The gravity spiral circuit is designed to extract and concentrate coarse gold from the recirculating load in the mill grinding circuit and hence prevent a build up within that circuit and the eventual escape of some of that gold into the C.I.L. tanks and thereon into the final tails. (See fig. 4)
For the spirals to work efficiently the feed supply must have consistent characteristics and be of a constant rate. Variations in the flow rate, the feed size distribution and percentage solids will have adverse effects upon separation. Generally the solids tonnage should give adequate loading of the concentrate and middlings areas and the pulp density should be low enough to ensure mobility of particles in these areas. BUY SPIRALS
Feed to the spirals may be adjusted by the moving of two splitter arms on either side of the cyclone underflow discharge box, this altering the volume of the feed passing over the splitter screen. (See fig. 5)
The feed may also be adjusted by varying the speed of the gravity feed pump. This is necessary when the mill feed has been dropped and it is impossible to get sufficient feed for the gravity pump by adjustment of the splitter arms. At such times the speed will need to be dropped and the water additionadjusted to provide optimum feed density.
The pulp density may be altered by the addition of water, before the splitter screen, in the gravity feed pump hopper or to the concentrate launder beneath the primary spirals. The latter option adjusts the density of the feed to the cleaner spiral only.
The static distributor (See fig. 6) at the head of the primary spirals ensures an accurate division of the pulp stream to the spirals. For maximum efficiency a constant head should be maintained in the head pot. The head can be adjusted by either altering the flow rate from the splitter screen and/or altering the annular gap between the head pot and the distributor body, by moving the head pot up or down as required.
Feed from the splitter screen passes down into the gravity feed pump hopper and from there it is pumped to the static distributor above six triplex type primary spirals. As the pulp passes down these spirals; separaration of particles occurs according to specific gravity and the heavier minerals progress to the inner profile while lighter minerals are forced towards the outer profile, along with most of the water and slimes. At the bottom of each spiral layer there are splitters which can be adjusted to ensure the optimum recovery of coarse gold. (See fig. 7)
The middlings and tailings from the primary spirals are directed to both the mill feed and the mill discharge pump. The proportion going to either may be adjusted so as to help achieve optimum grinding conditions.
The concentrate from the inner outlet of the cleaner spiral is fed directly on to the Wilfley table and the middlings and tailings report to the gravity sump pump which feeds into the mill discharge pump feed hopper.
The Humphreys Spiral Concentrator, which was invented by I. B. Humphreys and first used in 1943 for concentrating chromite in Oregon beach sands, consists of five or six spiral turns of a modified semicircular launder which is about the size of a conventional automobile tire. Feed enters the top spiral and the tailing discharges from the bottom one, while concentrate and middlings are cut off by outlet ports regularly spaced at each turn of the spiral, and the products passed through rubber hoses to common launders which run the full length of a bank of spirals. Wash water is supplied from a small wash-water channel paralleling the main channel.
Operating entirely by gravity flow and involving no mechanical parts, the separation of the heavy constituents of the feed is effected by the same centrifugal forces and flow gradients encountered in ordinary river or stream concentration.
A capacity of 38 tons per spiral was obtained in the 1000-ton per 24 hr. Oregon plant operating on about a minus 40-mesh feed and in the 5000-ton plant recently installed near Jacksonville to concentrate ilmenite 174 roughing, and 12 finishing spirals have replaced an installation of tables and flotation cells.
The Humphreys Spiral has been successfully applied to recovery of chromite from chrome sands, rutile, ilmenite, and zircon from sand deposits, tantalum minerals and lepidolite from their ores, gravity concentration of base metal ores and in the cleaning of fine coal.
How it works: Pulp is introduced at the top of the spiral and flows downward. As the pulp follows the spiral channel the light particles in the pulp stream move outward and upward into the fast flowing portion of the stream while the heavy particles move to the inner slow moving portion of the stream, where they are drawn off through concentrate ports.
