How Do Mixer-Settlers Extract Nickel and Cobalt from Sulfuric Acid Leachate of Low-Grade Nickel-Cobalt Resources?

With the rapid development of the new energy industry, power battery and high-end metallurgical sectors, high-grade primary nickel and cobalt mineral resources are increasingly depleted. Low-grade nickel-cobalt associated ores, tailings, smelting slags and secondary recovery materials have gradually become important sources of nickel and cobalt supply. The sulfuric acid leachate obtained by acid leaching of such low-grade raw materials generally faces industry challenges, including low concentration of metal ions, complex impurity components, high separation difficulty, low recovery rate of traditional purification processes and high production costs. How to efficiently, low-cost and on a large scale separate and enrich nickel and cobalt from complex sulfuric acid leachate has become a core technical demand urgently needed to be solved in the field of hydrometallurgy. Thanks to its advantages such as continuous operation, stable separation effect, strong adaptability and controllable energy consumption, the mixer-settler has become a core key equipment for nickel and cobalt extraction from sulfuric acid leachate of low-grade nickel and cobalt, which can effectively separate nickel and cobalt from impurity metals, realize enrichment and purification, and lay a solid foundation for the subsequent preparation of high-purity nickel and cobalt products through electrolysis and crystallization.

I. Analysis of Material Characteristics of Sulfuric Acid Leachate of Low-Grade Nickel-Cobalt Resources

There are obvious differences in the composition structure and physical and chemical properties between the leachate formed by sulfuric acid leaching of low-grade nickel-cobalt resources and that of high-grade ores. First of all, the content of effective nickel and cobalt metal ions is relatively low, with a large overall concentration range. It is difficult to achieve efficient recovery by directly using traditional precipitation and replacement processes, resulting in serious resource waste. Secondly, the leachate is accompanied by a large number of impurity ions such as iron, aluminum, magnesium, calcium and manganese. These impurities have similar physical and chemical properties to nickel and cobalt, which are very easy to interfere with the metal separation process and affect the purity of the final product. At the same time, the sulfuric acid leachate system has high acidity and complex ion types, which puts higher requirements on the corrosion resistance of process equipment and the adaptability of the extraction system. The mixer-settler can flexibly adjust process parameters and stage configuration according to the actual material characteristics of the leachate, adapt to the separation and enrichment needs of complex low-grade systems, and meet the requirements of industrial continuous production scenarios.

II. Working Principle of Mixer-Settlers and Core Advantages for Nickel-Cobalt Extraction

The mixer-settler completes metal separation based on the principle of liquid-liquid two-phase contact mass transfer. It uses the selective complexation ability of special nickel-cobalt extractants with nickel and cobalt ions in the sulfuric acid leachate to transfer nickel and cobalt ions from the aqueous phase to the organic extraction phase, and then transfers nickel and cobalt back to the aqueous system through stripping process, so as to realize the enrichment of nickel and cobalt and the separation of impurities. In the treatment scenario of sulfuric acid leachate of low-grade nickel and cobalt, the mixer-settler has prominent application advantages. First, the equipment structure is reasonably designed, with clear separation of mixing and clarification zones, sufficient two-phase mixing and mass transfer, and fast clarification and separation speed, which is suitable for the accurate capture and enrichment of low-concentration metal ions. Second, it can realize multi-stage countercurrent continuous operation, greatly improve the nickel and cobalt recovery rate through stage matching, and effectively make up for the shortcoming of low metal content in low-grade raw materials. Third, the acid and corrosion resistant material of the equipment is suitable for the strong corrosion working condition of sulfuric acid leachate, with stable operation and simple maintenance, which is suitable for long-cycle industrial mass production. Fourth, the process adjustment is flexible, and it can adapt to the treatment needs of leachate with different impurity contents by adjusting parameters such as phase ratio, residence time and pH value.

III. Complete Process Flow of Nickel and Cobalt Extraction from Sulfuric Acid Leachate by Mixer-Settlers

1. Pretreatment and Conditioning of Leachate

Before the low-grade nickel-cobalt sulfuric acid leachate enters the mixer-settler, a pretreatment process is carried out first. Suspended solid particles in the leachate are removed by sedimentation and filtration to avoid solid impurities affecting the two-phase mass transfer effect; then the physical and chemical indicators such as pH value and temperature of the leachate are accurately adjusted to match the optimal extraction conditions of the special nickel-cobalt extractant, reduce the co-extraction of impurity ions, and create basic conditions for the stable operation of the mixer-settler.

