aqua regia


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aqua regia

(äk`wə rē`jēə) [Lat.,=royal water], corrosive, fuming yellow liquid prepared by mixing one volume of concentrated nitric acid with three to four volumes of concentrated hydrochloric acid. It was so named by the alchemists because it dissolves gold and platinum, the "royal" metals, which do not dissolve in nitric or hydrochloric acid alone. Its fumes and yellow color are caused by reaction of nitric acid, HNO3, with hydrogen chloride, HCl, to form nitrosyl chloride, NOCl, chlorine, Cl2, and water; both chlorine and nitrosyl chloride are yellow-colored and volatile. The nitrosyl chloride further decomposes to nitric oxide, NO, and chlorine. Nitric acid is a powerful oxidizing agent (see oxidation and reductionoxidation and reduction,
complementary chemical reactions characterized by the loss or gain, respectively, of one or more electrons by an atom or molecule. Originally the term oxidation
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), but the chemical equilibriumchemical equilibrium,
state of balance in which two opposing reversible chemical reactions proceed at constant equal rates with no net change in the system. For example, when hydrogen gas, H2, and iodine gas, I2
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 for its reaction with gold, Au, only permits formation of a tiny amount of Au+3 ion, so the amount of gold dissolved in pure nitric acid is undetectable. The presence of chloride ion, Cl, allows formation of the stable chloraurate complex ioncomplex ion,
charged molecular aggregate (see ion), consisting of a metallic atom or ion to which is attached one or more electron-donating molecules. In some complex ions, such as sulfate, SO4−2
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, AuCl4. Because of the high concentration of chloride ion in aqua regia, the Au+3 is reacted almost as soon as it is formed, keeping its concentration low; this allows oxidation of more Au to Au+3, and the gold is dissolved. The gold may also react directly with the free chlorine in aqua regia, since chlorine is a powerful oxidizing agent.

Aqua Regia

 

a mixture of concentrated hydrochloric and nitric acids, usually one part nitric acid and three parts hydrochloric acid. Aqua regia is a yellow liquid with the odor of nitrogen oxides and chlorine. It has strong oxidizing properties owing to the liberation of chlorine in the reactions

3HCl + HNO3 = Cl2 + NOCl + 2H2O

2NOCl = 2NO + Cl2

Aqua regia dissolves all metals with the exception of silver, rhodium, and iridium. It even dissolves gold—hence the name “aqua regia,” given by alchemists who considered gold the king of metals. Aqua regia is used as a laboratory reagent in such processes as the refining of gold and platinum and the production of metal chlorides.

aqua regia

[¦äk·wə ′rē·jə]
(inorganic chemistry)
A fuming, highly corrosive, volatile liquid with a suffocating odor made by mixing 1 part concentrated nitric acid and 3 parts concentrated hydrochloric acid; reacts with all metals, including silver and gold.

aqua regia

a yellow fuming corrosive mixture of one part nitric acid and three to four parts hydrochloric acid, used in metallurgy for dissolving metals, including gold
References in periodicals archive ?
Chromium was only detected in nitric acid and aqua regia solutions of sample 6.
The aqua regia method of analysis is susceptible to acid interference, which makes it unreliable if used alone.
EN 16320:2013 + A1:2017 - Fertilizers and liming materials - Determination of mercury by vapour generation (VG) after aqua regia dissolution.
SGS Canada Inc carried out some or all of following methods to obtain the assay results for Callinex: G_LOG02 Pre-preparation processing, G_WGH79 Weighing and reporting, G_PRP89 Weigh, dry, crush, split, pulverize, G_SCRQC QC for crush and pulverize stages, G_CRU22 Crush >3kg, G_DRY11 Dry samples, GE_FAA313 @Au, FAS, AAS, 30g-5ml (Final mode), GE-IC14A Aqua Regia digestion/ICP-AES finish, GE_IMS14B Aqua Regia digestion/ICP-MS package, GE_IMS14 Aqua Regia digestion, GO_FAG303 30g, Fire assay, gravimetric finish (Au)(Final Mode), GO_FAG313 30g, Fire assay, gravimetric finish (Ag)(Final Mode), G0_ICP13B Ore Grade, Aqua Regia digest/ICP-AES.
Representative portion of each sample of concentrates, middlings and tails was treated with aqua regia and other acid mixture and the solutions were analyzed for Au, Ag and base metals (Cu, Zn, Pb, Cr, Ni, Co, Mn and Cd) by atomic absorption spectrometer in the geochemistry laboratory of NCE in Geology, University of Peshawar.
Samples are first tested with the "ME-ICP41m" procedure which analyzes for 35 elements using a near total aqua regia digestion.
Analytical procedures for both laboratories included the multi-element package, 32 element ICP 14B using aqua regia digestion and an AES finish and AU FAA 515 package for all samples on a 50gm aliquot with all samples greater than 5,000 ppb rerun using FAG 505 package standard.
Silver was analyzed as part of a multi-element ICP package using an aqua regia digestion; samples with more than 100 g/t silver (over limit) were analyzed by AA.
Aqua regia and cyanide leaching tests proved ineffective and resulted in extremely low gold and silver extraction.
Silver, copper and zinc were analyzed as part of a multi-element ICP package using an aqua regia digestion; samples with more than 100 g/t silver, 1% copper and/or 1% zinc were re-analyzed using 'ore grade' detection limits.