Adjustable splitters allow any portion to be removed through the ports. Tailing is discharged at the bottom of the spiral. Spirals are usually installed in double units, two spirals to a frame, in rows of two to twelve. Feed is split evenly to all spirals. At one plant 21 rows of 12 spirals each are fed by one pump.
The Humphreys Spiral Concentrator is a simple, efficient gravity concentrator which effects a separation between minerals of the proper size range that have sufficient difference in their specific gravity.
This concentrator is a spiral conduit of modified semi-circular cross-section, with outlets for removal of concentrate and middling. Pulp is introduced at the top of the spiral. As the pulp follows the spiral channel, lighter particles in the pulp stream move outward and upward into the fast moving part of the pulp stream. The heavy particles move to the inner, slow moving portion of the stream, where they are drawn off through concentrate or middling outlets. Adjustable splitters allow any portion of the concentrate or middling to be diverted through the outlets. Tailing discharges from lower end of spiral. A full- size spiral is used for laboratory testing. Two arrangements are suggested for test work.
In the closed circuit test unit illustrated, although a full-size spiral is used, as little as 20 pounds of material will indicate the possibility of spiral concentration in a batch test. By removing measured quantities of products, and adding like amounts of feed in repeated steps, substantial samples may be taken for analysis and estimates of capacity. Results from this procedure, using 100 to 300 pounds of material, are close to pilot test results.
Another arrangement, also using a full-size spiral, is a small pilot plant, and is suitable for test work where a larger quantity of material can be handled. The storage tanks may be built on the job from drawings supplied. This unit allows continuous feeding of material and permits accumulation of concentrate and tailing in separate tanks, which may then be re-run as feed for second stage concentration or scavenging of tailing.
Spiral concentrators are modem, high capacity, low costunits developed for the concentration of low grade ores. Spirals consist of a single or double helical sluice wrapped around a central support with a wash water channel and a series of concentrate take-off ports placed at regular intervals along the spiral (Figure 17). To increase the amount of material that can be processed by one unit, two or more starts are constructed around one central support. New spirals have been developed that do not use wash water. These new units have modified cross sections and only one concentrate-take-off port, which is
rapid wear of the rubber lining and irregular wash water distribution resulted in major production problems. Although still in use, the Humphreys cast iron spirals have been largely superseded by a variety of other types, notably the fiberglass Reichert spirals and new, lightweight Humphreys spirals.
The processes involved in mineral concentration by spirals are similar for all models. As feed containing 25-35% solids by volume is fed into the channel, minerals immediately begin to settle and classify. Particles with the greatest specific gravity rapidly settle to the bottom of the spiral and form a slow-moving fluid film. Thus the flow divides vertically: one level is a slow-moving fluid film composed of heavy and coarse minerals; the other level, the remainder of the stream, is composed of lighter material and comprises the bulk of the wash water. The slow-moving fluid film, its velocity reduced by friction and drag, flows towards the lowest part of the spiral cross-section (nearest the central support) where removal ports are located. The stream containing the lighter minerals and the wash water develops a high velocity, and is thrust against the outside of the channel (Figure 18). Separation is enhanced by the differences in centrifugal forces between the two: the lighter, faster flowing material is forced outward towards the surface, and the heavier, slower material remains inward towards the bottom.
Spiral concentrators are capable of sustained recoveries of heavy minerals in the size range of 3 mm down to 75 microns (6 to 200 mesh). They are suitable for use as roughers, cleaners, or scavengers. Feed rates may vary from 0.5 to 4 tons per hour per start, depending on the size, shape, and density of the valuable material. Some factors that affect recovery are the diameter and pitch of the spiral, the density of the feed, the location of splitters and take-off points, and the volume and pressure of thewash water. Individual spirals are easily monitored and controlled, but a large bank of spirals requires nearly constant attention.
