3

Journal of Hazardous Materials 279 (2014) 110

Contents lists available at ScienceDirect

Journal of Hazardous Materials

j o ur nal ho me pa ge: www.elsev ier .com/ locate / jhazmat

Coagulationocculation mechanisms in wastewplants through zeta potential measurements

E.A. Lpez-Maldonadoa,, M.T. Oropeza-Guzmana,b, J.L. Jurado-Baizavala,A. Ochoa-Ternb

a Centro de Invesq. Blvd Nogalb Centro de GraB.C., Mexico

h i g h l

A well plaing strategcessful coacess.

pZpH ploto plan poto discovemechanism

Previouslytrolytes resulting coagulatio

a r t i c l

Article history:Received 19 MReceived in reAccepted 6 JunAvailable onlin

Keywords:CoagulationPolyelectrolytElectroplatingContaminant

CorresponE-mail add

(E.A. Lpez-Ma

http://dx.doi.o0304-3894/ estigacin y Desarrollo Tecnolgico en Electroqumica, Unidad Tijuana, Carretera libre Tijuana-Tecate km 26.5,es Parque Ind. El Florido CP 22444, Tijuana, B.C., Mexicoduados e Investigacin en Qumica del Instituto Tecnolgico de Tijuana, Blvd. Alberto Limn Padilla s/n, Mesa de Otay, C.P. 22500, Tijuana,

i g h t s

nned polyelectrolyte dos-y plays a crucial role in suc-gulationocculation pro-

ts are a powerful toollyelectrolytes dosage andr coagulationocculations.

prepared polyelec-dispersions improvedwater quality after a

nocculation process.

g r a p h i c a l a b s t r a c t

e i n f o

arch 2014vised form 20 May 2014e 2014e 21 June 2014

occulation mechanisme complexing capacity

wastewaterPE interaction

a b s t r a c t

Based on the polyelectrolyte-contaminant physical and chemical interactions at the molecular level, thisarticle analyzed and discussed the coagulationocculation and chemical precipitation processes in orderto improve their efciency. Bench experiments indicate that water pH, polyelectrolyte (PE) dosing strat-egy and cationic polyelectrolyte addition are key parameters for the stability of metalPE complexes.The coagulationocculation mechanism is proposed based on zeta potential () measurement as thecriteria to dene the electrostatic interaction between pollutants and coagulantocculant agents. Poly-electrolyte and wastewater dispersions are exposed to an electrophoretic effect to determine . Finally,zeta potential values are compared at pH 9, suggesting the optimum coagulant dose at 162 mg/L poly-dadmac and 67 mg/L of occulant, since a complete removal of TSS and turbidity is achieved. Based onthe concentration of heavy metals (0.931 mg/L Sn, 0.7 mg/L Fe and 0.63 mg/L Pb), treated water met theMexican maximum permissible limits. In addition, the treated water has 45 mg O2/L chemical oxygendemand (COD) and 45 mg C/L total organic carbon (TOC). The coagulationocculation mechanism is pro-posed taking into account both: zeta potential ()pH measurement and chemical afnity, as the criteriato dene the electrostatic and chemical interaction between pollutants and polyelectrolytes.

2014 Elsevier B.V. All rights reserved.

ding author. Tel.: +52 6646453278.resses: [email protected], eduardo a [email protected]).

1. Introduction

The electroplating wastewater, in the semiconductor industry,contains dissolved and suspended heavy metals (such as Sn, Cr,Ni, Pb, and Cu, among others), making necessary to nd a suitable

rg/10.1016/j.jhazmat.2014.06.0252014 Elsevier B.V. All rights reserved.ater treatment

2 E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110

water treatment to remove them before disposal. Hazardous situa-tion are challenged when dissolved and suspended heavy metalsare not completely removed before being discharged into thesewage.

In recento regulateand focusinimprovemeconventionwastewatercoagulation[10,11]; zeobrane ltrat[17,18]. In organic maincluded.

