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Standard ASTM Humidity Cell

SGS is the global technical leader in the field of humidity cell analysis. We have years of experience helping mining and engineering companies worldwide document the Acid Rock Drainage (ARD) potential of their properties. Our automated laboratories offer complete static and kinetic ARD testing services, with highly trained professionals following fixed testing protocols to ensure reproducible results.

Humidity cell tests are designed to mimic weathering at the laboratory scale in a controlled fashion. The test determines the rate of acid generation, the variation over time in leachate water quality and thus allows you to develop mitigating strategies.

The standard humidity cell test is conducted at the bench scale. The sample is subjected to alternating cycles of dry and moist air to simulate precipitation cycles. The sample is soaked for a specific length of time with deionised water. The water percolates through the sample and is then collected. This leachate is analysed for a number of parameters including pH, sulfate, acidity, alkalinity, conductivity and metals (including Ca and Mg). The test design can be customised to better account for sample matrix effects by increasing or reducing the particle grain size or altering the shape of the cell and changing the flow rate.

Larger scale cells can test several parameters. The response of coarser samples more typical of waste rock can be assessed.  Various cover design options can be tested and the effectiveness of cover systems in reducing ARD can be assessed. 

Other humidity cell design options that SGS can support include the addition of bacteria, flooding of the sample, temperature cycling, variation of the humid-dry air cycle, and variable duration of the air/leach cycle. Depending on your circumstances, we can design a testing programme to truly reflect your operational site.

Humidity cells test results are reviewed monthly to check progress and determine if extended leaching is required. Tests typically run from 16 to 24 weeks. Tests of longer duration are run to evaluate ARD control options. Such tests are designed to provide data for mitigation strategies, thus lessening the effects of ARD. ARD reactions are complex and SGS has the technical expertise to help you with the interpretation of your results.

As the ARD generating and neutralising minerals leach away, the mineralogy of the leach sample will change. SGS’s high definition mineralogy services provide characterisation and documentation of these changes throughout the duration of the test. The integration of our environmental mineralogy expertise gives you a more complete picture of the mineralogical causes of ARD potential and neutralisation strategies.

All SGS sampling and laboratory analysis is performed in accordance with recognised global standards such as American Society for Testing and Materials (ASTM) and International Standards Organisation (ISO). Partner with us to ensure your ARD testing needs are met by industry experts, allowing you operate in an effective and environmentally responsible manner.

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