Kinetics of the bioremoval of selected heavy metal ions from wastewater by the application of modified Nigerian Bambara groundnuts shells

Abstract

Nigerian Bambara Groundnut Shells (BGS) were modified to obtain Raw Bambara Groundnut Shell (RBGS), Carbonized Bambara Groundnut Shell (CBGS) and Bambara Groundnut Shell Lignin (BGSL) and used as bio-adsorbents to remove Lead (Pb), Nickel (Ni) and Cadmium (Cd) ions from industrial wastewater. The adsorption study investigated the effects of bio-adsorbent dosage, wastewater pH and contact time. Preliminary analyses which include: an Atomic Adsorption Spectrophotometer (AAS) on the wastewater and Scanning Electron Microscopy (SEM) were carried out on the different modified BGS, while the mechanism of adsorption was described using adsorption kinetic models. AAS analysis revealed that the concentrations of the heavy metals of interest were above WHO permissible limits in wastewater. SEM analysis revealed that the microspores of the bio-adsorbents were covered after the adsorption process. After the adsorption process, 85 – 91% Pb and 80 – 85% Ni and 92 - 98% Cd were removed by the different bio-adsorbents at optimum conditions of adsorption capacity which occurred at 0.8g dosage, pH of 7 and 120 min contact time. Generally, equilibrium occurred within 90 minutes. The mechanism of Pb, Ni and Cd ions adsorption onto RBGS, CBGS and BGSL bio-adsorbents can be described with diffusion and chemisorption processes. Pseudo-second-order kinetics fitted the adsorption process, implying that it is the rate-controlling step. This study found that the modified Bambara groundnut shell bio-adsorbents can be used as an alternative to conventional adsorbents used to treat industrial wastewater effluent