Chemicaheavy metbetween thing agent rethe subsequ

The gene

Mn+ + nOH

where Mn+

precipitatinhydroxide. ply the permin wastewaon metal co

The collmetallic hyaration, as wreduce the solubility pubility of hwell knownter, make tdue to the corganic ma

Zeta potsolubility cois reached. formation oresidual wadepends on

Other chlast centurycost and str[29]. Also, sphate, but twater excee

New tecparticles, olar, the comto eliminatthough, remwater by coto the mixecles and memethod to coagulationchelating abis an alternpollutants [

This paper explores the chelating ability of commercial coagu-lant and occulant polyelectrolytes (PEs) used in real wastewatertreatments. Selected conditions for coagulationocculation arepresented, as well as removal mechanisms suggested for suspended

orga PE dexp

ing docheplannllutanions

rstplatiof apNATblishationd soli

exation) of treatd oater

effecselegulanoccuerfac

coag of tdoloation

teria

agen

iconPTIFommre u

ethod

Wasty

wasctor ng stn is uyed in acccess

ed pa(TSS)rticlec caritrog

Prepa was

wask. St years, several technologies have been developed the hazard of wastewater containing heavy metalsg in the decrease of wastewater volume and thent in recovered water quality [1,2]. Within theal physicochemical methods to treat electroplating, it can be mentioned: chemical precipitation [36];occulation [3,7]; otation [8,9]; electrocoagulationlites, clays and resins ion exchange [1216] and mem-ion (ultraltration, nanoltration and reverse osmosis)all these cases, wastewater content such as metals,tter (OM) and total suspended solids content are

l precipitation has been applied to remove dissolvedals. This method is based on the chemical reactione metallic cations and calcium hydroxide as precipitat-sulting in the formation of insoluble compounds, andent solid separation by sedimentation or ltration [19].ral reaction for this process is:

M(OH)n (1)

and OH represents the dissolved metal ions and theg agent, respectively, and M(OH)n is the insoluble metalChemical precipitation is, in many cases, unable to com-

issible limits due to the fact that metallic hydroxidester do not precipitate at the same pH [19], and dependsncentration.oidal nature of wastewater and surface charge of thedroxide could make more difcult the solidliquid sep-

ell as the presence of organic complexing agents thatremoval effectiveness [6]. Even if the pH condition androduct are known, it is uncertain to calculate the sol-eavy metals in electroplating wastewater [2022]. It is

that large amount of impurities, such as organic mat-he metal solubility greater than that expected, mainlyhemical interactions between the metallic cations andtter [23].ential () is an interfacial parameter related to the lowndition of dissolved metals when the isoelectric pointThere are inclusive precipitating agents that assist thef metal hydroxides by the zeta potential reduction ofter [24]. In all cases, the formation of metal hydroxides

the change of surface charge as a function of pH [2528].emical precipitation treatments have been tested in the, particularly those using sulde (Na2S); however, highuggle in the disposal of toxic sludges discourage its useodium phosphate was used to precipitate a metal phos-he concentration of residual phosphorus in the treatedds the maximum allowable limit [19,30,31].

hnologies are oriented to mixed pollutants removal (i.e.rganic matter and metals simultaneously). In particu-bined coagulationocculation process is addressed

e suspended particles and insoluble substances. Evenoval of toxic heavy metals from electroplating waste-agulationocculation remains being a challenge dued of chemicals such as organic matter, suspended parti-tallic cations. Until now, there are no physicochemicalnd the optimal dose for each contaminant removal byocculation, unless Jar test. However, exploring theility of coagulant and occulant polyelectrolytes (PEs)ative to optimize the removal of various the types of32].

solids,gies of

To occurrphysicwere PEpocondit

Theelectrolimits SEMARto estacoagulpende

Thecoagul = f(pHwater lant anwastewlel thein the of coadual the intin thenaturemethocoagul

2. Ma

2.1. Re

Semmac (O[32]. Cods wegrade.

2.2. M

2.2.1. industr

Thecondusamplipositioemplomade iing proIncludsolids (), paorganitotal n

2.2.2. The

of rawric anic matter and metallic cations for four different strate-osing.lain the mechanisms and interfacial phenomenauring coagulationocculation process under variousmical conditions, four different sets of experimentsed and developed. The mechanism elucidation ofts interactions can be used to set up the optimal process

for wastewater treatment. of four sets of experiments was the characterization ofng raw wastewater to compare against the permissibleplicable Mexican environmental regulation (NOM-002--1996); the second was to construct the = f(pH) graphs

different PE dosing strategies; and third, identify theocculation regions for the removal of metals, sus-ds and organic matter.perimental strategy, to study the conditions ofocculation process was to examine the proles ofcommercial PEs used in semiconductor assembly wastement plants. Once the isoelectric point of the coagu-cculant was determined, as well as that of the sampled, PE dosing was studied at different pH values. In paral-t of using an interpolyelectrolyte complex occulationcted window was tested. Finally, the effect efciencyt dose in the occulation selected window by the

lation process was established. Based on the nature ofial phenomena that occur between pollutants and PEsulation-occulation process and the electrochemicalhe measurements of zeta potential, the experimentalgy used allowed us to determine the mechanisms ofocculation.

