Use of Fly Ash as a Waste Minimization Strategy

Transcription

1 Use of Fly Ash s ste Miimiztio trtegy C. A. etz,* C. J. Moretti, K. R. Heke,.. Mw, d K. U. ike Uiversity of North Dkot ergy Reserch Ceter, Grd Forks, ND 58 Cost-effective lier mterils for wste disposl tht would meet stte regultory requiremets for lier permebility while reusig col combustio fly sh, reducig sh disposl costs were developed. ier developmet criteri icluded permebility of less th lo-' cmls d durbility comprble to tht of covetiol cly liers. Fly sh smples from six utility compies locted if;ve sttes were used. These smples were represettive of the lrge qutities offly sh rjilble from col-$red power plts. he mixed with -9.5% by weight portld cemet dlor lime, ech of the smples yielded liers with permebilities sigijictly less th O-' cmls d compressio stregths geerlly exceedig psig. ier costructio costs rged from 5.5 to 8. ft [], with the costs depedig o the qutities offly sh d dditives used, formultio mixig method, d plcemet d compctio methods for the 1ifts. tudies of lechte from ech fly sh foud tht oe of them would be hzrdous uder curret regultory guidelies. NTRODUCTON The most commo techology for the disposl of wste i the Uited ttes hs bee ldfills. Future ldfills will *C. A. et:: is curretly employed t Argoe Ntiol bortory, ergy d virometl ystems Divisio, 97 s. Cuss Ave., Argoe, ll. 69. Correspodece should be directed to this uutlior. 198 August, 1988 be more highly regulted th their predecessors. All ew ldfills re required to hve lier systems cotiig lechtes to protect groudwter. The liers my be costructed from vriety of mterils, icludig cly d membres of sythetic polymers, to meet striget regultory requiremets. hile ew regultios will cuse sigifict cost icreses i oth ldfill costructio d opertio, the ecoomic dvtge of ldfills is expected to cotiue to provide firly ttrctive ltertive to other tretmet d disposl techiques []. virometl Progress (Vol. 7, No. ) i

2 The electric utility idustry is highly depedet o fossil fuels. All col-burig utility plts produce lrge qutities of fly sh tht must either be used i ecoomicl pplictios or disposed of i evirometlly cceptble mer. Fly sh offers cemetitious properties tht could produce cceptble ldfill lier. The developmet of cost-effective liers bsed o fly sh for wste disposl sites t col-fired utility plts would be beeficil to both cosumers d the eviromet. everl previous studies hve exmied the use of fly sh for lier costructio. 198, the mpire tte lectric ergy Reserch Corportio (RCO) evluted the fesibility of usig fly sh s mjor compoet i the costructio of ldfill liers []. The fly sh i the RCO study, bsed o medium-sulfur Pesylvi col d low-sulfur est Virgii col, showed tht the dditio of betoite cly by 1% weight produced permebilities of less th lof6 cm/s. The Uiversity of iscosi, usig fly sh from subbitumious col, produced fly sh d sd mixtures with permebilities less th.8 x lo-'cm/s []. A third fesibility study, performed by Cosolidted diso Compy of New York with est i'irgii col determied, tht fly sh mixtures cotiig 6% by weight lime d.5% by weight sodium crbote hd permebilities less th cm/s []. Bsed upo experiece with clys d other soils, idividul sttes hve tte TAB 1. FY AH NR G.'JDN FOR UTTY AT DPOA T GG^ CTD TAT hliimum ier Thickess (fi) Permel)ilip Requiremet (cm/s) di Texs lliois Miesot North Dkot 51-7 bee promulgtig lier guidelies, show i Tble 1, tht will provide stisfctory evirometl protectio t wste disposl sites. The purpose of this study ws to develop cost-effective lier mterils for wste disposl sites usig mixtures of col combustio fly sh, lime, cemet, d wter, which would meet the sttes' regultory requiremets i Tble 1. The developmet of liers with permebilities less th lo-' cm/s, s well s stregth d durbilie