Volume 2, Issue 1

What’s New at MPL

The last few months has seen MPL very busy developing new methodologies and new services. Our entry into the Acid and Metalliferous mine Drainage (AMD) arena has seen us secure projects from all over the nation including samples from mining companies in Western Australia, the Northern Territory and New South Wales. The range of samples to date has been remarkable. The samples have not all been routine gold mine or sulphide ore based deposits either, they have included a prominent Newcastle based company engaging us in a coal based AMD project that included assessments of sodicity and dispersion issues.

Linking with MPL’s imminent NATA accreditation for Stage 1 and 2 AMD testing from the AMIRA guidelines, the Envirolab group has also achieved accreditation for Acid Volatile Sulphur (AVS – SEM) analysis suited to marine sediments and mono sulphidic black oozes (MBO’s).

In addition to the flurry of activity in AMD testing, the Envirolab group’s Sydney facility underwent a NATA assessment in early December for the full suite of Air Toxics testing. This expanded scope now covers the analysis of carbon tubes, thermal desorption tubes, canisters and tedlar bags. Accreditation has now been finalised. This is a fantastic achievement that positions the Envirolab Group as the premier OHS and Air Toxic lab group in Australia.

In other news, Sandra Taylor the Assistant Laboratory Manager from Envirolab Services in Sydney has joined the MPL team. Sandra will be filling in for Shuk Li who is on leave after giving birth to a daughter, Leela Sequoia Bevis on 23rd February. Sandra’s technical back ground is as a NATA signatory for all organic tests and her experience as an organic supervisor and chemist is a welcome addition to the team.

An Overview of AMD

AMD, or Acid and Metalliferous Drainage is now known internationally, and nationally as one of the most serious and potentially enduring problems for the mining industry. The ability to identify in advance any mine materials that could potentially produce AMD is essential for timely implementation of mine waste management strategies and AMD control.

A number of procedures have been developed to determine the characteristics of mine waste materials. The most widely used assessment methods for AMD characterisation are the Acid-Base Accounting (ABA) and the Net Acid Generation (NAG) test.

These methods are referred to as static procedures because each involves a single measurement in time. Kinetic test procedures involve a number of measurements over time, and are used to assess a range of AMD issues including sulphide reactivity, oxidation kinetics, metal solubility and the leaching behaviour of test materials. Kinetic NAG and Leach column tests are examples of kinetic procedures.

The AMIRA guidelines recommend a three staged approach:

Stage 1: Screening
Samples are screened and categorised using relatively rapid and inexpensive static tests.
The pH (1:2) and electrical conductivity (EC (1:2)) of a sample is determined giving an indication of the inherent acidity and salinity of the waste material when initially exposed in a waste emplacement area.
Net Acid Generation (NAG) and Net Acid Production Potential (NAPP) are used to determine if a sample is Non-Acid Forming (NAF), Potentially Acid Forming (PAF) or Uncertain (UC)
A material categorised non-acid forming (NAF) may still have existing acidity and salinity risks that make it unsuitable for surface or uncontrolled placement due to potential effects on drainage and vegetation.

Stage 2: Follow up testing
To obtain more information on acid forming capacities and resolve samples with uncertain classifications. A variety of static test methods and kinetic NAG tests are carried out at this stage
This testing is used to provide better definition of the AMD characteristics of samples and also to resolve issues of uncertainty identified in AMD screening tests. Detailed geochemical tests commonly used are as follows - Sequential NAG, Kinetic NAG, Acid Buffering Characteristic Curve (ABCC), Mineralogy and elemental composition. Site specific testing may also be required, such as Cation Exchange Capacity (CEC), Particle size distribution (PSD) or Emerson testing.

These tests may be used in various combinations depending on the nature of the sample material and what information is required. Each of these tests is described below and their application discussed.

Stage 3: Leach Column testing
Longer term kinetic column testing to provide data on reaction rates and leachate chemistry.
Leach columns are used to complement the other geochemical investigations described above.
Leach columns are normally loaded with 2-3 kg of crushed (not pulverised) waste rock or tailings and subjected to wetting and drying cycles to encourage oxidation and flushing of oxidation products. Water flushed through the column sample is collected and analysed for a variety of parameters to provide information on a range of issues including sulphide reactivity, oxidation kinetics, metal solubility and leaching behaviour. Sub-samples of leached solids may also be geochemically and mineralogically tested to track changes in mineral constituents with time.

The leach column test period varies depending on material characteristics and the investigation needs, usually the results are reviewed on a 6 monthly basis.

The consequence of AMD is the formation of acidic or metalliferous minewater and is commonly associated with, but not confined to, gold, nickel, copper, iron ore, lead and coal deposits. The drainage of acid and metalliferous water has the potential to impact on the quality of water resources. In Western Australia, most mine sites are located in arid to semi-arid climates. The low annual rainfall and extended drought periods are likely to reduce the risk of acid mine drainage. Even so, there is still potential to impact nearby rehabilitation sites, native vegetation, local groundwater and streams.

The MPL Christmas Party

At the 2010 client Christmas party held in December, MPL unleashed the inner child in many of Perth environmental consultants. The event was held at the Scitech centre and it wasn’t long (just a beer or two) before we saw many consultants “playing” with the science exhibits.

Managing Director Tania Notaras officiated on the night including the drawing of three incredible door prizes. Syed Ali won the first prize of a Tiger Moth Joy Flight, Jolyon Peart winning second prize, a dinner at Halo Restaurant and Scott Murray winning the third, a Jet boat ride.