United States Patent (19) 11 Patent Number: 4,588,498 Mair et al. (45) Date of Patent: May 13, 1986 (54) SINGLE FLOAT STEP PHOSPHATE ORE 4,514,290 4/1985 Swiatkowski et al..... 209/166 BENEFICATION FOREIGN PATENT DOCUMENTS (75) Inventors: Alexander D. Mair; Myra M. Soroczak, both of Florence, Ala. 93909 6/1982 U.S.S.R, .............................. 209/166 (73) Assignee: Tennessee Valley Authority, Muscle Primary Examiner-Bernard Nozick Shoals, Ala. Attorney, Agent, or Firm-Robert A. Petrusek (21) Appl. No.: 717,059 57 ABSTRACT 22) Filed: Mar. 28, 1985 A flotation process is taught for beneficiating phosphate ores containing, as impurities, silica and alkaline earth Related U.S. Application Data metal carbonates, particularly dolomite. Using a single flotation stage, the phosphate values are recovered in (63) Continuation of Ser. No. 708,914, Mar. 6, 1985, now the overflow and quite unexpectedly both the siliceous Defensive Publication No. T06,002. and the carbonate gangue minerals are simultaneously (51) Int, C. ............................................... B03D 1/02 removed in the underflow. Prior to flotation, surfaces of 52 e o O owda 209/9; 209/166 the minerals in the phosphate ore are selectively sulfi (58) Field of Search ............................ 209/166, 9, 167 dized with an insoluble copper-containing metal sulfide, (56) References Cited permitting use of sulfide mineral collecting reagents such as alkyl xanthates in the flotation step to achieve a U.S. PATENT DOCUMENTS high degree of selectivity. 1,094,760 4/1914 Terry ...................................... 209/9 3,405,802 10/1968 Preller et al. ....................... 209/166 23 Claims, No Drawings 4,588,498 1. 2 ineffectual in separating carbonate gangue from the SINGLE FLOATSTEP PHOSPHATE ORE phosphate values. BENEFICATION The presence of carbonate in the phosphate concen trate is undesirable; it not only acts as a P2O5 diluent, The invention herein described may be manufactured 5 but also is detrimental in subsequent chemical process and used by and for the Government for governmental ing of the rock. In phosphoric acid or superphosphate purposes without the payment to us of any royalty manufacture, for example, the presence of carbonates therefor. consumes additional sulfuric acid in the acidulation This application is a continuation of our previously steps without providing additional fertilizer values. filed application, Ser. No. 708,914, filed Mar. 6, 1985 10 Carbonate also exacerbates foam formation in the reac now Defensive Publication No. T106002. tor vessels thereby reducing their effective production The present invention relates to the beneficiation of capacity. The presence of appreciable MgO in the phos phosphate ores and more particularly, the present in phate concentrate (e.g., MgO) 1%), as derived from vention relates to a process for beneficiating phosphate dolomite or dolomitic limestone, is particularly objec ores containing siliceous and alkaline earth metal car 15 tionable in the manufacture of wet-process phosphoric bonate impurities. acid (hereinafter referred to for the sake of convenience simply as WPA) since a significant MgO content in the BACKGROUND OF THE INVENTION resulting product WPA causes deposits a sludges and 1. Field of the Invention scale during and after processing of the rock concen For the past forty years the normal procedure for 20 trate to phosphoric acid. Because of this inability of the beneficiating Florida phosphate rock from associated Crago double-float process to separate gangue minerals gangue minerals has included a double flotation (or other than silica, for example, carbonates such as dolo Crago flotation) step for that portion of the mineral feed mite and calcite, from the phosphate concentrate, it is in the size range of approximately 0.1-1 mm, which thus readily apparent that as the supply of high quality portion generally contains an appreciable fraction of the 25 phosphate ore is being depleted there is a most pressing phosphate values. In this flotation process, which re need for a flotation process suitable for Florida and moves the major contaminant (quartz sand), the de similar phosphate rocks whereby both the siliceous and slimed feed rock is first subjected to flotation using a carbonate impurities therein can be separated effec mixture of fatty acids and fuel oil as collector. The tively from the phosphate values. resultant overflow retains most of the phosphate min 30 2. Description of the Prior Art eral and some entrained quartz. After deoiling, this The prior art teaches that several attempts have been rougher concentrate is subjected to a reverse flotation made to develop processes for separating carbonate step using cationic collectors such as primary amines, minerals such as dolomite from the phosphate mineral which floats off most of the remaining quartz and re contained in Florida-like phosphatic ores where silica is tains a highgrade phosphate concentrate in the under 35 the principal impurity. In all the prior art where particle flow. Since its introduction, this flotation procedure, as size of the rock feed permits