Kinetic leaching of high sulphur mine rejects amended with biochar: Buffering implication

• Pyrite is responsible for acid mine drainage.
• Biochar addition reduces the acid production.
• It accelerates the neutralization and reduces sulphate production.
• It increases the alkali production.

In the present investigation, the effect of biochar incorporation into high sulphur mine rejects on buffering of the acid production was assessed. For this, kinetic experiments on pure mine rejects (LMR) and biochar amended mine rejects (LMRBC) were performed for 720 h. Leachate samples were collected at 0, 20, 40, 60, 168, 336, 504 and 720 h and characterized. Results revealed that incorporation of biochar inhibited the acid production rate (from 10.4 kg/Mt/h to 3.81 kg/Mt/h) and enhanced the alkali consumption (from 9.7 kg/Mt/h to 13.9 kg/Mt/h). Biochar was capable to neutralize all the acid produced. As a neutralizing agent, Mg2+ dominated over Ca2+. The efficiency of biochar to reduce the rate of acid production may be due to either the reduction in Fe3+ concentration or production of reduced sulphur compounds in reducing conditions of biochar. This is also supported by molar sulphur to iron ratio of leachate water. Principal component analysis applied on the data revealed that biochar altered the salt and carbon dissolution processes of mine rejects. It inhibits the acid production and accelerates the alkali releasing.

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