the two is floated at the surface of the liquid while the heavier product sinks. The heavy liquids commonly employed are inorganic salt solutions, such as of zinc chloride, or organic liquids, such as halogenated hydrocarbons.

Many years ago it was discovered that suspensions of finely divided solids in water closely approached the properties of heavy liquids in sink and float practice. If the solid phase of the suspension is ground to suitable fineness and mixed with water in correct proportion, a medium is obtained that is stable or so slow settling that a substantially uniform specific gravity can be maintained from top to bottom of the bath. As a consequence, no rising currents of water are necessary to assist in the separation of sink from float, nor is it necessary to supply strong mechanical agitation to maintain the medium in suspension.

When materials are separated in such a suspension or medium, they will inevitably contain some contaminating fines or slimes resulting from incomplete washing of the feed material and from abraded fines generated through particle attrition as the material passes through the separating vessel. An accumulation of contaminating fines and slime in the bath would affect its specific gravity and viscosity and reduce its separating efficiency. Thus, in a continuous process it becomes necessary to provide means for continually cleaning a portion of the medium to eliminate slime at the same rate at which it is introduced into the medium by the incoming feed.

One of the first commercial applications of a medium to effect a sink-float separation used a fine silica sand suspension for treating anthracite coal and is known as the Chance process. The method used for cleaning the medium is decantation which limits the minimum grain size of the solid in the suspension. Any sand that is too fine is discarded, along with the contaminating slime, and since a coarse sand must be used to maintain a uniform suspension in the bath it is necessary to use strong rising currents. The combination results in a separation relying more on hindered settling classification than on sink-float principles.

There are other sink-float processes for cleaning coal less generally used, but similar to the Chance process. They employ other solids such as clay, barite, flue dust, etc., in the suspension. The medium is cleaned by decantation alone, or a combination of decantation and froth flotation for the removal of contaminating fine coal. The application of these various sink-float processes has been limited to the treatment of coals where the specific gravity of the required bath is less than 1.8.

The lead sulphide mineral, galena, is sometimes used in the sink-float treatment of certain lead-zinc ores. Froth flotation may be used for cleaning the medium or a portion of the medium can be continuously replaced with a fraction of the final galena concentrate being produced in the subsequent treatment of the ore.

The heavy-media separation process, or HMS, employing ferrous media, usually ferrosilicon and/or magnetite, is the most generally used process for sink-float separations. A stable medium over the range of specific gravities from 1.25 to 3.40 can be maintained within close limits and is cleaned and recovered by magnetic means.

The heavy-media feed, crushed to the proper size, is screened, washed and drained on the Vibrating Screen to eliminate as much of the fines as possible. The fines removed will usually range from to 10-mesh and be reserved for separate processing by gravity or flotation methods.

The screened feed is fed to the separatory vessel which contains a suspension of finely ground ferro-silicon and/or magnetite in water, maintained at a predetermined specific gravity. The light fraction floats and is continuously removed by overflowing a weir. The heavy particles sink and are continuously removed by an airlift.

The float weir overflow and sink airlift discharge go to a longitudinally divided drainage screen. On the drainage section more than 90% of the medium carried with the float and sink drains through the screen and is returned to the separatory vessel by the SRL Medium Circulating Pump.

The undersize from the washing screen, consisting of medium, wash water, and fine, too dilute and contaminated to be returned directly as medium to the separatory vessel passes through magnetizing blocks to the Medium Thickener. The thickener overflow is returned by the water return pump and reused as wash water. The medium particles of magnetite or ferrosilicon are magnetized by the blocks causing their flocculation and a greatly increased settling rate so that a smaller thickener is used.

The SRL Pump elevates the thickener underflow to the primary and secondary magnetic separators operated in series. The tailing or reject from the secondary magnetic separator may go to waste or join the undersize of the feed preparation screen for treatment by some other method.

The clean magnetite or ferrosilicon reclaimed by the magnetic separators, flows to the Densifier for water removal and storage. By raising or lowering the screw in the densifier, the amount of medium returned to the separatory vessel is controlled to give the desired separating gravity. The medium has been magnetized by the blocks and the magnetic separators and is in a thoroughly flocculated state. In order to destroy the magnetic charge on the particles, and allow them to disperse uniformly through the water, the medium being returned to the circuit from the densifier, flows through a demagnetizing coil.

The flowsheet in this study illustrates the separatory vessel as a cone with an outside airlift. There are a large number of other type vessels in use but the basic flowsheet is essentially as shown regardless of the type separatory vessel used.

Three product separations, such as final float and sink products plus a middling with intermediate gravity are not uncommon in HMS plants. This requires additional separatory vessel, drainage and dewatering screen and medium circulating pump to be added to the basic flowsheet shown.

