Seawater Magnesium & Critical Minerals Lab

Model alkaline precipitation from desalination brine, fluidized bed dehydration, molten salt electrolysis, and the Levelized Cost of Clean Magnesium (LCOM).

Presets:
Net LCOM ($/t Mg)
$3,240/t
Levelized cost per tonne
Specific Power
14.4 MWh/t
Electrolysis + dehydration
Avoided Scope 1 CO2
336.2 kt/yr
vs Coal Pidgeon process
Connected Power
27.0 MW
Substation capacity

Hydrometallurgy & Cell Parameters

Magnesium Metal Production (tpa): 15,000 tpa
Brine Feed Mg²⁺ Tenor (ppm): 2,600 ppm
Raw seawater is ~1,290 ppm; SWRO reject brine concentrates Mg to 2,400–3,200 ppm.
Precipitation Recovery (%): 94 %
Molten Salt Cell Voltage (V): 6.6 V
Theoretical reversible voltage is ~2.6 V; overpotentials & electrolyte ohmic drop require 6.0–7.2 V.
Electrolytic Current Efficiency (%): 86 %

Energy, Reagents & Metal Market

Electricity Tariff ($/MWh): $48
Hydrated Lime Ca(OH)2 Cost ($/t): $110
Magnesium Metal Market Price ($/t): $4,200
Total Installed Facility CapEx ($M): $135M

Cost Stack Breakdown ($/t Mg Metal)

  • Electricity (Electrolysis & Aux): $691
  • Hydrated Lime Precipitator: $355
  • Thermal Fluidized Bed Dehydration: $280
  • Graphite Anodes & Cell Refractory: $210
  • Chemicals & HCl Makeup: $85
  • Operating Labor & Metallurgy QA: $392
  • Plant Maintenance (3.5% CapEx): $315
  • Total Operating Cost (OpEx): $2,328
  • Annualized Capital Amortization: $916
  • Net Levelized Cost of Magnesium: $3,244/t
Seawater & Brine Magnesium Recovery Flowsheet -85% Embodied CO2
BRINE FEED MG TENOR 2,600 ppm PRECIPITATION RECOVERY 94 % CELL OPERATING VOLTAGE 6.6 V ANNUAL METAL OUTPUT 15,000 t/yr NET PRODUCTION COST $3,240/t DESAL BRINE 2,600 ppm Mg Ca(OH)2 Lime THICKENER Mg(OH)2 Slurry DRUM Filter Cake FLUID BED Dehydration Anhydrous MgCl2 Closed-Loop HCl Recycle ◀ MOLTEN SALT CELL (700°C) FLOATING LIQUID Mg (1.58 g/cm³) MgCl2 → Mg + Cl2↑ Mg INGOT ► Pure Metal 1.74 g/cm³ Ultralight
Net Present Value
$78.2M
20-year @ 8% discount
Internal Rate of Return
18.6%
Project equity/debt IRR
Simple Payback
4.8 yrs
Capital amortization

5x5 Sensitivity Matrix: Levelized Cost of Magnesium ($/t Mg)

Brine Mg Tenor vs Electricity Tariff
Tenor \ Power $30/MWh $45/MWh $60/MWh $75/MWh $90/MWh

20-Year Project Pro-Forma Snapshot

Period Gross Revenue Total OpEx EBITDA Net Cash Flow Cumulative Cash

Mastery Assessment: Magnesium Metallurgy & Electrochemistry

1. What are the key sequential chemical stages for producing magnesium metal from ocean or desalination brine?
2. Why does seawater magnesium extraction dramatically reduce embodied greenhouse gas emissions compared to the dominant Pidgeon process?
3. In a molten salt electrolytic cell at 700°C, how is liquid metallic magnesium separated from the electrolyte bath?
4. What closed-loop chemical engineering strategy prevents hazardous emissions and cuts chemical costs in the electrolysis train?

Frequently Asked Questions

Seawater contains approximately 1,290 ppm of dissolved magnesium (Mg2+), which concentrates to 2,400 to 3,000 ppm in reverse osmosis desalination reject brine. In modern chemical-electrochemical extraction, hydrated lime (Ca(OH)2) or sodium hydroxide is mixed into the brine to selectively precipitate magnesium hydroxide (Mg(OH)2). The precipitate is filtered, converted into anhydrous magnesium chloride (MgCl2), and electrolyzed in molten salt cells to produce pure metallic magnesium ingots and recyclable chlorine gas.

Over 85% of global primary magnesium is manufactured via China's coal-fired Pidgeon process, which heats dolomite ore with ferrosilicon in retort furnaces at 1,200°C, emitting an extraordinary 22 to 28 tonnes of CO2 per tonne of magnesium. In contrast, seawater extraction eliminates mining and ferrosilicon smelting, cutting embodied carbon emissions by over 80% (to under 3.5 t CO2/t Mg when powered by renewable electricity).

Anhydrous magnesium chloride is electrolyzed in molten alkali chloride baths (MgCl2-NaCl-CaCl2) at 680°C to 720°C at cell voltages between 6.0 and 7.2 V. The cathode reduces Mg2+ to molten liquid magnesium (which floats to the top due to its lower density, 1.58 g/cm³ vs 1.70 g/cm³ bath), while chlorine gas evolves at graphite anodes. Modern electrolytic cells consume 11.5 to 13.5 kWh of electricity per kilogram of magnesium produced (~12,500 kWh/t Mg).

The primary operating expenses are electricity for electrolysis and drying (accounting for 40% to 55% of OpEx), lime or alkali precipitant reagents, and thermal energy for fluidized bed dehydration. Economic viability is significantly bolstered by co-producing high-value magnesia (MgO for refractories at $500–$800/t) and closing the chlorine loop by reacting anode chlorine with steam or hydrogen to generate HCl for digestion.

Magnesium is the lightest structural metal on Earth, 33% lighter than aluminum and 75% lighter than structural steel, with exceptional specific stiffness and vibration damping. Automotive manufacturers utilize magnesium die-castings for cross-car beams, transmission cases, and electric vehicle battery enclosures to reduce vehicle curb weight, which directly extends EV driving range and cuts lifetime battery pack sizing requirements.

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