Proprietary In-Situ Leach Technology for Boron Recovery
5E extracts boron from deep colemanite deposits using a patented in-situ leach (ISL) process, a closed-loop mining method with minimal surface disturbance, no open pit, and no tailings dams.
5E Advanced Materials uses a proprietary in-situ leach (ISL) mining process at the Fort Cady Project. The closed-loop system dissolves colemanite borates underground through directional horizontal wells and recovers boron-rich solution at the surface for crystallization-based processing into high-purity boric acid. The company filed a 167-claim omnibus U.S. patent application for this technology in December 2025.
A Fundamentally Different Approach to Mining
Fort Cady's colemanite deposit sits at depths that preclude conventional open-pit or underground extraction. In-situ leaching dissolves the mineral in place and recovers it through wells, eliminating the largest environmental and capital impacts of traditional mining.
| Factor | Conventional Mining | 5E ISL Process |
|---|---|---|
| Surface Disturbance | Extensive, open pit, waste dumps | Minimal, well pads only |
| Tailings Dams | Required | None |
| Waste Rock | Millions of tons stripped | No waste rock generated |
| Acid Management | External acid supply | Closed-loop, HCl regenerated in gypsum circuit |
| Water Intensity | High consumption | Recycled in closed system |
| Scalability | Large upfront earthworks | Modular, add wells to increase capacity |
| Carbon Footprint | Heavy equipment, haulage | Substantially lower, no material haulage |
How In-Situ Leaching Works at Fort Cady
The ISL process uses heated leach solution pumped underground through directional wells to dissolve colemanite borates in place. The boron-rich solution is then recovered at the surface for processing.
Injection
Heated leach solution (dilute hydrochloric acid) is pumped underground through directional horizontal wells into the colemanite deposit.
Dissolution
The solution dissolves colemanite borates in place within engineered underground caverns, creating boron-rich pregnant leach solution (PLS).
Recovery
PLS is pumped to the surface through recovery wells. Operated in a "push-pull" cycle that alternates injection and recovery through the same wells.
Processing
Surface plant extracts boric acid from PLS through crystallization. By-products (gypsum, CaCl₂) recovered. Acid is regenerated and recycled.
Horizontal Well Configuration
The Phase 1 mine plan calls for 27 directional horizontal wells arranged in a fishbone pattern. Wells target all three mineralized horizons to maximize resource recovery from each drill pad.
| Wellfield Parameter | Specification |
|---|---|
| Total Wells (Phase 1) | 27 directional horizontal |
| Target Horizons | UMH, MMH, LMH |
| Horizontal Offset | ~200 ft between laterals |
| Vertical Spacing | 120–180 ft between horizons |
| Well Pattern | Fishbone, branching laterals from directional pad |
| Operating Mode | Push-pull (alternating injection/recovery) |
| Mining Efficiency | 95.0% (July 2025 program) |
| Mining Recovery | 81.9% (colemanite dissolution) |
From Solution to Product: The Boric Acid Processing Circuit
Pregnant leach solution recovered from the wellfield enters a crystallization-based processing plant that produces high-purity boric acid and two saleable by-products.
Boric Acid Circuit
Two stages of vacuum chilled crystallization produce high-purity boric acid crystals. PLS is clarified, pH-adjusted, then cooled to precipitate. Crystals are filtered, washed, redissolved, and recrystallized for product-grade purity.
| Output | 130,000 stpa |
| Process Recovery | 95.1% |
Gypsum & HCl Circuit
Calcium chloride brine reacts with sulfuric acid to produce gypsum and regenerate hydrochloric acid. The regenerated HCl is recycled back into the leach solution, closing the acid loop and reducing reagent consumption.
| Gypsum Output | 129,000 stpa |
| HCl Regenerated | Recycled to wellfield |
Impurity Removal
A dedicated circuit precipitates magnesium as Mg(OH)₂, followed by evaporation to remove excess water and NaCl crystallization. Ensures product purity meets industrial specifications.
| CaCl₂ Output | 57,000 stpa |
| CaCl₂ Concentration | ~38% |
Revenue Diversification Through By-Product Recovery
Fort Cady's processing circuit produces two saleable by-products that offset operating costs and generate secondary revenue. Together they contribute approximately 6% of total project revenue and reduce the all-in sustaining cost of boric acid by $73 per ton.
