Recycling liquid effluents in a ceramic industry

w w w . e l s e v i e r . e s / b s e c v

Recycling

liquid

effluents

in

a

ceramic

industry

Bruno

Araújo

de

Almeida

a,∗

_,

_Margarida

_Almeida

a

_,

_Sónia

_Martins

b

_,

Vera

Alexandra

Mac¸arico

b

_,

_António

_Tomás

_da

_Fonseca

a

a_{DepartmentofMaterialsEngineeringandCeramic,UniversityofAveiro,Aveiro,Portugal}

b_{EUROCER,IndústriasdeSanitáriosS.A.,QuintaPeixoto,CarambachadeBaixo,Carregado,Portugal}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received28November2015

Accepted8April2016

Availableonline10May2016

Keywords: Ceramics Slipcasting Recycling Liquideffluents

a

b

s

t

r

a

c

t

Inthisworkispresentedastudyontherecyclingofliquideffluentsinaceramicinstallation

forsanitaryindustry.TheeffluentswerecharacterizedbyX-raydiffractionandinductively

coupledplasmatoevaluatetheircompositions.Itwasalsoassessedthedailyproduction

rate.Severalglaze–slurrymixtureswerepreparedandcharacterizedaccordingtoprocedures

andequipmentofthecompany’squalitylaboratory.Theresultsshowthatformostofthe

properties,thetestedmixturesexhibitedacceptableperformance.However,the

pyroplastic-ityparameterishighlyinfluencedbytheglazecontentandimposestheseparationofglaze

andslurryliquideffluents.Inaddition,itisnecessarytoinvestonastorageplant,including

tankswithconstantstirringandanewpipelinestructuretoimplementthereincorporation

methodontheslurryprocessing.

©2016SECV.PublishedbyElsevierEspa ˜na,S.L.U.Thisisanopenaccessarticleunderthe

CCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Reciclaje

de

efluentes

líquidos

en

una

industria

cerámica

Palabrasclave: Cerámica Moldeoenbarbotina Reciclaje Efluenteslíquidos

r

e

s

u

m

e

n

Estetrabajopresentaunestudiosobrelarecuperacióndeefluenteslíquidosenuna

insta-lacióndecerámicadesanitarios.LosefluentessecaracterizaronpordifracciónderayosX

yplasmadeacoplamientoinductivoparaevaluarsuscomposiciones.Tambiénseevaluó

latasadeproduccióndiaria.Seprepararonycaracterizaronvariasmezclasdeesmaltey

pastacerámicadeacuerdoalosprocedimientosyequiposdelaboratoriodecalidaddela

compa ˜nía.Losresultadosmuestranqueparalamayoríadelaspropiedades,lasmezclas

presentanuncomportamientoaceptable.Sinembargo,lapiroplasticidadestáfuertemente

influenciadaporlacantidaddeesmalteyrequierelaseparacióndelos2efluenteslíquidos.

Además,esnecesarioinvertirentanquesdealmacenamientoconagitaciónconstanteyuna

estructuradetuberíasparaimplementarelmétododereciclajeparalaproduccióndenueva

suspensióncerámica.

©2016SECV.PublicadoporElsevierEspa ˜na,S.L.U.Esteesunart´ıculoOpenAccessbajola

CCBY-NC-NDlicencia(http://creativecommons.org/licencias/by-nc-nd/4.0/).

∗ _{Correspondingauthor.}

E-mailaddress:[email protected](B.A.d.Almeida).

http://dx.doi.org/10.1016/j.bsecv.2016.04.004

0366-3175/©2016SECV.PublishedbyElsevier Espa ˜na,S.L.U.Thisisanopen accessarticleundertheCCBY-NC-NDlicense (http://

Introduction

The development of societies was accompanied by

politi-cal decisions with intent to improve the quality of living

ofcitizens and maintain the environmental balances. The

expansionof modern civilizationled toan intensegrowth

ofwastes,withtwomainorigins:urbanareasandindustrial

regions.Theconsequencesoftheriseontheproductionof

wastesare serious,notonlyfrom the economicand

finan-cial point of view, but especially related to public health.

Overtheyears,communitygovernmentslegislatedand

stim-ulatedpeopletoreducetheproductionofwastes.Inaddition,

several integrated systems are proposed to manage these

sub-products:recycling[1–13],composting[1],energetic

incin-eration[1,8,14]anddisposalinsanitarylandfills[1,8,14,15].In

EuropeandPortugal,severaldirectivesandlawshavebeen

establishedtoencourageandregulatethemanagementand

treatmentoftheindustrialresidues producedbyindustries

[16–19].Productmanufacturingofceramicindustriescauses

highvolumesofeffluents,withvariablecomposition,

depend-ingontheareasofthefactorywheretheyaregenerated.Raw

materials,ceramicproducts,decorationorfuelaresourcesof

wastesproducedondifferentstagesoftheprocessing.

