Environmental risk assessment of humic acid modified dealkalized red mud

Untreated accumulation of red mud that has been treated with acid mine drainage can cause serious harm to the environment. Soil improvement is a feasible method to consume it on a large scale. Humic acid is acidic and is a large molecular organic substance widely present in nature, and its effect on soil restoration and improvement is significant. To study the environmental risk of humic acid modified dealkalized red mud, humic acid combined with dealkalized red mud experiment was carried out. The physicochemical properties of the dealkalized red mud and its leachate were analyzed, and the leaching risk of dealkalized red mud after adding humic acid was evaluated. The results showed that the best effect of improving dealkalized red mud by humic acid with a mass percentage (humic acid/red mud) of 10% was achieved. Adding 10% mass percentage of humic acid could reduce pH of dealkalized red mud from 9.1 to around 7.8. It could increase the absolute value of the electric potential (Zeta potential) of dealkalized red mud from 20 to 28 at higher pH. The fulvic acid substances in humic acid would gradually transform into more stable humic acid substances. Humic acid could reduce the concentration of metal ions in the leachate of dealkalized red mud and had a positive effect on fixing metal ions in red mud. In summary, humic acid could improve dealkalized red mud and reduce its environmental risk.