Lithium-ion (Li) batteries have in recent years been seen as panacea to the world’s pollution ills. Their use in electric vehicles is critical as combustion engine vehicles contribute to approximately 10 per cent of global greenhouse emissions. But has it ever struck you that Li batteries could be contributing to pollution as well?

If not properly disposed, they can reach landfills, allowing toxic metals in these batteries to leak into the soil and water, causing an environment hazard.

In comes Mini Mines, a start-up with a patented method to recycle lithium from batteries. The company, which calls itself a sustainable cleantech company, has a patented solution that helps extract minerals for reuse at lesser cost using a method called ‘Hybrid-Hydrometallurgy’.

Anupam Kumar, CEO, Mini Mines, points out that India generates about 70,000 metric tonnes of waste lithium-ion battery every year, and that countries such as China buy back these waste so as to retain control over the supply chain.

It has been possible to recycle and extract minerals used in Li-ion batteries but traditional methods are costly and not environment-friendly.

Three step process

Any mechanism that involves solvents or liquids as the base for extraction of metals is called hydrometallurgy. This has been used by mankind for about 8-9 decades. “In Hybrid-Hydrometallurgy, we take the batteries through a three step process — extraction, selective separation and beneficiation or purification,” says Kumar.

Through this process, Mini Mines is able to recover valuable spherical graphite and separate compounds such as lithium, cobalt, nickel, manganese and other metal salts in the battery.

Using organic solvents to recover metal compounds is cost-effective only when the compound is costly to mine, as in the case of thorium or uranium used in nuclear reactors. This is where aqueous media or polar media recovery systems enter the picture.

Once the batteries get dissolve in the liquid, the solution becomes ready for extraction of minerals in the solvent. Aqueous media help break the compounds down to the ionic level.

In the pre-processing, batteries are deep-discharged for safely dismantling them. This is then shred to separate the aluminium and copper in the batteries from the black mass. (Black mass is an active ingredient present on the surface of the aluminium and copper electrodes in a battery. The mass has lithium, cobalt, nickel and manganese in metal oxide or metal complex form. These are integrated with the graphite lattice structure.) These two high-quality alloys can then be used afresh for industrial applications. The black mass recovered from this indigenously designed method reduces the aluminium and copper impurities to less than 0.5 per cent combined. 

Now comes the elemental extraction part. The traditional methods use organic solvents for extracting minerals but there are so few suppliers globally that make such solvents like — Solvay and Dow Chemicals. Other than the high costs, import dependence is a deterrence. And, to extract more than five different elements, one would need different solvents, each of which has a different boiling point and properties. This maked maintanence, storage, processing in them in a controlled environment, preventing the liquid from evaporating a costly affair. Additionally, the stoichiometric balancing of the reactions make the processing more complex.

The alternative is the Hybrid-Hydrometallurgy process, says Kumar. Here, “we separate elemental compounds from the graphite without damaging the graphite lattice structure. Using organic solvents makes the graphite structure deteriorate and it becomes unusable.” Spherical graphite, he says, is a precious natural resource for India. By using a single, aqueous medium, the company is able to recover all these elemental compounds. Meanwhile, the spherical graphite doesn’t lose its structural and chemical characteristics, and can be reused in Li-ion batteries. 

The next step is to selectively separate the elemental compounds — lithium, cobalt, nickel, etc. Each metal salt or oxide has different solubility at different temperatures, pH and pressure, in an aqueous solution. By changing the temperature ramp rate, pH range and pressure gradient in such a way that only one metal starts losing its solubility and starts “sedimenting in the reactor”, only that metal starts being separated from the rest of the dissolved minerals. 

“When the metal salt loses solubility it forms a slurry which is passed through a specialised, metal selective filtration system.” In other words, the liquid has all the elements minus one. “Instead of using five different organic solvents to separate each of the five minerals, we use one solvent but use a combination of temperature gradient, pH range and pressure gradient to separate each compound one by one.”

The final step is the purification process. After selective separation, the solid that we get is in the form of crystals, which have a little moisture over them. The crystals are nothing but impurities or the residue of the liquid. These are then subjected to a series of thermal processes. Each element has a different gradient for crystallisation. For example, cobalt hydroxide/sulphate has a particular range of temperature ramping rate where only cobalt salt will crystallise. “Then this is put through a series of washing processes by different proprietary solutions that we have developed — called aqua space solutions or benificator liquid.” These wash out all the other elements and purifies the solid crystallised minerals.

“We can increase the purity in this process up to 99.99 per cent which is the analytical grade,” says Kumar.

The recovered minerals have various industrial applications such as catalyst manufacturing, metallurgy or grease manufacturing, pharmaceuticals, among others.

The company also retains a few of those recovered minerals to make a base, cathode active material, which is useful for manufacturers of sodium-ion and lithium-ion cells. After recovery, Kumar says, Mini Mines combines these minerals in a certain ratio to make it useful for the cell manufacturers. 

The company’s original process ended at the elemental recovery stage. But the cathode active material is “a universe in itself” and a cell manufacturer is likely not able to do it themselves. “So we decided to forward integrate our recovered material, because having the source of these minerals after the recovery makes the forward integration easy, as we can control the purity, crystal structure and processing parameters at the source itself,” says Kumar.

He also points out that the process does not merely help reuse Li-ion batteries but actually regenerate these metals so that they can be reused in any chosen application such as in upcoming sodium ion battery plants. The company has also designed its machines indigenously, he says.

Effective and efficient

What would the costs savings be with Mini Mines’ process versus traditional methods? Kumar claims savings of 50-53 per cent reduction in costs compared with the mining process. If you consider other processes than solvent extraction, those can’t even recover elemental compounds, they recover an amalgam, he points out. That makes it difficult and costly to separate select elements out.

In terms of capital expenditure, the cost could be up to 66 per cent higher in traditional methods.

He explains: For one tonne of lithium ore, we can recover 2-7 kg of lithium hydroxide or lithium carbonate depending on the available quantities in the source batteires. When we recycle one tonne of lithium-ion batteries, we recover approximately 18-32 kg of lithium hydroxide or carbonate. Using organic solvents, it is possible to recover the same amount of lithium but the cost of doing that would be higher than even mining from the ores. Additionally the organic waste generated damages the environment.

The conventional recycling and mining of Lithium-ion battery raw materials are highly expensive, water and energy-intensive processes. Mini Mines’ hybrid-hydrometallurgy process reduces direct carbon dioxide emissions by 1.5 tonnes with every tonne of Lithium-ion battery recycled. The innovative process also saves approximately 2,00,000 liters of water for every tonne of the battery recycled. This process is a zero-liquid discharge process i.e. we do not create any kind of solid, liquid, or gaseous waste in the process, Kumar points out.

The company has also developed a proprietary solution so that when the Li-battery is dismantled, it does not catch fire. The solution deep discharges the Li-ion batteries and stabilises the Li+ ion. It combines with the Li+ and helps in the recovery of the lithium at the recovery stage. Favourable economics beckons the recycling industry.