Inde-pendentlyoftheoriginortypeofwaste,theeffluentsmustbe

treatedandprocessed,inordertominimizethe

environmen-talimpact.Thecasestudypresentonthisdocumentdescribes

Eurocer,aceramicfactoryfromtheSanitexGroup,producer

ofsanitarywarewhichgeneratesliquideffluentsduringthe

dailyworkontheplant.Ingeneral,theeffluentsproducedon

ceramicfactoriescontainthesameelementsastheraw

mate-rialsandmightbereincorporatedintheproductivecycle[20].

Evenso,thequantitativecompositionoftheeffluentsmightbe

differentwhencomparingtotheslurry.Thesedifferencesare

relatedwiththeseveralplacesoftheplantwheretheyare

gen-erated:areasofpreparationofglaze,slurryandgypsummolds,

glazingareas,castingroomsandtechnicallaboratories.

Cur-rentlyinEurocer,alltheproducedeffluentsaredirectedand

savedinastoragetank,withpermanentstirring,readyfor

pos-teriortreatment.Eachday,partoftheeffluentaccumulated

istransformedtocakeswith0.92×0.92×0.02m3_with30–35%

humidity,inafilterpressandsavedonaspecificareafor

poste-riortreatment.Thesecakesarethencollectedandtransported

byspecializedcompaniesintolandfillsfordisposal,involving

amaximumglobalcostof250D/ton.Thisfactisoneofthe

mainreasons fordevelopingaprojecttostudythe

possibil-itytotreattheseeffluentsinternallywithoutinterventionof

externalentities.Thetreatmentofindustrialresiduescanbe

performedusingtherecyclingtechnique[1,8,12,13].Withthis

inmind,themaingoalofthisworkistoassessthepossibility

toreincorporatethedailyproducedeffluentsonthe

prepara-tionofslurry.Fig.1showsaschematicexamplethatillustrates

theseveralstagesforthemanufacturingofsanitaryproducts

andtheareasoftheplantwhereliquideffluentsaregenerated

insignificantvolume.

The processing steps on Eurocer are similar to other

ceramicfactoriesproducingsanitaryware.Theprocess

ini-tiateswiththemillingandmixofthehardandplasticraw

materials,withwater.Afterthepreparationoftheslurryand

theglazeiscompleteandbeforegoingforproduction,bothare

controlledinthetechnicallaboratorytoensureallthequality

requirements.Theslurryisthenusedonthecastingprocess,

usinggypsummolds,followedbyadryingprocess.Afterthis,

theproductsareglazedinspecificshopsbeforegoingtothe

firingstep.Duringmostofthesemoments,liquideffluentsare

produced.Thetotalamountofgeneratedeffluentsissavedin

atank,withpermanentstirringanditsvolumecorresponds

tothesumofthepartialliquideffluentscreatedonthe

dif-ferentareasoftheplant:GSPE–glazeandslurrypreparation

effluents;MPE–moldspreparationeffluents;CE–casting

efflu-entsandGE–glazingeffluents.Toachievethementionedgoal,

theeffluentscanbeconsideredasrawmaterialsandmustbe

characterized.Inaddition,otherrequirementsaremandatory

toaddressafinalconclusionontheviabilityofthe

reincor-porationofthe effluentsinthe slurry:ensuretheavailable

amountofeffluentfortheslurrypreparation;characterizethe

effluentinadailybasistominimizethepropertiesvariation

andalso,ifnecessary,performpre-treatmentoftheeffluents.

ThemaingoalofthisworkistosavethecoststhatEurocer

currentlyhaswithliquideffluents.Ononehand,theuseof

the generatedeffluentsonthe preparationofslurryavoids

theneedofexternalentitiestocollect,transport,depositand

Plastic raw-materials Hard raw-materials Water Storage tank Preparation of slurry GSPE Characterization MPE CE Casting Molds preparation Drying Glazing Firing GE Water for general cleanings Final product

Fig.1–StepsofthemanufacturingprocessofEurocerandeffluentsgenerated:GSPE–glazeandslurrypreparationliquid effluents;MPE–moldspreparationliquideffluents;CE–castingliquideffluentsandGE–glazingliquideffluents.

treatthesesub-products.Ontheotherhand,byrecyclingthese

effluentstheamountoffreshwaterandrawmaterialsneeded

forpreparingtheslurrycanalsobereduced.

Materials

and

methods

Liquideffluents

Inthisworkitisthemaingoaltoassessthepossibilityof

rein-corporationofthedailyproducedeffluentsonthepreparation

ofslurry.Forthat,severaleffluentsampleswererecoveredand

identifiedaccordingtotheareaswheretheyweregenerated

andpreviouslydescribedinFig.1.AlsoinFig.1were

iden-tifiedtwospecificeffluents,generatedonthecastingrooms,

andidentifiedasCEforcastingliquideffluentsandMPEfor

moldpreparationliquideffluents.Theprocessforpreparing

theceramicpartsusedinEuroceristhetraditional

pressure-lesscasting,withgypsummolds.Thismeansthattheliquid

effluentsgeneratedontheseroomsarecomposedessentially

ofcalcium sulphatedehydrate (CaSO4·H2O), alsoknown as

gypsum.Thepresenceofthiselementontheslurrycanhave

adverseeffects,dependingontheparticle size.From

previ-ousstudies,gypsumnear-surfaceparticles withsizebelow

100␮mhavenodirecteffectonthesurfaceofglaze;however,if

thesizeisabove100␮m,defectscandevelopleadingtopores

orsuperficialdefectsontheceramicbodyproduct.Themost

problematiceffluentistheonegeneratedontheareaswhere

thegypsummoldsarepreparedtobeusedlaterduringcasting.

