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Mercury Remediation

Recovering Elemental Mercury and Associated Gold from Contaminated Mining Material

For centuries, mercury amalgamation was widely used to recover gold. Although effective at capturing fine particles, the process left elemental mercury in river sediments, mill tailings, sluice concentrates, and historic mining sites around the world.

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Much of this mercury remains in the environment today.

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Yuba Mining and Machine uses a combination of the Low-G Horizontal Centrifuge and Reverse Multi-Helix Spiral concentrators to separate and concentrate elemental mercury from properly prepared soils, sediments, and mine tailings.

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Because mercury is extremely dense, it responds strongly to gravity and centrifugal concentration. Our equipment can recover free liquid mercury, mercury-bearing amalgam, and associated heavy-mineral concentrates while reducing the total volume of contaminated material requiring specialized handling.

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Since 2010, we have continued developing mercury-recovery processes for river sediments and both historic and modern mill tailings. Our objective is to provide a practical physical-separation process that supports environmental cleanup while recovering gold and other valuable material associated with the mercury.

The Legacy of Mercury in Gold Mining

Mercury was historically mixed with gold-bearing material because it bonds with gold to form an amalgam.

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Once the amalgam was collected, it was commonly heated to separate the mercury from the gold. Historic handling practices frequently allowed mercury to spill, escape into process water, or remain mixed with tailings.

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Contamination may still be found in:

  • Historic dredge tailings

  • Sluice and jig tailings

  • River and stream sediments

  • Mill tailings

  • Settling ponds

  • Black-sand concentrates

  • Amalgamation areas

  • Equipment cleanup areas

  • Soil surrounding former processing plants

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Mercury may occur as visible liquid droplets, extremely fine divided particles sometimes called flour mercury, or amalgam containing residual gold.

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Even when mercury cannot be seen easily, it may still be concentrated in the dense fraction of the material.

Why Elemental Mercury Is Difficult to Recover

Mercury presents a different recovery challenge than conventional solid minerals.

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Fine Mercury Droplets

Elemental mercury can break into extremely small droplets during mining and processing.

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These droplets may remain dispersed throughout sand, silt, black sand, and tailings rather than collecting into one visible mass.

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Flour Mercury

Repeated agitation can divide liquid mercury into very fine beads. This flour mercury can travel with process water, become mixed with fine sediment, and be difficult to recover using basic settling equipment.

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Mercury Trapped in Compacted Material

Historic tailings and river sediments may become cemented, clay-rich, or densely compacted over time.

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Mercury trapped inside clay balls or consolidated material cannot be effectively separated until the material has been thoroughly broken down and liquefied.

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Association with Gold and Heavy Minerals

Mercury often occurs alongside gold, magnetite, sulfides, and other dense minerals.

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A recovery system must retain this valuable heavy fraction while rejecting as much clean, lighter material as practical.

Primary Recovery with the Low-G Horizontal Centrifuge

The Low-G Horizontal Centrifuge can serve as the primary concentrator when the material contains fine elemental mercury and relatively manageable quantities of competing heavy minerals.

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The centrifuge uses centrifugal force to drive dense particles into internal concentrate chambers. Mercury, amalgam, gold, and other heavy minerals are retained while lighter material continues through the machine.

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The Low-G Horizontal Centrifuge offers several advantages for mercury-bearing material:

  • Strong centrifugal separation

  • Recovery of fine dense particles

  • Large concentrate-holding capacity

  • Controlled batch concentrate collection

  • Operation with turbid or recycled process water

  • Integration into mobile or stationary plants

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At the end of the production period, the accumulated heavy concentrate is discharged into a contained receiving system for additional processing.

Mercury Recovery with Reverse Multi-Helix Spirals

The Reverse Multi-Helix Spiral is especially useful for mercury remediation because it provides an adjustable, continuous method of separating dense mercury-bearing material from lighter sediment.

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As the feed moves through the rotating barrel, mercury, gold, amalgam, and other heavy minerals settle into the internal spiral grooves. The reverse-running leads convey this dense material toward the concentrate discharge while lighter material is washed toward the tailings end.

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The spiral can be adjusted to prioritize maximum retention during the initial stages and progressively tighten the separation during cleaning and finishing.
 

24-Inch Spiral Rougher

The Rougher is used for higher-volume feed and broad initial concentration.

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It removes a large portion of the lighter soil or tailings while retaining the mercury-bearing heavy fraction.

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Multiple Roughers can be installed in parallel when higher throughput is required.

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16-Inch Spiral Cleaner

The Cleaner receives the Rougher or centrifuge concentrate and removes additional lighter material.

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This stage substantially reduces the volume of material requiring final handling.

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16-Inch Spiral Finisher

The Finisher makes the tightest separation.

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It further upgrades the mercury-, amalgam-, and gold-bearing concentrate before the material is transferred to an appropriate contained treatment, retorting, recycling, or disposal process.

Build the Remediation System Around the Site

A mercury-recovery plant may include:

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Some projects may require only the treatment of an existing heavy concentrate. Others may require a complete mobile plant capable of washing, scrubbing, classifying, concentrating, and securely collecting mercury-bearing material.

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The system should be designed around the actual contamination, site conditions, production requirements, and remediation objectives.

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