Effects of Polymer Molecular Weight on Adsorption and Flocculation in Aqueous Kaolinite Suspensions Dosed with Nonionic Polyacrylamides

Byung Lee,Mark Schlautman

doi:10.3390/w7115896

Abstract

The effects of polyacrylamide (PAM) molecular weights (MWs) on the PAM adsorption capacities and PAM-mediated flocculation of kaolinite suspensions were investigated using a series of nonionic PAMs with different MWs. Adsorption tests using aqueous kaolinite suspensions dosed with a series of PAMs with MWs of 1.5 kg/mol, 10 kg/mol, 0.6–1 Mg/mol, 5–6 Mg/mol, and 18 Mg/mol (referred to as 1.5 K, 10 K, 0.6–1 M, 5–6 M, and 18 M PAMs) indicated that the adsorption capacity of the kaolinite for PAM increased with increasing MW. However, the capacity for 18 M PAM was 20 times smaller than those for the 0.6–1 M and 5–6 M PAMs, although it has the highest MW. In steady-shear viscosity tests, a 1 g/L stock solution of 18 PAM was found to cause polymeric chain entanglements, which reduced the adsorption capacity. The 0.6–1 M and 5–6 M PAMs were further used in flocculation tests, in order to investigate the effect of PAM MW on the flocculation capability. The 5–6 M PAM was found to have higher flocculation capabilities than 0.6–1 M PAM; 5–6 M PAM was more subject to nonequilibrium flocculation, resulting in the development of unstable, stretched polymeric structures on solid surfaces and increasing particle-particle bridging and flocculation. Higher-MW PAMs are more effective flocculation agents, because of their higher adsorption capacities and flocculation capabilities. However, an extremely high-MW PAM, such as 18 M PAM, decreases adsorption/flocculation, and the preparation and handling of working solutions become difficult, because of polymeric chain entanglements.

Highlights

Soil erosion occurs in both urban and rural areas during storm events
5–6 M PAMs were further used in flocculation tests, in order to investigate the effect of PAM molecular weights (MWs) on the flocculation capability
The purpose of this research was to investigate the effect of PAM MW on adsorption, reconfiguration, and flocculation in aqueous kaolinite suspensions dosed with a series of nonionic PAMs with different

Summary

Introduction

Soil erosion occurs in both urban and rural areas during storm events. Colloidal-size clay particles are generally the most problematic soil particles, and if not controlled, they can enter various receiving water bodies, where the materials they carry (nutrients, toxicants, pathogens, etc.) can contribute to siltation of bottom sediments, algal blooms, oxygen depletion, and food-chain problems [1,2,3]. A series of physicochemical processes, such as adsorption, reconfiguration, and flocculation, occur in clay suspensions dosed with polymers [8]. The adsorption of polymeric molecules on clay particles is the first step, triggering reconfiguration and flocculation. Reconfiguration of the adsorbed polymeric molecules occurs on the clay particles. The adsorbed polymeric molecules reconfigure themselves as either flocculation-active standing or flocculation-inactive flat configurations on the clay particle surfaces, depending on the PAM

Objectives

Methods

Results

Conclusion