ls and methods

ts

ductor industry commercial polyelectrolytes Polydad-LOC C-1008) and Flocculant (Trident 27,506) were usedercial testing water quality reagents for Hach meth-sed. All other reagents used in this work were reagent

s

ewater sampling in the assembling semiconductor

tewater sampling protocol in the assembling semi-industry was followed as recommended by Mexicanandard (NMX-AA-003-1980). A detailed chemical com-ncertain due to the large amount of chemical mixtures

n the electroplating baths [33]. Sampling planning wasordance to regulation parameters, selected electroplat-

knowledge and water treatment control parameters.rameters are: metals (Sn, Pb and Fe), total suspended, turbidity, electrical conductivity (EC), zeta potential

size, color, pH, chemical oxygen demand (COD), totalbon (TOC), biochemical oxygen demand (BOD5) anden (TN).

ration of wastewater dispersionstewater dispersions were prepared by diluting 5 mLstewater with deionized water in a 50 mL volumet-ince the electroplating process was in continuous

E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110 3

operation according a timetable protocol, the sampled water con-tent was considered as process representative.

2.2.3. Nonstoichiometric polyelectrolyte complexes (NIPECs)preparation

Anionic 0.1 to 2 mg thoroughly

2.2.4. ColloA synthe

diluting thetion to 10 prepared soinitial . Thpotassium sstirred afteadditions wto turbidity

2.2.5. ChemThree w

into vials anby adding Nto settle dumeasure ,

2.2.6. MicroThe proc

dosage testgressive adwere madeand alloweddrawn to reand TOC me

The coaginto two parusing only o

2.2.7. AnalyImmedia

for biochemgen demanspectroscopby MexicanSCFI-2011 aand other psurements (Zetasizer Nperformed colorimeterMultiparamand Conduc

2.2.8. Scannenergy-disp

The samThe analysi6390 LV) mimages of rmicrometerin situ elem

2.2.9. SpeciMetal sp

software n

sophisticated algorithms) published by Ignasi Puigdomenech asa free tool for chemical equilibrium studies, considering pH andmetals concentration commonly used in electroplating baths. Iso-electric points of metallic compounds were also used to determine

le species [2628].

ults and discussions

aracterization of wastewater from electroplating processiconductor industry

shown in Table 1 selected electroplating wastewater pH isay from regulation range, zeta potential is high in order toe suspended particles. Organic content measured by BOD5C is not of concern. Metals, TSS, turbidity and COD contents

high so these are the critical parameters for the waste-treatment. All of them, as well as the zeta potential , arey related to the stability of the suspended solids. For rawater = 45 mV (pH 0.8), indicating the presence of positively

d particles suspended in water and probably related withic cations adsorbed on suspended particles. As particle sizese, longer sedimentation times are expected. Physical prop-as turbidity and TSS also indicate that raw wastewater is adispersion. Considering water properties, the separation ofmetases s

termater

he rnginthe ie en

rformus thd suspers

f(pHng tharge agul

5 me and

high1 th

rizati

eter

/L) g/L) /L) g/L) ity (FAS/cm) ) e size

g O2g C/L

(mg Og N/L)radab

thly aincludNIPECs synthetic solutions were prepared in ratios fromof cationic PE/mg anionic PE. Each solution was stirred

stirred before measurement.

id titrationtic solution of 10 mg polydadmac/L was prepared by

corresponding volume of 1.28 mM polydadmac solu-mL with distilled water in a volumetric ask. Thelution was poured into a 20 mL vial to measure theen, sequential amounts of 1.24 mM poly(vinyl sulfate)alt (PVSK) titrant solution were added. The solution wasr each addition and measurement recorded. Titrantere made to reach the isoelectric point corresponding

appearance in the solution [34].

ical precipitationaste water dispersions (see Section 2.2.2) were pouredd the pH of each was adjusted to 5, 7 and 9 respectivelyaOH 1 M. The vials were shaken for 2 min and allowedring 2 min. Finally the supernatant was separated toTSS, particle size and metals concentration.

