Wettability Modification of Lignite by Adsorption of Dodecyl Based Surfactants for Inhibition of Moisture Re-adsorption

Formulation Optimization and Performance Prediction of Red Mud Particle Adsorbents Based on Neural Networks

Red mud (RM), a bauxite residue, contains hazardous radioactive wastes and alkaline material and poses severe surface water and groundwater contamination risks, necessitating recycling. Pretreated RM can be used to make adsorbents for water treatment. However, its performance is affected by many factors, resulting in a nonlinear correlation and coupling relationship. This study aimed to identify the best formula for an RM adsorbent using a mathematical model that examines the relationship between 11 formulation types (e.g., pore-assisting agent, component modifier, and external binder) and 9 properties (e.g., specific surface area, wetting angle, and Zeta potential). This model was built using a back-propagation neural network (BP) based on single-factor experimental data and orthogonal experimental data. The model trained and predicted the established network structure to obtain the optimal adsorbent formula. The RM particle adsorbents had a pH of 10.16, specific surface area (BET) of 48.92 m2·g-1, pore volume of 2.10 cm3·g-1, compressive strength (ST) of 1.12 KPa, and 24 h immersion pulverization rate (ηm) of 3.72%. In the removal of total phosphorus in flotation tailings backwater, it exhibited a good adsorption capacity (Q) and total phosphorous removal rate (η) of 48.63 mg·g-1 and 95.13%, respectively.

Enhancement of Flotation Performance of Oxidized Coal by the Mixture of Laurylamine Dipropylene Diamine and Kerosene

Conventional hydrocarbon oil cannot adhere effectively to oxidized coal, resulting in a low yield of clean coal. In this study, a high-speed homogenizer was used to emulsify LDD (laurylamine dipropylene diamine) and kerosene, which enhanced the flotation efficiency of oxidized coal. The flotation results showed an increase from 4.12% (only kerosene) to 23.33% (emulsified oil). An increase in contact angle indicated that the mixture reagent can increase the hydrophobicity of coal particles, which is attributed to the adsorption of LDD onto the coal particle surface and the decrease of the oil droplet A lower surface tension of LDD allows it to produce a stable layer of froth than the layer generated by kerosene alone.

Effects of Surfactant Compounding on the Wettability Characteristics of Zhaozhuang Coal: Experiment and Molecular Simulation

It is important to study the mechanism of wettability of Zhaozhuang coal with surfactant compoundings in order to prevent dust disaster in the process of coal seam mining. By means of molecular simulation, the amounts of water absorbed by different systems, which are composed of monomer surfactant molecules and Zhaozhuang coal molecules or compounding surfactant molecules and Zhaozhuang coal molecules, were compared in this paper. The simulation results show that the system composed of 0.2% sodium dodecyl benzene sulfonate (SDBS) and 0.3% alcohol polyoxyethylene ether (AEO3) had the maximum water absorption amount of 479, which is significantly better than that of other compounding methods and of each monosurfactant system. Analysis results show that the interference of non-ionic surfactant can greatly reduce the electrostatic repulsion between ionic surfactants and make the adsorption sites on the Zhaozhuang coal molecule more compact. The experimental results show that the decreasing percentage of the contact angle of this type of compounding solution on Zhaozhuang coal was 83.74%, which is the best of the six compounding methods. It has a high degree of consistency with the simulation results, and the molecular simulation method applied in this paper shows that it is convenient and accurate. This research plays a guiding role in dustproof work in Zhaozhuang coal mining.

Synergistic Adsorption Mechanism of Anionic and Cationic Surfactant Mixtures on Low-Rank Coal Flotation

Mixed surfactants have a prominent synergistic effect and show advantages in many aspects. In this work, the effects of a mixture of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) on the flotation of low-rank coal were studied from the wetting rate, contact angle, surface tension, and zeta potential. Furthermore, the adsorption configuration of the mixed surfactant on the surface of oxygen-containing graphite was simulated at the molecular level by molecular dynamics simulation. The experimental results show that the combustible matter recovery of low-rank coal flotation is improved using the mixed surfactant, and the contact angle test and wetting rate test confirmed the synergistic effect of the mixed surfactant. In the mixed surfactant system, the addition of SDS with an opposite charge to DTAB can reduce the mutual repulsion between DTAB molecules and enhance the degree of DTAB alignment in solution, which was analyzed by surface tension and zeta potential tests. Meanwhile, the simulation results reveal the adsorption behavior of anionic and cationic surfactants on the surface of oxygen-containing graphite from the molecular level and also verify the experimental results. This investigation provides a good understanding of the interaction mechanism of mixed surfactants in low-rank coal flotation.