Advantages of spiral concentrators include low cost, long equipment life, low space requirements, and good recovery of fine material. They can also be checked visually to determine if the material is separating properly. For maximum operating efficiency, feed density should remain constant, the particle-size distribution of the feed should be uniform, and fluctuations in feed volume should be minimized. Spiral concentrators will tolerate minor feed variations without requiring adjustment. Spiral concentrators, like cone concentrators, are efficient, low-maintenance units that should be considered for any large- scale gravity separation system.
The newer Humphreys spirals are capable of recovering particles as small as 270 mesh (53 microns). In a test at CSMRI, a new Mark VII Reichert spiral recovered 91.3% of the free gold contained in the feed in a concentrate representing only 5.4% of the feed weight. The unit showed little decrease in gold recovery efficiency with material down to 325 mesh (45 microns) (Spiller, 1983).
Since it was introduced in 1943 to recover chromite from Oregon beach sands, the Humphreys spiral concentrator has proved successful in several fields of wet mineral beneficiation. By the end of 1957, 9390 Humphreys spirals had been manufactured. Most of these are still in service.
Requirements for Spiral Concentration: Valuable heavy minerals to be recovered must generally be 14 + 200 mesh, but outstanding examples will be discussed later where these size ranges are exceeded in commercial practice at both ends of the size scale.
by these requirements for spiral concentration. The separation of mica and vermiculite from gangue minerals such as quartz, feldspar, and ferromagnesian minerals is dependent on the flaky shape of the micaceous minerals rather than on a significant difference in specific gravity.
Phosphate rock is another application where specific gravity differences are not involved in spiral separation. The phosphate rock pulp, generally 28 mesh, is reagentized at high pulp density with the usual reagents involved in phosphate rock flotation, such as fuel oil and tall oil. Stated simply, in the reagentized pulp the quartz gangue is wetted by water and the oiled phosphate rock is not. The wetted quartz gangue settles to the inside or lower part of the spiral channel where the velocity is low and is removed as a tailing via the normal heavy mineral draw-off port, which on most other ores delivers heavy mineral.
Fine coal below x 0 can be cleaned with Humphreys spirals. The model 24-C spiral used for coal cleaning has six turns of the helix in about the same headroom required for five turns in the model 24-A metallurgical spiral. In other words, the pitch is flatter. Only in the Pennsylvania anthracite region are there commercial plants for cleaning fine coal, but numerous pilot plant tests have demonstrated that many bituminous coals respond well to spiral treatment.
A very simple system has been devised by the Humphreys Investment Co. engineers to avoid such difficulty almost entirely and permit a multi-stage spiral plant to operate on coarse feed. The rougher spiral concentrate is composed of all sizes of heavy minerals present in the feed, but the gangue content is generally finer than 28 mesh. Consequently, treatment of the rougher concentrate in the simple elutriation or single-pocket sizer produces an underflow of very high grade heavy mineral that is finished coarse concentrate. The overflow, stripped of coarse heavy mineral, is ideally suited for the feed to the cleaner spiral section.
Field of Application: Processing Florida beach sands for the recovery of ilmenite, rutile, zircon, stauriolite, and monazite is the largest single type of application of Humphreys spiral concentrators. The ore is ideally suited to spiral concentration, since it completely satisfies the requirements for successful spiraling. The size range is substantially 100 pct 35 mesh + 200 mesh, the minerals are completely liberated, and there is significant difference of specific gravity between the gangue and heavy minerals.
Humphreys Gold Corp., mining affiliate of the Humphrey Investment Co., operates three plants in Florida under various contract agreements with E. I. du Pont de Nemours & Co. and the National Lead Co. There are 3374 spirals35.9 pct of all spirals manufactured up to the end of 1957employed in the three Florida beach sand plants.
The northern U. S. iron ore ranges account for the second largest group application of Humphreys spiral concentrators. On the iron ore ranges there are 1712 spirals, or 18.2 pct of all spirals manufactured to the end of 1957.
