Gravity Separation Testing

This FLSmidth laboratory includes bench and pilot scale gravity separation equipment. Resources are available to determine the amount of gravity recoverable minerals in your ore samples of any size and description.

  • GRG Test
  • GGT Test
  • Alluvial Gold Test
  • Bulk Screening and Analysis
  • Grinding Test
  • Gemini table upgrading and concentrate...
  • CVD Pilot Testing


The Gravity Recoverable Gold (GRG) Test is a widely accepted industry test used to determine the theoretical maximum amount of gold that can be recovered from a sample. It is the most popular test performed in FLSmidth's Knelson Research and Technology Centre.

This test is a multi stage test that utilizes the laboratory scale Knelson™ concentrator KC-MD3 with sequential grinding. A 30kg of sample crushed to -1.7mm (sample crushing can be arranged at an extra charge) is required to perform a GRG test.

FLSmidth's GRG test includes all assays at an independent lab and a comprehensive metallurgical test report detailing testing results and analysis.


Gravity Grade Test (GGT) is a derivative of the industry standard Gravity Recoverable Gold test. It utilizes enhanced gravitational forces combined with patented FLSmidth Knelson technology to provide a comprehensive grade estimation for the given test sample. With this test, sample head grades can be precisely measured by alleviating the nugget effect associated with sub-sampling. The FLSmidth Knelson Gravity Grade Test is a great tool for those involved in resource estimation of gold where high confidence in reported results is desired.

Test Description

  • Sample is processed in its entirety
  • Free gold is recovered with high efficiency in a small concentrate mass ad fire assayed to extinction to account for all gold recovered
  • Test tailings can be sub-sampled and assayed with confidence because any remaining gold is finely disseminated
  • Fire assay results from the two streams are combined in a metallurgical balance to provide overall sample grade


  • Improve confidence in reported results
  • Maximize gold resource value
  • Minimize nugget effect
  • Ability to analyze large samples


FLSmidth provides a range of testing options for alluvial gold samples. Alluvial samples will generally be tested using a 2-pass batch test. These tests will not involve any grinding.

A minimum sample size of 50kg is recommended in order to reduce the difficulties of getting a representative alluvial gold sample. Samples must be 100% minus 1.7mm (10 mesh). Samples that do not meet this size requirement take longer to complete and will require special pricing.

The following guidelines will be used to select the appropriate concentrator for certain sample sizes.


 Dry Sample Mass Range

 Batch Concentrator







Bulk Screening

FLSmidth is capable of performing the bulk screening custom test procedure utilizing a dry vibrating screen. All bulk screening will be performed dry. Smaller samples can be wet screened on a vibrating deck.

Screen Analysis

Detailed screen analysis can be performed at FLSmidth Knelson using premium quality screens in a full range of sizes. For fine sizes a vibrating wet screening device is utilized.

Typically screen analysis requires approximately 200 grams of sample. However, sample size may vary if additional testing or analysis is required on the screened fractions.

Grinding Test

Custom grinding is performed using a lab scale rod mill. FLSmidth can batch grind samples ranging in size from 1kg to 10kg per grind. If a specific grind size is desired an extra sample should be included so that a grind test can be performed.

Samples sent for milling should be crushed to less than 3mm. This top size is variable depending on ore hardness. We can also do crushing. Maximum top size for crushing is 63".

FLSmidth focuses on the customer's needs by providing objective results that enable confident, mineral processing and metallurgical project decisions.

Gemini Table

Gemini table upgrading and concentrate cleaning service, provided by the FLSmidth, offers crisp mineral separations for final concentrates.

The Gemini table can be used to upgrade gold concentrates to a smeltable grade. The table has a capacity of 30kg/hour and produces separate concentrate, middlings, and tailings streams.

A minimum sample of 3kg is required to run the Gemini table upgrading or concentrate cleaning service. A minimum amount of sample is required in order to run the service effectively. The maximum particle size should not exceed 1mm.

CVD Pilot Test

The Knelson™ continuous variable discharge concentrator (CVD) is applicable to high mass yield applications that typically range between 1 and 30%. The mass yield is completely controllable from zero to 100%. The pilot facility can currently handle testing feed percentage solids between 10 and 40%.

The pilot facility consists of 2 large agitated sample tanks, pumps, piping, and a pilot CVD6. A full range of support equipment including size analysis, sample-drying equipment etc, supports the pilot plant.

CVD testing is custom work and requires consultation with FLSmidth Knelson staff. CVD testing is performed at a pilot scale and requires at least 500 kg of sample. Particle size should not exceed 2mm. It is the responsibility of the client to provide a sample that is representative of the stream to be tested.

FLSmidth focuses on the customer's needs by providing objective results that enable confident, mineral processing and metallurgical project decisions.