Abstract

Due to the significant magnesium content, ferronickel slag is potentially a secondary magnesium resource and a subject for CO₂ fixation. The current techniques require high energy consumption and involve physical and chemical processes. The biohydrometallurgical method can be applied to extract magnesium from ferronickel slag to minimize the energy required. However, the information about bioleaching magnesium from slag is still limited. Also, it is essential to investigate the selectivity of magnesium over iron dissolution because iron is also one of the major elements in the slag. In this study, ferronickel slag was subjected to bioleaching experiments using sulfur-oxidizing mixotrophic bacterium (Citrobacter freundii) at ambient conditions, which was capable of producing organic acid and secreting extracellular polymeric substances and utilizing iron and sulfur as energy sources. The effect of pulp density (75–150 g/L), particle size fraction (less than 74 μm to 105–149 μm), and elemental sulfur addition (0–15 g/L) on magnesium recovery was investigated. The experimental results showed that the bacterium could improve the dissolution of magnesium-bearing minerals in the slag. Increasing pulp density, particle size fraction, and elemental sulfur concentration were detrimental to the selectivity of magnesium over iron. The highest selectivity of 0.90 was reached in the biotic system using a size fraction < 74 μm and a pulp density of 100 g/L in 24 h. The result showed that magnesium dissolution was affected by bacteria, whereas iron dissolution was related to the pH trends during bioleaching. The iron concentration remained lower than 1 g/L under all experimental conditions, suggesting that the dissolution of iron could be restricted during bioleaching experiments. In addition, pH adjustment before bioleaching was not necessary, and the pH value during leaching was above 4.5, which could decrease the cost and ease the tailing treatment.

Graphical Abstract

中文翻译：

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室温下硫氧化混合营养菌对镍铁渣中镁的选择性溶解

摘要

由于镁含量高，镍铁渣是潜在的次生镁资源和固定 CO ₂的对象。目前的技术需要高能耗并且涉及物理和化学过程。生物湿法冶金法可用于从镍铁渣中提取镁，以最大限度地减少所需的能量。然而，关于从渣中生物浸出镁的信息仍然有限。此外，有必要研究镁对铁溶解的选择性，因为铁也是渣中的主要元素之一。本研究采用硫氧化混合营养菌 ( Citrobacter freundii ) 对镍铁渣进行生物浸出实验。) 在环境条件下，它能够产生有机酸和分泌细胞外聚合物，并利用铁和硫作为能源。研究了纸浆密度（75–150 g/L）、粒度分数（小于 74 μm 至 105–149 μm）和元素硫添加量（0–15 g/L）对镁回收率的影响。实验结果表明，该菌能改善渣中含镁矿物的溶解。增加纸浆密度、粒度分数和元素硫浓度不利于镁对铁的选择性。在生物系统中使用 < 74 μm 的尺寸分数和 24 小时内 100 g/L 的纸浆密度达到了 0.90 的最高选择性。结果表明镁的溶解受细菌的影响，而铁溶解与生物浸出过程中的 pH 趋势有关。在所有实验条件下，铁浓度均低于 1 g/L，表明在生物浸出实验期间铁的溶解可能受到限制。此外，生物浸出前无需调节pH，浸出过程中pH值在4.5以上，可降低成本，便于尾矿处理。

图形概要