Publications

The presence of Ca compounds may be an important factor contributing to oxidation of Cr(III) to Cr(VI) during the incineration of tannery sludge. In this study, Cr(III) oxidation was inhibited by preventing Ca participating in Cr(III) oxidation reactions via incorporating it in phosphate minerals. Cr(III) oxidation was remarkably suppressed through immobilizing Ca in phosphate minerals. Around 16% of Cr(III) would be oxidized in samples without phosphate heated at 900°C for 1h, which could be reduced substantially to 0.25% with the addition of phosphate at n(P)/n(Ca)=2. Moreover, phosphate not only captured free CaO, inhibiting Cr(III) oxidation, but seized Ca from CaCrO4, resulting in formed Cr(VI) being reduced. Inhibition of Cr(III) oxidation performed resistant to elevating temperature over 1000°C and prolonged retention time, due to the irreversible incorporation of Ca into phosphate mineral species. Moreover, incorporating Ca into phosphate minerals thoroughly eliminated the potential of Ca to trigger Cr(III) oxidation. Additionally, the P-hosting phases produced (e.g., Ca(PO3)3 and Cr(PO3)3) were also able to capture free CaO and inhibit Cr(III) oxidation, so Cr(III) oxidation continued to be inhibited during flue gas cooling and fly ash reheated process. A case study, in which tannery sludge was heated, confirmed that adding phosphate effectively inhibited Cr(III) oxidation. Adding phosphate could therefore be an effective way of inhibiting Cr(III) oxidation when solid waste containing Cr(III) is heated.

The incorporation of hazardous solid waste in fired bricks fabrication is a viable way. However, the physical and mechanical properties of products were negatively influenced due to the involvement of hazardous solid waste. Three fluxing agents, waste glass powder (WGP), Na-feldspar and K-feldspar, were introduced in this study to eliminate these negative influences. Physical and mechanical properties were tested by standard method. Microstructure and pore structure of bricks were conducted by Scanning Electron Microscopy (SEM) and nitrogen adsorption and desorption isotherm. The change in mineral phase was detected by X-Ray Diffraction (XRD). The leaching toxicity of heavy metals were carried out by Toxicity Characteristic Leaching Procedure (TCLP) and Netherlands tank leaching test. The introduction of fluxing agents can greatly promote effectively compressive strength and decline water absorption. When 30 wt% (weight percent) of fluxing agents are added, water absorption reduced by more than 50%, and compressive strength increased by more than one time. XRD and SEM analysis showed that fluxing agents can promote the formation of glass-ceramic phase, which were mainly formed by the self-melting reaction of fluxing agents and the interaction with silicon-aluminium oxides. These dense glass phases could reduce the porosity and promote the compactness of microstructure. The formation of glass-ceramic phases could also reduce the leachability risk of heavy metals. Combing with properties of brick and price of fluxing agents, WGP is considered to be more suitable for improving properties of fired bricks containing hazardous waste. This study could provide some useful parameters and knowledge for improving properties and leaching toxicity risk when hazardous wastes were utilized in the production of fired brick.

It has always been a great challenge to transform the huge waste PET plastic (wPET) resources into reusable monolithic materials under atmospheric pressure and low temperature. Herein, we reported a novel one-step method for transforming wPET into 3D monolithic structure material (3DMSM) at atmospheric pressure and low temperature (98 °C) without catalyst. The main idea of this paper is to use special solvent (a mixture of C6H5OH and C2H2Cl4 with a 1:1 vol ratio) to dissolve wPET, then introduce polymethyl methacrylate (PMMA) and aluminum dihydrogen phosphate (AHP) to react and generate new chemical bonds in 3DMSM, so as to transform wPET into 3DMSM with excellent mechanical strength and stability even under extreme conditions. The resulting 3DMSM (0.546 g) can support a beaker containing 5000 mL of water without deformation, and max compressive strength and compressive modulus reaches 5.5 ± 0.5 MPa and 34.3 ± 0.5 MPa 3DMSM can maintain structural stability in extreme conditions such as strong acid and alkali. XRD, FTIR and 13C solid-state NMR analysis confirmed that the chemical bonds of wPET will not break when dissolved in a special solvent, and chemical bond breakage mainly occurred in the reaction process. Utilizing chemical bonds to break and recombine, two new substances, C9H9ClO3 (benzoicacid, 5-chloro-2-methoxy-, methylester) and Al3(PO4)2(OH)3, were formed, and the possible structure formula was provided. The innovation of this work is that it presents a novel method to dispose of wPET at atmospheric pressure and low temperature, which provides a possibility for the subsequent large-scale realization of wPET resources.

