Encapsulating sulfidic coal-mine waste-rock using coal-combustion ash to prevent acid mine drainage generation – a case study M Candra Nugraha D (a*), Sukandar (b), Yulianti Pratama (a), Kamila Khalishah (a)
a) Institut Teknologi Nasional Bandung
Jl. PHH Mustofa 23 Bandung
* candra.nugraha[at]gmail.com
b) Institut Teknologi Bandung
Jl. Ganesha 10 Bandung
Abstract
Coal is still a backbone of Indonesia to generate electricity. Of the 58,519 MW electricity produced, 61% comes from coal-fired power plants.
The need for coal is supplied by many mines in Indonesia, and in the process of obtaining it often causes an environmental problem, namely acid mine drainage (AMD) generation. In addition, coal-combustion ash in power plants also have the potential to cause environmental problems. To manage these two potential problems at once, AMD and coal-combustion ash generation, a study on the use ash as a cover for sulfidic coal-mine waste-rock was conducted.
The results of the geochemical static tests conducted on fly ash (FA), bottom ash (BA), and waste rock (PAF) showed that BA has a high Acid Neutralizing Capacity (ANC), which is 771.5 kg H2SO4 / ton, and in contrary, PAF has a Maximum Potential Acidity (MPA) of 260.71 kg H2SO4 / ton.
Based on these results, a free draining column test was then performed, to understand the long-term tendencies of leachate water quality characteristics drained from the column.
Leachate water quality test from the base material (FA, BA, FABA, PAF) for several wet-dry cycles show FA, BA, and FABA mixtures (with composition 1:1) showing an average pH value of 11.4, which means it has potential as a neutralizer. While PAF shows a consistently low pH average value of 2.51.
To find out the effectiveness of FA and BA as the encapsulating material of PAF, kinetic test was also carried out for the layering composition (from top to bottom) as FA-BA-PAF; BA-FA-PAF; and FABA-FABA-PAF.
The test results show that the composition of the BA-FA-PAF layer gives a better pH value compared to the other compositions, with an average pH value of 6.75. In the composition of the BA-FA-PAF layer, the BA layer will function as the dominant layer to stabilize the moisture of the underlying material (FA and PAF) which is dominated by clay. The swelling condition of clay can cover the space between pores so that the potency of sulphide minerals oxidation in PAF is lower.
