Abstract:
Calcium and magnesium are two dominant species that contribute to water hardness.
The aim of this study was to develop a poly (vinylidene fluoride-co hexafluoropropylene) (PVDF-HFP) composite membrane for treatment of water
hardness. The synthesis of PVDF-HFP composite membranes was confirmed by X ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric
analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The
concentrations of the hardness causing agents in both the simulated and real hard
water samples were investigated in batch studies wherein parameters such as pH,
contact time, temperature, and adsorbent were optimised. The maximum adsorption
efficiency of 56 and 45 mg/g (evaluated by Langmuir isotherm) for Ca(II) and Mg(II)
ions were obtained. These were achieved at an optimum pH of 7 and adsorption
dosage of 0.5 mg/L using the 3% PVDF-HFP/cellulose acetate (CA) and 1% nitrogen
doped multiwalled carbon nanotubes (N-MWCNTs)/CA composite membranes
respectively. The adsorption kinetics and isotherm models were all consistent with the
pseudo-second order and Freundlich isotherm models for all the membranes
suggesting that the sorption process met heterogeneous adsorption. Furthermore, the
thermodynamic parameters indicated that the adsorption is physical and endothermic
in nature. Reusability studies showed that all the PVDF-HFP based membranes can
be recycled at least 3 times and for Ca(II) ions an adsorption loss of only 0.35 % was
recorded while using a 3% PVDF-HFP/CA composite membrane. These results were
further confirmed by XRD, TGA and inductively coupled plasma mass (ICP-MS)
spectrometry. Thus, the findings from this study have shown that the PVDF-HFP
based membranes could provide valuable material for hardness removal to acceptable
level.
