Qiwu Zhang

Innovated Application of Mechanical Activation To Separate Lead from Scrap Cathode Ray Tube Funnel Glass

The disposal of scrap cathode ray tube (CRT) funnel glass has become a global environmental problem due to the rapid shrinkage of new CRT monitor demand, which greatly reduces the reuse for remanufacturing. To detoxificate CRT funnel glass by lead recovery with traditional metallurgical methods, mechanical activation by ball milling was introduced to pretreat the funnel glass. As a result, substantial physicochemical changes have been observed after mechanical activation including chemical breakage and defects formation in glass inner structure. These changes contribute to the easy dissolution of the activated sample in solution. High yield of 92.5% of lead from activated CRT funnel glass by diluted nitric acid leaching and successful formation of lead sulfide by sulfur sulfidization in water have also been achieved. All the results indicate that the application of mechanical activation on recovering lead from CRT funnel glass is efficient and promising, which is also probably appropriate to detoxificate any other kind of leaded glass.

Destruction of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) by Ball Milling

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have received high concerns due to their extreme persistence, and very few technologies have been reported for their complete destruction. For sound PFCs wastes disposal, mechanochemical method was employed using a planetary ball mill. Potassium hydroxide (KOH) was identified as the best comilling reagent and nearly complete destruction of both PFOS and PFOA was realized. The measured water-soluble fluoride accounted for most of the organic fluorine. The final products of PFOS after treatment were shown to be KF and K2SO4 by XRD analysis. The mass ratio between PFOS and KOH significantly affected the fluoride recovery but not for PFOS destruction and the sulfate recovery. The gradual formation of sulfate and fluoride reveals that the degradation of PFOS is initiated with the dissociation of the sulfonate group. FTIR spectra further showed the disappearance of the -CF3 and -CF2- groups with the generation of sulfate. The cleavage of C-F bonds in PFOS and the formation of fluoride ion were also identified by XPS spectra. On the basis of these results, possible reaction pathways were proposed. The approach was also successfully applied for the destruction of PFOS and PFOA homologues with different chain lengths.

Mechanochemical processing of molybdenum and vanadium sulfides for metal recovery from spent catalysts wastes

This work describes the mechanochemical transformations of molybdenum and vanadium sulfides into corresponding molybdate and vanadate, to serve as a new environment-friendly approach for processing hazardous spent hydrodesulphurization (HDS) catalysts solid waste to achieve an easy recovery of not only molybdenum and vanadium but also nickel and cobalt. Co-grinding the molybdenum and vanadium sulfides with oxidants and sodium carbonate stimulates solid-state reactions without any heating aid to form metal molybdates and vanadates. The reactions proceed with an increase in grinding time and were enhanced by using more sodium carbonate and stronger oxidant. The necessary conditions for the successful transformation can be explained on the basis of thermodynamic analyses, namely a negative change in Gibbs free energy.

Synthesizing slow-release fertilizers via mechanochemical processing for potentially recycling the waste ferrous sulfate from titanium dioxide production

The goal of this study is aimed to develop a novel process to recycle the ferrous sulfate, the by-product of titanium dioxide industry. Zinc sulfate was added in the process of milling ferrous sulfate with calcium carbonate (CaCO3). The sulfates were transformed into carbonates to serve as slow-release fertilizers by co-grinding the starting materials of FeSO4·7H2O, ZnSO4·7H2O, and CaCO3 with small amounts of water in a planetary ball mill. The prepared samples were characterized by X-ray diffraction (XRD) analysis and quantitative measurements of the soluble ratios in water and 2% citric acid solution. It was found that Fe and Zn ions as sulfates were successfully combined with CaCO3 to form the corresponding Fe and Zn carbonates respectively. After milling, the release ratios of Fe and Zn nutrients in distilled water could be controlled at 0.1% and 0.7% respectively. Meanwhile, the release ratios of them in 2% citric acid solution were almost 98% and 100%. Milling speed was the critical parameter to facilitate the transformation reaction. The proposed process, as an easy and economical route, exhibits evident advantages, namely allowing the use of widely available and low-cost CaCO3 as well as industrial wastes of heavy metal sulfates as starting samples to prepare applicable products.

Precursor preparation of Zn–Al layered double hydroxide by ball milling for enhancing adsorption and photocatalytic decoloration of methyl orange

An amorphous photocatalyst was prepared via simple dry milling of Zn basic carbonate (Zn4CO3(OH)6·H2O) and Al hydroxide (Al(OH)3) as a precursor of Zn–Al layered double hydroxide (LDH) and the precursor was agitated in water to simply synthesize the Zn–Al LDH for comparison. The adsorption and photocatalytic activity of the Zn–Al LDH and the precursor were studied via the removal of methyl orange (MO) and decoloration of MO under ultraviolet light irradiation in aqueous solution, respectively. The precursor exhibits much higher decoloration efficiency towards MO than the Zn–Al LDH product because of the synergistic effect of the intercalation reaction and its photocatalytic activity. The amorphous precursor could easily incorporate MO molecules to form MO intercalated LDH, allowing easy access of the organic pollutant to the photocatalyst sample, resulting in an obvious improvement in photocatalytic performance. The novel idea to use the precursor sample instead of the synthesized final product may be applied in other fields to increase the required performances.

