The recognition of lumpish coal and gangue of different coal sorts was conducted using X-ray technique. Gas coal, fat coal and coking coal were used in this study, and the ash content was found to roughly increase linearly with the density independently of coal sort. Al₂O₃, SiO₂, Fe₂O₃ and SO₃ were detected to be the major oxides for the increase in ash content as the density increased. The gray value of coal was larger than that of gangue and decreased with the increase in thickness and density independently of coal sort and energy zone. The gray value in the high energy zone was found to overlap with that in the low energy zone. Material attribute value (R) was applied for estimating the accuracy of the recognition, and the highest accuracy was given at R = 1.3.

There are still many problems in the stirring dissolution of flocculants: The law of stirring dissolution of flocculants with different molecular weights is not clear, the microstructure of settling floc with different particle sizes of coal slime is still to be explored, and how to apply the law of flocculant dissolution to industrialization? To solve these problems, firstly, mechanical stirring dissolution tests are carried out on anionic polyacrylamide (APAM) with different molecular weights to explore the stirring dissolution law of APAM with 3–25 million molecular weights. Results indicated that the optimal stirring speed of APAM with 3–6 million molecular weight is 800 r/min. The optimal stirring speed of 8–16 million molecular weight APAM is 600 r/min. The optimal stirring speed of 18–25 million molecular weight APAM is 800 r/min. The stirring power formula for APAM dissolution is improved by fitting the experimental data of 3–25 million molecular weight APAM stirring dissolution. Secondly, through APAM performance test, it is verified that the solubility of powdered APAM is the best under optimal solution. Thirdly, through the image measurement and analysis test of settling floc of coal slime, the change law of equivalent diameter of settling floc of different particle sizes of coal slime under the optimal dissolution parameters are explored. Results showed that when the mixing speed is 600 r/min, the equivalent diameter of −0.5 mm slime settling floc is the largest. When the mixing speed is 200 r/min or 400 r/min, the equivalent diameters of 0.5–0.25 mm, 0.25–0.125 mm, 0.125–0.075 mm, 0.075–0.045 mm and −0.045 mm slime settling floc are the largest. The equivalent diameter is positively correlated with the size of slime, and the equivalent diameter of −0.045 mm slime settling floc is the largest. The size of slime is the dominant factor in the change of fractal dimension. The fractal dimension of −0.5 mm slime settling floc is the largest, and the fractal dimension is little affected by mixing speed. Finally, the relationship between the important dissolution parameters of the APAM stirring dissolution test is numerically fitted. In view of the different geometrical parameters of the stirring barrel, a method of deducing the dissolution and stirring time of industrial flocculants is proposed.

Hydrothermal carbon (HTC) was prepared by the one-step hydrothermal method for Cr (VI) removal from wastewater, which was considered a green chemistry method. The specific surface area (S_BET) of HTC was 85m²/g with the pore size in range of 2.024.0nm. FT-IR spectra analysis showed that the HTC had abundant chemical surface functional groups. The influence of adsorption parameters such as pH, HTC dosage, Cr (VI) concentration, and contact time on the removal efficiency of Cr (VI) had been investigated. When the initial concentration was 50mg/L, pH=6, amount of adsorbent was 0.2g/50ml, and adsorption time was 90min; the Cr (VI) absorbed rate of HTC reached 98. Batch adsorption experiments indicated that Cr (VI) adsorption data of HTC fitted the Freundlich isothermal and pseudo-second-order kinetic models. Overall, our findings provide a promising material in treatment of Cr (VI)-rich wastewater and give a clear picture of its application, which is worthy of further study.

The jet flow field is characterized by the dispersion and mixing of multiphase flow, which is widely used in the field of coal slime flotation. In this paper, the behavior of coal slime surface modification, the behavior of material suspension and the effect of different jet fluids on coal slurry blending were studied. Based on the action mechanism of the jet flow field, a jet device suitable for coal slime graded mixing was proposed, and the mixing effect of the jet device was tested. The results show that the jet flow field has strong effects on material dissociation and dispersion, and the mixing effect of a single jet is equivalent to that of the laser particle size analyzer’s own agitation device after stirring for 2.5 min at 500 r/min speed. The SEM test of material surface morphology and the changes of Al and Si elements measured by EDS show that the jet flow field can effectively remove the fine mud wrapped on the surface of coal particles. The precondition of material suspension is to have the just-suspended capacity. The critical jet velocity of coal slime suspension is in the range of 6 m/s~9 m/s. The mixing ability of the jet stream has certain limitations. The increase or decrease of the jet height will cause the decrease of the suspension percentage of sampling points in the tank. The gas jet mode can promote the reagent acting on the surface of the bubble liquid film to form oil bubbles, which is more suitable for hydrophobic mineral flotation. The optimal speed of the gas jet is 0.86 m/s, and the shortest cycle period is 1.0 T (T is one material cycle period). The flotation perfection index of 0.5–0.25 mm and less than 0.075 mm coal slime increased by 2.67% and 26.78%, respectively, indicating that the overall idea of the jet mixing device proposed based on the experimental conclusion is feasible.

The parameters of jet mixing devices have an important influence on the mixing process, particle movement and interface regulation. At present, jet mixing devices are widely used in the coal slime flotation field, and their variable parameters lack systematic optimization. In this paper, the performance of reagent mixing and the distribution characteristics of flow field are taken as the evaluation indexes, and computational fluid dynamics (CFD) software (FLUENT) is used to optimize the variable parameters of the device. The results show that when the area ratio $A_r=1.96~3.24$, the throat-nozzle distance $L_e=0.2D_h~0.6D_h$, the suction tube is located 1/4~1/2 $L_z$ to the left of the nozzle outlet and is symmetrically arranged, the length of the throat tube $L$ is from 6$D_z$ to 12$D_z$, the mixing performance of the jet mixing device was optimal. The flow field distribution characteristics showed that the area ratio has a more significant effect. The larger the area ratio is, the more favorable the mixing of the working fluid and the injection fluid is. The throat-nozzle distance has little effect on the flow field distribution, and its optimal value ranges from 0.3$D_h$ to 0.6$D_h$. The fog droplet size test showed that the dispersion effect was the best when the area ratio $A_r=3.24$. The diameter size test of the injected bubbles was carried out to verify the performance of the jet mixing device after parameter optimization. The experimental results and the simulation results confirm each other, which proves the correctness of the numerical simulation results.

To optimize air-drawing capacity and working effectiveness of jet flotation machine’s stirring device, theoretical analysis has been performed on jet stirring device. Two jet stirring devices with different structural parameters have been designed, hydrodynamic governing equation of different parameters has been established, and pilot-scale test and particle image velocimetry (PIV) test experiments have been conducted in 6m³ test sink and 1.2m³ glass sink, respectively. The results show that flow core vanished apparently and air-drawing capacity improved because of diffuse fluid in the throat by adding the guide blade in the nozzle, which can diffuse fluid in the throat and improve air-drawing capacity; the air-drawing capacity of a long throat is better than that of a short one, besides, energy exchange and mixing effect of slurry and bubble in the former is better than the latter. The guiding blade in nozzle can guide fluid flowing, therefore reducing secondary eddy current and decreasing local loss by 10%~25%; the energy loss of jet stirring device is mainly from the throat, a two-fold increase of throat length leads to almost a threefold local resistance coefficient. Umbrella-shaped diffuser at the end of the throat goes against dispersion and mineralization of material.