Thiseffluentishighlyrichingypsumthatcanseriously

dimin-ishtheceramicbody productsqualityifintroduced onthe

slurrypreparation.Thecastingeffluent,althoughitcontains

gypsumonthecomposition,itisresidualanditisexpected

tohavenoimpactontheslurryproperties.Evenso,toavoid

problemswithgypsumandinordertodisregarditsinfluence

onthe mainpropertiesofthe slurry,theseliquid effluents

producedoncastingareasand moldpreparationroomsare

directedtoadifferenttankandtreatedseparately.Thiscanbe

achievedoncethelinesthattransportsthedifferenteffluents

betweentheareaswheretheyaregeneratedandthestorage

tankareseparated.Thiswayitispossibletoexcludefrom

theanalysisthesegypsum-richeffluents.Foralltheremaining

effluents,GSPE,GEandSTE,wascollectedadaily,weeklyand

monthlysample,duringaperiodof28consecutivedaysalways

atthesameperiodofdayandaconstantvolumeof5L.To

char-acterizethesolidfractionofalleffluents,thesampleswere

driedfor2h at105◦C.Crystalline phaseswere revealed by

X-raydiffraction(XRD)intherangeof2 valuesbetween4

and80◦,at3◦/min,withaRIGAKUGeigerflexdiffractometer,

equippedwithaNifilterandgraphitemonochromator,using

CuK␣radiation(=1.54056 ˚A).Thepeakswereidentifiedby

comparisonwithpublishedJCPDSstandardfiles.Inaddition,

afewrestrictedsampleswereselectedtoquantifythe

con-centrationofelementsand/oroxidespresentontheeffluents

usingInductivelyCoupledPlasma(ICP)technique.Also,the

particlesizedistributionwasdeterminedbyFraunhoferlaser

scattering,inCoulterLS230equipment,withameasurement

rangebetween0.04and2000␮mandusingwaterasfluid.

Animportantparameterforthisstudyisdeterminingthe

totalamountofliquideffluentproducedoneachday.Because

Table1–Preparedmixtureswithdifferentglaze–slurry proportions.

Mixture I II III IV V VI

Glaze,vol.% 1.2 1.7 2.7 5.2 8.7 12.8

Slurry,vol.% 98.8 98.3 97.3 94.8 91.3 87.2

it was notpossible tostop the productionon the plantto performtheseveralmeasurements, itwasusedanindirect methodtoassesstheamountofeffluentproduced.This vol-umewascalculatedusingtwovariables:theestimatedvolume variation on the storage tank and the amount of effluent processedascakesinafilter-pressprocess.Thefirstwas deter-minedbymeasuringthelevelofthetankwithliquideffluent anditsdensity,everydayatthestartandendtimeof work-day. Thesecond,amount ofeffluentprocessedascakesin filter-press,isevaluatedregisteringthenumberoffilter-press processes performed duringeach dayand using the cakes propertieslikehumidityanddimension.

Glaze–slurrymixtures

After the characterization and discussion of the resultsof theeffluents,severalmixturescontainingdifferentglazeand slurry proportions(Table1)were preparedaccording tothe

chemicalcompositionobtainedforthetankeffluent.Thisway

itispossibletosimulatetheconditionsofreincorporationof

theeffluentontheslurryproduction.

As previous, the prepared mixtures were characterized

by XRD, ICP and Coulter. Also, several other

characteriza-tionmethodswereemployed,accordingtoEurocer’squality

laboratory. Density,viscosity andthixotropicbehaviorwere

evaluatedtoassesstherheologicalperformanceofthe

sus-pensions.Wasalsoestimatedtheamountofsulphatesusing

fromeachsampleavolumeof5mLinaLASA100equipment,

modelLCK153.Thepermeabilitycoefficient,another

impor-tantparameter,wasdeterminedusinganinternalequipment

andprocedureofEurocer.About140gofslurrywasintroduced

intoaspecificcontainerandthenairpressureisapplied

forc-ingwatertopassthroughafilterpaper.Theinitialandfinal

valuesofmassandtemperaturewereregistered,mi,mf,Tiand

Tfrespectively.ItwasalsoobtainedacoefficientCusingthe

temperaturedifferencemeasuredpreviouslyandaconversion

tablespecificofEurocer.Then,iscalculatedthepermeability

factor,P,usingEq.(1):

P= m2−m1

3 ×C (1)