It would be worthwhile to discuss in detail some areas where the Humphreys spirals are definitely not suitable. With one exception, spirals have no application in recovery of sulfide minerals, where flotation has been shown to do a satisfactory and superior job.
The installation in 1948 of a Humphreys spiral concentrator section at the Hill-Trumbull plant of The Cleveland-Cliffs Iron Co. is the latest commercial method on the Mesabi Range being used for the recovery of fine iron ore. In two stages of concentration 84 spirals treat approximately 120 long tons per hour of minus 1/8 in. ore. These spirals augment the production of the heavy-density plant which recovers the plus 1/8 in. iron from the plant crude ore. Structure of the ore is such that, when crushed, about 50 pct of the plant crude is minus 1/8 in. size. After desliming in a 66 in. Akins classifier, grinding the classifier product in a ball mill and again desliming in a 78 in. Akins classifier about 15 pct of the crude ore remains to be treated in the spiral plant.
Overall recovery of the ball mill feed in the Hill-Trumbull spiral plant during the 1948 season was about 53 pct of the weight and 66 pct of the total iron content. Of the actual feed delivered to the spirals from the 78 in. classifier 64.9 pct of the weight was recovered containing 73.7 pct of the total iron. The average analysis of the spiral concentrate is 55.05 pct Fe and 14.83 pct SiO2.
Preparation of ore for the heavy-density plant is near standard practice. A slight divergence begins where the minus in. size material leaves the 66 in. Akins classifier as a product and is routed to a 6 by 10 ft Allis-Chalmers ball mill. The ball mill operates in open circuit, is charged with 2 in. diam balls, driven by a 200 hp motor and has a throughput of approximately 150 long tons of solids per hour. Pulp density in the mill is approximately 65 pct solids. The purpose of the ball mill is to subject the ore to a differential grind which liberates silica from the iron ore particles, and middling from the ore particles and from silica. It also assists in breaking down porous iron oxide particles. The ground product flows into a 78 in. Akins classifier which makes a size separation at nearly 200 mesh. The slime or overflow waste analyzes about 25 to 30 pct Fe and 50 to 60 pct SiO2. Classifier product containing about 75 pct solids drops onto a 4 by 8 ft
All 84 spirals are policed by one operator who removes extraneous matter from the spirals, adjusts pulp density of spiral feed, and adjusts splitters and quantity of wash water. He also has time for additional duties including sampling and tending to the ball mill, pumps, classifiers, and screen.
Spiral operators are easily trained and after a reasonable length of time can become proficient. They are required to observe structure of the ore and to note changes which would suddenly increase or decrease the pulp density. When such changes occur, water is added or decreased to maintain the proper pulp density and launder make-up water. Occasionally, the Hill-Trumbull plant crude ore does not provide a sufficient amount of minus 1/8 in. material to adequately feed the spiral section. Before ringing for more feed the spiral operator consults the heavy-density plant foreman to determine how much more feed his section can stand. If the heavy-density plant is operating at maximum capacity and there is not enough orecoming to the spirals, this material is pumped to the 60 in.
The 6 by 10 ft Allis-Chalmers ball mill was fed 150 long tons of solids per hour. Preliminary laboratory tests on this ore showed a distinct advantage in both grade and recovery if the fine ore were given a differential grind. Grinding is fast and in open circuit. Table 5 shows the size distribution before and after abrasion grinding giving analysis of samples from a single shift and illustrating results obtainable from abrasion grinding of this ore.
In spiral concentration of an ore in which a large percentage of the weight and values is in the plus 35 mesh size, it is usually necessary to operate with a feed pulp density of about 40 pct solids and a pulp rate of 25 to 30 gpm.
