Paper No.
5996
Water Chemistry Impacts on Cooling Water System Iron Oxide Dispersants
Zahid Amjad, Libardo Perez, and Robert W. Zuhl
The Lubrizol Corporation, Energy and Water, 29400 Lakeland Blvd., Wickliffe, Ohio 44092, USA
ABSTRACT
The effects of water chemistry such as total dissolved solids, polyvalent metal ions, pH, and
temperature on particulate iron oxide dispersion by a variety of polymeric additives have been
investigated. The deposit control polymers (DCPs) evaluated include synthetic polymers (of varying
composition and molecular weight). Results reveal that DCP iron oxide dispersant performance
strongly depends on dosage and architecture (e.g., type and amount of monomers, monomer functional
group ionic charge, molecular weight). Data show that pH changes cause varying but relatively small
changes in DCP dispersant performance. The results also suggest that low levels of divalent and
trivalent metal ions reduce DCP dispersant performance.
Keywords: iron oxide, dispersion, deposit control agents, mono-, di-, and trivalent metals effect
INTRODUCTION
Solid/liquid dispersion technology has many domestic and industrial applications. The dispersion is
generally defined as a suspension of insoluble particles formed either through de-flocculation or
breaking down of agglomerated particles, or from the stabilization of small suspended particles.
Industrial applications of dispersant technology includes water treatment, oil and gas recovery, paints,
inks, cosmetics, and paper manufacturing.1 Suspended matter encountered in industrial water systems
generally carries a slight negative charge. The type, size, and concentration of suspended mater affect
their behavior in water systems. Therefore, anionic polymers are normally the most efficient
dispersants because they increase the negative surface charge and keep particles in suspension.
Dispersed systems can be achieved by controlling the surface charge of the powders in solution, for
example, by the adsorption of charged polymers referred to as polyelectrolytes.2 Suspension of clays,
metal oxides, pigments, ceramic materials, and other insoluble particulate solids in aqueous systems
through the use of small quantities of synthetic polymers, polyphosphates, and other polyelectrolytes
has become an increasingly important area of study with high technological relevance.
A previous study reported the influence of ammonium polyacrylate (NH4PAA) in dispersing
concentrated alumina suspension.3 A 3.5k molecular weight (MW) NH4PAA was found to be an
effective dispersant for a Bayer* processed alumina that had a point of zero charge at pH 8.0. Garris
and Sykes4 in their study on the evaluation of a variety of polyamino acid analogs of biomineral proteins
as dispersants for various substrates e.g., clay, calcium carbonate, calcium phosphate, iron oxide,
reported that performance of these dispersants was comparable to synthetic polymeric dispersants. In
another study by Dubin5 it was shown that acrylic acid and maleic acid based DCPs performed better
*
Trade name
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NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
1
than polyphosphates and phosphonates as iron oxide dispersants. Bain et al.6 tested the performance
of poly(aspartic acid) [or PASA] as a dispersant for kaolin clay. Their study results show that low MW
PASA performed better than poly(acrylic acid) [or PAA], in dispersing clay in aqueous system.
In another study, Amjad7 evaluated a variety of homo-, co-, and terpolymers containing different
functional groups as iron oxide dispersants. Among the homopolymers evaluated in this study, PSA
[poly(2-acrylamido-2-methylpropane sulfonic acid)], performs better than PAA and PMA [poly(maleic
acid)], suggesting that –SO3H group present in PSA imparts more negative charge on iron oxide
particles than –COOH present in PAA and PMA. The data further reveal that incorporating –SO3H
containing monomers such as SA or SS (sulfonated styrene) results in dramatic increase in co- or
terpolymer performance suggesting that incorporation of co-monomers help sterically stabilize iron
oxide particles. Similar observations were also reported by Amjad and Zuhl in their studies on the
dispersion of iron oxide,8 clay,9 hydroxyapatite,10 and silica.11
Iron fouling often occurs in cooling water and desalination processes as a result of clarifier carryover
where iron salts are used as a coagulants or where the raw water (e.g., well water) contains high iron
levels. When the circulating water iron levels are ≤1 mg/L, the system can normally be controlled by
incorporating a dispersant in the water treatment formulation. In cooling waters, Fe2O3 (hematite) and
FeO (iron oxide or wustite) are the two most common iron deposits. However, magnetite (Fe3O4) is
rarely encountered in cooling systems because it needs high temperatures and/or anaerobic conditions.
