Microbial leaching is the process by which metals are dissolved from are bearing rocks using microorganism.

1. BIOLEACHING

3. INTRODUCTION :-
 Microbial leaching is the process by which metals are
dissolved from are bearing rocks using microorganism .
 The world there are vast quantities of such low grade
copper ores that cannot be profitably purified by
conventional chemical method. but that could by
microbial leaching.
 There are also significant quantities of nickel , lead and
zinc ores which could be leached.
 Leaching was discovered as a process occurring in
pumps and pipelines installed in mine pits containing
acidic water.

4.  It was subsequently developed foe the recovery of metal
from low grade ores. For many metals, there are now
leaching methods which permit extraction from metal or
other ores.
The metals are converted to water – soluble metal sulfates
with the aid of biochemical oxidation processes.
 commonly used microorganisms are:
 Mesophiles
 moderately
 extremophiles

5. MICRORGANISM USED IN BIOLEACHING:-
TWO most commonly used organism in microbial leaching
are thiobacillus thiooxidans and thiobacillus terrooxidans.
 A number of others may also be used including:
• Thiobacillus concretivorus , pseudomonas fluorescens , P.
achromobacter , bacillus licheniformis, B. polymyxa and
several thermophilic bacteria including thiobacillus
thermophilica , .
• The heterotrophic organism listed have not as yet
actually been used ,but it seems likely that processes will
be developed by which metals are extracted from ores
with microbially produced organic acid via chelate and
salt formation .

6. CHEMISTRY OF BIOLEACHING :-
 The reaction mechanisms are of two types,
1 Direct bacterial leaching
2 indirect bacterial leaching
1. Direct bacterial leaching
in this process, a physical
contact exist between bactria and ores and
oxidation of minerals takes place though
enzymatically catalysed steps

7. ex; pyrite is oxidised to ferric sulphate
2FeS2+ 7O2+ 2H2O 2Feso4 + 2H2so4
2 indirect bacterial leaching
IN THIS process the microbes are
not in direct with minerals , but leaching agents are
produced by these microbes which oxidize the ores.

8.  The process involving thiobacillus
ferroxidans is being used since 1960 s in
canada for uranium recovery , and since
1970 s in south africa for recovery of gold
.
 In USA and some other countrics it is
being used mainly for the recovery for
copper ; about 10-20 % of the world
copper supply is derived by this process .

9. COMMERCIAL PROCESS OF BIOLEACHING :-
 Naturally occur bioleaching process is very slow . For
commercial extraction of metal by bioleaching the
process is optimized by controlling the Ph ,
temperature.
Three method of the commercial process used in
bioleaching : -
i. Slope leaching
ii. Heap leaching
iii. In-situ leaching

10. 1 Slope leaching
Finely ground ores ( up to 10,000 tons) are
dumped in large piles down a mountainside and continuously
sprinkled with water containing thiobacillus .
The water is collected at the bottom and reused after metal
extraction and possible regeneration of the bacteria in an
oxidation pool.
2 HEAP LEACHING
The ore is arranged in large heaps and
treated as in slope leaching .

11. 3 IN SITU – LEACHING
• In this process the ore remains in its original
position in earth .
• Surface blasting of earth is done to increase the
permebility of water.
• Water containing is pumped through drilled
passages to the ores.
• Acidic water seeps through the rocks and collect at
bottom.
• Again water is pumped from bottom
• Mineral is extracted and water is reused after
generation of bacteria.

13. Bioleaching
of some metals:

18. MERITS of using microbes for ore leaching:-
It does not require high energy imputs
It can be applied both on small and large scales
It is self – regenerating if soluble iron is present since
fe+2 is oxidised to fe+3 by T. ferroxidance
The process can be used to extract a variety of metals

19. LIMITATIONS OF MICROBIAL ORE LEACHING:-
 The desired metal is recovered as a dilute solution
of its salf and not as elemental metal.
 This makes a recovery process from the solution
essential.
 The microorganisms must be kept viable by
providing approprite conditions