Soil Washing Remediation Plant

Contaminant

Plant Settings

Hydrocyclone cut size d₅₀ 75 μm

Attrition scrub intensity 60%

Wash passes 2

Plant Readouts

Contaminant removed

Clean coarse recovered

Residual conc. in treated soil

— mg/kg

Vs. regulatory threshold

—

How it works

Ex-situ soil washing exploits one fact: contaminant mass is not spread evenly across a soil sample — it concentrates on the fine (clay/silt) particles, because adsorption scales with specific surface area, which grows as particle diameter shrinks:

q(d) = q₀ · (d_ref / d)^a      (specific loading, mg contaminant per kg particle)

where a is the contaminant's fines-affinity exponent (higher for strongly-sorbing PAHs/heavy metals, lower for TPH). A hydrocyclone classifier then splits particles into a coarse underflow and a fine overflow using a partition curve centred on the cut size d₅₀:

E_coarse(d) = 1 / (1 + (d₅₀ / d)^n)      (Plitt-type reduced efficiency curve)

Attrition scrubbing mechanically abrades fine contaminated coatings off the surface of sand grains before classification, liberating that mass into the fines stream rather than leaving it stuck to particles that would otherwise report to the clean coarse output. Each wash pass then applies a further first-order rinse to whatever remains attached:

C' = C · (1 − η),   η = η_max · scrub · (1 − (1 − rinse)^passes)

Cut size d₅₀ — lower it and more of the mid-size silt reports to the contaminated fines stream (cleaner coarse output, less mass recovered); raise it and more silt stays with the reusable coarse fraction (more mass recovered, more residual contamination).
Scrub intensity — how aggressively coatings are stripped off coarse grains before separation; low intensity leaves contaminated films on "clean" sand.
Wash passes — repeated rinsing of the coarse fraction, each pass removing a further fraction of what is still attached.

The coarse underflow (typically 70–90% of the original soil mass) can often be returned to site as clean fill; the fine overflow slurry is dewatered and sent for further treatment or licensed disposal — this is why soil washing works best on sandy/gravelly soils and struggles on soils that are mostly clay.

Low contamination High contamination

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