Succinylated Salvia spinosa hydrogel: Modification, characterization, cadmium-uptake from spiked high-hardness groundwater and statistical analysis of sorption data

Herein, we synthesized sodium salt of succinylated Salvia spinosa hydrogel (NaS-SSH), a novel and green polysaccharide-based ion-exchanger for cadmium uptake from deionized water (DW) and spiked high-hard ground water (HGW). The S. spinosa hydrogel (SSH), succinylated SSH (S-SSH) and its sodic form (NaS-SSH) were characterized through Fourier transform infrared spectroscopy, solid-state CP/MAS 13C-NMR spectroscopy, scanning electron microscopy-energy dispersive spectroscopy, and thermogravimetric analysis. The surface charge on NaS-SSH was calculated by performing point of zero charge pH, i.e., pHZPC analysis and it was found to be 4.77 ± 0.35. Cd(II) uptake efficiency of NaS-SSH was accessed on pH (1–7), sorbent dosage (10–90 mg/100 mL), initial concentration of Cd(II) ions (10–250 mg L−1), contact time (5–150 min), and temperature (298–338 K). Sorption data fitted well to Langmuir isothermal model and sorption maxima (Qmax) was calculated as 344.83 mg g−1 for DW and 312.5 mg g−1 for HGW and found comparable with the experimental sorption capacities. The sorption kinetics followed the pseudo-second-order kinetic model and occurred through the exchange of ions via chemisorption. Thermodynamics of the sorption process was judged through negative values of thermodynamic triplets (ΔG°, ΔH°, and ΔS°) and revealed spontaneous and exothermic in nature. Competitive studies indicated the potential of NaS-SSH for metal removal from a binary mixture of Ni(II)-Cd(II). Moreover, NaS-SSH was regenerated and could be used over several repetitive cycles. Comparing the sorption efficiency of NaS-SSH with already reported succinylated biosorbents having similar structural features, it was noted that our developed biosorpbent is more effective for Cd(II) uptake.