Insights into Activation Pathways of Recovered Carbon Black (rCB) from End-of-Life Tires (ELTs) by Potassium-Containing Agents

Abstract

This study explores the conversion of recovered carbon black (rCB) from end-of-life tires (ELTs) into activated carbons (ACs) using potassium-based activators, targeting enhanced textural properties development. The research focuses on the interaction between potassium and rCB, with the aim of understanding the underlying mechanisms of rCB activation. The study investigates several parameters of KOH activation, including the KOH/rCB mass ratio (1:3 to 1:6), activation temperatures (700−900 °C), activation time (1−4 h), and heating rate (5−13 °C/min). It also assesses the effects of different potassium salts (KCl, K 2 CO 3 , CH 3 COOK, and K 2 C 2 O 4 ) on porosity and surface characteristics of the rCB/ACs. Furthermore, the role of the physical state of KOH as an activator (solid and gas−solid) was examined, alongside a comparative analysis with NaOH to evaluate the distinct effects of potassium and sodium ions. Optimal conditions were identified at an 800 °C activation temperature, a 7 °C/min heating rate, a 1:5 KOH/rCB ratio, and a 4 h activation period. X-ray diffraction analysis showed the formation of several K-phases, such as K 2 CO 3 , K 2 CO 3 •1.5H 2 O, K 4 (CO 3 ) 2 •(H 2 O) 3 , KHCO 3 , and K 2 O. The effectiveness of the potassium salts was ranked as follows: KOH > K 2 C 2 O 4 > CH 3 COOK > K 2 CO 3 > KCl, with KOH emerging as the most effective. Notably, the gas−solid reaction of KOH/rCB was indicated as a contributor to the activation process. Additionally, it was concluded that the role of KOH in enhancing the textural properties of rCB was primarily due to the interaction of K + ions with the graphite-like structure of rCB, compared to the effects observed with NaOH. This research introduces novel insights into the specific roles of different potassium salts and KOH activation conditions in optimizing the textural characteristics of rCB/ACs.