Removal of thorium from simulated acid process streams by fungal biomass: Potential for thorium desorption and reuse of biomass and desorbent

Abstract

When thorium was biosorbed by biomass of Rhizopus arrhizus or Aspergillus niger it could be removed by treatment using carbonate solutions, but not by phosphates or distilled water. Desorption was rapid, reaching completion in 15 and 30 min respectively. Desorption efficiency was independent of the desorbent concentration above 0.05 mol dm⁻³ but was strongly dependent on the biomass concentration, decreasing as the biomass concentration increased for both species. Biomass from both species could be regenerated by desorption using sodium carbonate solutions and reused for biosorption. In both species, the efficiency of biosorption and desorption fell as the number of exposures increased although there was an initial rise in desorption efficiency for R. arrhizus. Biosorption and desorption efficiencies of A. niger biomass showed the steeper decline but both were severely reduced in R. arrhizus after five treatments. There was also a significant loss of biomass during repeated treatment but this was not apparently related to the loss of biosorption and desorption efficiencies. The same batch of sodium carbonate solution could be used to repeatedly desorb batches of biomass. The total amount of thorium removed was greater with increasing sodium carbonate concentration up to 0.1 mol dm⁻³. It was considered that reuse of both biomass and desorbent did not yield significant improvements in process economics.