Most magnetite found in cooling systems arrives via airborne or water borne solids.
In our earlier investigations, we reported the influence of various factors including water chemistry, pH,
temperature, and impurities (both soluble & insoluble) on the performance of scale inhibitors. It was
shown that, impurities typically exhibit negative impact on scale inhibitor performance. The focus of this
study is to examine the effects of water impurities [e.g., metal ions (mono-, -di-, trivalent ions), total
dissolved solids (TDS)] on the performance of commercially available DCPs. The influence of pH and
temperature on iron oxide dispersants performance was also investigated.
EXPERIMENTAL
Materials
Grade A glassware and analytical grade chemicals were used. Stock solutions of calcium chloride,
sodium sulfate, sodium bicarbonate and sodium carbonate were prepared from the respective
crystalline solids (Merck†) using distilled water, filtered through 0.22-µm filter paper and standardized as
previously described.12 Iron oxide (Fe2O3) used in this investigation was obtained from Fisher Scientific
Co.† Powder X-ray diffraction showed that it consisted exclusively of α-Fe2O3 (hematite). Table 1 lists
the commercial DCPs tested including several Carbosperse† K-700 polymers and polymers containing
AMPS† monomer (SA). Additives stock solutions were prepared on a dry weight basis. The desired
DCP concentrations were obtained by dilution.
Table 1: Deposit Control Polymers Tested
Polymer
K-752
K-7028
CPAAP
CPMA
K-766
K-775
K-798
CTPD
†
Composition
Solvent polymerized poly(acrylic acid) or “SPPAA”
Water polymerized PAA or “WPPAA”
PAA with phosphinate groups
Poly(maleic acid) or “PMA”
Sodium polymethacrylate or “PMAA”
Poly(acrylic acid : 2-acrylamido-2-methylpropane sulfonic acid]) or
poly(AA/SA) with 74/26 monomer weight ratio
Poly(AA : SA : sulfonated styrene) or “AA/SA/SS”
Poly(AA: SA : non-ionic) or “AA/SA/NI”
MW
2k
2.3k
<4k
<1k
5k
<15k
Acronym
PAS1
PAW1
PAAP
PMA
PMAA1
CP1
<15k
4.5k
TP3
TP4
Trade name
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NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
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2
Dispersion Test Protocol
A known amount (0.12 g) of iron oxide was suspended in an 800-mL beaker containing 600 mL of
simulated industrial water containing known polymer concentration (dispersant). Table 2 shows the
three types of water compositions used all with pH in the 7.6 to 7.8 range.
Table 2. Water Types Studied
Type
Polymer (mg/L)
Fe2O3 (mg/L)
1
2
1.0
1.0
200
200
60 mg/L HCO3, 22 mg/L Na
100 mg/L Ca, 30 mg/L Mg, 314 mg/L Na, 571 mg/L Cl, 192 mg/L SO4, 60 mg/L HCO3
Composition
3
0.25
50
25 mg/L Ca, 7.5 mg/L Mg, 78.5 mg/L Na, 143 mg/L Cl, 48 mg/L SO4, 60 mg/L HCO3
All dispersion experiments were done at room temperature (≈22°C). In a typical test, six experiments
were run simultaneously using a gang stirrer at 120 revolutions per minute. At known time intervals
transmittance readings (%T) were taken with Brinkmann† Probe Colorimeter equipped with 420-nm
filter. The absorbance of several filtered (0.22 µm) suspensions was measured as %T at 420 nm; the
absorbance contribution due to dissolved species was insignificant (<3%). DCP performance as percent
iron oxide dispersed (%D) was calculated based on %T readings taken as a function of time and using
Equation 1 below which includes an adjustment for readings obtained in the absence of DCP.
