Secondary aluminum dross (SAD) has been identified as a hazardous waste because it contains refractory AlN, fluoride, and other salts. Considering that Al(OH) produced during the hydrolysis of AlN in SAD hinders spontaneous AlN hydrolysis, which is amplified by the partial embedment of AlN in other oxide phases present in SAD particles, the complete removal of AlN from SAD is difficult. Herein, we propose a new catalytic hydrolytic denitrification process of SAD, which requires a low additive dose. By changing the time at which the additive (NaOH) was added to the SAD slurry, the proportion of nitrogen removed from SAD was increased. The additive (NaOH) reacted with Al(OH), thereby mitigating its hindering effect on spontaneous AlN hydrolysis and facilitating the complete hydrolysis of the semi-encapsulated AlN in SAD particles. Concurrently, the reaction between NaOH and AlO and SiO phases present in SAD was mitigated, resulting in the maximal retention of residual materials (phases other than Al resources) in the solid phase. A SAD denitrification efficiency of 99.0% was achieved under optimal processing conditions ( = 95 °C, = 240 min, Liquid-to-solid ratio = 6:1, stirring speed = 400 rpm, and the addition of 7 wt% NaOH at 0.5 h), and a slightly lower efficiency of 98.2% was achieved when 50% lower amount of NaOH (3 wt%) was used. Thus, approximately 50% less additive is required for nitrogen removal from SAD, relative to that used in traditional catalytic water-washing processes.

中文翻译：

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延迟添加低剂量氢氧化钠水浸过程中二次铝渣（SAD）的反硝化机理

二次铝浮渣 (SAD) 已被确定为危险废物，因为它含有难熔氮化铝、氟化物和其他盐类。考虑到SAD中AlN水解过程中产生的Al(OH)3阻碍了自发的AlN水解，而AlN在SAD颗粒中存在的其他氧化物相中的部分嵌入会放大这种自发水解，因此从SAD中完全去除AlN是困难的。在此，我们提出了一种新的SAD催化水解脱氮工艺，该工艺需要较低的添加剂剂量。通过改变将添加剂(NaOH)添加到SAD浆料中的时间，从SAD中去除的氮的比例增加。添加剂（NaOH）与Al（OH）反应，从而减轻其对AlN自发水解的阻碍作用，促进SAD颗粒中半包封AlN的完全水解。同时，NaOH 与 SAD 中存在的 Al2O3 和 SiO2 相之间的反应得到缓解，从而最大限度地保留固相中的残留材料（Al 资源以外的相）。在最佳工艺条件下（= 95 °C，= 240 min，液固比= 6:1，搅拌速度= 400 rpm，添加7 wt% NaOH，浓度为0.5），SAD反硝化效率达到99.0%。 h)，当 NaOH 用量减少 50% (3 wt%) 时，效率略低，为 98.2%。因此，与传统催化水洗工艺中使用的添加剂相比，从 SAD 中脱氮所需的添加剂大约减少 50%。