As compliance with green mining regulations becomes a mandatory threshold for the commissioning and operation of salt lake lithium extraction projects, near-zero liquid discharge and closed-loop production of all material streams have emerged as core priorities for both project owners and regulators. Mechanical vapor recompression (MVR), once treated merely as a concentration unit, is now repositioned as a critical hub enabling water resource closure and waste salt reduction in salt lake facilities. Its value lies not in the equipment itself, but in process synergy with upstream impurity removal, downstream crystallization and mother liquor recovery. This synergy determines whether a salt lake production line can reliably meet environmental compliance requirements and deliver long-term commercial value.
The salt lake lithium extraction process continuously generates multiple types of process streams, including lithium precipitation mother liquor, membrane concentrate, washing wastewater and resin regeneration wastewater. These waste streams feature high salinity and complex constituents such as lithium, magnesium and boron. Direct discharge would lead to the loss of valuable resources and pose risks to local soil and water environments. Reliance solely on conventional evaporation ponds requires extensive land occupation and produces mixed waste salt solids that are difficult to dispose of, driving up environmental compliance and treatment costs. This challenge is especially pronounced in salt lake producing regions across Latin America and globally, where standards including GISTM tailings management and zero liquid discharge are becoming increasingly stringent. The value of MVR lies in separating water from salts through high-efficiency concentration, enabling water reuse and targeted salt precipitation to cut waste salt volume at the source.
For MVR to function effectively as the hub of a closed-loop system, systematic pre-treatment of feed water is a prerequisite. If lithium precipitation mother liquor and various concentrated streams are fed directly into the MVR, ions such as calcium, magnesium, boron and silicon readily reach supersaturation during concentration and form hard scale on heat transfer surfaces. This triggers a sharp rise in evaporation energy consumption, frequent shutdowns for cleaning, uncontrolled salt crystallization and barriers to salt resource recovery. Accordingly, BICHEM integrates MVR concentration into the overall mass balance framework. Upstream processes employ chelating resins for deep calcium and magnesium removal, together with membrane technology to retain colloidal silica and suspended solids, bringing feed hardness and colloid levels within target ranges and establishing stable operating conditions for the evaporation section. Meanwhile, brine ionic models are used to simulate salt crystallization behaviour at different concentration ratios. Feed loading, circulating concentration and salt discharge strategies are optimised to direct salt crystal formation inside the crystallization chamber rather than on heat exchange tubes, fundamentally resolving scaling and energy intensity challenges via process design.
The coupled MVR section directly supports the delivery of near‑zero liquid discharge targets. The condensate generated by evaporation can be purified and reused for brine leaching, equipment washing and process solution preparation, establishing an on‑site closed water circuit that substantially cuts freshwater intake and eases constraints imposed by water scarcity in salt lake producing areas. Residual lithium contained in the concentrated mother liquor is recirculated back to the main process to raise overall lithium recovery and reduce the unit cost of lithium carbonate. Enriched waste salts are separated and reduced via fractional crystallization, converting hard‑to‑handle mixed salts into manageable by‑products and lowering solid waste output and stockpile burden. In this way, MVR is no longer an independent concentration unit, but a closed‑loop hub linking water reuse, lithium recovery and waste salt reduction.
For overseas compliance, this closed‑loop capability directly addresses key concerns of regulators and financiers. Salt lake projects equipped with near‑zero liquid discharge and waste‑salt reduction capacity stand a better chance of passing environmental approval, ESG due diligence and supply chain qualification audits by downstream battery customers, reducing uncertainties in project financing and execution. As a full‑process process technology provider, BICHEM delivers integrated solutions covering water quality assessment, process design, system integration and operation optimisation, enabling salt lake projects to achieve synergistic gains in water resources, lithium recovery and ecological benefits while maintaining environmental compliance.
Against the backdrop of tightening green mining compliance and ESG requirements, the role of MVR has evolved from a mere wastewater treatment unit into a closed-loop production hub. Only by embedding evaporative concentration into the full-stream mass balance and linking upstream impurity removal, concentration and crystallization, mother liquor recovery and water reuse seamlessly can salt lake projects genuinely achieve near-zero liquid discharge and waste salt reduction, and realise both economic benefits and environmental compliance.