%D = [100 - (1.11 x % transmittance)]
(1)
The data presented in this study were reproducible (± 5% or better). DCP performance was determined
by comparing the %D values for the slurries containing and without DCPs. Increasing %D values
suggest more effective dispersion.
RESULTS AND DISCUSSION
DCP Performance
DCPs evaluated (see Table 1) represent a wide range of compositions (monomer type, amount), ionic
charges (attributable to monomer functional groups), and MW. The following section discuss results
using the protocol described above to runs a series of iron oxide dispersion tests to study the effect of
various parameters [e.g., dispersion time, dispersant dosage, polymer composition, metal ions (mono-,
di-, and trivalent), solution pH, and temperature].
Test Duration and Dispersant Dosage Effects
Figure 1 presents the results showing the performance of TP3 as iron oxide dispersant using Type-1
water composition, at varying DCP dosage and as a function of time. Figure 1 data indicate %D values
increase with both increasing time and increasing TP3 dosage. For example, %D values obtained in
the presence of 1.0 mg/L at ½ hr and 1 hr are 25% and 41%, respectively. Increasing the test duration
by a factor of three (i.e., from 1 to 3 hr) increases the %D value by >25%. Increasing the test duration
another hour (i.e., from 3 to 4 hr) has an insignificant effect on the %D value. Therefore, we conclude
that test duration (i.e., TP3 contact time with iron oxide particles) plays an important role in iron oxide
particle dispersion in aqueous solution. Other factors including particle size and surface area may play
a role in iron oxide dispersion.
†
Trade name
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3
Figure 1: Iron Oxide Dispersion vs. TP3 Dosage
using Type-1 Water
% Iron Oxide Dispersed
80
60
40
0.25 mg/L
20
0.50 mg/L
1.0 mg/L
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Time (hr)
TP3 dosage impact on iron oxide dispersion was also studied. Figure 1 shows that TP3 iron oxide
dispersion performance strongly depends on polymer dosage but the relationship is not linear. For
example, %D values obtained at 3 hr in the presence of 0.25 and 0.50 mg/L TP3 are 43% and 55%,
respectively. Doubling the TP3 concentration (i.e., from 0.50 to 1.0 mg/L) increases the %D value only
≈12% (from 55 to 67%). This is not surprising considering that the extent of adsorption depends largely
on the DCP conformation on the iron particles. Although outside of the scope of the work herein,
studies of adsorption mechanism(s) would help provide a better understand this behavior of the DCPs.
Figure 1 data clearly show that iron oxide dispersant performance depends on DCP concentration.
Metal Ions Effect
Monovalent Ions
The influence of monovalent metal ions (i.e., Na+) on the performance of TP3 was investigated by
conducting dispersion experiments in the presence of varying sodium chloride concentrations using
Type-1 water. Figure 2 dispersion data collected at 3 hr for 1.0 mg/L TP3 clearly show that adding a
small amount (49 mg/L) of sodium chloride (NaCl) enhances performance. For example, %D values
obtained in the presence of 49 mg/L NaCl is 89% compared to 70% without NaCl (≈20% improvement).
As shown, increasing the NaCl concentration from 49 to 110 mg/L results in TP3 performance
increasing ≈10%. However, increasing the NaCl concentration (ionic strength) further has an
insignificant effect on TP3 performance.
Divalent Ions
Homopolymers: High hardness waters either due to harsh feed waters or high cycles of concentration
(COC) are well known to create difficult operating conditions that demand high performance
dispersants. A series of experiments was conducted with Type-1 water to determine the influence of
Ca2+ ions on PAA (i.e., PAS1 and PAW1) performance. Figure 3 presents dispersion data in the
presence of 1.0 mg/L PAAs and varying concentration of Ca2+ ions. In the absence of Ca2+ ions, both
PAAs exhibit excellent iron oxide dispersion performance.
