Using shrimp shells and concrete to mitigate leaching for metals from waste rock

The capability of shrimp shells or construction demolition concrete as amendments to immobilize elements, primarily Pb and Zn, generated from mine waste weathering, was investigated via standard batch leaching test (L/S 10 cm³/g, 24 h). The effect of the amendment was tested at waste rock-to-residue ratios 9:1, 9.5:0.5, and 9.8:0.2 (weight:weight, w/w), with seawater as leachant. The effect of freshwater vs. seawater on the leaching pattern was investigated. The elemental contents of rock varied largely. Elemental levels in shells and concrete had much lower values than waste rock. Leaching results showed that amendment in both cases had high capacity to immobilize Pb and Zn. A decrease of concrete-to-rock ratio from 1:9 to 0.2:9.8 (w/w) led to more leaching of Pb but less of Zn. Similarly, decreasing shrimp-to-rock ratio increased and decreased leaching of Pb and Zn, respectively. Increasing experimental time to 5 and 10 d in a shrimp-amended batch caused less leaching of Pb and more of Zn. Both Pb and Zn immobilization in the concrete amendment was considered due to the increase of pH by concrete amending. The Pb leaching in the present study was considered controlled primarily by a sorption process, whilst the leaching for Zn might have been influenced by other factors such as pH and DO. Pb leaching from rock was much higher in seawater than in freshwater, with same range for Zn leaching, irrespective of leachant. It showed consistence between the laboratory data and the field conditions. Calculation procedures were established for amendment to mitigate mine drainage.