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

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.

Simultaneous Removal of Pb2+ and Zn2+ Heavy Metals Using Fly Ash Na-X Zeolite and Its Carbon Na-X(C) Composite

“…It is related to the decrease in the value of the surface charge density due to the formation of an additional number of negatively charged groups on the adsorbent surface. This phenomenon results from the interaction of metal cations with the solid surface groups, according to the equations [ 51 , 52 ]: −SOH + Pb 2+ ⇌ −SO − Pb 2+ + H + 2(−SOH) + Pb 2+ ⇌ (−SO − ) 2 Pb 2+ + 2H + −SOH + Pb 2+ + H 2 O ⇌ − SO − PbOH + + 2H + −SOH + Zn 2+ ⇌ − SO − Zn 2+ + H + 2(−SOH) + Zn 2+ ⇌ (−SO − ) 2 Zn 2+ + 2H + −SOH + Zn 2+ + H 2 O ⇌ −SO − ZnOH + + 2H + …”

Study of flocculation performance and mechanism of ultrafine montmorillonite particles with NPAM

“…Mpofu et al (Mpofu et al, 2004) studied the effects of PAM and non-ionic polyethylene oxide (PEO) structure types on the flocculation, interface chemistry, particle interaction and dehydration behavior of montmorillonite dispersion by means of electric potential measurement, rheology measurement and scanning electron microscopy. There are other studies that are similar (Akimkhan, 2013;Fijałkowska et al, 2019;McFarlane et al, 2008;Vanerek et al, 2006;Wiśniewska et al, 2019Wiśniewska et al, , 2018. Although a number of experiments have investigated the mechanism of interaction between polyacrylamide and montmorillonite surfaces, it would be much clearer if the interaction between polymers and solid surfaces could be visualized at the molecular level.…”

Comparison of Physicochemical Properties of Fly Ash Precursor, Na-P1(C) Zeolite–Carbon Composite and Na-P1 Zeolite—Adsorption Affinity to Divalent Pb and Zn Cations

“…The point of zero charge indicated the pH value at which the charge of the solid surface equals zero. At a pH higher than the pH pzc of the solid, its surface takes a negative charge, and correspondingly, at a pH lower than the pH pzc , the surface of the solid becomes a positive charge [49]. Despite the unfavorable electrostatic repulsion at pH 5, adsorption of cations occurs on positively charged solids due to the unique structure of zeolites.…”