In general, we can observe Hydrogen cyanide, sodium cyanide, and potassium cyanide easily in the environment where we have industrial activities.

Sodium Cyanide: White powder, A slight, bitter, almond-like odor in dump air.

Potassium Cyanide: White powder, A slight, bitter, almond-like odor in dump air.

Hydrogen Cyanide: Colorless Gas, A faint, bitter, almond-like odor.

Chemical composition of Sodium Cyanide
CNNa * Na+ + CN-
NaC*N
Produced by carbon monoxide and ammonia.

INTRODUCTION

My peers and I researched the use of cyanide in gold leach mining last quarter. (Energies Research Project, CYANIDE, Fall ‘97) I specifically looked up the chemistry of cyanide and found the complexity of it associated with hydrology and geochemistry. The process is what follows: cyanide (CN) is mixed with sodium (Na), then this sodium cyanide (NaCN) meets water (H2 O), then sodium cyanide solution meets crashed rocks that contains gold (Au) and many other heavy metals such as silver, arsenic and mercury. The negatively charged cyanide (CN2 ) attract positively charged metals. Various cyanide compounds such as K2 Fe(CN)2 , and other metal cyanide complexes will be created in the results.
 
 

1.  Put the low grade ore into the super heavy duty grinder. 2.  Add the sodium cyanide solution.  Then, grind and mix them very well.       2Au + 4NaCN +2H2O + O2

 

3.  Pour the slurry into the large bowl.  Let it rest for a while.   =2NaAu(CN)2 + 2NaOH +H2O2  2Au + 4NaCN + H2O2=2NaAu(CN)2 + NaOH  4Au + 8NaCN + O2=4NaAu(CN)2 + 2NaOH

4.  Then add some zinc (Zn) dust.

          Zn + 4NaCN + NaAu(CN)2 = Au + Na2Zn(CN)2+ 2NaCN

5.  Gold is recovered by electrowinning.

BIOREMEDIATION

Bioremediation is the process of breaking and transforming hazardous materials into simple nontoxic substances by a biological treatment. Cyanide can be broken in to simpler substances by microorganisms in the wastewater, piles and in the soil. Some bacteria and fungus can decompose cyanide and cyanide compounds. The biological treatment methods do not depend on the supply of electricity or other energy sources. The bacterial detoxification would be safer, quicker, and less costly than the chemical treatment to handle cyanide wastes. The process that demands oxygen is an aerobic biodegradation and the process that occurs in the absence of oxygen is an anaerobic biodegradation.
 
 

• It relies on natural processes to remove hazardous compounds.
• It is an "in situ" (at the site) treatment application.
• It does not need any power sources such as electricity.
• It is cost-effective and environmentally sound.
• Generally, the bacteria occurs naturally in site.

COMPOSITION OF CYANIDE

The chemistry of cyanide is CN. The biodegradation of cyanide seems very simple: it breaks into carbon and nitrogen.
 

BIODEGRADATION OF CYANIDE

The bacteria oxidizes the cyanide, breaking it down into harmless compounds. In many cases, cyanide-oxidizing bacteria are naturally present in processing ponds and waste piles.

1. Under aerobic conditions, biological process may consume hydrogen cyanide and generate hydrogen cyanate as shown in the equation below. The hydrogen cyanate is in turn hydrolysed into ammonia and carbon dioxide.

 Equations of aerobic biodegradation of hydrogen cyanide (HCN):

   1) 2HCN + O2 + enzyme = 2 HCNO

   2) HCNO + H2 O = NH2+ CO2

The direct oxidation of cyanide CN2 requires a mineralogical, bacteriological, or photochemical (sunlight) catalyst, and produces cyanate ions (CNO2):

  3) 2CN2 + O2 + catalyst = 2CNO2

2. Anaerobic biodegradation of cyanide and hydrogen cyanide is restricted to the moderately to strongly reduced portions of the heap environment and can only occur if HS2 or H2 S are present. The sulphur species present will depend on pH. At a pH value greater that 7, HS2 is the dominant species. At a lower pH, H2 S will be present.

