Of contaminated sites, acacias and climate change adaptation! | Part 2

Renaturation after mining

Anyone who has ever been to the Ruhr region or Lusatia may remember the huge lunar landscapes that mining leaves behind in the earth. The ground is turned upside down, removed and filled in elsewhere. Huge holes are created by the extraction of coal or other materials. In order to limit the damage caused by mining, the Federal Mining Act obliges mining companies in Germany to restore, i.e. renaturalize, the worked area after mining has ceased. Typical examples of this in Germany are quarry ponds. The area is rehabilitated, the embankment secured, the hole possibly filled with water, plants planted and a new natural area is created. That’s the theory.

Of course, this type of renaturation is not possible everywhere. In “Issue No. 6 – War & Environment”, we already reported on the so-called perpetual costs in the Ruhr region. In some cases, old shafts have to be secured and the groundwater level has to be maintained for ages by pumping, as otherwise entire cities like Essen would be under water. Elsewhere, contamination of the groundwater with toxic substances and heavy metals must be prevented by continuously pumping out and purifying mine water.

In principle, however, the aim of this law is to return the area to nature after the end of opencast mining. In many cases, it is actually possible to turn old open-cast mining areas into near-natural areas that also serve as recreational areas for the local population. The Leipzig lake district is a good example of this.

Acacias and manioc in Vietnam

From an environmental and climate protection perspective, mining should always be avoided. However, where this is not (yet) possible, the obligation to renaturalize can limit the damage caused by mining. Vietnam is one of the countries that cannot yet do without the proceeds of mining. It still obtains a third of its energy from burning hard coal, which is extracted using the open-cast mining method. In addition, the mining of other raw materials such as bauxite, tungsten and metal ores is also of economic importance in Vietnam.

However, Vietnam is imposing increasingly strict environmental regulations on the extraction of raw materials and renaturation is also an important issue. In this respect, Germany is considered a role model for some mining companies and visits have already taken place to learn from each other’s renaturation measures.

In order to comply with increasingly strict environmental regulations and at the same time enable scientific research into land use, UfU is working in Vietnam with the state-owned mining company Vinacomin and the private mining company Massan High-Tech Materials. Massan operates the Nui Phao Mine, the largest tungsten mine outside China. The background to the research is a problem that we are also familiar with in Germany: Conflict over land.

Urbanization, sealing, increased energy demand, expansion of infrastructure and the growing population in Vietnam are creating an increasing demand and thus also conflict over land, especially for agriculture – Vietnam is one of the largest rice exporters in the world. As mining typically covers particularly large areas, there is an interest in Vietnam not only to renaturalize former mining areas in the future, but also to be able to use them for other purposes, such as agriculture. In other words, Vietnam does not want to create huge quarry ponds, but agricultural land that is suitable for food production.

However, the quality of the soil on former opencast mining sites stands in the way of this goal. As described in the previous article, areas where industrial processes have taken place are often considered contaminated, in the case of mining by heavy metals. In principle, there are different approaches to dealing with contaminated soils, depending on the level of pollution. However, the primary objective is always to protect the soil in order to prevent the spread of pollutants, e.g. through erosion or leaching by precipitation. Ideally, soil contamination is even reduced by treating the soil with decontamination measures.

The former mining areas in Vietnam are therefore not suitable for food production for the time being. However, as Vietnam is still heavily dependent on fuels, the idea arose to use the former mining areas for planting energy crops, i.e. plants that can be used to produce bioethanol or pellets. Back in 2014, UfU carried out a feasibility study and found that post-mining sites in Vietnam are particularly suitable for the cultivation of energy crops, as they have a large area of potential and have already been developed in terms of infrastructure.

For this reason, our projects examine two core questions:

A: Are the former mining areas suitable for agricultural use with energy crops?

B: What effects does the permanent cultivation of the soil have on soil quality and the toxic substances introduced?