A novel strategy for improving the immobilization of heavy metals during the use of electroplating sludge in the production of clay bricks, was proposed by the addition of waste glass. Waste glass addition reduced open porosity and surface area, and enhanced compressive strength remarkably. With the adding amount of waste glass powder up to 30 wt.%, surface area and open porosity declined from 0.84 to 0.05 m2/g and from 10.69 to 1.16%, respectively. Compressive strength increased from 20 to 32.7 MPa. Moreover, the leaching concentration of heavy metals decreased considerably and met the regulation standard. Heavy metals, Cu and Zn, have been incorporated into stable spinels phase and adding waste glass was favored to the formation of spinel. It was regarded that waste glass and andesine melted and formed liquid phase during firing process, which improved the mass transfer and the reaction kinetic of spinels formation. The liquid phase filled in the pores and densified bricks body, which also play a important role in preventing heavy metals from releasing. Overall results suggested the addition of waste glass powder was a promising method in improving immobilization of heavy metals during the use of electroplating sludge in production of clay bricks.

Electroplating sludge is usually regarded as the hazardous waste because of the considerable amount of heavy metals. The vitrification process or firing clay bricks mixing of electroplating sludge is an alternative way to disposal it. The reaction behaviors of heavy metals in electroplating sludge at high temperature are closely associated with the leachability of heavy metals from fired products. In this work, an available thermodynamic model, slag activity calculation model, was used to examine the reaction behaviors and predicate the phase transformation of heavy metals under different conditions. CaO would preferably combine with SiO2 and form CaSiO3 at 1100–1500 K. Most of Cr, Zn and Cu would exist in a form of oxides and spinel phases. Cr would be preferably incorporated into ZnO·Cr2O3 and CaO·Cr2O3 rather than CuO·Cr2O3 except metal oxide; Zn would be preferably incorporated into ZnO·Cr2O3 and ZnO·Fe2O3 rather than 2ZuO·SiO2 and ZnO·Al2O3; Cu would be preferably incorporated into CuO·Al2O3 and CuO·Fe2O3 rather than CuO·Cr2O3. Elevating the basicity facilitated Zn to transform into ZnO·Al2O3, ZnO·Fe2O3 and CuO·Fe2O3, while hindered Zn and Cu being incorporating into 2ZnO·SiO2 and CuO·Cr2O3. Increasing the amount of Fe2O3 in system suppressed the formation of heavy metal oxides (i.e. Cr2O3, ZnO and CuO) and spinel species containing Cr, while promoted the formation of spinel species containing Fe, especially for ZnO·Fe2O3 and CuO·Fe2O3. This work can provide some useful information for reaction behaviors and phase transformation of heavy metals during heating solid waste containing heavy metals.

The introduction of industrial solid waste in fired clay brick is a promising way to consume this waste, however, physical and mechanical properties were seriously impacted due to the incorporation of these solid waste. In current study, various particle diameters of waste glass powder (WGP) were introduced in the preparation process of brick to examine the difference in improving physical and mechanical performances of products, and to obtain the optimal particle size of waste glass for applying in the preparation of fired brick. Results showed the incorporation of WGP in larger particle size (100 and 300 meshes) can effectively improve properties, like bulk density, water absorption and compressive strength, but decrease thermal conductivity slightly. XRD and SEM analysis revealed that WGP with particles size of 100 and 300 meshes would become glass–ceramic phase or form albite, which can improve effectively physical and mechanical properties. However, part of WGP with particle size of 600 and 800 meshes might melt and crystalize into quartz at high temperature. The addition of WGP in particle size of 100 and 300 meshes can decrease much leachability of heavy metals from fired bricks and promote environment safety comparing with WGP with particle size of 600 and 800 meshes. Above results suggested that there is no necessary to grind WGP in much smaller particle size during introduction of waste glass for improving fired brick property. The conclusions from this research give some useful information for the incorporation of WGP in the preparation of fired brick.

Cr(VI) compounds at high temperature usually tend to decompose and reduce into Cr(III) due to thermodynamically instability for Cr(VI). This study found Cr(VI) could be reduced into Cr(V) instead of Cr(III) in the presence of CaO during heating solid waste containing Cr(VI). CaCrO4 is prepared and mixed with CaO as simulated solid waste containing Cr(VI). It was found that CaCrO4 reacted with CaO and formed a new product Ca5(CrO4)3O0.5 at temperature range of 800 and 1000 °C. The valence state of Cr in Ca5(CrO4)3O0.5 is determined to be +5 b y XPS analysis, and the color for new formed Cr(V) is observed in green, similar to Cr(III) compounds. The temperature and CaO are two keys to arouse the reduction reaction of Cr(VI) into Cr(V). In particular, the reduction of Cr(VI) into Cr(V) is strongly depended on temperature (800–1000 °C), this reaction can be balanced within 10 min, while prolonging sintering time has little help for promoting the reduction of Cr(VI) to Cr(V). Additionally, it was found Cr(V) can keep stable and not be re-oxidized into Cr(VI) at 800–1000 °C. Above results offers some new understanding and knowledge about the formation of Cr(V) in presence of much CaO or CaCO3 during heating solid waste containing Cr(VI).