Differences of Flocculating Characteristics of Difficult−to−settle Coal Slime Water Between Polyacrylamide−grafted Starch Copolymer and Polyacrylamide
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摘要:
高岭土等黏土矿的存在是煤泥水沉降效果差的主要原因，目前尚未有关于难沉降煤泥水动态絮凝过程的研究。相较于聚丙烯酰胺（PAM）合成单体的毒性，淀粉接枝丙烯酰胺（SAM）合成的单体可降解性好。为此，以高岭土为研究对象，系统对比了SAM与PAM对高岭土动态絮凝过程的影响。首先，考察了不同SAM与PAM用量下的沉降速度和絮凝效果。随后，通过聚焦光束反射测量（FBRM）和颗粒录影显微镜（PVM）技术研究了高岭土悬浮液在SAM和PAM作用下的不同粒级颗粒数量变化。沉降实验和FBRM−PVM测试结果表明，PAM能够形成更多的+100 μm大絮团，使得PAM具有更好的沉降效果；SAM形成的絮团更稳定，对细颗粒的絮凝效果更好。最后，通过FBRM获得的数据，基于Smoluchowski模型计算了PAM和SAM作用下高岭土的絮凝动力学参数，发现PAM作用下的絮凝指数明显高于SAM，同时−30 μm和30～60 μm颗粒数量的动态变化主导了絮凝动力学中絮团的形成过程。总体而言，PAM可以形成更多的、松散的大絮团，有利于高岭土的快速沉降，但对微细颗粒絮凝效果不佳。相较于PAM，SAM独特的多链立体网状结构，有利于微细颗粒絮凝和形成稳定的絮团，从而避免选煤厂洗水系统中细泥的循环积聚。
Abstract:There is currently no research on the dynamic flocculation process of difficult−to−settle coal slurry water. The presence of clay minerals such as kaolin is the main reason for the poor settling effect of coal slurry water. Compared to the toxicity of polyacrylamide (PAM) synthesized monomers, starch−grafted acrylamide (SAM) synthesized monomers have better degradability.Therefore, the effects of SAM and PAM on the dynamic flocculation process of kaolin were systematically compared. Firstly, the sedimentation rate and flocculation performance were investigated under different dosages of SAM and PAM. Subsequently, the changes in the number of different particle sizes of kaolin suspension under the action of SAM and PAM were studied using focused beam reflectance measurement (FBRM) coupled with particle video microscopy (PVM). The settlement and FBRM−PVM results indicate that PAM can form more large flocs of +100 μm, which leads to a better settling effect using PAM. The flocs formed by SAM are more stable, resulting in a better flocculation performance for ultrafine particles. Finally, the flocculation kinetic parameters of kaolin using PAM and SAM were calculated by fitting the data obtained from FBRM to Smoluchowski’s model. It was found that PAM produced a significantly higher flocculation index compared to SAM. Meanwhile, the changes in the number of −30 μm and 30−60 μm particles dominated the formation process of flocs in flocculation kinetics. In conclusion, PAM can form more loose and large flocs, which is beneficial for the rapid settlement of kaolin. However, SAM has a superior flocculation performance of ultrafine particles than that of PAM. Compared to PAM, the unique multi−chain three−dimensional network structure of SAM is conducive to the flocculation of fine particles and the formation of stable flocs, which can avoid the cyclic accumulation of fine mud in the washing water system of coal preparation plants.
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Key words:
- starch /
- graft copolymer /
- polyacrylamide /
- FBRM−PVM /
- flocculation kinetics /
- kaolin
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