TECHNICAL PAPERS
Selenium Management in Mining Using Electro-Reduction
Presented at COM 2024 in Halifax, this paper traces the development of BQE Water’s Selen-IX™ electro-reduction technology, from the regulatory pressures driving it to the chemistry behind it and the full-scale results now underpinning its use as an established selenium treatment option.
TECHNOLOGY
Selen-IX™ (Ion Exchange + Electro-reduction)
APPLICATION
Selenium electro-reduction chemistry, technology development and full-scale plant performance
LOCATION
Canada and USA
PUBLISHED
Conference of Metallurgists (COM) 2024, Halifax, Canada
AUTHORS
Maryam Mohammadi, David Kratochvil, H.C. Liang
SCOPE
Technology development history, the selenium electro-reduction mechanism and full-scale performance data
KEY TOPICS COVERED
- Why selenium is a priority contaminant across mineral deposits and metallurgical processes
- Regulatory drivers for selenium treatment, covering aquatic life and drinking water standards
- Where biological selenium treatment falls short
- The chemistry and mechanism of selenium electro-reduction
- Eight years of Selen-IX™ development and full-scale performance results
TECHNICAL SUMMARY
Selenium is ubiquitous across mineral deposits, from base and precious metal ores to uranium deposits, and its regulation has advanced significantly as toxicologists have better understood its chronic, bioaccumulative effects on aquatic life. Water quality standards for selenium now sit as low as 1.5 to 2 ppb in some jurisdictions, orders of magnitude stricter than drinking water limits, reflecting how much more sensitive fish are to selenium than humans.
When these regulations were first introduced, biological treatment was the only recognized Best Available Technology. This paper sets out its shortcomings in detail: dilution dependency, generation of highly bioavailable organo-selenium species, added BOD/COD and nutrient load in the effluent, no long-term evidence of residue stability, and poor adaptability to flow and temperature swings. Meeting emerging regulation required a disruptive innovation rather than incremental improvement of biological systems.
Selen-IX™ addresses this by combining selective ion exchange with electro-reduction. The ion exchange circuit pre-concentrates selenate from feed water by a factor of 20 to 2,000 times into a small brine volume, which is then treated in the electro-reduction circuit (ERC). The ERC generates a ferrous-ferric double layer hydroxide with high reductive capacity, capturing selenate and reducing it to elemental selenium fixed in a compact, stable solid that passes TCLP testing and is suitable for co-disposal with tailings.
The paper traces roughly eight years of development, from proof-of-concept lab testing through pilot trials to full-scale plants, representing around $6 million of investment and more than 20,000 assays. It closes with a wider point: Selen-IX™’s ion exchange and electro-reduction approach extends beyond selenium to other metalloid oxyanions, including molybdenum, antimony, arsenic, boron and chromium, positioning the technology as a platform rather than a single-contaminant fix.
KEY FINDINGS
- Selen-IX™ pre-concentrates selenate by a factor of 20 to 2,000x before stabilization, reducing treatment volumes significantly
- Full-scale plants have achieved treated water selenium below 1 ppb
- Electro-reduction produces a stable, low-volume solid residue that passes TCLP testing and is suitable for tailings co-disposal
- Roughly eight years and $6 million of development, backed by over 20,000 assays, underpinned commercialization
- The technology is broadly applicable to other metalloid oxyanions beyond selenium, including molybdenum, antimony, arsenic, boron and chromium