Valorisation of titanium dioxide waste: enhanced polyferric sulfate production via iron, titanium, and calcium modification.

The titanium dioxide industry generates 6-8 tons of impure FeSO4·H2O per ton of TiO2, creating serious environmental and economic problems. This work presents a novel method to valorise this waste into high-performance polyferric sulfate (PFS) coagulants. A key innovation is using iron powder to simultaneously neutralise free acid (16.32%) and enrich iron content. Under optimal conditions (Fe/FeSO₄·H₂O molar ratio = 0.24), the solid PFS product contained 20.33% total iron with 16.63% basicity and achieved 80.20% turbidity removal. Modification with titanium oxysulfate (Ti/Fe = 0.4) improved removal to 92.1%, while calcium modification (Ca/Fe = 0.01) reached 91.25% at lower cost. Characterisation confirmed Ti⁴⁺ incorporation and formation of Ti-O-Ti/Ca-O bonds, enhancing coagulation. This waste-to-resource strategy reduces production costs by 25-35% compared to conventional methods, offering an economically viable circular economy solution for the TiO₂ industry.