Investigation of different amendments for dump reclamation in Northern Vietnam

• We investigate three locally-available amendments to restore dumps.
• Sieving of spoil leads to enhanced spoil conditions for re-vegetation.
• Charred rice straw with grass ameliorated the spoil to soil-like conditions.
• Power station ash originating from the coal power station in Uông Bí is not effective.
• Pyritic fine spoil material is not suitable for fast reclamation.

Giant spoil dumps originate in the course of open-cast mining. The initial properties of Triassic spoil as well as pedogenesis are characterized by weathering processes. Due to the poor conditions in dump spoil a natural succession of plants or a re-vegetation is a lengthy process. The Chinh Bac field experiment (Ha Long City, Quang Ninh province, Vietnam) was planned to investigate the possible impacts of three amendments – charred rice straw, power station ashes and fine material originating from the mining area in combination with sieved spoil of substrate quality – to enhance plant growth. The main focus of this study was directed towards the impact of added amendments on spoil chemical parameters. The investigations demonstrated that simply sieving the spoil leads to better substrate conditions. It increases the fine material which in turn leads to easier plantation conditions. At the same time oxidative processes and leaching acid products are stimulated which raises the pH values afterwards. The application of charred rice straw increased the amount of alkaline cations, in particular potassium, boosting the pH value. This led to an enhanced supply of nutrients for the plants in comparison to the other amendment variations which were very poor in nutrient availability. Adding power station ash resulted in a short-term pH value increase, however potential pollution caused by heavy metals cannot be ruled out. The pyrite containing fine material was identified as the poorest amendment. It may allow vegetation to grow quickly, however the proceeding weathering processes cause a strong acidification. This mobilizes heavy metal and aluminum ions which prevent healthy plant growth.