At present, the cobalt-nickel metallurgical raw materials have been gradually transformed from the previous cobalt-sulfide nickel ore to cobalt-nickel miscellaneous materials, cobalt-nickel oxide ores (containing cobalt, nickel laterite), etc., the treatment process is by traditional fire-making matte, wet separation Combined with the process of leaching and purifying full wet process. Cobalt and nickel raw materials come from different sources, the composition of the leaching solution is complex, and precipitation and ion exchange processes are difficult to achieve the separation of drill, nickel and cobalt nickel from other impurity ions such as calcium and magnesium. The solvent extraction method has the advantages of good selectivity, high metal recovery rate, and fast mass transfer speed. Especially, the new extraction agent and extraction system developed based on the difference in ion properties and extraction theory have optimized the extraction effect. Therefore, it is fundamental to find out the differences in the properties of cobalt and nickel, and to analyze the principles of the existing cobalt and nickel separation process, which is of guiding significance for the development of new extractants and extraction processes.
1. The difference between cobalt and nickel
Cobalt-nickel atomic numbers are adjacent to each other, and are the same as Group VIII elements of the fourth cycle. Only the number of d electrons in the outer layer is different. This difference in properties can be used for extraction separation.
2. Extraction and separation of cobalt and nickel
Solvent extraction is one of the important methods for the separation of cobalt and nickel. It has good separation effect, high metal yield, strong adaptability to feed liquid, and easy process automatic control. With the development of new extractants and extraction systems and the gradual improvement of extraction theory, the solvent extraction method has become more and more widely used in cobalt-nickel hydrometallurgy.
From the crystal field coordination theory, it is known that Ni (Ⅱ) in solution is stable when it is 6 coordination, while Co (Ⅱ) is 4 or 6 coordination, the stability is close, it can exist at the same time, and it can be converted under certain conditions. . At present, this principle is widely used to separate cobalt and nickel by phosphorus extractants.
At present, the phosphorus (phosphine) extractants used in the separation of cobalt and nickel are mainly P204, P507 and DZ272, which have large differences in the extraction of cobalt and nickel. According to reports, when extracting cobalt and nickel with P204, P507, and DZ272, the half-extraction pH differences were 0.53, 1.43, and 1.93, respectively. Obviously, the ability to extract and separate cobalt and nickel is gradually increasing. This difference is due to the extraction capacity and spatial structure of the three extractants.
From P204, P507 to DZ272, the acidity gradually weakened, and the steric hindrance gradually increased. The extraction compound of nickel must always maintain the octahedral configuration, and the difficulty of forming the 6-coordinate between the extractant and nickel increases, so the distribution ratio of nickel decreases. However, the cobalt extract can be transformed into a tetrahedral configuration, which compensates for the decrease in the distribution ratio due to the weakened acidity of the extractant and the increased steric hindrance. The distribution ratio of nickel is reduced, while the distribution ratio of cobalt is basically unchanged, and the separation effect of cobalt and nickel is getting better and better. Therefore, the extraction agent with weaker extraction binding strength and larger steric hindrance can achieve better separation of cobalt and nickel.
With the gradual depletion of high-quality cobalt-nickel sulfide ore resources, the development and utilization of cobalt-nickel oxidized ores have attracted more and more attention. It can directly extract the cobalt and nickel (DSX) from the higher acidity system, and it has an extraction effect on calcium and magnesium. The main research directions are:
1) Development of new extraction agents, especially chelating extraction agents, which may be the first choice of extraction of cobalt and nickel directly from calcium and magnesium-containing solutions in the future;
2) Development of new extraction systems, with the Extraction theory, especially the development of co-extraction theory, study the synergistic effect of extractant, so as to achieve better separation effect;
3) Development of new extraction equipment, some of the cobalt and nickel extraction process has good thermodynamic values, but dynamics The rate is slow and new extraction equipment is needed to enhance the extraction process.