Heap leaching amenability

Heap leaching testwork services

In place of heaps and dumps, laboratory testing is ultimately conducted in columns of various sizes. Column leaching using cyanide solution to assess heap-leaching potential of gold bearing ores usually follows the following processes:

• Agglomeration testing. After sample preparation and crushing to the target crush size, samples destined for column testing will very often require agglomeration testing. This includes assessment of moisture and binder additions (cement and/or lime) required to produce suitable agglomerates, as appropriate, to enable the cyanide solution to percolate through the column (heap) to be collected via the impermeable base layer. Agglomeration is performed in a modified cement mixer suitably sized for sample charges of 3kg to 15kg.
• Percolation testing. Agglomerated batches are tested in small scale columns to assess the degree of solution percolation through the sample mass and the flow characteristics (i.e. laminar or tunneling). The correct moisture level is critical to achieving competent agglomerates. Cement additions should provide agglomerates with sufficient strength to ensure integrity is largely retained under flooded conditions resulting in adequate percolation rate and minimal slump in the small-scale test. The test should also result in drain solution pH in the approximate range of 9.5 to 11.5 such that the ore’s alkalinity demand is sufficiently met. The empirical test outcomes considered suitable in the small-scale tests are: <10% slump and >10,000 L/m²/hr drain rate.
• Small scale column testing. The new facility now allows for a large number of column tests, of varying dimensions, to be operated concurrently. The multi-level platform allows easy and safe access to the top of all columns. Each leach column is equipped with a matched carbon column for removal of gold / silver from rich solutions and the recycle of the spent solution. Dosing pumps are fitted with quick-connect fittings allowing single pump operation to deliver solution to ore and carbon columns. All columns have spill trays located beneath to safely contain solution in the event of spillage. All tests are monitored daily for solution volume and subsamples collected for pH and free cyanide determinations as well as metals analysis. Where possible columns are fabricated from clear PVC to allow visual assessment of agglomerate structure and integrity.
• Larger scale column testing. Similar to the small-scale columns, larger scale columns can be fabricated to suit the program requirements and run in the same manner.
• Ancillary carbon adsorption testing
• Determination of performance and auxiliary parameters.

An important consideration in laboratory test programs is that the prepared samples have a size distribution that approximates a commercial crushing plant output for the desired top-size. This may require appropriate adjustment of the primary crushed product to avoid a disproportionate distribution in the coarse-end sizing.

ALS has also conducted sequential column tests whereby leach solution from one column is used to irrigate a second column in series. Loaded leach solutions can be passed through activated carbon columns and the regenerated cyanide solution recycled.

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Associated testwork services

Related testwork

Gold ores and the associated free milling metallurgical testwork results very often don’t fit into nice categories and packages and will often require other testwork, such as:

• Flotation
• Roasting
• High pressure oxidation
• Bacterial leaching

Click on the above links or contact us for further information. We can integrate a full program for you if required.