High levels of organic carbon are vital for soil health, creating a better structure to hold water and nutrients which ultimately help produce healthy plants and better crop yields.
Current land usage and agriculture is slowly diminishing the reserves of soil carbon that are slow to accumulate, making it necessary to add organic matter to maintain soil health, and in turn food and fibre security.
A Federation University Australia researcher is studying lignite, or brown coal, that is used to fire Gippsland’s Loy Yang Power Station to determine if substances that can contribute to soil health can be produced from the coal.
PhD candidate Andrew Hood said raw low-rank brown coal naturally contains humic substances, including humic and fulvic acids, which are used in commercial soil additives. These organic acids are formed from the decomposition of plants. But producing humic acid from the coal requires selective mining to get coal with a high humate content, or chemically modifying lower-grade coal to increase the proportion of humic acids.
For agricultural use, the humate-based soil additives are not classed as fertilisers, but can be blended with them. This helps soil hold on to the fertilisers, making nutrients and minerals more available to plants and less likely to leach out after heavy rain. It can be applied as a foliar spray – diluted by the farmers – or as a granular product. The additives also support soil microbes, helping improve nitrogen levels and speeding up plant growth.
“Humates are something that occur naturally – they are formed when bacteria decompose biological matter. You find them in compost, soil, peat and even rivers,” Mr Hood said.
“They have been commercially extracted out of the local lignite here from Loy Yang for two decades, but there's no guarantee that the current source lignite, which is naturally rich in humates, will be available as a feedstock into the future. We're looking at whether we can use a run-of-mine coal which has a much lower natural extractability, and upgrade it chemically to get a similar product or maybe something better.”
The project has partnered with Gippsland-based commercial producer Omnia, which currently uses a feedstock naturally rich in humates.
“In order to ensure future supply, we’re looking at run-of-mine coal, which is abundant and cheap, but lower in humate yield. This requires chemically upgrading it to increase those yields. The question we’re asking is can we make an equivalent, or possibly better product, and can we do it cost effectively?”
Coal rank is a measure of how much transformation has taken place from the original biomass. It also relates to how useful it is as a fuel. Black coal includes the higher ranks of coal – bituminous and anthracite – and is used worldwide for power generation. Brown coal is considered low rank, and not as well suited to burning, but has been used in the Latrobe Valley for thermal power generation owing to the ease and low cost of extraction.
Brown coal, having undergone less chemical transformation, has higher amounts of humic substances, which are very scarce in black coal. The very properties that makes brown coal less suitable for combustion makes it ideal for extracting useful products.
“Oxidation of coal has been done before but we haven't really studied the changes that occur to Loy Yang coal in detail and ours is a particularly good one here because it's got low ash and low sulfur, which is rare among worldwide deposits.” Andrew Hood
Work in the laboratory involves adding hydrogen peroxide, a common oxidising agent and an ingredient often found in toothpaste. In the longer term, the project will determine if optimising the production of humates and fulvates for agriculture will be viable on a large-scale level.
The project has the backing of Australian Carbon Innovation (ACI) and the Australian National Low Emission Coal (ANLEC) Research and Development, with the research being closely watched for other potential applications, including carbon fibre production and quantum nano dot technology.
“We’ve got one of the lowest ranked coals which is not really efficient for burning, despite the fact that's what it has been used for. We’re hoping we can use this coal for something more sustainable by producing higher value products from it.
“It's still somewhat early days, but we’ve been able to get a lot more yield out of it by adding the hydrogen peroxide and chemically changing it. The goal is to increase the oxygen content, and break apart the larger chemical structure of the lignite. This will transform it into a higher value material and produce more humic and fulvic acids.”