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Six kinds of waste liquids produced in the treatment process of leachate in a waste incineration plant were used to improve the adsorption effect of raw kaolin on heavy metal chloride. The capture performances of these modified kaolin on PbCl 2 and CdCl 2 vapor were investigated in a two-stage fixed bed combustor. The results indicated that the adsorption effects of raw kaolin on PbCl 2 and CdCl 2 were improved in some experimental groups, main effective component was Na + in the leachate, but the influences did not change regularly with the increase in the concentration of Na  +  introduced into kaolin. The adsorbents formed by modifying 10 g kaolin with 21.25 ml leachate 2 were the best adsorbents for PbCl 2 and CdCl 2 . The capture efficiencies of PbCl 2 and CdCl 2 can reach 95% and 63.88%, with the increase of 36% and 53%, respectively. Using leachate as modifying agent had the same effect as directly using Na + . Adsorptions of PbCl 2 and CdCl 2 were still mainly chemical adsorptions. After adsorption of PbCl 2 , the modified kaolin not only generated PbA1 2 Si 2 O 8 , but also produced other chemical compounds. The adsorption of CdCl 2 by modified kaolin did not generate CdAl 2 Si 2 O 8 , but other chemical reactions occurred to generate CdAl 2 O 4 and Pb 8 Cd (Si 2 O 7 ) 3 ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Kaolinite can be used as in-furnace adsorbent to capture gaseous semi-volatile metals during combustion, incineration, or gasification processes for the purposes of toxic metals emission control, ash deposition/slagging/corrosion inhibition, ultrafine particulate matter emission control, and so on. In this work, the adsorptions of typical heavy metals (Pb and Cd) and typical alkali metals (Na and K) by meta-kaolinite were investigated by the DFT calculation. The adsorption energies followed the sequence of NaOH-Si surface > KOH-Si surface > PbO-Al surface ≈ CdO-Al surface ≈ NaOH-Al surface > KOH-Al surface > NaCl-Al surface ≈ Na-Si surface > Na-Al surface > KCl-Al surface > Pb-Al surface > PbCl₂-Al surface > CdCl₂-Al surface ≈ K-Si surface ≈ PbCl-Al surface > K-Al surface > CdCl-Al surface > NaCl-Si surface > KCl-Si surface > Cd-Al surface. Si surface was found available to the adsorptions of Na, K, and their compounds, although it was invalid to the adsorptions of Pb, Cd, and their compounds. The interactions between adsorbates and surfaces were revealed. Furthermore, the discussion of combining with the experimental data was applied to the subject validity of calculation results and the effect of chlorine on adsorption and the effect of reducing atmosphere on adsorption.

It was a challenge to deal with the concentrated leachate (CL) produced by membrane treatment technique in the waste incineration. In this study, the characteristics of the condensate and solid precipitation produced from treatment of CL by lab-scale direct contact evaporation system were investigated, and a process for the treatment of CL with no waste produced was put forward. The air was heated by exhaust steam and high temperature flue gas in the waste incineration to 500℃ and used for evaporating CL. The results showed that the concentrations of COD, NH3-N, and Cl− in the condensate were 17.6 mg/L, 3.1 mg/L, and 40 mg/L at the condition of the volume of hot air = 600 L/h, pH = 7.2, and concentration factor (CF) = 10, which were lower than the limited values in the water quality standard for industry uses (GB/T 19923–2005) in China, and the condensate can be used in circulating cooling water system for supplying water. Solid precipitation consisted of K2Ca(SO4)2·H2O, NaCl, KNO3, and NaNO3. CF was not over 10 because a larger amount of CaSO4 precipitated on the wall of pipe for passing through hot air, which hindered the continuous operation of the evaporation equipment, when CF > 10. Based on thermogravimetric analysis of solid phase precipitation, the most of organic matter in CL were oxidized and decomposed, while inorganic salts were not volatilized when the heating temperature reached about 760℃. The process for the treatment of CL with no waste produced can produce char and inorganic salts such as KCl and NaCl for waste recycling. [ABSTRACT FROM AUTHOR]

