Experimental Study On The Heavy Metals Release From The Sediments In The Liyun River

With the development of industry, the pollution of the sediments in the city river is very serious. In order to study the process that the heavy metals release and adsorb between the sediments and the water, the experiment is done with the sediments from the four sections across the Liyun river. Firstly, content of the heavy metals in the sample is analyzed. Secondly, the process that the heavy metals release and adsorb between the sediments and the water is simulated in the lab. In order to know the main factors on the heavy metals release from the sediments, isothermal adsorption test is made. At last, the model is built to simulate the process.The main results are drawn from this paper as follows:(l)The heavy metals of the sediment in the Liyun river is serious: the quality fraction of cadmium at each monitoring point is greater than its background value in soil of Huai'an suburb, and the maximum at monitoring points is 15.73 times of the background value;the quality fractions of arsenic and sulfide are decreasing along the river, but the average values of arsenic at the sections of Yinhe Road and the paper plant are beyond their background values in soil;the maximum quality fraction of arsenic is 2.45 times as high as that of soil of grade-III, and the quality fractions of heavy metals in the middle of black mud layers are the highest in vertical direction, and the pollution caused by heavy metals at the riverbank is more serious than that at the center of the river at the same profile of polluted sections.(2)Under a static state, the amount of the discharge from the heavy metal Cd of the sediment will increase gradually to the maximum first, and then it will decrease to a certain amount. The amount of the discharge from As and sulfide will gradually increase first, and finally become a certain amount. The causes which will increase the rate of the amount of the discharge from the heavy metals of the sediment include the increase of the amount of the heavy metals from the sediment, the decrease of the diameter of the particles from the sediment, the increase of the intension of the vibration, the increase of the temperature in the water, the increase of the speed of the stream, and so on.(3)The value of pH and the concentrations of the irons are the two main factors on the adsorption ability of the heavy metals. With the increase of the pH value or with the increase of the quality concentration of NaCl in the overlying water, the quality concentration of cadmium increase in the overlying water and decrease in the sediment.(4) The model is established which is used to simulate the process that the heavy metal releases in sediment-water interface. The release and the adsorb coefficient of the cadmium in the sediment of Liyun river is obtained, which is 0.015 and 0.049.The pollution of the sediments in the Liyun river is very serious. The content of the heavy metals in the river maybe increase when the environmental conditions of the river changed. So it is necessary for the river to be dredged.