Toevaluatetheflexuralstrength,severalspecimenswere

processedwith150mmlength,37mmwidthand11mm

thick-ness. The trial was performed using equipment Gabrielli,

model Crab-3,witha spanof130mm anda constant load

of8.5kg/s.Itwasalsodeterminedthewallthickness

forma-tionusingabout0.5Lofslurryafterrestingperiodsof40and

80min.Thisparameterisrelatedtotheprocessingmethod

oftheceramicpieces,wheretheslurryispouredingypsum

moldsandbycapillarysuctionoftheporousmoldthepiece

isdried.Thisallowsevaluatingthewallthicknessformation

10 20 30 40 2θ Relativ e intensity 50 60 70 GSPE GE STE RS Quartz Calcite Anorthite Kaolinite Gypsum Ilite Zirconium silicate

Fig.2–XRDresultsofthemainsamples:RS–reference sample(slurryproduction);STE–storagetankliquid effluent;GE–glazingliquideffluentandGSPE–glazeand slurrypreparationliquideffluent.

Anotherimportantpropertytobeassessedisthethermal

behavior.Thethermal expansionwas performed on

speci-menswith50mmlengthandpreviouslyfiredat1230◦C,using

aNeutzsch402dilatometeruntilamaximumtemperatureof

835◦Candatheatingrateof10K/min.Wasalsodetermined

thepyroplasticdeformationusingaconventionalmethod

dur-ingfiringprocess.

Results

and

discussion

Liquideffluents X-raydiffraction(XRD)

Thecrystallinephasesofthedifferenteffluentscollected

dur-ingtheexperimentalperiodaswellasthereferencesample

extractedfromtheproductionslurryarepresentedinFig.2.

Theanalysisofthediffractogramsallowsunderstandthat

themainphasesarecommon inall samples.Startingwith

the reference sample (RS), extracted from the slurry

cur-rently used inproduction, it is possible toidentify quartz

(SiO2)asmainpeak,thenkaolinite(Al2Si2O5(OH)4),anorthite

(CaAl2Si2O8), calcite (CaCO3) and also,insmaller amounts,

illite(K0.7Al2(Si,Al)4O10(OH)2).Whenevaluatingtheglazing

liq-uideffluent(GE),producedontheglazingareasofthefactory,

thepreviousenhancedphasesarealsopresent.Thisresultis

expectedbecausealthoughtheproportionsoftheusedraw

materialsaredifferent,theoverallcompositionoftheglazeis

similartotheslurry.However,onthiseffluent,itstandsouta

differentphasethatdoesnotexistonthereference:zirconium

silicate(ZrSiO4). Thismaterial,mainly usedhasopacifying

agentonceramicindustry,ispresentonlyontheglaze

com-positionanditwilltakeakeyroleonthiswork.Theglazeand

slurrypreparationliquideffluent(GSPE),whichbasically

con-sistsontheeffluentsgeneratedontheareaswhereslurryand

glazeareprepared,isconstitutedbyalltheenunciatedphases,

includingzirconiumsilicate.Finally, thestoragetankliquid

effluent(STE),asexpected,presentsalsoallthephasesalready

described,onceitaccommodatesalltheeffluentgeneratedon

theplant,includingtheprocessingsectionwhereresiduesof

SiO₂ Al₂O₃ CaO Zr Na₂O Phases Wt., % K₂O STE GE GSPE SR GR MgO Ba Others

Fig.3–ICPdataobtainedforthedifferenteffluents:STE– storagetankeffluent;GE–glazingeffluent;GSPE–glaze andslurrypreparationeffluent;SR–slurryreferenceand GR–glazereference.

gypsumcomingfromthemoldsarealsopresent.Althoughthe

hydratedcalciumsulphate(CaSO4·H2O)peakappearsonthe

STEdiffractograms,allfurthertestswereperformedassuming

thatthegypsumwillbeseparatedandtreatedproperlyfrom

theremainingeffluents.

Inductivelycoupledplasma(ICP)

Inordertoquantifytheelements/oxidespresentonthe

efflu-ents,afewselectedsampleswereselectedforICPanalysis.

TheresultsaredisplayedinFig.3.

FromFig.3,itispossibletoassessthatthemainphases

presentontheeffluentsareSiO2,Al2O3andCaO.Insmaller

quantitieswerealsodetectedandquantifiedZr,Na2O,K2O,

MgandBa.Residualelements/oxidessuchasTiO2,P2O5,MnO,

Cr2O3,Ba,Ni,Sr,YandNb,werealsodetectedandclassified

incategory“others”.Fromtheresultsitispossibletoobserve

thatthecompositionoftheeffluentsismoreclosetotheglaze

anddeviatesmorefromtheslurrycomposition.Indeed,the

contentontheeffluentsofphasessuchasCaOorAl2O3are

stronglyaffectedbythepresenceoftheglaze.Inaddition,the

quantificationofZr,presentonlyontheglaze,allowsestimate

the fractionofglaze andslurry onthe effluents.Using ICP

datafortheZrcontentontheeffluent(%ZrICP)andEq.(2)itis

possibletoestimatetheamountofglazeonthestoragetank

effluent(%GSTE):

%GSTE=

%ZrICP×M(Zr)

(%ZrSiO4)GC×M(ZrSiO4)×

%SolSTE (2)

where(%ZrSiO4)GCisthepercentageofzirconiumsilicateon

thecompositionoftheglaze,%SolSTEthefractionofsolidson

thestoragetankeffluentandM(Zr)andM(ZrSiO4)themolar

weightofzirconiumandzirconiumsilicate,respectively.The

variationofglazecontentonthestoragetankeffluentis

rep-resentedinFig.4.