If a fluid is available whose specific gravity is intermediate between that of two solids which it is desired to separate, no simpler process could be desired than to suspend the mixed solids in the fluid, allow one to rise and the other to sink, and draw off separate products from top and bottom of the separating vessel. A typical example is the separation of wood chips from gravel or sand, using water as the medium.

Since all minerals are heavier than water, water is not suitable for the practice of float-and-sink separation. Some aqueous soluitions are available, however, whose specific gravity is sufficient to permit coal to cream while associated impurities sink. Organic liquids having a specific gravity well above 2.75 but under 3.5 are available. They can be used to reject, as a light layer, the common gangue minerals quartz and calcite, but they are relatively expensive. Liquids having a specific gravity over 3.5 are few and very expensive even for laboratory and research purposes.

Heavy pseudo liquids can be made by suspending solids in water, and these fluids can be used almost like true liquids, provided the particles to be separated are coarse in comparison to the size of the medium particles, provided the medium is thin enough not to acquire plastic properties, and provided the medium is agitated enough not to settle.

Pseudo liquids are very much cheaper than organic liquids of high specific gravity, so the practical disadvantage of fluid loss is not nearly so significant. On the other hand, the use of pseudo liquids is not so simple as that of high-specific gravity liquids.

Laboratory Use of Heavy Liquids. In the laboratory, heavy liquids are very useful for assessing the optimum separation obtainable by gravity concentration: by the use of a series of fluids of graduated specific gravities, a crushed solid can be separated into fractions whose specific gravity lies within narrowlimits, as 1.40 and 1.45, or 2.75 and 2.85. In this way, locked particles are segregated from free particles and locked particles of different compositions are separated from each other.

The procedure has not been applied to extremely fine particles, but can readily be used for all sieve sizes and the coarsest .sub-sieve sizes. For example, 200-mesh quartz settles approximately 4 in. in water in 15 sec. In this case, the viscosity is about 0.01 poise, and the apparent specific gravity is 1.65. If separation to 0.01 unit in specific gravity is desired and if t he viscosity of the fluid is ten times as large as that of water (corresponding to the viscosity of a free-flowing oil), the settling time should be some 1,650 times as large, or about 7 hr. for 4 in. Because of its reduction in settling time, centrifuging permits an extension of the float-and-sink procedure to subsieve sizes.

One of the most useful heavy fluids is acetylene tetrabromide (or tetrabromethane) whose specific gravity is 2.96. This fluid can be diluted with carbon tetrachloride and give solutions of lower specific gravity down to 1.59, the specific gravity of carbon tetrachloride.

Figure 127 represents the results obtained by float-and-sink on one sample of coal. This figure is typical of the studies currently made on the washability of coal. Determinations were made of the ash content of specific gravity fractions averaging, respectively, 1.28, 1.30, 1.38, 1.50, 1.70. 1.90, and 2.20. These fractions were obtained by the use of heavy fluids; their relative weights were determined. From the specific gravities and cumulative weights, curve I (specific gravity vs. cumulative weight) was drawn.

From the ash content calculated on a cumulative basis and the cumulative weight percentage, curve II was drawn. Curve III records also the elementary or actual ash content of each fraction against cumulative weight.

Thus if a separation is made by float-and-sink testing at specific gravity 1.40, the raw coal (containing 16.0 per cent ash) yields clean coal weighing 78 per cent of the raw coal (pointA curve I) and containing 8.6 per cent ash (point B on curve II). If gravity methods are used, such a separation is the most that can be expected of that coal without further comminution.

(Curves IV and IYa are designed to give a measure of the difficulty in separating the raw coal into cleaned coal and wasteat any specific gravity. Thus if a leeway of 0.10 in specific gravity of individual particle is permissible at 1.40 specificgravity, about 67 per cent of the coal falls between 1.30 and 1.50specific gravity (point C curve IV). This indicates extreme difficulty of practical separation at that specific gravity. If, on the other hand, separation is attempted at a specific gravity of 1.50, and a leeway of 0.10 is permissible, about 14 per cent.

Calcium chloride solution having a specific gravity of approximately 1.4 is used for the separation, which takes place in a cylindrical tank 6 to 10 ft. in diameter with a conical bottom, the total height being nearly 30 ft. Raw coal freed of dust and fines is introduced near the center of the tank after mixing with the separating solution in a mixer. The cleaned coal rises to the top where it is removed by a chain scraper and delivered to draining towers. The slate and bone are lifted from the bottom by a bucket conveyor and dumped in draining towers. After draining, the coal and the slate are washed, the wash liquor returning to the supply of calcium chloride. Further washes are required to free the coal completely of chloride; these go to waste.

