Application of the Fe₃O₄/alginate/diatomite nano-adsorbent for the adsorption of palladium and cyanide from wastewater: optimisation, kinetic and equilibrium studies

In this research, the adsorption rates of cyanide and palladium onto Fe3O4/alginate/diatomite nano-adsorbent (FADA) were evaluated. The co-precipitation technique was applied to synthesis of FADA. The response surface methodology (RSM) was employed to investigate the relation between input-independent factors (initial pollutant concentration, contact time, FADA dosage and pH) and one dependent output response (removal efficiency). The best model was selected based on the results of the ANOVA analysis.SO model due to R-2 of 0.929 and the insignificant lack of fit (0.12) for cyanide and also R-2 of 0.98 and the insignificant lack of fit (0.12) for palladium was selected as an appropriate model for adsorption of both pollutants. Therefore, prediction and optimisation of the adsorption of the pollutants onto FADAwere done based on SO model. The best conditions for the adsorption of cyanide (95.65%) and palladium (92.66%) onto FADA were obtainedat (pH, 5.45; palladium concentration, 15.13 mg L-1; contact time, 104.8 min and FADA dosage, 0.98 g L-1) and (pH,7.0; cyanide concentration, 4.88 mg L-1; contact time, 91.06 min and FADA dosage, 2.05 g L-1), respectively. Investigation of the non-linear isotherm models indicated adsorptions of cyanide (R-2 = 0.995) and palladium (R-2 = 0.999) ontoFADA have reasonably fit to the Sips model.The maximum adsorption capacities of cyanide and palladium per mass unit of FADA were 208.55 mg g(-1) and 60.2 mg g(-1), respectively.The pseudo-first-order (R-2 = 0.99) and the intra-particle diffusion (R-2 = 0.96) were found to agreement well with the adsorption experimental data obtained for cyanide and palladium, respectively. Results indicated the sorption reactions of cyanide and palladium onto FADA were endothermic and exothermic, respectively.The present study indicated diatomite magnano composite boosted with alginate polymer beads due to high operating groups and also a high surface-to-volume ratio and porosity can be applied as an efficient adsorbent for the removal of cyanide and palladium from aqueous solutions.