 Vat leaching is used mainly for ores with higher concentrations of gold due to the cost of milling the ore to a very small particle size.Alternative lixiviant (leaching) chemicals to cyanide (for example thiourea, sodium bromide) have been investigated for many years, but they are generally less effective and/or economical than cyanide, and they also present environmental risks that can be greater than cyanide.Because cyanide is toxic if not properly handled, its use is highly regulated in most countries.