Adsorption of CdII by synthetic zeolite under multi-factor using response surface methodology

The remediation of heavy metal contamination was urgent owing to their toxicity and non-biodegradability. In this study, a synthetic zeolite originated from natural low-grade molybdenum ore (NMO) was used to adsorb CdII from wastewater under simulated multi-environmental factors. X-ray diffraction spectroscopy proved that faujasite was successfully synthesized. The specific surface area of the synthetic zeolite was up to 652.3 m2/g, based on the nitrogen adsorption and desorption isotherms. X-ray photoelectron spectroscopy confirmed that ion-exchange was a major mechanism of CdII adsorption. Batch adsorption experiments showed that synthetic zeolite has an excellent adsorption capacity for CdII at pH above 4. The theoretical maximum adsorption capacity was 249.63 mg/kg, as evidenced by the adsorption model fitting. Systematic adsorption experiments showed that the quadratic regression model can be used to predict the CdII adsorption amount of synthetic zeolite (predicted r² = 0.9027) under six environmental factors. The fitted results showed a decreasing influence on adsorption capacity in the following order: CdII concentration > adsorbent dosage > CaII concentration > NaI concentration > pH > Temperature. In all, the synthetic zeolite has a great potential for treating CdII-containing wastewater. Especially the application could be optimized with the predicted adsorption based on the response surface plots.