Spiral concentrators are widely used in the iron ore industries to concentrate heavy iron oxides from light silica gangue minerals. The operation of a WW-6 spiral for the concentration of an iron oxide ore is analyzed through the size recovery or partition curves of the minerals. Several tests conducted following a factorial design using wash water addition, feed rate and slurry solid concentration as studied factors show that for the tested conditions the wash water addition has the most important effect on the spiral performance with its effect being mainly located on coarse particles.
Iron ore concentration is a mineral-specific concentration process within the mineral processing industry. Multotec has custom-developed mineral processing concentration equipment to suit all requirements pertinent to iron ore concentration.
Dense medium cyclones from Multotec are the ultimate in alumina tiled cyclone engineering design, and minimise turbulence. Our dense medium cyclones are cast in 27% high chrome cast iron, providing maximum wear resistance in harsh operating conditions. This means reduced maintenance requirements and less plant downtime.
The Longi-Multotec Heavy Media Drum Separator (HMDS), supplied in standard drum sizes of 900 and 1 200 mm diameter, and widths from 1.2 to 3 metres, improve grade and recovery. The drum shells are constructed from SUS 304 Stainless Steel, and rubberor ceramic wear linings can be installed when required. Custom designed larger machines are manufactured on request means our HMDS meets all your iron ore concentration needs.
Multotecs Hammer Cross Belt Samplers are designed so it is easier to install and retrofit than cross stream samplers. They provide a reliable sampling operation that ensures your samples, from a moving conveyor belt, comprises the product you require. It can be set up to suit all conveyor belt installations from 450 to 2100 mm wide, has idler trough angles of between 20 and 38 and have a durable stainless or Mn steel sample cutter scoop design.
Our mineral spiral concentrators for separate iron ore mineral sizes from 1.5 to 0.04 mm. Available in three ranges, each of which reduces plant footprint by over 33%, their modular housing frames enclose two spiral assemblies, and their optional features can be fully dismantled for retrofitting purposes. The components used are designed to provide longer life, increased production and ease of repair, contributing to reduced downtime.
Multotec Sievebend Housings are available with static and reversible housing units. Both of these are suited to polyurethane and wedge wire sievebends, and each has three standard dimensions, from 800 to 1600 mm arc length. Tailor-made sievebend housings to suit your iron ore concentration application requirements are made to order.
Reducing the initial load of material prior to vibrating screensis among the reasons Multotec has designed its application specific static screens. Additionally, to ensure our customers find the perfect fit for their iron ore concentration applications, our static screen wetted surfaces can be polyurethane, rubber or ceramic. Different assembly methods make Multotecs static screens ideal for numerous screening applications, including media recovery, dewatering and de-sliming trash removal.
As a turnkey supplier of gravity concentration equipment across the world, Multotec can deliver end-to-end spiral solutions, from process audits and test work, to complete spiral concentration plants optimised for your process. With our global branch network, we support your application with tailored field service and complete availability of spares for your plant.
Your local Multotec branch will help you with end-to-end solutions for your gravity concentration plant, from testing equipment through to field service, ongoing optimisation and any maintenance. We keep a wide range of spares and accessories for your spirals, reducing lead times to ensure maximum processing uptime.
We have a range of spirals, from 3 to 12 turns, with high-, medium- and low-gradient profiles. Our high capacity spirals (the HX series) provide a per-start tonnage rating of 4 to 7.5 tons per hour, depending on the mineral type, and is especially suited for the treatment of low-grade ore, where large tonnages are processed.
Mineral spiral separator components include the spiral trough; sliding or auxiliary splitters; launders; distributor and piping; feed box; product box and stainless steel product splitters; and the discharge chute at the bottom of the modular housing frame. Our spiral separators have a diameter of +/- 950 mm.
Our single- and double-stage spiral separators are optimised for coal particles in the size range of 1 to 0.1 mm, providing enhanced coal washing for slurries. Their compact, modular design provides flexibility when building or upgrading your plant.
