Decades of mining pollution are slowly catching up with the environment, directly impacting on agriculture. A former head of the Geology department at Wits, Prof Terence McCarthy, is regarded as a leading authority on wetland geomorphology. He warns that the impact of new mining permits in the Chrissiesmeer area in Mpumalanga will be devastating. Susan Botes reports.
Why the HUGE media fuss about
mines continually polluting rivers?
Mining generates a lot of money, boosting SA’s economy and bringing in foreign currency. Salaries are one of the mining industry’s biggest expenses and many people are dependent on this. Our country’s economy will remain minerals-driven for a while, but we have to do it responsibly.
People are more aware of pollution than they were in the past, but the mining industry seems stuck in the mindset of a few decades ago when conservation wasn’t as important. The industry might pay lip service to nature, but acting on it would mean shareholders would earn fewer dividends. But the time when we didn’t know any better has passed.
Do all types of mines pollute the same way?
No. Coal and gold mines are the worst, while a few others aren’t associated with pollution. For example, mining for building stone has an aesthetic impact and a minimal environmental impact.
How does mine pollution start?
Rocks associated with coal and gold mining contain pyrite, a sulphide also known as fool’s gold. When this is exposed to water and oxygen, it undergoes oxidation and forms sulphuric acid and rust.
After the coal has been removed, the pit is backfilled with the broken, pyrite-bearing waste rock and the surface is rehabilitated. Rainwater flows into and through the mass of broken rock and the pyrite oxidises. This acidic water eventually leaks out or is pumped to the surface. The process is known as acid mine drainage (AMD) and it starts the moment mining commences.
The acidic water in the mine also leaches heavy metals from the broken rock, including manganese, copper, zinc, and in rare instances nickel, cobalt and cadmium. It also becomes aluminium-enriched. AMD occurs in coal mines, gold mining heaps and in the underground workings.
Which areas are influenced by AMD and which are not?
The Secunda-Evander area in Mpumalanga has both coal and gold mines. Coal is mostly mined in northern KwaZulu-Natal and in the Witbank-Middelburg area of the eastern Highveld. Gold is mined mostly in the Witwatersrand, Carltonville, Krugersdorp, Klerksdorp, Welkom, Barberton and Pilgrim’s Rest areas. There is little mining in the Cape.
How does influence agriculture?
Polluted groundwater is the biggest problem. High salt content can cause health problems for livestock. Long-term irrigation may damage the soil by increasing its salt content and acidifying it.
Mining dust can also be a problem, as dusty leaves could reduce photosynthesis, lowering productivity, and could lead to farmers’ lands becoming acidic. This will add to farmers’ input costs, as they’ll have to add even more lime to their lands.
Water pollution will also lead to a major loss in animal life, particularly in rivers. Fish, frogs, crabs, insects and many aquatic plants can’t live in this water.
Just to illustrate the impact of chemical pollution – in July numerous pineapple farmers couldn’t export their produce after using a zinc sulphate fertiliser from China with high amounts of cadmium. We haven’t seen anything like this due to AMD yet, but the future impact is uncertain. Things will only get better if mines reduce AMD.
There’s another aspect of coal mining, especially opencast mining, to consider. After mining is completed, the surface is restored and grass is planted. Although the land surface seems fine, it won’t be possible to obtain drinkable borehole water on such properties for centuries. Farmers there will need to truck in drinking water for themselves and their livestock.
Can mines combat before the water flows into the main water system?
By adding limestone mining companies can neutralise the acid as it’s formed. The pyrite-bearing rock is mixed with crushed limestone before it’s put back in the holes left by opencast mines. The yellow gold heaps can be neutralised in the same way – mix lime with the crushed rock when it is dumped in tailings heaps.
If this is done properly during mining it’s a once-off solution to the problem. It will neutralise the acid and prevent the spread of heavy metals, but it won’t completely stop the pollution. Water from the mined material will still be sulphate-enriched, but will be low in most heavy metals.
