Inhibition of Ca₃(PO₄)₂, CaCO₃, and CaSO₄ Precipitation for Industrial Recycling Water

In an attempt to control Ca3(PO4)2, CaCO3, and CaSO4 deposits in industrial recycling water systems, an acrylic acid (AA)–allylpolyethoxy carboxylate (APEC) copolymer was examined as a nonphosphorus inhibitor. The synthesized AA–APEC copolymer was characterized by FT-IR. The performance of AA–APEC on inhibition of Ca3(PO4)2, CaCO3, and CaSO4 precipitation was compared with that of current commercial inhibitors. It was shown that AA–APEC exhibited excellent ability to control inorganic minerals, with approximately 82.88% CaSO4 inhibition and 99.89% Ca3(PO4)2 inhibition at levels of 3 and 6 mg/L AA–APEC, respectively. AA–APEC also displayed ability to prevent the formation of CaCO3 scales. Transmission electron microscopy (TEM) images indicated that the outstanding performance of AA–APEC on Ca3(PO4)2 inhibition resulted from a decrease in size of Ca3(PO4)2 solid particles thereby dispersing these particles throughout a fluid, while CaCO3 inhibition was attributed to the formation of ribbon-shaped structures and CaSO4 inhibition resulted from loose CaSO4 crystallites speculated on scanning electron microscopy (SEM) images. The proposed inhibition mechanism suggests the formation of complexes between the side-chain carboxyl groups of AA–APEC and calcium ions on the surface of inorganic minerals, and the excellent solubility of complexes resulted from a number of hydrophilic polyethylene glycol (PEG) segments.