Cadmium and lead remediation using magnetic and non-magnetic sustainable biosorbents derived from Bauhinia purpurea pods

Abstract

Bauhinia purpurea (Kaniar) pods were dried, powdered, and utilized for cadmium and lead removal. Bauhinia purpurea (Kaniar) pod powders (KPP) were converted into magnetic Bauhinia purpurea (Kaniar) powders (MKPP) by co-precipitation. Iron(II) sulfate and iron(III) sulfate were used as iron precursors. The biosorbents were extensively characterized using zero point charge measurements (pH_PZC), ultimate and proximate analyses, Fourier transform infrared (FTIR) and FT-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), BET surface area (S_BET) measurements, physical properties measurement system (PPMS), scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (EDXRF) techniques. The S_BET of MKPP (52.0 m² g⁻¹) was higher than KPP (1.8 m² g⁻¹). Optimum Cd²⁺ and Pb²⁺ removal by KPP and MKPP was obtained at pH 5.0 and 4.5, respectively. Metal–ligand chelation, ion-exchange and hydrogen bonding were possible mechanisms for Cd²⁺ and Pb²⁺ removal. KPP and MKPP showed maximum Langmuir adsorption capacities of 11.1 and 4.8 mg g⁻¹ for Cd²⁺ and 16.4 and 14.1 for Pb²⁺, respectively. Lead and cadmium kinetic data were best described using a pseudo-second-order equation. Cd²⁺ and Pb²⁺ removal was affected by the presence of Cu²⁺ during adsorption from a multicomponent aqueous environment. Cd²⁺ and Pb²⁺ remediation from actual groundwater was demonstrated. Fixed-bed studies for Pb²⁺ removal by KPP were also performed with a column capacity of 18.8 mg g⁻¹ (column dia 2.0 cm; column length 40 cm; bed height 6.0 cm; pH 4.5; flow rate 5.0 mL min⁻¹; Pb²⁺ conc. 10 mg L⁻¹). Spent KPP was regenerated using 0.1 N HCl. Approximately 85% of total Pb²⁺ recovery was achieved using 100 mL 0.1 N HCl.