Aluminium extraction and leaching characteristics of Talcher Thermal Power Station fly ash with sulphuric acid

Towards the Utilization of Fly Ash as a Feedstock for Smelter Grade Alumina Production: A Review of the Developments

“…This observation is aligned to the findings of Petruševski et al [24], who found that aluminum does not readily react with either dilute or concentrated nitric acid unless the acid contains Cl -ions and Cu 2? ion to catalyze the reaction. In another study involving the use of H 2 SO 4 , Nayak and Panda [23] showed that extraction efficiency could increase from 2.7 to 41.3 % by increasing the concentration of H 2 SO 4 from 1.5 to 18 M. The temperature range used was 150-200°C while the liquid: solid (acid: ash) ratio was fixed at 1 over a leaching time of 4 h. However, extraction efficiency as high as 84.2 % was achieved when the liquid:solid ratio was increased to 2 and when other variables were held constant. The researchers attributed the lowextraction efficiency at low liquid:solid ratio to the formation of an acid-insoluble calcium sulfate layer which inhibited further dissolution of the metal by impeding mass transfer.…”

“…Several methods of extracting aluminum from CFA by direct acid leaching have been documented [10,[21][22][23]. A range of acids have been investigated as potential lixiviants, these include nitric acid, hydrochloric acid, and sulfuric acid.…”

“…A range of acids have been investigated as potential lixiviants, these include nitric acid, hydrochloric acid, and sulfuric acid. The use of acid as lixiviants has been found to be attractive because silica, the major gangue mineral in CFA, is considered insoluble in acidic medium [23]. In the literature, researchers used varying concentrations of acids under diverse conditions to leach CFA achieving a wide range of extraction efficiencies.…”

“…Figure 1 shows a summary of the conceptual flow sheet for the direct acid leaching of coal fly using various acids with the subsequent recovery of alumina from solution using the crystallization technique. What came out clearly from the work of these researchers was that the leaching of aluminum compounds from CFA at low concentration and ambient or even elevated temperature gives low-extraction efficiencies [10,21,23]. For instance, in the work of Hill and Raistrick [10] that used HNO 3 with a concentration of 30 % (wt) to leach aluminum in a 3-step process, despite raising the operational temperature to 220°C, only 27 % extraction of the contained aluminum was achieved.…”

Recovery of Alumina from Coal Fly Ash by CaCl2 Calcination Followed by H2SO4 Leaching

“…The effects of reaction time, H 2 SO 4 concentration and liquid/ash weakened according to the order. The alumina extraction efficiency remains less than 5% without calcinated addition, which is confirmed by Nayak [20]. Therefore, it can be seen that in CFA, mullite, quartz and glass phase can't be destroyed by sulfuric acid without calcinating with additive.…”