Dissolution of Al from metakaolin with carboxylic acids produced by Aspergillus niger, Penicillium bilaji, Pseudomonas putida, and Pseudomonas koreensis

The dissolution of aluminum from metakaolin was tested in spent media of Aspergillus niger, Penicillium bilaji, Pseudomonas putida and Pseudomonas koreensis. Based on HPLC analysis, the main carboxylic acids in spent media were citric, gluconic, and oxalic acid. Gluconic acid was the dominant metabolite (10.8–14.4 g/l) in A. niger and Pseudomonas spent media whereas citric acid (6.2 g/l) predominated with P. bilaji. Aluminum solubilization from metakaolin in spent media was tested at 50, 60, 70, and 80 °C. The highest yields of aluminum solubilization were obtained at 80 °C, ranging between 67 and 74%. The corresponding activation energy (Ea) values for Al solubilization ranged from 86.9 to 98.6 kJ/mol, indicating that aluminum solubilization rates were subject to chemical reaction control and not diffusion limitation.