Gold, precious forever but especially lately, is a tricky metal. Bound up in consumer electronics, jewelry and the ores that it comes from, gold is difficult to extract, and most modern processes do it with a highly toxic combination of cyanide salts. The cyanide leaches the gold out, but the cyanide can seep into the ground, causing environmental problems and posing threats to human health.
Researchers at Northwestern University recently stumbled upon a solution that uses cornstarch instead. It involves some complex chemistry, but it's cheap, biologically friendly and nasty-ingredient-free.
Led by Sir Fraser Stoddart, a chemistry professor at Northwestern, the team discovered this method by accident when looking for something else. A postdoc named Zhichang Liu was trying to make three-dimensional cubes out of gold and starch, aiming to use them as storage containers for gases and small molecules. But a liquid mixture of dissolved gold-bromide salts and a starch-derived sugar didn't form cubes, it formed needles. This was strange, so the team decided to try to replicate it and tested different forms of sugars.
Alpha-cyclodextrin, a cyclic starch fragment with six glucose molecules, is the best way to isolate gold, they found. "Zhichang stumbled on a piece of magic for isolating gold from anything in a green way," Stoddart says in a statement. The spontaneous bundle of needles is made of thousands of nanowires, each 1.3 nanometers in diameter, which contain a charged gold atom inside four bromine atoms.
The interaction between the starch fragment and the gold allows the precious metal to be selectively recovered from other materials, including platinum, palladium and others. The researchers already developed a process to isolate gold from scraps, and they hope this will lead to an environmentally friendly, cheap way to recover gold from anything. The research is published in Nature Communications.
Best news all year.
I love accidental science. This is great news
Amazing, another toxic problem solved.
they discover this while gold prices are in free fall?
Maybe this is why gold prices are going down.
I doubt that this is a practical solution (pun intended, ha!) for heap leaching of gold. Cornstarch will form a strain-hardening solution when mixed with water, so pumping it from the plant to the top of the heap will not be easy.
I hope the the method is quickly industrialized.
Did the Mayans use cynaide? Maybe that's why their calendar ended. All kidding aside, this process is a-maze-ing.
Borax and cornstarch. Laundering my gold. Hmmm. I've got a chunk of fairly good hard rock ore that I've thought about crushing up for a while. Mebbe I'll just go check that link.
Think of the thousands of years no one ever thought of this!
Does anybody here have a clue or know any chemistry? The story says cornstarch was used to precipitate gold from a bromide solution not dissolve it. Cyanide is used in gold mining to dissolve the gold so in the story bromide takes the place of the cyanide used in gold mining, not the cornstarch. However, to dissolve gold as a bromide complex requires hydrobromic acid (in excess) and an oxidant (bromate, nitric acid, perchloric acid, etc.). The HBr, HNO3, and H2ClO4 are toxic. Bromine and bromate are toxic on a long term basis since bromine replaces iodine in thyroid hormones and when this happens the tyroid hormone produced is biolotically inactive. Cyanide is handled much more easily than most people imagine. Cyanide is stable at a pH range of 9.0 to 10.5 and concentrations used in treating gold ores in in the range of 0.1% to 0.2%. No one, to my knowledge, has ever died or suffered serious effects, or long term injury from the cyanide solutions used in gold mining. The liver also has an enzymatic pathway that detocifies cyanide since low condentrations of cyanide occur naturally in many plants and seeds (almonds, peach and apricot pits - yea I eat them on occasion)as an insect deterent. In gold mining the Au(CN)2- complex is absorbed on activated charcoal or an ion exhange resin because the Au concentration in the pregnant solution is low (<20 ppm). The collector is then stripped to make a more concentrated solution from which the gold is then plated on steel wool. Constarch might be able to be used as the precipitant from the strip solution but at what point can it replace cyanide. If silver is a substantial metal in the ore, then stripping is usually done with zinc powder which precipitats both the gold and silver. In this case cornstarch may not precipitate the silver. Cyanide is also easily destroyed by oxidants such as sunlight+O2, sodium hypochlorite (bleach), SO2). There are also bacteria that at low cyanide concentration can break down cyanideto carbon dioxide and nitrogen (cyanide is CN-) The have only been 2industrial accident deaths from cyanide, one in the plating industry in Chicago and one at a plant manufacturing cyaide (DuPont). In the first case the worker who died didn't speak or read English and didn't know cyanide was being used. In the second case, the worker went into a restricted area alone without safety gear in violation of work rules.
This is the most ridicules paper I have ever seen. It is not related to gold recovery from cyanide at all, and it is really interesting how their authors have claimed cornstarch can be used for recovery of gold from cyanide solution while they have precipitated out the gold from HBr!!!!