Application of new griffithite–hydrocalumite–katoite materials synthesized from salt cake in the purification of biodigested wine distillery wastewater by Fenton’s process

Novel materials based on Na 2 S 2 O 4 –modified griffithite and griffithite–katoite–hydrocalumite hybrid composites have been prepared to be applied as catalysts in Fenton–type processes for biodigested distillery wastewater (BDW) purification using salt cake as aluminum source. The catalysts were thus based on a natural Fe–rich clay and on Ca–Al synthetic cheap materials, all with layered structure. The characterization of these materials showed the presence of phases with catalytic activity in heterogeneous Fenton processes such as Fe 2 O 3 and Fe 3 O 4 . The sample Griffithite–2μm–750 and the hybrid material Griffithite@HC–750 were the most effective in removing the total organic carbon (TOC) and chemical oxygen demand (COD) from BDW. The best reaction conditions were determined using Griffithite–2μm–750 as heterogeneous Fenton catalyst and considering pH, [H 2 O 2 ]:COD ratio and catalyst dosage as key parameters. In addition, the Griffithite–2μm–750 sample was subjected to a cyclic (5 cycles) and long–term (∼200 h of time–on–stream) study, showing excellent stability. Scavenger experiments confirmed that the process proceeds predominantly via a radical mechanism, with hydroxyl radicals (OH•) playing the main role.