Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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53 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 large surface area for the adsorption of dis- solved chemical species. The solids con- centration usually ranges from <5 to >200 mg/L, but can go up to >50,000 mg/L. 5 Particle sizes that are >200 nm usually impart a visible turbidity to waters. The fouling of heat exchangers and RO mem- branes and the clogging of pipes by sus- pended solids is becoming a major con- c e r n f o r t h e e f f i c i e n t o p e r a t i o n o f industrial systems. Since the complete removal of suspended solids from process water is not feasible when large volumes are used, dispersants are normally incor- porated into water treatment formulations to stabilize or disperse suspended solids. Commonly used di sp ersants for wat er treatment applications include natural and synthetic polymers. The inf luence of suspended matter on the efficacy of polymers as calcium phos- p h a t e i n h i b i t o r s h a s b e e n re p o r t e d . 6 Results of this study reveal that the addi- tion of clay particles to calcium phosphate supersaturated solutions adversely impact the inhibitory property of polymers. This is due to the adsorption of the polymers by the clay particles, which reduces the avail- a b l e p o ly m e r f o r s c a l e i n h i bit i o n . In another study, Amjad, et al. reported that the addition of clay to silica supersatu- rated solution did not exhibit any signifi- cant effects on the performance of silica polymerization inhibitors. 7 Recent labora- tory research has shown that the presence of small amounts (a few milligrams) of sus- pended matter exhibits an antagonistic effect on the performance of gypsum scale inhibitors. 8 The focus of the present inves- tigation is to study the impact of iron oxide (Fe 2 O 3 ) on the inhibition of CaCO 3 precipi- t a t i o n b y p o l y m e r i c a d d i t i v e s . T h i s research is a part of an ongoing investiga- tion in understanding the role of soluble and insoluble impurities on the perfor - mance of scale inhibitors commonly used in water treatment formulations. Experimental Procedures Reagents-grade chemicals and Grade A glassware were used. A stock solution of calcium chloride (CaCl 2 ) was prepared using distilled water filtered through 0.22- µm filter paper. Stock solutions of sodium bicarbonate (NaHCO 3 ) and sodium car - bonate (Na 2 CO 3 ) were prepared on the day of each experiment. The additives tested were comm ercial mat erial s, and sto ck solutions with these additives were pre- pared on a dry weight basis. The desired c o n c e n tra t i o n s of th e a d dit iv e s w e re obtained by dilution. Table 1 lists the com- position, functional group, ionic charge, and acronym of each additive tested. The additives tested as CaCO 3 inhibitors vary significantly in terms of composition and ionic charge. The Fe 2 O 3 used in this study was charact eri zed by x-ray dif fraction (XRD) as hematite with some minor reflec- tions, which does not correspond to any indexed iron oxides. The particle size dis- tribution data as measured by a Beckman Coulter Counter (Model LS230 † ) revealed that the majority of Fe 2 O 3 particles were between 20 and 100 µm with the largest vol% at ~50 µm. The CaCO 3 precipitation experiments were conducted by adding a known volume of the sodium bicarbonate and sodium car- bonate stock solutions to a known volume of water in a 100-mL bottle. A known volume of CaCl 2 stock solution was added to this † Trade name. TABLE 1. ADDITIVES TESTED Additive Functional Group Ionic Charge* Molecular Weight Acronym Poly(acrylic acid) -COOH Negative 2k HP1 (A) Carboxymethyl inulin -COOH Negative 4.5k HP2 (B) Poly(2-ethyloxazoline) Neutral 5k HP3 (C) Poly(diallyldimethylammonium chloride) Positive 10k HP4 (D) Poly(methacrylic acid) -COOH Negative 5k HP5 (A) Poly(maleic acid) -COOH Negative <1k HP6 (D) Poly(acrylic acid:2-acrylamido-2-methylpropane sulfonic acid) -COOH, -SO 3 H Negative <15k CP1 (A) Poly(acrylic acid:2-acrylamido-2-methylpropane sulfonic acid:s-styrene) -COOH, -SO 3 H Negative <15k TP1 (A) Poly(acrylic acid:2-acrylamido:2-methylpropane sulfonic acid:s-acrylamide) -COOH, -SO 3 H Negative <15k TP2 (D) *At the pH of the working solution; SI = logIAP/Ksp, calcite (1.71); aragonite (1.61); vaterite (1.16) (A) K-752, K-766, K-775, K-798 (Carbosperse™ K-700 polymers supplied by The Lubrizol Corp.), (B) Dequest™, (C) PCI, (D) experimental.

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