Inhibition of Ca 3 (PO 4 ) 2 , CaCO 3 , and CaSO 4 Precipitation for Industrial Recycling Water

Published: August 20, 2011

r 2011 American Chemical Society 10393 dx.doi.org/10.1021/ie200051r | Ind. Eng. Chem. Res. 2011, 50, 10393–10399

ARTICLE

pubs.acs.org/IECR

Inhibition of Ca3(PO4)2, CaCO3, and CaSO4 Precipitation for IndustrialRecycling WaterFu Change,†,‡ Zhou Yuming,*,† Liu Guangqing,† Huang Jingyi,† Sun Wei,§ and Wu Wendao§

†School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, P. R. China‡Nanjing College of Chemical Technology, Nanjing, 210048, P. R. China§Jiangsu Jianghai Chemical Co., Ltd., Changzhou 213116, Jiangsu, P. R. China

ABSTRACT: In an attempt to control Ca3(PO4)2, CaCO3, and CaSO4 deposits in industrial recycling water systems, an acrylic acid(AA)�allylpolyethoxy carboxylate (APEC) copolymer was examined as a nonphosphorus inhibitor. The synthesized AA�APECcopolymer was characterized by FT-IR. The performance of AA�APEC on inhibition of Ca3(PO4)2, CaCO3, and CaSO4

precipitation was compared with that of current commercial inhibitors. It was shown that AA�APEC exhibited excellent ability tocontrol inorganicminerals, with approximately 82.88%CaSO4 inhibition and 99.89%Ca3(PO4)2 inhibition at levels of 3 and 6mg/LAA�APEC, respectively. AA�APEC also displayed ability to prevent the formation of CaCO3 scales. Transmission electronmicroscopy (TEM) images indicated that the outstanding performance of AA�APEC on Ca3(PO4)2 inhibition resulted from adecrease in size of Ca3(PO4)2 solid particles thereby dispersing these particles throughout a fluid, while CaCO3 inhibition wasattributed to the formation of ribbon-shaped structures and CaSO4 inhibition resulted from loose CaSO4 crystallites speculated onscanning electron microscopy (SEM) images. The proposed inhibition mechanism suggests the formation of complexes betweenthe side-chain carboxyl groups of AA�APEC and calcium ions on the surface of inorganic minerals, and the excellent solubility ofcomplexes resulted from a number of hydrophilic polyethylene glycol (PEG) segments.

1. INTRODUCTION

For environmental and economic reasons, a greater number ofcycles for industrial water should be used. However, it cannot berealized without development of scale control methods.1�3 Thepotential of mineral precipitation continues to be by far the mostcostly design and an operating problem in recycling-watersystems.4�6 Alkaline scales such as calcium carbonate can beeasily controlled by acidifying and maintaining pH below 7.5.Due to its low cost, sulfuric acid is usually used for pH controlthereby increasing the potential of calcium-sulfate scaleformation.1,2,7 In addition, using sulfuric acid to control pHcan also cause system corrosion, which in turn can be anadditional source of fouling.8,9 Thus, an ideal scale inhibitorwould be able to prevent both calcium-carbonate precipitation athigh pH and calcium-sulfate precipitation at low pH (neutral orslightly acidic).

In industrial recycling water systems, another troublesomeissue is the precipitation of corrosion products.5,8 Phosphonates,such as polyamino polyether methylenephosphonate (PAPEMP),1-hydroxyethylidine-1,1-diphosphonic acid (HEDP), and2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) are usedto prevent mineral formation and/or metallic corrosion bycreating protective films on metal surfaces of industrial equip-ment.9�14 However, phosphonates can create serious problemssuch as insolubility of phosphonate complexes, and they are alsosusceptible to breakdown to form orthophosphates under theinfluence of hydrolysis and/or chlorination thereby increasingthe potential of formation of calcium-phosphate deposits in thepresence of excessive amounts of calcium.15�17 In addition,phosphonates, when reverted to orthophosphates, are potentialnutrients for algae.18 Thus, an ideal scale inhibitor would be

nonphosphorus and effective to control the formation ofcalcium-phosphate, calcium-carbonate, and also calcium-sulfate deposits.

