颗粒粒径和含固率对疏浚泥沙絮凝沉降的影响

为保护海洋生态环境，合理利用海洋倾倒区，防止悬浮泥沙扩散，采用絮凝处理工艺，在不考虑外部环境的影响下，探讨颗粒粒径和含固率对疏浚泥沙的絮凝作用的影响；采用湿筛法对珠江口疏浚泥沙进行分组，将疏浚泥沙分为混合样、粒径>74 μm、粒径<74 μm、粒径<37 μm和粒径<15 μm的5个粒径段，研究不同粒径段和不同含固率泥沙在加入不同量聚合氯化铝 (PAC) 后，絮凝前后的粒径分布变化特征。结果表明：粒径>74 μm的泥沙颗粒不发生絮凝作用；向含固率为10%的泥沙中加入相同量的絮凝剂后，絮凝沉降速率由慢到快、沉积泥含水率由高到低、沉积泥体积由高到低的粒径段均依次为混合样、粒径<74 μm、粒径<37 μm和粒径<15 μm；对不同含固率的泥沙进行絮凝调理后，25~37 μm粒径段的粒径占比均呈现出随泥沙含固率的增大先增大后减小的趋势，当含固率为5%~10%时粒径占比最高，累积质量分数差异较大的粒径段出现在28~32 μm；对含固率为10%的泥沙进行絮凝处理后，<30 μm的粒径段，絮凝前的占比>絮凝后的占比；30~40 μm的粒径段，絮凝后的占比>絮凝前的占比；不同含固率的泥沙粒径占比峰值由23 μm分别变为33、32.8、32.1、31.6和32.2 μm，且粒径<30 μm的细颗粒含量明显减少，粒径>30 μm的细颗粒含量明显增加。
综上所述，在不考虑外部环境的影响下，30 μm为该区域泥沙的絮凝临界粒径；泥沙含固率在5%~10%时，不利于PAC对泥沙的絮凝作用；絮凝后，泥沙絮团粒径为30~40 μm。本研究成果可为疏浚物海洋倾倒前环保处理技术提供关键参数和依据，并为泥沙的絮凝机理的进一步探索提供参考。

Effect of particle size and solid content of dredged sediment on its flocculation settlement

In order to protect the marine ecological environment, rationally utilize the marine dumping site and prevent the diffusion of suspended sediment, the flocculation process was adopted. The influence of particle size and solid content on the flocculation of dredged sediment was discussed without considering the influence of external environment. The dredged sediment in the Pearl River Estuary was divided into 5 particle size segments: mixed samples, particle >74 μm, particle size <74 μm, particle size <37 μm and particle size <15 μm. The variations of particle size distribution characteristics of dredged sediment with different particle size segments and different solid content were studied before and after flocculation with adding different amounts of polyaluminum chloride (PAC). The results show that the sediment with particle size >74 μm did not flocculate. When the same PAC dosage was added to the sediment with 10% solid content, according to the flocculation-sedimentation rate from slow to fast, the sediment water content from high to low, and the sediment volume from high to low, the order of particle size segments were following: mixed sample, particle size <74 μm, particle size <37 μm and particle size <15 μm. After flocculating and conditioning the sediment with different solid content, the particle size proportion of the 25~37 μm particle size segment firstly increased and then decreased with the increase of solid content. The particle size proportion of the 25~37 μm particle size segment was the highest when the solid content was 5%~10%, and the particle size segment with large difference in cumulative mass fraction occurred in 28~32 μm. After flocculating the sediment with solid content of 10%, the proportion of particle size segment <30 μm before flocculation was higher than that after flocculation, while the proportion of particle size segment 30~40 μm before flocculation was smaller than that after flocculation.
The peak proportion value of particle size distrbution of sediment with different solid content changed from 23 μm to 33, 32.8, 32.1, 31.6 and 32.2 μm, respectively, the fine particle content in particle size segment <30 μm decreased significantly, while the fine particle content particle size segment >30 μm increased significantly. In conclusion, without considering the influence of external environment, 30 μm was the critical particle size of sediment flocculation in this area. The sediment solid content with 5%~10% was not conducive to PAC flocculation. After flocculation, the particle size of the sediment floc was 30~40 μm. The research results can provide key parameters and basis for environmental protection treatment of dredged materials before dumping in the ocean, and provide a reference for further exploration of sediment flocculation mechanism.