Xinzhong Liu

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.

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.

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.