Enhanced copper pyrophosphate complex removal from high salty wastewater by using nanoconfined Ti-Zr binary metallic oxides: Multivariate complexation mechanism

The salt ions (typically > 1000 mg/L) present in copper plating wastewater limit the application of ion exchange in the deep treatment of copper complexes (such as copper-pyrophosphate (Cu-PPi)). Metal nanoparticle immobilization is an effective method, and bimetallic nanoparticles have more potential than monometallic ones. In this study, bimetallic nanocomposite Ti-Zr-201 was successfully synthesized by confining Ti-Zr oxide nanoparticles in the pores of anion exchange polymer (D201). The obtained new adsorbent Ti-Zr-201 with bimetallic doped structure had more active sites (7.22 mmol/g), higher hydroxyl content (3.51 × 10²² OH/ nm²) and larger specific surface area (31.65 m²/g) than monometallic nanocomposite adsorbents (Zr-201 and Ti-201). The results showed that Ti-Zr-201 has better Cu-PPi adsorption capacity (24.82 mg Cu/g) than Zr-201 (21.48 mg Cu/g) and Ti-201 (21.71 mg Cu/g) in the high salt water (2000 mg/L NO₃^–). Further mechanistic studies revealed that Cu-PPi removal as a whole was mainly realized via ternary complexation (Ti/Zr-O-Cu-PPi of Type-A, Ti/Zr-O-PPi-Cu of Type-B) and quaternary complexation (Ti/Zr-O-PPi-Cu-PPi of Type-B) both formed during the adsorption. The saturated Ti-Zr-201 can be regenerated more than 90% rapidly and had good stability. Moreover, the novel adsorbent also had a excellent removal effect on several other phosphorous copper complexes (tripolyphosphate, methyl dihydrogen phosphate, etc.). Therefore, the nanocomposite Ti-Zr-201 exhibited promising application on the deep removal of complex-state Cu with phosphorus ligands from high salty wastewater.