无机盐与表面活性剂在低阶煤表面的协同吸附

Synergistic adsorption of inorganic salt and surfactants on the surface of low rank coal

针对低阶煤表面含氧官能团多、亲水性强、可浮性差等问题,采用非离子型表面活性剂——壬基酚聚氧乙烯醚(NP-10)和无机盐(NaCl、CaCl_2、Al Cl_3)对低阶煤泥表面进行吸附改性研究,分析其协同改性行为。吸附试验表明,NP-10在低阶煤泥表面的平衡吸附量随着其浓度增加逐渐升高,达到一定值后趋于稳定,吸附符合Langmuir等温吸附模型。吉布斯自由能(ΔG)和标准吸附焓(ΔH)为负值,说明该吸附过程为放热且自发过程,吉布斯自由能(ΔG)随温度升高逐渐减小,说明温度的升高能促进吸附过程。吸附动力学研究表明,准二级动力学方程适合描述NP-10在低阶煤泥表面的吸附动力学机制。Na^+、Ca^(2+)、Al^(3+)三种离子能促进低阶煤泥对NP-10的吸附,其中Al^(3+)的促进效果最好,Ca^(2+)次之,最后为Na^+。X射线光电子能谱(XPS)试验表明,低阶煤泥表面吸附NP-10后,煤泥表面碳元素含量显著增高,氧元素含量明显降低,说明NP-10的亲水基与低阶煤泥表面的含氧官能团结合,实现了对煤泥表面含氧官能团的有效覆盖,提高了低阶煤泥的疏水性。Na^+、Ca^(2+)、Al^(3+)三种阳离子电解质的加入,使低阶煤泥表面的氧元素含量分别降低了5.79%、6.77%、7.42%,含氧官能团含量进一步减少,尤其对C—O官能团影响最为显著。3种阳离子电解质都能促进低阶煤泥对壬基酚聚氧乙烯醚(NP-10)的吸附,促进效果为Al^(3+)>Ca^(2+)>Na^+。

The Low rank coal surface with oxygen-containing functional groups was strong hydrophilicity and poor floatation. This study used the non-ionic surfactant nonylphenol polyoxyethylene ether( NP-10) and inorganic salt( Na Cl,Ca Cl2,Al Cl3) to adsorb and modify the surface of low rank coal,and further to investigate the synergistic modification behavior.Adsorption experiments show that the equilibrium adsorption capacity of low rank coal slime on NP-10 gradually increases with the increased of its concentration,after that it tends to be stable when it reaches a certain value.The adsorption is in accordance with Langmuir adsorption model.Gibbs free energy( ΔG) and standard adsorption enthalpy( ΔH) with negative value show that the adsorption process is spontaneous exothermic.ΔG gradually decreases with the increase of temperature,indicating that increasing temperature can promote adsorption.Adsorption kinetics results show that quasi-second order kinetic adsorption mode is suitable for the adsorption of NP-10 on low rank coal surfactants.The addition of Na+,Ca2+,Al3+can promote the adsorption of NP-10 on the low rank coal slime,among which the promotion effect of Al3+is the best,followed by Ca2+,and finally Na+.X-ray photoelectron spectroscopy( XPS) results show that the content of carbon element on coal surface significantly increases after adsorption,while the content of oxygen element significantly decreases. It reveals that the hydrophilic group of NP-10 is combined with the oxygen-containing functional groups on the surface of low rank coal,which effectively covers the coal surface and improves the hydrophobicity of coal slime.Due to addition of Na+,Ca2+and Al3+,the content of oxygen element on the surface of coal after adsorption are reduced by 5.79%,6.77% and 7.42%,respectively. The contents of oxygen-containing functional groups on the surface of the low-rank coal also decrease,especially C—O functional groups.All the three cations could promote the adsorption of NP-10 on the surface of lowrank coal slime,the promotion efficiency of three cations is Al3+>Ca2+>Na+.