Simultaneous synthesis of ettringite and absorbate incorporation by aqueous agitation of a mechanochemically prepared precursor

Co-grinding of calcium hydroxide, aluminum hydroxide and gypsum was performed to prepare an activated precursor for synthesizing ettringite (simple formula 3CaO·Al2O3·3CaSO4·32H2O). Agitation of the precursor in an aqueous solution with a target absorbate, even at room temperature, allowed not only the synthesis of ettringite, but also absorbate incorporation at stoichiometric amounts accompanying the synthesis reaction. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric differential thermal analyses (TG-DSC) were conducted to characterize the precursors and synthesized products. Potassium phosphate was used as the target absorbate to evaluate possible incorporation of both sulphate and phosphate coexisting in the ettringite structure. This confirmed that the novel idea of incorporating pollution components in a reaction may allow for removing efficiencies that are much higher than obtainable from traditional sorption operation.

Mechanochemical pre-treatment for viable recycling of plastic waste containing haloorganics

Chemical recycling technologies are the most promising for a waste-to-energy/material recovery of plastic waste. However, 30% of such waste cannot be treated in this way due to the presence of halogenated organic compounds, which are often utilized as flame retardants. In fact, high quantities of hydrogen halides and dioxin would form. In order to enabling such huge amount of plastic waste as viable feedstock for recycling, an investigation on mechanochemical pre-treatment by high energy ball milling is carried out on polypropylene containing decabromodiphenyl ether. Results demonstrate that co-milling with zero valent iron and quartz sand ensures complete debromination and mineralization of the flame retardant. Furthermore, a comparative experiment demonstrates that the mechanochemical debromination kinetics is roughly proportional to the polymer-to-haloorganics mass ratio.

Separation of Cu(II) from Cd(II) in sulfate solution using CaCO3 and FeSO4 based on mechanochemical activation

Cadmium and its compounds are important resources in different industries; on the other hand, cadmium is one of the most toxic heavy metals which can cause various health problems. Therefore it is important to develop effective methods for the separation of cadmium from other commonly associated metals from the stance of both resource recycling and environmental purification. Lime neutralization (Ca(OH)2) and ferrite are widely used to precipitate heavy metals. Limestone (calcium carbonate: CaCO3) is too stable to be used directly for this purpose. Mechanochemical activation was introduced to increase the activity of CaCO3. Fe(II)sulfate heptahydrate (FeSO4·7H2O) was used as a selective precipitation agent. As a result, Cu(II) was preferentially precipitated as (Fex,Cuy)O while the Cd(II) remained in the solution. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of Cd(II) ions remained in aqueous solution. Then, Cu(II)–Cd(II) separation was achieved by a simple solid–liquid separation.

Transforming Hematite into Magnetite Using Mechanochemical Approach as a Pretreatment of Oolitic Hematite

ABSTRACT Potential transformation of oolitic hematite into magnetite by mixing iron powder using the mechanochemical method has been achieved and discussed in this paper. The phase transition of pure hematite in the preliminary test was identified by X-ray diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The experimental results have shown that the crystallographic planes of magnetite, (220), (311), (400), and (511) were observed clearly in the Fe/α-Fe2O3 mixture after milling for 15 h, indicating that α-Fe2O3 had been effectively transformed into Fe3O4. The diffraction peaks of magnetite were also observed at d = 0.29605 nm (2θ = 30.163°), 0.25226 nm (2θ = 35.559°), 0.24156 nm (2θ = 37.190°), and 0.20898 nm (2θ = 43.458°) after 13 h milling-time. It suggests that the oolitic hematite is transformed into magnetite successfully by mechanochemical processing. The processing might be applied potentially for the magnetic separation of oolitic hematite.

Decomposition pathways of polytetrafluoroethylene by co-grinding with strontium/calcium oxides

ABSTRACT Waste polytetrafluoroethylene (PTFE) could be easily decomposed by co-grinding with inorganic additive such as strontium oxide (SrO), strontium peroxide (SrO2) and calcium oxide (CaO) by using a planetary ball mill, in which the fluorine was transformed into nontoxic inorganic fluoride salts such as strontium fluoride (SrF2) or calcium fluoride (CaF2). Depending on the kind of additive as well as the added molar ratio, however, the reaction mechanism of the decomposition was found to change, with different compositions of carbon compounds formed. CO gas, the mixture of strontium carbonate (SrCO3) and carbon, only SrCO3 were obtained as reaction products respectively with equimolar SrO, excess SrO and excess SrO2 to the monomer unit CF2 of PTFE were used. Excess amount of CaO was needed to effectively decompose PTFE because of its lower reactivity compared with strontium oxide, but it promised practical applications due to its low cost.