According to the obtainedresults, the amount of glaze

elementsonthesolidfractionoftheeffluentrangesin

aver-age between 4 and 12wt.%. This represents the amount

0.0% Sample D1 D2 D3 D4 D5 D6 D7 W1 _D10 W2 _D16 W3 _D23 W4 M1 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% % G STE

Fig.4–Glazecontentonstoragetankeffluentsindifferent samples.

processing, if all the effluent is used as source of water.

Thisinformationishighlyrelevantinordertoevaluatethe

impact of these quantities on the different characteristics

of the slurry. The more fusible behavior of the glaze can

becomeproblematic,especiallyonthethermalexpansionand

pyroplasticity.

Particlesizedistribution

Fig.5showstheparticle sizedistributionofaverageweekly

samplesforthedifferenteffluentscollected,aswellforthe

referencesample,obtainedfromtheproductionslurry.Itis

alsopresentedonTable2,thecumulativevaluesforcertain

particlesizesandtheD50value.

Theparticlesizedistributionoftheeffluents,Fig.5shows

thatalthoughit ispossibletoobservesomedeviationfrom

thereference,itisacceptable.Takinginaccountthestandard

qualityvaluesrequiredbythefactory,Table2,itshowsthat

for48and96␮mthecumulativevalueofparticlesizeisvery

closetotheonesmandatorybyEurocer.However,forvalues

lowerthan16and2␮mparticlesize,thedeviationfromthe

120 100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 12 15 Day Vtotal effl. (m 3) 17 18 19 20 21 22 23 Experimental data Average 24 25 26 27

Fig.6–Variationoftheamountofstoragetankeffluent, producedduringtheexperimentalperiodofthework.

standardisstronger.Thisfactcanbejustifiedbythecurrent

layout oftheplant. Nowadays,theeffluents areconducted

fromtheareasoftheplantwheretheyaregeneratedtothe

storagetankthroughapipelineandpumpingsystem.During

thispath,somefractionoftheparticlescansedimentonthe

tubes,creatingaslightdistortionontherealparticlesizeof

thegeneratedeffluents.

Effluentproduction

Averyimportantparameterofthisstudyisrelatedwiththe

amountofgeneratedeffluentduringaregularworkingday.

Thisvaluewillinfluencethereincorporationprocess,

espe-ciallyintermsofquantityandquality.Inordertoassessthe

amountofproducedeffluents,itwasmeasured,duringthe

experimentalperiod,thedensityandlevelofeffluentonthe

storagetankandnumberoffilter-pressduringeachday.This

allowscalculatethevolumeofliquideffluentproduced,

pre-sentedinFig.6.

TheanalysisofFig.6showsthattheproductionofeffluent

isunstable.Themaximumvaluewasobtainedonday19with

anamountof96.7m3_{,whileintheoppositeaminimumvalue}

of4.3m3_{wasfoundforthe6thday.Regularly,thedaily}

pro-ductionplanofslurryrequiresabout55m3_{offreshwater,and}

asseeninFig.5,duringtheexperimentperiod11dayswere

belowthisvalue.Thismeansthatthesourceofwaterforthe

0 0.01 0.1 1 10 Particle size (μm) GSPE GE STE Cum ulativ e v alues , % 100 1000 20 40 60 80 100

Week 1 Week 2 Week 3 Week 4 Standard

a

_b

_c

0 0.01 0.1 1 10 Particle size (μm) 100 1000 20 40 60 80 100 0 0.01 0.1 1 10 Particle size (μm) 100 1000 20 40 60 80 100

Fig.5–Particlesizedistributionforeachtypeofeffluentandforthereferencesample(slurryproduction):(a)GSPE–glaze andslurrypreparationeffluent;(b)GE–glazingeffluentand(c)STE–storagetankeffluent.

Table2–Cumulativevaluesfor2,16,48and96␮mparticlesizeandalsoD50.

Particlesize(␮m) Cumulativevalues(%)

2 16 48 96 D50

GSPE 20.3 61.6 93 100 11.7

GE 32.4 78.7 98 100 5.3

STE 25.3 70.0 95 100 7.3

Reference 17.4±2 77.0±2 100±2 100±2 7.8±1

processingofslurrymightcomefromthegeneratedeffluent but,toavoidinstabilityoftheprocessduringthepreparation ofslurry,it ismandatorytoensuretheavailableamountof effluenteverydayfortheslurryproduction.Thiscanbe pos-sibleusinganaccumulationprocedureofthegeneratedliquid effluentsinstoragetanks.Thistopicwillbefurtherdiscussed onthisdocument.