Recently, Kessler19 reported a novel inhibitor for calcium-phosphate deposits. It is a copolymer of maleic anhydride (MA)�ammonium allylpolyethoxy sulfate (APES). Although it possessesexcellent calcium phosphate inhibition at a low dosage, it cannotcontrol the formation of calcium-sulfate scales until the dosageexceeds 32 mg/L, and it also cannot prevent precipitation ofcalcium carbonate at any levels of dosage. The aim of the presentwork is to provide a nonphosphorus copolymer of acrylic acid(AA)�allylpolyethoxy carboxylate (APEC) as an ideal inorganicmineral inhibitor. Such an inhibitor can control both calcium-carbonate scales at pH 9.0 and calcium-sulfate scales at pH 7.0. Inthe presence of excessive calcium ions and orthophosphates, italso can prevent the precipitation of calcium phosphate.

2. EXPERIMENTAL SECTION

2.1. Materials and Characterization. APEC, APES, andMA�APES were synthesized in our laboratory according toearlier publications.19,20 Acrylic acid (AA), MA, and ammoniumpersulfate employed were analytically pure grade and suppliedby Zhongdong Chemical Reagent Co., Ltd. (Nanjing, Jiangsu,P. R. China). Commercial inhibitors of poly(acrylic acid) (PAA,1800 MW), hydrolyzed polymaleic acid (HPMA, 600 MW),

Received: January 10, 2011Accepted: August 20, 2011Revised: July 9, 2011

10394 dx.doi.org/10.1021/ie200051r |Ind. Eng. Chem. Res. 2011, 50, 10393–10399

Industrial & Engineering Chemistry Research ARTICLE

polyepoxysuccinic acid (PESA, 1500MW), acrylic acid�hydrox-ypropyl acrylate (AA�HPA or T-225, 2100 MW), PAPEMP(615 MW), HEDP(206 MW) and PBTC (270 MW) weretechnical grade and supplied by Jiangsu Jianghai Chemical Co.,Ltd. (Changzhou, Jiangsu, P. R. China). Distilled water was usedin all the studies.Fourier-transform infrared (FT-IR) spectra were measured on

a Bruker FT-IR analyzer (VECTOR-22, Bruker Co., Germany)by using the KBr-pellet method (compressed powder). Theshapes of calcium-phosphate and calcium-carbonate scales wereobserved with a transmission electron microscope (TEM, JEM-2100SX, Japan). The shape of calcium-sulfate scales was ob-served with a scanning electron microscope (SEM, S-3400N,HITECH, Japan).2.2. Experimental Procedure. 2.2.1. Synthesis of AA�APEC.

A 5-neck round-bottom flask equipped with a thermometer and amagnetic stirrer was charged with 70 mL of distilled water and 40g of AA, and heated to 70 �C with stirring under nitrogen.Subsequently, 40 g of APEC in 18 mL of distilled water(APEC/AA mass ratio = 1:1) and the initiator solution (3.0 gof ammonium persulfate in 18 mL of distilled water) were addedseparately at constant flow rates over a period of 1.0 h. Thereaction mixture was heated to 80 �C and maintained at thistemperature for a further 1.5 h, to ultimately afford an aqueouscopolymer solution containing approximately 35% solid. Thisproduct was decanted into a 10-fold volume of acetone withstirring. The resulting insoluble products were filtered andextracted in a Soxhlet extractor for 20.0 h to remove theremaining AA and APEC. The crude products were dried in avacuum oven to constant weight to yield the desired AA�APECas a reddish viscous liquid. The synthesis procedure employed forthe preparation of AA�APEC from AA and APEC is shown inScheme 1.2.2.2. Precipitation Conditions. All precipitation experiments

were carried out in triplicate and all inhibitor dosages given beloware on a dry-inhibitor basis. Analytical reagents and A gradeglassware were used throughout. Water used was distilled water.All Ca2+ ions concentration as CaCO3 was standardized throughEDTA titrimetric method. Procedure of calcium-phosphateprecipitation experiments was described in an earlier publi-cation.20 The precipitation experiments were done underthe conditions of 250 mg/L Ca2+, 5 mg/L PO4