Simulated solid waste was incinerated in a fixed bed, while continuously collecting volatized Pb and Cd to investigate the dynamic volatilization behavior. The dynamic data revealed the reducing atmosphere generated by the fixed bed as the main reason for the lower initial volatilization temperatures of Pb and Cd compared to PbO and CdO melting points during chlorine-free incineration. CdO was easier to reduce than PbO; consequently, Cd volatilized stronger than Pb in the chlorine-free fixed bed. However, CdO volatilization was expected to be weaker than PbO volatilization in an air atmosphere. In contrast to the reduction in a fixed bed, the addition of PVC led to indirect chlorination of Pb and Cd at 300–400 °C and 400–500 °C, respectively and their volatilization was significantly enhanced via chlorination. NaCl directly chlorinated Pb and Cd at comparatively high temperatures of 800–900 °C and 700–800 °C, respectively via involvement of SiO 2 and Al 2 O 3 . Moreover, CaO absorbed HCl from PVC, resulting in volatilization inhibition of Pb and Cd at a temperature below 700 °C. However, chlorine was released at a higher temperature. Furthermore, CaO had no effect on NaCl-induced volatilization enhancement of Pb and Cd. [ABSTRACT FROM AUTHOR]

Particulate lead emission control by kaolin was performed in a fluidized bed incinerator at 850–1000°C. The inhalable particulate lead was sampled after a cyclone by a low pressureimpactor. The lead capture process is proposed as three steps: 1) after capture the kaolin particle reacts with lead vapor to form PbO·Al2O3·2SiO2, then 2) lead nanoparticles from homogeneous nucleation of lead vapor conglutinate onto the melting surface of kaolin, and 3) simultaneously, fine particles containing lead conglutinate onto coarse kaolin particles. The kaolin was added in two modes: 1) mixing with solid fuel, and 2) injecting with secondary air. Compared with mode one, kaolin injection caused a much higher concentration of kaolin in the flue gas which led to the capture characteristic difference between two modes. The optimum temperature for mode one to achieve the maximum capture efficiency of submicron lead was 950°C. The optimum kaolin addition proportion for mode two to achieve the maximum capture efficiency was 3%. Overall, kaolin injection is a more effective mode to control submicron lead emission over the temperature range from 850°C to 900°C, while kaolin mixed with the fuel is a simple mode and is more effective at 950°C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbothermal reduction was proposed as a new method of MSWI fly ash purification. • Excessive carbon was adversed to heavy metal separation for NaCl/KCl condensation. • Zn & Pb in condensate had recovery value for their concentration up to 20% & 7%. • Finally, two paths for ash utilization were proposed for industrial applications. Thermal separation of heavy metals from municipal solid waste incineration fly ash (MSWI FA) is a promising approach for both fly ash purification and heavy metal recovery. However, its commercial viability is hindered by excessive energy consumption. In this study, we introduce carbothermal reduction for MSWI FA treatment as an innovative strategy to enhance heavy metal volatilization and reduce the required heating temperature. By incorporating carbon (FA/Carbon = 1:0.2), the volatilization fractions of Pb, Cd and Zn reached 96.5 %, 100 %, and 63.9 %, respectively, when subjected to 900 °C for 2 h. Remarkably, these volatilization amount surpassed the volatilization fractions attained when raw fly ash (RFA) was independently calcined at 1000 °C for 2 h: Pb (90.2 %), Cd (92.9 %) and Zn (30.2 %). Conversely, Cu volatilization was impeded by carbon inclusion. Comparable trends were shown in washing fly ash (WFA). Notably, concentrated carbothermal reduction led to substantial concentrations of Pb (2.5–7.1 %) and Zn (4.9–20.7 %), rendering them amenable for recycling through metallurgical routes. Intriguingly, higher carbon content (FA/Carbon = 1:0.3) hindered rather than enhanced heavy metal volatilization from RFA. We found that condensation of NaCl and KCl occurred in carbon pores, causing the formation of molten eutectic which trapped the heavy metals at high temperatures. Therefore, more carbon showed more enhancement of heavy metal volatilization from WFA which was free of NaCl and KCl. Ultimately, two comprehensive pathways for the resourceful utilization of fly ash based on carbon thermal reduction were proposed and compared. This study demonstrates carbothermal reduction as an effective approach for simultaneous purification and metal recovery of MSWI FA, exhibiting promising potential for industrial application. [ABSTRACT FROM AUTHOR]

