The phosphate-bearing formations in the West constitute relatively thick beds of phosphatic sandstones and shales that can be mined on a large scale employing open pit methods. The mineralogical characteristics vary considerably and require various treatment conditions for specific areas. ForPhosphate,flotation is, in general, very important to upgrading the phosphate rock and is employed in this study to beneficiate a 20% P2O5 feed content to a 30-32% P2O5 content.
The growing fertilizer industry has increased the demand for phosphate rock from which super-phosphates are produced. The fertilizer market is very competitive. Transportation costs and market specifications are often important factors. The phosphate beds in the Western United States comprised of Utah, Wyoming, Idaho, and Montana have received increasing interest and exploitation to fulfill the agricultural needs in the West and in the Mississippi Basin.
The flowsheet in this study is applicable to treating certain Western phosphate ores although some modifications may be necessary in specific instances. Truck haulage to the mill is common practice. Crushing, which is not shown on the flowsheet described, is usually accomplished using conventional jaw crushers for primary reduction and then impact or cone-type crushers for secondary reduction in closed circuit with vibrating screens.
Wet rod mill grinding to approximately 35-mesh is employed as only a moderate degree of grinding is required and the production of slimes must be minimized to effect maximum recovery. The Rod Mill operating in closed circuit with a Cyclone Classifier is effective in accomplishing the liberation of the phosphate minerals.
The complete removal of slimes is essential to successful phosphate flotation. The cyclone classifier overflow is partially deslimed and densified using a Spiral Classifier. The deslimed sands at uniform density from the spiral classifier are subjected to attrition scrubbing at approximately 60-70% solids to thoroughly clean the mineral particles of slime producing material. A 4-cell Attrition Scrubber is used for this purpose. The discharge from the scrubber is thoroughly deslimed using cyclones which produces a slime free sand underflow for flotation.
The cyclone underflow which varies in its density is discharged to a Spiral Densifier to produce a uniform and dense feed to the Heavy Duty Duplex Conditioner. Reagents (fuel oil and fatty acid) are added to the conditioner which is operated at 60 to 70% solids. Flotation is accomplished at 30% solids in two stages with intermediate densification and conditioning with additional reagents for optimum recovery. The free flow type Sub-A Flotation Machine with supercharged air is used due to the high tonnages that must be handled. Double overflow machines are used for the rapid removal of froth because a large proportion of the feed reports as concentrate. Flotation is very fast if the feed is properly deslimed and conditioned. The large tonnages usually treated require several parallel flotation sections but only one section is shown on the flowsheet for simplicity.
Double cleaning of the froth without additional reagents is illustrated to insure a uniform product meeting market specifications. The cleaner tailings are returned to the head of the rougher flotation circuit and subjected to desliming and conditioning before being retreated. Unlike the practice often required in the Florida phosphate area, the flotation concentrates are not subjected to reflotation for the removal of silica as a froth product.
The flowsheet shows the overflows from the first two cyclones and the primary densifier being recycloned with the final overflow going to the tailing thickener. The cyclone underflow is fed to the second stage of flotation. This extra cyclone step functions as a scavenger for fine phosphate particles that may have been rejected in the initial desliming phases.
The cleaned flotation concentrate filters very rapidly due to its granular and deslimed characteristics. A horizontal vacuum pan filter is ideal for this application. Drying, which is required by market specifications and freight charges, is accomplished by a concurrent direct fired Rotary Dryer. The dried concentrates are stored preparatory to shipment.
The flowsheet shows the entire tailing being thickened for the recovery of water for reuse. The slimes require flocculation for settling in the thickener due to their earthy clay-like composition. The thickener underflow is pumped to the tailing pond.
The feed, final concentrate, slime tailing, flotation tailing, and composite tailing represent the key points for automatic sampling. Reliable samples cut at 15 minute intervals are essential to efficient operation.
Phosphate deposits vary considerably throughout the world and represent a challenge to the metallurgist. Simple washing and screening techniques apply to some ores whereas flotation is often required for other ores. Granular phosphate particles ( 20, +35 -mesh) require reagentizing and agglomerate separation using tabling, spiraling, and other methods. Calcining is sometimes effective to remove organic matter or other gangue constituents. Therefore, thorough test work is a prerequisite to any successful phosphate milling operation.
