Rhodium, is a silvery white hard metal with high reflectivity. Rhodium metal typically does not form oxides, and even when heated, oxygen in the atmosphere is only absorbed at the point of heating to the melting point of rhodium, but is released during solidification. Rhodium has a higher melting point than platinum and a lower density than platinum. Rhodium is insoluble in most acids. It is completely insoluble in nitric acid and slightly soluble in aqua regia. The element symbol Rh, derived from rhodon, meaning "rose", was discovered and separated by vlaston in 1803 because the solution of rhodium salt presented the reddish color of the rose. Rhodium belongs to platinum elements.
Electroplated layer of rhodium is mainly extracted from natural rhodium and is a rare precious metal. The color is silver white, metallic luster, opaque. Hard 4~4.5, relative density 12.5. High melting point is 1955 ℃. Chemical stability. As rhodium gold is corrosion-resistant and has a good gloss, it is mainly used in the electroplating industry, where it is applied on other metal surfaces. The coating is firm in color, not easy to be worn and reflective. Valence 2, 4 and 6. First ionization energy is 7.46 electron volts. It also resists most common acids (including aqua regia) at moderate temperatures. In 200-600 ℃ with concentrated sulfuric acid, hot hydrobromic acid, sodium hypochlorite and halogen free up chemical reactions. Does not react with many molten metals, such as gold, silver, sodium and potassium, and molten alkali.
The deposits are of various types, but most of the reserves are concentrated in symbiotic or associated ore deposits. The types of platinum group metal deposits in China include magmatic remelting, hydrothermal remoulding and placer platinum, and some are contained in black rock series, hydrothermal or skarn type polymetallic deposits and porphyry copper molybdenum deposits. According to the reference industrial index of platinum group metals determined by the national committee on mineral reserves (1985), the boundary grade of primary ore is 0.3-0.5g /t, and the industrial grade is 0.5g/t. Platinum-group metal deposits in China can be divided into three types: single ore, cogenetic ore and associated ore. According to the statistics in 1996, 93.4% of platinum-group metals (proven reserves) are symbiotically or associated with copper-nickel sulfide, polymetal.