Anotherimportantparameterthatneedstobediscussedis theamountofliquidandsolidsontheeffluentstoragetank. Theresultsforsolid concentrationof theSTE samplesare presentedinFig.7.

Theevaluationofthesolid fractiononthe storagetank

effluentallowsunderstandthatmostoftheeffluentsamples

containanaverageamountofsolidsontherange1.5–2.0wt.%,

followedbythesolidconcentrationhigherthan2.5wt.%.For

solidscontentbetween1and1.5wt.%theamountisminimal,

lessthan10wt.%.

Thepreviousdiscussedresultsshowthatitmightbe

pos-siblereincorporateontheprocessingofslurrythegenerated

effluents. The chemical results, XRD and ICP, showed the

expectedphases;particlesizedistributiondoesnotdeviates

excessivelyfromthereferencerequiredbythecompanyand

theamountofgeneratedeffluentcanbeenoughtobeused

assourceofwaterontheslurrypreparation.Thenextstepis

understandtheinfluenceoftheglazecontentontheslurry

properties and for that, several glaze/slurry mixtures with

compositionvaryingfrom1to13weightpercentofglazewere

prepared(Table1). 0% 1-1.5% 1.5-2% 2-2.5% Solid concentration (wt %) >2.5% 10% 20% 30% 40% 50% 60% V o lume , %

Fig.7–Variationofthesolidconcentrationofthestorage tankeffluent.

Glaze–slurrymixtures X-raydiffraction(XRD)

Thecrystallinephasesoftheslurryreferenceandofmixture

slurry–glazeIIIareexhibitedinFig.8.

TheXRD data ofthe severalslurry–glaze samplesshow

thatalltheexpectedcrystallinephasesarepresent,including

zirconiumsilicate. 10 20 30 40 2θ Relativ e intensity 50 SR Quartz Calcite Anorthite Kaolinite Ilite Zirconium silicate III 60 70

Fig.8–XRDresultsof:SR–slurryreferenceand slurry–glazemixtureIII.

SiO₂ Al₂O₃ Na₂O Phases Wt., % K₂O I II III IV V VI SR GR MgO Ba Others CaO Zr

Fig.9–ICPdataobtainedforglaze–slurrymixturesI–VI, withcompositiondescribedinTable1alongwithreference samples,SR–slurryreferenceandGR–glazereference.

Table3–Cumulativevaluesfor2,16,48and96␮mparticlesizeandalsoD50fortheseveraltestedmixtures.

Particlesize(␮m) Cumulativevalues(%)

2 16 48 96 D50 I 19.0 75.9 98 100 7.7 II 18.2 74.7 97 100 8.1 III 18.5 74.0 97 100 8.1 IV 12.9 62.8 98 100 10.5 V 12.6 62.7 97 100 10.6 VI 11.7 61.9 97 100 10.9 Standard 17.4±2 77.0±2 100±2 100±2 7.8±1

Inductivelycoupledplasma(ICP)

TheICPresultsforthepreparedmixturesare presentedin

Fig.9andallowunderstandingthequantitativecomposition

ofthesamples.

These results are important toestimate the amount of

glazeoneachsampleinordertoassessthelimitofglaze

vol-umethatcanbeincorporatedontheslurryprocessingwithout

reducingthequalityparametersdefinedbythecompany.

Particlesizedistribution

Theresultsforparticlesizeoftheglaze–slurrymixturesare

presentedinTable3.

Theresultsshowthattheparticlesizedistributionofthe

samplesisaffectedbythepresenceofglaze.OnlymixtureI,

withglazecontentof1.2%volume,iscompletelywithinthe

desiredresultsbyEurocer.Althoughtheremainingsamples

areoutofspecification,whenthecontentofglazedecreases,

theresultsareclosertothestandardvalues.

Sulphateanalysis

Theevaluationofthequantityofsulphatesontheeffluentsis

aqualityparameterthatneedstobeassessedduetothe

intrin-sicproblemsoftheSO42−ionsonthedeflocculationofslurry.

Theresultsforthedifferenttestedmixturesaredisplayedin

Fig.10.

Theresultsshowthattheamountofsulphatesonthe

mix-turesisalwaysbelowthemaximumvaluedefinedbyEurocer.

Thiswayitispossibletoconcludethatforglazecontentbelow

13wt.%,theamountofsulphatesontheslurryiswithinthe

specified.

1 3 5 7

Glaze fraction (% vol.)

S (ppm) _Smax

9 11 13

Fig.10–Variationofthesulphatescontentondifferent glaze/slurrycomposition(Smax–maximumcontentof sulphatesaccepted).

Permeabilityfactor

Another importantparameter to assess the quality of the

slurryisthepermeabilitycoefficient.Itallowsevaluatingthe

capabilityofthewatertoflowthroughthecakeformedon

filtratingmediumwhentheslipissubjectedtotheactionof

compressedair.TheresultsarepresentedinFig.11.

