Effects of salinity and particle size on radium desorption from river sediments in the Qinghai-Tibet Plateau

Natural radium isotopes have been widely used to study groundwater discharge in different systems. Therefore, it is of great significance to understand the desorption behavior of radium isotopes on sediments to trace waterland exchange processes. However, there is very limited studies observing the desorption Ra isotopes to lake water of the brine lake. Ra-224 desorption experiments with different salinities and particle sizes were carried out by collecting samples of brackish water from Qinghai Lake, brine from Dabuxun Lake and river sediments entering the lakes. The results show that the desorption activity of Ra-224 from the river sediments to lake water of Qinghai Lake is 0.2 dpm/g when the salinity is 10.07 parts per thousand. The maximum desorption activity of Ra-224 from river sediments to lake water of Dabuxun Lake is 0.195 dpm/g at a salinity of 40.81 parts per thousand. A salinity of 41.81 parts per thousand and particle size of 16.28 mu m are the threshold points affecting the desorption behavior of Ra. When the salinity is less than 40.81 parts per thousand, the desorption activity of Ra increases linearly with increasing salinity. When the salinity is greater than 40.81 parts per thousand, the desorption activity of Ra decreases nonlinearly with increasing salinity and tends toward a stable low value. When the particle size is larger than 16.28 mu m, the small particle size promotes desorption. The smaller the particle size is, the greater the desorption activity is. When the particle size is less than 16.28 mu m, the small particle size inhibits desorption. The smaller the particle size is, the smaller the desorption activity. The co-precipitation of Ra2+ with supersaturated Ca2+, SO42- and other ions may be the main reason for the threshold point of salinity and particle size in Ra desorption process in salt lake system.

Automated summary

The desorption behavior of Ra isotopes in salt lake systems is influenced by salinity and particle size, with threshold points identified. Ra desorption activity increases linearly with salinity below 40.81 parts per thousand, but decreases non-linearly above this threshold. A particle size larger than 16.28 μm promotes desorption, while a smaller size inhibits desorption. Co-precipitation of Ra2+ with Ca2+, SO42-, and other ions is suggested to be the main cause of the observed threshold points.