Comparison of adsorption affinity of anionic and cationic polyacrylamides for montmorillonite surface in the presence of chromium(VI) ions

Erosion, which is considered to be global problem, is the process of soil environment degradation due to the impact of wind (soil blowing, deflation) and water (soil washing, deep erosion). This leads to destruction of its structure, nutrients removal and finally bedrock exposition and desertification. One of the ways to prevent this phenomenon is the soil conditioners usage. These substances, also called soil flocculants, are macromolecular compounds which contribute to the reinforcement of soil structure as a result of its adsorption on the mineral surface. The soil conditioners commonly used in agriculture is ionic polyacrylamide (PAM)—both anionic and cationic. These macromolecular substances affect soil surface properties and adsorption behaviour of substances present in the environment—nutrients, organic molecules and also hazardous compounds as well as toxic heavy metals (i.e. chromium(VI) ions). The aim of this study was to investigate the impact of solution pH, type of ionic groups in the polyacrylamide macromolecules and chromium(VI) ion concentration on the adsorption mechanism of Cr(VI) and PAM on the montmorillonite surface. The adsorption and electrokinetic properties of the montmorillonite—AN PAM or CT PAM/Cr(VI) systems were examined by means of spectrophotometry, potentiometric titration, SEM, XRD and DRS methods. It was shown that in the adsorbed layer composed of PAM-Cr(VI) complexes reduction of Cr(VI) to Cr(III) takes place.