Valorization of regenerated spent bleaching earth for porous alumina membrane supports

Abstract Conventional ceramic membrane supports remain expensive, which motivates the use of mineral wastes as alternative precursors. Spent bleaching earth (SBE) is a silica- and alumina-rich by-product of edible-oil refining, but its retained oil can destabilize ceramic bodies during firing. Here, SBE was regenerated by hot-water, acetone, and n-hexane extraction, and the regenerated material was incorporated into tubular Al₂O₃-based supports prepared by horizontal centrifugal casting. N-hexane gave the highest oil removal efficiency (94.7%) and produced the thermally most stable precursor, with residual oil below 2 wt%. Increasing SBE loading strengthened the silicate signature of the supports, shifted the phase assemblage toward a quartz-rich framework, increased water absorption (33.8 to 57.6%) and porosity (41.1 to 64.1%), and reduced water contact angle from 41.6° to 29.0°. At the same time, the structural response was non-monotonic: SBE35 yielded the narrowest surface pore-size distribution (~ 11.2 μm mean), a mesoporous network with 45.2 nm average pore diameter, and much better chemical stability than SBE55. These results show that regenerated SBE acts simultaneously as a ceramic precursor and a pore-generating phase. Moderate incorporation provides the most balanced architecture for support development, while permeation and mechanical evaluation remain important future steps.