Oral Presentation International Solvent Extraction Conference 2025

Direct Injection of a pH Control Agent in Metal Extraction Columns (121675)

Laura Budeus 1 , Andreas Jupke 1
  1. RWTH Aachen University, Aachen, NORTH RHINE-WESTPHALIA, Germany

Introduction

Lithium-ion battery (LIB) technology is crucial to the decarbonization of the global transportation sector. However, the mining of metals for LIB production is often associated with significant environmental and social challenges. Recovering these valuable metals from end-of-life LIBs could significantly reduce reliance on critical mineral extraction. [1]

The recycling process of end-of-life LIBs typically involves mechanical and thermal pre-treatment steps that generate the so-called "black mass”. The black mass contains valuable metals such as manganese, cobalt, nickel, and lithium. In a subsequent hydrometallurgical process step, these valuable metals are leached from the black mass by adding acid. From the resulting acidic solution, the individual metal ions are selectively separated by a pH-controlled reactive solvent extraction process. [2]

In a single-stage extraction process, isothermal pH-dependent thermodynamic equilibria determine extraction efficiency and selectivity. However, the pH changes throughout the extraction process due to the extraction mechanism. The extractant, diluted in an organic solvent, releases protons into the aqueous phase when extracting metal ions. A common method to control the pH in an extraction apparatus, such as an extraction column, is to partially saponify the extractant and thereby replacing protons with sodium ions. [3] However, depending on the process, pH control through saponification might be difficult. On the one hand, the limited saponification degree limits the share of extractant which can take part in the extraction, on the other hand, a saponified extractant leads to an increased tendency for emulsification. [3–5] With a direct injection of a pH control agent in metal extraction columns we aim to maximize the share of extractant, reduce emulsification and maximize extraction efficiency and selectivity by realizing an optimal pH profile.

 

Methodology

We present a direct-injection approach for local pH adjustment in a DN32 Kühni extraction column (active height: 1350 mm, 48 rotor-stator compartments) using 0.05 M CaCl2 and 0.05 M MgCl2 as the aqueous phase and D2EHPA in kerosene as the organic phase. Three injection points (IP1, IP2, IP3) are positioned at different heights in the active part of the extraction column, allowing flexible NaOH dosing. The column is additionally equipped with seven sampling points (SP1 to SP7), enabling comprehensive monitoring of both pH and metal concentration, as demonstrated in Figure 1. By dosing NaOH within the extraction column, we neutralize proton release during metal extraction, creating targeted pH gradients along the column. This setup enables flexible adaptation to varying feed streams – particularly relevant for battery recycling with changing feed compositions due to different battery compositions. At the same time, local pH control enhances selectivity by lowering unwanted co-extraction and contributes to producing battery-grade metal products.

 

Results

By adding NaOH as a pH control agent, we achieved higher extraction efficiencies and better selectivity of calcium over magnesium in column experiments compared to single-stage batch tests. Both the pH and concentration profiles can be controlled by adjusting the injection parameters NaOH concentration and flow rate. We discuss different injection configurations and elaborate on why no NaOH injection close to the organic phase outlet has been particularly promising for achieving selective separation. This approach reduced calcium extraction efficiency by about five percentage points from its peak performance, resulting in 93 % extraction efficiency. However, it also lowered magnesium co-extraction by a factor of ten compared to the next best injection strategy, reaching just 0.2 % magnesium co-extraction. The low pH near the organic phase outlet created a stripping effect, removing co-extracted impurities and contributing to a high purity extract. Nevertheless, NaOH injection also affected the column fluid dynamics, resulting in larger droplet sizes and poorer phase separation. Through this direct-injection approach for local pH adjustment, we aim to maximize both extraction efficiency and selectivity in the recycling of lithium-ion batteries in the future. Thereby we hope not only to improve the recovery of valuable metals but also to contribute to the production of high-purity battery-grade materials.67e12a2ae826a-Kolonne.svg

Figure 1: Column setup of an agitated Kühni DN32 column with injection and sampling points for direct injection of a pH control agent

 

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  2. [2] J. Neumann et al., "Recycling of Lithium‐Ion Batteries—Current State of the Art, Circular Economy, and Next Generation Recycling," Advanced Energy Materials, vol. 12, no. 17, 2022, doi: 10.1002/aenm.202102917.
  3. [3] I. R. Rodrigues, C. Deferm, K. Binnemans, and S. Riaño, "Separation of cobalt and nickel via solvent extraction with Cyanex-272: Batch experiments and comparison of mixer-settlers and an agitated column as contactors for continuous counter-current extraction," Separation and Purification Technology, vol. 296, p. 121326, 2022, doi: 10.1016/j.seppur.2022.121326.
  4. [4] C. Lupi and D. Pilone, "Effectiveness of saponified D2EHPA in Zn(II) selective extraction from concentrated sulphuric solutions," Minerals Engineering, vol. 150, p. 106278, 2020, doi: 10.1016/j.mineng.2020.106278.
  5. [5] Y. Liu, S. H. Sohn, and M. S. Lee, "Methods for the substitution of common saponification systems for the solvent extraction of REEs," Geosystem Engineering, vol. 20, no. 2, pp. 111–118, 2017, doi: 10.1080/12269328.2016.1223558.
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