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
4
Figure 2: Iron Oxide Dispersion by 1 mg/L TP3
in Presence of NaCl using Type-1 Water
% Iron Oxide Dispersed
100
80
60
40
20
0
Control
49 mg/L NaCl
110 mg/L NaCl 440 mg/L NaCl 659 mg/L NaCl
Figure 3: Iron Oxide Dispersion by Polyacrylates
in Type-1 Water as a Function of Ca2+ Concentration
% Iron Oxide Dispersed
100
80
PAS1
PAW1
60
40
20
0
0
15
50
150
Ca2+ (mg/L as Ca)
Figure 3 shows that adding Ca2+ ions has an antagonistic effect on PAA performance. The data
indicate that PAS1 performs better than PAW1 especially at a higher Ca2+ ions concentration (i.e.,
150 mg/L). This difference may be attributed to poor compatibility with Ca2+ and/or poor adsorption of
PAW1 on iron oxide particles.
To study the impact of Ca2+ on iron dispersion by homopolymers of acrylic acid and maleic acid of
varying molecular weight (MW), several dispersion experiments were carried out in the presence of
1.0 mg/L DCP and 150 mg/L Ca2+ using Type-1 water. Results presented in Figure 4 clearly show that
homopolymer performance is affected by Ca2+ to a varying degrees and can be ranked (highest to
lowest) as PAS1 ≈ PMA >PAW1 ~ PMAA1 > PAAP. This DCP performance trend is consistent with an
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
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5
earlier study on the calcium ion tolerance by homopolymers.13 The effect of Ca2+ on DCP performance
may be attributed to several factors including Ca-DCP complexation, Ca-DCP salt precipitation, and
iron oxide particle surface charge.
Figure 4: Iron Oxide Dispersion
by Homopolymers (1 mg/L) using Type-1 Water
% Iron Oxide Dispersed
100
0 mg/L Ca
150 mg/L Ca
80
60
40
20
0
PAS1
PAW1
PAAP
PMAA1
PMA
Co/terpolymers: The role of DCP functional group(s) was investigated by conducting a series of iron
oxide dispersion experiments using Type-1 water and 1.0 mg/L co/terpolymers (e.g., CP1, TP3, TP4)
containing several functional groups [e.g., ionic (-COOH, -SO3H)] and comparing performance to
various homopolymers. Figure 5 shows 3-hr dispersion data for PAW1 and TP3 collected in the
presence of varying Ca2+ ion concentrations leading to three observations:
1. In the absence of Ca2+, PAW1 performs better than TP3,
2. At low Ca2+ (i.e., <50 mg/L), TP3 outperforms PAW1, and
3. PAW1 and TP3 performance decreases with increasing Ca2+ concentration.
Figure 5: Iron Oxide Dispersion by Polymers (1 mg/L)
as a Function of Ca2+ Concentration using Type-1 Water
100
% Iron Oxide Dispersed
PAW1
TP3
80
60
40
20
0
0
15
25
50
150
300
600
Ca2+ (mg/L as Ca)
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6
From a practical viewpoint, Figure 5 data suggest that incorporating TP3 (a terpolymer) used in a low
hardness water system (e.g., a boiler) treatment program would be expected to perform better than
PAW1 (a homopolymer). This is because TP3’s carboxyl content is lower than for PAW1 and thus is
more tolerant to Ca2+ ions
Figure 6 presents dispersion data for several polymers using Type-1 water conducted in the absence
and presence of 150 mg/L Ca2+. The data in the absence of Ca2+ ions show that the two
homopolymers (i.e., PAS1 and PAAP) perform better than the co/terpolymers. However, all DCPs lose
dispersion activity in the presence of Ca2+ and the extent of the performance loss is dependent on
polymer architecture (e.g., manufacturing process, MW, type and amount of co-monomers). More
specifically, co/terpolymers resist perform loss much better in the presence of 150 mg/L Ca2+ than the
homopolymers. This polymer trend observed is consistent with an earlier study focusing on DCP
calcium ion tolerance.13
Figure 6: Iron Oxide Dispersion by Polymers (1 mg/L)
Impacted by 150 mg/L Ca2+ using Type-1 Water
100
% Iron Oxide Dispersed
0 mg/L Ca
150 mg/L Ca
80
60
40
20
0
PAS1
PAAP
CP1
TP3
TP4
Trivalent Ions
Aluminum and iron-based compounds (e.g., alum, sodium aluminate, ferric sulfate) have been used for
decades as coagulant aids in municipal and industrial water clarification processes. These inorganic
flocculating agents neutralize the charge of water borne turbidity particles and hydrolyze to form
insoluble hydroxide particles that entrap additional particles. In most cases, these large particles (or
flocs) are removed via settling in a clarifier and extracted as sludge. Occasionally, clarifier upsets
cause these metal-ion containing flocs and/or fugitive flocculants to carry over or escape pretreatment
systems and become contaminants or impurities in cooling or boiler feed waters and can adversely
impact treatment program performance.