-Jar testsedure was as described in Section 2.2.5 but this time PEs (micro-Jar tests) were performed in 20 mL vials. Pro-ditions of microliters of 0.1093 g/L occulant solution. After each addition, the vials were shaken for 2 min

to settle for 2 min. Finally the supernatant was with-alize turbidity, , TSS, metals concentration, BOD5, CODasurements.ulationocculation experiments are generally dividedts: single occulation, optimum condition for operationne PE and dual PE occulation.

tical techniquestely after the samples treatment, they were analyzedical oxygen demand in 5 days, BOD5, chemical oxy-

d, COD, and metals quantitation by atomic absorptiony, all of them following the test methods established

Standards (NMX-AA-028-SCFI-2001, NMX-AA-030/2-nd NMX-AA-051-SCFI-2001) similar to ISO standardsublished methods. Zeta potential and size particle mea-were performed following manufacturer instructionsano-ZS, model ZEN3500). All other measurements werein accordance to Hach methods using a Hach DR 890, a Hach Digital Reactor DRB200 (digestor) and HQ40deter (Luminescent dissolved oxygen LD0101-01 Probetivity Meter CDC401-01 Probe).

ing electron microscopic (SEM) images andersive X-ray spectroscopy (EDS) microanalysisples were analyzed by SEM and X-ray microanalysis.s was performed on a SEM coupled to EDS (JEOL, JSM-icroscope to observe the composition. SEM provides

ough material with a resolution down to fractions of a, whereas energy-dispersive X-ray spectroscopy offersental analysis.

ationecies were approached by predominance area diagramsamed MEDUSA (making equilibrium diagrams using

insolub

3. Res

3.1. Chin a sem

As far awstabilizand TOare toowater directlwastewchargemetalldecreaerties stable heavy proces

3.2. Dewastew

In tby chawhen could bthe pepH. Thsity anthe disin a =

Usithe chand coculantdensityrequireIn Fig.

Table 1Characte

Param

Sn (mgPb (mFe (mgTSS (mTurbidEC (m (mVParticlColor pH COD (mTOC (mBOD5TN (mBiodeg

a Monb Not ls, and suspended solids using coagulationocculationeems to require the addition of negatively PEs.

ination of the isoelectric point for the electroplating

st stage (coagulation) suspended solids are destabilizedg the water pH and proting that tends toward zerosoelectric point is approached. A simple pH variationough to stabilize or destabilize dispersions. Moreover,ance of polymeric PEs is inuenced by the wastewater

e pH value may control both polyelectrolyte charge den-pended particles surface charge. The isoelectric point ofion generated in the electroplating process is detected) plot.e colloidal titration method ( = 0, as detection point)density (CD) of the anionic and cationic PE (occulantant) is determined as polydadmac 22 meq/g and oc-q/g. These values conrm the polydadmac high charge

its use as a coagulant, while the occulant does not charge density to accomplish the solid agglomeration.

e = f(pH) plot shows the charge density variation for

on of electroplating wastewater.

Electroplatingwastewater

Maximumpermissible limita

4854 NIb

1044 1.0683 NI4510 40

U) 2990 NI74 NI45 NI

(nm) 346 NIMilky NI0.8 5.510

/L) 1432 NI) 125 NI2/L) 30 30

50.6 NIility (BOD5/COD) 0.02 NI

verage limit of NOM-002-SEMARNAT-1996.ed in the standard.

4 E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110

Fig. 1. Electro20.8 mg/L poly

suspended achieve thethat polydareaches it at5, occulanmore effectish its char[35].

To corrointerfacial particle diadiscussed bdosage inu

3.3. Chemic

Accordinthe electropcompoundsthe chemicrange are dchemical spIn electroplin dissolvedcomplexed and micro aof the wastto their corand Pb(OH)organic mawaste watecal precipitof Sn whichinformationin suspensipH increasefactor in thcles. Sn parsurface chametallic catdue to thison SnO par11.7 mV.

