Bioleaching of trace metals from coal ash using Acidithiobacillus albertensis, Acidithiobacillus thiooxidans and local isolate from coal ash pond

• Main Author: Pangayao, Denvert Canaria
• Format: text
• Language: English
• Published: Animo Repository 2016
• Subjects: Bacterial leaching; Leaching; Coal ash; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/501
• Institution: De La Salle University

Bioleaching of trace metals from coal ash using mixed culture of Acidithiobacillus albertensis and Acidithiobacillus thiooxidans and isolated microorganism from coal ash pond was investigated. Based on the coal ash characterization, the total metal contents of the coal ash are 0.96 mg/kg Zn, 4.13 mg/kg Mn, 0.81 mg/kg Cr and 2.22 mg/kg Cu. Also, the minerals detected were quartz-SiO2, lime-CaO, anhydrite, tricalcium aluminate, and the major elemental composition are calcium, silicon, aluminum, iron and sulfur. High calcium oxide levels greatly contributed to the alkalinity of the ashes.Using the Box-Behnken experimental design for bioleaching of trace metal from coal ash using mixed culture of A. albertensis and A. thiooxidans, there are three variable parameters used namely: initial bacterial inoculum, % pulp density and weight % sulfur added. After fifteen days of bioleaching, the maximum percentage metals leached were 56.69% Zn, 70.68% Mn, 79.86% Cr and 69.32% Cu at different variable parameters. Also, the solution which had an initial pH value of 2 was decreased to a value ranging from 0.61 to 1.39 due to the oxidation of sulfur via microbial activity. Moreover, optimization results indicate that the significant parameters are 5% pulp density and 3 grams initial mass of sulfur. Using these optimal parameters, the maximum percent metal leached were 56.63% Zn, 70.88% Mn, 85.01% Cr and 74.46% Cu.Using the optimum parameters, controlling mechanism and kinetic parameters were determined. After 30 days of bioleaching, the maximum trace metal extracted were 63.96% Zn, 90.41% Cr, 81.84% Mn and 85.77% Cu. The pH value decreased after 30 days with the value of 0.29. Based on the Shrinking core model, the controlling mechanism for all metal leached is diffusion though liquid film.Possible bioleaching microorganism was isolated from different coal ash pond of coal-fired power plant in the country. From the different coal ash samples, only 8 isolate of Pseudomonas spp were identified from PP 3, PP 4 and PP 6 power plants. Moreover, Pseudomonas spp. is used in bioleaching experiment along with Acidithiobacillus spp Based on the PCR result, possible Pseudomonas spp isolates are the same in PP 3-1, PP 3-2, PP 6-1 and PP 4-1 to PP 4-4. On the other hand, only 2 samples have different consortia of Pseudomonas spp namely: PP 3-2 and PP 4-1. Pseudomonas aeruginosa is present in 7 samples namely (PP 3-1, PP 3-3, PP 6-1 and PP 4-1 to PP 4-4) and Pseudomonas putida in PP 4-2.After 15 days of bioleaching, maximum metal leached were 10.63% Zn and 4.34% Mn from PP 3-1 Pseudomonas spp isolate and 8.04% Cr and 12.05% Cu from PP 3-2 Pseudomonas spp isolate. Based on the result, Pseudomonas spp extracted less metal compared to A. albertensis and A. thiooxidans.Using the isolated Pseudomonas spp from PP 3-2, the maximum growth was obtained on the 13th hour with the optical density of 0.679 and pH value of 7.28. After 30 days of bioleaching, 13.77% Cr were leached at pH value of 8.61.