ACID ROCK DRAINAGE
Actlabs offers Static and Kinetic Testing, Leachate Quality Analyses, Humidity Cell testing and Vegetation Growth potential analyses as described below.
Acid Base Accounting (ABA) is used to assess the ability of a rock body to produce acid rock drainage. As mineralogy or rock forming minerals in the sample affects the accuracy of ABA analysis, it is advised to obtain information of the mineralogy of the samples.
Acid Base Accounting (ABA) is used to make static measurements of Acid Rock Drainage potential. Measurements of total sulphur or sulphide-sulphur are used to estimate the amount of acid bearing material. Using this information the Neutralization Potential (NP), Acid Producing Potential (AP) and Net Neutralization Potential (Net NP) are reported.
The Sobek package is the original method described by Sobek for the US EPA. The modified Sobek package is that by Lawrence and Wang. The Siderite correction package applies a method to limit the overestimation of Net NP in the Sobek method caused by the presence of siderite.
Actlabs offers the following ABA packages:
|Parameter||Acid/Base Package||Acid/Base Enhanced Package||Acid/Base Supreme Package|
|NP: MPA Ratio||•||•||•|
|Acid Soluble Sulphate||•||•|
The amount of acid that could be generated by the sulphur contained within a sample. This is done assuming that all sulphur occurs as reactive pyrite.
A direct oxidation method used to estimate the acid forming potential of a sample. The sample is reacted with hydrogen peroxide to oxidize any sulphide minerals present. The sample must be acid generating and not acid neutralizing. This causes acid generation and acid neutralization to occur simultaneously, with the end result being a direct measurement of the net amount of acid a sample can generate. If the reacted sample has a pH of 4.5 or less it is likely to be acid generating. Titration of the mixture is used to determine the amount of acidity generated. False positive results may occur if a high organic content is present. This false positive can be identified by combination with a NAPP test. In order to analyze for metals in the leachate a full second leach must be performed. Therefore the procedure will be charged twice.
Acid buffering inherent to the sample caused by a reaction of produced acid with other minerals contained within the sample. The ANC is determined using the Modified Sobek Method. A known amount of hydrochloric acid is added to a sample and allowed to react. The sample is then back-titrated with sodium hydroxide to determine the amount of unreacted HCl. The amount of acid consumed by the reaction with the sample is calculated and expressed as kg H2SO4 /t.
Amount of acid potentially produced by a sample after allowing for inherent neutralizing capacity (ANC). The NAPP is calculated using the formula:
NAPP = Maximum Potential Acidity – ANC
This test provides an indication of the reactivity of sulphides contained within a sample. It is used to provide a qualitative assessment of the likely lag time before the onset of acid conditions in the field. The test is performed like the NAG test, however the pH and temperature are monitored. The reaction kinetics are then extrapolated to the field situation.
Samples with high sulphide content may need to be reacted with hydrogen peroxide more than once in order to ensure complete oxidation of all sulphides has occurred. A sample is reacted several times and at the end of each stage the sample is filtered to separate the solids and NAG liquor. The NAG liquor is then assayed for pH and acidity, following the method for a standard NAG test. The solids are then recovered for repeat oxidation. The total NAG capacity of the sample is determined by adding the individual acid capacities from each stage.
ABCC is determined by acidifying a sample with dilute acid to approximately pH of 3 in a 16 to 24 hour time period. This method typically accounts for more readily available carbonates, such as calcite and dolomite, as this is a less aggressive treatment than the ANC method. When carbonates are present in sufficient quantity they will typically buffer a waste rock at near neutral pH. This is required to maintain low metal solubilities.
These columns are used in addition to environmental geochemical investigations on mine rock and waste materials to determine drainage chemistry. The columns simulate field weathering conditions in order to provide data for sulphide reactivity, oxidation kinetics, metal solubility and leaching behavior of test materials. The procedure simulates a weekly wet-dry cycle and a monthly leaching cycle.
Used to obtain leached elements of interest, such as As, Se and Hg from a sample. Leached elements are analyzed using ICP-MS and measurements of pH and conductivity are reported.
Parameter Leachate Extraction & Analysis SWEP • TCLP • EPA ( includes metals and Hg) • MWEP (leach only for metals) •
This method accelerates the natural weathering rate of a sample causing diagnostic weathering products. The weekly parameters measured are pH, Eh, conductivity, sulphate-ion concentration, acidity and alkalinity. Selected metals are measured on a less regular basis (weeks 0, 1, 2, 4, 8, 12, 16 and 20). Weekly cycles are used with three days of dry air, followed by three days of water saturated air. Day 7 uses a leach with water. It is recommended that a test duration of 20 weeks is to be used.
|Humidity Cell set-up|
|Weekly Humidity Cell test|
|Metal Measurements (Cu, Zn) (cost per analysis)|