Double start spirals reduce the requirements of height and floor space in a plant, and reduce capital and operating costs. The MX7 spiral separator is ideal for difficult-to-wash coals, improving the overall efficiency of tougher separation applications.
Spiral concentrators are simple low energy-consuming devices used for mineral separation mainly on the basis of density or by shape. Spirals are widely used in mineral processing as a method for pre-concentration and have proven to be metallurgically efficient and cost-effective.
As the mineral stream is fed from the top of the spiral, a combination of forces act on particles as they move down the trough of the spiral circuit. These forces include gravitational forces, centrifugal force, hydrodynamic drag, and lift and friction forces. Apart from the forces acting on a spiral, the properties of the slurry flowing on a spiral including, solids concentration, feed rate and wash water also plays an important role in the separation on the spiral.
During separation, the heavy particles migrate toward the inner region of the trough, with lighter-density particles migrating to the outer edge of the trough. In a dry spiral separation, materials are sorted by shape. Rounder particles travel faster, are forced to the perimeter of the spiral, from where they can be collected separately from non-round material.
Get an effective, low-cost device for the gravity beneficiation of ores. Outotec spiral concentrators are used in most applications, particularly for concentrating low-grade ores. Manufactured from lightweight, corrosion and abrasion-resistant materials, our spirals require minimal maintenance and upkeep.
This type of spiral is used in most applications, particularly for concentrating low-grade ores. The only water required is added with the solids prior to introducing feed onto the spiral. Concentrates are removed either at the bottom directly into the product box or at several intermediate take-off points down the spiral.
Washwater spirals require the addition of water at various points down the spiral providing more efficient washing of the concentrate, i.e., transporting away light gangue (silica) from the concentrate band.
During separation, the slurry enters the spiral through a feed box and then flows on to the spiral surface. As the slurry travels down the spiral, mineral grains settle and sort according to size, shape, and specific gravity.
Spiral separation uses a flowing film principle based on the size and specific gravity difference present in a mineral suite. When fed a dilute pulp mixture of minerals of different specific gravities, the lighter minerals are more readily suspended by the water and attain relatively high tangential velocities so that they climb toward the outer rim of the spiral trough. At the same time, the heavier, non-suspended grains migrate by saltation (non-linear motion that is a combination of rolling and bouncing) along the spiral surface at the lowest portion of the spiral cross section. In a spiral, heavy mineral concentrate is selectively directed into the spiral trough near the inside of the spiral surface through the use of adjustable product splitters. The concentrate then flows through product discharge outlet ports down the length of the helix.
Like most concentrating devices that utilize physical separation principles, the spiral works best on a closely sized feed, though in select cases the unit has some tolerance for wide size ranges. In general, a coarse size limit would be about 1 mm (20 mesh) and a fine limit of approximately 45m (325 mesh). For best performance, feed should be relatively free of slimes as a high slime content may act like a heavy medium and decrease the effective differences in specific gravity between the minerals to be separated. If slime is in excess of 10% by weight, desliming prior to spiral concentration will almost certainly result in improved spiral performance.
A gravity feed slurry distributor, mounted centrally on top of the spiral module, ensures even distribution of feed to each spiral start. The distributor body is constructed of fiberglass and the wetted surfaces are lined with wear resistant polyurethane. The center mixing column and hoses (not shown) are made of durable and replaceable HDPE and the outlet pipes are constructed of polyurethane. Standard distributors are available with up to 48 outlets in either top-fed or bottom-fed configuration. An example of a top-fed 8-way distributor is illustrated in figure above.
During testing, various parameters can be changed to achieve the desired separation results, keeping in mind that a spiral will normally achieve a 3:1 upgrading ratio (ratio between headfeed grade of heavy minerals and concentrate grade). Therefore, as with most gravity concentrators, a multi-pass flowsheet is often required to achieve the desired grade and recovery of heavy minerals.