Descriptionof Ore:Phosphatic sandstone and shale. Assay of Ore:20.0% P2O5 Method orProcess:Sub-A Flotation Concentrateand Recovery: Cleaned Flotation.31.0% P2O5 Recovery70.0% Reagent,Lbs. Per Ton: Fatty acid.0.7 Fuel oil.0.5 MiscellaneousData:Grind 35 mesh, scrubbed and thoroughly deslimed prior to flotation ata pH of 8 to 9. Caustic soda is sometimes used in conjunction withthe fatty acid and fuel oil.
Many new mines overseas have also become significant. This includes countries such as Senegal, Togo, Israel, Spanish Sahara, and Jordan. Limited production, often as by-products, has been noted in South Africa, Brazil, and other countries. In recent years, and even recent months, we have learned of many new areas being considered as potential sources of phosphate rock. This includes Australia, Saudi Arabia, Mexico, Colombia, and Brazil. Many other developing countries have discoveries and are considering their new deposits, often with difficult beneficiation problems, as potential sources of phosphate.
Florida phosphate occurs in a sand-clay matrix overlaid by unconsolidated overburden of sand and sandy clays, ranging from 10 feet to 45 feet in depth. The matrix usually occurs in fairly horizontal and continuous beds ranging from 3 feet to 25 feet in thickness, and is composed of clay minerals from the montmorillonite family, silica sand, and phosphate particles from to 200 mesh. The particles coarser than 14 mesh are referred to as pebble phosphate while the particles finer than 14 mesh are referred to as flotation feed.
As with most of the mining industry in general, the trend in Florida is toward mining of leaner deposits. Some of the factors associated with leaner deposits and with todays economic conditions are listed following.
Agricos Fort Green Mine is located in the southwest corner of Polk County and is directly adjacent to Manatee, Hillsborough, and Hardee Counties. The washer began operation in the spring of 1975, while the recovery plant started up 9 months later. With some minor differences, Fort Green is typical of a modern Central Florida plant. Rated capacity is 3,000,000 plus tons of product per year.
Briefly, slurried matrix is pumped to rotary trommel screens, 7/8 inches, for washing; the trommel oversize is sent to hammermills where it is crushed and returned to the trommel screens, or pumped to tailings if minor impurities (Fe2O3, Al2O3, MgO) are high. The trommel undersize is pumped to 14 mesh stationary flat screens. The flat screen oversize is subjected to three stages of 14 mesh vibrating screening and two stages of logwashing in order to produce a final pebble product. The flat screen undersize is pumped to two stages of cyclone desliming (150 mesh) prior to sizing.
In actuality, Fort Green was designed to accept feeds from two distinct mining areas simultaneously a pebble rich area associated with low-grade flotation feeds and a pebble-lean area associated with higher-grade flotation feeds. Because of the staggered start-up (washer first, recovery plant later), draglines were placed in the pebble rich areas.
Phosphate was first discovered in Jordan at the turn of the present century during the excavation of railroad cuts in the Ruseifa and El Hassa areas. In 1977 these two areas are still the sites of the total present phosphate mining in Jordan. Underground mining methods were used at both sites in the past but currently all mining is open pit.
The phosphate deposits cover an estimated 60% of the country and are located in the upper Cretaceous and Eocene formations. Potential reserves have been estimated at two billion tons. Over 300 million tons of reserves have been confirmed and drilling of new areas continues to confirm improvements in their reserve picture. It is interesting to note the publication of a map by Jordan Phosphate Mines Co., Ltd.
Ruseifa, the first mine site in Jordan, is only a short drive northeast of Amman. The newest open pit mining operation, which has been expanded considerably in the 1975-1976 period, is over two hours drive south of Amman over the desert highway. This site, called El Hassa, is located in a very arid, treeless country closely resembling desert country in the southwestern United States.
The Catalao pipe is most interesting. This deposit is located some 18 kilometers northeast of the town of Catalao. Catalao itself is on the main highway from Sao Paulo to the capitol at Brasilia and is actually some 3% hours drive south of Brasilia. The magmaticdeposit at Catalao consists of red, earthy-clay materials with inclusions of massive formations of magnetite and apatite. The overburden ranges from 20 to 40 meters in depth and the ore from 20 to 35 meters in thickness. Ore grades range from 12% P2O5 to 22% P2O5. Mining is planned by open pit methods at Fosfago.
