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

In an attempt to control Ca 3 (PO 4 ) 2, CaCO 3, and CaSO 4 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 Ca 3 (PO 4 ) 2, CaCO 3, and CaSO 4 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% CaSO 4 inhibition and 99.89% Ca 3 (PO 4 ) 2 inhibition at levels of 3 and 6 mg/L AA–APEC, respectively. AA–APEC also displayed ability to prevent the formation of CaCO 3 scales. Transmission electron microscopy (TEM) images indicated that the outstanding performance of AA–APEC on Ca 3 (PO 4 ) 2 inhibition resulted from a decrease in size of Ca 3 (PO 4 ) 2 solid particles thereby dispersing these particles throughout a fluid, while CaCO 3 inhibition was attributed to the formation of ribbon-shaped structures and CaSO 4 inhibition resulted from loose CaSO 4 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.