Factors influencing illegal dumping of hazardous waste in China.

In recent years, illegal dumping of hazardous waste (IDHW) in China has become a recurring problem. Effective identification and exploration of the factors influencing illegal dumping are crucial for incident prevention and hazardous waste management, but its analysis has rarely been reported. Thus, this study focused on 568 cases of IDHW officially reported by the government. Through regular expressions, the categories of dumped wastes and the provinces where the incidents occurred were extracted. Furthermore, a comprehensive set of influencing factors was constructed by text mining for the case content and by the integration from the existing literature. On this basis, the unstructured and structured data were integrated using a Boolean dataset to respectively explore the association rules of influencing factors for the overall IDHW and for major waste categories, in conjunction with the extracted province information. Subsequently, a Bayesian network was constructed by utilizing the results of association rules mining and the key factors were identified through corresponding analysis. The findings of this study reveal a close connection between various influencing factors, with distinct key factors identified for different categories of hazardous waste. Among them, law-enforcement emerges as a crucial factor in most IDHW cases, while the factor of public monitoring for metallic hazardous waste and the factor of government supervision for distillation residue waste and other waste play a key role in their respective cases of illegal dumping. These findings offer a fresh research perspective for investigating the factors influencing IDHW and present helpful insights for developing effective strategies to prevent and control such incidents.

Temporary Consolidation of Marine Artifact Based on Polyvinyl Alcohol/Tannic Acid Reversible Hydrogel.

Underwater artefacts are vulnerable to damage and loss of archaeological information during the extraction process. To solve this problem, it is necessary to apply temporary consolidation materials to fix the position of marine artifacts. A cross-linked network hydrogel composed of polyvinyl alcohol (PVA), tannic acid (TA), borax, and calcium chloride has been created. Four hydrogels with varying concentrations of tannic acid were selected to evaluate the effect. The hydrogel exhibited exceptional strength, high adhesion, easy removal, and minimal residue. The PVA/TA hydrogel and epoxy resin were combined to extract waterlogged wooden artifacts and marine archaeological ceramics from a 0.4 m deep tank. This experiment demonstrates the feasibility of using hydrogel for the extraction of marine artifacts.

Removal of Calcareous Concretions from Marine Archaeological Ceramics by Means of a Stimuli-Responsive Hydrogel.

The presence of calcareous concretions on the surface of marine archaeological ceramics is a frequently observed phenomenon. It is necessary to remove these materials when the deposits obscure the feature of ceramics. Unfortunately, calcareous concretions provide distinctive documentation of the burning history of ceramics. The interaction of acid solution or detachment of the deposit layers in physical ways leads to the loss of archeological information. To prevent the loss of archeological information and to achieve precise and gentle concretion removal, responsive hydrogel cleaning systems have been developed. The hydrogels synthesized are composed of networks of poly(vinyl acetate)/sodium alginate that exhibit desirable water retention properties, are responsive to Ca2+ ions, and do not leave any residues after undergoing cleaning treatment. Four distinct compositions were selected. The study of water retention properties involved quantifying the weight changes. The composition was obtained from Fourier transform infrared spectra. The microstructure was obtained from scanning electron microscopy. The mechanical properties were obtained from rheological measurements. To demonstrate both the efficiency and working mechanism of the selected hydrogels, a representative study of mocked samples is presented first. After selecting the most appropriate hydrogel composite, a cleaning process was implemented on the marine archaeological ceramics. This article demonstrates the advantages of stimuli-responsive hydrogels in controlling the release of acid solution release, thereby surpassing the limitations of traditional cleaning methods.

Synthesis of Graphene Quantum Dots Enhanced Nano Ca(OH)2 from Ammoniated CaCl2.