In a plant operation, it is important to maintain a consistent feed rate to the spiral concentrator banks. The variations in feed tonnages to the spirals should not exceed 10%. It is also important to properly distribute the feed to each individual spiral so all spirals within a circuit stage are separating the same.Proper distribution is normally achieved using a spiral slurry feed distributor. Standard distributors divide the feed into 12, 24, 36 or 48 ways but other sizes are available.When selecting a distributor one should be chosen which is closest to the number of spiral starts to be operated. The plumbing to each spiral concentrator should be routinely inspected to insure that no plugging or excessive wear has occurred.
Efficient concentration depends on proper selection of draw-off ports and the splitter openings used. Heavy minerals such as ilmenite or hematite settle out rapidly in a spiral concentrator and they should be removed as soon as a good wide band forms. Since the concentrate band is wider at the top, splitters near the top of the spiral concentrator should be opened wider than those near the bottom. This means that the splitters collect concentrate at a relatively uniform grade rather than uniform rate.
The product discharge boxes are provided with two heavy-duty splitters for separating into three products, i.e. concentrate, tails and middling. Product boxes are manufactured of solid-cast polyurethane and are designed to collect product from each spiral start.
The H9000 series spirals are wear-resistant polyurethane/fiberglass construction helixes designed for separating high concentrations of heavy minerals. Each spiral start has up to six super concentrate collection splitters designed for easy adjustment and repeatable positioning.
H9000 series spirals are available in either wash-water or wash-waterless design, and are offered in both 7 and 5-turn sizes. The wash-water model (H9000W) is suited for treatment of high-grade feeds, like iron ore, which might benefit from supplementary wash water to remove gangue minerals. Each spiral turn on the H9000W is equipped with our patent-pending wash-water cups. A wash-water distributor proportionately distributes water to each cup down the length of the column, regardless of changes in flow rate.
The HC8000 model spiral is a seven-turn, wear-resistant polyurethane/fiberglass construction helix designed for separating high concentrations of heavy minerals. Each spiral start has up to six super concentrate collection splitters designed for easy adjustment and repeatable positioning.
Experiments were carried out using a spiral concentrator test rig containing feed conditioner, centrifugal pump and a spiral concentrator with feed to spiral and recirculation. Time samples of concentrate and tails were collected, weighed, dried analysed. Regression equations were developed for Concentrate yield, grade and percent recovery of iron values using Box Behnken Model and Minitab 19 software. The optimised yield, grade and percent recovery are 69.98, 64.98 and 79.20 against the target values of70.00, 65.00 and 80.00 respectively at 16.00% solids, 2.20m3/h feed rate and 14.40cm splitter position. Surface (wire mesh) plots were drawn using Minitab 19 to explain the relation between independent variables and response variables. Maximum yield predicted was 80.24% by weight at a feed consistency of 20.00% solids, feed rate of 1m3/h and at a splitter position of 16.00cm whereas the minimum yield predicted was 17.19% by weight at a feed consistency of 30.00% solids, feed rate of 3m3/h and splitter position of 12.00cm. Maximum grade predicted was 68.73%Fe at a feed consistency of 30% solids, feed rate of 1.00m3/h and splitter position of 12.00cm, whereas the minimum grade predicted was 61.03%Fe at a feed consistency of 10% solids, feed rate of 1m3/h and splitter position of 16.00cm. The maximum percent of iron values recovery predicted was 86.19 at a feed consistency of 20.00% solids, feed rate of 1.0m3/h and splitter position of 16.00cm whereasthe minimum recovery predicted was 18.82% at a feed consistency of 30% solids, feed rate of 3m3/h and splitter position of 12.00cm. Surface plots were used to explain the variation in response variables concentrate yield, grade and recovery of iron values.
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The authors sincerely thank the management of NMDC Limited for approving to conduct beneficiation studies and permitting to publish this paper. The authors also wish to acknowledge the lively discussions and suggestions by their colleagues at R&D Centre, NMDC Limited.
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