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PLEASE DO NOT REMOVE FROM LIBRARYiRIi i901SBureau of Mines Report of Investigations/1986Large-Scale Dewateri ng of Phosphati cClay Waste From Polk Cou nty, FLBy D. R. Brooks, B. J. Scheiner, A. G. Smelley,and J. R. Boyle, Jr.UNITED STATES DE PARTMENT OF TH E INTERIOR

Report of Investigations 9016Large-Scale Dewatering of PhosphaticClay Waste From Polk County, FLBy D. R. Brooks, B. J. Scheiner, A. G. Smelley,and J. R. Boyle, Jr. ECEIVt:::DRItAU M INE JUN 05198'·UNITED STATES DEPARTMENT OF THE INTERIORDonald Paul Hodel, SecretaryBUREAU OF MINESRobert C. Horton, DirectorThis report is based upon work done under an agreement between the University of Alabama and theBureau of Mines.

Library of Congress Cataloging in Publication Data: -Large-scale dewatering of phosphatic clay waste fromPolk County,FL.(Report of investigations; 9016)Bibliography: p.8.Supt. of Docs. no.: 128.23: 9016.1. Phosphate industry-Florida-Polk County-Waste disposal. 2.Clay wastes-Dewatering. I. Brooks, D. R. (Donald R.l. n. Series:Report of investigations (United State s . Bureau of Mines) ; 9016.TN23.U43[TD899.P45]6228 (628.5'42]86-600016

CONTENTSAbstract . . . .Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Acknowledgments . . .u II; Small-scale experiments Large-scale experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Conclusions . . . . . .References . . . " . .1233388ILLUSTRATIONS1.Flowsheet for the FTU . . . . . . . . . . . .2.3.Dewatering of clay waste on a static screen Dewatering of clay waste on a trommel screen Dewatered material in the disposal pit 22 days after filling was completed.4.4557TABLES1.2.3.4.Averages of small-scale testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Typical results obtained during FTU experiments Test results from filling of pit at the Fort Meade plant Consolidation of clay waste in pit from FTU operation 3467

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORTftfootlbpoundgalgallonlb/stpound per short tongal/mingallon per minutepctpercenthhourr/minrevolution per minuteininchwt petweight percent,!

LARGE.SCALE DEWATERING OF PHOSPHATIC CLAY WASTEFROM POLK COUNTY, FLBy D. R. Brooks, 1 B. J. Scheiner, 2 A. G. Smelley, 3and J. R. Boyle, Jr.402ABSTRACTThe Bureau of Mines has tested a dewatering technique for phosphaticclay waste. The technique utilizes a flocculant, polyethylene oxide(PEO), that forms strong, stable flocs that can be dewatered on a staticscreen followed by further dewatering on a rotary screen or trommel. Infield tests conducted in central Florida, clay wastes containing approximately 4 pct solids have been consolidated to greater than 20 pct solids. The rate at which PEO-treated material continues to dewater ina mine cut also was monitored. Preliminary results indicate that PEOtreated material will dewater to 30 pct solids in 80 days. Pretreatmentof phosphatic clay waste with lime lowers the PEO dosage required fordewatering.1Metallurgist.2Supervisory metallurgist.3Supervisory research chemist.4Mining engineer.Tuscaloosa Research Center, Bureau of Mines, Tuscaloosa, AL.

2INTRODUCTIONPhosphatic clay waste is one of theprincipal waste products resulting fromthe mining and benefication of Floridaphosphate ore.This wastematerial,which is comprised of u1trafine particles(70 pct less than 1 m), responds poorlyto conventional solid-liquid separationtechniques and is currently disposed ofby impoundment behind earthen dams.The overall natural settling rate ofphosphatic clay waste is extremely low(l).5 Generally, impounded clay wastesthicken from a nominal 3 pct solids to10 pct solids in about 3 months. Densification to about 18 pct solids may require a year, and to reach solids contents of 20 pct or higher may requireseveral years. Data indicate that approximately 90 pct of the water pumped tothe settling pond is eventually recovered. The remaintng 10 pct of the waterlost by storage with the waste clays andby evaporation amounts to about 5 st foreach short ton of phosphate concentrateproduced (2).The discharge :rate of phosphatic cLaywaste to settling areas ranges between20,000 and 80,000 gal/min. To accommodate the waste, impoundments covering 400to 600 acres, with dam heights rangingfrom 20 to 40 ft, are required ( -1). Atpresent, there are approximately 80,000acres of active and inactive clay settling areas in Florida.To eliminate the use of abovegrounddisposal, which appears to be the ultimate goal of the State of Florida, newtechnology is required to process thewastes generated by most of the Floridaphosphate mines. To use only mined-outareas for disposal of the clay wastes requires that the solids content of thematerial be consolidated from a nominal3 pct to a final 30 to 38 pct. Generally, at this degree of consolidation,the volume of clay waste mixed with thesand from the phosphate beneficiation5Underlined numbers in parentheses refer to the list of references at the endof this report.sequence would fit into the mine cutand eliminate the need for abovegroundstorage.The Bureau of Mines has tested a dewatering technique forphosphatic claywaste that may assist in eliminatingstorage by impoundment (4-10). A portionof the water now being los using conventional waste disposal methooS-also can berecovered, and at the same time the dewatered solids produced may be more suitable for land reclamation. The procedureconsists of flocculating the clay wastewith a long-chain polymer, polyethyleneoxide (PEa). Combining the phosphaticclay waste with PEa forms strong f10cswhlch are tough enough to be dewatered ona screen. In previously reported work,this technique was tested using a fieldtest unit (FTU) at Estech General Chemical Corp.'s Silver City Mine, near Bartow, FL, and at Occidental Chemical Co.'sSuwannee River Mine, near White Springs,FL. At feed rates between 60 and 165gal/min, the FTU was able to consolidatec.lay .a.s.te f.rUID.-a0.mi.na1 3 lLct solids to20 pct solids (6, 11). To determine ifthe PEa-treated -material continued toconsolidate, the treated clay wastes werepumped into storage pits. The pits weresampled over a period of time to determine the solids content. At both sites,the clay waste consolidated to approximately 27 pct solids in 60 days. At theSilver City Mine, an additional 30 dayswas needed to attain 30 pct solids. Theclay waste at the Suwannee River Mineneeded an additional 80 days to consolidate to 30 pct solids (6, 11).This report describes further testingof the PEa dewatering technique. At therequest of the Mobil Chemical Co., thesmall-scale unit (8 to 18 gal/min) andthe FTU (200 gal/min) were operated atMobil's Fort Meade Mine. The small unitwas used to develop the parameters ofoperation for the FTU. The FTU was usedto fill a pit with dewatered clay wasteso that any further consolidation of thewaste with time could be monitored.