effective separation by described by A. Crago (U.S. Pat. No. 2,293,640), has flotation, siliceous materials, such as quartz sand, and been successfully employed for siliceous central Florida alkaline earth metal carbonates, such as dolomite, are phosphate deposits with little subsequent process modi removed in separate flotation steps. The silica is re fication. moved using one or both stages of the Crago double However, the ore of the Florida Bone Valley Forma float method. The carbonate is subsequently or some tion most suited to this beneficiation procedure is rap times previously removed from the phosphate values in idly being depleted. Lower quality ore from the south another separate and distinct flotation stage, often re ern extension of the central Florida phosphate field is quiring a different collector reagent and, in all instances, now of necessity becoming commercially exploited. 45 use of a flotation depressant for either phosphate or This lower quality ore from the Hawthorn Formation is carbonate. somewhat mineralogically different from that of the For example, in U.S. Pat. No. 4,287,053 (assigned to Bone Valley Formation. The Hawthorn ore is generally the assignee of the instant invention), J. R. Lehr et al less weathered or altered and usually contains apprecia teach that dolomite was removed from the phosphate ble quantities of alkaline earth metal carbonate minerals 50 mineral by floating off the dolomite using fatty-acid such as dolomite. Surface chemical properties of car collectors while depressing the phosphate mineral flota bonate minerals such as dolomite, calcite, or dolomitic tion by addition or organic phosphonic acids. In an limestone are often very similar to the surface chemical other such related teaching, R. E. Snow in U.S. Pat. No. properties of the predominant phosphate mineral in the 4,364,824 discloses that dolomite was floated off using ore, a sedimentary marine carbonate-apatite known as 55 sulfonated fatty-acid collectors while the phosphate francolite. For instance, the generally recognized simi mineral flotation was suppressed by addition of depres larity in response of calcite, dolomite, and francolite sants such as sodium tripolyphosphate. Conversely, in minerals to fatty-acid flotation collectors is believed U.S. Pat. No. 4,144,969 R. E. Snow teaches that the largely due to specific adsorption and bonding of the phosphate mineral was preferentially floated using pri fatty acid to the mineral surface by salt-like complexing 60 mary amine collectors, while dolomite was removed in of the fatty-acid carboxyl moiety with the surface cal the underflow using fluoride as a depressant. cium ions common to all these minerals. Because of All such beneficiation schemes supra are complex, these surface similarities, it is difficult to separate car with the severe disadvantage that maintenance of two bonates from the phosphate minerals by physical benefi or usually three separate and distinct flotation circuits ciation methods such as flotation, which are dependent 65 are necessary to ensure removal of both siliceous and for their success on exploiting dissimilarities in the sur dolomitic impurities. An attendant problem exists in face properties of the minerals to be separated. Hence, that each flotation stage generally requires a separate the Crago double-float process has unfortunately been conditioning step and often an additional processing 4,588,498 3 4. step to remove reagents used in the previous flotation process, said phosphate concentrate will produce a stage from the mineral surfaces prior to the next flota high-quality acid with a soluble MgO content suffi tion stage. None of these processes have proven entirely ciently low to be acceptable to commercial processors successful and, as yet, no completely satisfactory benefi and users of phosphate rock and products associated ciation scheme exists for dolomitic phosphate ores of 5 therewith. the Florida type. Still further and more general objects and advantages Thus it is apparent that it is becoming increasingly of the present invention will appear from the more desirable that there be developed or devised an im detailed description set forth below, it being under proved method of beneficiating these ores, preferably stood, however, that this more detailed description is by a technically less complex and more economical 10 given by way of illustration and explanation only and process requiring fewer flotation stages to remove both not necessarily by way of limitation since various carbonate, particularly dolomite, and siliceous impuri changes therein may be made by those skilled in the art ties from the phosphate ore. without departing from the true spirit and scope of the Our new and unexpected discovery comprising the present invention. instant invention provides such a process wherein the 5 surface properties of the ore are selectively and substan DESCRIPTION OF THE PREFERRED tially modified in a novel manner by selectively coating EMBODIMENTS the phosphate mineral surfaces with a molecular layer In the preferred embodiment of the present invention, of metal sulfide.