Co-stabilization/solidification of heavy metals in municipal solid waste incineration fly ash and electrolytic manganese residue based on self-bonding characteristics

Phase reconstruction behavior and mechanism analysis of the electrolytic manganese residue decoupled residue pyrolysis process

Decoupled electrolytic manganese residue (DEMR) is the electrolytic manganese residue (EMR) after the removal of harmful components by double salt oxidation decoupling separation. An important direction for the bulk resource utilization of electrolytic manganese residue involves reconstructing its mineral phase composition, regulating the microstructure of the surface interface, improving the reactivity of the physical phase, and applying it to building materials through calcination. In this study, the thermal reaction behavior and pyrolysis mechanism of DEMR were revealed through thermodynamic and kinetic analysis combined with molecular dynamics (MD) simulations. The results show that the DEMR process can be divided into four stages. Stage 1 involves the first-order chemical reaction of the aqueous mineral phase removing free water, with an average activation energy (ΔG) of 6.85 kJ/mol. Stage 2 consists of stochastic nucleation and growth reactions, involving the decomposition of unstable sulfate, the removal of crystalline water from the aqueous mineral phase, and the decomposition of the carbon-containing organic matter, with an average ΔG of 126.43 kJ/mo1. Stage 3 is characterized by the phase boundary control reaction of heat-absorbing reconstruction of the stable mineral phase, with an ΔG of 255.46 kJ/mol. Stage 4 involves the heat-driven phase‒solid‒phase boundary chemical reaction of unstable minerals, with a ΔG of 205.54 kJ/mol. MD calculations show that there is a certain interaction energy between the oxides and CaSO4 in DEMR, and Al2O3-Fe2O3 and Al2O3-MgO easily form relatively stable compounds. Between other mineral phases, which may adsorb to each other or form unstable complexes. CaSO4-Al2O3, CaSO4-Fe2O3, Al2O3-Fe2O3, and Al2O3-MgO readily form relatively stable compounds through hydrogen bonding or chemical bonding. What's more, Al2O3-SiO2 and Fe2O3-SiO2 form less stable compounds via van der Waals and Coulomb forces.

Co-treatment of municipal solid waste incineration fly ash and alumina-/silica-containing waste: A critical review

Municipal solid waste incineration fly ash (MSWI-FA) is a hazardous by-product of the incineration process, characterized by elevated levels of heavy metals, chlorides, and dioxins. With a composition high in calcium but low in silicon/aluminum, MSWI-FA exhibits a poor immobilization effect, high energy demands, and limited pozzolanic activity when it is disposed of or reutilized alone. Conversely, alumina-/silica-containing waste (ASW) presents a chemical composition rich in SiO2 and/or Al2O3, offering an opportunity for synergistic treatment with MSWI-FA to facilitate its harmless disposal and resource recovery. Despite the growing interest in co-treatment of MSWI-FA and ASW in recent years, a comprehensive evaluation of ASW's roles in this process remains absent from the existing literature. Therefore, this study endeavors to examine the advancement in the co-treatment of MSWI-FA and ASW, with the focus on three key aspects, i.e., elucidating the immobilization mechanisms by which ASW improves the solidification/stabilization of MSWI-FA, exploring the synergies between MSWI-FA and ASW in various thermal and mechanochemical treatments, and highlighting the benefits of incorporating ASW in the production of MSWI-FA-based building materials. Additionally, in the pursuit of sustainable solid waste management, this review identifies research gaps and delineates future prospects for the co-treatment of MSWI-FA and ASW.

