The effect and implication of impurities on the calcination of α spodumene for lithium extraction

IF 4.8 2区 材料科学 Q1 METALLURGY & METALLURGICAL ENGINEERING
Mark G. Aylmore, Martin A. Wells, Zakaria Quadir, William D.A. Rickard, Kai Rankenburg, Brent I.A. McInnes
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Abstract

A suite of spodumene samples from albite-spodumene type pegmatites, mined for their lithium content, in the Archaean North Pilbara and Yilgarn Cratons regions of Western Australia, were examined to assess the influence of trace element impurities in spodumene and associated gangue phases on the thermal transformation of spodumene. Calcination of spodumene is required to convert the natural, monoclinic α-spodumene form into the tetragonal β-spodumene form, which is more amenable to recovering lithium during hydrometallurgy processing.
Spodumene contains minor concentrations of Fe (500–10,000 mg/kg), Mn (200–1400 mg/kg) and other trace element impurities incorporated within the crystal structure. Primary gangue mineralogy comprises quartz, Na/K-feldspar and mica, with secondary alteration predominantly as ‘sericitic’ phyllosilicates (muscovite-lepidolite, chlorite/cookeite mixtures) variably enriched in Fe, Mn, Mg and K relative to spodumene.
Primary and secondary mica undergo thermal dehydroxylation at temperatures (<950 °C) below the spodumene transformation temperature (970–1100 °C). Decomposed micas form melts that coat the surface and partially encapsulate the calcined spodumene grain surfaces. Feldspar decomposition at 1060 to 1200 °C, coincides with spodumene transformation, and can also result in melt formation, depending upon the composition of the feldspars (K-feldspar, albite). The thermal degradation of other mineral contaminants, such as biotite, pyroxene and amphibole from the presence of country rock (mafic, ultramafic) in the concentrate also coincides with the α- to β-spodumene phase transformation. The generated melts that coat grains can reduce the rate of α-β spodumene conversion and the subsequent ability to extract lithium from calcined spodumene.
Primary Fe and Mn impurities in spodumene, and those hosted by mica impurities within spodumene have a marked effect in decreasing the temperature of the α-γ-β spodumene conversion. Spodumene is not a strong conductor of heat, and the highly exothermic reaction of Fe and Mn oxidation within both mica and spodumene during thermal alteration affects thermal conductivity, leading to increased heat transfer within spodumene particles, which promotes the thermal transformation of spodumene at a lower temperature.
However, calcined spodumene particles with high Fe and Mn contents (> ∼ 0.5 wt%) showed black, open sintered regions, accompanied by the generation of fine (<5 μm) particles, and exsolution of Fe/Mn-oxides particles. The sintering and the generation of fines in the calciner will lead to reduced lithium recovery from calcined products.
This study illustrates the importance of minimising micaceous and feldspar components in the concentrate during the beneficiation stage, which can potentially lead to a decrease in lithium recovery during the extraction process. However, the fine-integrated nature of micas associated with spodumene alteration and those associated with fine fractures within spodumene are unlikely to be liberated without costly fine grinding and cleaning processes before the calcination process.
Alternative calcination processes that target reducing the effect of gangue materials on clinker formation and encapsulation of spodumene particles are available and discussed.
杂质对α锂辉石煅烧提锂的影响及意义
研究了西澳大利亚太古宙北皮尔巴拉和伊尔加恩克拉通地区钠长石-锂辉石型伟晶岩的一套锂辉石样品,以评估锂辉石及其伴生脉石相中微量元素杂质对锂辉石热转化的影响。将天然的单斜α-锂辉石形式转化为方形的β-锂辉石形式,需要对锂辉石进行煅烧,使其更适合湿法冶金过程中锂的回收。锂辉石含有微量的铁(500-10,000 mg/kg),锰(200-1400 mg/kg)和其他微量元素杂质。原生脉石矿物学包括石英、钠钾长石和云母,次生蚀变主要为绢云母层状硅酸盐(白云母-锂云母、绿泥石/库克石混合物),相对于锂辉石,Fe、Mn、Mg和K含量不同。原生云母和次生云母在低于锂辉石转化温度(970-1100℃)的温度(<950℃)下进行热去羟基化。分解云母形成的熔体覆盖在表面并部分包裹了煅烧的锂辉石颗粒表面。长石在1060 ~ 1200℃分解,与锂辉石的转变相一致,也可能导致熔体的形成,这取决于长石的成分(钾长石、钠长石)。其他矿物污染物如黑云母、辉石、角闪石等的热降解也与α-向β-锂辉石相变相吻合。生成的包裹晶粒的熔体降低了α-β锂辉石的转化速率和随后从煅烧锂辉石中提取锂的能力。锂辉石中的原生Fe和Mn杂质以及锂辉石内部的云母杂质对降低α-γ-β锂辉石转化温度有显著作用。锂辉石不是强导热体,热蚀变过程中云母和锂辉石内部Fe和Mn氧化的高度放热反应影响了锂辉石的导热性,导致锂辉石颗粒内部的热传递增加,促进了锂辉石在较低温度下的热转化。然而,高铁和高锰含量(> ~ 0.5 wt%)的锂辉石颗粒煅烧后呈现黑色、开放的烧结区,并伴有细小(<5 μm)颗粒的生成和Fe/Mn氧化物颗粒的析出。煅烧炉中的烧结和细粒的生成将导致煅烧产物中锂的回收率降低。该研究说明了在选矿阶段尽量减少精矿中云母和长石成分的重要性,这可能会导致提取过程中锂回收率的降低。然而,与锂辉石蚀变相关的云母的精细整合性质以及与锂辉石内部细裂缝相关的云母性质,如果在煅烧过程之前没有昂贵的精细研磨和清洗过程,则不太可能被释放出来。针对降低脉石物料对熟料形成和锂辉石颗粒包封影响的替代焙烧工艺是可行的,并进行了讨论。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Hydrometallurgy
Hydrometallurgy 工程技术-冶金工程
CiteScore
9.50
自引率
6.40%
发文量
144
审稿时长
3.4 months
期刊介绍: Hydrometallurgy aims to compile studies on novel processes, process design, chemistry, modelling, control, economics and interfaces between unit operations, and to provide a forum for discussions on case histories and operational difficulties. Topics covered include: leaching of metal values by chemical reagents or bacterial action at ambient or elevated pressures and temperatures; separation of solids from leach liquors; removal of impurities and recovery of metal values by precipitation, ion exchange, solvent extraction, gaseous reduction, cementation, electro-winning and electro-refining; pre-treatment of ores by roasting or chemical treatments such as halogenation or reduction; recycling of reagents and treatment of effluents.
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