Modified strawberry calyx as an efficient adsorbent for Ni(II) ions adsorption: a central composite design approach for multivariate sorption optimization

In this study, strawberry calyx waste was converted to efficient adsorbent by treating with 0.5 mol L-1 HCl for the uptake of Ni(II) ions from environmental aqueous samples. Multivariate sorption optimization was carried out by the central composite design model, contained 18 experiments. Removal of Ni(II) ions was achieved 98.5% with relative standard deviation (RSD) <= 3.5% at optimum pH 8.0, sorbent dose 70 mg, concentration of Ni(II) ions 50 mg L-1, shaking speed 100 rpm and shaking time 95 min at temperature 25 degrees C. The different interactive effects of two factors on the response were studied simultaneously. Analysis of variance reveals that the numerical value of P is <= 0.05 for all effects except the effect of adsorbent dosage and shaking time which indicated that all the null hypotheses are rejected except the interactive effect of adsorbent dosage and shaking time. Langmuir and Dubinin-Radushkevich isotherms fitted well to adsorption data with correlation coefficient (R-2) of 0.995 and 0.989, respectively. Monolayer sorption capacity of adsorbent for the uptake of Ni(II) ions was found to be 45.3 +/- 2.4 mg g(-1). The sorption energy was found to be 14.81 +/- 1.5 kJ mol(-1) which indicated that Ni(II) ions were adsorbed onto the adsorbent by chemisorption or ion exchange mechanism. The method was applied on real environmental aqueous samples for the removal of Ni(II) ions.