3�, pH = 9.0,T = 80 �C, t = 10 h according to the national standard of P. R.China concerning the code for the design of industrial recirculat-ing cooling-water treatment (GB 50050-95). Polymer efficiencyas a calcium-phosphate inhibitor was calculated according to aprevious publication.20

Calcium sulfate was precipitated from supersaturated solu-tions prepared by mixing of CaCl2 and Na2SO4 solutionsaccording to the national standard of P. R. China concerningthe code for the design of industrial oilfield-water treatment(SY/T 5673-93). The salts of CaCl2 and Na2SO4 both wereanalytical reagents from Zhongdong Chemical Reagent Co., Ltd.

The prepared solutions, 250 mL of CaC12 (13 600 mg/L Ca2+)and 250 mL of Na2SO4 (14 200 mg/L SO4

2�), were kept inseparate glass bottles at room temperature for 5 h to stabilizetheir temperature. After that time, at the beginning of experi-ments, these solutions were mixed in a flask of 500-mL capacityimmersed in a temperature-controlled bath. To avoid the con-centration of the solution by evaporation especially at a hightemperature, we condensed the vapor by means of a cooler.Precipitation of these calcium-sulfate supersaturated solutionswas monitored after these solutions were heated for 6.0 h at80 �Cby analyzing aliquots of the filtered (0.22 μm) solutions forCa2+ ions concentration by using EDTA complexometry titra-tion according to the national standard of P. R. China concerningthe code for the design of industrial recirculating cooling-watertreatment (GB/T 15452-2009). The pH of the calcium-sulfatesupersaturated solutions was adjusted to 7.0 by using dilutesolutions of sodium hydroxide and/or hydrochloric acid and keptconstant with borax buffer solutions. In another series of experi-ments under the same conditions as described above, theprecipitation of calcium-sulfate solutions was studied in thepresence of chemical scaling inhibitors added to the CaC12solutions before mixing with Na2SO4 solutions. A number ofinhibitors of AA�APEC, MA�APES, PAA, HPMA, PESA,T-225, PAPEMP, HEDP, and PBTC were tested.Inhibitor efficiency as a calcium�sulfate inhibitor was calcu-

lated by using the following equation:

Inhibition ð%Þ ¼ ½Ca2þ�final�½Ca2þ�blank½Ca2þ�initial�½Ca2þ�blank

� 100%

where [Ca2+]final is concentration of Ca2+ ions in the filtrate inthe presence of inhibitor after calcium-sulfate supersaturatedsolutions were heated for 6.0 h at 80 �C, [Ca2+]blank is concen-tration of Ca2+ ions in the filtrate in the absence of inhibitor aftercalcium-sulfate supersaturated solutions were heated for 6.0 h at80 �C, and [Ca2+]initial is concentration of Ca2+ ions at thebeginning of the experiment.Procedure of calcium-carbonate precipitation experiments was

also carried out similarly to calcium-sulfate precipitation experi-ments, except that the prepared solutions, 250 mL of CaC12(13 600 mg/L Ca2+) and 250 mL of Na2SO4 (14 200 mg/LSO4

2�), were changed into solutions of 250 mL of CaC12 (480mg/L Ca2+) and 250 mL of NaHCO3 (1464 mg/L HCO3

�)according to the national standard of P. R. China concerning thecode for the design of industrial recirculating cooling-watertreatment (GB/T 16632-2008).

