How Rotary Dryers are Used for Processing Lithium Compounds

Lithium demand looks ready to skyrocket with the rising need for electric vehicle (EV) batteries and stationary energy storage systems. To support sustainable lithium extraction, a piece of industrial equipment invented in the 19th has become essential to the metal’s processing. The industrial rotary dryer was invented in 1873 by British industrialist Frederick Ransome. Though these machines didn’t initially achieve commercial success, his patented designs became the basis for industrial rotary dryers in the United States from the 1890s, with their use later spreading globally.

Industrial rotary dryers are widely used today in the processing of lithium. As mining equipment, they’ve been used for the processing of an array of other minerals as well, including aluminum, chromite, graphite, manganese, phosphorus and zinc. Additionally, rotary dryers have been slated for systems designed for recycling batteries containing lithium. As mining equipment and for processing batteries, industrial rotary dryers have become integral for the processing of lithium and, as such, those involved in lithium processing should understand the basics of how they work.

Lithium Mining Equipment & the Use of Industrial Rotary Dryers

Though there exist 145 minerals containing lithium, only six of these can be cost-effectively extracted in commercial operations that involve processing of lithium. Mining equipment for lithium concentrates on extracting only five of these minerals: amblygonite, eucryptite, lepidolite, petalite and spodumene. For many mined minerals, drying is critical to their processing, and those containing lithium require drying during processing as well.

The robust construction of industrial rotary dryers that are designed to process minerals make them important within systems designed for mineral mining and processing. They are used to control moisture content in order to reduce shipping costs, make further processing easier and result in a purer form of the metal that’s necessary for making batteries containing lithium. Mining equipment like industrial rotary dryers are thus very capable of withstanding the harsh conditions involved in lithium processing.

Some advantages of industrial rotary dryers include: 

• Accepts more flue gasses than other dryer styles
• Cost-efficient due to lower need for maintenance
• Highest capacity of any industrial dryer
• Less sensitivity to particle size

While they do offer these benefits, industrial rotary dryers work less well for material with exceptionally fine particles as they normally require huge amounts and high velocities of gas.

Parts of an Industrial Rotary Dryer & How They Operate

Industrial rotary dryers consist of a cylindric shell or an inclined drum that’s usually fitted internally with lifters or flights. Rotating slowly upon bearings, material to be dried flows through this drum via a cascading action in an either concurrent or counter-current flow that involves heated air or other gasses. These gasses are what reduces the moisture content of the feed material, either through direct or indirect contact with the heated gasses. Rotary dryers act similarly to clothing dryers, utilizing a tumbling action to process the material.

The basic parts of an industrial rotary dryer include: 

• Dryer shell: Typically made from rolled mild steel plate that is welded into a cylinder. 
• Refractory lining: Typically, when drying materials at elevated temperatures, an internal lining made from either cast concrete or refractory bricks is used to thermal protect the dryer shell. The lining can also be used to minimize abrasion and/or corrosion from the materials processed. 
• Riding rings: Also known as tires, these support the dryer shell at the ends an are normally each made from a non-welded steel forging. The riding rings are machined so that the dryer shell rotates smoothly. 
• Support rollers: Also known as trunnions, these support the riding rings. Each riding ring is paired with two support rollers equipped with shafts and made from non-welded steel forgings. The rollers are machined for smooth shell rotation.
• Roller bearings: These support the shafts of the support rollers. Each shaft is paired with two bearings. Though capable of handling high five loads and temperature exposure, they require protection from dust and heat from the dryer.
• Holding rollers: Also known as thrust rollers, these rollers usually rest against the riding ring’s sides, support the dryer, and keep it from slipping off the support rollers. The holding rollers can withstand the axial forces of the shell movement. 
• Shell main drive: The shell main drive can be sprocket & chain type for lower power requirements or ring and pinion gear type for the larger dryers. The chain drive will be more accommodating to any axial and radial movement of the dryer shell. The drive can be constant or variable speed, the latter control is used to allow wider control of the drying time.
• Auxiliary drive: As it’s dangerous for an industrial rotary dryer to stand stationary should the power to the drive fail, typically there’s a backup drive powered by a smaller electric motor that uses an independent power source, though this may instead involve various other sources, eg., compressed air cylinder, fuel-powered generator, etc.. 

