Development of a Green Technology for Mercury Recycling from Spent Compact Fluorescent Lamps Using Iron Oxides Nanoparticles and Electrochemistry

TL;DR: In this paper, the authors describe a two-step green technique to remove and recycle mercury from spent compact fluorescent lamps (CFLs) using magnetite (Fe3O4) and maghemite (γ-Fe2O3) nanoparticles.

Abstract: The widespread use of energy efficient mercury containing lamps and impending regulations on the control of mercury emissions has necessitated the development of green mercury control technologies such as nanosorbent capture and electrolysis regeneration. Herein we describe a two-step green technique to remove and recycle mercury from spent compact fluorescent lamps (CFLs). The first element included the assessment of capture efficiencies of mercury vapor on magnetite (Fe3O4) and maghemite (γ-Fe2O3), naturally abundant and ubiquitous components of atmospheric dust particles. Around 60 μg of mercury vapor can be removed up to 90% by 1.0 g of magnetite nanoparticles, within a time scale of minutes. The second step included the development of an electrochemical system for the mercury recycling and regeneration of used nanoparticles. Under optimized conditions, up to 85% of mercury was recovered as elemental mercury. Postelectrolysis regenerated iron oxide nanoparticles were used in several sorption–electroly...

Summary

Introduction

• Mercury has been known to humanity for several millennia and has key uses in fields including medicine, catalysis, optics, and energy-efficient technology.
• Yet it remains one of the most toxic global pollutants in the environment.
• 1−3 Mercury compounds are known for being persistent, toxic, and bioaccumulative pollutants of global interest.
• 4 Among the recommendation of the Minamata convection (2013) is indeed the reduction of mercury emission from Hg containing lamps, which is the subject of the present study.
• Eckelman et al. evaluated that only 20% of these lamps are recycled in the Organization for Economic Co-operation and Development (OECD) countries, 5% in.

Experimental section

• FeCl24H2O and FeCl36H2O, NaCl, and hydrous NaOH pellets were used as purchased.
• Commercial magnetite and maghemite nanoparticles were purchased from Sigma-Aldrich without further purification.
• Platinum gauze and iron mesh wire were used.
• Electrolyte solutions were prepared using ultrapure water from a Millipore Milli-Q (18.2 M Ohmcm).
• Two different brands of CFLs were chosen to use in this study respectively.

Synthesis and Characterization of Iron

• Magnetite (Fe2O3FeO) NPs were prepared according to the method reported by Massart.
• The precipitate was washed with deoxygenated water for three times.
• Fe3O4 and γ-Fe2O3 nanoparticles were characterized by complementary analytical methods.
• High-resolution transmission electron microscopy (HR-TEM) images were obtained using a Philips CM200 kV TEM with energy-dispersive X-ray spectroscopy (EDS).
• Brunauer−Emmett−Teller (BET) specific surface area (SSA) was analyzed using the nitrogen adsorption method on a TriStar 3000 V6.07 surface area analyzer at 77 K.

Iron Oxides Nanoparticles Loaded with Elemental Mercury

• Three-necked round-bottomed flasks were coated with dimethyldichlorosilane prior to use so as to prevent mercury vapor from adsorbing onto the inner glass surfaces of the vessels.
• Control mercury vapor adsorption experiments were carried out using the Schlenk technique.
• Blanks are taken of the air inside the vessel in triplicate before the lamp is broken.
• CV-AFS was equipped with a Tekran Model 2600 CVAFS Mercury analysis system.
• After the electrolysis experiment, the iron mesh cathode was transferred to a silylated 4 L spherical Pyrex vessel with an iron bar.

Elemental Mercury Analysis.

• The removal efficiency and electrochemical regeneration efficiency were calculated based on the concentrations of mercury vapor by complementary CVAFS and GC− MS.
• The authors used the value of saturated mercury vapor pressure to make the calibration curve for the two detection methods.
• Aqueous mercury ion analysis was measured with PerkinElmer FIMS-400 Cold Vapor Mercury analysis system with Amalgam accessory.

Characterization of the Iron Oxides NPs.

• As shown in Figure 1 , the identities of iron oxides nanoparticles were confirmed by comparing X-ray diffraction patterns to standards in the Joint Committee on Powder Diffraction Standards database.
• The adsorption capacities can be measured by calculating the removal efficiency (RE) of mercury vapor as described in eq 2, where CInitial and CFinal are the mercury vapor concentrations in treated flask.
• 15 We observed that the smaller size and larger BET surface area of Fe3O4 NPs demonstrated more elevated adsorption https://pubs.acs.org/doi/abs/10.1021/acssuschemeng.5b01612 capacity.the authors.the authors.
• As the results are shown in Figures 3 and 4 , the magnetite and maghemite nanoparticles are effective for the adsorption of mercury vapor.
• It should be noted that the pH value of the solution during electrolysis also affects the mercury recovery efficiency.

𝑟𝑒𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 (%) =

• 𝐴𝐶 𝑟𝑒𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑒𝑑 𝐴𝐶 𝑓𝑟𝑒𝑠ℎ × 100 (10) With each adsorption/regeneration cycle, transfer losses of the iron oxides nanoparticles accounting for 5% by mass.
• Therefore, it is of great advantage to develop supported iron oxides nanoparticles to avoid the loss and dispersion of nanoparticles to the setup environment.
• The authors adjusted for the loss in mass of the nanoparticles for in the calculation of their regeneration efficiencies.
• As shown in Table 2 , the regeneration efficiencies of the iron oxides nanoparticles ranged from 94% to 112% over three regeneration cycles with surface area and adsorption capacity of the magnetite nanoparticles relatively constant.

Concluding Remarks.

• The authors have developed an efficient system for the recovery of mercury vapor from spent CFLs using nanosorbents capture and electrolysis recovery.
• Mercury vapor can be recovered up to 85% in 4.0 h though absorption times can be greatly reduced through cooling of the sorbent trap to promote adsorption and heating of the spent CFL containing vessel to promote desorption.
• As for the cheapest magnetic nanoparticles, maghemite can uptake mercury vapor quickly with warm white light irradiation although it is not an ideal sorbent for electrochemical recovery.
• Results from their study and other group showed supported magnetite nanoparticles are efficient methods for the removal of pollutants.
• Further study is needed to operate the electrochemistry by solar energy and optimize for particular industrial operations.

Frequently asked questions

Q1. What have the authors contributed in "Development of a green technology for mercury recycling from spent compact fluorescent lamps using iron oxides nanoparticles and electrochemistry" ?

Herein the authors describe a two-step green technique to remove and recycle mercury from spent compact fluorescent lamps ( CFLs ). The first element included the assessment of capture efficiencies of mercury vapor on magnetite ( Fe3O4 ) and maghemite ( γ-Fe2O3 ), naturally abundant and ubiquitous components of atmospheric dust particles. The second step included the development of an electrochemical system for the mercury recycling and regeneration of used nanoparticles. 

Q2. What are the future works mentioned in the paper "Development of a green technology for mercury recycling from spent compact fluorescent lamps using iron oxides nanoparticles and electrochemistry" ?

Further research on detailed chemical speciation and quantification of different compounds, within the electrochemical chambers is recommended. It offers potential to upscale the experiments for future industrial use. In addition, such studies will provide a means for further optimization of recycling system. The mercury adsorption setup is easy to assemble and can be scaled up for potential use in industry by increasing the size of the trap and increasing the mass of sorbent to increase the total adsorption capacity.