3. RESULTS AND DISCUSSION

3.1. Characterization of AA�APEC. The FT-IR spectra ofAPEC and AA�APEC are shown in Figure 1. The fact that the(—CdC—) stretching vibration at 1646 cm�1 appears in curvea, while it disappears completely in curve b reveals that freeradical polymerization between APEC and AA had happened.The 1725 cm�1 strong intensity absorption peak (—CdO) incurve a and b clearly reveals that both APEC and AA�APECcontain carboxyl groups.3.2. Effect of Inhibitor on Calcium-Phosphate Scales.

The ability of AA�APEC to control calcium-phosphate depositswas compared with that of other scale inhibitors as shown inFigure 2 and in Table 1. As is apparent from Figure 2, theinhibitor dosage of AA�APEC strongly affected its performance on

Scheme 1. Synthesis of AA�APEC



calcium�phosphate inhibition, and there existed an obviousthreshold of 6 mg/L AA�APEC. When the dosage ofAA�APEC was below 6 mg/L, the inhibition on calcium-phosphate scales substantially increased when the dosage ofAA�APEC increased, while it was not variable with the dosagewhen the dosage of AA�APEC exceeded 6mg/L. Themaximuminhibitory power on calcium-phosphate scales was obtainedwhen AA�APEC was at a level of 6 mg/L. Similar results wereobtained from the data of MA�APES in Figure 2. It should benoted that the similar tendency of the dosage on the perfor-mance behavior has been reported in earlier studies onpolymeric threshold inhibitors.5,17,21,22

The data shown in Figure 2 also indicate that, except forAA�APEC and MA�APES, the other inhibitors investigateddisplay poor calcium phosphate inhibition under the sameexperimental conditions. Compared to MA�APES, a recentmost effective inhibitor for calcium-phosphate scales, AA�APEC displays superior ability to inhibit the precipitation ofcalcium phosphate, with 100% inhibition at a level of 6 mg/L,whereas it is 90% for MA�APES at the same dosage. The datalisted in Table 1 indicate that the calcium phosphate inhibition ofthe investigated inhibitors is still lower than that of AA�APECeven though the inhibitor dosage increases to 35 mg/L, anunacceptable dosage for economic and environmental reasons.What deserves to be mentioned is that the calcium phosphateinhibition of PAPEMP, the most popular calcium phosphateinhibitor, really increases to 81% at a level of 35 mg/L. However,PAPEMP belongs to a type of phosphorus inhibitor; on thecontrary, AA�APEC only possesses three elements of carbon,hydrogen, and oxygen, belonging to a type of nonphosphorusinhibitor. Furthermore, when compared to AA�APEC, thedosage of PAPEMP is much higher whereas the inhibition ismuch lower.The presence of scale inhibitors influences not only the growth

rate but also the morphology of the crystal.1,3,8 TEM images ofcalcium-phosphate crystals grown in the absence and in thepresence of 4 mg/L AA�APEC are shown in Figure 3, andindicate that the inhibitor of AA�APEC obviously decreased thesize of calcium-phosphate solid particles thereby dispersing themthroughout a fluid. In the absence of inhibitor, massive needle-shaped calcium-phosphate particles of a size of about 200 nmwere obtained (Figure 3a), while in the presence of 4 mg/LAA�APEC, the irregular calcium-phosphate particles of a size ofabout 5�100 nm were produced (Figure 3b).3.3. Effect of Inhibitor on Calcium-Carbonate Scales.

