Industrial production generates billions of tons of solid waste annually, among which the accumulated stockpile of lead-bearing jarosite waste from zinc hydrometallurgy has exceeded 50 million tons. In this type of hazardous solid waste, the neurotoxic heavy metal lead (Pb) is primarily incorporated into the sodium jarosite lattice via isomorphous substitution, posing long-term leaching toxicity and environmental leakage risks. Therefore, selectively separating and extracting lead from the iron-rich matrix is a core prerequisite for source toxicity reduction and safe disposal of such industrial hazardous wastes.

However, existing pyrometallurgical and hydrometallurgical separation technologies are both constrained by thermodynamic equilibrium limitations, facing significant selectivity bottlenecks. Traditional pyrometallurgical processes typically require temperatures above 1000°C to drive phase separation, resulting in extremely high energy consumption accompanied by multi-component co-volatilization. Conventional hydrometallurgical leaching relies on strong acid chemical potential to drive dissolution, which readily causes non-selective co-leaching of matrix metals such as iron. This lack of selectivity not only substantially increases the process and economic burden of subsequent purification and separation, but also readily generates secondary pollution, constituting a key challenge in the current clean treatment of complex industrial solid wastes.

To address the above issues, a joint team from South China University of Technology, Central South University, and other institutions conducted in-depth research using ZEPTOOLS' in-situ TEM measurement system. The team proposed a novel strategy based on kinetics-controlled lattice relaxation, which induces defect generation through mild calcination and rapid quenching, and exploits differences in ion diffusion kinetics to overcome traditional thermodynamic equilibrium limitations, achieving highly selective and efficient lead extraction from lead-bearing jarosite hazardous waste.

Title: Kinetics-controlled lattice relaxation enables selective lead extraction from hazardous jarosite waste 
Journal: Chemical Engineering Journal 
URL: https://doi.org/10.1016/j.cej.2026.179771

Facing the technical bottlenecks of high energy consumption, high chemical consumption, and limited selectivity in conventional thermodynamic equilibrium-based metallurgical processes, the research team proposed a heavy metal selective separation strategy based on kinetics-controlled lattice relaxation. This method targeted the typical hazardous solid waste from zinc hydrometallurgy—lead-bearing jarosite residue—and systematically constructed a reaction system combining moderate calcination with rapid quenching in cold salt solution. Experimental results demonstrated that under multi-cycle processing conditions of mild calcination at 400°C and rapid quenching in low-temperature sodium chloride solution, the process achieved a lead extraction efficiency of 74.6% and a Pb/Fe separation selectivity as high as 14.74:1 in real jarosite waste residue. Compared with conventional strong-acid leaching processes, this method improved the lead-iron separation selectivity by a factor of 14, fundamentally overcoming the separation burden caused by massive co-dissolution of matrix iron in traditional hydrometallurgical leaching, and establishing a novel technological route for clean and efficient separation of heavy metals from complex solid wastes.

To elucidate the microstructural evolution of the jarosite lattice during calcination, the research team conducted in-situ transmission electron microscopy analysis using ZEPTOOLS' in-situ heating chip sample holder. Under fine stepwise heating in the in-situ observation environment, the sample maintained well-preserved long-range ordered crystal structure and clear lattice fringes from room temperature to 300°C. However, within tens of seconds after heating to 400°C, significant lattice distortion was rapidly induced, with the (1̄20) interplanar spacing sharply decreasing from 3.7 Å to 3.4 Å. In-situ microscopic characterization directly confirmed that moderate thermal input promoted the dehydration and precipitation of hydroxyl groups in the jarosite structure, forming high-density oxygen vacancies and other defect states within the lattice. This in-situ dynamic evolution result clearly revealed the thermal activation effect of moderate calcination on the lattice structure, confirming that the reaction system successfully transformed into a highly active metastable structure, laying the microstructural foundation for subsequent quenching-induced selective release.

Combining post-quenching ex-situ structural characterization and ab initio molecular dynamics simulations, the research team deeply revealed the selective ion migration behavior of the metastable lattice during the quenching relaxation process. Rapid quenching effectively froze the metastable activated structure generated by high-temperature calcination and drove the lattice system to spontaneously relax and reconstruct toward the stable sodium jarosite structure during cooling. Dynamic simulations and mean square displacement analysis clearly demonstrated that during lattice reconstruction, the abundant Na⁺ ions in the quenching medium exhibited a far higher diffusion rate than Pb²⁺ ions. This significant diffusion kinetic advantage enabled Na⁺ to preferentially re-occupy lattice vacancies and efficiently expel the original Pb²⁺ ions. Meanwhile, the framework iron atoms consistently maintained stable iron-oxygen octahedral and tetrahedral coordination configurations, and their rigid network effectively hindered the dissociation and loss of iron, thus elucidating the fundamental reason for the ultra-high selectivity of lead-iron separation at the microscopic kinetic level.

Based on density functional theory calculations and validation with actual industrial waste residue, the research team further demonstrated the defect-assisted migration mechanism and industrial application potential. Theoretical calculations showed that although the vacancy formation energy of lead in the jarosite lattice is lower than that of iron, the energy barrier for its migration from the bulk phase to the particle surface is as high as 3.251 eV, constituting the rate-limiting step for lead release. The abundant oxygen vacancies introduced by calcination-quenching successfully altered the migration pathway of lead, reducing its diffusion energy barrier by 35% to 2.119 eV, significantly promoting the rapid diffusion of lead to the surface and its chloride-coordinated dissolution. In the evaluation of actual industrial hazardous waste treatment, this process operates at an extremely low calcination temperature of 400°C and uses environmentally friendly sodium chloride medium, with a basic energy and material cost of only $0.35 per kilogram of jarosite residue treated. This not only substantially outperforms conventional high-cost advanced solvent leaching routes, but also demonstrates excellent universal separation potential in other solid wastes such as zinc leaching residue.

ZEPTOOLS, as a Chinese本土 high-end precision instrument company, is a first-class supplier of in-situ electron microscopy characterization solutions. Its PicoFemto series of in-situ transmission electron microscopy characterization solutions have successively provided technical support for significant research results of domestic and international users. The following figure shows the ZEPTOOLS in-situ TEM sample holder product used in this research: