adminTapuwa Mashangwa
OVER the past five years we have seen the mining industry grow to become one of the most lucrative ventures in Zimbabwe. Be it through the extraction of gold, platinum, coal, diamonds or tantalite ore, more money has been made in mining annually.
The gold mining sector has the most participants being taken up by the rural folks, the urbanites, political figures and business executives just to mention a few.
Beautiful and inspiring as this fact stands, we cannot be ignorant of the utilisation of cyanide during the purification process of gold.
Cyanide is a triple-bonded molecule with a single negative charge consisting of one atom of carbon in the +2 oxidation state and one atom of nitrogen in the -3 oxidation state.
Immensity of cyanide amount in environment is mainly due to metal finishing and mining activities.
While cyanide can be removed and recovered by several processes, it is still usually discussed and examined due to its potential toxicity and environmental impact.
The chemical speciation of cyanide depends on their sources and also in response to a variety of environmental factors.
Cyanide is a fast-acting broad spectrum toxin and it affects all living organisms.
Cyanide ion exerts an inhibitory action on certain metabolic enzyme systems, most notably cytochromeoxidase, the enzyme involved in the ultimate transfer of electrons to molecular oxygen.
In the presence of even weak acids, HCN gas is liberated from cyanide salts.
Cyanide poisoning can occur through inhalation, ingestion and skin or eye contact.
One teaspoon of a two percent solution can kill a person.
In general, fish and other aquatic life are killed by cyanide concentrations in the microgramme per litre range (part perbillion), whereas bird and mammal deaths result from cyanide concentrations in the milligramme per litre range (part per million).
The release of cyanide from industries worldwide has been estimated to be more than 14 million kg/yr.
Cyanide and its related compounds can be removed from industrial effluent through various physical, chemical and biological/biodegradation treatment methods.
Physical methods for cyanide treatment can be accomplished using dilution, adsorption, membranes, electro-winning and hydrolysis or distillation.
Adsorption is commonly used in physical treatment methods for the removal of cyanide.
In chemical methods, some of the more common processes used to degrade cyanide are the hydrogen peroxide process, alkaline chlorination, sulphur dioxide-air oxidation, electrolytic oxidation etc.
These methods are used to purify effluents for discharge by concentrating and recovering the cyanide for recycling.
On the other hand, oxidation processes are used to destroy the cyanide and include various biological, catalytic, electrolytic, chemical and photolytic methods.
These aforesaid methods are really effective removal methods but have a few draw backs over biodegradation method.
These are much expensive, produce secondary pollution also and suitable for low concentration of cyanide, some time pre-treatment is also required.
In Zimbabwe, considering that most people face financial difficulty, it would be recommendable to try bioligical degradation of cyanide.
Biological degradation is the process of breaking and transforming hazardous materials into simple non-toxic substances by a biological treatment.
Cyanide can be broken into simpler substances by micro-organisms in waste water and piles in the soil.
Some bacteria, fungus, algae and plants can decompose cyanide and cyanide compounds.
The bacterial detoxification would be safer, quicker and cheaper 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.
Cyanide-oxidising bacteria normally break it down into harmless compound.
Under aerobic conditions, biological process may consume hydrogen cyanide and generate hydrogen cyanate.
It has been concluded that, biological treatment method is an ecosociable substitutional approach for removal of cyanide.
It can be less expensive than chemical and physical methods, and much faster than natural oxidation with efficiency equalor exceed those of chemical or physical methods.
Lower plant construction and operating cost, that is, no chemical handling equipment or expensive control instrument are needed.
Costs are relatively uniform and greater volumes of waste do not necessarily increase the costs proportionately.
Efficiency wise, biodegradation provides superior resistance to shock loading, as well as recovery from such upsets and results in lower production of total dissolved solids and sludge making it environmental friendly.
The future is definitely green and the co-existence of a viable mining/metal processing sector and agricultural sector is possible.
All we have to do is regulate and ensure all the necessary requirements and corresponding requisites are met.
- The writer is Tapuwa Justice Mashangwa, a young Bulawayo-based entrepreneur, founder and CEO of Emerald Agribusiness Consultancy. He can be contacted on +263739 096 418 or e-mail: [email protected].
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