Particle build-up on gas-solid fluidization column wall due to electrostatic charging causes significant operational challenges including reactor shutdown in industrial processes such as gas-phase ethylene polymerization to produce polyethylene. It is well acknowledged that in fluidization process electrostatic charges are generated as a result of continuous particle-particle and particle-vessel wall contacts. However, the mechanism of charged particle attraction towards the fluidization column wall and their adhesion has received minimal attention. This work proposes a mechanism for particle build-up on the column wall by experimentally investigating the fouled particles charge distribution using a charged particle separator apparatus. The experiments were carried with two types of linear low-density polyethylene resins in a pressurized pilot-scale gas-solid fluidization system. Experimental results showed that the polyethylene layer built-up on the column wall contained both positively and negatively charged particles. A mechanism was proposed indicating that charged particle migration towards the metallic column wall was due to the image and electrostatic forces. The image forces were attributed to the particle -wall contacts while the electrostatic forces were between the charged particles fouled on the column wall and those oppositely charged within the bulk of the bed. In addition, the net space charge of the bulk particles contributed to the migration of the particles towards the column wall. (C) 2017 Elsevier B.V. All rights reserved.