We have been planting various energy crops at three locations for some time in collaboration with the local mining companies and are investigating both the soil quality and the proportion of toxins in the plants. We have planted various types of acacia and cassava as test plants. Cassava is a plant that produces starchy root tubers and is particularly suitable for the production of bioethanol. But acacia biomass can also be used to produce energy.

Why bioethanol?

Bioethanol production is normally viewed critically by environmental organizations. For good reasons. On the one hand, the path dependency on technologies such as the combustion engine or gas heating will be further promoted if we burn organic substances instead of fossil fuels in the future. Secondly, however, the cultivation of energy crops competes for land with food production. This means that agricultural land that could actually be used for food production will be lost due to the cultivation of energy crops or, in a worse scenario, new agricultural land will be developed through deforestation or other measures, which in turn means a loss of unused and wild natural areas. Added to this are problems such as the use of pesticides and fertilizers and the destruction of soil.

This classic trade-off conflict between food and energy crop cultivation is defused on former mining areas due to the contamination and thus the exclusion of food production, or does not arise at all. What’s more, the hope is that the cultivation of energy crops on these areas could possibly even remove the toxins from the soil and make it suitable for growing food again in the future, i.e. the soil is improved by the measure.

As described above, Vietnam is still heavily dependent on fossil fuels. An increase in bioethanol in the total amount of available fuels would reduce Vietnam’s carbon footprint. In addition, if scaled up accordingly, mining companies would benefit economically from processing the previously cultivated land. This results in an increase in biodiversity, jobs are secured and people in the region benefit from the region even after the end of open-cast mining activities. The latter is particularly important in a country like Vietnam – Vietnam is still an emerging economy.

Using a life cycle assessment, we are currently investigating which boundary conditions must be met in order to achieve the greatest possible_{reduction in CO2} compared to fossil fuels.

We accompany the pilot cultivation of energy crops by spatially and temporally resolved soil sampling to investigate the material load and selected physical and chemical soil properties.

We are currently examining the cultivated energy crops for their heavy metal content in order to determine the extent to which the plants absorb the pollutants, i.e. how high the transfer from the soil to the plant is. This would make it possible to estimate a time horizon until the soil has been cleaned of the pollutants through the cultivation of energy crops and is therefore suitable for agricultural use again at some point. However, this type of soil remediation cannot yet be clearly assessed from a nature conservation perspective.

On the one hand, there is an opportunity to reduce the heavy metal content in the soil to such an extent that the soil will be available for food production again in the foreseeable future. On the other hand, heavy metals are persistent, i.e. resistant, pollutants that cannot be broken down either microbially or chemically. For this reason, attempts should always be made to prevent the further spread of heavy metals in the environment and to reduce, i.e. concentrate, the volume of pollution wherever possible. This is why we are currently investigating which of our test plants absorb the pollutants and where the pollutants are concentrated in the plant.

An example: If we were to find that heavy metals are particularly concentrated in the leaves of our plants, this would be rather detrimental, as the heavy metals would tend to be dispersed into the environment through the shedding of wilted leaves.

Furthermore, it is currently still unclear what effect the heavy metal content in the plant will have on further steps in the value chain, such as bioethanol production. Special processes would have to be used here to ensure that the pollutants are not dispersed through further processing.

So why this effort and this type of soil remediation? Costs are a major factor here. Professional remediation, in this sense the removal of heavy metals from the entire soil, is not possible due to the area and soil structure. Mining sites are huge in terms of surface area, the soil is churned up, removed in one place and backfilled in another. The contaminated soil remains contaminated and cannot be fully remediated in an economically viable scenario. However, as Vietnam cannot/will not leave such large areas lying fallow due to land conflicts and economic pressure, we are trying to achieve a subsequent use with these projects that removes the heavy metals from the soil and at the same time enables a subsequent use that has a positive impact on the_{CO2 balance} in Vietnam.

The large increase in biodiversity at the pilot sites so far is already positive. The plants are growing well and dense acacia forests are developing. The cassava harvest has also been relatively positive, considering the unfavorable soil conditions.

Further research results are expected shortly.