Effect Of Surface Hydrophobic Modification On Sedimentation And Filtration Of Highly Slimed Coal Slurry

The mechanized coal mining method will cause some clay minerals to enter the raw coal,and the clay minerals are easy to slime when encountering water during the coal washing process,which not only seriously affects the sedimentation and clarification effect of the coal slurry,but also has an adverse influence on the subsequent dewatering process.This paper,aims at the current situation of difficult settling and dewatering of highly slimed coal slurry in coal preparation plants.The initial sedimentation velocity,supernatant turbidity,and sediment height were used as the evaluation indicators of sedimentation tests.The different inorganic coagulants and surfactants were selected by settling effects of the coal-bearing clay minerals on the basis of adding anionic polyacrylamide.The pressure filtration tests of highly slimed coal slurry were carried out with the selected chemicals.The mechanism of interaction between the agents and particle surface were analyzed through the characterization of agglomeration image observation,infrared spectroscopy,XPS analysis,wetting heat and Zeta potential.Adding flocculant PAM alone can effectively increase the settling rate of fine particles,but the turbidity of supernatant does not decrease significantly.In the combination of inorganic coagulant and PAM,PAC+PAM has the best settling effect.When the dosage of PAM is 80 g/t and the dosage of PAC is 1800 g/t,the sedimentation effect is better,the corresponding sedimentation speed is 48.03 m/h,the turbidity of supernatant is 196 NTU and the height of sediment is 14 mm.In the combination of surfactant and PAM,cationic surfactant has the best effect.The addition of DTAB and CTAB can promote the formation of large aggregates of fine particles,improve the initial settling velocity and greatly reduce the turbidity of supernatant.The settling effect of CTAB+PAM combination is better than that of DTAB+PAM.When the dosage of CTAB and PAM are 1800 g/t and 80 g/t,The initial settling velocity,turbidity of supernatant and settlings height are 43.32 m/h,76 NTU and 19 mm,respectively And the maximum diameter of the agglomerate can reach 2.6 mm.Among the ternary agents,Al Cl₃+NaOL+PAM has the best settling effect..When the dosage of Al Cl₃ is 1800 g/t,the dosage of PAM is 80 g/t and the dosage of NaOL is 1000 g/t,The initial settling velocity,turbidity of supernatant and settlings height are 47.88 m/h,34 NTU and 21mm,respectively.The pressure filtration test of the preferred agent shows that under the action of the combination of PAC+PAM,CTAB+PAM,Al Cl3+NaOL+PAM,the perforation time for forming the filter cake is greatly reduced,and the dehydration effect of the CTAB+PAM combination is better than Well,when the dosage of the agent is 1800g/t,the maximum reduction range of perforation time is 73.57%.PAM adsorbs particles by"bridging",connecting particles to form irregular flocs,which promotes settling and dewatering of fine particles.PAC can compress the electric double layer on the surface of particles,reduce the electrostatic repulsion between particles,and promote the settling and dewatering of particles.The results of infrared spectroscopy,XPS,contact angle and wetting heat analysis show that the adsorption of surfactant on the particle surface can mask the oxygen-containing functional groups on the particle surface,increase the hydrophobic functional groups,reduce the absolute value of wetting heat,increase the contact angle and enhance the hydrophobicity of the particle surface.Facilitates settling and dehydration of particles.The surface hydrophobicity of particles is enhanced after the reaction of anionic surfactant NaOL,but the electrostatic repulsion between particles cannot be reduced because of the negative charge of the polar base band of Naol.Therefore,the agglomeration is small and the settlement effect is not ideal.When the cationic surfactants DTAB and CTAB interact with the mineral surface,the hydrophilic groups move towards the particle surface,and the electrostatic repulsion between the particles is reduced by the reduction of the negative potential of the particle surface through the electric neutralization.At the same time,The hydrophobic base is arranged away from the particle surface,which enhances the hydrophobicity of the Particle surface and promotes the particle hydrophobicity to agglomerate and settle.Compared with DTAB,CTAB has longer alkyl chain,so it has stronger ability of hydrophobic modification on mineral surface and better settling effect of particles.Although CTAB can slightly reduce the surface tension,the large agglomerates generated will be mixed with water.Therefore the perforation time is greatly shortened and the water content of filter cake is increased.A small part of the non-ionic surfactant AC1202 is cationic in the solution.The electric neutralization on the particle surface can reduce the surface negative potential.When AC1202 acts on the particle surface,its hydrophobic groups are arranged outward.The hydrophobic modification on the particle surface promotes the hydrophobic aggregation of fine particles,which makes the particles easier to aggregate and settle.When Al Cl₃ and NaOL are used together,it is difficult to adsorb on the particle surface due to the negative charge of the hydrophilic base band of NaOL.While Al³⁺can reduce the negative potential on the particle surface and and then reduce the electrostatic repulsion between particles,which makes NaOL easier to adsorb on the particle surface and enhance the hydrophobicity of the particle surface.enhancing the hydrophobicity of the particle surface,Hydrophobic aggregation of particles occurs,which promotes settling.