Mechanism of pore wetting degree affecting the floatability of lignite
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摘要: 孔隙润湿度是影响多孔煤泥可浮性的重要因素之一，然而煤的孔隙润湿度与其可浮性之间的内在联系鲜见报道。由于煤泥颗粒小、数目多，其孔隙被水润湿的行为难以被准确检测，采用形状规则的圆柱体多孔活性炭材料开展孔隙润湿度的机制研究，并将结果用于解释孔隙润湿度对褐煤可浮性的影响机制。通过正硅酸四乙酯和十六烷基三甲氧基硅烷对多孔活性炭进行疏水化改性，采用接触角和傅里叶变换红外(FTIR)表征活性炭改性前后表面疏水性等特性，结果表明:活性炭经改性后亲水性基团含量降低以及疏水性基团产生，接触角增加67°，疏水性显著增加。采用低场核磁共振(LF-NMR)测定改性前后的亲/疏水活性炭样品在不同浸泡时间下的孔隙润湿度，结果表明:随着浸泡时间增加，亲/疏水两种样品的T2谱的信号幅度均增加，且亲水样品的信号幅度要远大于疏水样品。亲水样品的T2g在任意浸泡时间下均高于疏水样品的T2g值，表明在相同浸泡时间下亲水样品孔隙润湿度均高于疏水样品。而当浸泡时间为10 min时，亲/疏水样品中的孔隙均会被水较好地润湿，两种样品润湿度差值最小。通过将亲/疏水样品的T2g值与浸泡时间进行非线性拟合发现两者之间的指数函数关系式符合一级浮选动力学模型，亲水样品的润湿速率约为疏水样品的3.85倍，进一步说明亲水样品的孔隙较疏水样品更易被水润湿。不同预润湿时间下的褐煤浮选实验结果表明:褐煤的浮选回收率随着预润湿时间增加而降低，较长的润湿时间增加了孔隙被水的润湿程度，从而在多孔褐煤表面形成厚且稳定的水化层，阻碍了气泡与褐煤颗粒的粘附，褐煤的浮选结果与活性炭孔隙润湿行为特性相一致，这较好地阐述了多孔煤泥可浮性与其孔隙润湿度之间的内在联系。Abstract: Pore wetting degree is one of the important factors affecting the floatability of porous fine coal. However,the intrinsic relationship between the pore wetting degree of coal and its floatability is rarely reported. It is difficult to accurately detect the behavior of its pore wetted by water due to the small size and large number of fine coal particles.Thus,in this paper,the porousactive carbon material with a cylindrical of regular shape is used to study the mechanism of pore wetting degree. This study aims to explain the mechanism of pore wetting degree affecting the floatability of lignite. The porous active carbons are modified using tetraethyl orthosilicate and cetyltrimethoxysilane. The contact angle and Fourier transform infrared spectroscopy (FTIR) are used to characterize the surface hydrophobicity of the active carbon before and after modification. The results show that the content of hydrophilic group decreases and the hydrophobic groupisgenerated,and the contact angle is improved by 67° after the modification of the active carbon,which improve its hydrophobicity. Low-field nuclear magnetic resonance (LF-NMR) is used to determine the pore wetting degree of hydrophilic and hydrophobic active carbons at different immersion times. The results show that the signal amplitude of the T2 spectrums of both hydrophilic and hydrophobic samples increases with the increase of immersion time. The signal amplitude of the hydrophilic samples is much larger than that of the hydrophobic samples at each immersion time. The T2g value of the hydrophilic samples is larger than that of the hydrophobic samples at each immersion time,indicating that the pore wetting degree of the hydrophilic samples is higher than that of the hydrophobic samples at the same immersion time. However,the difference in the pore wetting degree of the two samples is the smallest and the pores in the hydrophilic and hydrophobic samples are both wetted by water well when the immersion time is 10 min. The relationship between T2g value of hydrophilic/hydrophobic samples and immersion time is nonlinearly fitted to the exponential function,which is the same as the first-class kinetic model of flotation. The wetting rate of hydrophilic samples is about 3.85 times of that of the hydrophobic samples,further indicating that the pores of hydrophilic samples are easily wetted by water compared with the hydrophobic samples. The results of lignite flotation experiments at different pre-wetting times show that the flotation recovery of concentrate decreases as the pre-wetting time increases. The long wetting time increases the pore wetting degree of lignite to form a thick and stable hydration film on its surface,resulting in a decrease in the adhesion efficiency of coal particles and bubbles.The flotation results of lignite are consistent with the behavior of pore wetting of active carbons,which also better reveals the intrinsic relationship between the floatability of porous fine coal and its pore wetting degree.
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Keywords:
- immersion time /
- pore /
- LF-NMR /
- wetting degree /
- wetting rate
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