Adsorption Isotherm Kinetics of Cu2+, Pb2+ and Cd2+ onto Mukurweini’s Raw Kaolinite and Alkali Modified Kaolinite

Abstract

It is essential to remove heavy metal ions from industrial or domestic waste before they are released into water sources, as their presence in water, even in small concentrations, is a significant environmental concern. Industrial, domestic, and agricultural activities are the primary sources of heavy metal ion contamination in water sources. This study sought to find the best-fitting isotherm and kinetic models, and to evaluate the thermodynamic feasibility, the study used Mukurweini Kaolinite and alkali-modified Kaolinite for lead, copper, and cadmium adsorption from an aqueous solution using a batch adsorption process. Two samples of raw clay earthly mineral each weighing 3 kg were excavated from Mukurweini using a shovel (grid method). The samples were further processed by separate calcination at 700°C in a furnace at for 2 hours that maximised dehydroxylation reactions within the clay material. One sample (3 kg), was converted to Alkali modified kaolinite (AMK) by weighing out 50 g of the freshly calcined brown clay material and subsequently modified using NaOH (v=50 mL; c= 7 mol. L-1) in an orbital shaker under agitation for 30 minutes at a temperature of 60°C to obtain a homogenous paste. The calcined raw and alkali modified kaolinite samples were separately placed in a pressure cooker, heated for 3 hours, washed with ethanol, oven-dried at 110°C for 1 hour, and finally activated in a muffle furnace at 700°C for 2 hours. Of the three isotherm models investigated (Langmuir, Freundlich, and Temkin), the Freundlich model gave the best fit to the experimental data. The result of kinetic studies indicated that the adsorption process followed a pseudo-second-order, spontaneous physical progression.