Simultaneous and clean separation of titanium, iron, and alumina from coal fly ash in one spot: Electrolysis-hydrolysis method

Abstract

Large amounts of heavy-metal-containing coal fly ash can cause serious environmental hazards. The separation and extraction of titanium, iron, and alumina from coal fly ash can provide economic and environmental benefits. This work presents an electrolysis-hydrolysis method to alter the precipitation order of iron and alumina by changing the ion charge sequence to extract iron and alumina in an orderly manner while recovering the waste heat to polymerize the precipitated titanium. The separation and extraction of titanium, iron, and alumina in one spot can shorten the process and make full use of the electric energy. Under optimal conditions, the efficiencies of iron, titanium, and alumina were 97.6%, 93.1% and 88.5%, respectively. The iron product had a composition of 95.8% Fe2O3, 0.5% Al2O3, 0.3% CaO, 0.1% SO3, and 0.4% TiO2. The alumina product had a composition of 88.7% Al2O3, 0.1% Fe2O3, 0.2% CaO, 9.1% SO3 and 0.2% TiO2. The titanium product had a composition of 63.78% TiO2, 3.11% Al2O3, 8.15% Fe2O3, 0.28% CaO, 4.12% SiO2, and 9.6% SO3. Moreover, in the entire electrolysis process, no expensive membranes or chemical additives were required, avoiding the limitations of membranes and high costs. Fe, Al(OH)3, Ti(OH)4, O2, and H2 were generated during the electrolysis-hydrolysis process; therefore, no harmful substances were produced. Thus, this study proposes an alternative electrolysis-hydrolysis process for the simultaneous separation and extraction of titanium, alumina, and iron from coal fly ash leachate in one spot.