Phann Idol, Tanaka Yu, Yamamoto Sae, Okibe Naoko
Department of Earth Resources Engineering, Kyushu University, Fukuoka, Japan.
Front Chem. 2022 Oct 10;10:1011518. doi: 10.3389/fchem.2022.1011518. eCollection 2022.
While spent catalysts can cause serious environmental pollution, they can be considered an essential secondary metal source due to their high critical metal grades. The formation of the amino acid-metal complex is often seen in nature, and its potential application in hydrometallurgy can be foreseen. Alanine (Ala) was first screened as the most effective type of amino acid to be used for the selective leaching of spent hydrodesulfurization catalyst (consisting of MoS and CoS supported on AlO, at 10% Mo and 2.4% Co grades). The sequential 3-step leaching (Step-1: Alkaline Ala leaching at 45°C, Step-2: Hot water leaching at 70°C, Step-3: Second alkaline Ala leaching at 45°C) was conducted where the role of Ala was found to be at least three-fold; 1) maintaining alkalinity by amino acid's buffering capacity to assist Mo leaching, 2) selectively precipitating Co by forming Co-Ala complex with a distinctive pink color, which can readily re-dissolve in hot water to be separated from spent catalyst particles. 3) Effectively suppressing unwanted dissolution of Al throughout the reaction without needing pH control. Consequently, highly metal-selective, two separate Co-rich (<1% Mo and 79% Co dissolved, Al not detected) and Mo-rich (96% Mo, 19% Co, and 2.1% Al dissolved) leachates were obtained. This study highlighted the potential utility of amino acids as non-toxic, alternative metal lixiviant as well as a metal precipitant for selective leaching of critical metals from spent hydrodesulfurization catalyst.
虽然废催化剂会造成严重的环境污染，但由于其高临界金属品位，可被视为一种重要的二次金属来源。氨基酸 - 金属络合物在自然界中经常出现，其在湿法冶金中的潜在应用也可预见。丙氨酸（Ala）首先被筛选为用于选择性浸出废加氢脱硫催化剂（由负载在AlO上的MoS和CoS组成，Mo品位为10%，Co品位为2.4%）的最有效氨基酸类型。进行了连续三步浸出（步骤1：在45°C下用碱性丙氨酸浸出，步骤2：在70°C下用热水浸出，步骤3：在45°C下进行第二次碱性丙氨酸浸出），发现丙氨酸的作用至少有三个方面；1）通过氨基酸的缓冲能力维持碱度以协助钼浸出，2）通过形成具有独特粉红色的Co - Ala络合物选择性沉淀钴，该络合物可在热水中轻易重新溶解以与废催化剂颗粒分离。3）在整个反应过程中无需控制pH即可有效抑制铝的不必要溶解。因此，获得了高度金属选择性的、两种单独的富含钴（<1%的钼和79%的钴溶解，未检测到铝）和富含钼（96%的钼、19%的钴和2.1%的铝溶解）的浸出液。这项研究突出了氨基酸作为无毒替代金属浸出剂以及从废加氢脱硫催化剂中选择性浸出关键金属的金属沉淀剂的潜在用途。