When thspecies predconferring metallic caof Fe and P

ontam

atedincr

.H 9

e advle p

oups of metal hydroxides and oxides particles are completely and confer stability to the suspended particles.

removal of suspended metals is determined by the particled surface charge of formed metal species. The content ofed metals is determined by the relative amount of metallic

complexed with organic ligands. removal efciency of metals from waste water treatmenty chemical precipitation at different pH values is shown in2. Also the values of the supernatant. It is observed thatremoval efciency increased as pH does. The resulting EDSM analysis of obtained solids from this neutralization is pre-

in Fig. 3. The EDS spectrum shows that the chemical contentds follows the order: O > Sn > P > Pb > Fe > Si > Al. This orderms to contents presented in Table 1, except for phosphorus,kinetic properties of the dispersion of wastewater from electroplating,dadmac and 21.9 mg/L occulant.

particles in wastewater, as well as the proper pH to isoelectric point. In the same plot it can be observeddmac does not reach an isoelectric point and occulant

very low pH. These results imply that at pH higher thant is expected to be very efcient, while polydadmac isive at pH

E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110 5

Fig. 3. SEM micrograph and EDS spectrum of the solid obtained from electroplating process wastewater.

increases, reaching the maximum removal efciency of 60% Sn, 50%Pb and 50% Fe at pH 9. The metals removal remains practically con-stant at pH 10 despite that, accordingly to value; the suspendedparticles are expected to be more stable in suspension.

At the isoelectric point, pH 7, corresponding to the neutraliza-tion of wastewater the separation of the solids is not the mostefcient due to factors such as particle size, metal complex stabilityand gravity sedimentation time.

3.4. Process coagulationocculation (single occulation A)

The aniothe coagula

groups (partially ionized) that confer negative charge density. ThusPE chains acquire a slightly extended conguration (see Fig. 4). Inthe low PE dose region, before the electroplating wastewater iso-electric point, the ionized surface groups of the macromolecules areable to interact with both positives surface groups of metal particlesand with dissolved metals.

When the electroplating waste water isoelectric point is reachedat pH 5 by subsequent PE dosing, all suspended metals are separatedand exceeding PE can complex the remaining dissolved metals. Inthe region of PE overdose stable aggregates (particlePEmetal)are formed. The elimination of Sn shows a very similar behav-ior of SST removal, suggesting that most of SST correspond tonic PE has its isoelectric point at pH 23; therefore in

tion step at pH 5 the PE has some ionized functional SnO.Fig. 4. PEcontaminant interaction and coagulationocculation mechanism at pH 5.

6 E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110

Fig. 5. TSS and occulation of residual metals at pH 5 using single occulant.

Fig. 5 shows the variation of residual metals and TSS contentin the single occulation A at pH 5. TSS removal requires higherdoses, up to 100%, compared with the single occulation at pH 7.At a occulant dose of 33.5 mg/L the maximum removal of TSS isreached, while at pH 7 15.6 mg/L of occulant are required.

This fact shows the pH effect on the charge density of the oc-culant (see Fig. 1) that decreases at lower pH corresponding tonegative values. The residual concentration of Pb and Fe decreasesslowly compared to the Sn diminution. The optimal occulant doseof 33.5 mg/L for TSS removal implies a residual metal content of66 mg/L of Sn, 105 mg/L of Pb and 120 mg/L of Fe.

At a higher dose than the optimal dose for TSS removal, 40 mg/L,the maximum metal removal is reached (Sn 65 mg/L, Pb 89 mg/Land Fe 74 mThis establi

removal. However, the residual metal concentration in the super-natant is higher (50% Sn, 60% Pb and 51% Fe) compared with singleocculation supernatant at pH 7.

At a higher dose than the optimal dose of 40 mg/L, the TSSremoval decreases and the dissolved metal content increases, thusthis is the particles re-dispersion region. It is noteworthy thatthe re-stabilization is less pronounced compared to the overdoseregion of single occulation at pH 7.

This is because at pH 7 the charge density is increased andany increase in concentration greater than the optimum doseresults in stabilization of suspended particles. Furthermore, theocculation window for removing TSS shifted at higher concen-trations (33.540 mg/L) compared with single occulation at pH 7.It is noteworthy that in the occulation window of 33.540 mg/Lof occulant residual Sn concentration remains virtually con-stant (6765 mg/L), while the concentration of Pb (15089 mg/L)and Fe (12074 mg/L) has a higher diminution. The minimumresidual metal concentration in the optimal occulant dose of40 mg/L is related to the afnity of the occulant to each metalliccation.

3.5. Process coagulationocculation (single occulation B)

As discussed above the isoelectric point of the waste water is pH7. However, the settling time of the solids by gravity is about 1 hwithout addition of PE and the supernatant exceeds the maximumpermissible metals content and suspended solids. This demon-strates the need to adding PE to favor the settling rate of suspendedsolids.

