Red mud valorization an industrial waste circular economy challenge; review over processes and their chemistry

Abstract

Significantly unexploited red mud contains 0.5–1.7 kg/ton of rare earth metals (REMs) and 14–45% Fe, 5–14% Al, 1–9% Si, 1–6% Na, and 2–12% Ti which is currently being stockpiled. Reasonably, the red mud can be a suitable secondary resource of REMs, and other valuable metals, if not for the contained base metals. Stockpiled red mud locks down these technologically important and supply chain critical metals. Though quantitatively minor, the value perspective of REMs in red mud is significant. Global red mud inventory could reach 4 billion tons by 2020 and being generated 120–150 million tons per year worldwide. Analysis indicated that industrial-scale valorization could unlock approximately $4.3 trillion worth of REMs from stockpiled red mud. The current review discusses the valorization of red mud through metal value recovery which is an industrial waste circular economy challenge. Unlike other reported reviews, the current review intensively discusses circular economy challenges and opportunities associated with the red mud valorization. Finally, a suitable conceptual sequential metal recovery process has been proposed based on a comprehensive review of various processes which can technically be a feasible process for sequential recovery of various metal values from the red mud. Comprehensive cutting-edge research, broader risk assessment, and cost and benefit analysis of the proposed process can ensure broader valorization. Broader valorization can address several issues through the proposed process like; (i) metal value recovery, (ii) REMs circular economy, (iii) closed-loop process with the industry, and (iv) lower the futuristic carbon economy, simultaneously.

Graphical abstract

KEYWORDS:

• Process chemistry
• red mud
• REEs
• valorization