Bauxite residue (BR) is a by-product of bauxite refining using Bayer process for alumina production, which contains numerous valuable components: iron (Fe), aluminum (Al), and rare earth elements such as scandium (Sc). The main issue of previous research for the Sc extraction from BR was the low extraction efficiency or high Fe co-extraction. This article shows that Fe co-extraction can be significantly reduced after reductive leaching of BR in the presence of Fe(II). This effect was achieved due to the formation of magnetite (FeO) after reductive leaching of bauxite. Magnetite is practically insoluble in HSO at pH > 2. The effect of temperature (T), time (t) and liquid to solid ratio (L:S ratio) on the leaching process was revealed. The results show that under optimum conditions (pH = 2, = 90 °C, = 2 h, L:S ratio = 10:1), Sc extraction can reach 57%, with a simultaneous co-extraction of Fe <1.3%. At the same parameters about 10% of Fe is extracted from the raw BR. The Fe content in the residue after leaching increased from 58.3 to 66.2 wt%, corresponding to the iron concentrate. Thus, the Sc extraction from a modified BR by dilute HSO creates the conditions for the complete valorization of this technogenic waste, and improved extraction selectivity.

中文翻译：

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铝土矿残渣的还原浸出以及随后的硫酸浸出提取钪 – 初步评估

铝土矿残渣 (BR) 是采用拜耳法生产氧化铝的铝土矿精炼的副产品，其中含有许多有价值的成分：铁 (Fe)、铝 (Al) 和钪 (Sc) 等稀土元素。以往研究从BR中提取Sc的主要问题是提取效率低或Fe共提取率高。本文表明，在存在 Fe(II) 的情况下，对 BR 进行还原浸出后，可以显着减少 Fe 的共萃取。这种效果是由于铝土矿还原浸出后形成磁铁矿（FeO）而实现的。当 pH > 2 时，磁铁矿几乎不溶于 HSO。揭示了温度 (T)、时间 (t) 和液固比（L:S 比）对浸出过程的影响。结果表明，在最佳条件下（pH=2、=90℃、=2h、L:S比=10:1），Sc萃取率可达57%，同时共萃取Fe<1.3%。在相同的参数下，从原始 BR 中提取出约 10% 的 Fe。浸出后残渣中的铁含量从 58.3 wt% 增加到 66.2 wt%，与铁精矿相对应。因此，通过稀 HSO 从改性 BR 中提取 Sc 为这种技术废物的完全增值创造了条件，并提高了提取选择性。