Theresultsobtainedfortheseveralmixturesshowsthat

the permeability factor is alwayswithin the limitsdefined

byEurocer,fortheexperiencedmixtures.Althoughis

possi-ble toidentifysomeinfluence,it isnotnegativeenoughto

compromisetheslurry’spermeability.

Flexuralstrength

ThemechanicalpropertytestedinEurocerondriedspecimens

isflexuralstrengthtoassesstheabilityoftheproducttoresist

a3-pointflexuralload.TheresultsareexhibitedinFig.12.

ItispossibletoobserveinFig.10that,whentheglaze

con-tentonthemixtureisincreasing,theflexuralstrengthofthe

specimensdiminishesuntiltheminimumvalue.Evenso,all

thevaluesarewithintheacceptablerangedefinedbyEurocer.

Wallthicknessformation

Another factortoconsider isthe wallthickness formation,

whichallowscharacterizingtheslurryintermsoffacilityto

increase itswallthickness duringslipcastingprocess.The

resultsforbothrestingtimesof40and80minareexhibitedin

Fig.13(a)and(b),respectively.

Theobtainedresultsshowadirectinfluenceoftheglaze

contentonthe thicknessofthewallformedduringcasting

P Pmax=Pmin+δ1

Pmin

1 3 5 7

Glaze fraction (% vol.)

9 11 13

Fig.11–Variationofthepermeabilitycoefficientforthe differenttestedsamples(Pmin–minimumpermeability valueaccepted;Pmax–maximumpermeabilityvalue accepted;ı1–valuedefinedbyEurocertodefinePmax).

1 3

σmax=σmin+δ2

σmin

σ(Mpa)

5 7

Glaze fraction (% vol.)

9 11 13

Fig.12–Flexuralstrengthofdriedspecimenswith differentglazecontent(min–minimumflexuralstrength accepted;max–maximumflexuralstrengthaccepted;ı2– valuedefinedbyEurocertodefinemax).

1 3 5 7

Glaze fraction (% vol.) Lmin,40 Lmin,80 RT=40 min. WT (mm)

a

b

WT (mm) RT=80 min. L_max,40=L_min,40+δ3 Lmax,80=Lmin,80+δ4 9 11 13 1 3 5 7

Glaze fraction (% vol.)

9 11 13

Fig.13–Wallthickness(WT)formationofthesamples,at restingtimesof40and80min(Lmax,40andLmax,80– maximumwallthicknessallowedat40and80min, respectively;Lmin,40andLmin,80–minimumwallthickness allowedat40and80min,respectively;ı3andı4–value definedbyEurocertodefineLmax,at40and80min, respectively).

1 3 5 7

Glaze fraction (% vol.) αmin,500 αmin,700 T=500 ºC

a

b

T (ºC) T=700 ºC T (ºC) αmax,500=αmin,500+δ5 αmax,700=αmin,700+δ6 9 11 13 1 3 5 7

Glaze fraction (% vol.)

9 11 13

Fig.14–Thermalexpansioncoefficientoffiredsamples,at 500and700◦C(˛max,500and˛max,700–maximumthermal expansionallowedat500and700◦C,respectively;˛min,500 and˛min,700–minimumthermalexpansionallowedat500 and700◦C,respectively;ı5andı6–valuedefinedby Eurocertodefine˛max,at500and700◦C,respectively).

process.After40minofcasting,thesamplescontaininghigher

glazecontent,8.7and12.8wt.%,exhibitedavalueoutof

spec-ificationrequiredbyEurocerwhileafter80minrest,alsothe

samplecontaining5.2wt.%ofglazewasoutofrequirement.

Thismeansthat,forthisproperty,toensurethequality

stan-dardsdefinedbythe company,theamountofglazecannot

exceed2.7wt.%ontheslurry.

Thermalexpansion

Thethermalpropertiesoftheproductaretheonesthat

poten-tiallycanbemoreaffectedbythereincorporationprocessdue

tothepresenceofglaze.Theregularcharacteristicsofglaze,

forexamplemorefusible,candecreasethethermalqualities

oftheslip.Oneofthetwoparametersstudiedwasthethermal

expansioncoefficientat500and700◦C,whereFig.14presents

theresultsforthetestedmixtures.

Thenegativeimpactoftheglazeonthispropertyisevident

onbothtemperatures,asexpected.Thethermalexpansionat

500◦Cstartstobecomeexcessiveforthesampleswithglaze

contenthigherthan1.7wt.%,whileat700◦Conlyforthe

sam-pleswithcontenthigherthan2.7wt.%.Thecompositionofthe

glaze,richerinfusibleelements,directlyinfluencesthe

1.2 1.7 2.7

Glaze fraction (% wt.)

PImax

PI (mm)

5.2 8.7 12.8

Fig.15–Pyroplasticdeformationofthesamples(PImax– maximumpyroplasticindexaccepted).

theallowableamounttoreincorporateontheslurrycannot

overcome1.5wt.%.