Figure 7 presents the impact of varying Al(III) and Fe(III) concentrations on TP3 iron oxide dispersion
performance using Type-1 water. Low levels of trivalent metal ions exhibit antagonistic effects on TP3
performance; e.g., %D values obtained in the presence of 0.25 mg/L Al(III) is 67% compared to 73% in
the absence of Al(III). Increasing the Al(III) concentration fourfold (i.e., from 0.25 to 1.0 mg/L)
decreases the TP3 %D by 33% (from 73 to 40%). Increasing Al(III) from 1.0 to 5.0 mg/L further
decreases TP3 performance. As shown, Fe(III) concentrations also have an antagonistic effect on TP3
performance which is less impactful than Al(III). The iron dispersant performance decrease caused by
trivalent metal ions may be attributed several factors:
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
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7
1. Dispersant concentration is reduced due to possible polymer removal via adsorption by freshly
formed Al(III) and Fe(III) hydroxide particles,
2. Al(III) and Fe(III) may form soluble and/or insoluble complexes with polymer,
3. Al(III) and Fe(III) may interfere in the adsorption of polymer-iron oxide particles, and
4. Combinations of the processes above.
Figure 7: Iron Oxide Dispersion by TP1 (1 mg/L)
Impacted by Trivalent Ions using Type-1 Water
80
% Iron Oxide Dispersed
Al3+
Fe3+
60
40
20
0
0.00
0.25
1.00
3.00
Trivalent Ion Concentration (mg/L)
5.00
The antagonistic effect of trivalent ions on TP3 iron oxide dispersant performance has also been
observed for scaling systems, e.g., calcium phosphate, calcium phosphonate, calcium sulfate
dihydrate.14-16
Effect of pH
Increasing cooling system pH has two key effects on system performance: (1) decreases metal
corrosion rates and (2) increases potential scaling due to increasing supersaturation of scaling salts
(e.g., calcium carbonate, calcium phosphate, and calcium phosphonates).
To study solution pH impact on PAW1 and TP3 performance, a series of dispersion experiments were
conducted using Type-2 water. Figure 8 presents results indicating that DCP iron oxide dispersion
performance varies with solution pH. The performance for both PAW1 and TP3 at 1 mg/L dosages
increases as pH increases from 2.5 to 9.2 with more dramatic increase observed for TP3. The DCP
performance on solution pH dependence may be attributed to the increased ionization of the “–COOH”
and “-SO3H” groups present in PAW1 and TP3, respectively. Similar solution pH vs. DCP performance
profiles have been reported in a calcium sulfate dihydrate seeded growth inhibition using PAA.17
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
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8
% Iron Oxide Dispersed
80
Figure 8: Iron Oxide Dispersion by Polymers (1 mg/L)
as a Function of pH using Type-2 Water
PAW1
TP3
60
40
20
0
2.5
4.0
6.0
7.8
9.2
Test Solution pH
Temperature Effect
It is well known that water chemistry parameters including pH, total dissolved solids (TDS) water
composition, and temperature affect the solubility of scale forming salts. The solubility of most scale
forming salts (e.g., calcium carbonate, calcium sulfate, and calcium phosphate) is inversely dependent
on solution temperature. This solubility-temperature relationship suggests that scaling tendency is
greater at heat exchanger surfaces than in the other parts of the circulating water system. Figure 9
shows the effect of temperature on iron oxide dispersion of PAW1 and TP3 at 1 mg/L dosages. It is
evident that temperature, within the range studied (i.e., 23 to 60°C), exhibits insignificant effect on DCP
performance.