t lest comprble to covetiol cly liers, were studied. Furthermore, the fly sh liers should exhibit lechig behvior tht would ot dversely ffect either the soil or groudwter er the wste disposl site. TAB. FY AH AMP FROM X UTTY COMPAN Utility Compy octio Col Bured Commets horther ttes Power Co. (NP) Bsi lectric Power Coopertive (Bsi) Texs Utilities Geertig Co. (Texs Utilities) outhwester lectric Power Co. (P) Norther di Public ervice Co. (NP) Cetrl lliois Public ervice Co. (CP) Riverside ttio, MN rpy Creek subbitumious col.telope Vlley Beulh ligite ttio, ND Big Brow ttio, TX Texs ligite H.. Pirkey ttio, TX Texs ligite R.M. chhfer ttio, K lliois #6 bitumious col Meredosi ttio, lliois #6 bitumious col ime-bsed dry scrubbe1 powder Fly sh d scrubber powder Fly sh oly Fly sh oly Fly sh d scrubber sludge from wet lime scrubber Fly sh from pod TAB. PHYCA AND CHMCA PROPRT OFTH FY AH TUDD. (A UNT AR X GHT PRCNT UN OTHR XOTU.) Property Texs NP Bsi Utilities P NP CP Compositio K hl go A i P5 so CO K Ti Fez Totl oss o igitio Fly sh wtersoluble frctio pecific surfce re (m/g) o o ' to! "Results were ot reproducible. virometl Progress (Vol. 7, No. ) August, %

3 FY AH CHARACTRZATON The fly sh smples used i this study were obtied from six utility compies i five sttes. These smples were represettive of the lrge qutities of fly sh vilble t utility plt site. Tble describes the source of ech of the fly sh smple used i this study d idetifies the mes d loctios of the utilities. The physicl, chemicl, d mierlogicl properties of fly sh ifluece its hdlig, use, d disposl. ch of the six fly sh smples were chrcterized i Tble ccordig to physicl d chemicl properties. The elemetl lysis ws performed with eergy-dispersive X-ry fluorescece. The mierl compositio ws determied by powder X-ry diffrctio. The loss-o-igitio property (ATM Method C 11-68) mesured the ubured crbo cotet of the wste. The wter-soluble frctio of the fly sh smples ws mesured usig simple lechig techique. The specific surfce re ws mesured with Qutchrome, sigle-poit, moosorb istrumet usig the BT liquid itroge dsorptio priciple. The fly sh smples were lyzed by the PA-P btch lechig test to determie if the fly sh should be TAB. CONCNTRATON OF ACHAT CONTAMNANT FOR RCRA HAZARDOU AT CAFCATON FOR HA MTA N ACHAT lemet Arseic Brium Cdmium Chromium ed Mercury eleium ilver Mximum Cocetrtio Permitted (mg/) clssified s hzrdous wste uder the regultios of the Resource Coservtio d Recovery Act (RCRA) defied i Tble [5]. Tble 5 shows the P lechte results for the six fly shes studied. Bsed o the results i Tble 5, ll of the fly shes studied produced P lechtes with trce metl TAB 5. P ACHAT ANAY FOR FY AH AMP (mg/) lemet NP Texs Bsi Utilities P NP CP Arseic Brium Cdmium Chromium ed Mercury eleium i 1 ver Fil ph <.1 c. CO..6 <. <. co. < <. <.5 <. <..5 co C.. <. c C..5 c. c..15 < CO.. <. (..1 c <.5. <..5 CO.5 5. TAB 6. PRhlABTY RUT FOR TH KR COPNC TT Fly Ash NP Bsi Texs Utilities P NP CP Test Mixture Compositio % lime, % portld cemet, d 9% fly sh % lime, / portld cemet, d 9% fly sh % lime, % portld cemet, d 97 fly sh 5% lime, 5% portld cemet, d 9% fly sh 5% lime, 5% portld cemet, d 9% fly sh (scrubber wste mixture) 6% lime, 6% portld cemet, d 88% fly sh ter Added ( totl dry weight) s 1 Permebility (cm/s) 9. x x lo-" 1.8 x lo-" 6. x lo-".8 x x x x lo-" 5. x x lo-" 1. x x lo-" 8. x lo-" 1. x lo-". x 9. x x 1.7 x. x lo-" 9. x 1-7. x x lo-".5 x 1-5. x lo-". x. x x 1-8. x 6.5 x lo-" 8. x 1-7 August, 1988 virometl Progress (vel. 7, No. )