• Interactions of multiple-metals with kaolin were studied in two-stage fixed bed. • PbCl 2 vapor in flue gas promoted CdCl 2 capture by kaolin. • CdCl 2 vapor in flue gas promoted PbCl 2 capture by kaolin. • PbCl 2 or adsorption products inhibited CdCl 2 desorption rate to capture more CdCl 2. • Eutectic melting led to new active sites in internal layer to boost Pb and Cd capture. Using kaolin for capturing hazardous metals is an effective and promising technology. However, interactions of multiple-metals with kaolin are not been clearly understood. Interactions of PbCl 2 capture and CdCl 2 capture by kaolin in high-temperature PbCl 2 -CdCl 2 -Kaolin reaction system were investigated in a two-stage fixed bed at 800 °C. Capture efficiency considering kaolin dihydroxylation and Pb/Al or Cd/Al were used to evaluate capture performance of kaolin. The results showed that kaolin captured more PbCl 2 or CdCl 2 in the cases that kaolin captured PbCl 2 and CdCl 2 at the same time, kaolin captured CdCl 2 after its first capture of PbCl 2 and kaolin captured PbCl 2 after its first capture of CdCl 2 than in the case that kaolin only captured PbCl 2 or kaolin only captured CdCl 2. PbCl 2 vapor promoted absorption of kaolin for CdCl 2 , and CdCl 2 vapor also promoted adsorption of kaolin for PbCl 2. Heavy metal capture effects were controlled by chemical kinetics due to small particle size of kaolin and short contract time between heavy metal chloride and kaolin. PbCl 2 vapor or adsorption products on kaolin surface promoted capture effect of CdCl 2 through inhibiting desorption rate of CdCl 2. Adsorption products promoted eutectic melting of kaolin surface, and slightly melted kaolin surface exposed new layers with more active sites to continue reactions of kaolin with PbCl 2 and CdCl 2. Therefore, PbCl 2 vapor in the gas flow promoted absorption of kaolin for CdCl 2 , and CdCl 2 vapor also promoted adsorption of kaolin for PbCl 2. The results can provide an important reference for Pb and Cd capture during MSW incineration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Review the advanced thermal separation methods for heavy metals in MSWI fly ash. • Chlorination of heavy metals by NaCl/KCl requires excitation of Si-Al matrix. • Chlorides make heavy metals more volatile, but molten salts system does not. • XAFS is beneficial for exploring the thermal separation mechanism of heavy metals. • Recovery of heavy metals has good social benefits but poor economic benefits. Municipal solid waste incineration (MSWI) fly ash is categorized as a hazardous waste owing to the presence of heavy metals. The thermal separation of heavy metals from MSWI fly ash has the potential to not only purify the fly ash, but also enable the recovery of heavy metals. The main thermal separation methods include calcination thermal separation (700-1200℃), chlorination thermal separation (700-1000℃), reduction thermal separation (700-1000℃) and molten salts thermal separation (600-800℃). This paper presents a comprehensive review of these four thermal separation methods, comparing them in terms of separation effectiveness, economic feasibility, technical maturity, and environmental impact, etc. Additionally, the possibility of urban mining from MSWI fly ash was evaluated, and the results indicated that while it may be less cost-effective, it could bring significant environmental and social benefits. Finally, the limitations of the existing thermal separation methods and the focus of further research, including both mechanisms and experimental investigations were outlined. [ABSTRACT FROM AUTHOR]