During the last two decades, investigations on polymeric inhibi-tors to prevent or retard calcium-carbonate scales have caughtmuch attention of academic and industrial researchers.7,8 Com-mon inhibitors evaluated include PAA, HPMA, T-225, PESA,PBTC,HEDP, PAPEMP, andMA�APES etc., containing acrylicacid or maleic acid and other monomers with different function-alities (i.e., �CONH2, �COOR, SO3H).In this work, we also studied the influence of these inhibitors

on the prevention of calcium-carbonate scales as shown inFigure 4. It was suggested that the inhibitor composition hasan interesting impact on inhibitor effectiveness. As effectiveinhibitors on calcium-carbonate deposits, phosphonates, suchas PBTC, HEDP, PAPEMP (marked with solid lines in Figure 4),exhibited significant ability to control calcium-carbonate scales,

Figure 2. Inhibition on calcium phosphate as a function of inhibitordosage.

Table 1. Required Minimum Dosage of Inhibitor for Maximum Ca3(PO4)2 Inhibition

inhibitor abbreviation maximum Ca3(PO4)2 inhibition (%) minimum dosagea (mg/L)

acrylic acid�allylpolyethoxy carboxylate AA�APEC 100 6

maleic anhydride�ammonium allylpolyethoxy sulfate MA�APES 90 6

polyacrylic acid (1800 MW) PAA 73 35

hydrolyzed polymaleic acid (600 MW) HPMA 53 30

polyepoxysuccinic acid PESA 41 8

acrylic acid�hydroxypropyl acrylate T-225 54 12

polyamino polyether methylenephosphonate PAPEMP 81 35

1-hydroxyethylidine-1,1-diphosphonic acid HEDP 71 25

2-phosphonobutane-1,2,4-tricarboxylic acid PBTC 49 12aRequired minimum dosage to obtain maximum Ca3(PO4)2 inhibition.

Figure 1. FT-IR spectra of APEC (a) and AA�APEC (b).



and their inhibition on calcium carbonate is superior to that ofthe other investigated nonphosphorus inhibitors includingAA�APEC (marked with dotted lines in Figure 4). However,it can be seen from Figure 4 that the copolymer of AA�APECdisplayed the best ability to control calcium-carbonate depositsamong nonphosphorus inhibitors investigated, namely, PAA,HPMA, T-225, PESA, PBTC, and MA�APES.It is also worth mentioning that PAA, HPMA, andMA�APES

inhibitors, containing carboxyl groups and possessing molecular

structure similar to AA�APEC inhibitor, can hardly controlcalcium-carbonate deposits even at a high dosage. This factsuggests that the side-chain polyethylene glycol (PEG) segmentsof APEC and carboxyl groups of AAmight play an important roleduring the control of calcium-carbonate scales. TEM images inFigure 5 show the effect of AA�APEC on the crystal morphol-ogy of calcium carbonate and they indicate that the copolymer ofAA�APEC resulted in the formation of ribbon-shaped structuresthereby preventing the precipitation of calcium carbonate.3.4. Effect of Inhibitor on Calcium-Sulfate Scales.Calcium-

sulfate scales can be formed by using sulfuric acid to maintainthe pH value of the solution below 7.5 in an attempt toeliminate alkaline scales such as calcium carbonate and mag-nesium hydroxide. The performance of AA�APEC on cal-cium sulfate precipitation, listed in Table 2, was comparedwith that of several other calcium-sulfate inhibitors both at alevel of 2 mg/L and their threshold dosages under theconditions of 6800 mg/L Ca2+, 7100 mg/L SO4

2�, pH =7.0, T = 80 �C, t = 6.0 h.In addition to its outstanding ability to control calcium-

phosphate scales, AA�APEC also exhibited significant abilityto control calcium-sulfate scales, and it was 16 times moreeffective against the formation and precipitation of calcium-sulfate scales than MA�APES at a level of 2 mg/L. Themaximum calcium sulfate inhibition was 83% at a level of 3mg/L for AA�APEC, whereas it was 71% at its threshold dosageof 32 mg/L for MA�APES. It indicated that AA�APEC hasexcellent ability to control not only calcium-phosphate scales but

Figure 5. TEM images of calcium-carbonate crystals: (a) in the absenceof inhibitor and (b) in the presence of 4 mg/L AA�APEC.