Direct vs. Indirect Heating 

Industrial rotary dryers use high temperatures to vaporize water (or other volatiles) or cause a reaction as the material is processed, like when removing waters of hydration. These can be either directly or indirectly heated.

 Dryers that utilize direct contact between the heating gas and material are very effective and have higher heat transfer rates. Dryers that utilize indirect contact between the heating gas and material have lower heat transfer rates, but discharge much lower exhaust gas flow and therefore have reduced emissions. Both technologies can be configured for either concurrent or counter-current flow operation. 

Indirect-fired industrial rotary dryers are used in situations when: 

• Application involves solids that are finely divided.
• Material must be processed in inert environment.
• Processing equipment requires tight control.

Indirect-fired dryers may also be used in other processing applications where contact between the material and heated gasses is undesirable.

Processing Lithium-Based Minerals for Batteries with Industrial Rotary Dryers 

Regardless of the mineral being processed, the lower the moisture content, the easier the material is to handle. Lithium is no exception. If lithium is too dry, it results in dust issues and is more likely to degrade. If it is too wet, the minerals can cake, or mold colonies can even develop. In fact, dry rooms are essential in producing lithium-ion batteries, where moisture concentrations must remain below 100 parts per million. This is because electrolytes used in these batteries, like lithium hexafluoride, react with water, so even small moisture content adjustments will affect the life and capacity of any cells produced.

As water is used for processing in hard-rock lithium mining, equipment like industrial rotary dryers makes sense for such applications simply from a material handling point. With lithium mining, equipment like mills or crushers will normally break down minerals containing lithium before they go through a beneficiation process. This often requires a wet process followed by a drying stage that helps remove unwanted impurities. If lithium-laden minerals contain too much moisture, it can cause problems with flowability, obstructing the conveyance of material throughout the system, including in bins, on conveyers, within hoppers, and at transfer points.  

Lithium-rich minerals are often sourced from brines and underground water sources, so removing moisture in these cases is simply part of the lithium extraction process. In fact, most lithium extraction on a commercial basis is done via a chemical process that involves evaporation rather than actual lithium mining. Equipment in such cases must be used to dry ores from evaporation ponds, which will often require industrial rotary dryers for roasting. The most important of these ores is spodumene, which involves first crushing the mineral and then roasting it at temperatures around 2012°F (1100°C), after which it’s leached with sulfuric acid at a temperature of about 482°F (250°C). Processes to extract lithium from lithium-bearing clays are also being tested, a process in which industrial rotary dryers can also play a part.

Industrial Rotary Dryers for Recycling Lithium-Based Batteries

While industrial rotary dryers are mostly used for processing raw minerals into purer forms of lithium, they can also be used for recycling lithium batteries. This involves a process called calcination, which can be accomplished with Heyl Patterson rotary equipment.

Heyl Patterson Industrial Rotary Dryers

Heyl Patterson Thermal Processing makes industrial rotary dryers that are both robust and adaptable. As workhorses within the material processing sector, our rotary dryers can be customized for processing specific types of lithium-bearing minerals, from powdered bulk solids to liquid slurries. Customizations can be made that include air velocity, beginning and ending moisture content, drying temperatures, material retention times, and temperature parameters for the material.

Heyl Patterson can customize industrial rotary dryers to specific applications, including:

• Combination, forced-draft, and induced-draft airflow systems
• Control systems, from those that feature only burner management to completely computer-operated process controls
• Designs for co-current and counter-current flow of material or gas
• Lengths of over 100 feet (30.5 m) and diameters of as much as 16 feet (4.9 m)
• Temperatures approaching 2200°F (1204°C) for inlet gas
• Tested lifting flight design that provides the most efficient drying retention times and material movement

 To learn more about our industrial rotary dryers and other lithium mining equipment, contact the thermal processing experts at Heyl Patterson today.