Contrastive analysis of nickel (II), iron (II), copper (II), and chromium (VI) removal using modified Chlorella vulgaris and Spirulina platensis: Characterization and recovery studies

The concurrent removal of Nickel (II), Chromium (VI), Iron (II), and Copper (II) using chemically modified Chlorella vulgaris and Spirulina platensis biomass from water has been studied. The Brunauer-Emmett-Teller (BET) revealed surface areas of 10.9, 9.6, 14.0, and 17.5 m(2)/g for the modified biosorbents CV-NC, CV-KC, SP-KC, and CV-KC respectively while the unmodified biosorbents were 1.5 and 2.7 m(2)/g for CV and SP respectively. The maximum removal efficiencies of Ni (II), Fe (II), Cr (VI), and Cu (II) ions from the multi-metal biosorption media were 100%, 96%, 85%, and 57% respectively. Similarly, the optimum pH conditions for maximum removal of Ni (II), Fe (II), Cr (VI), and Cu (II) were pH 5, 2-3, 2, and 6 respectively using a biosorbent dosage of 0.3 g and at a temperature of 25 degrees C. The maximum biosorption capacities were 16.2, 14.2, 26.7, and 9.4 mg/g for CV-NC, CV-KC, SP-KC, and CV-KC, respectively. The Fourier transform infrared (FTIR) spectra showed the presence of amide peaks (1659-1535 cm(-1)) which improved the metal removal efficiency. The Energy dispersive spectroscopy (EDS) data showed the presence of Na+, Ca2+, Mg2+, and K+ cations in both algae species which promoted the binding properties of the biosorbents. The equilibrium data were best modelled by Langmuir > Freundlich > Temkin models respectively. The Freundlich constant n values were between 1.52 and 7.38, suggesting favourable biosorption. The Gibbs free energy (delta G degrees) values for Ni (II) were from 0.9 to 5.8, Cu (II) from 6.6 to 9.9, Cr (VI) from 4.3 to 5.9, and Fe (II) from 0.5 to 3.4 kJ/mol which confirmed physisorption. Cu (II) showed the maximum desorption of 56.1% (HNO3) and 47.3% (H3PO4) from the spent SP-KC and SP-NC respectively. This study has shown that modified algae biomass is suitable for the effective removal of multi-metal ions from water.