Cadmium immobilization in aqueous solution by Aspergillus niger and geological fluorapatite.

Abstract

This study investigated the application of fungus Aspergillus niger and geological fluorapatite (FAp) to cadmium (Cd) immobilization in aqueous solution. The initial Cd concentrations were set at 100, 50, 25, and 10mgL-1. The mineralogy of the products was investigated by using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy(EDS), and attenuated total reflection-infrared spectroscopy (ATR-IR). In both A. niger + FAp + Cd and A. niger + Cd treatments, A. niger secreted abundant oxalic acid, then dissolved the FAp, and reacted with Cd2+ cations to produce relativelyinsoluble Cd oxalate. Meanwhile, FAp can provide P source to improve microbial growth. The fungal tolerance to Cd2+ was identified at around 100mgL-1. The final Cd concentrations of 13.7, 3.2, and 0.2mgL-1 were recorded for A. niger + FAp + Cd treatments with initial Cd concentrations of 50, 25, and 10mgL-1 respectively. Meanwhile, it was observed that the Cd concentration at 25mgL-1 stimulated higher bioactivities of A. niger, which further enhanced Cd bioremediation. The immobilization efficiency (%) of the treatments at low to medium Cd concentrations was in the order: Asp + FAp > Asp > FAp, while FAp alone was most efficient at the high Cd concentration of 100mgL-1. This research provides insights into the mechanisms of combining fungus and FAp as a composite to Cd contamination at various Cd levels.