Mining<unk>  is mainly produced for the mining of gold and silver: It helps dissolve these metals allowing separation from the other solids. In the<unk>  process, finely ground high-grade ore is mixed with the<unk>  (at a ratio of about 1:500 parts NaCN to ore); low-grade ores are stacked into heaps and sprayed with a<unk>  solution (at a ratio of about 1:1000 parts NaCN to ore). The precious metals are complexed by the<unk>  anions to form soluble derivatives, e.g., Au<unk> 2− and Ag<unk> 2−. Silver is less "noble" than gold and often occurs as the sulfide, in which case redox is not invoked (no O2 is required). Instead, a displacement reaction occurs: The "pregnant liquor" containing these ions is separated from the solids, which are discarded to a tailing pond or spent heap, the recoverable gold having been removed. The metal is recovered from the "pregnant solution" by reduction with zinc dust or by adsorption onto activated carbon. This process can result in environmental and health problems. A number of environmental disasters have followed the overflow of tailing ponds at gold mines.<unk>  contamination of waterways has resulting in numerous cases of human and aquatic species mortality. Aqueous<unk>  is hydrolyzed rapidly, especially in sunlight. It can mobilize some heavy metals such as mercury if present. Gold can also be associated with arsenopyrite (FeAsS), which is similar to iron pyrite (fool's gold), wherein half of the sulfur atoms are replaced by arsenic. Gold-containing arsenopyrite ores are similarly reactive toward inorganic<unk> . Industrial organic chemistry The second major application of alkali metal<unk> s (after mining) is in the production of<unk> -containing compounds, usually nitriles. Acyl<unk> s are produced from acyl chlorides and<unk> . Cyanogen, cyanogen chloride, and the trimer cyanuric chloride are derived from alkali metal<unk> s. Medical uses The<unk>  compound sodium nitroprusside is used mainly in clinical chemistry to measure urine ketone bodies mainly as a follow-up to diabetic patients. On occasion, it is used in emergency medical situations to produce a rapid decrease in blood pressure in humans; it is also used as a vasodilator in vascular research. The cobalt in artificial vitamin B12 contains a<unk>  ligand as an artifact of the purification process; this must be removed by the body before the vitamin molecule can be activated for biochemical use. During World War I, a copper<unk>  compound was briefly used by Japanese physicians for the treatment of tuberculosis and leprosy. Illegal fishing and poaching<unk> s are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. The practice is controversial, dangerous, and damaging but is driven by the lucrative exotic fish market. Poachers in Africa have been known to use<unk>  to poison waterholes, to kill elephants for their ivory. Pest control M44<unk>  devices are used in the United States to kill coyotes and other canids.<unk>  is also used for pest control in New Zealand, particularly for possums, an introduced marsupial that threatens the conservation of native species and spreads tuberculosis amongst cattle. Possums can become bait shy but the use of pellets containing the<unk>  reduces bait shyness.<unk>  has been known to kill native birds, including the endangered kiwi.<unk>  is also effective for controlling the dama wallaby, another introduced marsupial pest in New Zealand. A licence is required to store, handle and use<unk>  in New Zealand.<unk> s are used as insecticides for fumigating ships.<unk>  salts are used for killing ants, and have in some places been used as rat poison (the less toxic poison arsenic is more common). Niche uses Potassium ferrocyanide is used to achieve a blue color on cast bronze sculptures during the final finishing stage of the sculpture. On its own, it will produce a very dark shade of blue and is often mixed with other chemicals to achieve the desired tint and hue. It is applied using a torch and paint brush while wearing the standard safety equipment used for any patina application: rubber gloves, safety glasses, and a respirator. The actual amount of<unk>  in the mixture varies according to the recipes used by each foundry.<unk>  is also used in jewelry-making and certain kinds of photography such as sepia toning. Although usually thought to be toxic,<unk>  and cyanohydrins increase germination in various plant species. Human poisoning Deliberate<unk>  poisoning of humans has occurred many times throughout history. Common salts such as sodium<unk>  are involatile but water soluble, so are poisonous by ingestion. Hydrogen<unk>  is a gas, making it more indiscriminately dangerous, however it is lighter than air and rapidly disperses up into the atmosphere, which makes it ineffective as a chemical weapon. Poisoning by hydrogen<unk>  is more effective in an enclosed space, such as a gas chamber. Most significantly, hydrogen<unk>  released from pellets of Zyklon-B was used extensively in the extermination camps of the Holocaust. Food additive Due to the high stability of their complexation with iron, ferrocyanides (Sodium ferrocyanide E535, Potassium ferrocyanide E536, and Calcium ferrocyanide E538) do not decompose to lethal levels in the human body and are used in the food industry as, e.g., an anticaking agent in table salt.
Cyanide
Lewisite
Bromide
Hydrogen fluoride
Carbonated water
Carbon monoxide
Isothiocyanate
Metaldehyde