Figure 3. TEM images of calcium-phosphate crystals: (a) in theabsence of inhibitor and (b) in the presence of 4 mg/L AA�APEC.

Figure 4. Inhibition on calcium carbonate as a function of inhibitordosage.



also calcium-sulfate scales at a low dosage, whereas MA�APESonly has ability to control calcium-phosphate scales and cannotcontrol calcium-sulfate scales at a low dosage. The data listed inTable 2 also showed that, at their respective threshold dosage,AA�APEC has the same calcium sulfate inhibition as PAA orHPMA, the two most effective, commonly used nonphosphorusinhibitors for calcium sulfate control. Furthermore, at a level of 2mg/L, HPMA seemed more effective than AA�APEC forcalcium sulfate inhibition. However, the inability to inhibitcalcium-phosphate scales makes both PAA and HPMA lessdesirable inhibitors. It is worth mentioning that, although theperformance of PAPEMP on calcium sulfate inhibition is equal tothat of PAA, HPMA, and AA�APEC at their threshold dosages,PAPEMP does not have ability to control calcium-phosphatescales until the dosage exceeds 30mg/L, an unacceptable massivedosage in industrial recycling water systems; these weaknessesmake PAPEMP a less desirable inhibitor.The SEM images in Figure 6 show that regular rod-shaped

calcium sulfate tight particles were obtained in the absence ofinhibitor (Figure 6a), and loose calcium sulfate particles wereproduced in the presence of AA�APEC (Figure 6b). It alsoindicates that the use of only 2.5 mg/L AA�APEC had aprofound effect on the calcium sulfate crystal morphologyand size.3.5. Inhibition Mechanism Toward Ca3(PO4)2, CaCO3, and

CaSO4 Scales. AA�APEC is a structurally well-defined biblockcopolymer, depicted in Figure 7a; one block is AA, and the otheris APEC. The main chains are composed of allyl-terminated AA,denoted as PAA (marked with green ribbons in Figure 7), and theside chains are made of carboxylate-capped polyethylene glycol(PEG) segments (marked with black ribbons in Figure 7). BothPAA and PEG segments are hydrophilic blocks and existrandomly in water (Figure 7b). When calcium ions are addedinto AA�APEC solutions, carboxyl groups in AA�APEC ma-trixes can recognize and encapsulate or react with positivelycharged calcium ions either in solutions or on the surface ofinorganic minerals, such as Ca3(PO4)2, CaCO3, and CaSO4.

23�26

Encapsulation or interaction, between calcium ions and carboxylgroups, leads to the spontaneous formation of AA�APEC�Cacomplexes (Figure 7c). On the other hand, when negativelycharged PO4

3�, SO42�, or CO3

2� ions are added into solutions,the positively charged calcium ions also interact with thesenegatively charged ions thereby forming Ca3(PO4)2, CaCO3,andCaSO4 crystal embryos. As a result, calcium ions acting as tiessimultaneously link AA�APEC through carboxyl groups andPO4

3�, SO42�, or CO3

2� ions through an electrostatic attractiveforce. At the same time, water-compatible PEG segments,27�33

that is to say, long side chains of AA�APEC, surrounding thesurfaces of Ca3(PO4)2, CaCO3, and CaSO4 crystal embryos, arestable toward aqueous phase because of their high hydrophilicproperties (Figure 7b). Thus, Ca3(PO4)2, CaCO3, and CaSO4

