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

Małgorzata Wiśniewska,Gracja Fijałkowska,Katarzyna Szewczuk-Karpisz,Grzegorz Wójcik,Teresa Urban,Agnieszka Nosal-Wiercińska

doi:10.1007/s10450-018-9990-x

Małgorzata Wiśniewska, Gracja Fijałkowska + Show 4 more

Open Access

https://doi.org/10.1007/s10450-018-9990-x

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Abstract

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.

Highlights

Dispersed colloidal particles of various minerals form the so-called soil sorption complex
(1) Higher adsorption of polyacrylamide on the montmorillonite surface is observed in the case of the polymer with a quaternary amine groups due to the more favourable electrostatic attraction occurring between the positively charged macromolecules and the negatively charged surface of montmorillonite
(3) Anionic and cationic PAM captures C rO42− and HCrO4− ions effectively from the solution by electrostatic attraction between the chromium(VI) anion and the cationic polymer quaternary amine groups as well as formation of hydrogen bonds between the PAM amide groups and the chromium(VI) ions which contributes to a significant increase in their adsorption

Summary

Introduction

Dispersed colloidal particles of various minerals form the so-called soil sorption complex. Silicates and products of their transformation—aluminosilicates form the main mineral component of soils. They are formed as a result of silicon, oxygen, metal ions, as well as water molecules binding. The structural unit of silicates is the silicate anion— SiO44− (Handke 2005; Sarbak 2009) A characteristic property of these minerals is the ability to exchange silicon atoms for aluminum ones in their crystal networks. As a result of this isomorphic substitution, minerals with an aluminum atom in the center of the tetrahedron (aluminosilicates) are created. Clay minerals which are hydrated aluminosilicates have a characteristic layered structure. Depending on the relative location of tetrahedral and octahedral units these minerals can be divided into the layered 2:1, 1:1 or amorphous aluminosilicates (Kunert and Zaborski 2006)

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