3ACKNOWLEDGMENTSauthors wish to express appreciation toAl Propp, project manager, for coordinating the work at the Fort Meade Mine.This research was conducted under amemorandum of agreement between the Bureau of Mines and Mobil Chemical Co. TheSMALL-SCALE EXPERIMENTSCommercially manufactured PEO was usedPEO concentration, flow rate, and mixeras the f10ccu1ant inall dewateringspeed affected the dewatering. Since thetests. The polymer is a linear, non character of clay waste changed from hourionic, water-soluble molecule composed ofto hour, the results of individual testsrepeating units of CH 2 CH 2 -O and having awere grouped together to obtain a trend.molecular weight of approximately 5 mi1The data were divided into three majorlion. Solutions containing 0.25 pct PEOgroups:(1) dewatering the clay wastewere - p.r-ep-ar.ed- f-rom the solid po1yme.J;. - -f-J;.omt-he sump without any treatment,These solutions were then diluted to con(2) addition of lime prior to PEO f10 cu centrations between 0.01 and 0.05 pct.1ation, and (3) addition of 3 to 10 1b/stDeep-well water was used for preparationlime, mixing, and allowing the 1imeand dilution of the PEO solution.treated clay waste to stand overnight.Initial tests were conducted, usingFor each of these groups all the test resmall-scale equipment with a throughputsu1ts were averaged to obtain a singlecapacity of 8 to 18 gal/min, to determinenumber for dosage and solids content.how this clay waste responds to f1occu1aThe average results are shown in table 1.tion with PEO. Clay waste used in theseThe averages given in table 1 represent aexperiments was obtained from the pumpingwide range of results; for example, thesump at the Fort Meade plant. The claysolids content ranged from 7 to 21 pctwaste entered a 400-ga1 tank and was thenand the PEO dosage f r om 0.88 to 2.53 1b/pumped to a mixer, where PEO was added.st. The results indicate that PEO willThe resulting f10cs were dewatered on aflocculate this clay waste and that thestatic screen, followed by further dewaresulting floc could be dewatered on thetering in a tromme1 screen. Tests weretromme1 screen. Also, the addition ofconducted to determine how variables suchlime lowers the PEO dosage.as lime addition, aging time, PEO dosage,LARGE-SCALE EXPERIMENTSBased on results of the small-scale experiments, the mobile FTU was moved tothe test site. Figure 1 shows the flowsequence for the FTU. Clay waste wassupplied to the unit from the plant claywaste pipeline. The clay waste from thepipeline flowed· to a holding tank-.- Fr-omthis tank it was pumped to the FTU at apredetermined rate. The static screen,shown in operation in figure 2, is 8 ftwide by 4 ft high and has openings 0.03in wide. The tromme1 screen has a 3-ftdiam, is 12 ft long, and was constructedof 10 esh stainless steel. The first-4 ft f-rom the feed end was lined with asecond screen of 48-mesh stainless steelTABLE 1. - Averages of small-scale testing dataNo treatment.Lime addition.Lime addition plus standing overnightPEO dosage,1b/st1.61.31.1Dewatered product,pct solids16.414.716.3

40.25 pctWaterPEO holdingtanksholding0.05 ondClaywasteholdingtankClayL.---""' --wasteinFIGURE l. - Flowsheet for the FTU.to prevent loss of solids as the flocculated material flowed onto the screen.During operation,the clay waste forms aroll in the trammel, as shown in figure 3.In addition to the dewateringscreens, the equipment includes a systemfor making PEO solutions; holding tanksfor PEO solutions and the clay waste; andvarious pumps to transport solutions,slurries, and consolidated material.Initial experiments were conducted todetermine the optimum mixing speed forthe clay waste-PEO mixer. It was determined that 45 r/min gave the best results. Based upon this information, theFTU was operated at 45 r /min. Resul ts ofa series of tests, shown in table 2, indicate that 19.5 to 25.1 pct solids canbe obtained with 0.99 to 1.33 Ib/st PEO.TABLE 2. - Typical results obtained during FTU experimentsFeed solids content,wt pctLime addition,Ib/stPEO dosage,lb/stTrommel discharge,wt 323.022.123.625.124.224.024.5l-c}.520.5

5FIGURE 2. - Devyatering of clay waste on a static screen.FIGURE 3. - Dewatering of clay waste on a trommel screen.