Removal of Zn(II) ions from aqueous solutions by ethyl xanthate impregnated activated carbons

• Increasing loading capacity of origin AC(AC0) for Zn(II) after modification by potassium ethyl xanthate(PEX)
• Increasing loading capacity of base treated AC(ACB)&acid/base treated AC(ACAB) after modification by PEX
• Decreasing kinetics of Zn(II) adsorption onto ACB&ACAB after modification by PEX
• Modeling of the equilibrium & kinetic data for the adsorption of Zn(II) ions onto the PEX modified ACAB
• Assessment of adsorption mechanism of Zn(II) ions onto the modified AC through instrumental analysis

A coconut shell based granular activated carbon (AC) was aged in solutions containing different amount of potassium ethyl xanthate (PEX) for 24 h and then separated from the solutions, rinsed with distilled several times and used for Zn(II) ion removal. It was shown that the loading capacity of PEX impregnated AC at an initial Zn(II) concentration of 112 mg/L slightly increased by increasing PEX preloading, so that it increases from 1.56 to 1.88 mg/g by increasing the PEX concentration in the aging solution from zero to 200 mg/L.Aging of AC in 0.1 N sodium hydroxide solutions containing different amounts of PEX was also performed for 24 h and it was shown that the loading capacity of the resultant AC samples for Zn(II) ions at an initial Zn(II) concentration of 112 mg/L slightly increased by increasing PEX loading, so that it increases from 7.18 to 8.06 mg/g by increasing PEX concentration in aging solution from zero to 600 mg/L.Aging of nitric acid oxidized AC in 0.1 N sodium hydroxide solutions containing different amounts of PEX also performed for 24 h. It was shown that the loading capacity of these modified AC samples for Zn(II) ions at an initial Zn(II) concentration of 112 mg/L increased by increasing PEX loading, so that it increases from 15.11 to 16.43 mg/g by increasing PEX concentration in aging solution from zero to 1000 mg/L.It was revealed that the impregnation of AC samples with PEX results in the decreasing of adsorption kinetics of Zn(II) ions, since the hydrophobic nature of PEX molecules retards solution diffusion onto PEX impregnated AC samples.In order to get the highest Zn(II) loading capacity, the optimum condition for surface modification was determined to be oxidizing of AC with 4 M nitric acid solution and then aging in 0.1 M sodium hydroxide solution containing 661 mg/L PEX for 24 h. These surface modified activated carbons were named ACABPEX. The effect of Zn(II) initial concentration in the range of 59 to 165 mg/L on its adsorption kinetics and loading capacity onto ACABPEX was investigated. The equilibrium and kinetic data were best represented by the Koble–Corrigan isotherm model and the pseudo second order kinetic model, respectively. It was understood that three mechanisms play main roles in the adsorption of Zn(II) onto ACABPEX.