Hydrometallurgical unit operations are typically used to recover palladium (Pd) from its ores and secondary resources with high selectivity owing to their low energy consumption, cost effectiveness, and volume flexibility. Herein, diluted HNO solutions with added nitrate salts were used to dissolve Pd powders. Moreover, solutions of nitrates with same valency cations (such as HNO, LiNO, NaNO, KNO, CsNO, and NHNO) and same period cations (such as NaNO, Mg(NO), and Al(NO)) were used to reveal the involved beneficial effects of the nitrates on the Pd dissolution in an environment friendly way with low acidity of the solutions. Among all added alkali metal nitrates, LiNO resulted in the highest Pd dissolution efficiency, which was attributed to the higher dissociation constant of LiNO, resulting in a higher concentration of free nitrate and hence a higher oxidation potential of the overall system. The dissolution process was systematically investigated to determine the optimal temperature (353 K), LiNO and HNO concentrations (6 and 1 mol L, respectively), stirring speed (500 rpm), and reaction time (5 h). These optimal conditions yielded a dissolution efficiency of 99.6%. Notably, as the reaction proceeded, the Pd powder surfaces corroded to form numerous holes, indicating that internal diffusion control also affected Pd dissolution.

中文翻译：

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碱金属硝酸盐对硝酸溶液中钯溶解的影响

湿法冶金单元操作通常用于从矿石和二次资源中高选择性地回收钯 (Pd)，因为其能耗低、成本效益高且产量灵活。在此，使用添加硝酸盐的稀释 HNO 溶液来溶解 Pd 粉末。此外，使用同价阳离子（如 HNO、LiNO、NaNO、KNO、CsNO 和 NHNO）和同周期阳离子（如 NaNO、Mg(NO) 和 Al(NO)）的硝酸盐溶液来揭示涉及硝酸盐对钯溶解的有益影响，以环境友好的方式和溶液的低酸度。在所有添加的碱金属硝酸盐中，LiNO 的 Pd 溶解效率最高，这是由于 LiNO 的解离常数较高，导致游离硝酸盐浓度较高，从而整个系统的氧化电位较高。对溶解过程进行了系统研究，以确定最佳温度 (353 K)、LiNO 和 HNO 浓度（分别为 6 mol L 和 1 mol L）、搅拌速度（500 rpm）和反应时间（5 h）。这些最佳条件产生了 99.6% 的溶解效率。值得注意的是，随着反应的进行，钯粉末表面腐蚀形成许多孔，表明内部扩散控制也影响了钯的溶解。