4 -. NP :i ClP 5 io9 1 ter Additio to i e r To r m u t i o (wt %> Figure 1. Permebility scopig test for NP od ClP fly sh. < x + - U C - io Bsi 1 ter Additio to i e r Fo r m u t i o (wt %) Figure. Permebility scopig test for bsi electric od NP fly sh. 1 cocetrtios well below the cocetrtio levels specified by the RCRA regultios for hzrdous wste cocetrtios (Tble ). DVOPMNT OF COPNG TT Followig the chrcteriztio of the six fly shes, scopig tests were performed to determie the pproximte mouts of lime, cemet, d wter dditio required to produce cceptble liers. Hydrted lime, portld cemet, d wter were selected s the dditives for this fly sh lier study becuse they hve bee widely used with fly sh to produce highwy costructio mterils. dditio to hvig desirble physicl properties such s low permebility d high sher stregth, fly sh liers should outlst covetiol cly liers, which re subject to crckig, erosio, d root peetrtio. Bsed o the results of the scopig tests, desiged experimets were lter coducted with vrible dditive levels to develop specific formultios for producig lier mterils..a series of scopig tests were iitilly performed to determie the pproximte rges of lime, cemet, d wter required to produce cceptble fly sh lier. These prelimiry scopig tests used reltively high levels of lime d cemet d vryig mouts of wter. Throughout the permebility tests, the lier mixtures were compcted i PVC tubes with 1.5 ich iside dimeters d ich legths; the tubes were scored o the ier surfce to esure stisfctory sidewll sel. A fixed-wll type of permebility test ws performed o -ech of the compcted lier mixtures usig 1 psig of costt hed differetil cross the lier smple. everl of the lier smples were lso tested usig flexible membre prmeter to compre those results with the fixedwll test for possible sidewll lekge. The correltio betwee the fixed-wll tests d the flexible membre tests geerlly produced o idictio tht sidewll lekge ws occurrig i the fixed-wll tests. virometl Progress (Vol. 7, No. ) The levels of lime d cemet fo the scopig tests were determied by tril d error to meet or exceed the followig cceptble lier criteri: 1. Permebilib of less th lo-' cm/s.. Ucofied compressio stregth greter th psig followig 8-dy cure t O'F (ATX C-59). < v c x 1 - t J Figure. Permeobility scopig test for Texs utilities d sweep fly osh. August,

5 TAB 7. RUT OFTH XPRMNTA PROGRAM FOR TH NP NR FORMUATON Fly Ash ter (7 of ime Cemet 7-Dy tregth 8-Dy tregth Permebility (wt7) dry wt) (wt%) (wt"/o) (psi) (psi) (emfs) ,5 1,,5.75,1 1,8 56 1,15 1,65 1, ,15 1,1,56.5,1 1, ,15 1,1.8 x x 1-7. x 6.9 x lo-".5 x 1. x 1. x x lo-" 7.6 x O-".5 x x x 1-7. x.8 x x lo-". Ucofied compressio stregth greter th psig fter 7-dy cure t 1 F d vcuum sturtio tretmet (ATM C-59). The lier scopig tests, show i Tble 6, resulted i permebilities geerlly i the rge of lo-' cm/s with lime d cemet dditive mouts rgig from % to 6% by weight ech. The wter dditio levels for the scopig tests rged from 1% to % by weight of the totl dry weight.. The pemiebility dt, whe compred with levels of wter dditio, resulted i the U-shped curves show i Figures 1,, d, which were uique for ech of the fly sh smples tested. The miimum permebility developed with ech of these U-shped curves correspoded to specific wter dditio level for tht fly sh. The wter dditio levels used i the subsequet experimetl progrm were selected from rge ecompssig either side of the miimum permebility poit o the represettive fly sh scopig dt curve. This rge ws estblished by multiplyig the miimum permebilie obtied i the scopig tests by fctor of 8 d the selectig the wter dditio level correspodig to this higher permebility vlue from the U-shped curve. The fctor of 8 ws bsed o the reltive stdrd devitio of the permebility test dt d ws selected to esure tht the permebility cotributio would be sufficiet to be distiguished from possible rdom experimetl error. XPRMNTA PROGRAM The results of the scopig tests were used to desig series of experimets to study the lier formultios. The primv purpose of the experimetl progrm ws to determie the miimum mouts of