One Minute at Room Temperature: Rice University's HACl Breakthrough Rewrites the Rules of Battery Metal Recovery

Introduction

The headline number is striking enough on its own: roughly 65% of the critical metals inside a spent lithium-ion battery, dissolved and ready for recovery, in sixty seconds, at room temperature, using a water-based solution that avoids the corrosive acids and high-heat furnaces that define conventional recycling. That is the central finding of a study published April 27, 2026 in the journal Small by researchers at Rice University's Department of Materials Science and Nanoengineering.

The paper, authored by Simon M. King and colleagues in the lab of Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Engineering, introduces aqueous hydroxylammonium chloride (HACl) as a leaching agent capable of outperforming most existing alternatives on the dimension that matters most for commercial viability: speed. For several of the target metals, recovery climbs above 75% with only modest additional processing time, and the recovered materials were successfully reprocessed into new battery-grade compounds, closing the loop.

The timing is not incidental. Battery waste volumes are rising faster than recycling infrastructure can absorb them. The volume of battery materials available for recycling worldwide is forecast to reach 1.4 million tonnes by 2030, up from roughly 200,000 tonnes in 2020, and is projected to exceed seven million tonnes by 2040. At the same time, less than 10% of battery waste is currently recycled at all, according to Gautam Chandrasekhar, a doctoral student in the Ajayan group who contributed to the study. A technology that dramatically lowers the energy and time barriers to recycling does not merely improve an existing process; it potentially redefines what a recycling facility can look like and where it can operate.

The Chemistry: Why HACl Works When Other Systems Struggle

Understanding why HACl performs so well requires a brief tour of the leaching landscape it is being compared against. Conventional hydrometallurgical recycling relies primarily on inorganic acids, including sulfuric acid, hydrochloric acid, and nitric acid, to dissolve metal oxides from spent cathode material. These acids are effective; under optimized conditions, sulfuric acid combined with hydrogen peroxide can recover 97 to 99% of cobalt and lithium. But the process typically demands temperatures around 80 degrees Celsius, reaction times of 30 minutes to two hours, and generates toxic byproducts including chlorine gas and sulfur trioxide. Equipment must be built to resist aggressive chemical corrosion, and waste streams require careful management.

The industry's response to these problems over the past decade has been an intensive investigation of deep eutectic solvents (DESs), mixtures of hydrogen bond donors and acceptors that form stable liquids at relatively low melting points. DESs are genuinely less toxic than mineral acids and have shown impressive recovery rates; one choline chloride and ethylene glycol system achieved 98.9% lithium recovery. The catch is time and temperature. That same system required 180 degrees Celsius and 72 hours to reach quantitative dissolution. Even optimized DES protocols typically run at 90 to 100 degrees Celsius for 24 hours. Life cycle assessments have further complicated the DES picture, finding that the complexity of their synthesis can generate greater global warming potential than simpler alternatives, partially negating their environmental appeal.

HACl sits in a conceptually different category. The Rice team categorizes it as an aqueous amino chloride salt, a class of water-based lixiviants that the paper positions explicitly beyond the DES framework. Crucially, HACl is not simply relying on acidity or chloride ion concentration to dissolve metals, mechanisms that both acid and chloride-rich DES systems exploit. Through a combination of laboratory experiments and computational modeling, the researchers identified a third driver: a built-in redox-active nitrogen center within the HACl molecule that actively participates in electron transfer reactions and drives metal dissolution independently of solvent polarity or pH.

Corresponding author Sohini Bhattacharyya, a research scientist in the Ajayan lab, put it directly: "While the rapid metal dissolution is very interesting, what is most exciting is that this highlights the generic chemical properties that are the major drivers for efficient leaching. That redox capability gives it a major advantage over other similar systems we tested." The practical consequence is that HACl does not need to be heated to unlock its reactivity. The redox mechanism is available at room temperature, and using water rather than a viscous organic solvent means molecules move freely through the solution, accelerating mass transport and shortening the time required for metals to reach the leaching front.

Performance Data and What It Means in Context

The numbers reported in the Small paper are worth examining carefully, because they tell a nuanced story about where HACl currently sits relative to the competition. The one-minute, room-temperature result of approximately 65% overall extraction is the headline, and it genuinely has no close parallel in the published literature at those conditions. For several individual metals, recovery exceeds 75% within slightly longer but still rapid treatment windows. First author Simon M. King, who completed this work as a summer research fellow and is notably a sophomore studying chemical and biomolecular engineering, captured the team's own surprise: "We were surprised by just how fast the reaction occurs, especially without the involvement of high temperatures. Within the first minute, we're already seeing the majority of the metal extraction take place."

To be precise about the trade-offs: HACl does not yet match the 97 to 99% recovery rates achievable with optimized sulfuric acid processes, nor the near-quantitative yields reported under the best DES conditions. What it offers is a fundamentally different position on the speed-energy-toxicity frontier. A process that achieves 65 to 75% recovery in one to several minutes at room temperature, using a water-based, relatively low-toxicity reagent, represents a different industrial proposition than a process that achieves 99% recovery in 24 to 72 hours at 100 to 180 degrees Celsius. For high-throughput, continuous-flow recycling facilities designed to handle large volumes of mixed battery waste, speed and ambient operability may matter more than squeezing out the final percentage points of yield, particularly when multi-pass processing is architecturally feasible.

Professor Ajayan highlighted the practical upside: "A big advantage of this system is that it works under relatively mild conditions. That opens the door to more sustainable and scalable recycling technologies." The team also demonstrated that the system completes the recycling loop: metals recovered via HACl leaching were successfully reprocessed into new battery-grade cathode materials, confirming that the gentler extraction chemistry does not degrade the downstream usability of the recovered metals.

