Chemical and electrochemical study of the inhibition of calcium carbonate precipitation using citric acid and sodium citrate

Abstract

A B S T R A C TThis work investigated the inhibitive effect of citric acid (CA), sodium citrate (SC), and their mixture (CA-SC) on the CaCO 3 scale. The study was carried out using chronoamperometry, impedancemetry, and fast-controlled precipitation methods. The electrochemical study showed that CA provides a slight inhibition of CaCO 3 deposit at a concentration of 70 ppm on stainless steel surface. The use of SC alone inhibits very little the formation of scale. The use of the mixture (50% of CA and 50% of SC) with small concentration led to significant inhibition of the CaCO 3 formation. The deposits formed were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The XRD showed that the intensity of the preferential orientation (1 0 4) corresponding to crystallographic plans of calcite decreases and the SEM demonstrated a decrease in calcite crystal size from 10 to about 2 μm.

Effect of CaO in the thermal crosslinking of maltodextrin and citric acid: A cooperative action of condensation and ionic interactions

“…The intensity of the band decreases when CaO is added to the system containing MAL and CA (MC). This may be a consequence of the ionic interactions between the Ca 2+ and the carboxyl groups of CA not involved in the ester formation with MAL . Apart from the CO stretching band, a new band at 1590 cm −1 assigned to carboxylate form can be clearly identified for the composition containing 3% of CaO.…”

“…According to the chelation activity of CA reported by Welling et al . a portion of Ca 2+ would form Ca‐Cit − complexes which later become calcium citrate tetrahydrate . The rest of Ca could interact with CA in the form of HCit 2— and H 2 Cit — .…”

“…This may be a consequence of the ionic interactions between the Ca 21 and the carboxyl groups of CA not involved in the ester formation with MAL. 24,32 Apart from the C@O stretching band, a new band at 1590 cm 21 assigned to carboxylate form 33,34 can be clearly identified for the composition containing 3% of CaO. This band may be assigned to the interaction of carboxyl groups of CA with Ca 21 , still remaining after purification.…”

“…According to the chelation activity of CA reported by Welling et al a portion of Ca 21 would form Ca-Cit 32 complexes which later become calcium citrate tetrahydrate. 24,32 The rest of Ca could interact with CA in the form of HCit 22 and H 2 Cit 2 . Furthermore, although it was not possible to prove, it is proposed that, as shown in Scheme 2, other interactions of Ca takes place with the free carboxyl groups of CA molecules which are attached to MAL chains by another carboxyl group.…”

“…For instance, it has been reported the use of metal ions as crosslinkers in polymer compositions containing poly(acrylic acid), by the interaction between the metal ions and the carboxyl groups of the poly(acrylic acid) . It is also well known the interaction of polycarboxylic acids with metal ions in water treatments and wine industry.…”