42 Cyanide

Cyanide Detoxification and Recovery of

Gold from Gold Effluent

A. J. Kiruthika and Shrinithya

Abstract

Growing global concern on environmental health is forcing all the processing to adopt

greener and cleaner manufacturing practices. Cyanide is one of the most potential toxic

chemicals, which has a tremendous application in various fields and is also the main source of

contamination of water basins with heavy metals. About 20% of cyanide is used in the gold

mining industries. Mine wastes have heavy metals, acids which causes acute, chronic illness

not only to human being but also to other organisms. The traditional treatment method

followed for cyanide destruction was non profitable with more toxic by products such as

liquid chlorine. Microbes have the ability to bind metals. Hence, to save the environment

from pollution and find a method, which is rapid, efficient, inexpensive with low level of

technology the biodegradation process of Pseudomonas fluorescens is to be carried out. The

green algae Chlorella vulgaris bind noble metals like gold, silver, platinum regardless of the

pH conditions with the use of microbes, not only the heavy metal is destructed but also

recovery of noble metals can be achieved which is the main aim of our work. The strong bond

link between metals and microorganisms helps in destruction and recovery of metals.

Keywords: Cyanide destruction, Pseudomonas fluorescens, gold recovery, Chlorella

vulgaris.

20 | Advanced Biotech | August 2008

Research Article

21 | Advanced Biotech | August 2008

toxic for most living organisms because it

forms very stable complexes with transition

metals that are essential for protein function,

i.e., iron in cytochrome oxidase.

Consequently, organisms growing in the

presence of cyanide must have a cyanideinsensitive

metabolism, such as the

alternative oxidase described for plants or the

cytochrome bd (or cyanide-insensitive

oxidase) in bacteria. The biological

assimilation of cyanide needs, at minimum,

the concurrence of three separate processes,

i.e., a cyanide resistance mechanism, a system

for metal acquisition, and a cyanide

assimilation pathway. Although all of these

factors in conjunction with one another have

never been taken into account, a number of

microorganisms are able to degrade cyanide

and its metal complexes. From a chemical

point of view, the biological treatment of

industrial effluents contaminated with

cyanide requires an alkaline pH in order to

avoid the formation of the volatile HCN.

Gold is one of the rarest metals on earth, and

its importance has been known since

antiquity. Because of the increased demand

for gold in industry and nanotechnology,

exploration for new gold deposits in the

natural environment has become very

important. On the other hand, gold in waste

solutions from several industrial processes,

e.g., gold mining and gold electroplating

effluents could be recovered and reused.

Therefore, there is an essential need to

develop alternative, cost effective and

environmentally sound methods for

recovering gold from waste solutions.

The chemical processes that exist are not

economical for treating a large volume of

water bodies of dilute metal concentration. In

this endeavour, microbial biomass has

emerged as an option for developing

economic and eco friendly wastewater

treatment processes. Non-living and dead

microbial biomass may passively sequester

metal(s) by the process of biosorption from

dilute solutions.

The algae like Anabaena and Chlorella are

used for copper, cadmium, lead and zinc

extraction. A process, which could selectively

recover the noble metals from old mining

dumps, mineral leaching operations, and

industrial processes using them would clearly

have tremendous commercial potential. It has

now been unexpectedly discovered that

certain microorganisms under controlled

conditions of pH and salt concentration can be

used to selectively bind gold, silver or

platinum, while essentially preventing the

binding or causing the release of a number of

competing metals.

This biosorption technology has advantages

of low operating cost, is effective in dilute

solutions and generates minimum effluent.

Here the dead microbial biomass functions as

an ion exchanger by virtue of various reactive

groups available on the cell surface such as

carboxyl, amine, imidazole, phosphate,

sulfhydryl, sulfate and hydroxyl. The process

can be made economical by procuring natural

bulk biomass or spent biomass from various

fermentation industries.

This work employs the purification of

cyanide-containing waste water using

P s e u d o m o n a s f l u o r e s c e n s v i a

bioaugmentation which can be applied in

gold-mining industry as well as in nonferrous

metallurgy and then the noble metals

such as gold, silver, platinum etc are also

bioaccumulated or biosorped using Chlorella

vulgaris. Both dead and living cells were used

and provide a simple, inexpensive, low

technology method of extracting valuable

metals from even dilute aqueous solutions

without the necessity of using costly ionexchange

resins.

This method also provides a simple procedure

for eluting metals other than gold, silver,

mercury and platinum from microbial cells to

which they are bound. It has also been found

that the metals like gold, silver and mercury

can be selectively recovered from microbial

cells to which they are bound, even if other

unwanted metals are also bound to the

microbial cells, regardless of the pH at which

binding occurs.

300 ml of Pseudomonas culture of kings B

medium was taken and to that 200 ml of

autoclaved distilled water, 0.5 mg of cyanide

and 1 g of glucose was added as carbon source

(SAMPLE 1).

300 ml of Pseudomonas culture of kings B

medium was taken and to that 200 ml of

autoclaved distilled water, 0.5 mg of cyanide,

1 g of glucose was added as carbon source and

1 g of sodium

...