Phytomining scandium using <i>Portulaca grandiflora</i> in red mud with addition of cow dung manure

Abstract Red mud, a by-product of the Bayer process in aluminum production, contains significant quantities of heavy metals, including scandium. However, its high alkalinity limits the bioavailability of these metals for plant uptake. This study aims to enhance scandium availability in red mud by modifying pH and electrical conductivity (EC) through the addition of cow dung manure, thereby improving scandium uptake by plants. Red mud samples were treated with a 10% cow dung manure mixture to reduce pH and EC. Changes in pH, EC, scandium availability, and plant uptake were monitored over 0, 14, and 28 days. Initially (day 0), red mud had a pH of 11.45, EC of 1085 μS cm −1 , and scandium availability of 11.45 mg/kg. By day 14, pH had decreased to 10.8, while EC increased to 3623 μS cm −1 , leading to scandium availability of 38.15 mg/kg and plant uptake of 1.238 mg/kg (lower plant) and 0.3 mg/kg (upper plant). On day 28, pH further decreased to 10.54, EC increased to 4070 μS cm −1 , scandium availability stabilized at 36.2 mg/kg, and plant uptake increased to 1.9 mg/kg (lower plant) and 0.6 mg/kg (upper plant). The findings demonstrate that reducing pH enhances scandium bioavailability in red mud, facilitating greater uptake by plants. These results highlight the potential of organic amendments, such as cow dung manure, in optimizing phytomining strategies for scandium recovery.