Rehabilitation effect of the combined application of bamboo biochar and coal ash on ion-adsorption-type rare earth tailings

Abstract

The massive mining of ion-adsorption-type rare earth ore has led to a series of problems such as soil acidification, land degradation, and water pollution, and thus, an effective method of treating rare earth tailings is urgently needed. The goal of this study was to explore the rehabilitation effect of the combined application of bamboo biochar (BB) and coal ash (CA) on ion-adsorption-type rare earth tailings. We collected samples from an abandoned ion-adsorption-type rare earth tailing deposit in Jiangxi, China. Four treatment experiments involving amendments of 0%, 1%, 2.5%, and 5% CA and 1% BB and a control were performed. The soil mechanical composition (MC), bulk density (BD), pH, organic carbon (OC), cation exchange capacity (CEC), available nitrogen (AN), available phosphorus (AP), available potassium (AK), cabbage growth, fresh weight, and rare earth element (REE) concentrations of the cabbage were measured. The cabbage did not grow when the soil was only treated with bamboo biochar, but it grew when both bio-charcoal and coal ash were applied. The REE concentrations of the cabbage decreased with increasing coal ash dosage. The pH, OC, and CEC of the amended tailings were significantly increased, while the BD and AP of the amended tailings were significantly decreased compared with those of the control. Moreover, the AN and AK of all of the treatment experiments, except for the application of only BB, were significantly decreased. The application of a combination of biochar and coal ash effectively improves rare earth tailings and promotes the growth of Chinese cabbage. These results are likely related to the improvement of the basic physical and chemical properties of the tailings.