lime d cemet, d the optimum wter levels to produce cceptble lier from ech of the six fly shes studied. The criteri used to evlute the lier mterils i this experimetl progrm were the sme s those used durig the scopig tests. The trgeted mximum permebility of lo-' cm/s ws selected for this study becuse the prticiptig sttes hve promulgted similr regultios for liers t wste disposl sites (see Tble 1). The experimetl progrm for ech fly sh used Box- Behke- three-vrible desig with eqully spced levels [6]. The mesured resposes for ech lier mixture icluded permebility, %-dy ucofied compressio stregth, d 7-dy ucofied compressio stregth fter vcuum sturtio tretmet. A totl of 15 lier mixtures were tested for ech of the six fly shes i this desig progrm. The cetroid of the desig spce ws tested i triplicte to develop the mgitude of experimetl August, 1988 error. The dt obtied from these formultio experimets for the NP fly sh re show i Tble 7 d is represettive of the type of dt for the other five fly shes studied. ch of the six fly sh smples produced experimetl results tht were the lyzed by multiple lier regressio to develop qudrtic model for the three respose vribles [q. The regressio equtios developed for the NP fly sh re s follows: Permebility: log P = (.69)Zl - (.) - (.)' + (.5)1 + (.) + (.6)Z (1) 7-dy ucofied compressio stregth fter vcuum sturtio: 7 = [.7 + (5.5)Zl + (.8))]' () %dy ucofied compressio stregth: R Cemet (wt Z) Figure. Permebility s o fuctio of lime od cemet dditio for the NP fly sh. virometol Progress (vel. 7, No. )

6 1 Cemet (wt %) Figure 5. evedy ucofied compressio stregth for the NP fly sh. i Cemet (wt %) Figure 6. Twety-eight-dy ucofied compressio stregth for the NP fly sh. 8 = [6. - (9.)Zl + (5.6)]' () where: Z1 = (% lime - )/, = (' cemet - )/, d = (5% wter - 8)/. urfce respose cotour plots were the geerted from the qudrtic models for ech of the vribles studied. These cotour plots were used to develop lier formultios for the six fly shes, usig miimum dditive levels to meet the previously selected lier permebility d stregth criteri. The NP experimetl dt were used to develop cotour plots for permebility (Figure ), Fly.sh NP NP CP Texs Utilities P Bsi TAB 8. ~N\UM PHMABT FHOM TH PHMNTA PROCHA1 Permebility (cm/s) 1.8 x lo-8 1. x lo-" 5. x 1-5. x x 8. x lo-' - - OM. b, ; N (wt %) Figure 7. ffect of sodium cotet o the wter soluble frctio of the fly-sh smples. virometl Progress (Vol. 7, No. ) - h + d P) 1 i i (wt %) Figure 8. ffect of silico dioxide o permebility of fly-sh liers. August,

7 -7, 1-8 < u v x e U 1, ~ 5 (wt %) MgO (wt %) Figure 9. ffect of mgesium oxide o permebility of fly sh liers. Figure 11. ffect of phosphtes o permebility of fly sh liers. 7-dy ucofied compressio stregth (Figure 5), d 8-dy ucofied compressio stregth (Figure 6). The dt from the other five fl~. shes i the study were treted i similr mer, the used to develop their respective regressio equtios d cotour plots. DCUON Becuse the relevt stte regultor). gecies hve geerlly focused o permebility for fly-sh lier cri- teri, it would be desirble to develop methodology to predict lier permebility. To compre the physicl, chemicl, d mierlogicl properties of fly sh to permebility, it ws decided to use the miiml level of permebility obtied i the experimetl progrm for ech fly sh. This criteri resulted i the miimum permebilities show i Tble 8 for the six fly shes. These miimum permebilities rged from high of 1. x cm/s for NP to low of. x lo- cm/s for Bsi. All of these results were cosiderbly below the lo- cm/s stte guide lies. 1-~ -? r - ; l ), 1-8 i Ti (wt %) Figure 1. ffect of titium dioxide o the permebility of fly osh liers. August, U ;, r , O^ (wt %) Figure 1. ffect of sulftes o permebility of fly sh liers. virometl Progress (Vol. 7, No. ).... :.

