Removal of Zn(II) ions from aqueous solution using Moringa oleifera Lam. (horseradish tree) biomass

The removal of Zn(II) ions from aqueous solution using pure and chemically pretreated biomass of Moringa oleifera was investigated at 30 ± 1 °C in this study. The experimental results explored that the maximum pH (pHmax) for efficient sorption of Zn(II) was 7 ± 0.1 at which evaluated biosorbent dosage and biosorbent particle size, were 0.5 g/L, <0.255 mm, respectively. The cellular Zn(II) concentration increased with the concentrations of Zn(II) in solution. Pretreatment of M. oleifera biomass affected the sorption process and the uptake capacity (mg/g) of biomass for Zn(II) uptake was in following order: NaOH (45.76) > H2SO4 (45.00) > CTAB (42.80) > Ca(OH)2 (42.60) > Triton X-100 (42.06) > H3PO4 (41.22) > Al(OH)3 (41.06) > SDS (40.41) > HCl (37.00) > non-treated biomass (36.07). There was significant increase in uptake capacity of M. oleifera biomass, which suggested that affinity between metal and sorbent can be increased after some sort of pretreatment. Both Langmuir and Freundlich isotherm model fitted well to data of Zn(II) biosorption as represented by high value of their correlation coefficient (i.e. R2 ≈ 1). Kinetic studies revealed that Zn(II) uptake was fast with 90% or more of uptake occurring with in 40 min of contact time and the equilibrium was reached in 50 min of contact time. The sorption rates were better described by a second order expression than by a more commonly applied Lagergren equation. Finally it was concluded that pretreatment of M. oleifera biomass can achieve superior Zn(II) uptake capacity in comparison to non-pretreated biomass.