In the entire history of human civilization such an unusually high demand has never been placed on natural resources of our planet. The consequences of this over-exploitation of mineral wealth have to be serious, drastic and enormously damaging to the entire biosphere. These can be summed up as follows:
1. Rapid Depletion of High Grade Mineral Deposits:
Exploitation of mineral wealth at a rapid rate shall naturally deplete our good quality deposits. The ever rising demands shall compel miners to carry on the extraction from increasingly lower and lower grade of deposits which possess a poorer percentage of the metal. For example copper was extracted from ores containing 8-10% of metal content about 500 years ago.
Now we are using deposits which contain only 0.35% of copper. To produce one ton of copper metal we have to dig out 285 tons of ore. This shall naturally involve a large amount of energy expenditure as well as a large quantity of waste material production.
We may never reach an end as matter is indestructible. Most of the metals we require are present in highly dispersed state in the soil, the rocks and the trash or wastes we discard. With a sophisticated technology we can fulfill most of our requirements from these sources, But the overall cost could be I heavy, causing the metals to become more and more costly.
2. Wastage and Dissemination of Mineral Wealth:
Most of our mineral deposits occur as a complex mixture of a number of mineral elements. After removal of top soil and rocks we dig out the desired mineral leaving behind others which are often left in the open as waste materials. Extraction of one element usually scatters and wastes a number of other elements, many of which are in short supply.
This wastage rises as more and more ores are extracted and processed. Worldwide smelting of minerals for extraction of metals introduces an enormous quantity of sulphur, heavy metals such as mercury, cadmium, nickel, arsenic, zinc etc. into the environment which are separately mined elsewhere.
We are technologically competent enough to extract these metals from the wastes produced from one mining industry rather than excavating fresh deposits. The cost could be heavier indeed but the practice shall pay in the long run. It will conserve our resources and also reduce the burden of pollutants which we have to introduce in the environment.
3. Pollution of Environment from Mining and Processing Wastes:
Mining is a dirty industry. It has created some of the largest ‘Environmental disaster’ zones in the world. The mining and processing of minerals generally involves following steps:
1. The soil and rock overlying the mineral deposits, called the ‘over-burden’ in miner’s language, has to be removed before actual mining operations commence.
2. The ore is then mined and crushed.
3. After being converted to fine powdered state it is run through concentrators which remove impurities.
4. The concentrated ores are then reduced to crude metal often at a high temperature by various methods depending upon the chemical nature of the ore.
5. Crude metal is then refined or purified in refineries.
Each step in mining and processing operations produces large quantities of waste materials. As most of today’s mines are simple surface excavations, the first task of a miner is to remove whatever lies over the mineral deposit, be it a mountain, a forest or an agricultural field. Underground mining with a system of shaft and tunnels does not produce as much waste as open cast mining does.
In 1988, over-burden, the material overlying the mineral deposits in U.S. A., amounted to about 3.3 billion tons of matter moved. This material even if chemically inert, clogs streams, gets deposited in lakes and clouds the air over large areas. If it contains sulphur and other reactive elements apart from wastage of our precious resource a number of other problems are caused (Young, 1992).
Almost similar problems arise from the disposal of waste material produced after concentration of an ore. This material is called ‘tailings’ in miner’s language. As most of the ores contain a large amount of sulphur its oxidation and leaching results in formation of acidic leachates (Water containing dilute sulphuric acid).
The finely grounded state of ores makes metal contaminants which were earlier bound in solid rocks, available to acidic waters. Thus, these leachates contain appreciable amounts of heavy metals and toxic trace elements. Tailings may contain residue of organic chemicals such as toluene etc. which cause another type of problems. Ponds full of acidic leachates covering thousands of hectares of land surface now surround copper mines in U.S.A. These waters cause serious problems of water pollution if they happen to contaminate our surface or underground acquifers.
The grade of ore is important in determining the overall impact of mining activity. An ore containing 20% of metal content shall produce only four tons of tailings or waste material per ton of metal extracted but a low grade ore containing 1% of metal shall produce 99 tons of tailings per ton of metal obtained.
Gold mining is particularly damaging in this respect as the metal content of gold deposits is at best expressed as parts per million. Miners at Gold Strike mine in Nevada – the largest in USA move about 3, 25,000 tons of ore to produce about 50 kg of gold per year.
In Amazon basin, Brazil, miners use a technique called hydraulic mining which involves blasting the gold bearing hillside with high pressure stream of water following by guiding the sediments through ducts where the gold being heavier settles down from tons of non-valuable material.
This silt and sediments are finally washed down into some local stream. The practice has silted local rivers and lakes while the use of mercury to trap gold from sediments has contaminated large areas. Miners release an estimated 100 tons of mercury into the waters of Amazon river annually.
In North America, miners use ‘Heap Leaching’ a technique which allows gold extraction from a very low grade ore. The technique involves sprinkling of cyanide solution over a heap of low grade ore. While trickling down the solution dissolves gold. It is collected and later gold is recovered from it. Both cyanide solution reservoirs and contaminated tailings are left behind after the gold extraction.
These pose hazards to wild life and threaten surface waters as well as under-ground acquifers. In October 1990 about 45 million litres of cyanide solution from a reservoir at Brewer Gold Mine, South Carolina, spilled over into a tributary of local Lynch River, killing more than 10,000 fishes. Thousands of birds die each year when they mistakenly consume cyanide solution from these impoundments.
4. Pollution Caused by Heavy Energy Requirement of Mining Industry:
Moving huge amounts of sand silt and clay etc. requires energy. Concentration of ore requires energy. Smelting and refining operations require energy. Electrolytic processes used for refining of some metals, like Aluminium, require energy.
Disposal of solid or liquid wastes or tailings requires energy. Transportation of solid or liquid wastes or tailings requires energy. Transportation of finished products requires energy. The overall worldwide requirement of energy in mining industry adds up to an enormous amount. This energy comes from diverse sources which mostly include fire-wood, coal, petroleum, natural gas and electricity. In order to provide energy to mining industry a huge quantity of these materials are burned which causes a variety of pollution problems.