Novel and green metallurgical technique of comprehensive utilization of refractory limonite ores

Abstract

Limonite ores are a common and widely distributed refractory iron oxide ores in the world. In this paper, in view of the growing development of steel and iron industry, the depletion of easy-processing iron ores and growing environmental concerns, a novel and green technique route was proposed to comprehensive utilize limonite ores by asynchronously recovering various valuable elements. The technique route included three stages: recovery (enrichment) of Fe and Mn by removal of impurities (Al and Si phases) via microwave-assisted roasting-acid leaching process using alkali lignin and Na2CO3-Na2SO4 binary sodium salts as roasting additives, where Na2SO4 was favorable for the aggregation and growth of iron-rich grains, Na2CO3 could enhance the activation of Al and Si phases and then improve the acid leaching of Al and Si, and alkali lignin has a favorable effect on the leaching; recovery of Si by ripening the acid leached liquor, where Si was enriched and extracted in the form of silica gel through the polymerization of silicic acid; and stepwise recovery of small amount of leached Fe and Mn as well as Al by neutralizing and precipitating of filtrate from the 2nd stage using NaOH solution and NaHCO3 solution as precipitating reagents, respectively. The final Na2SO4 and Na2CO3 filter liquor could be recycling used in the roasting process by evaporation pretreatment, achieving zero pollution and zero waste. By performing acid leaching process on the roasted ore treated at 200 °C, 600 W for 30 min in the presence of 5% alkali lignin, 5% Na2CO3 and 5% Na2SO4, an iron concentrate assaying 57.08% Fe with the corresponding iron recovery ratio of 92.04% and yield of 64.66% was obtained from the refractory limonite ore containing 40.10% Fe, 8.69% Mn, 9.40% Al, and 6.92% Si. Besides, Mn was simultaneous enriched in the iron concentrate with a Mn recovery ratio of 71.73% and a Mn grade of 9.64%. Simultaneously, 84.11% of Si and 80.26% of Al existed in the limonite ore were extracted, and leaching ratios of Fe and Mn were only 7.96% and 28.27%, respectively. Subsequently, silica gel containing 93.31% SiO2 and Al(OH)3 precipitate containing 41.59% Al2O3 and Mn-Fe precipitate with 33.08% Fe and 14.83% Mn were successfully stepwise obtained by the last two stages. The proposed technique with the advantages of mild reaction conditions and discharge reducing, meeting the demands of green metallurgy, would potentially be a feasible route for the utilization of limonite ores, easing the shortages of iron and promoting the sustainable development of steel and iron industry.