Nitric acid, Melting Point : -42 °C

 nitric acid in gold mining gold acts like a sponge and absorbs nitric acid, one of the mining chemicals. this enables the nitric acid to clean the gold, such as gold nuggets or free gold taken from black sands. Most gold found in nature contains other metals, but some of these cannot be taken down in nitric acid (such as the platinum family).  nitric acid alone can dissolve some unwanted minerals (such as pyrite) from gold ore, it is unable to penetrate large gold bodies or refine relatively pure gold. Aqua regia -- a mixture of nitric acid and hydrochloric acid -- can dissolve gold itself, allowing pollutants to be filtered off so that very pure gold can be extracted as a precipitate.  nitric acid properties • cas no. : 7697-37-2• hazard class: 8• un no.: 2031• toxicity: oral rat ld50: > 90 ml/kg• standard: industrial grade • purity: 68% and below• appearance: transparent liquid• grade standard:   industrial grade,  reagent grade • application: mining, metallurgy, water treatment, fertilizer production. Reagent grade nitric acid specifications: item industrial grade regent grade gr ar cp hno3 % 58 68 65-68 65-68 65-68 hno2 % 0.2 0.2 -- -- -- chroma -- -- ≤20 ≤20 ≤25 residue on ignition(so4) 0.02 0.02 ≤0.0005 ≤0.001 ≤0.002 oxide(cl)% -- -- ≤0.00005 ≤0.00005 ≤0.0002 sulfate(so4)% -- -- ≤0.0001 ≤0.0002 ≤0.001 fe % -- -- ≤0.00002 ≤0.00003 ≤0.0001 as % -- -- ≤0.