Variation in the Adsorption of Lead(II) by a Range of Electrolytic Manganese Dioxides: Chemometric Examination of Correlation with Physical Properties

Abstract

The adsorption of lead(II) by a range of ‘boutique’ electrolytic manganese dioxide (EMD) samples which differ in a range of physical properties has been followed at pH 5, 20°C and an ionic strength of 0.5, employing a wide range of initial lead ion concentrations from 5 × 10⁻⁵ mol/dm³ to 5 × 10⁻² mol/dm³. Adsorption isotherms all fitted quite well to a simple Langmuir adsorption equation. The Langmuir parameters vary significantly for the different samples and good correlations between them and some physical properties (% water content, open circuit voltage and average crystallite size) are apparent. Further, Principal Component Regression (PCR) reveals excellent correlations between the lead(II) adsorption isotherms and some of the physical properties (water content, average crystallite size, density, total pore volume, electric conductivity, porosity, etc). A qualitative understanding of the relationship between the isotherms and the physical properties can be achieved. Adsorption of lead on partially chemically reduced EMD samples falls as the degree of reduction increases, associated with a drop in available hydrolysable surface groups with increasing degree of reduction.