Abstract
Germanium recovery from coal fly ash by hydrometallurgical procedures was studied at the pilot scale (5 kg of fly ash/h). Results were used to design the equipment of a demonstration-sized plant (200 kg of fly ash/h). The process is based on hydrometallurgical operations: firstly a germanium extraction from fly ash by leaching and a consequent Ge separation from the other elements present in the solution by solvent extraction procedures. Based on the experimental results, mass balances and McCabe-Thiele diagrams were applied to determine the number of steps of the solvent extraction stage. Different arrangements have been studied and a countercurrent process with three steps in extraction and six steps in elution was defined. A residence time of 5 min was fixed in both the extraction and elution stages. Volumetric ratios in extraction and stripping were: aqueous phase/organic phase = 5 and organic phase/stripping phase = 5, so a concentration factor of 25 is achieved. Mixers and decanters were completely defined. The maximum extracted and eluted germanium was estimated and a global efficiency of 94% was achieved. The cost-effectiveness of the equipment was estimated using the Lang factors.
Highlights
Germanium is not very abundant in the Earth’s crust, occurring only at a concentration of 1 to 7 ppm [1]
The most important application of germanium is in the manufacturing of semiconductors, but innovative uses for germanium in new and high technological industrial applications have led to an increase in its price, so it is currently more attractive to process raw materials with low contents of germanium and considerable quantities of other elements
Due to the uses for germanium in new and high technological industrial applications, germanium metal and oxide have increased in price (1800 $/kg of germanium metal in September 2013) [2], and alternative sources such as combustion [3] and gasification [4] coal fly ashes
Summary
Germanium is not very abundant in the Earth’s crust, occurring only at a concentration of 1 to 7 ppm [1]. Due to the uses for germanium in new and high technological industrial applications, germanium metal and oxide have increased in price (1800 $/kg of germanium metal in September 2013) [2], and alternative sources such as combustion [3] and gasification [4] coal fly ashes. Germanium occurs in relatively high contents in the fly ash (FA) produced in the Puertollano (Spain). Germanium is completely volatilized during gasification and subsequently condenses during gas cooling to form sulphides and oxide species [8]. The solvent extraction (SX) method for the recovery of germanium from fly ash is based on the germanium-1, 2-dihydroxybenzene (catechol, CAT) (C6O2H6) chelate and the subsequent extraction of the complex using tri-n-octylamine (TOA) ((C8H17)3N) and stripping with alkaline solutions. This paper shows the design of a demonstration plant from experiments carried out at the pilot scale regarding leaching and SX process
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