The residual concentration of Pb and Fe decreases slowlycompared to the Sn diminution. At the optimal occulant dose(15.6 mg/L) for the TSS removal (0 mg/L) indicates that the opti-mal dose complies the maximum permissible limit of TSS content,

eta Fig. g/L) without re-stabilization and particles dispersion.shes the optimum dose for both the TSS and metals

while mFe (seeFig. 6. PEcontaminant interaction and coagulationocculls content is 30 mg/L of Sn, 90 mg/L of Pb and 65 mg/L of7).

ation mechanism at pH 7.

E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110 7

Fig. 7. TSS and occulation of residual metals at pH 7 using single occulant.

At a higher occulant dose of 20.1 mg/L, higher metal removalis obtained (30.4 mg/L Sn, 56 mg/L Pb and 38 mg/L Fe) indi-cating that increasing metal removal requires an overdose ofocculant. At higher occulant doses than 20.1 mg/L, TSS andmetals content increases, this corresponds to the re-dispersionregion.

The occulation dose range for TSS removal of 15.620.1 mg/Lbut occulation dose for maximum metal removal is punctually20.1 mg/L of occulant. Within the occulation range residualSn concentration remains virtually constant (31 mg/L) whichmeans that lower occulant concentration is required to achievemaximum pared to th(15.620.1 m

Fe concentration from 65 to 38 mg/L and wastewater COD contentfrom 1558 to 122 mg O2/L. However, TOC remains broadly constantat 119 mg C/L (see Fig. 6).

3.6. Process coagulationocculation (single occulation C)

NIPECs were prepared at a ratio of 1.5 mg polydadmac/mgocculant with the following characteristics: size 132 nm and = 25 mV (Fig. 7). The formed complexes are used as a new occu-lant destabilizing the dispersed solids of the electroplating processwastewater (see Fig. 8).

At NIPECs dose of 35.6 mg/L maximum metals removal isprovided (34 mg Sn/L, 42 mg Pb/L and 30 mg Fe/L). At the opti-mal NIPECs dose interval (2435.6 mg/L) the removal of TSS andresidual metal content slightly decrease. At doses greater than41 mg NIPECs/L TSS and residual metal concentration increases(see Fig. 9).

3.7. Process coagulationocculation (dual occulation D)

The maximum removal by chemical precipitation of metals isachieved at pH 9 where the particles have a negative surface charge, = 18.6 mV. Therefore the cationic PE was added in the coagula-tion step to neutralize the surface charge of the dispersed particles(see Fig. 10).

Fig. 11 shows the residual metal content and TSS dual oc-culation at pH 9 using polydadmac and occulant. At 162 mg/Lpolydadmac dose, TSS and metals removal is strongly dependenton the occulant dosage. At occulant dose of 26.36 mg/L a maxi-mum TSS removal is provided (0 mg/L); however, the concentrationof metals (16 mg Sn/L, 45 mg Pb/L and 28 mg Fe/L) exceeds themaximum permissible limits.

The optimal occulation window of TSS removal is wider mg/L of occulant) compared to single NIPECs occulation5 anal, thSn removal and a greater Snocculant afnity com-e other two metals. Within the occulant windowg/L), Pb concentration is decreased from 90 to 56 mg/L,

(2667at pH removFig. 8. NIPECspollutant interaction and coagulationoccud 7. Within the occulation window of optimal TSSe tendency is of decreasing residual dissolved metals

lation mechanism at pH 7.

8 E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110

Fig. 9. TSS and residual metal concentration of occulation at pH 7 using singleNIPECs.

concentration as occulant dose increases to 67 mg/L, as well asin other single occulation cases, without particles re-stabilizationfor its dispersion.

However, occulation dose of 67 mg/L provides maximum metalremoval (0.931 mg Sn/L, 0.627 mg Pb/L and 0.7 mg Fe/L). This oc-culation condition comply the maximum permissible limits ofMexican regulation. Unlike single occulation, the residual Sn con-centration decreases from 16 to 0.9 mg/L within the occulationwindow. By adding a occulant excess (77 mg/L) TSS and the resid-ual metals concentration increases. Fig. 10 shows that at this dosethe value is 16.7 mV, indicating increased stability of the dis-persed part

Fig. 11. TSS and residual metals dual occulation at pH 9 using polydadmac andocculant.

