Evaluation of the potential release of phosphorus from phosphate waste rock piles in different environmental scenarios

Abstract

The effect of phosphate waste rocks dumped in the Three Gorges Reservoir Region on water quality has been disregarded. For this reason, the leaching behaviours of six phosphate waste rock piles deposited in Xiangxi River watershed were characterised in this study in accordance with Method 1313 and Method 1316 standards of the Leaching Environmental Assessment Framework to determine the potential release of phosphorus from phosphate waste rocks in different environmental scenarios. Phosphorus leaching characteristics were investigated at pH 2.0–13.0 and at liquid-to-solid ratios ranging from 0.5 mL/g dry material to 10 mL/g dry material. Results indicated that higher amounts of phosphorus were likely released from waste rocks in acidic environments than in neutral or basic environments. Phosphorus released in acidic environment was determined as one or two orders of magnitude greater than that in neutral or basic environment. Although the paste pH of waste rocks was maintained in a weakly basic range (7.5–9.0) by long-term leaching effect, liquid-phase concentrations of phosphorus released by most waste rocks exceeded the availability threshold (0.5 mg/L), as influenced by short- and long-term leaching. In addition, the chemical equilibrium between acid neutralisation capacities of waste rocks and local acid rain could be a dominant factor in phosphorus leachability affected by long-term leaching. Therefore, phosphate waste rocks deposited in the study areas should be considered as phosphorus point pollution sources, which could threaten adjacent surface water environments. As such, future management practices would be highly effective if water infiltration could be prevented and inner environment pH of waste rock piles could be maintained at paste pH.