Fitting Into Rice's Broader Battery Recycling Research Push

The HACl study does not arrive in isolation. It is the latest output from an Ajayan group that has become one of the more productive academic research programs focused specifically on battery recycling chemistry. Just weeks earlier, in March 2026, a related Rice team published results from a plasma-assisted recycling approach in which spent battery black mass was exposed to microwave-induced plasma for 15 minutes, followed by a citric acid leach at room temperature; that process recovered more than 90% of all metals while also capturing graphite in a form suitable for reuse in new batteries. The plasma technology has been patented and is moving toward commercialization, with early technoeconomic analysis suggesting it can outperform current industrial methods.

The two approaches, HACl leaching and plasma-assisted processing, attack the battery recycling problem from different angles and may ultimately prove complementary rather than competitive. The plasma method's 90-plus percent metal recovery over 15 minutes at room temperature is impressive, but its reliance on specialized plasma generation equipment constrains where and at what scale it can be deployed. HACl leaching requires only mixing tanks, pumps, and conventional hydrometallurgical downstream processing, infrastructure that already exists in the mining and chemical industries worldwide.

Chandrasekhar's observation about the recycling gap frames the stakes bluntly. Less than 10% of battery waste is currently recycled, he noted, despite growing urgency. That is not primarily a policy failure; it is an economics and logistics failure. Processing black mass typically requires energy-intensive industrial furnaces and strong acids, both of which raise costs, complicate permitting, and limit geographic flexibility. Technologies that can operate at ambient temperature with lower chemical hazard profiles lower every one of those barriers simultaneously. The HACl work is explicitly oriented toward commercial translation; the paper notes that future work will focus on scaling the system for commercial use.

The Supply Chain Pressure That Makes Recycling Speed Matter

The urgency behind battery recycling research is not abstract. The global lithium-ion battery recycling market, estimated at approximately USD 287 million in 2025, is projected to reach USD 2.74 billion by 2033, a compound annual growth rate of 30.9%. Global lithium-ion battery cell demand is expected to reach 4,700 gigawatt-hours by 2030. Experts are projecting that lithium demand may exceed primary supply as early as the second quarter of 2026, with demand growth running at 15 to 18% annually.

Cobalt presents an even sharper constraint. Multiple supply chain analyses have concluded that battery production alone could consume more than 10% of global cobalt reserves under high-growth scenarios, and that global reservoirs of both lithium and cobalt are not sufficient to meet projected demand through primary mining alone. The European Union's New Regulatory Framework for Batteries, approved in July 2023, reflects this reality by mandating 90% recovery of cobalt, copper, lead, and nickel, and 50% recovery of lithium from batteries by 2027. Meeting those targets with current technology would require either massive capital investment in conventional facilities or a step change in recycling efficiency.

Building on my analysis of the broader push toward closed-loop battery material recovery in my April 2026 coverage of the DOE's $69 million Critical Minerals and Materials Accelerator program and the EnergyX and tozero demonstration projects, the Rice HACl work fits into a recognizable pattern: academic breakthroughs providing new chemical mechanisms that industrial demonstration programs then need to translate. The gap between a journal paper demonstrating 65% recovery in one minute in a laboratory flask and a commercial facility processing thousands of tonnes of battery waste per year is real and should not be minimized. But the directionality of the science is now pointing consistently toward faster, cooler, and less chemically aggressive processes, and HACl represents perhaps the most dramatic single demonstration of that trend to date.

If recycling is scaled effectively across the supply chain, modeling suggests it could reduce lithium and nickel demand by 25% and cobalt demand by 40% by 2050. Technologies that lower the cost and complexity of recycling are therefore not supplementary to the critical minerals supply problem; they are a central part of the solution.

Conclusion: Speed as a Design Principle

What the Rice HACl study ultimately contributes is not just a new leaching agent but a new design principle for thinking about battery recycling chemistry. The field has long accepted that higher recovery rates require more energy, more time, or more aggressive reagents. The finding that a redox-active nitrogen center in a simple water-based solution can drive 65% metal extraction in sixty seconds at room temperature challenges that trade-off directly. It suggests that the chemical mechanism, not just the conditions, can be engineered to deliver speed without sacrificing safety or scalability.

The team's demonstration of closed-loop functionality, extracting metals and reprocessing them into new battery materials without quality degradation, is equally important. A recycling process that recovers metals quickly but renders them unsuitable for reuse in batteries solves only half the problem. HACl appears to avoid that failure mode, at least at laboratory scale.

Considerable work remains before this chemistry operates at industrial scale. Recovery rates above 75% for some metals under slightly extended conditions are promising, but commercial processes typically target 90% or above to justify the capital and operating costs of a dedicated facility. Understanding how HACl performs on mixed cathode chemistries, in the presence of electrolyte residues and separator materials, across multiple leaching cycles, and with real-world battery waste rather than controlled laboratory samples will be essential steps. The question of reagent regeneration and recycling within the process loop, a known challenge for any lixiviant-based system, will also need to be addressed before a credible technoeconomic case can be constructed.

Nevertheless, the publication in Small marks a genuine advance. Room-temperature hydrometallurgy at this speed has not been demonstrated before with a water-based, low-toxicity system. At a moment when battery waste volumes are accelerating, recycling infrastructure is undersupplied, and regulatory pressure is intensifying, a technology that makes the first minute of metal recovery both fast and manageable is precisely the kind of foundational chemistry that commercial innovation builds on.