Abstract
In 1963, Archambault described a direct alkaline processing route to produce lithium carbonate from calcined lithium-bearing silicate minerals of the spodumene type, thereby eliminating the need for conversion to an intermediate lithium sulphate phase. The primary objective of this process was to simplify lithium recovery by enabling the direct hydrometallurgical reaction of the lithium silicate phase with sodium carbonate in aqueous media under controlled temperature and pressure conditions. The process results in the formation of lithium carbonate and an aluminosilicate residue considered to be environmentally benign.
Although documented more than six decades ago, variations of this direct alkaline processing approach have received renewed attention in recent years as demand for lithium has increased and greater scrutiny has been placed on the environmental and economic impacts of sulphuric acid–based extraction flowsheets. Several contemporary process developments have been presented as novel; however, these approaches generally offer some advancements in reaction kinetics, solid–liquid separation, and process integration (e.g. incorporation of Solvay-type circuits for sodium carbonate regeneration) rather than the introduction of fundamentally new hydrometallurgical flowsheet.
This paper revisits the alkaline lithium extraction technology originally proposed by Archambault and demonstrates that direct soda ash conversion of lithium silicates has long been recognized as a technically viable processing route. A systematic comparison is presented between conventional sulphuric acid leaching and direct soda ash conversion to produce 25 ktpy LCE from hard-rock lithium resources. The comparison focuses on reaction chemistry, leaching operating conditions, process chemistry, reagent and energy consumption, impurity control, and residue stability. The respective technological, economic, and environmental implications of each flowsheet are evaluated to define their advantages and limitations.