embryos incorporate into the polymer matrix of AA�APEC, andthey are coated with double layers of PAA (inner layer) and PEG(outer layer). As a consequence, the aggregation of Ca3(PO4)2,CaCO3, and CaSO4 solid particles is blocked. In addition, thelong PEG side chains in AA�APEC matrix result in steric andelectrostatic repulsion. Therefore, the existing minerals do notprecipitate in the presence of AA�APEC through its excellentability to disperse solid particles such as calcium-phosphatescales. The fact that AA�APEC has excellent dispersancy activitytoward precipitation of calcium phosphate seems fit to TEMimages of calcium-phosphate crystals in Figure 3b, while it maybeemphasizes that the copolymer of AA�APEC has superior abilityto inhibit the precipitation of calcium carbonate and calciumsulfate by the excellent solubility of AA�APEC�Ca complexesdue to water-compatible PEG segments. It should be mentionedthat the hypothesis of inhibition mechanism is consistent withthose of Antonia et al.,6 who reported that cationic polymersexhibited higher inhibitory performance resulting from theinteractions between polycation (polymer) and polyanion(silica). The study15 of Achilles et al. showed that the role ofpolycarboxylic acids as inhibitors of calcium-phosphate crystalgrowth was to bind calcium ions with polycarboxylates. However,Ca cations formed high hydrophilic complexes originate frominorganic minerals, such as Ca3(PO4)2, CaCO3, and CaSO4, as aresult, structure matching between complexes and inorganicminerals is an important factor during the process of inhibition.For this reason, AA�APEC exhibited excellent Ca3(PO4)2 and

Table 2. Comparison of Calcium-Sulfate Inhibition

inhibitor

dosage,

mg/L

CaSO4

inhibition (%)

dosage of

threshold, mg/L

maximum CaSO4

inhibition (%)

AA�APEC 2 39 3 83

MA�APES 2 2 32 71

PAA 2 38 3 81

HPMA 2 79 2 79

PAPEMP 2 30 4 80

Figure 6. SEM images of calcium sulfate crystals: (a) in the absence ofinhibitor and (b) in the presence of 2.5 mg/L AA�APEC.



CaSO4 inhibition, while it exhibited only passable ability tocontrol CaCO3 deposits.

4. CONCLUSIONS

(1) A nonphosphorus inhibitor, the copolymer of AA�APECwas synthesized and exhibited 100% calcium phosphateinhibition at a level of 6 mg/L and 83% calcium sulfateinhibition at threshold dosage of 3 mg/L. AA�APEC alsodisplayed significant ability to control calcium-carbonatescales in solutions, showing approximately 65% inhibitionwhereas the popular nonphosphorus inhibitors of PAA,HPMA, PESA, and T-225 exhibited only 20�60% cal-cium carbonate inhibition.

(2) Compared to the recent nonphosphorus inhibitor ofMA�APES, AA�APEC showed an excellent inhibitoryefficiency both on calcium phosphate and calciumsulfate precipitation, whereas MA�APES only showedsuperior calcium phosphate inhibition and displayedinability to control calcium-sulfate scales at a lowdosage. For calcium carbonate inhibition, AA�APECexhibited ability to prevent the formation of calcium-carbonate scales to a certain extent, whereas MA�APES exhibited hardly any ability to control calcium-carbonate scales.

(3) The inhibition mechanism toward Ca3(PO4)2, CaCO3,and CaSO4 deposits was proposed that the formation ofthe excellent solubility of AA�APEC�Ca complexes dueto high hydrophilic PEG segments in the AA�APECmatrix.

’AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected]. Tel.: 86-25-52090617.

’ACKNOWLEDGMENT

We acknowledge National Nature Science Foundation ofChina (50873026); Key Program for the Scientific ResearchGuiding Fund for Basic Scientific Research Operation Expendi-ture of Southeast University (Grant 3207040103); Science andTechnology Projects on Production, Teaching and Research,Changzhou, Jiangsu Province of China (CV20090002); SupportProgram for Training of 333High-Level Talent, Jiangsu Provinceof China (BRA2010033); Additionally, Nature Science Fund ofJiangsu Province (BK2011692) is also appreciated.

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’NOTE ADDED AFTER ASAP PUBLICATION

After this paper was published online August 26, 2011, acorrection was made to Table 1. The revised version was publishedAugust 30, 2011.

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