Barry on Batteries: Waste Treatment of Solids, Liquids and Gases in Battery Recycling

Recently, I had the opportunity to visit two different battery recycling plants. One plant received black mass from a variety of sources and produced battery-grade chemicals through an interesting hydrometallurgy process.

The second plant brought in lithium-ion batteries from a variety of sources, including small-format consumer batteries, medium-format consumer “power-tool” batteries and production scrap, as well as large-format batteries of cells, modules or packs from electric vehicles to produce black mass.  This black mass then continued downstream in the plant with the hydromet process to produce cathode-active, or CAM, material and pre-CAM materials. 

During these visits, I realized that each plant handled various types of emissions, including solids, such as dust from ferrous and non-ferrous metals and plastics; liquids, such as wastewater and electrolyte solvents; and gaseous emissions of volatile organic compounds (VOCs) and hydrofluoric acids. 

Managing Energy Discharge and Treatment Emissions

Let’s begin this environmental discussion with the first step in the recycling process to discharge the energy from the batteries. The discharging step ensures the downstream processes are safe. 
 
There are three possible options to discharge energy from batteries. They include a saltwater or brine bath, a resistive load bank and battery-cycler electronic discharge. Regarding environmental emissions, the brine-soaking approach has the most significant environmental impact, producing both gaseous emissions and wastewater contamination.

This approach generates flammable hydrogen gas as well as toxic chlorine gas.  In addition, there are wastewater emissions from the used brine that contain electrolytes, mixed metal oxides and other battery debris as well as other dissolved solids and liquid components.

After discharging, there are several methods for mechanical treatment of the batteries. The dry approach conducts the shredding and granulating in an inert nitrogen environment so while dust is generated in the process, these are controlled first by being conveyed into the downstream vacuum dryer and then a dust-handling system. The dust includes the metals—lithium, nickel, cobalt and manganese—as well as aluminum, copper, plastics, iron and graphite.  

If wet shredding is employed, which is an alternative to the “discharging to dry treatment” process, the wastewater generated has many contaminants depending upon the battery type and battery chemistry. For example, the electrolyte material can contain carbonates, additives for improved battery performance, lubrication components, salts and the binder material.  

A third treatment option would be a pyrolysis approach where the batteries are conveyed into a rotary kiln that heats the batteries to drive off the electrolyte and dries the battery materials before mechanical treatment in shredders and mills. This approach results in VOC and acid gas emissions.

Taking a step back, if dry shredding is the approach, there is a vacuum-drying step that also generates dust, VOCs and acid gas of hydrofluoric acid.  

Black Mass to Battery-Grade Processing

Following the steps of recovering the black-mass solids and electrolytes, the next step is sorting and classifying the materials. In this step, which varies by the technology, dust is generated via the milling process, air classification and sieving screens.  

Now, moving further down the battery supply chain, battery-grade materials need to be manufactured from the recycled materials. As we discussed in previous columns, there are downstream metallurgical processes to produce battery-grade material from the recovered lithium, nickel and the other components.  Each hydromet process has specific emissions of gas, solids or dust emissions, liquid chemical emissions and energy byproduct emissions.  

To control acid gas emissions, scrubbers are employed using a scrubbing liquid, such as potassium hydroxide, to neutralize the gas. These will typically operate at 99+% efficiency.  After the gas is neutralized, the VOCs are handled via high-temperature thermal oxidizers, which incinerate the VOCs. These also operate at 99+ percent efficiency.  

For dust control, cyclones and bag-filtration systems are employed with different filter media to remove and recover the solids. The design of the cyclones, filter media and HEPA or U-HEPA filters depend upon the particle-size distribution as well as the explosivity of the particles themselves.  

For wastewater, there are many alternatives depending upon the types of metal contaminants and their concentration, which is determined by the percentage of total suspended and total dissolved solids in the water, pH, temperature, viscosity and chemical components. Treatment can include neutralization, precipitation, solid-liquid separation, ion-exchange resins, activated carbon and electro-chemical processes.  

If you have a chance to visit a specialty chemical plant, you will find a host of similar environmental controls for external or community safety as well as internal operator safety, as described above. Environmental engineers can easily transfer this chemical industry expertise because the recycling process is similar to the production of specialty chemicals.