Extraction of Rubidium from Gold Waste by Optimization of Sulfation Roasting-Water Leaching Process

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Specific physical and chemical properties of rubidium have attracted the attention of researchers for extraction of rubidium from its resources, which as a rare alkali metal in recent years the expansion of its commercial uses has been experienced. The main research conducted in this field has been related to recovery of this element as a byproduct of mining process of lithium minerals. In this study, we have discussed the extraction of rubidium from tailings dam of Mouteh gold processing plant in Iran by modeling the hydrometallurgical procedure used for lithium processing. For this purpose, first the pickling process of sample was done using 5M nitric acid in 85°C for 5 hours to remove most of the impurities. Then, the roasting process was optimized using central composite experiment design in two steps. 81.11% recovery rate of rubidium per 1/0.29/0.51 mass ratio of sample/sodium sulfate/calcium chloride was increased to 90.95% recovery rate per 1/0.11/0.45 mass ratio of sample/sodium sulfate/calcium chloride at the same temperature. Finally, 97.14% recovery rate of rubidium was achieved by optimization of water leaching process of roasted sample in 1.69 solid to liquid ratio, 58.51°C temperature within 31.36 minutes.
Rubidium is a rare alkali metal in the first group in periodic table, which was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff using flame spectrometry. Chemical reactions of this element resemble those of the alkali metals of potassium and cesium, and acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide, nitrate and sulfate salts of this element can be easily solved in water. The most striking physical properties of this silvery white element include softness, malleability and low melting point (39°C), and it is also the fourth light metallic element [1].
The application of rubidium in ionic engines (like spacecraft engines) as fuel, in photocell and photoelectric appliances due to photonic effect, its use to produce methanol and other alcohols, styrene and butadiene as catalyst, use of various rubidium compounds in electrical appliances due to semiconducting and piezoelectric properties, in analytical chemistry for identification of manganese, zirconium and noble metals, in incandescent and cathode ray lamps because of transparency of infrared radiation as well as many other applications indicate the unique properties of this valuable element [1,2].
The annual production of rubidium in the world amounts to several tens of kilograms. Because of the variety of applications, supply and demand of rubidium has been constantly growing since 1990, and its price has increased in the international market.
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