Impurity Removal (Mg/Ca) Prior to Crystallization
When refining lithium from brines, the presence of divalent cations, such as magnesium (Mg²⁺) and calcium (Ca²⁺), poses a persistent challenge. These ions interfere with crystallization, contribute to scaling, and reduce product purity. Left unchecked, they complicate downstream lithium carbonate or hydroxide crystallization, leading to operational headaches, increased reagent consumption, and lower recovery rates.
Whiting Equipment Canada, working with its licensee Swenson Technology, designs refining trains centered on evaporation and crystallization. These systems are engineered to isolate lithium and efficiently remove contaminants. While crystallization is the core purification step, the performance of those crystallizers is highly dependent on how well upstream impurity removal is handled.
Removal Methods (Lime, IX, Membranes)
Several established technologies are used to reduce Mg/Ca levels before crystallization:
- Lime Treatment: Adding lime (Ca(OH)₂) precipitates magnesium as Mg(OH)₂. This is one of the most widely used steps in salar brine pre-treatment. However, lime addition must be carefully controlled to avoid excess calcium carryover, which can create new scaling risks.
- Ion Exchange (IX): IX resins designed for selective divalent cation removal can polish brines where magnesium or calcium remains above acceptable thresholds. IX offers high selectivity but comes with resin regeneration costs.
- Membrane Processes: Nanofiltration and selective reverse osmosis membranes can strip divalent ions from complex brines, often paired with chemical dosing to improve rejection rates. Membranes can be integrated as polishing units ahead of the evaporation process.
Impact on Downstream
The consequences of poor Mg/Ca removal extend far beyond the pre-treatment block:
- Scaling in Evaporators: Magnesium and calcium salts deposit on heat transfer surfaces, reducing efficiency and driving up energy costs.
- Crystal Quality: High impurity loads disrupt controlled crystal growth, leading to variable morphology and lower battery-grade yields.
- Operational Uptime: Excess scaling increases the frequency of shutdowns for cleaning and maintenance, limiting throughput.
Swenson’s crystallization systems are specifically designed to mitigate fouling and scaling. Pilot testing facilities generate data on impurity behavior, informing flowsheet design to protect heat exchangers, crystallizer bodies, and downstream solid-liquid separation units.
Monitoring & QA
Robust quality assurance requires continuous tracking of impurity levels through multiple checkpoints:
- Bench & Pilot Testing: These stages deliver baseline impurity data, yield, and morphology that serve as calibration references.
- Inline Monitoring: Our industrial control systems (PLC, SCADA, Volta regulators) monitor flows, temperatures, and power. We can extend that framework to conductivity, turbidity, or proxy sensors for impurity breakthrough.
- QA Integration: Data from inline sensors can be trended and logged, with alarm thresholds established for Mg/Ca levels that threaten crystallizer stability or product purity.
Cost & Dosing
Chemical dosing rates and costs vary by brine chemistry, but several guiding principles apply:
- Lime dosing is typically modeled during bench testing and confirmed at pilot scale to ensure just enough reagent is added to precipitate magnesium without leaving excess calcium.
- IX resin operating costs are tied to regeneration cycles and reagent usage, which must be balanced against the value of higher recovery.
- Membranes have higher capex but lower chemical OPEX; performance modeling is critical for cost forecasts.
Swenson’s design process, paired with Whiting’s manufacturing excellence, emphasizes modeling and simulation to balance thermodynamics, chemical behavior, and economics. This same philosophy applies to sizing lime systems, IX beds, or membrane units upstream of the crystallization process.
Instrumentation
Instrumentation is key for both process control and QA:
- pH and ORP Meters: Essential for controlling lime dosing and precipitation efficiency.
- Conductivity Sensors: Provide a quick proxy for total dissolved solids and breakthrough monitoring in IX or membrane systems.
- Flow and Pressure Transducers: Critical for membranes to detect fouling or scaling onset.
- Centralized Control: As with Whiting’s metallurgical systems, integration into SCADA allows real-time trending, alarm management, and operator dashboards.
Waste Handling
Impurity removal steps inevitably generate secondary waste streams:
- Sludge Management: Lime treatment produces Mg(OH)₂ sludges that require dewatering and disposal or reuse.
- Brine Concentrates: Membrane reject streams must be handled, often routed into evaporation ponds or further treated.
- Regeneration Liquors: IX resins produce saline regeneration wastes that must be neutralized or blended.
Our team’s philosophy of engineering for durability and sustainability also applies here. By-products, such as sodium sulfate, are already viewed as potentially recoverable co-products rather than pure waste. Extending that logic to Mg/Ca waste streams can help align operations with ESG and circular economy goals.
Conclusion
Removing magnesium and calcium before crystallization is not a side task—it’s fundamental to stable operations, efficient energy use, and the production of battery-grade lithium. Whether through lime precipitation, IX, or membranes, the right approach depends on the unique impurity profile of the brine feed.
Whiting Equipment Canada and our licensee, Swenson Technology, bring decades of experience in crystallization and evaporation, backed by pilot testing, modeling, and customized engineering. Our systems are designed to minimize scaling, maximize yield, and integrate impurity management into the heart of the refining process.
Struggling with Mg/Ca headaches in your lithium refinery? The Whiting experts can help you design impurity removal and crystallization trains tailored to your brine chemistry. Contact us to explore solutions that cut fouling, improve uptime, and deliver battery-grade results.
