A Comparative Performance Evaluation of Some Novel “Green” and Traditional Antiscalants in Calcium Sulfate Scaling

Abstract

A relative ability of industrial samples of four phosphorus-free polymers (polyaspartate (PASP); polyepoxysuccinate (PESA); polyacrylic acid sodium salt (PAAS); copolymer of maleic and acrylic acid (MA-AA)) and of three phosphonates (aminotris(methylenephosphonic acid), ATMP; 1-hydroxyethane-1,1-bis(phosphonic acid), HEDP; phosphonobutane-1,2,4-tricarboxylic acid, PBTC) to inhibit calcium sulfate precipitation is studied following the NACE Standard along with dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) technique. For the 0.5 mg·dm−3dosage, the following efficiency ranking was found:MA-AA~ATMP>PESA (400–1500 Da)>PASP (1000–5000 Da)≫PAAS (3000–5000 Da)~PBTC~HEDP. The isolated crystals are identified as gypsum. SEM images for PESA, PASP, PAAS, and HEDP and for a blank sample indicated the needle-like crystal morphology. Surprisingly, the least effective reagent PBTC revealed quite a different behavior, changing the morphology of gypsum crystals to an irregular shape. The DLS experiments exhibited a formation of 300 to 700 nm diameter particles with negativeζ-potential around −2 mV for all reagents.Although suchζ-potential values are not capable of providing colloidal stability, all three phosphonates demonstrate significant gypsum particles stabilization relative to a blank experiment.

Insight into the Mechanisms of Scale Inhibition: A Case Study of a Task‐Specific Fluorescent‐Tagged Scale Inhibitor Location on Gypsum Crystals

“…HEDP‐F was tested for fluorescent activity and gypsum scale inhibition efficacy, following the National Association of Corrosion Engineers (NACE) Standard TM0374‐2007 . HEDP‐F is found to have emission and excitation spectra quite similar to those obtained for polyacrylate‐tagged 1,8‐naphtalimide (PAA‐F1),, Table , while its antiscaling efficacy relative to gypsum deposition was very close to that one of HEDP, Table .…”

DLS study of a phosphonate induced gypsum scale inhibition mechanism using indifferent nanodispersions as the standards for light scattering intensity comparison

“…At the same time, we have found for a gypsum scale in the NACE brines that the more effective antiscalants do not change the morphology of gypsum, while the less effective one (phosphonobutane-1,2,4-tricarboxylic acid, PBTC) does [19]. As far as the change of the crystal morphology is usually interpreted as a direct approval of the inhibition mechanism, one could expect that the most effective antiscalant should cause the maximal distortion, while the least effective one would reveal the minimal change in the crystal morphology if any.…”

“…However, our recent observation of zeta-potentials of CaCO 3 and CaSO 4 ·2H 2 O scales [18,19] formed in NACE brines [20] in the presence of conventional inhibitors, reveal that antiscalants do not change the interfacial electrostatic charge values relative to the blank solutions. Moreover, the zeta-potentials for all reagents appear to be insufficient to prevent scale particles aggregation.…”

“…Formation of calcium complexes with an antiscalant molecule under a large excess of calcium ions in the systems studied [18,19] is also an inadequate explanation for scale formation inhibition in NACE brines. In [18,19] we have supposed that the possible mechanism of scale inhibition in a bulk solution is associated with the reduction of initial number of nucleation centers.…”

“…In [18,19] we have supposed that the possible mechanism of scale inhibition in a bulk solution is associated with the reduction of initial number of nucleation centers.…”