Abstract
The environmental effects of whole phosphogypsum-based cemented backfill material (WPG-CBM) with self-cementing properties have always been a concern. This study aimed to evaluate the immobilization effect of harmful elements in the WPG-CBM. It showed that the setting rate and strength of WPG-CBM were relatively stable when the quicklime content exceeded 1 %. The self-cementing properties deteriorated significantly as the dissolved phosphorus content exceeded a certain threshold. WPG-CBM leaching tests during the bleeding, hydration and hardening periods indicated that the leaching amounts of phosphate and fluoride fluctuated noticeably in early self-cementing period and then changed regularly due to the coupling effect of chemical reactions, eutectic phosphorus dissolution, decreasing pH value, and common ion effect. Moreover, three designed leaching tests for in-situ underground conditions showed that the influence of WPG-CBM backfill on groundwater could be ignored in the open dynamic leaching. In the closed dynamic or static leaching conditions, phosphate and fluoride were continuously enriched within the values permitted by national standard. According to microstructural analysis, the good self-cementing properties of WPG-CBM were attributed to the immobilization of phosphorus and fluorine in phosphogypsum by quicklime. The self-cementing properties and environmental effects of WPG-CBM with a pH of 7.5–8.5 were the most satisfactory.
Published Version
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