Assessment of heavy metals mobility and correlative recovery and decontamination from MSWI fly ash: Mechanism and hydrometallurgical process evaluation.

Fly ash from municipal solid waste incineration (MSWI) enriches many leachable toxic metals which readily migrate into the environment, posing serious risks to the ecosystem and human. In this study, the elements mobility, leaching availability as well as the potential maximum amounts of heavy metals in fly ash were thoroughly evaluated. To decontaminate the toxic elements from resulting fly ash leachates, The aqueous zinc (Zn) was recovered using Cyanex 572, cadmium (Cd) and copper (Cu) were effectively removed through adsorption process by a self-assembled hierarchical hydroxyapatite (HAP) nanostructure. The removal mechanism of Cd, Cu and Zn by leaching, extraction and adsorption was revealed with the results from XRD, ICP-MS and SEM. The results showed that fly ash has a high mobility under maximum availability leaching test (95% of fly ash was dissolved), a recovery rate of 91% for Zn can be obtained using Cyanex 572, and a high adsorption rate (> 95% for both Cu and Cd) was reached using HAP for the pristine fly ash leachate. The outcomes from isothermal and kinetic study revealed that Langmuir isotherm and pseudo-second order model can well describe the Cd and Cu adsorption behavior. Economic assessment suggested that the application of HAP for the removal of Cd and Cu is a technically sound and economically feasible approach. The findings of this study demonstrated that this comprehensive process integrated leaching, solvent extraction and consequential decontamination can be a practical strategy for MSWI fly ash treatment.

Development of highly efficient bundle-like hydroxyapatite towards abatement of aqueous U(VI) ions: Mechanism and economic assessment.

The exploration of emergency materials with ultra-fast adsorption rate and great adsorption capability of released U(VI) ions is essentially urgent. The present work successfully fabricated bundle-like hydroxyapatite (B-HAP) microstructures which composed of numerous nanorods by employing a facile and green method. The B-HAP was applied to treat the U(VI) containing wastewater. The abatement of U(VI) by B-HAP was very rapid and the saturated adsorption capacity was superior; over 96.7 % of U(VI) was abated within 5 min, and the maximum adsorption capacity was as high as to 1305 mg/g, signifying the feasibility and effectiveness of this B-HAP in the treatment of uranium-contaminated wastewater due to nuclear accidents. It is worthy to note that other ions in solution exhibited relatively low interference on its performance, indicating that B-HAP has great application potential to capture U(VI) from radioactive-contaminated wastewater as well. The U(VI) removal mechanism by B-HAP was confirmed with results from XRD, FT-IR and XPS. Chernikovite [H2(UO2)2(PO4)2·8H2O] was newly formed after U(VI) abatement by B-HAP. Economic assessment suggested B-HAP and its application on U(VI) abatement were cost-effective. With characteristics of high adsorption rate, large capacity, and strong antijamming ability, B-HAP has great application potential as an emergency treatment material for nuclear accidents.

Removal of U(VI) from nuclear mining effluent by porous hydroxyapatite: Evaluation on characteristics, mechanisms and performance.

The effluents from nuclear mining processes contain relatively high content of radionuclides (such as uranium), which may seriously threaten the environment and human health. Herein, a novel adsorbent, porous hydroxyapatite, was prepared and proven highly efficient for removal of uranyl ions (U(VI)) given its high U(VI) uptake capacity of 111.4 mg/g, fast adsorption kinetics, and the potential stabilization of adsorbed U(VI). A nearly complete removal of U(VI) was achieved by porous HAP under optimized conditions. Langmuir model could well describe the adsorption equilibrium. The data fit well with pseudo-second-order kinetic model, suggesting that U(VI) adsorption is primarily attributed to chemisorption with porous HAP. Intraparticle diffusion analysis showed that the intraparticle diffusion is the rate-limiting step for U(VI) adsorption by porous HAP. After removal by porous HAP, the adsorbed U(VI) ions were incorporated into tetragonal autunite, which has a low solubility (log Ksp: -48.36). Our findings demonstrate that the porous HAP can effectively remediate uranium contamination and holds great promise for environmental applications.