Characteristics and Treatment Challenges of Wastewater in Lithium Battery Production

1. Background of Oil-Contaminated Wastewater

With the increasing demand for lithium batteries, the number of lithium battery manufacturing companies is also growing. However, during the production process of lithium batteries, it is inevitable that waste gases, wastewater, and waste residues will be generated. The wastewater produced is typical of high-concentration wastewater. If not treated and directly discharged, it can result in severe penalties, affecting production. 

Taking positive electrode wastewater as an example, the positive electrode materials are a major water consumer in the industry and also the largest producer of wastewater. For this type of wastewater, a sedimentation process is used. An ion mixture is added to a flocculant and stirred to produce a sedimentation reaction. The sludge is then filtered through a filter press, and the filtered water is reused in circulation, while the filter cake is disposed of. Negative electrode wastewater, on the other hand, has a more complex composition, containing a large amount of lithium cobalt oxide, lithium iron phosphate, methyl pyridinium ketone, nano ultrafine carbon powder, and small molecules such as esters. Although the water volume is relatively small, the wastewater has a complex composition, poor biodegradability, and certain toxicity. 

A large amount of wastewater is produced during lithium battery production, which contains sodium sulfate, sodium chloride, or ammonium chloride, as well as heavy metals like nickel, cobalt, and manganese, along with small amounts of COD impurities. Currently, multi-effect evaporation or MVR (Mechanical Vapor Recompression) evaporation is used to treat this wastewater. 

In practical use, wastewater treatment is usually easier, but handling the concentrated liquid is more difficult. The concentrated liquid contains concentrated impurities such as nickel, cobalt, manganese, and COD, which can easily adhere to equipment walls, causing a decrease in evaporation efficiency (i.e., it is easy to evaporate at first, but as time passes, the water volume decreases, the concentration of the mother liquor increases, and the boiling point rises, resulting in a decrease in the evaporation equipment's processing capacity), or clog the tubes in the heat exchanger. 

2. Treatment Challenges

Lithium battery production wastewater usually has the following characteristics:

·Complex Oil States: It contains free oil, dispersed oil, and highly stable emulsified oil, which makes it difficult to completely separate using traditional methods.

·Diverse Composition: In addition to oil and grease, it often contains NMP (N-Methyl-2-pyrrolidone), binders, conductive agents, and trace metals such as lithium, cobalt, and nickel.

·Strict Discharge Standards: For example, in China, discharge must meet the Battery Industry Pollutant Discharge Standards (GB 30484) and the stringent requirements for petroleum-based indicators in local environmental regulations.

·Water Resource Reuse Requirements: Driven by water conservation and the circular economy, the treated water must meet the specified standards.