A Novel Process for Preparing Aluminium Fluoride from Coal Fly Ash Using Hydrofluorosilicic Acid Leaching and Seeding Techniques

Abstract

With the exponential growth in coal fly ash production and its consequential environmental impact, there is an urgent need to maximize its utilization. Despite this necessity, only around 60% of coal ash in India is currently being utilized. One of the key challenges hindering efficient utilization lies in the complex structure of the mullite matrix, making the recovery of alumina from coal fly ash a daunting task that demands precise reaction conditions. This study proposes an innovative hydrometallurgical approach for coal fly ash utilization to tackle this challenge. Here, hydrofluorosilicic acid (H2SiF6), a waste by-product from the fertilizer industry, takes center stage as the leaching agent. Alumina can be effectively dissolved by utilizing this acid, breaking down the stubborn mullite matrix. This method not only facilitates the extraction of alumina but also generates aluminium fluoride through a seeding technique alongside other valuable by-products. Maintaining a specific concentration of aluminium fluoride in the solution proves crucial for ensuring efficient precipitation. Moreover, the spent solution from this process can be recycled within the system, enhancing its sustainability and minimizing waste. The study achieved an impressive 95% alumina leaching efficiency following a mixed control kinetic model as the rate-controlling step. Aluminium fluoride produced in this process has a purity of 97.6%. Beyond addressing solid and liquid waste management concerns, this novel process opens doors for more effective resource utilization, marking a significant step toward sustainable industrial practices.