you can deploy Copilot Let's delve into the details for each method:

### 1. **Solvent Extraction**

**Reagents Used**: Commonly used extractants include **quaternary ammonium salts** (e.g., Aliquat 336) and **phosphonium salts** (e.g., Cyanex 272). These extractants are mixed with an organic solvent like kerosene or aliphatic hydrocarbons.

**Conditions**: The extraction is typically performed at **ambient temperature** (around 25°C) and **pH 2-3** to ensure the rare earth metals are in their cationic form.

### 2. **Selective Precipitation**

**Reagents Used**: Common precipitating agents include **oxalic acid** and **sodium carbonate**. Oxalic acid is particularly effective for precipitating rare earth oxalates, while sodium carbonate is used for rare earth carbonates.

**Conditions**: The precipitation is usually carried out at **60°C** and a **pH of 8-10**. Maintaining stoichiometric reagent consumption is crucial to avoid co-precipitation of impurities.

### 3. **Ion Exchange**

**Reagents Used**: Ion exchange resins such as **strong acid cation exchange resins** (e.g., Amberlite IR-120) and **chelating resins** (e.g., Chelex 100) are used.

**Conditions**: The ion exchange process is typically conducted at **ambient temperature** and **pH 2-3** to ensure the rare earth metals are in their cationic form.

### 4. **Electrochemical Methods**

**Reagents Used**: Electrolytes such as **sulfuric acid** or **nitric acid** are used to facilitate the electrochemical deposition of rare earth metals.

**Conditions**: The electrochemical deposition is performed at **ambient temperature** and **pH 1-2**. The current density and electrolytic time are optimized to achieve high purity and recovery rates.

For the electrochemical recovery of rare earth metals, the **current density** and **electrolytic time** are crucial parameters that need to be optimized for efficient recovery:

### Current Density

The range of current density typically varies from **10 to 100 mA/cm²**. However, the optimal current density can depend on the specific rare earth metal and the electrolyte used. Higher current densities can lead to faster deposition but may also increase the risk of impurities and defects in the deposited metal.

### Electrolytic Time

The electrolytic time can vary widely depending on the desired thickness of the deposited layer and the concentration of rare earth metals in the solution. Typically, electrolytic times range from **30 minutes to several hours**. Longer electrolytic times can result in thicker deposits but may also require careful control to avoid over-deposition and maintain purity.

### 5. **Membrane Separation**

**Reagents Used**: No specific reagents are required, but the choice of membrane material is crucial. **Polymeric membranes** and **ceramic membranes** are commonly used.

**Conditions**: The separation process is typically conducted at **ambient temperature** and **pH 2-3** to ensure the rare earth metals are in their cationic form.

### Practical Methods from Recent Efforts

1. **Ionic Liquids and DESs**: These have been successfully used in recent studies for the recovery of rare earth metals from various sources, including industrial wastes. They offer a greener alternative to traditional solvents and have shown high efficiency in extracting rare earth metals.

2. **Bioleaching**: This method uses microorganisms to leach rare earth metals from waste materials. It is an environmentally friendly approach that has gained attention for its potential to recover rare earth metals from electronic waste.

3. **Supercritical CO2**: This technique uses supercritical carbon dioxide to extract rare earth metals from waste materials. It is a promising method due to its low environmental impact and high efficiency.

4. **Hydrometallurgical Processes**: Recent advancements in hydrometallurgy have focused on optimizing leaching conditions and using selective reagents to enhance the recovery of rare earth metals.

These methods represent some of the latest advancements in the field of rare earth metal recovery. Each method has its own set of advantages and challenges, so the best approach will depend on your specific requirements and the composition of your leached solution.

https://patents.google.com/patent/US3575687A/en

Article Characteristics of Precipitation of Rare Earth Elements with...

Article Selective Precipitation of High-Quality Rare Earth Oxalates ...

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A combination of precipitation and SX methods. Use a suitable precipitant to remove calcium first, followed by SX (D2EHPA or Cyanex 932).