Study On The Characteristics Of Different Grain Sizes Sediments Adsoption-desorption For Lead In West Liaohe

Heavy metal Pb migration and transformation by the carrier of sediment, while the particle heavy metal Pb is the main input form by rivers. To estimate with the amount of lead that the sediment particle migration and the releasing flux of adsorbed lead from different grain sizes sediments, which can probide a theory evidence for amount of lead and releasing flux of lead. According to analysis of different grain size of sediments from West Liaohe in the article and the study pb adsorption and desorption on different grain size of sediments, which provide a basis of adsorbed Pb flux estimates into the sea by equilibrium adsorption;desorption equilibrium.Batching experiments of equilibrium adsorption were carried out to investigate the enrichment characteristics of lead from different grain sizes sediment in Western Liao River. The results indicated that lead enrichment characteristics of different grain sizes sediment: clay(1.66), slit(1.48), fine sand(0.85) and coarse sand(0.48), respectively, which were equivalent to 3.46,3.08 times of coarse sand. The enrichment effect of fine sand size sediment was relatively stronger, which may be due to two reasons. Firstly, fine grain size sediments humus content level was significantly higher than coarse sand size. Secondly, stably combined humus has higher proportion in fine sand size of sediment. Stably combined humus are important adhesive material in the formation of loose organo-mineral complexes. The sorption mechanism of lead on organo-mineral complexes may be microhole filling. It plays a leading role in the enrichment of lead. There were significantly positive correlations between enrichment coefficient and total humus content(p < 0.01)with the correlation coefficient of 0.964. The mass average percentages of adsorption state lead carried by clay and silt were estimated as 106.02 mg/kg and 98.71mg/kg respectively in the Xiliao River under wet season.According to different grain size sediments on desorption characteristic of lead was investigated by batch experiment of equilibrium desorption. Results indicated that desorption ratio and desorption hysteresis index can described the holding characteristics of lead on different grain sizes sediments well. The order of desorption ratio(Dr) of adsorbed lead from different grain sizes sediments is: clay(0.65%), slit(0.68%), fine sand(15%) and coarse sand(28.85%)respectively; the order of desorption hysteresis index(TII) is: clay(0.59), slit(0.53), fine sand(0.34) and coarse sand(0.08) respectively. It means that holding ability of fine grain sizes sediments for lead is stronger than coarse grain sizes sediments. Desorption ratio(Dr) of coarse sand is much larger than other grain sizes and desorption hysteresis index is less than others. Lead of fine grained size aggregate cause irreversible transformation of aggregate structure, which was fundamental cause of desorption ratio lower and hysteresis index higher.The releasing flux of adsorbed lead of different grain sizes sediment of sequence is: coarse sand(22.42mg/kg); fine sand(11.83mg/kg); slit(0.61mg/kg) and clay(0.67mg/kg). Although the contents of absorbed lead of coarse sand sizes is not high(77.31mg/kg), the desorption ratio is relatively high(28.85%), which leads to release flux is larger(22.30mg/kg). Absorbed lead from coarse grain sizes sediments has lager environment risk effort on overlying water, however, clay and slit grain sizes sediments is a integral part of geochemical cycles.