Pyroplasticdeformation

Theotherthermalpropertystudiedonthisworkisthe

pyro-plasticity,consistingonthedeformationofaspecimenduring

thefiringprocess.Theformationofliquidphaseandits

viscos-itycanbeinfluencedbythecomposition,especiallywhenthe

amountoffusibleelementsincreases,andthereforedefects

candeveloponthe finalproduct. Theresultsforthe

pyro-plasticdeformationofspecimensofglaze/slurrymixturesare

presentedinFig.15.

Allthespecimenstestedexhibitedapyroplastic

deforma-tionhigherthantherequiredbyEurocer.Independentofthe

glazecontent,theresultsshowthatdepyroplastic

deforma-tion is deeplyaffected bythe presenceofglaze There are

severalapproachestosolvethisproblem:physicalor

chem-icaltreatments to completely remove the solid fraction of

the effluent; reformulatethe slurry’s composition to

com-pensatethe glazecontent presentonthe liquideffluentor

separatethetwomaineffluentsandstorethemindifferent

tanks.

Proposedlayout

Theanalysisoftheresultsobtainedforseveraltestsperformed

onglaze–slurrymixtureswithdifferentcompositionreveals

thatalthoughinsomepropertiestheglazecontentdoesnot

reducethequalityoftheslurry(sulphatesanalysis,

perme-abilitycoefficient,flexuralstrength),forothersalthoughthe

impactisminimum,the amountofglazeneedstobe

con-trolled (wall thickness formation and thermal expansion).

However,thepyroplastic deformationofthe specimensfor

thetestedmixturesrevealedthattheamountofglazeneeds

tobecompletelyeliminated.Therearetwooptionsfor

rein-corporate the liquid effluents on the slurry preparation. A

hypothesisisthereformulationoftheslurrycompositionin

ordertoaccommodatetheincorporationoftheglazesolids

oftheeffluent.However,thevariabilityoftheglazecontent

andsolidconcentrationoftheeffluentconstitutesaserious

drawback toimplementthis method.Inaddition,this

vari-abilitywouldrequireadailycharacterizationoftheeffluent

withindicationofsolidcontentandglazeamountthatwould

involveaninvestmentinequipmenttoproducesuchresults

suchasquantitativeanalysistoestimatetheglazecontent.

Anotherdisadvantageofthismethodistheneedto

reformu-latethecompositionoftheslurry,everyday,dependingonthe

amountofglazeoftheliquideffluent.Insuchindustrial

envi-ronment,itisimpossibletochangeeverydayorevenevery

weekthecompositionoftheslurry.Forallthesereasons,this

methodcannotbeappliedforsolvingtheproblemofthe

pres-ence ofglaze.Asecond hypothesis,and probablythemost

viable,isthecompleteseparationofthetwomaineffluents

generated,glazeandslurry.Indeed,itispossibletoseparate

thetwoeffluentsandstoretheminindividualtanks,oncethey

aregeneratedindistinguishpartsoftheplant.Thismethod

wouldrequireaninitialinvestmentonstoragetanks,asystem

ofconstantstirringandapipelinestructuretotransportthe

effluents.Inthisway,theslurryeffluentscanberecycledand

usedonthepreparationofslurryandtheglazeeffluentscan

bestoredinadifferenttank,filterpressed,andbeshippedby

apropercompanytobetreatedanddepositedinappropriate

landfills.

Conclusions

Theanalysisoftheresultsallowsconcludingthatitis

possi-bletoachievethemaingoalofthework,thereincorporation

ofpartofthedailyproducedliquideffluentsonthe

prepara-tionofslurry.Mostofthequalityparametersaresatisfiedif

theglaze contentisensured tobelessthan1.2wt.%ofthe

slurry.Itisobservedfromtheresultsthatthemajor

inconve-nienceofthepresenceofglazeisthepyroplasticdeformation,

whichisabovethelimitdefinedbyEurocer,forallthetested

mixtures.Toovercometheinherentproblemoftheeffecton

theslurrypropertiesoftheincorporationofglaze,itis

neces-sarytoseparatetheliquideffluentswithoriginintheslurry

preparationfromtheliquideffluentsgeneratedonthe

glaz-ingareasandontheglazepreparationareas.Thiswayitis

possibletoreincorporatetheslurryliquideffluentsonthe

pro-cessofpreparationofslurry.Theglazeeffluents,unfortunately

needstocontinuetobetreatedbefore,meaningbyanexternal

entity.Oncetheproductionofliquideffluentsisunstable,itis

mandatorytheimplementationofastoringsystem,

indepen-dentforslurryandforglaze,toensuretheenoughamounts

ofeffluentsforthedailyproductionalongwithafully

char-acterization every day the stored effluents to ensure that

thequalityparametersareaccordingtotheonesdefinedby

Eurocer.

Acknowledgements

TheauthorswouldliketogratefullythankEurocer,Indústria

deSanitáriosS.A.forfinancialandtechnicalsupportduringall

theprojectandalsothestaffoftheDepartmentofMaterials

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