14.7 Future Aspects

215

14.5.2

Silver

The supernatant from culture of A. ferrooxidans was used for the extraction of sil-

ver from spent battery. Technique for solubilization of metal for the development of

two-stage reactor system was identified as 98% silver dissolved during bioleaching

process in an indirect leaching mechanism for recovery of silver from used silver

oxide-zinc button cell battery, and this can be applied for industrial application [29].

Pseudomonas sp. also secrete cyanide which helps in the bioleaching of elements of

Ag, from ores, slag, and e-wastes [30].

14.5.3

Copper

Moderate thermophiles were used for the copper bioleaching from e-wastes using

columns at laboratory scale, stirred tanks, and shake flask. Use of mesophilic strains

resulted in 90% of extraction from PCBs. The findings proved that 94% and 99% of

copper can be obtained using cultures of mesophilic and moderate thermophiles

within six days using shake flask at temperatures of 30 and 50 ^∘C [30, 31]. A mixed

consortium of Sulfobacillus thermosulfidooxidans and Leptospirillum ferriphilum

was used in spent medium process which resulted in 93.4% of Cu [32].

14.5.4

Nickel

Studies were carried out for using A. ferrooxidans using bioleaching method which

resulted in about 96% extraction of copper from LED waste powder, and this strain

was found to be effective for LED waste bioleaching. 92–97% Ni was bioleached using

A. thiooxidans from spent petroleum catalyst [33].

14.6

Large-Scale Bioleaching of E-Waste

In year 2003, bioleaching for large-scale production for metal recovery was first

established [34]. They used two successive reactors for the recovery of metal from

Ni–Cd batteries where indigenous Acidithiobacilli was inoculated in bioreactor

using series of steps from generation of sulfuric acid to thickening of slush with

the help of settling tanks. Later, the effluent was passed to leaching reactor that

contained the powder obtained from Ni–Cd batteries. Recovery of maximum

percentage of Cd and Ni during entire process was obtained which took 50 days.

Studies were carried out to determine the effect of retention time in both bioreactor

and leaching reactor on recovery. Cobalt and nickel were retrieved by applying the

same methodology.

14.7

Future Aspects

Biomining process is a supportable and effective approach used for extracting met-

als from electronic wastes. This paper is a review of previously published results