Sorption of Sr in granite under typical colloidal action.

The sorption behaviour of Sr into granite was studied with the presence or absence of typical colloids (goethite, bentonite and humic acid). A batch technique was used to analyse the influencing process of colloids and key factors. