Microbially-Produced Organic Acids as Leaching Agents for Metal Recovery Processes

Figures & Tables

Organic acid	Acidolysis reactions	pK_a	Complexolysis reactions
Gluconic	C₆H₁₂O₇ → C₆H₁₁O⁻₇ + H⁺	3.86	n[C₆H₁₁O⁻₇] + Mⁿ⁺ → M[C₆H₁₁O₇]_n
Oxalic	a) C₂H₂O₄ → C₂HO⁻₄ + H⁺ b) C₂HO⁻₄ → C₂O₄²⁻ + H⁺	1.254.14	a) n[C₂HO₄⁻] + Mⁿ⁺ → M[C₂HO₄]_n b) n[C₂O₄²⁻] + Mⁿ⁺ → M₂[C₂O₄]_n
Malic	a) C₄H₆O₅ → C₄H₅O₅⁻ + H⁺ b) C₄H₅O₅⁻ → C₄H₄O₅²⁻ + H⁺	3.405.11	a) n[C₄H₅O₅⁻] + Mⁿ⁺ → M[C₄H₅O₅]_n b) n[C₄H₅O₅²⁻] + Mⁿ⁺ → M₂[C₄H₄O₅]_n
Citric	a) C₆H₈O₇ → C₆H₇O₇⁻ + H⁺ b) C₆H₇O₇⁻ → C₆H₆O₇²⁻ + H⁺ c) C₆H₆O₇²⁻ → C₆H₅O₇³⁻ + H⁺	3.094.756.40	a) n[C₆H₇O₇⁻] + Mⁿ⁺ → M[C₆H₇O₇]_n b) n[C₆H₆O₇²⁻] + Mⁿ⁺ → M₂[C₆H₆O₇]_n c) n[C₆H₅O₇³⁻] + Mⁿ⁺ → M₃[C₆H₅O₇]_n

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 1022.4Citric 5533.2 30Gluconic 894.6	30	27	300	8	56.1 Cu15.7 Al20.5 Pb49.5 Zn8.1 Sn	[93]
Aspergillus niger	Citric 8131, 8064Oxalic 1095, 973Malic 1212, 1086Gluconic 2065, 2153	Room temperature	21	120	0.092	98.57 Zn43.95 Ni64.03 Cu	[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 Li94 Cu72 Mn62 Al45 Ni38 Co	[11]
Penicillium simplicissimum	Citric 5237Gluconic 3666Oxalic 1287Malic 188	30	15	130	1	100 V40 Ni	[76]
Kombucha-consortium(the bacterium Komagataeibacter hansenii, and the yeast Zygosaccharomyces lentus)	Gluconic 25500Acetic 9608	Room temperature	14	300	2.8	(stationary bioleaching) 5.2 of REE^*	[44]
	Gluconic 25500Acetic 9608	Room temperature	14	300	2.8	(shaken-mode bioleaching) 7.9 of REE	[44]
Aspergillus niger	Oxalic 17185Gluconic 4539Citric 1042Malic 502	60	7	130	9	83 V30 Ni	[75]
Aspergillus niger	Gluconic 2126Malic 1251Oxalic 1170Citric 8078	30	30	130	2	69.8 Al60.0 Ti25.4 Fe	[89]

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]

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)2.55 Ce0.57 La0.36 Nd	[30]
Enterobacter Aerogenes		30	18	120	2	(indirect bioleaching)0.66 Ce0.16 La0.12 Nd	[30]
Aspergillus sp.	Non-characterized supernatant	37	20	150	2	79 Mn	[65]

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]
Gluconobacter oxydans	Gluconic < 30	30	1	150	1.5	FCC^*** catalyst 49% of total REE	[77]
Alternaria alternata	Not reported	30	2	150	1	8285.3 mg/kg V6662.0 mg/kg Al4973.8 mg/kg Si3990.2 mg/kg Mo177.7 mg/kg Mg118.2 mg/kg Fe	[81]
Alternaria alternata	Not reported	30	2	150	5	29.9 mg/kg As9872.7 mg/kg Al6839.0 mg/kg Si2115.8 mg/kg Mo1903.0 mg/kg V279.6 mg/kg Mg	[81]
Aspergillus niger	Citric and Gluconic < 98	30	60	130	1	3% La	[66]
					3	52% La
					5	33% La