Zero-tailings processing: Cobalt-bearing tailings case study
Overview
BacTech Environmental Corporation proposes the deployment of its proprietary zero-tailings extraction technology to treat cobalt-bearing tailings. This process recovers critical metals while converting secondary elements into multiple revenue-generating products, including ammonium sulphate fertilizer and magnetite for the steel or pigment industries. It offers a practical, profitable, and environmentally responsible solution for the remediation and reprocessing of sulphide-rich mine residues.
Mineralogy and Processing Approach
The targeted tailings are believed to contain cobalt hosted primarily within pyrite, residual copper in chalcopyrite and bornite, and minor silver and gold values locked within siliceous gangue and oxide minerals—making conventional recovery difficult.
At the core of the system is bioleaching, a commercially proven technology used globally for over 40 years. It employs naturally occurring bacteria to oxidize sulphide minerals in aerated stirred reactors (5–6 day residence time), liberating metals such as cobalt, copper, silver, and gold. This is particularly effective for finely disseminated cobalt, which is hard to recover via flotation alone.
Zero-Tailings Concept and By-Product Recovery
BacTech’s innovation lies in achieving zero tailings:
Iron and sulphur released during bioleaching are converted into magnetite and ammonium sulphate, rather than being discarded.
Residual silver and gold can be recovered from the final residue.
Remaining silicate material can be repurposed for construction products, mine backfill, or landscaping.
This eliminates the need for long-term tailings impoundments and their associated liabilities while creating new revenue streams and conserving water—critical in arid regions. Process water is continuously recycled, and the system operates at atmospheric pressure with no hazardous reagents, supporting rapid permitting and low environmental risk.
Modular, Scalable Deployment
The technology is modular, allowing for a staged rollout:
A small-scale prototype can be retrofitted into existing plants to generate early cash flow and prove site-specific performance.
Revenues from this phase can fund scale-up to full commercial operations, reducing upfront capital requirements and risk.
Integration is straightforward: rougher scavenger concentrate or other sulphide-rich streams can be fed into the bioleach system, recovering cobalt and copper as sulphide/hydroxide products or metals, while producing magnetite and fertilizer. Inert gangue minerals are reused, effectively lowering cut-off grades, extending mine life, and improving overall resource utilization.
Advantages Over Conventional Methods
Conventional flotation and hydrometallurgical circuits struggle with variable tailings mineralogy. In contrast, bioleaching:
Handles variable sulphide hosts (pyrite, pyrrhotite, etc.) without process changes.
Consistently liberates cobalt, copper, silver, and gold.
Operates in controlled conditions (pH, temperature, aeration) for stable performance.
Uses modular bioreactors that can be tuned or expanded incrementally.
The system also converts variability into value: higher sulphur boosts fertilizer output, while higher iron increases magnetite production—turning what are usually risks into additional revenue opportunities.
Water Management and Environmental Benefits
The closed-loop design recycles water with zero discharge, avoiding the water losses common in conventional tailings storage. This is especially beneficial in water-scarce regions. It also eliminates the accumulation of unrecovered sulphides in tailings, cutting long-term liabilities and supporting ESG goals.
Flowsheet Integration and Safety Net Role
Rather than replacing flotation, zero-tailings acts as a downstream safety net:
Flotation captures most copper, gold, and silver into a high-grade concentrate.
The bioleach treats residual tailings to recover metals that escaped flotation.
Captured metals can be blended back into primary concentrates or sold separately.
This dual-path setup stabilizes performance, reduces lost recovery risk, lowers the effective cut-off grade, and provides operational flexibility—allowing flotation to prioritize concentrate grade without permanently losing metal value.
Economic Impact
Applying zero-tailings to a representative rougher scavenger concentrate stream (0.14% Cu, 2.3 g/t Ag, 0.22 g/t Au, 200 g/t Co assumed) shows strong economics:
Metals revenue (per tonne):
$2 silver
$13 copper
$13 gold
$10 cobalt
Subtotal: $38/t
By-product revenue (per tonne):
$50 ammonium sulphate
$27 magnetite (combined from pyrite conversion and residue)
Subtotal: $77/t
Total estimated revenue: ~$115 per tonne processed
1,000 tpd operation: ~$40M/year
3,750 tpd operation: ~$150M/year
(Note: potential value from silicate residue is excluded, representing further upside.)
Capital Costs:
1,000 tpd prototype: ~$45M
Expansion to 3,750 tpd: +$100M
Direct 3,750 tpd build: ~$120M
Operating Costs:
~$25/t (mainly ammonia reagent and aeration power)
~$10M/year at 1,000 tpd; ~$33M/year at 3,750 tpd
NPV / IRR (15-year life @ 8% discount):
Staged build (1,000 → 3,750 tpd): ~US$500M NPV, ~40% IRR
Direct 3,750 tpd build: ~US$750M NPV, ~70% IRR
Project Development Pathway
The proposed development sequence includes:
Laboratory scoping tests to assess leachability and product potential
Desktop study
Pilot-scale continuous operation
Demonstration plant (generating early revenue)
Full feasibility study and commercial installation
Broader Project Benefits
Increases total metal recoveries
Provides operational flexibility to flotation circuits
Allows processing of lower-grade ore, extending mine life
Generates multiple revenue streams, reducing price-risk exposure
Eliminates pyrite-rich tailings and associated liabilities
Aligns strongly with ESG mandates and green financing frameworks
Technology Development and Track Record
BacTech’s zero-tailings system integrates proven bioleaching with downstream ammonia-based recovery. It has progressed through lab validation, independent verification (MIRARCO and ALS), and is under patent protection (filed 2024–25). Pilot-scale continuous testing is underway to optimize conditions and demonstrate scalability.
BacTech has over three decades of experience designing, building, and operating bioleach plants on three continents. Its projects have consistently shown the ability to recover valuable metals while neutralizing harmful elements and reducing long-term environmental risks.
Conclusion
BacTech’s zero-tailings extraction technology provides a holistic, adaptive, and modular solution for cobalt-bearing tailings. It:
Maximizes recovery of cobalt, copper, gold, and silver
Produces valuable by-products (fertilizer and magnetite)
Conserves water and eliminates tailings storage
Offers strong financial returns and ESG credentials
By turning what was once waste into revenue, the zero-tailings approach redefines the economics and sustainability of tailings reprocessing.
