The hydrometallurgical process for the recovery of nickel and cobalt requires a complex and expensive impurity removal process. Solvent extraction is widely used in industry for the separation, purification, and concentration of metals. However, current commercial extractants encounter some difficulties when cobalt and nickel are extracted from solutions containing a large amount of impurities such as manganese and calcium. There is an urgent need to develop new reagents for the selective extraction of Ni and Co. In this study, N-(2-ethylhexyl)-pyridine-4-carboxamide (NEHPCA) was synthesized, and the metal extraction capacity of its synergistic solvent extraction (SSX) system with dinonylnaphthalene sulfonic acid (DNNSA) and tributyl phosphate (TBP) modifier was examined. The experimental results show that the selectivity of the new SSX system has the order Cu > Ni > Co > Zn > Mn > Ca > Al ≈ Cr (III) ≈ Mg ≈ Fe (III), with excellent selectivity for nickel and cobalt. Using an organic phase composed of 0.7 M NEHPCA, 0.35 M DNNSA, and 0.2 M TBP under 1:1O/A operation, after three-stage theoretical extraction, more than 99% of nickel and cobalt can be recovered from a synthetic leaching solution of nickel laterite ore. Mechanistic studies showed that NEHPCA and water molecules participate in the internal coordination of metals, and DNNSA provided coordination anions to achieve charge balance, forming the Ni complex in this SSX system which existed most likely in the form of [Ni(NEHPCA)₂(H₂O)₄](DNNS)₂ in the organic phase.

用于回收镍和钴的湿法冶金工艺需要复杂且昂贵的杂质去除工艺。溶剂萃取在工业中广泛用于金属的分离、提纯和浓缩。然而，当从含有大量杂质如锰和钙的溶液中提取钴和镍时，目前的商业萃取剂会遇到一些困难。迫切需要开发用于选择性萃取镍和钴的新试剂。本研究合成了 N-(2-乙基己基)-吡啶-4-甲酰胺 (NEHPCA)，并对其协同溶剂的金属萃取能力进行了研究。考察了具有二壬基萘磺酸 (DNNSA) 和磷酸三丁酯 (TBP) 改性剂的萃取 (SSX) 系统。实验结果表明，新型SSX体系的选择性顺序为Cu > Ni > Co > Zn > Mn > Ca > Al ≈ Cr (III) ≈ Mg ≈ Fe (III)，对镍和钴具有优异的选择性。使用由 0.7 M NEHPCA、0.35 M DNNSA 和 0.2 M TBP 组成的有机相，在 1:1O/A 操作下，经过三阶段理论萃取，可从镍红土矿石。机理研究表明，NEHPCA与水分子参与金属的内部配位，DNNSA提供配位阴离子以实现电荷平衡，在该SSX体系中形成Ni络合物，最有可能以[Ni(NEHPCA)形式存在。对镍和钴具有出色的选择性。使用由 0.7 M NEHPCA、0.35 M DNNSA 和 0.2 M TBP 组成的有机相，在 1:1O/A 操作下，经过三阶段理论萃取，可从镍红土矿石。机理研究表明，NEHPCA与水分子参与金属的内部配位，DNNSA提供配位阴离子以实现电荷平衡，在该SSX体系中形成Ni络合物，最有可能以[Ni(NEHPCA)形式存在。对镍和钴具有出色的选择性。使用由 0.7 M NEHPCA、0.35 M DNNSA 和 0.2 M TBP 组成的有机相，在 1:1O/A 操作下，经过三阶段理论萃取，可从镍红土矿石。机理研究表明，NEHPCA与水分子参与金属的内部配位，DNNSA提供配位阴离子以实现电荷平衡，在该SSX体系中形成Ni络合物，最有可能以[Ni(NEHPCA)形式存在。₂ (H ₂ O) ₄ ](DNNS) ₂在有机相中。