Exploring the applicability of a geopolymer and a biopolymer as an environmentally benign treatment option for heavy metals contaminated water

Background: Two environmentally friendly materials (lateritic clay-based geopolymer; LGP and Grewia biopolymer; GBP) were successfully processed from the locally available resources in Cameroon and their applicability for removal of Ni(II) and Co(II) from aqueous solution was explored.Methods: The materials were characterized by FTIR, BET, XRD, Zeta potential and SEM. Metal ion concentrations were quantified using ICP-OES.Significant Findings: Crystalline LGP showed higher specific surface area (73.32 m2/g) than GBP (22.73 m2/g). Removal of Ni (19.62%) and Co (22.22%) (initial metal ion concentrations 5 mg/L) achieved using LGP (2 g/L) were lesser than that achieved using GBP (0.6 g/L) (60.15%, and 57.68%, respectively) at the identical conditions. Higher adsorptive capacity of GBP was ascribed to the presence of negatively charged groups (glucuronic, galacturonic) in its structure. Langmuir and Dubinin-Radushkevic adsorption isotherm models fit well to Co(II) and Ni(II) removal data on LGP (R2 = 0.989 and 0.949, respectively). However, Freundlich isotherm renders best fit for both ions (R2 = 0.969 and 0.989, respectively) using GBP. Combined use of the adsorbents showed much higher removal efficiency (~80%) for both the metal ions (pH 5) indicating that LGP and GBP can be used together to achieve better removal of heavy metals from contaminated water.