Simultaneous removal of silica and TOC from steam assisted gravity drainage (SAGD) produced water using iron-hydroxide-coated walnut shell filter media

Abstract

Extracting Alberta’s bitumen by SAGD requires a growing supply of steam, which is mainly generated from recycled produced water (PW). Traditionally, a warm lime softener (WLS), followed by walnut shell filter (WSF) and weak acid cation exchange (WAC) units have been employed to minimize the concentrations of silica, TOC, and hardness from PW. In this study, we enhanced TOC and silica removal in a WSF unit by modifying the surface of the walnut shell media. The walnut shells were modified by anchoring low mass percentages (e.g., < 5 wt%) of iron(hydroxide) nanoparticles under moderate hydrolysis conditions. The nanoparticle-anchored walnut shell particles (WS-NPs) were fully characterized, and their ability to remove TOC and silica was tested using batch and column experiments. In the batch tests, up to 85 % of silica and TOC was removed. In the column tests, which mimicked industrial operations, WS-NPs significantly improved the breakthrough behavior without reaching pressure drop limitations. The column breakthrough behaviors were successfully described by a dimensionless advection-axial dispersion model. The model accurately captured the commercial breakthrough behavior, indicating the possibility of scaling up the filter using a combined unit that removes silica and TOC simultaneously without using WLS and WAC.