Clean production of porous-Al(OH)₃ from fly ash

Fly ash is one of the largest solid waste and causes serious environment problems. Extraction of Al(OH)₃ from fly ash is beneficial to environment and economy. We developed a clean electrolysis method to generate hydroxyl groups in situ to extract Al(OH)₃ from fly ash leachate without adding chemicals or using expensive membranes, avoiding the introduction of new impurities, secondary pollutants generation, and membrane limitations. Batch experiments yielded porous electrolytic products with BET surface areas from 11.7610 to 25.5267 m²/g, pore volumes from 0.1935 to 0.1643 cm³/g and pore sizes from 65.7960 to 25.7434 nm. The composition of the electrolytic products was 86.43 wt% Al(OH)₃, 9.00 wt% SO₃, 1.67 wt% Fe(OH)₃, and 0.29 wt% Ca(OH)₂. The current efficiency was 90.51 % under optimized conditions of c (Al³⁺) = 0.1 M, t =2 h, and J = 750 A/m². Mean particle size was from 24.1-98.1 μm. Impurities mainly affected the composition of the electrolytic products. The OH- generated by H₂O reduction reacted with Al³⁺, Fe³⁺, and Ca²⁺ to generate a hydroxide. Fe³⁺ preceded Ca²⁺ into the hydroxide. H₂ released continuously from H₂O reduction, resulting in a porous hydroxide. The wastewater was reused as a leaching reagent to promote zero-pollution discharge.