Figure 9: Iron Oxide Dispersion by Polymers (1 mg/L)
as a Function of Temperature using Type-2 Water
% Iron Oxide Dispersed
100
PAW1
TP3
80
60
40
20
0
23°C
40°C
60°C
Test Solution Temperature
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
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9
Cycles of Concentration Effect
It is well known that increasing the cycles of concentration (COC) in cooling water systems increases
the potential for scaling salt formation and/or deposition of unwanted materials on equipment surfaces.
Under normal conditions, the water treatment additive (e.g., antiscalant, dispersant, corrosion inhibitor)
concentrations also increase with increasing COC. However, at high COC, scaling potential increases
dramatically and/or the re-circulating water suspended matter loading increases and may exceed the
inhibitor’s ability to provide control even if product dosages are increased.
To understand the impact of COC on TP3 performance, a series of experiments were conducted using
Type-3 water. The experiments were designed such that both iron oxide particles and TP3
concentrations were increased directly with COC increases. Figure 10 shows that TP3 performance
increases as COC increases from one to four and then levels out; i.e., TP3 performance increases only
slightly when COC doubles (goes from 4 to 8). The observed dependence of TP3’s iron oxide
dispersion properties with increasing COC may be attributed to several factors including water
chemistry changes, kinetics of TP3 adsorption and/or desorption on suspended iron oxide particles,
and TP3’s conformational changes in aqueous solution.
% Iron Oxide Dispersed
90
Figure 10: Iron Oxide Dispersion by TP3 (1 mg/L)
as Function of COC using Type-3 Water
80
70
60
50
40
30
20
10
0
1 COC
2 COC
3 COC
4 COC
8 COC
Figure 11 presents iron oxide dispersion data using Type-3 water, eight COC, and TP3 dosages
ranging from 1 to 10 mg/L. The data indicate no change in TP3 performance as dosage increases
which is likely due to a combination of two competing processes summarized below:
1. Hardness ion concentration increase due to COC increase thereby decreasing TP3 performance,
2. TP3 dosage increasing from 1 to 10 mg/L should increase TP3 adsorption thereby increasing TP3
performance.
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
10
Figure 11: Iron Oxide Dispersion
as Function of TP3 Dosage using Type-3 Water
90
% Iron Oxide Dispersed
80
70
60
50
40
30
20
10
0
1
2
4
TP3 dosage (mg/L)
10
SUMMARY
This study on the effects of water chemistry on performance of iron oxide dispersion by deposit control
polymers (DCPs) indicates:
1. Fe2O3 particle dispersion increases with increasing DCP concentration and contact time.
2. Fe2O3 dispersant performance strongly depends on DCP architecture, e.g., monomer type(s) and
amounts, functional group(s), and molecular weight.
3. The ranking (best to worst) of DCPs evaluated as iron oxide dispersants is:
Terpolymer > Copolymer > Homopolymer
4. Metal ions charge and concentration are the two most important water quality factors impacting
DCP performance.
5. Metal ion antagonistic impact ranking (greatest to least) on DCP performance is:
Trivalent Ions [(Al(III) > Fe(III)] >> Divalent Ions > Monovalent Ions.
6. Temperature (23 to 60°C range) has minimal impact on DCP performance.
7. DCP performance increases as solution pH increases from 2.5 to 6.0 and incrementally above pH
6.0.
ACKNOWLEDGEMENTS
The authors thank The Lubrizol Corporation for support to conduct this research and present the
findings at NACE International’s annual convention.
©2015 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084. The material presented and the views expressed in
this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
11
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