Gold panning non-submersible car

I have previously mooted the possibility of using eddy currents induced by magnetic fields to winnow tiny gold particles from seafloor sediments.

However, there is probably more gold to be found on the roads - dropped rings, broken jewellery and the like. And these items, being bigger, would sustain a larger induced eddy current.

MaxCo. is therefore about to start cruising the streets in its latest gold-panning roadster.

Mounted crosswise beneath the body of the otherwise normal-looking Aston (did I mention it was an Aston? No matter.) is a drum, set at a height to travel a couple of inches above the road surface. Stupidly powerful magnets are fixed inside the drum, with their poles outwardmost, and an electric motor spins this drum at a couple of thousand RPM, in the same direction as the wheel rotation.

A few inches behind the drum is a scoop (which, as a bonus, produces extra downforce, which is always handy in an Aston).

Meanwhile, up the front end of the car, a powerful fixed magnet is, ah, fixed. This (like the roller) spans the full width of the car. A motorised blade, activated every few seconds, can scrape from right to left along this magnet.

With the system activated, we set off on the streets of a prosperous district.

Most of the metallic road debris will be ferrous. This is picked up by the front, fixed magnet and is periodically scraped off by the blade and dumped back on the roadside.

Non-ferrous debris, however, is passed over by the fixed magnet. A moment later, the fast-spinning roller passes over said non-ferrous debris and, due to the speed of the spinning magnets, substantial eddy currents are induced in the debris. These, in turn, create reciprocal magnetic fields with the result that the non-ferrous debris is lifted and flung backwards, to be collected by the scoop.

At the end of a long drive, we inspect the haul. Most of it will be aluminium ring-pulls or squashed cans (themselves worth something). However, any pieces of gold, silver or platinum jewellery will also have been harvested.

What sort of yield can we expect? Well, let's assume that the average adult (say, 40 million people in the UK) loses two pieces of jewellery in a lifetime (a conservative estimate). That's 80 million items lost per year.

Assume also that 1% of these items are lost on roads. That's 800,000 items landing on the roads every year.

Assume also that each item sits on the road for 5 days (many will sit for longer, being squashed and unnoticed; some will be spotted and picked up sooner; very few will be washed or blown away, so 5 days is a fair average). That means that there are on average 11,000 items of jewellery on Britain's roads at any one time.

There are roughly 100,000 miles of road in Britain, meaning that on average there is one item of jewellery lying in the road every 10 miles or so, at any given time.

If we assume that we can harvest just 10% of these items (for instance, because the other 90% have been squashed and wedged into the road surface), that gives us one item of jewellery for every 100 miles driven. If the average item contains just 1 gram of gold (conservatively - a wedding ring, for instance, will weigh several grams), we are recovering about £25-worth of gold for every 100 miles driven.