Ca(OH)2 nanoparticles are effective materials for cultural heritage restoration, hazardous substance absorption and photocatalyst. However, many methods are complex, and the particle sizes are usually above 80-100 nm, involving mediocre efficacy for application in the stone restoration field. In this work, Nano Ca(OH)2 with diameters less than 70 nm and composited with Graphene Quantum Dots (GQDs) were successfully synthesized in aqueous media. The morphology and structure of the nanoparticles were investigated with TEM, HRTEM, XRD, Raman and FTIR. The particle size distribution and relative kinetic stability of the Ca(OH)2 in ethanol were performed using a laser particle size analyzer and spectrophotometer. Firstprinciple calculations based on the spin-polarized density functional theory (DFT) were carried out to study the reaction process and combination model. The nanoparticles, as prepared, are composed of primary hexagonal crystals and high ammoniated precursors, which have a positive effect on reducing the grain size, and interacted with the GQDs hybrid process. According to the First-principle calculations results, the energy variation of the whole reaction process and the bonding mode between Ca(OH)2 and GQDs can be understood better.

Transformation of Cr under sintering of Ca-rich solid waste with kaolin: Analysis of multi-element coupled interactions.

The high toxicity of Cr-Ca compounds generated during the heat treatment of solid waste will heavily threat the environment. In this work, a kind of Ca-rich river sludge which is bound with Ca and heavy metals was combusted with kaolin under 900 °C for 3 h in a muffle to study the transformation of Cr. The effects of kaolin on Cr transformation were investigated through sequential extraction, the risk assessment of heavy metals, and constant pH leaching test, also combined with crystal phase analysis of Ca-Al-Si minerals. The experimental results showed that the formation of Ca10(SiO4)3(SO4)3Cl2 was inhibited by the addition of 10% (mass fraction) kaolin and the released Cl promoted the evaporation of target elements in priority while 30% kaolin addition further inhibited the solidification of Cr. Furthermore, the effect of NaCl and CaCO3 on the Cr solidification by kaolin were also explored by leaching procedure or XRD analysis of calcination products of their mixtures. It should be noticed that the addition of kaolin in Cr2O3-CaCO3 mixture will directly react with CaCrO4 and fixed the generated Cr2O3 into internal layered structure, preventing its re-oxidization by the free CaO. This work aims to help illustrate the Cr transformation with existence of Ca during sintering of Ca-rich solid wastes and reduce the Cr contamination in future.

Green production of a novel sorbent from kaolin for capturing gaseous PbCl2 in a furnace.

The pollution of semi-volatile heavy metals is one of the key environmental risks for municipal solid waste incineration, and in-situ adsorption of metals within the furnace by mineral sorbents such as kaolin has been demonstrated as a promising emission control method. To lessen the consumption of sorbent, a novel material of amorphous silicate was produced from kaolin through pressurised hydrothermal treatment. Its performance of gaseous PbCl2 capture was tested in a fixed bed furnace and compared with unmodified kaolin and metakaolin. With increasing temperature, the adsorption rates for all sorbents declined due to higher saturated vapour pressure, while the partitions of residual form lead increased which indicated higher stability of heavy metals in the sorbent because of melting effect. The new sorbent with a larger surface area and reformed structure presented 26% more adsorption efficiency than raw kaolin at 900 °C, and increasing the modification pressure improved these properties. Additionally, the production of this high-temperature sorbent was relatively inexpensive, required little thermal energy and no chemicals to produce and no waste effluent was generated, thus being much cleaner than other modification methods.

Experimental study of biomass gasification with oxygen-enriched air in fluidized bed gasifier.

Considering the universality, renewability and cleanness of biomass, an experimental research is carried out using rice straw in a two-stage fluidized bed. The experimental analysis identified the relevant parameters in the operation of the two-stage fluidized bed to investigate the properties of biomass enriched air gasification. Results show that higher gasification temperature is conducive to enhance the gasification performance. An increasing ER is shown to go against adding gas heat value. When oxygen concentration increases from 21% to 45%, the gas heating value increases from 4.00MJ/kg to 5.24MJ/kg and the gasification efficiency increases from 29.60% to 33.59%, which shows higher oxygen concentration is conducive to higher quality gas and higher gasification efficiency. A secondary oxygen injection leads to reduction of tar concentration from 15.78g/Nm3 to 10.24g/Nm3. The optimal secondary oxygen ratio is about 33.00%. When the secondary oxygen ratio increased to 46.86%, monocyclic aromatics reduced from 28.17% to 19.65% and PAHs increased from 34.97% to 44.05%, leading to the increase aromatization of tar.