How to check a gold plant's iron separator for gold losses
Gold can leave a washing circuit with iron-rich material when particles are trapped in magnetic clumps or carried along by the separator discharge. To check for losses, collect a representative sample of that discharge, weigh it, recover and examine its gold content, and compare the result with feed and operating conditions. A few visible specks alone do not establish the size of the loss; the gold content must be considered alongside the amount of material being discarded.
In a Gold Washing Plant with Iron Separator, the first task is to establish where the magnetic fraction goes. It may be discarded, stockpiled or returned to another recovery stage. That destination determines whether detected gold is a final loss or material that still has another opportunity to be recovered.
Map the separator before taking a sample
Identify the separator feed, magnetic discharge and non-magnetic discharge on the actual flow sheet. Confirm whether the unit is removing tramp iron, separating magnetic minerals from concentrate, or performing another duty. A belt magnet over coarse feed presents different sampling difficulties from a wet drum treating fine slurry.
Trace the magnetic discharge far enough downstream to see whether it mixes with another stream. Sampling after dilution or mixing can obscure the source of a loss. Also check for spills, material sticking to guards and buildup around discharge chutes: these may bypass the intended sample point or accumulate until cleaning.
Record the operating conditions that could affect the result, including feed rate, water addition, material size, separator settings and whether the plant is running steadily. Note changes in ore type or clay content. A sample taken during startup, a blockage or a washdown should be identified as such rather than treated as normal production.
Collect a sample that represents the discharge
Agree on the sampling point and method before starting. The aim is to capture the whole cross-section of the discharge at intervals throughout the assessment period, not to scoop a convenient handful from the surface of a pile. Gold particles can settle or segregate, so an incomplete cut can give a misleading result.
- Use an approved collection arrangement. A properly designed diverter or accessible collection container may allow a complete timed cut. Do not reach across a moving belt or place a hand-held container in an unsafe discharge path.
- Take repeated increments. Collect several complete cuts across the agreed operating period and combine them when the purpose is to assess average performance. Keep separate samples when comparing different feed conditions or separator settings.
- Identify and secure the sample. Label each container with the stream, date, collection period, operating conditions and sample collector. Prevent spillage and retain the material needed for verification.
- Measure the associated discharge. Establish the mass of the sampled stream over the same period, or use a documented mass-flow measurement. For slurry, account for water and report results on a consistent dry-solids basis.
If a full-stream cut cannot be collected safely or reliably, treat a grab sample as a screening test only. It can reveal that gold is present, but it should not be used on its own to calculate plant loss. Arrange a suitable sampling point or obtain a sampling specialist’s help before making a quantitative decision.
Separate and examine the retained material
Dry, weigh and reduce the sample using a documented procedure that preserves representativeness. Coarse gold can be unevenly distributed, so excessive splitting or discarding coarse particles may produce a falsely low result. Screen size fractions where practical and inspect both coarse and fine material. Record the dry mass of each fraction and retain enough material for a repeat check.
Carefully break up magnetic clumps and wash away adhering sediment. A hand magnet, protected by a removable cover, can help divide magnetic and non-magnetic material for examination. Inspect the washings and both fractions: free gold is not normally attracted to a magnet, but it can remain attached to iron, enclosed in composite particles or trapped mechanically among magnetic grains.
Pan or use an appropriate small-scale gravity method to concentrate heavy particles, then examine the concentrate. Avoid assuming that every yellow particle is gold; where identification is uncertain, or gold is too fine to assess visually, submit representative material for a suitable laboratory assay. Tell the laboratory that coarse or unevenly distributed gold may be present so sample preparation and assay selection can address that risk.
Turn a concentration into a loss estimate
Calculate the gold mass associated with the separator discharge by multiplying its dry-solids mass by its measured gold grade, using consistent units. For example, a grade reported in grams per tonne must be paired with a discharge mass in dry tonnes. Compare that estimated gold mass with the gold entering the relevant part of the circuit over the same period. If feed mass or grade is unknown, report the discharge grade and mass separately rather than presenting an unsupported recovery percentage.
Repeat sampling helps distinguish a persistent loss from a short-lived event. Where assay results are close to the laboratory’s reporting limit, or duplicate results vary widely, the uncertainty may be too large to support a precise loss estimate. Preserve the records and investigate sampling and preparation before changing equipment settings.
Use the evidence to locate the cause
Gold found in the magnetic discharge does not automatically mean the magnet is too strong. Look at the particles and operating record together:
- Gold in loose magnetic clumps: Check for buildup, poor dispersion or insufficient washing. Clay and compacted fines can hold non-magnetic particles in the discarded fraction.
- Gold attached to iron or locked in composite particles: Washing alone may not release it. Assess whether a downstream recovery step or controlled reprocessing is appropriate for that material.
- Losses rising with feed surges: Examine feed distribution, loading and discharge behavior. Overloading can cause unwanted material to be swept into the magnetic stream.
- Gold found in spills rather than the intended discharge: Inspect chute alignment, containment and housekeeping arrangements before attributing the loss to magnetic separation.
Change one controllable factor at a time, within the equipment manufacturer’s operating limits. Depending on the separator, that might involve feed rate, wash water, belt speed or the position of an adjustable component. Collect comparable before-and-after samples and record the setting. An improvement in one stream is not enough: check the other discharge too, so that reduced gold loss is not achieved by allowing unacceptable iron contamination downstream.
Upstream supply conditions also matter when the washing plant receives dredged material. The YLCSD550 Cutter Suction Dredger is intended for dredging and sand excavation in inland waterways, lakes and coastal areas. Its supplied slurry can form part of a mining process where the overall system is designed accordingly, but the dredger itself does not establish separator performance. Sampling should reflect the actual feed reaching the separator, particularly when material or flow conditions change.
Plan the inspection around stored energy and moving equipment
Use the site’s isolation and lockout procedures before opening guards, clearing blockages or removing retained material. Isolate relevant electrical, hydraulic and mechanical energy sources, verify a safe state, and secure components that could move or fall. Strong magnets can attract tools and interfere with medical implants; keep susceptible items clear and follow the equipment’s safety instructions.
Wet sampling introduces slip and splash hazards, while dry sample preparation can generate dust. Select containment and protective equipment for the material and task, and use approved lifting arrangements for heavy containers. Do not use mercury or other hazardous recovery chemicals as an informal field test.
Keep the sample identifiers, dry masses, assay reports, operating settings and any corrective action together. Recheck after an adjustment under comparable conditions. If representative sampling remains impossible, results are inconsistent, or gold appears locked in iron-bearing particles, further metallurgical assessment is needed before declaring the separator acceptable or redesigning the circuit.