Gypsum (CaSO₄·2H₂O)
Produced in the HCl regeneration circuit. Sold into California construction and agriculture markets. Simultaneously regenerates hydrochloric acid for recycling back to the wellfield.
Calcium Chloride (~38% CaCl₂)
Produced as a co-product of the boric acid extraction circuit. Industrial applications include de-icing, dust control, and oil and gas completions fluids. Marketed as a liquid concentrate.
Proprietary Technology Protected by Patent
In December 2025, 5E Advanced Materials filed a 167-claim omnibus U.S. patent application covering its in-situ leach extraction process for boron recovery from colemanite deposits. The application covers the complete ISL system including wellfield design, leach solution chemistry, push-pull operating methodology, and surface processing integration.
This filing establishes a significant intellectual property moat around the company's core technology, a process developed and refined through decades of field testing and now validated at commercial pilot scale at the Fort Cady facility.
Patent Application Highlights
| Filing Date | December 2025 |
| Type | Omnibus U.S. patent application |
| Coverage | ISL extraction process, wellfield design, solution chemistry, operating methodology |
| Status | Filed — establishing IP protection for core technology |
Minimal-Impact Mining
The ISL process fundamentally changes the environmental profile of boron extraction compared to traditional hard-rock and open-pit operations.
By dissolving ore in place, ISL eliminates the need for large-scale earthmoving, haul road construction, waste rock management, and the permanent landscape alteration associated with conventional mining. All process water and reagents are recycled within the closed-loop system.
The gypsum circuit simultaneously serves a dual purpose: producing a saleable by-product while regenerating the hydrochloric acid used in the leach solution, significantly reducing fresh reagent requirements.
Learn About 5E's Sustainability Approach →Mining & Processing FAQ
In-situ leach (ISL) mining is a mineral extraction method that dissolves ore underground using a leach solution pumped through wells. Unlike conventional mining, ISL does not require excavation, blasting, or material haulage. At Fort Cady, heated hydrochloric acid solution dissolves colemanite borates at depth, and the boron-rich solution is pumped to the surface for processing into boric acid.
5E uses directional horizontal wells arranged in a fishbone pattern. Wells are drilled from surface pads to intersect three mineralized horizons (UMH, MMH, LMH) with approximately 200-foot horizontal offsets and 120–180-foot vertical spacing. The wells operate in a push-pull cycle, alternating between injection and recovery to maximize contact with the colemanite deposit.
The ISL process operates under a Class 3 Underground Injection Control permit from the U.S. EPA, which regulates the injection of solution mining fluids. The system is closed-loop: acid is regenerated in the gypsum circuit and recycled, process water is reused, and the operation requires no open pit, no tailings dam, and no waste rock disposal. The surface footprint is limited to well pads and processing infrastructure.
The plant produces three products: boric acid (130,000 short tons/year, the primary product), gypsum (129,000 tons/year), and calcium chloride (57,000 tons/year). Boric acid accounts for approximately 94% of project revenue. Gypsum and calcium chloride are saleable by-products that offset operating costs by $73 per ton.
Yes. In December 2025, 5E Advanced Materials filed a 167-claim omnibus U.S. patent application covering its in-situ leach extraction process for boron recovery from colemanite deposits. The application covers wellfield design, leach solution chemistry, operating methodology, and surface processing integration.
Cautionary Note
This page contains forward-looking statements regarding production targets, processing recovery rates, and technology performance. Actual results may differ materially from those projected. Mining recovery, mining efficiency, and processing recovery rates are based on pilot-scale testing and the July 2025 horizontal well program, as reported in the SK-1300 Pre-Feasibility Technical Report dated August 7, 2025. Patent application is pending; there is no assurance the patent will be granted. For complete risk factors, see SEC filings.
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