Some 320 liter of liquor is withdrawn from the separating tank by each metric ton of raw coal. The specific gravity of the liquor is dropped from 1.4 to about 1.2 by the wash water and the inherent moisture of the coal. This 320 liter of liquor, now increased to about 640 liter, is concentrated by evaporation to the original volume. The loss of calcium chloride liquor is of the order of 2 to 3 liter per ton of raw coal.

The Lessing process has been installed in Wales and has produced extremely clean coal; the clean coal is even freer of chloride than the raw coal. It would seem, however, that the cost of thermal concentration of the separating liquor will stand in the way of widespread adoption of the process.

The Bertrand or Ougree-Marihaye process also utilizes a calcium chloride solution as separatingmedium and is applicable only to deslimed feed. In practice, particles varying from 1 to 5 mm. in diameter are treated by this process in Belgium. It differs from the Lessing process in that the raw coal is introduced into the system countercurrent fashion, from water to separating solution, the purified coal and the waste being withdrawn in a similarly countercurrent fashion. There are five circulating liquors, viz., hot water, weak solution, medium solution, strong solution, and separating solution.

The results obtained by these processes are excellent, coal of extremely high grade being obtained in amounts substantially in agreement with theoretical yields. Coal containing less than 1 per cent ash is said to be obtained by the Bertrand process. Coal of such purity is in demand for the manufacture of special electrode coke, for the preparation of colloidal coal, for hydrogenation, as fuel in Diesel engines of the Rupa type, and as fuel in automotive gas producers.

Du Pont Process. The Du Pont process, an outgrowth of the Nagelvoort process, is a practical adaptation of the laboratory heavy-liquid separation which has already been described. In basic principle, it does not differ from that laboratory procedure. But several requirements have had to be met in order for the process to become commercial. These are as follows:

Of these various requirements, the most important wasrequirement 5, inasmuch as reasonable reagent consumption could not be expected if it were not met. So-called active agents have been devised to keep the minerals wetted by water rather than by parting liquid. In the case of coal, the active agents are starch acetate or tannic acid. The concentration of active agent in water is of the order of 0.01 per cent.

The main expense in the Du Pont process is for the parting liquid, which is a mixture of several halogenated hydrocarbons. The consumption of medium is said to be very low, and often well under 1 lb. per ton of coal treated.

Clearly the separating process although simple in principle requires a number of adjunct operations for the sake of economy in reagents and from a physiological standpoint. The process is not applicable to fine particles. It is therefore limited to the treatment of minerals in a coarse state of subdivision, and such a treatment cannot be expected to be successful unless the ore is coarsely aggregated or if low standards are permissible.

Industrial processes using heavy suspensions have behind them the record of many years practice in the washing of coal, but their application to ores in which a separation is to be made at a specific gravity of over 2.6 is still very recent.

For cleaning coal, the Chance process has been in use for about 20 years. The medium consists of a suspension of sand in water. The sand must be of relatively uniform size, 40 + 80-mesh being preferred. Coarse sand tends to accumulate in the bottom of the separating vessel, and fine sand is harder to retrieve, as well as likely to accumulate in the upper stratum of the separator.

The Chance cleaner (Fig. 128) consists of a separating vessel (cone separator) in which the sand suspension moves gently upward. An agitator, by stirring the suspension, prevents packing. The overflow of clean coal and sand passes over clean-coal screens which desand and dewater the coal, spray water being used for desanding. The underflow of the separator passes through refuse valves (two of these valves enclosing a refuse chamber are used to provide a water seal) on refuse screens. These work like the coal screens to desand the refuse. The diluted sand, including sludge coal, is purified in a cone thickener, the sludge coal being wasted. The regenerated medium is returned to the system with new feed.

In the Vooys process, the suspension consists of clay and finely ground barite (150 or 200 mesh) in water. As the process is applied at the Sophia Jacoba mine (Holland), the specific gravity is adjusted at 1.47 and in so far as possible, particles of raw coal finer than 100-mesh are excluded.

Since the solids in the medium are much finer than in the Chance process, the coal that can be treated can also be much finer. This perhaps explains why a coal containing as little as 3.3 to 3.4 per cent ash is steadily produced, with a yield practically equal to the theoretical float-and-sink yield.

Regeneration of the medium requires the use of a thickener; the loss of barite is of the order of 2 lb. per ton of raw coal. The operating cost for the whole plant is given by Berthelot as 1.13 francs per metric ton, or approximately 3 cts. per short ton of raw coal on the basis of treatment of 150 tons per hr. The cost seems lower than for a corresponding jig plant, and the results are better.

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