Stability of lead immobilization by Aspergillus niger and fluorapatite under different pH conditions

The combination of Aspergillus niger (A. niger) and fluorapatite (FAp) has been applied in lead (Pb) immobilization. However, the different pH can affect the stability of the immobilized Pb minerals. This experiment explored the stability of Pb immobilization by A. niger and FAp under different pH conditions. A. niger can grow normally in a pH range from 2.5 to 6.5 conditions. Meanwhile, more than 99 % of Pb cations were removed by A. niger and FAp under a pH range from 3.5 to 6.5. More importantly, only less than 1.23 % Pb was released again under pH 3.5-5.5. The strong acidic conditions (pH 1.5) inhibited the growth of A. niger and caused a lower Pb removal ratio of 37.86 %. In addition, the formed minerals of lead oxalate and lead/calcium oxalate coprecipitate dominate the Pb remediation by A. niger and FAp. The pH > 5.5 condition could decrease the stability of Pb immobilization via the low calcium/lead ratios. The combination of A. niger and FAp shows great potential in Pb remediation at a pH range from 3.5 to 5.5, suitable for fungal growth and Pb minerals stability. This research provides new insight into Pb remediation by phosphate-solubilizing fungi and FAp in various acidic environments.