Adsorption behavior and mechanism of mixed heavy metal ions by zeolite adsorbent prepared from lithium leach residue

Zeolite NaA was prepared from lithium leach residue (LLR) via the traditional hydrothermal synthesis method. The adsorption characteristics of zeolite on Pb2+ and Cd2+ were lucubrated to solve the problems caused by heavy metal wastewater and industrial waste LLR. The influence factors in the synthesis process were systematically explored. The cubic zeolite NaA was synthesized at 100 °C for 12 h when n(SiO2)/n(Al2O3) was 2 and the alkalinity was 60 g/L. The performance of zeolite NaA to adsorb Pb2+ and Cd2+ in the mixed solution was also assessed in detail. Results showed that zeolite NaA had excellent adsorption property for Pb2+ and Cd2+, and the maximum adsorption capacities of Pb2+ and Cd2+ were 487.805 and 193.798 mg/g. Moreover, the initial pH value of the solution and the adsorbent dosage greatly influenced the removal rates of Pb2+ and Cd2+. The isotherm and kinetic analysis of the adsorption process revealed that Langmuir model and pseudo-second-order model agreed well with the adsorption process. The adsorption mechanism was accredited to the ion exchange and hydroxyl groups on the zeolite NaA surface. This work provided a rational process route of synthesizing zeolite NaA adsorbent from LLR, and it was well applied to the removal of Pb2+ and Cd2+.