The commercial operation by Fosfago will be quite similar to the pilot operations with some changes in equipment. The milling stages will include impact crushers, rod, and ball mills. Primary magnetic separation will be made at 10 mesh followed by a secondary magnetic separation after finer grinding. Desliming will be accomplished in high pressure 4 hydrocyclones. Double-paddle attrition scrubbers will also be used. Flotation will be accomplished in 300 cubic foot cells which will include a rougher and two cleaner units. The apatite concentrates will go to a thickener with the thickened underflow being pumped to a remote location, which will include a smaller thickener, belt filter, and dryer. Rail loading from dry storage silos will be accomplished at this point.
The present phosphate deposit being mined in eastern North Carolina is located near Aurora, not far from Washington, N. C. The city of Washington is located directly on the Pamlico River which in turn empties into Pamlico Sound in the vicinity of Cape Hatteras. Geologists indicate this marine sedimentary deposit was formed in the Miocene seas along the Atlantic Coastal Plain some 15 million years ago.
Compared to most Florida deposits currently being mined, this matrix disintegrates readily with water on the washer. Feed grades are generally very good in this area, often containing 17-18%, after desliming. After removing the pebble on vibrating screens, the clay fractions are discarded as overflows from hydrocyclone sand report to thickeners where recycle water is reclaimed to return to the processing plant, and the clays sent to impounding areas. Clays in North Carolina settle very rapidly as compared to most Florida clays.
MSEL has agency agreements with reputed manufacturers to sell Cone Crushersequipment, which are required in tertiary crushing (-30/10 mm) of Rock Phosphate for subsequent grinding to even smaller sizes.
Reciprocating Feedersare built for high capacity reclamation from surge bins, bunker and hoppers and also as feeding equipment. A wide range of sizes is available in MSEL offerings. Heavy Duty versions with larger drives and heavier pans can be selected for coarse ores and normal versions for fine ores.
Grizzly Screens/ Feedersare used in primary crushing operation in Rock Phosphate Mining as scalping screen of the Primary Ore Crusher to separate undersized and oversized ore. Typical separation is at 80 mm. Grizzly Screens/ Feedersare also used as Feeders to reclaim ore from Hoppers/Bins.
Circular Motion Screensare used to segregate various size fractions in various mineral streams. Sometimes Circular Motion Screensare used to reduce load on crushers by removing fraction which is already smaller than required size and sometimes Circular Motion Screensare used to recirculate oversize fractions from crushed product stream back to crushers. Possible application is in Mines before despatch to power plants. Circular Motion Screensare available in 1, 2 and 3 decks to get 2, 3 and 4 size fractions respectively. Each size fraction may be requiring different post processing.
High Particle Acceleration Screensare ideally suited for screening applications for higher level of moisture and fine grain size materials (3 mm to 10 mm) with screening capacities up to 250 metric TPH. In Iron Ore & Steel industry High Particle Acceleration Screensare used for fine screening in Flux Crushing & Screening circuits. The Inner frame is agitated by means of eccentric shaft drive. The vibration is passed on to the Outer frame via flexible thrust springs.
Screening mats between the inner and outer frame are clamped and flexed by the two vibrating frames. The relative movement of both screening frames creates a trampoline effect in the screen mats to create-
In Rock Phosphate beneficiation plants usually the process involves transporting of Ore Slurry (suspension of Crushed/ Ground Ore in Water) between various stages. This is done by use of Slurry Pumps. MSEL has a vast range of Horizontal and Vertical Centrifugal Pumps catering to Slurry Pumpsrequirements.
In second stage additional bank of Flotation Cellsare used to remove carbonate (rejects) as froth and Phosphate Concentrates as underflow, which is then processed through cleaner flotation Cells before taking for thickener concentration and filtration.
Banana Screensare multi-slope vibrating screens, come in single/ two deck configurations and are used in place of Circular Motion Screens when higher capacities (above 400 tph) are to be processed. The angle of deck decreases from feed end to discharge end.
Vibrating Tube Mills are for continuous or batch grinding of materials to a very fine end product. Two vibrating/ grinding cylinders are placed either directly above the other or inclined at 30 degrees to perpendicular. Located between the two tubes, an eccentrically supported weight is driven to produce a small circular vibration. The tubes are charged with ball or rod media to aid in the grinding action (attrition) from the constant impulses. Material is ground as it travels from the input end of the tube to the outlet end.
Vibrating Tube Millshave a very small size and low energy consumption compared to other mill types and are used in manufacture of paints and varnishes where ultra- fines (of the order 10-20 microns) are required. Output is restricted to 5-10 tph. We offer Vibrating Tube Millsfrom our Baroda plant.Get in Touch with Mechanic