Red Mud as a Secondary Source of Scarce Metals - Recovery using Red Microalgae

Red mud is a by-product of the production of alumina from bauxite ore. Less than 2% of the red mud produced is currently being reused. The red mud contains a number of residual elements, some at a considerable concentration. The red microalga Galdieria sulphuraria was used to test the accumulation of scarce metals from red mud. Algal cells were cultured autotrophically and mixotrophically in a liquid medium with an alternative addition of glycerol as a source of carbon. Red mud was added into the growth medium as the acidic extract (in 10% HNO3). The growth of the cultures was monitored. The content of single scarce metals in the red mud extract and the biomass, was determined using ICP-MS. The most abundant element in red mud was Fe followed by Na and Al (53%, 17% and 12% respectively). The most abundant lanthanides were Ce, Y and La. The growth of cultures grown in the presence of red mud was comparable with the control. The red alga Galdieria sulphuraria can grow in the presence of red mud and accumulate scarce metals from it. The accumulation is more effective under the mixotrophic regime, shoing Y as the most accumulated lanthanide.