Development of saleable chloride free iron oxide from hazardous waste in titanium industries via layered double hydroxide formation.

Mining and metal processing industries constitutes a major source of environmental pollution, albeit its huge impact on a nation's economic and industrial growth. The collaborative approach in waste management where wastes in one process/industry turns out to be a resource for another is extremely useful to sustain industries. Titanium dioxide pigment production industry operating via chloride process expels hazardous iron oxide waste byproduct rich in chloride content. The slow leaching of highly acidic and chloride rich effluents (2-5 wt.%) along with toxic heavy metals from iron oxide storage ponds in titanium industries pose serious threat to the human health and environment. The present paper describes the development of an innovative zero discharge chloride removal process via formation of layered double hydroxides (LDHs) from iron oxide waste byproduct, thereby enabling the end use applications of iron oxide. It is the first such study reported on the value addition of hazardous industrial residues via LDH formation. The developed co-precipitation process recorded maximum chloride removal efficiency in the range of 85-95%. The resultant precipitate i.e., the Friedel's salt was characterized by various techniques such as XRD, XRF and SEM-EDX and confirmed the effective removal of chlorides. The application potential of the process in real iron oxide wash waters with 95% removal efficiency and the possible reusability of precipitate utilizing the "memory effect" of LDHs were found to be highly promising. The study demonstrated the unique application potential of the process in chloride rich iron oxide wash waters unlike other industrial/domestic wastewaters, wherein other anionic species has a detrimental effect. The value added iron oxide can find application in steel industries and can mitigate the environmental and health concerns arising from the long term storage of hazardous iron oxide in mineral processing industries.