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Acid drainage can be prevented and effectively managed through correct assessment of acid generating materials (acid sulfide soils or sulfidic mine waste) prior to their exposure.
Management and identification of acid generating materials require an analytical methodology that can provide the accuracy and precision required to confidently assess the inorganic oxidisable sulfur content of materials that are likely to be disturbed by the prescribed activity.
Acid sulfate soils are a major source of environmental damage when mismanaged. The source of the problem is their iron sulfide content. When the iron sulfide content of soils is exposed to air it oxidises and creates acid. When it rains, acid in the soil washes out into the natural waterways and kills fish and other aquatic organisms. Acid waters can mobilise aluminium and other metals which, when in the presence of acid, can also be lethal to aquatic organisms and severely degrade the environment. Low lying lands in the coastal regions which are drained can turn acidic due to acid sulfate soils. The acid generated causes severe deterioration of the lands rendering them useless for agricultural production. Canefields and low-lying pastures are also at risk for the same reasons. In mining, quarrying and major excavations where soils and rocks containing sulfides are exposed, the sulfides readily oxidise and generate acid. If this acid is allowed to escape into the environment it can cause serious environmental harm through its inherent acidity and the metals it contains.
Significant money is spent annually by the mining, land development and agricultural industries on the management and remediation of acid drainage. In the USA and Canada it is estimated at US$1.2 billion to US$2.0 billion annually. In Australia alone the annual cost is estimated to be AUD$160 million.
[Source: John Harries - Acid Mine Drainage In Australia - Supervising Scientist’s Report 125, 1997].
For effective management and remediation of problems caused by acid sulfate soils, industries, authorities, research organisations, laboratories and private companies all need a portable, cost-effective, reliable and efficient instrument to analyse the level of the sulfide component of acid-producing compounds in soil and rock samples.
Academic staff attached to the Southern Cross University devised a method based on established science which provides a reliable, economic and efficient way of determining the level of the sulfide component of acid-producing compounds in soil and rock samples.
RISATEC has developed a portable device: Reduced Inorganic Sulfur Analyser (RISA) for the field measurement of the CRS concentration in acid-producing compounds in soil and rock samples.
The Chromium Reducible Sulfur (CRS) analytical procedure is suitable for determination of inorganic sulfur that can be directly equated with the quantity of pyritic sulfur present. The method is not subject to interference from organic sulfur or sulfates.
The portable RISA can carry out a test, at the site, in approximately 20 minutes, two-to-three times faster than the fastest laboratory methods.
The RISA apparatus can provide fast, accurate and reliable results at a fraction of the cost of comparable currently used analytical methods.
The RISA analysis is an automated procedure that relieves the potential for human error, and provides consistently uniform results.
Determining the severity or potential impact of acid sulfate soils has proven difficult, with many of the techniques available providing misleading results and incorrect concentrations. Analysis has been based on techniques that determine acidity directly or calculate the amount of iron sulfide present that, if oxidised, will generate acid . Measuring iron sulfide is normally done by calculating the amount of sulfur in the sampled material. To do this one must first determine the total amount of sulfur then subtract from it the total sulfate sulfur (some acid-producing, some benign) and the amount of organically bound sulfur (benign). These methods, now being used, give inconsistent values which cannot be relied upon. The testing is currently carried out in laboratories - a procedure that is time consuming and logistically difficult. Lab testing is also expensive, both in its actual cost but more so in the cost of delay in obtaining results. There are about thirty labs in Australia and the average cost of a complete analysis, using conventional methods, is in excess of $100 .