Bidirectional Catalysis Disintegration and Mineral Polymerization via Endogenous Iron(III) from Iron-Rich Sludge in Synergy with Waste Incineration Fly Ash

To enhance the utilization of solid waste in cement kiln co-processing, this study analyzed the multifaceted synergy of pyrolysis and mineralization processes of iron-rich sludge (SS) and waste incineration fly ash (FA) at optimal blending ratios. Based on the physicochemical properties of SS and co-pyrolysis experiments, it was found that Fe acted as a positive catalyst in pyrolysis between 700 and 1000 °C, while the endogenous polymerization effect of Fe(III) mineral groups dominated above 800 °C. Additionally, the study investigated the solidification and migration of heavy metals and the transformation of harmful elements (S, Cl, and P). Results indicated that the best mixture ratios for SS and FA were 6:4 and 9:1, respectively, and synergistic pyrolysis and mineral co-curing effects were observed in the pyrolysis temperature range of 50-1000 °C. The synergy between SS and FA allowed for the decomposition and solidification of harmful organic components and heavy metals, reducing environmental risks. Furthermore, in actual production, by mixing 100 tons of SS and FA with Portland cement with a daily output of 2500 tons, the compressive strength during early hydration stages can reach 34.52 MPa on the third day, exceeding the highest performance of Portland cement (62.5R) strength index specified in the standard.

Unraveling the cation adsorption of geopolymer binder: A molecular dynamics study

Geopolymers play a significant role in remediation of heavy metal contamination and are attracting increasing interests. Sodium aluminosilicate hydrate (NASH) is the prime hydration substance of geopolymers which exhibits excellent adsorption capacity, however, the mechanism of metal cation adsorption at the NASH interface remains unclear. In this study, the adsorption behavior of cations at the NASH interface was investigated in depth, and the effects of Si/Al ratios, ion concentration and ion type on adsorption behavior were also analyzed. Furthermore, three Si/Al ratio models of NASH gel were modified and developed by molecular dynamics simulation, and validated by experiments. The result showed that electrostatic attraction and ion exchange played the major role in adsorbing three cations on the surface of NASH gel. For cations with the same charge number, ionic radius was inversely proportional to the cation exchange and adsorption capacity. Cations with lower ionic potential, among those with different charge numbers, were easier to be adsorbed onto the NASH surface. Therefore, the adsorption capacity of NASH for the three adsorbents was in the order of Na⁺ > Cs⁺ > Pb²⁺. The adsorption capacity of NASH gel for cations increased with the increasing of Al/Si and decreased with the increasing of cation concentration, which was attributed to the increased electrostatic attraction on the NASH surface and the limited number of adsorption sites. The derived microstructure and dynamics information are beneficial for profoundly understanding the adsorption mechanisms of geopolymers on cations.

Characteristic pollutants risk assessment of modified manganese residue utilization in sintered product

The resource disposal of electrolytic manganese residue can effectively solve the problem of environmental pollution caused by it, among which the problem of heavy metal pollution is the most prominent. In this study, a new type of eco-friendly brick mixed with electrolytic manganese residue was designed. The influence of the content of electrolytic manganese residue on its macroscopic properties, microscopic properties, and leaching characteristics was analyzed by test methods such as compressive strength test, radioactivity test, XRF, XRD, FTIR, and ICP test of bricks. The results showed that the manganese content in the EMR leachate was 8120 mg/L, which exceeded the Chinese standard. The leaching experiment of ordinary aqueous solution of sintered bricks mixed with 20% EMR showed that the content of heavy metals was far lower than the Chinese national standard. There was no non-carcinogenic risk of heavy metals in the strong acid leaching solution of sintered bricks mixed with 20% EMR. Only the carcinogenic risk values of Cr for adults and children were 4.21 × 10^-4 and 9.82 × 10^-4 respectively, both exceeding the USEPA limit, but the application scene of sintered bricks was difficult to achieve strong acidity, so it was judged that it had no carcinogenic risk to the human body. Characteristic heavy metals such as Mn, Cr, and As existed stably in sintered bricks through substitution and encapsulation. In addition, the compressive strength and radioactivity of EMR sintered bricks met the requirements of the Chinese national standard "Fired Ordinary Bricks." This product can be used as national standard MU20 grade brick. This study provided an efficient method for the safe and environmentally friendly disposal of EMR in a sustainable control system.