Adsorption of thorium (IV) ions by metal ion doped ZnO nanomaterial prepared with combustion synthesis: Empirical modelling and process optimization by response surface methodology (RSM)

Highlights: • Metal ion-doped nano ZnO (nano-ZnO:Al) material synthesized by the microwave-assisted gel combustion method. • Characterization techniques such as XRD, SEM, BET and zeta potential were performed to observe changes in the host ZnO adsorbent structure. • The adsorption capacity of Th(IV) was calculated. • The mechanism of Th(IV) adsorption was endothermic. • The CCD model was used and the F value according to the model was evaluated statistically. Environmental problems have reached enormous dimensions, driving efforts to remove and recycle waste from energy and industrial production. In particular, removing the radionuclide contamination that occurs as the nuclear industry grows is difficult and costly, but it is vital. Technologic and economical methods and advanced facilities are needed for the separation and purification of radioactive elements arising from the nuclear industry and uranium and thorium mining. With the adsorption method, which is the most basic separation and recovery method, the use of high-capacity nanomaterials has recently gained great importance in reducing the activity of the waste, reducing its volume by transforming it into solid form, and recovering and removing liquid radioactive wastes that might harm the ecological environment. This study aimed to determine the adsorption properties of metal ion-doped nano ZnO (nano-ZnO:Al) material synthesized by the microwave-assisted gel combustion method for the adsorption of thorium (IV) from aqueous media. First, characterization processes such as XRD, SEM, BET and zeta potential were performed to observe changes in the host ZnO adsorbent structure caused by the doping process. Later, this was optimized via the response surface method (RSM), which is widely used in the characterization of the adsorption properties of thorium (IV) from aqueous solutions. Such characterization is commonly used in industrial research. We tested how pH (3–8), temperature (20–60 °C), Th (IV) concentration (25–125 mg/L) and adsorbent amount (0.01–0.1 g) affect adsorption efficiency. The best possible combinations of these parameters were determined by RSM. It was calculated by RSM that the design fits the second order (quadratic) model using the central composite design (CCD) for the design of experimental conditions. R² and R² adjusted values from the parameters showing the model fit were 0.9923 and 0.9856, respectively. According to the model, the experimental adsorption capacity was 192.3 mg/g for the doped-ZnO nanomaterial under the theoretically specified optimum conditions. Also, the suitability of Th (IV) adsorption to isotherms was examined and thermodynamic parameters were calculated.