From fly ash waste slurry to functional adsorbent for valuable rare earth ion separation: An ingenious combination...

Acid extracting aluminum from fly ash would produce pestilent secondary fly ash slurry with strong acidity, high content of Cl^- and residual Al³⁺ that is difficult to be further used. In order to achieve the zero emission, a potential integrated treatment process for reutilization was proposed in this paper. By intelligent use of residual Al³⁺ in sludge as catalyst, hydrophobic modification of solid particle was taken with fatty acid via a heterogeneous esterification at normal temperature. Due to the solvophobic force, moisture content of its filter cake was 36.46%, which reduced 11.14% compared with the unmodified one, hydrophobicity scale can achieve 100% with modifier accounting for only 0.8% of solid content and the Cl^- concentrations decreased from 20 to 0.102 g/L in wash liquor, thus greatly saving water for washing and energy for drying. Subsequently, based on the appearance of hydrocarbon chains on particle surface, a high-efficiency ultraviolet-induced grafting polymerization was implemented to fabricate density polyacrylic acid decorated fly ash particles from the surface "CH" sites, the resultant composite was proved to efficiently separate valuable rare-earth Gd³⁺ from wastewater with outstanding adsorption and regeneration performance, hence bringing high added-value utilization for these hazardous waste.