ASS: How Does Pyrite Get There?
What causes ASS?
ASS are any material or sediment that contains iron sulfides that, when disturbed or drained, forms sulfuric acid. In most cases, the iron sulfide present is pyrite (FeS2, also known as Iron (IV) Sulfide). This pyrite is very reactive.
It is usually the smaller crystals of pyrite found in ASS. The pyrite reacts with oxygen to create sulphuric acid (therefore disturbing the soil creates the acid, as the pyrite is exposed to the air). The smaller pyrite framboids (raspberry shaped granules) are more reactive than the larger ones as there is more surface area exposed to the oxygen.
How does the Pyrite get there?
The production of pyrite is a very specific procedure, requiring certain conditions, facilitators and ingredients. Sulfate …show more content…
It is a log scale meaning that every number (e.g. 7) is ten times more acidic than the number after it (e.g. 8).
This means that something with a pH of 3 would be 10000x more acidic than distilled water, which has a pH of 7.
How does temperature/the presence of salinity affect the oxidation rate?
Pyrite oxidation generates O2 and produces heat. Due to this, the acidity and temperature of the surrounding soil/solution will affect the overall reaction rates (4). Biological oxidation only occurs between 0oC and 55oC with an optimum range of 24oC – 45oC (4), but chemical oxidation can happen at a much higher temperature. It is predicted that the PASS will oxidize at a much faster rate if the temperatures are at the higher end of the scale as it is known that higher temperatures increase the speed of reactions (reference).
It is also known that as the salinity of water decreases, oxygen solubility rises. Since the slurry of ASS will be made using water with the pre-set amount of salt already dissolved, the ASS will come into contact with more dissolved oxygen (in water with less salt dissolved in it), and it will oxidize
ASS are any material or sediment that contains iron sulfides that, when disturbed or drained, forms sulfuric acid. In most cases, the iron sulfide present is pyrite (FeS2, also known as Iron (IV) Sulfide). This pyrite is very reactive.
It is usually the smaller crystals of pyrite found in ASS. The pyrite reacts with oxygen to create sulphuric acid (therefore disturbing the soil creates the acid, as the pyrite is exposed to the air). The smaller pyrite framboids (raspberry shaped granules) are more reactive than the larger ones as there is more surface area exposed to the oxygen.
How does the Pyrite get there?
The production of pyrite is a very specific procedure, requiring certain conditions, facilitators and ingredients. Sulfate …show more content…
It is a log scale meaning that every number (e.g. 7) is ten times more acidic than the number after it (e.g. 8).
This means that something with a pH of 3 would be 10000x more acidic than distilled water, which has a pH of 7.
How does temperature/the presence of salinity affect the oxidation rate?
Pyrite oxidation generates O2 and produces heat. Due to this, the acidity and temperature of the surrounding soil/solution will affect the overall reaction rates (4). Biological oxidation only occurs between 0oC and 55oC with an optimum range of 24oC – 45oC (4), but chemical oxidation can happen at a much higher temperature. It is predicted that the PASS will oxidize at a much faster rate if the temperatures are at the higher end of the scale as it is known that higher temperatures increase the speed of reactions (reference).
It is also known that as the salinity of water decreases, oxygen solubility rises. Since the slurry of ASS will be made using water with the pre-set amount of salt already dissolved, the ASS will come into contact with more dissolved oxygen (in water with less salt dissolved in it), and it will oxidize