According to the waste water characteristics (TSS and metals),in the simplest systems and dual occulation is observed that TSSremoval requires lower doses of occulant than those requiredto increase metal removal. Furthermore, according to Lopez et al.[32] this is due to the degree of afnity of the occulant withthe metals present in the waste water, lower doses of occulantare required for the Sn removal compared to Pb and Fe. The pro-posed organic removal mechanism is shown in Fig. 12. Once theoptimal dose of occulant for the removal of TSS and metals isreached, the cationic PE interacts with organic matter and simul-taneously occulant compete for metallic cations complexed. So ata occulant dose of 67 mg/L treated water has both COD and TOC

d.icles. reduceFig. 10. PEcontaminant interaction and coagulation-occulation mechanism at pH 9.

E.A. Lpez-Maldonado et al. / Journal of Hazardous Materials 279 (2014) 110 9

occu

4. Conclus

Based oimental daprocess meknowledge tions.

In the sinSST removatreated wat

Throughlant dose ofTSS and turconcentratiand 0.7 mgwater has ameet the m

The ocpended pardual occulpromotes c

Acknowled

AuthorsA., which thresearch groentic workTreatment PBaja CaliforCornejo-Brament for zgives his grogy (CONACstudies.

nces

. Kurnhniqu98.Babelng co

wit967hareritationFig. 12. PEcontaminant interaction and coagulation

ions

n literature thermodynamic information and exper-ta obtained in this work, coagulationocculationchanisms is proposed, contributing to a better processfacilitating the selection of optimal treatment condi-

gle occulation techniques at pH 5 and pH 7 completels is achieved but heavy metals content remains high in

Refere

[1] T.Atec83

[2] S. usied951

[3] L. Cciper. the occulation process at pH 9, the optimum coagu-

162 mg polydadmac/L and 67 mg occulant/L completebidity removal is achieved. The remaining heavy metalson in the treated water (0.931 mg Sn/L, 0.627 mg Pb/L

Fe/L) represents a removal greater than 99%. Treated COD of 45 mg O2/L and TOC of 45 mg C/L. These resultsaximum permissible limits of Mexican regulations.culant dose not only depends on the amount of sus-ticles, but also on the amount of dissolved metals. Theation shows that the addition of 162 mg polydadmac/Loagulation and organic matter removal.

gements

acknowledge the enterprise International Rectiers, S.rough Manuel Gonzlez, Eng., gave a condent vote to aup situated in Tijuana, to develop a systematic and sci-

that helped for a better operation of their Waste Waterlant. Authors also thank the Autonomous University ofnia, Mexico, UABC, which throughout Dr. Jos Manuelvo; provide all facilities to use the Zetasizer equip-eta potential measurements. E. A. Lpez-Maldonadoatitude to the National Council of Science and Technol-YT) in Mexico, for the fellowship received in his Ph. D.

[4] O. TnayRes. 28 (1

[5] M.E. Andapplicatio

[6] B. Chen, phorus reassessme

[7] Y.J. Li, X.copper-ePurif. Tec

[8] N.K. Lazanion ex373378

[9] F.M. Doylof Cu2+ an

[10] N. Kongs(Cr6+) fro109117

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[13] E. lvarezlites, Wat

[14] S.H. Abdeindustria(2003) 16

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Coagulationflocculation mechanisms in wastewater treatment plants through zeta potential measurements1 Introduction2 Materials and methods2.1 Reagents2.2 Methods2.2.1 Wastewater sampling in the assembling semiconductor industry2.2.2 Preparation of wastewater dispersions2.2.3 Nonstoichiometric polyelectrolyte complexes (NIPECs) preparation2.2.4 Colloid titration2.2.5 Chemical precipitation2.2.6 Micro-Jar tests2.2.7 Analytical techniques2.2.8 Scanning electron microscopic (SEM) images and energy-dispersive X-ray spectroscopy (EDS) microanalysis2.2.9 Speciation

3 Results and discussions3.1 Characterization of wastewater from electroplating process in a semiconductor industry3.2 Determination of the isoelectric point for the electroplating wastewater3.3 Chemical precipitation3.4 Process coagulationflocculation (single flocculation A)3.5 Process coagulationflocculation (single flocculation B)3.6 Process coagulationflocculation (single flocculation C)3.7 Process coagulationflocculation (dual flocculation D)

4 ConclusionsAcknowledgementsReferences