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Rough Science 3 New Zealand: Mike Bullivant's Diary: Treasure Hunt

Updated Tuesday 27th February 2007

Mike Bullivant's diary about the challenge for the Treasure Hunt programme, from the BBC/OU series Rough Science 3

Mike Leahy and Mike Bullivant Copyrighted image Icon Copyright: Production team

Day 27 -  Extracting Gold
Only two more programmes to go but some of us already have our sights set on home. Not me! For this fifth programme, I'm teamed up with Mikey L again. He's fun to work with, though you sometimes have to kick his arse to get things going! We have to extract gold from the gold-bearing rock that we brought down after our overnight stay in Programme 3. Luckily for us, we're given a huge lump of cinnabar, an ore of mercury from which we can make some mercury. We can then use this to form a mercury/gold amalgam, from which it's an easy enough process to recover the gold. At least, I think it is.

The first job is for Mikey to crush our gold-bearing ore into a fine powder; only then will it react with the mercury. Problem is that we have absolutely no idea how much gold is in the rock; it could be parts per million, or even parts per billion, as far as we know.

While Mikey does his strong-arm stuff on the rock, I set about heating the cinnabar up in a boiling tube. Before long, silvery mercury droplets start to distil over. It's not quite that straightforward, however. Mercury's a pretty nasty metal because inhaling its vapour is dangerous and even at room temperature, there'll be a lot of mercury vapour where we'll be working; it can't be avoided. Neither should mercury be allowed to come into contact with your skin, so we take all kinds of precautions to ensure that the risks are minimized.

It really is a beautiful transformation from pink/red ore to a silvery, liquid metal. It's just the kind of thing that used to fascinate me when I was at school, and that led to my interest in chemistry. Sadly, however, it's not the kind of thing that today's school students are likely to be exposed to as it's far too 'dangerous'.

By the end of Day 1, we have a little crushed, gold-bearing rock (what has Mikey been up to all day?) and enough mercury to have a decent stab at extracting some of the gold from it. Should be a pleasant, stress-free day tomorrow.

Day 28 - Extracting Gold
What was that I was saying about it being a good day today? It turns out that I spend most of the day being driven to and from the nearest hospital in Greymouth to get some X-rays taken. I was involved in a bad car crash last night, and it turns out that I've broken four ribs and punctured a lung. That's going to slow me down a bit. The pain is bad. I can hardly move without a searing pain shooting through my chest. I just feel like going to bed, and that's exactly what I end up doing. I wonder how I'm going to feel tomorrow.

Day 29 - Extracting Gold
Well, I feel pretty bad this morning, but the show must go on ... what with it being show business and all that! I find it very difficult to move freely but everyone's so sympathetic and understanding. I feel a right passenger. Thank goodness that making the gold-mercury amalgam won't be that time-consuming, or physically demanding.

It turns out that Mikey managed to crush most of the rock while I was away yesterday, so we should be ready to rock (no pun intended) and roll by 10am. All we have to do today is react the gold with the mercury to form an amalgam and then recover the gold (in a purified form). To do this, you grind the crushed ore with the mercury in a pestle. In doing so, you can see the physical nature of the mercury change as it reacts with the gold in the rock. The amalgam is a grey semi-solid that looks neither like gold nor mercury. The amalgamation process is similar to dissolving the gold in the mercury, only it's not quite that simple. Most metals will form an amalgam with mercury and it's a process that's been used for years to purify metals like gold.

The weird thing about amalgams is that it's easy to recover the original metals. All you have to do is heat the amalgam up and, hey presto, you recover both the gold and the mercury. The problem is that mercury's really toxic and we have to be careful that, by heating the amalgam, we don't force the mercury to evaporate into the atmosphere. Mikey L comes up with a really neat Rough Science way of doing it safely - using a potato. All you do is place the amalgam under a potato that's been cut in two lengthways, with a small indentation cut into one of the raw sides. Placing the indentation over the amalgam and heating the potato up, drives off the mercury and re-generates the gold. The beauty of the process is that as the mercury evaporates, it's taken up into the flesh of the potato, and never has a chance to escape into the atmosphere.

Neat eh!? By the end of the day, we've extracted and purified all of our gold using the amalgamation process. We end up with quite a sizeable nugget as things turn out.

 

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