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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52 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 CHEMICAL TREATMENT D The infuence of iron oxide (Fe 2 O 3 ) on the performance of calcium carbon- ate (CaCO 3 ) inhibitors was investigat- ed. Results show that the addition of a small amount (10 to 100 mg) of Fe 2 O 3 to the CaCO 3 supersaturated solution exhibits a marked antagonistic effect on inhibitor performance. Part 1 of this article describes the experimen- tal work and Part 2 (December 2014 MP) will cover the effects on the in- hibitors. Deposition of various types of mineral scales on heat exchangers and reverse o sm o si s ( RO ) m e m bra n e s i s a m aj o r problem in water treatment processes such as boiler, desalination, geothermal, and oil pro duction . Min eral scal e s c ommonly e n c o u n t e re d i n i n d u s t r i a l p r o c e s s e s include carbonate, sulfate, phosphate, and f luoride salts. The problem of calcium c a r b o n a t e ( C a C O 3 ) s c a l e i s m o r e pronounced at ele vat ed t emp eratures, since the solubility of scaling salt decreases with increasing temperature. Also, scaling is often accompanied by corrosion, which leads to damage of metallic parts. In many instances, scale removal leads to the break- down of systems. 1 CaCO 3 is one of the most commonly encountered scale deposits in industrial water systems. It occurs in different crys- talline forms: calcite, aragonite, vaterite, CaCO 3 monohydrate, and CaCO 3 hexahy- drate. 2 The precipitation and stabilization of these deposits depends upon precipita- tion conditions such as degree of supersat- uration, pH, ionic medium, and concentra- tion and type of impurities. 3 O ver the years, various approaches have been tried to prevent the precipitation and deposition of CaCO 3 . These include: • The addition of acid to control pH • The use of a sequestering or complex- ing agent • Operation of the system at reduced recovery or cycle of concentration • The use of a precipitation inhibitor or antiscalant The influence of polymeric inhibitors to p re v e n t o r re t a rd C a C O 3 s c a li n g h a s attracted the attention of researchers. Common inhi bitors e valuat ed include homopolymers of aspartic acid , acr ylic acid , maleic acid , itaconic acid , meth- acrylic acid, and copolymers containing maleic acid or acrylic acid and other mono- m e r s c o n t a i n i n g di f f e re n t f u n c t i o n a l groups. Evaluation of these and several other mineral scale inhibitors suggests that inhi bitor ef fe c tiv en e ss d e p en d s up on molecular weight (MW), functional groups, and composition. 4 Suspended solids such as clay, corro- sion products, silica, algae, bacteria, and metal carbonates are commonly encoun- tered in feed or recirculating waters; they are not completely soluble and are present as particles. These suspended particles lead to high turbidity and also provide a Impact of Iron Oxide on Calcium Carbonate Inhibitors— Part 1 Zahid amjad and jeremy L. Penn, Walsh University, North Canton, Ohio

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