8 io-' r + - d U ) R oss o gitio (wt %) Figure 1. ffect of loss-o-igitio o the permebility of fly sh liers. C l pecific urfce Are (m/s> Figure 1. ffect of specific surfce re o the permebility of fly sh liers. The elemetl compositio should be useful i predictig the cemetitious rectivity of the sh d estimtig the mouts of lime d cemet dditives tht my be required to produce cceptble lier mteril. For exmple, reltively high clcium cotet idictes tht the fly sh should exhibit fvorble cemetitious properties [8]. The totl silicoe oxide d lumium oxide cotet of the wstes rged betwee 1% d 9% by weight, idictig the potetil for pozzolic rectivities with the dditio of lime. The wter-soluble frctio could ffect the performce of fly sh liers. A compriso of the fly sh N cotet versus wter-soluble frctio (Tble ) resulted i excellet correltio, show i Figure 7. This is becuse of the high solubilityof sodium compouds i the fly sh [9]. The oxides of silico, mgesium, d titium were preset i sigifict qutities, s show i Tble. ch of these solid prticles re isoluble i wter d their presece should lower the permebility of the fly sh liers. Figures 8, 9, d 1 illustrte this chrcteristic for ll three of these isoluble mierls i fly sh. O the other hd, the presece of phosphte d sulfte s sodium compouds i fly sh could be expected to icrese the permebility of the liers. Figures 11 d 1 illustrte the occurrece of this pheome. Ubured crbo cotet my ihibit cemetitious rectios, which re usully beeficil i reducig the permebility of the wste fter disposl. he loss-oigitio for the fly sh ws compred to the miimum permebilities i Figure 1, the permebilities were directly proportiol to the crbo cotet remiig i the sh. ice crbo is highly porous, its presece reduced the miimum permebility. pecific surfce re would be iflueced by the frctio of fier-sized prticles i the fly sh. The dt i this study idicted the greter the umber of these fie prticles, the more difficult it is to produce low-permebilib liers. This pheome is illustrted i Figure 1, which shows tht the specific surfce re is directly proportiol to the miimum permebility for the fly sh liers studied. CONOMC ANAY The mjor ecoomic fctors tht determie the cost of costructig fly sh liers iclude the qutity of fly sh used, the cost of the dditives, the method of mixig the fly sh d dditives, d the plcemet d compctio of the lifts. The optiml lier compositios show i Tble 9 were selected from the formultio tests for the preferred dditive levels to chieve the lier criteri. TAB 9. OPTMA FY AH NR FORMUATON Fly Ash NP Bsi Texs Utilities P NP CP ime (w-t%) Portld Cemet (wt"/.) ter (dry wt%) virometl Progress (Vol. 7, No. ) August,

9 Fly Ash ource TAB 1 UMMCRY OF COT ANAY 6 FOR FY Portld Hydrted Cemet ime ier Price Price Formul ($/to) ($/to) Astl NR Dry Desity of Fly Ash ier ( 1 b/f?) cost of ier Additives ($/ft) Bsi, North Dkot ligite NP, subbitumious col, scrubber powder Texs Utilities, Texs ligite P, Texs ligite NP, lliois #6 col, scrubber sludge mix CP, lliois #6 col, sh tke from holdig pod % lime % lime % lime % cemet % lime 5% cemet % lime 5% cemet 6 7.5% lime 6% cemet Bsed upo these optiml formultios, ecoomic lysis ws performed to determie the uit cost of the dditives required to mke cceptble fly sh liers. The summry of these dditive costs, show i Tble 1, used the curret prices for lime d cemet delivered to the costructio site. Additive prices, which were obtied from the respective utility compies, determied the dditive costs per cubic foot for the fly sh lier mterils. These dditive costs rged betwee $.1 d %.ift [] for the six fly shes studied. The dditive costs for the CP fly sh were the highest -whe compred to the others. The cost of mixig the