Distribution Characteristics And Treatment Strategies Of Heavy Metals In Sediments Of Different Particle Sizes In Typical Northern River

This paper focuses on the seasonal river sediment in Shandong Province as the main research object.To address the issue of heavy metal contamination in the study area,a screening scheme and resource utilization strategy for heavy metal contaminated sediment were proposed.This was achieved by exploring the grain size and distribution rule of heavy metal sediment,as well as the temporal and spatial characteristics of the migration and transformation of heavy metal contaminated sediment under alternating dry and wet conditions.The main research findings are as follows:(1)The particle size and heavy metal characteristics of sediment were studied.The results showed that the sediment particle size of Yihe River was mainly distributed in the range of less than 38～75μm.The sediment content of 0～38μm,38～75μm,75～150μm,150～300μm,300～600μm and 600～1180μm were 19.7%,43.6%,19.8%,9.5%,4.6% and 2.7%,respectively.The sediment particle size of the boundary river is mainly distributed in the range greater than 600～3260μm,and the sediment content of the boundary River with the particle size < 75μm,75～150μm,150～300μm,300～600μm,600～1180μm and 1180～2360μm is 2%,2%,9%,20%,39%and 28%,respectively.The sediment particle size of Xiaoqing River is mainly distributed in the range of less than 38～150μm,in which the sediment content of0～38μm,38～75μm,75～150μm and 150～300μm is 11.8%,52.9%,30% and 5.3%,respectively.The heavy metal concentrations of Cr and Zn in the sediment of Yihe River exceeded the background values by 4.84 and 1.81 times,respectively,indicating pollution.Based on the potential ecological hazard index method,16.7% of the study area points were classified as having slight risk,44.44% as moderate risk,and 38.89%as strong risk,with the pollution risk mainly attributed to the metal element Hg.The highest concentrations of heavy metals in the sediment of Yihe River,Jiehe River,and Xiaoqing River were found in the small particle size fractions,and the concentrations of heavy metals decreased with increasing particle size.In Yihe River,80% of heavy metals were enriched in the sediment particles of 0～150 μm.In Jiehe River,70% of heavy metals were enriched in the sediment particles of 0～150 μm.In Xiaoqing River,85% of heavy metals were enriched in the sediment particles of0～150 μm.Furthermore,the extractable content of heavy metals in sediment increased with decreasing particle size.(2)The study focuses on the temporal and spatial characteristics of sediment migration and transformation,specifically in relation to heavy metals.The results show that heavy metal content decreases during the dry-wet alternating process.Chromi μ m(Cr)is mainly in a residual state,while Copper(Cu)is mainly in a residual and oxidizable state during this process.The distribution of heavy metals in the constant hμmidity group and alternating wet and dry group is similar.The dissolved organic carbon(DOC)content in sediment shows a decreasing trend during the alternating process of dry and wet,with a greater decrease observed in the alternating wet and dry group compared to the constant wet group.Protein-like components are the main components of the dissolved organic matter(DOM)in sediment before and after dry-wet alternation,but the percentage of h μ mus-like components increases after dry-wet alternation.The pH in the sediment changes minimally and tends to be neutral or weakly alkaline,while the oxidation-reduction potential(ORP)in sediment decreases gradually and then stabilizes during the dry-wet alternation process.Cu content in sediment during dry-wet alternations is significantly correlated with Cr content,and is negatively correlated with pH and ORP,but significantly positively correlated with DOC.Cr content is negatively correlated with pH,and positively correlated with ORP,and significantly positively correlated with DOC.(3)Based on the analysis of regularity and variation of different heavy metals in the wet period and normal period of the seasonal channel,it is concluded that Cr and Zn are the main heavy metal elements in the sediment,with significant fluctuations along the river course and higher concentrations observed in the wet season compared to the normal season.Based on the standard limit value of recycling heavy metals and existing screening technology,two potential options for screening contaminated sediment are ultrasonic vibrating screen technology and high-efficiency unit combined vibrating screen technology.The specific particle size ranges of sediment that can be utilized for various purposes are as follows:Sediment with a particle size of 0～38μm: This can be used for brick or cement making.Sediment with a particle size of 38～75μm: This can be used for garden or land use.Sediment with a particle size greater than 75μm:This can be used for all resource utilization methods.Alternatively,if the sediment has a particle size of 0～150μm,it can be utilized for garden or land utilization,while sediment with a particle size greater than 300μm can be used for all resource utilization methods.Specifically,for the plain river study area(such as Xiaoqing River),the sediment can be applied to all resource utilization methods regardless of the particle size.