Potential Effect of Porosity Evolution of Cemented Paste Backfill on Selective Solidification of Heavy Metal Ions

• Main Authors: Yixuan Yang, Tongqian Zhao, Huazhe Jiao, Yunfei Wang, Haiyan Li
• Format: Article
• Language: English
• Published: MDPI AG 2020-01-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: cemented paste backfill; tailings management; underground water pollution; heavy metal ions; selective solidification
• Online Access: https://www.mdpi.com/1660-4601/17/3/814

Cemented paste backfill (CPB) is a common environmentally friendly mining approach. However, it remains undetermined whether CPB pollutes underground mine water. Tank leaching analysis of a CPB mass in distilled water was performed for 120 d, and water quality was tested in situ for a long-term pollution assessment. Computerized tomography was also used to determine the CPB micro-pore structure and ion-leaching mechanism. The dissolved Zn²⁺, Pb²⁺ and As⁵⁺ concentrations in the leachate peaked at 0.56, 0.11 and 0.066 mg/L, respectively, whereas the Co²⁺ and Cd²⁺ concentrations were lower than the detection limit. The CPB porosity decreased from 46.07% to 40.88% by soaking, and 80% of the pore diameters were less than 13.81 μm. The permeability decreased from 0.8 to 0.5 cm/s, and the quantity, length, and diameter of the permeate channels decreased with soaking. An in-situ survey showed novel selective solidification. The Zn²⁺ concentration in the mine water was 10−20 times that of the background water, and the Pb²⁺ concentration was 2−4 times the regulated value. Although the Pb²⁺ content decreased significantly with mining depth, there remains a serious environmental risk. Mine water pollution can be reduced by adding a solidifying agent for Pb²⁺ and Zn^2+, during CPB preparation.