lier formultios with pug mill hs bee estimted to be bout $./ft [] versus the cost of mixig the lier mteril i plce of O.l5/ft []. A pug mill should dequtely mix the fly sh, lime, cemet, d wter, the truck it to the disposl site. Aother techique could ivolve the plcemet of fly sh, lime, d cemet o the disposl site, followed by mixig ito the soil. A wter spry could the be pplied to these dry mterils t the site d icorported with soil tiller. Pug mill mixig would llow better cot~ol of the dditive levels icorported s well s esurig more uiform mixig. O the other hd, mixig i plce would probbly be less expesive th i pug mill. The costs for plcemet d compctio of the lier lifts hve bee estimted to rge betwee 5. d $O.O6/ft []. The use of compctio rollers with peumtic tires or vibrtory steel drum rollers similr to those used for rod costructio would be desirble. The icorportio of fly sh ito the lier elimites orml disposl expeses for tht mteril. Norml fly sh disposl expeses vry gretly d re usully site-specific. For the purposes of this study, the cost for fly sh disposl hs bee estimted to be 5lto. Assumig lier desity of 1 lb/ft [], the fly sh lier credit for the fly sh use would be bout %.5/ft[]. The combitio of these mjor ecoomic fctors should result i overll lier costructio cost tht could rge from $.5 to %./ft[]. CONCUON This fly sh lier study hs led to the followig coclusios regrdig the dptbility of fly sh for wste disposl sites: 1. The use of fly sh i the costructio of disposl liers represets ecoomic miimiztio strtegy for this lrge-volume wste.. igifict ecoomic fctors i costructig the fly sh liers re: the mout of fly sh used, the qutities of lime d portld cemet dditives eeded, 6 August, 1988 the method of mixig the lier formultio, d the method used to plce d compct the lifts for the lier.. The dditio of portld cemet d/or lime i the rge of -9.5% by weight ws required to produce lier mterils with permebilities sigifictly lower th lo- cm/s d ucofied compressio stregths geerlly exceedig psig.. ch of the fly shes could produce cceptble permebilities of less th lo- cm/s usig portld cemet d/or lime i the lier formultios. 5. The cost of costructig the lier from fly sh rged from $.5 to $./ft []. ACKNODGMNT This reserch ws performed t the Uiversity of North Dkot ergy Reserch Ceter with fuds provided by the U.. Deprtmet of ergy, Morgtow ergy Techology Ceter, uder Coopertive Agreemet No. D-FC1-86MC167. TRATUR CTD U.. virometl Protectio Agecy. Desig, Costructio d vlutio of Cly iers for ste Mgemet Fcilities, Report PA/5-\V-86-7, shigto, D.C. (Mrch 1986). chdev, D. R., d hl. Amdurer, Fly Ash As ste Pile ier Mteril: Fesibility tudy, fil report prepred by virosphere Co. for the mpire tte lectric erg) Reserch Corp., New York (Oct. 1985). Tucer,. B., Fly Ash ier Reserch, Progress Report to the iscosi lectric Power Co., hlilwukee (Feb. 1986). Hrder, P. J., hf. J. Mrcik. N. J. chlotter,... hotk, d. M. Duedll, The Fixtio of Fly Ash: Physicl d echte Properties, drft fil report to Cosolidted diso Co. ofru ew York (1981). 5. Code of Federl Regultios, Title, Prt 61., U. Govermet Pritig Office, shigto, DC, 65 (1985) DuPot DeNemours & Co., c., trtegy of Formultio xperimets, ilmigto, Del., 8-1 to 8-1 (Dec. 1978). 7. A stitute, c., A Users Guide: totistics, Versio 5, Cry. N. C., (1985). 8. Americ ociety for Testig d hlterils, todrd pecifictio for Fly Ash od Other Pozzolosfor Use with ime, ATM C 59-, Phildelphi (1986). 9. Moretti, C. J., d ;. R. Heke, oste Chorocterizutio, fil report to U.. Dept. of erg?, Uiversity of North Dkot ergy Reserch Ceter, Grd Forks. App. F (Jue 1986). 1. Hollis, B. C., d N. D. Fwcett, Rods d Rood Costructioti,517 (J. 16). virometl Progress (Vol. 7, No. ) ,-.!