ground rock is treated with a solution of sodium cyanide. The extract is absorbed onto carbon. The gold can be removed from the carbon by using a strong solution of caustic soda and cyanide. Gold cyanide is then converted to relatively pure gold by a variety of methods. The technique using dissolution with alkaline cyanide has been highly developed over recent years. It is particularly appropriate for low grade gold and silver ore processing (e.g. less than 5 ppm gold) but its use is not restricted to such ores. There are many environmental hazards associated with this extraction method, largely due to the high acute toxicity of the cyanide compounds. A major example of this hazard was demonstrated in the 2000 Baia Mare cyanide spill, when a break in holding pond dam at a mine waste reprocessing facility near Baia Mare in northern Romania released approximately of waste water contaminated with heavy metal sludge and up to of cyanide into the Tisza River. As a consequence, most countries now have strict regulations for cyanide in plant discharges, and plants today include a specific cyanide-destruction step before discharging their tailings to a storage facility. Mercury process Historically, mercury was used extensively in placer gold mining in order to form mercury-gold amalgam with smaller gold particles, and thereby increase the gold recovery rates. Large-scale use of mercury stopped in the 1960s. However, mercury is still used in artisanal and small-scale gold mining (ASGM), often clandestine, gold prospecting. Business Small operations While most of the gold is produced by major corporations, millions of people work independently in smaller, artisan operations, in some cases illegally. Artisanal mining refers to workers who use rudimentary methods to extract and process minerals and metals. Socially and economically marginalized communities mine to escape extreme poverty, unemployment and landlessness. In Ghana, the galamseys are estimated to number 20,000 to 50,000. In neighboring francophone countries, such workers are called orpailleurs. In Brazil, such workers are called garimpeiros. The word garimpeiros is also used in Venezuela, Suriname and French Guiana, because many illegal gold prospectors are from Brazil. There are an estimated 10 to 15 million artisanal and small-scale gold miners worldwide. 4.5 million of them are women. Miner's risks include persecution by government, mine shaft collapses, and toxic poisoning from unsafe chemicals used in processing. The high risk of such ventures was seen in the collapse of an illegal mine