2. Multi-Stage Extraction, Separation and Enrichment

The conditioned sulfuric acid leachate and the prepared organic extractant are fed into the mixer-settler in proportion. In the mixing section, the aqueous phase and organic phase are fully contacted through mechanical stirring, and the extractant selectively combines with nickel and cobalt ions to transfer them to the organic phase; the mixed liquid after mixing enters the clarification section, and the organic phase loaded with nickel and cobalt is completely separated from the raffinate containing impurities by natural stratification due to density difference. According to the impurity complexity and nickel-cobalt grade of the leachate, a multi-stage countercurrent extraction mode is adopted to gradually improve the nickel and cobalt extraction rate, and at the same time, impurities such as iron, aluminum and magnesium are left in the aqueous raffinate to realize the preliminary separation of nickel and cobalt from impurities.

3. Washing and Purification of Loaded Organic Phase

The loaded organic phase after extraction will entrain a small amount of impurity ions. To ensure the purity of nickel and cobalt products, the loaded organic phase is sent to the washing stage of the mixer-settler, and countercurrent washing is carried out with a special washing solution. By accurately controlling the washing process conditions, the impurity metal ions entrained in the organic phase are removed, the nickel and cobalt components in the organic phase are retained to the greatest extent, and the separation accuracy is further improved.

4. Stripping to Obtain High-Concentration Nickel-Cobalt Solution

The washed and purified loaded organic phase enters the stripping process of the mixer-settler, and countercurrent stripping treatment is carried out with a special stripping agent. The complex structure between the extractant and nickel and cobalt ions is broken, so that nickel and cobalt ions are transferred from the organic phase back to the aqueous phase, forming a high-concentration and low-impurity nickel-cobalt enriched solution. The metal concentration of the enriched nickel-cobalt solution is greatly improved, which can be directly sent to subsequent processes such as electrolysis and evaporation crystallization to prepare high-purity nickel sulfate, cobalt sulfate and other products.

5. Recycling of Organic Phase

After conditioning treatment, the blank organic phase after stripping can be returned to the front end of the mixer-settler for reuse. The extractant loss is low, the material utilization rate is high, which effectively reduces the overall production auxiliary cost, and meets the production demand of low-cost recovery of low-grade nickel-cobalt resources.

IV. Optimization of Mixer-Settler Process Parameters to Improve Nickel-Cobalt Extraction Effect

In view of the characteristics of low concentration and multiple impurities of sulfuric acid leachate of low-grade nickel and cobalt, reasonable optimization of the operating parameters of the mixer-settler can significantly improve the nickel and cobalt recovery rate and product purity. Optimize the phase ratio of aqueous phase and organic phase, control the appropriate two-phase ratio to ensure sufficient mass transfer and extraction of nickel and cobalt ions; adjust the stirring speed in the tank to balance the mixing mass transfer efficiency and two-phase clarification and stratification effect, avoid working condition fluctuation; accurately control the pH value and temperature of each stage of extraction, washing and stripping, lock the selectivity of the extractant to nickel and cobalt, and inhibit impurity extraction; at the same time, reasonably set the material residence time to adapt to the slow mass transfer characteristics of low-grade ions, and ensure industrial continuous and stable production.

V. Industrial Application Value and Significance of Industry Development

In the fields of new energy metal resource recycling and comprehensive recovery of low-grade minerals, the mixer-settler provides a mature and reliable industrial solution for nickel and cobalt extraction. Compared with traditional separation processes, the mixer-settler treatment process has a higher comprehensive recovery rate of nickel and cobalt, which can fully tap the economic value of low-grade nickel and cobalt resources and reduce resource waste; the whole process has high continuity and automation, can be mass-produced on a large scale, and effectively reduces the unit metal production cost. At the same time, the process route is green and environmentally friendly, and the raffinate can be recycled back to the leaching process after treatment to realize closed-loop material utilization, which is in line with the development trend of energy conservation, consumption reduction, green and low carbon in the metallurgical industry. With the continuous increase of the proportion of low-grade and secondary nickel-cobalt resources, the mixer-settler will play a more important role in the field of nickel and cobalt separation and purification in hydrometallurgy, and become one of the core equipment to ensure the stability of the new energy metal supply chain.