Fig. 1
Fig. 2
Reactions involved in acidolysis and complexolysis mechanisms for metal recovery
| Organic acid | Acidolysis reactions | pKa | Complexolysis reactions |
|---|---|---|---|
| Gluconic | C6H12O7 → C6H11O−7 + H+ | 3.86 | n[C6H11O−7] + Mn+ → M[C6H11O7]n |
| Oxalic |
| 1.25 |
|
| Malic |
| 3.40 |
|
| Citric |
| 3.09 |
|
Bioleaching at laboratory scale for metal recovery from industrial wastes using OA-producing microorganisms
| Microorganisms | Leaching agent (mg/L) | Temperature (°C) | Time (days) | RPM | Pulp density % (w/v) | Recovery (%) | References |
|---|---|---|---|---|---|---|---|
| Mixed fungal cultures: Purpureocillium lilacinum (71.9%) and Aspergillus niger (27.9%) were dominant species. Others (0.2%) include: Pseudallescheria sp., Malassezia obtuse, Tomentella sp., Davidiellaceae sp., Talaromyces sp., Fungi sp., Herpotrichiellaceae sp., Meyerozyma guilliermondii Wickerhamomyces anomalus, and Malassezia furfur. | Oxalic 1022.4 | 30 | 27 | 300 | 8 | 56.1 Cu | [93] |
| Aspergillus niger | Citric 8131, 8064 | Room temperature | 21 | 120 | 0.092 | 98.57 Zn | [94] |
| Aspergillus niger | Less than 14000 of gluconic acid, less than 4000 of citric and oxalic acid, less than 3000 of malic acid | 30 | 30 | 130 | 1 | 100 Li | [11] |
| Penicillium simplicissimum | Citric 5237 | 30 | 15 | 130 | 1 | 100 V | [76] |
| Kombucha-consortium(the bacterium Komagataeibacter hansenii, and the yeast Zygosaccharomyces lentus) | Gluconic 25500 | Room temperature | 14 | 300 | 2.8 | (stationary bioleaching) 5.2 of REE* | [44] |
| (shaken-mode bioleaching) 7.9 of REE | |||||||
| Aspergillus niger | Oxalic 17185 | 60 | 7 | 130 | 9 | 83 V | [75] |
| Aspergillus niger | Gluconic 2126 | 30 | 30 | 130 | 2 | 69.8 Al | [89] |
Comparison of the reported characteristics of organic and inorganic acids in leaching processes
| Organic acids (OA) | Inorganic acids (IA) | References |
|---|---|---|
| Less emission of hazardous gases | High emission of sulfur, chloride, and nitrous oxides | [35] |
| Serve for soil nutrient acquisition, mineral weathering | Can lead to high consumption either of water or chemicals | [29] |
| Less risky manipulation during the process. | Risky manipulation during the process. | [82] |
| Biodegradable | Non-biodegradable | [20, 35] |
| Delay the corrosion of equipment | Cause prompt corrosion of equipment | [82] |
| Can be used more than once in metal recovery processes | Cannot be reused in metal recovery processes | [35] |
| Are costlier than IA, but the process is considered cost-effective due to the environmental impact | Have low cost, but the process is not considered cost-effective due to environmental impact | [37] |
| Solely act as leaching agents; hence, separation nd purification are still needed | Solely act as leaching agents; hence, separation and purification are still needed | [35] |
Bioleaching at laboratory scale for metal recovery from ores using OA-producing microorganisms
| Microorganisms | Leaching agent (mM) | Temperature (°C) | Time (days) | RPM | Pulp density (% w/v) | Recovery (%) | References |
|---|---|---|---|---|---|---|---|
| Enterobacter Aerogenes | Mixture of malic, gluconic and acetic acids < 18 for both direct and indirect bioleaching | 30 | 18 | 120 | 1 | (direct bioleaching) | [30] |
| 2 | (indirect bioleaching) | ||||||
| Aspergillus sp. | Non-characterized supernatant | 37 | 20 | 150 | 2 | 79 Mn | [65] |
Bioleaching at laboratory scale for metal recovery from catalysts using OA-producing microorganisms
| Microorganisms | Leaching agent (mM) | Temperature (°C) | Time (days) | RPM | Pulp density (% w/v) | Recovery (%) | References |
|---|---|---|---|---|---|---|---|
| Gluconobacter oxydans | Gluconic < 30 | 30 | 1 | 150 | 1.5 | RPP* maximum 2% of REE** | [77] |
| FCC*** catalyst 49% of total REE | |||||||
| Alternaria alternata | Not reported | 30 | 2 | 150 | 1 | 8285.3 mg/kg V | [81] |
| 5 | 29.9 mg/kg As | ||||||
| Aspergillus niger | Citric and Gluconic < 98 | 30 | 60 | 130 | 1 | 3% La | [66] |
| 3 | 52% La | ||||||
| 5 | 33% La |