🎓 Lesson 17
D5
Florida Phosphate REE Project: Scaling from Lab to Full-Scale
Scaling up a lab-tested method for recovering rare earth elements (REEs) from Florida phosphate waste into a full-size mine water treatment plant means carefully adjusting chemistry, flow rates, and equipment size so it works safely, efficiently, and profitably at industrial scale.
🎯 Learning Objectives
- ✓ Calculate mass and volume scaling factors from lab batch data to pilot- and full-scale continuous flow systems
- ✓ Design a solvent extraction circuit using distribution coefficients and stage-wise McCabe–Thiele analysis
- ✓ Analyze pH-dependent REE speciation and co-precipitation risks using aqueous geochemical modeling (e.g., PHREEQC)
- ✓ Explain how gypsum saturation and sulfate interference impact REE recovery efficiency in phosphate-derived waters
- ✓ Apply EPA and FDEP water quality criteria to evaluate effluent compliance of scaled REE recovery streams
📖 Why This Matters
Florida’s phosphate industry generates ~1 billion tons of phosphogypsum waste and discharges ~50 million gallons/day of REE-rich process water—containing 10–100 ppm total REEs (especially Nd, Y, Dy). Recovering these critical minerals while meeting strict water discharge standards isn’t just economically strategic—it’s essential for U.S. supply chain resilience and sustainable mining. But what works in a 250-mL beaker often fails catastrophically at 500-gpm flow. This lesson reveals *how* and *why* scale-up fails—and how to engineer success.
📘 Core Principles
Scale-up rests on three pillars: (1) Geometric similarity—maintaining consistent reactor aspect ratios and mixing energy per unit volume; (2) Kinetic fidelity—ensuring reaction time scales match residence time distributions (RTDs), especially for slow ligand exchange in solvent extraction; and (3) Thermodynamic consistency—preserving solution chemistry (ionic strength, Eh/pH, complexation) despite dilution, heating, or solids carryover. In phosphate systems, key complications include Ca²⁺/SO₄²⁻ supersaturation (gypsum scaling), Fe/Al hydroxide fouling, and phosphate competition for REE-binding sites. Lab-to-pilot scale-up typically uses dimensionless numbers (e.g., Reynolds, Damköhler) to diagnose transport vs. reaction limitations; full-scale design adds regulatory thresholds (e.g., FDEP Chapter 62-520), material compatibility (HDPE vs. Hastelloy), and real-time control logic.
📐 Mass Scaling Factor
The mass scaling factor converts lab-scale reagent dosing or precipitate yield to full-scale requirements, correcting for differences in concentration, flow rate, and retention time. It ensures stoichiometric integrity and avoids under/over-dosing that causes poor REE recovery or hazardous sludge formation.
Mass Scaling Factor (MSF)
MSF = (Q_full × t_res) / V_labConverts batch lab reagent mass or product yield to continuous full-scale mass flow rate.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| Q_full | Full-scale volumetric flow rate | L/min | Design flow rate of treated water stream |
| t_res | Target hydraulic retention time | min | Required contact time for reaction or separation |
| V_lab | Laboratory test volume | mL | Volume used in bench-scale experiment |
Typical Ranges:
Phosphate water REE SX circuit: 200–400 kg/hr D2EHPA
Citric acid leach of phosphogypsum: 0.1–0.3 M acid concentration
💡 Worked Example
Problem: Lab test: 200 mL of phosphate process water (12 ppm ΣREE) treated with 0.8 g D2EHPA extractant → 92% REE recovery. Full-scale flow = 300 gpm (≈1136 L/min); target retention time = 5 min. Calculate required D2EHPA mass flow rate.
1.
Step 1: Convert lab volume to equivalent full-scale volume: 1136 L/min × 5 min = 5680 L = 5.68×10⁶ mL
2.
Step 2: Compute scaling ratio: 5.68×10⁶ mL ÷ 200 mL = 28,400
3.
Step 3: Scale reagent mass: 0.8 g × 28,400 = 22,720 g = 22.7 kg per 5-min cycle
4.
Step 4: Convert to continuous rate: 22.7 kg / 5 min = 4.54 kg/min = 272 kg/hr
Answer:
The system requires 272 kg/hr of D2EHPA. This falls within the typical range of 200–400 kg/hr for 300-gpm REE SX circuits treating phosphate water.
🏗️ Real-World Application
The Mosaic Company’s 2022–2024 pilot at its New Wales facility used 5-L mixed-culture bioreactors to validate citric acid-assisted leaching of REEs from aged phosphogypsum stacks. Lab tests showed >85% Y and Nd dissolution at pH 2.8. At pilot scale (200 L/day), however, gypsum dissolution spiked Ca²⁺ to 4,200 mg/L—causing rapid D2EHPA saponification and 40% drop in extraction efficiency. Engineers resolved this by adding staged pH adjustment (pH 3.2 → 4.1) and pre-filtration via sand–anthracite dual-media filters—restoring >78% recovery. This informed the full-scale design’s integrated lime softening + microfiltration front-end now under construction (FDEP Permit #2024-0128).
🔧 Interactive Calculator
🔧 Open Mine Water Treatment & Resource Recovery Calculator📋 Case Connection
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