Kelian Equatorial Mining (KEM)
Biological treatment of acid mine drainage in Kalimantan
Storm has been engaged in a long and well-considered mine closure project in Kalimantan. Mining gold results in acid mine drainage which is can be very difficult to manage and often creates devastating effects on the receiving waters environment. The operational phase is usually well resourced however those resources disappear on closure but the acid mine drainage does not.
The site is located about 14 hours of very unpleasant driving north east of Balikpapan on the west coast of the island. The Indonesian government has set strict water quality requirements for the site runoff and KEM were committed to ensuring compliance for a minimum or 100 years with minimal maintenance.
Pyrite rock is a key concern during operation and closure as the exposure to both air and water produces acid which in turn releases iron (Fe) and manganese (Mn). Of lesser concern are lead (Pb), Zinc (Zn) and sulphate (SO4). The acid mine runoff emanates from the waste materials and the open pit walls.
The closure technical team had diverse skills including hydrology, science, water treatment, geology, hydrogeology, geo chemists, geo technical, civil and structural. A range of management strategies were ultimately employed to minimise the opportunity for acid generation including complex and rudimentary ground covers as well as water covers. The open pit was filled with river water that had reasonable pH buffer capacity and the pit was also bombed with lime to fast track to the expected long term pH condition.
A number of biological technologies where investigated by way of literature reviews, laboratory trials as well as large scale research trials to prove the technology. The final treatments adopted are:
- Free water surface wetlands
- Rock lined channels
- Microbial mats
The research trials were very successful and the final design was based on the design criteria generated from the trial results.
The configuration of wetlands and rock channels is shown in Figure 1 above. The microbial mats are planned as redundancy only as they can be fabricated and placed in the pit upstream of the outlet in a short timeframe.
A final inspection was undertaken in July 2014 some years after construction. The system was performing very well with typically over 90% reduction in Mn. Although the design flow rate was approximately 200L/s there was up to 600L/s passing through the system. Most of the removal was in the first rock channel and wetland where over 20Kg per day of Mn has been collected.
There were occasions where Mn export occurred and this was very concerning for KEM. Storm analysed the available records in detail to determine the most likely cause of the export and it is directly related to maintenance activities.
Adjustments to the methods of maintenance particularly water level manipulation were able to be tweaked in the Operation and Maintenance Plan which is expected to overcome this issue.
Compliance is readily met and KEM is very proud with the success of the project.