Attachment of APAM to mineral particles in seawater

Odd Gunnar Brakstad; Dag Altin; Marianne Aas; Jørgen Skancke; Trond Nordtug; Julia Farkas

doi:10.1016/j.scitotenv.2020.143888

Attachment of APAM to mineral particles in seawater

Sci Total Environ. 2021 Mar 1:758:143888. doi: 10.1016/j.scitotenv.2020.143888. Epub 2020 Dec 3.

Authors

Odd Gunnar Brakstad¹, Dag Altin², Marianne Aas³, Jørgen Skancke³, Trond Nordtug³, Julia Farkas³

Affiliations

¹ SINTEF Ocean AS, Environment and New Resources, Trondheim, Norway. Electronic address: odd.g.brakstad@sintef.no.
² BioTrix, Trondheim, Norway.
³ SINTEF Ocean AS, Environment and New Resources, Trondheim, Norway.

PMID: 33333302
DOI: 10.1016/j.scitotenv.2020.143888

Abstract

Polymer injection is used in enhanced oil recovery (EOR) when an oil field ages and the pressure in the reservoir decreases, or for oil fields with heavy oil. By polymer injection, the viscosity of the water injected for pressure support is increased by mixing with a high concentration of a polymer solution. Polymers used in EOR operations are often high molecular weight polyacrylamides, including anionic polyacrylamide (APAM), which may subsequently enter the marine environment with produced water releases. Since seawater (SW) contains mineral particles (MPs) in low concentrations, and polymers like APAM are known to flocculate MPs, we investigated if APAM at different concentrations (0.5-10 mg/L) would attach and flocculate MPs, when these occurred in concentrations relevant for oceanic SW (1 mg/L). Two types of MPs, diatomaceous earth and kaolin, were exposed to fluorescence-tagged APAM (APAM-TAG). A low-energy carousel system with natural seawater (SW) was used for incubation of MPs and APAM-TAG at a temperature relevant for the Norwegian Continental Shelf (13 °C). Attachment to MPs and aggregates of these were analysed by fluorometry and fluorescence microscopy. Particle analyses showed that only minor fractions of the MPs aggregated. When samples were separated in steel filter with a mesh size of 20 μm, APAM-TAG was mainly measured in the flow-through fraction (<20 μm), and the results therefore showed that the polymer mainly remained in the water-phase, or was attached to small particles (<20 μm). For the small fraction of APAM attaching to aggregated MPs, attraction to kaolin was higher than to diatomaceous earth, and fluorescence microscopy analyses confirmed the presence of fluorescent particles at the higher APAM concentrations. MPs at concentrations relevant for oceanic SW are therefore not expected to significantly contribute to sedimentation of APAM dissolved in the water column.

Keywords: APAM; Diatomaceous earth; Flocculation; Kaolin, attachment; Polymer.