BGS Risk List (6)

After the rather morbid post for the 7^th most at risk element (Mercury) hopeful this week’s centre stage element will be a nicer story to tell! So let us explore our number 6 ranking metal, Strontium.

RANKING:

6

ELEMENT NAME AND SYMBOL:

Strontium (Sr)

RELATIVE SUPPLY RISK INDEX:

8.6

WHY?:

Strontium is not found isolated in the crust, instead it has to be processed from the minerals celestine (SRSO4) and strontianite (SrCO3). Despite this is the 15^th most abundant element on Earth, so why the high at risk status?

It is not currently recycled, so we are constantly depleting our supply at the

moment. And once again, as is becoming quite a pattern, China is both the

leading producer and reserve holder, making the element vulnerable to

high export taxes when being sold to the rest of the world.

LEADING PRODUCER:

China

TOP RESERVE HOLDER:

China

WHY THE DEMAND?:

Strontium came into the limelight firstly in it’s role of producing sugar from sugar beet, but now has many other uses too. I shall talk you through a couple of these now:

In week three we saw barium and it’s use in fireworks; well strontium also has a hand in your bonfire night festivities, because it is what gives fireworks their red colour! Strontium alloy is used in the metal of choice for BMW, who use it in their car and motorcycle engines. And finally, a more scientific use; strontium isotope tracing is used in groundwater movement.

One upside of climate change

Slightly off-topic perhaps but I came across an article on the New Scientist website, showing there may be at least one advantage to climate change...

Rice, wheat and some other crops have been proven to increase in yield at higher carbon dioxide concentrations, and another staple to diet in Africa and Asia, the sweet potato, follows this trend.

The IPCC predicts carbon dioxide concentration to rise to 500-1000ppm by 2100. If, at a mid estimate, it increases to 750ppm then sweet potatoes will almost double in size! This could be fantastic news for the people who rely on them, but tests still need to be done to see if their nutrition also increases in proportion. Otherwise it will simply mean having to consume double the volume of sweet potatoes to receive the same amount of nutrients from half that amount today.

Diamonds are forever

Diamonds are a desirable, highly economic, and extreme form of carbon. The can only formed under intense heat and pressure deep within the Earth; the upper mantle. But if so how do they get brought up to the surface for us to mine them? The answer is kimberlite pipes, the hottest and deepest known rock found on Earth, which periodically erupted through the crust when the Earth was younger and much hotter than it is today. An excellent animation of how this occurs can be found on the 'How stuff works' website.

By looking for kimberlite rocks (which have a slightly blue hue) veins containing diamonds can be found. One such place abundant in diamonds is Akwatia: Ghana’s biggest mining town. It used to contain predominantly large-scale mines, but an exponential trend to small and artisanal mines has prevailed in recent years, as total mining has decreased. This is because these small mines generally set up on the sites that larger companies have already mined, meaning their only option is to scavenge lower carat diamonds.

Graph illustrating the huge increase in small and medium sized mines, compared to large GCD (Ghana Consolidated Diamonds Ltd) owned mines (Yelpaala and Ali, 2005)

Yelpaala and Ali (2005) produced a paper looking at the effects of mining in Akwatia. Compared to the predominantly mined commodity in Ghana, gold, diamonds pose relatively little harm, as the chemical processing involved cyanide and mercury is not required. However, as artisanal and illegal mines grow in the numbers other sources of risk to human health and the environment will rise (a UN study in 2000 estimated that 50,000-80,000 people were engaged in illegal mining in Ghana).

In the process of mining for diamonds, pits must be excavated and then the removed material sifted through for the crystals. GCD (one of the major mining companies in Akwaitia) does this at just 30 to 60% efficiency (GCD, 2002), creating a huge amount of waste and unnecessary environmental disruption.

Men digging a small-scale mine pit

In digging the pits and then refilling them with the waste a great deal of land degradation occurs. Although GCD re-vegetate some of their sites, their small budget doesn’t allow for much. This leads to a loss of plant biodiversity, many of which are medicinal plants relied upon by the local people, particularly in the illegal mining sites where no attempt at protecting the environment is imposed.

When pits are left unfilled they pose human risks; both from a safety aspect of locals falling into them and injuring themselves, and because they fill with water and subsequently become mosquito breeding grounds. For a country with a serious malaria problem that is a dangerous consequence. However, GCD and other companies simply do not have the money to be able to fill all the pits.

To move forward, as is the case in all developing countries, a balance between economic growth and environmental and human impacts clearly needs to be achieved. Sadly there does not seem to be an easy answer as to how this can be done.

BGS Risk List (7)

So last week we learnt some facts about the little known barium. This week’s at risk element will be more familiar to you I’m sure: it’s mercury! So without further ado let us carry on with the countdown!

RANKING:

7

ELEMENT NAME AND SYMBOL:

Mercury (Hg)

RELATIVE SUPPLY RISK INDEX:

8.6

WHY?:

Mercury is extremely rare, it’s presence in Earth’s crust being only 0.08ppm (parts per million). Concentrated mercury ores do exist, but it is more widely found in the red mineral cinnabar (HgS).

The mining of mercury is at risk mainly due to environmental hazard reasons. It is extremely toxic, and so there are worries about both the health of miners, and the risks of it tainting groundwater as drinking water will subsequently be toxic too.

LEADING PRODUCER:

China

TOP RESERVE HOLDER:

Mexico

WHY THE DEMAND?:

Mercury is special in the fact it is liquid at room temperature! It is the only element that exhibits this unusual state aside from bromine. Thanks to this quality it used to be used in thermometers, but that practice has been largely stopped due to health hazards, and alcohol is now more commonly used.

Now it is mainly used in fluorescent lights to produce UV light, which occurs when electricity is passed through mercury. It is also used in ‘silver’ dental fillings, under the name of amalgam, which is a mercury alloy. Aside from these two common uses the rest of mercury’s applications are in scientific research.