Influence of High Sulfate Mine Water on Spontaneous Combustion of Coal

Preparation of dopamine-modified sea squirt cellulose hydrogel dust-fixing agent to prevent raising of dust

Sea squirts, a tunicate, are found in all oceans and can foul marine ports and aquaculture, mainly affecting shipping and biodiversity. In this study, cellulose was extracted from sea squirts, and its hydrophilic properties were improved by substituting the hydrogen ions of the cellulose -OH with dopamine. The modified cellulose was used to prepare a hydrogel for use as a dust-fixing agent (CDP) to reduce air pollution caused by dust. After response surface method optimization, the proportions of binder, water-retaining agent, wetting agent, and antifreeze in CDP were 0.97, 1.44, 0.23, and 6.32%, respectively. This composition improved the wetting ability and permeability of CDP on particle surfaces. CDP exhibited good water retention at -11-50 °C. CDP reduced the wind erosion rate of dust at a wind speed of 12 m/s to 1.18%. The molecular dynamics method was used to analyze the wetting process and mechanism of CDP, revealing that hydrogen bonds were the dominant force at the solid-liquid interface. The adsorption of CDP onto the surface of coal increased the number of hydrophilic points. Water molecules were adsorbed on these hydrophilic points through hydrogen bonding, improving the binding energy between the solid and liquid interfaces. The application of ascidian cellulose in dust control makes full use of the biological value of ascidians, promoting sustainable development of the global biological economy.

Experimental Study on Catalytic Action of Intrinsic Metals in Coal Spontaneous Combustion

In order to study the effect of inherent metals in coal on spontaneous combustion, Hongmiao lignite and Hongqingliang long-flame coal were demineralized by hydrochloric acid, the raw coal and demineralized coal were characterized by Fourier transform infrared spectrometry, X-ray diffraction, and synchronous thermal analysis experiments, and the corresponding ash content was detected by inductively coupled plasma mass spectrometry. The results show that the effect of demineralization on the volatile matter of low-rank coal is small, and the change of crystallite structure is not significant. The removed parts are mainly water-soluble salts and soluble minerals, such as carbonates and metal ions, that are not tightly bound to the organic matter of coal structure. The removed metal elements are mainly alkali metals Na and K, alkaline earth metals Ca, Mg, Sr, and Ba, and transition metals Fe, Mn, Ti, and so forth. The temperatures corresponding to the end of weight loss, ignition, and maximum weight loss rates were elevated on the thermogravimetric curves of the demineralized coal samples. The heat absorbed by evaporation of water in coal and the heat released by oxidation and combustion of coal are decreased to different degrees, indicating that the spontaneous combustion tendency of coal after demineralization is reduced, and alkali metal, alkaline earth metals, and transition metals in coal have a catalytic effect on spontaneous combustion of coal. After adding the metal chelating agent ethylenediaminetetraacetic acid (EDTA), the apparent activation energy decreased by 33.08 and 2.42%, respectively. EDTA and the alkali metal, alkaline earth metal, or transition-metal ions formed a stable chelate in coal. The catalytic activity of metals is weakened or even lost, thereby inhibiting spontaneous combustion of coal, and verifying the catalytic effect of internal metals in coal on the spontaneous combustion of coal.

Mining Polyethylene Glycol-Based Thermosensitive Hydrogel Materials: Preparation and Flame Retardant Properties

A new type of efficient and anti-extinguishing materials to inhibit coal spontaneous combustion is required because of the current situation of the short activity cycle of existing anti-extinguishing technology. Now, polyethylene glycol (PEG) was used as a water-absorbing monomer to polymerize various substances to prepare an AB-type mining thermosensitive hydrogel that was obviously thermoresponsive. The thermosensitive hydrogel, which is low-cost and stable, can be stored for a long time, and it is prepared by compounding A and B components. The orthogonal experiments determined the optimal ratio of component A, while the controlling variable experiments determined the optimal ratio of component B. The thermal stability and flame-retardant properties of the AB-type thermosensitive hydrogel were analyzed during the process of natural oxidation of coal, and the temperature responsiveness of thermosensitive hydrogels was investigated at different temperatures. The results showed that the optimal ratio of polyethylene glycol:methyl cellulose:sodium carboxymethyl cellulose:guar gum of component A was 6:6:1.2:1.5; and the ratio of bentonite:kaolin:Mg(OH)₂ of component B was 2:1:1. When the ratio of component A to component B was 1:2, the AB-type thermosensitive hydrogel shows the best flame retardant properties. When this ratio of gel was applied to coal samples, the weight loss was just 6%, and the reduction of CO was as high as 72.6%. The gel, which was convenient for transportation in mining pipelines, had strong fluidity at low temperatures and rapid temperature response. As the temperature rose, a phase transition occurred gradually, and after the phase transition, a high-viscosity solid substance was formed, whose viscosity was approximately 11 times that of the room temperature. It plugged the pores effectively, and in the high-temperature region, the occurred phase transition gathered to extinguish the fire. It is a new type of high-efficiency anti-extinguishing material with excellent properties.