Selective adsorption of Co(II)/Mn(II) by zeolites from purified terephthalic acid wastewater containing dissolved aromatic organic compounds and metal ions

Abstract

Selective separation and recovery of Co(II)/Mn(II) from purified terephthalic acid (PTA) production wastewater is very important to reduce the Co(II)/Mn(II) catalysts consumption and control the pollutant discharge. This work employed zeolites NaA, NaX, and HZSM-5 with different pore sizes and Na(I) contents to selectively separate and recover Co(II)/Mn(II) from PTA wastewater and to understand the adsorption mechanism. It is found that only NaA can exclusively adsorb Co(II)/Mn(II) through ion-exchange without adsorbing any aromatic organic compound (AOC); oppositely, HZSM-5 shows the highest adsorption capacity for AOCs but almost no adsorption for Co(II)/Mn(II); and NaX exhibits moderate adsorption capacities for both Co(II)/Mn(II) and AOCs. Moreover, pH can significantly impact the adsorption of both Co(II)/Mn(II) and AOCs due to the competitive adsorption between H(I) and Co(II)/Mn(II) and the electrostatic repulsion between AOCs and zeolites. The adsorption kinetics, isotherms, and thermodynamics were also investigated to lay a good basis for process development. Importantly, bench-scale experiments for simulating the industrial operation were carried out, and the results show that the adsorption capacity of the NaA particles for Co(II)/Mn(II) from the industrial PTA wastewater is 9.1/8.6 mg/g, respectively, without adsorbing any AOC. Therefore, an efficient strategy to selectively separate and recover Co(II)/Mn(II) from PTA wastewater was successfully developed.