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CHEMICAL TREATMENT FIGURE 5 Fe2
dispersion in the presence of 1.0 ppm of CMI-25 and various synthetic homo- and copolymers.
O3 FIGURE 6
presents comparative performance data collected in the presence of 1.0 ppm of biopolymer (CMI-25); synthetic polymers poly(acrylic acid (P-AA) and poly(maleic acid) (P-MA); copolymers of acrylic acid:2-acryalamido-2-methylpropane sulfonic acid (P-AA:SA); and acrylic acid:2-acrylamido-2-methylpropane sul- fonic acid:sulfonated styrene (P-AA: SA:SS). Under similar experimental con- ditions, copolymers containing two or three functional groups perform better than P-AA, P-MA, and CMI-25 contain- ing only one functional group (–COOH). The improved performance of copoly-
mers over homopolymers including bio- polymers may be attributed to higher negatively charged groups present in co- polymers. Polymers (e.g., CMI-25, P-AA, P-MA) containing only one functional group (e.g., –COOH) exhibit similar performance in terms of dispersing Fe2
O3
particles dispersed in the presence of (a) 0 ppm, (b) 1.0 ppm of CMI-25, and (c) 1.0 ppm of terpolymer.
Fe2O3
their performance is very sensitive to high temperatures normally encountered in treating boiler water. Humic and fulvic acids, commonly found in natural envi- ronments, are polymeric molecules whose molecular weights range from several hundred to several thousand. These acids contain mostly phenolic and carboxylic acid functionalities, and can behave as negatively charged colloids and anionic polyelctrolytes in surface waters. The dispersion data collected in the presence of 1.0 ppm of natural additives are illustrated in Figure 4. For perfor- mance comparison, %D value for CMI- 25 is also shown. These additives exhibit poor to mediocre performance. The poor performance shown by starch may be attributed to high molecular weight and
52 MATERIALS PERFORMANCE March 2012
poor interaction or adsorption of the non- ionic group with Fe2
O3 particles. On the
other hand, additives that contain either –COOH (e.g., ALG), –COOH and –OH groups (e.g., TA and FA), or SO3
H group
(e.g., LS) show mediocre (<40% D) to good performance (<60% D) at 1.0 ppm level. Thus, it is clear from Figure 4 that the additive containing the –SO3
H group
(i.e., LS) performs better than additives containing –COOH (i.e., ALG) and –COOH/OH (i.e., FA and TA).
Synthetic Additives
particles. Figure 5 also presents dispersion data on poly(acrylamide) (P-AM), a non- ionic, and poly(diallyldi methyl ammonium chloride, a cationic polymer. It is interest- ing to note that compared to all polymers containing negatively charged functional groups, both P-AM and P-DAC are in- effective Fe2
O3 O3 dispersants, indicating that
the ionic charge of the functional groups plays an important role in dispersing Fe2
particles.
Size Reduction by Polymers The Fe2
O3
Biopolymers and Synthetic Polymers as Iron Oxide Dispersants for Industrial Water Applications
particles collected at the
end of the dispersancy experiments were evaluated for particle morphology and size by optical microscopy. Figure 6 pres- ents photographs of Fe2
O3 dispersions in
the absence of a polymer (Figure 6[a]), the presence of 1.0 ppm of CMI-25 (Figure 6[b]), and the presence of 1.0 ppm of P-AA:SA:SS (Figure 6[c]). It is evident from Figure 6(c) that terpolymer com- pared to CMI-25 exhibits a marked effect in breaking down (or deagglomerating) large Fe2
O3
particles. The superior per- NACE International, Vol. 51, No. 3