<p>The purpose of this research was to conduct a comprehensive systematic literature review on non-ammonium-based lixiviants for metal recovery from ionic adsorption clays (IACs) and weathered crust elution-deposited (WCED) ores, aiming to evaluate their performance, mechanisms, and sustainability potential as alternatives to conventional ammonia-based systems. Using a systematic literature review methodology that covers pre-leaching, leaching, and post-leaching aspects of IACs/WCED processing, the following specific objectives were established: (i) to assess the performance and selectivity of non-ammonium lixiviants compared to conventional ammonium-based systems, (ii) to investigate how different lixiviant types influence desorption mechanisms during leaching processes, and (iii) to evaluate the environmental, economic, and downstream processing implications of transitioning to non-ammonium-based systems. A total of 121 peer-reviewed articles were analyzed, sourced from the Scopus database, selected through the PRISMA method, and systematic screening criteria. Four critical findings emerged: (i) pre-leaching mineralogical and structural characterization is a prerequisite for technology selection, emphasizing on the clay minerals and weathering level; (ii) non-ammonium lixiviants, particularly MgSO₄ and organic acids, achieve performance comparable or superior to ammonium salts with significantly higher selectivity against aluminum; (iii) lixiviant type fundamentally governs the desorption mechanism, shifting from outer-sphere ion exchange (ammonium) to inner-sphere complexation and chelation (LMWOAs); and (iv) the transition to non-ammonium systems eliminates ammonia-nitrogen pollution and is compatible with diverse downstream enrichment routes—including precipitation, solvent extraction, membrane separation, and ionic liquid systems—offering a viable pathway for sustainable IAC processing in developing countries.</p>