Equations of anaerobic biodegradation of cyanide:

  4) CN2 + H2 S = HCNS + H2
  5) HCN + HS2 = HCNS + H2

The HCNS will then hydrolyze to form NH2 , H2 S and CO2 . Compared to the aerobic biodegradation of cyanide, anaerobic biodegradation is much slower and anaerobic bacteria have a cyanide toxicity threshold of only 2 mg/l compared to 200 mg/l for aerobic bacteria. Consequently anaerobic biodegradation is a much less effective cyanide removal mechanism. (The Chemistry and Treatment of Cyanidation Wastes by Adrian Smith and Terry Mudder, Mining Journal Books Limited, 1991)

Microbes

Wastewaters in the mining industry, in which CN serves as an ore extractanct, are often high in Ni, Cu, Zn, and Fe. The following cyanide degrading bacteria occurs readily in nature. They eat cyanide, CN, as a sole nitrogen source. (Toxicity and Environmental Fate of Cyanate, Thiocyanate and Cyanogen Chloride by Dean Boening and Christine Coffey, ICF Kaiser Engineers, Inc., 1994)
 

Bacteria	Enrichment Source
Pseudomonas putida	Sewage sludge, Soil, Creek water
Pseudomonas pickettii	Soil
Pseudomonas paucimobilis	Mining wastewater
Klebsiella pneumoniae	Soil, Creek water
Klebsiella sp.	Creek water
Alcaligenes xylosoxidans	Soil

There are some other enzymes capable of CN transformation. Cyanase is an enzyme that catalyzes the hydrolysis of cyanate to ammonia and bicarbonate. Escherichia coli (E. coli), and Flavobacterium speicies also eats cyanate as a sole nitrogen source.

Ammonia and carbon dioxide are the major end products of aerobic CN metabolism. The primary end products from anaerobic cyanide transformation are formate and bicarbonate, but the mechanisms of adaptation to and degradation of cyanide in anaerobic systems are not well understood.

Nutrients for bacteria.
Phosphates encourage bacterial populations to grow and to break the cyanide down into carbon and nitrogen. (Bacteria eat mining wastes, News Notes Geotimes, 1993)

Environment for biodegradations
It is known that the pH in particular plays a significant role in the and reactivity of these compounds, although further studies must be conducted. (The Chemistry and Treatment of Cyanidation Wastes, Smith and Mudder, 1991)
 

CONCLUSION
Many biological treatment application have been developed to clean up various hazardous, wastes such as arsenic, cyanide and radioactive materials. This application should involve hydrology, geochemistry, and micro-organisms, and therefore the results are complex. In the next century, developing biological treatments will be the very exciting and the potential area in Research & Development arena not only in science but in economic as a proficient, economically feasible, technically viable, applications as well as environmentally sound. Currently serious R & D efforts are underway to find leachants that are less toxic and dissolve precious metals at faster rates than cyanide.
 
 

The Chemistry and Treatment of Cyanidation Wastes
  by Adrian Smith and Terry Mudder
  Mining Journal Books Limited, 1991

Bacteria eat mining wastes, Geotimes, News Notes
 by Sandy Cleva, Office of Public Informations
  U.S. Bureau of Mines, December ,1993

Let them eat cyanide, Geotimes, News Notes
 by Sandra Cleva
  U.S. Bureau of Mines, July, 1995

Tosicity and Environmental Fate of Cyanate, Thiocyanate and Cyanogen Chloride by Dean Boening and Christine Coffey
  ICF Kaiser Engineers, Inc., 1994

Microscopic Secret Agents
 by Jeannie Woodring
  Alaska Magazine, June 1992
 
 

Use bacterial degradation to get rid of cyanide
 by S.M. Kang and D. J. Kim
  Korea Steel Chemical Co.,
   Biotechnol Letter, 1993
 

References
 

In-situ Groundwater Biodegradation - Vendor Companies.
(http://bordeaux.uwaterloo.ca/bio1447new/…/bioremidiation_in_situ_groundwater.html)
 

ENSR CONSULTING AND ENGINEERING

GEO-MICROBIAL TECHNOLOGIES, INC.

GAIA RESOURCE, INC.

IT CORPORATION

GROUNDWATER TECHNOLOGY, INC.

YELLOWSTONE ENVIRONMENTAL SCIENCE, INC.

WASTE STREAM TECHNOLOGY, INC.

MICRO-BAC INTERNATIONAL, INC.

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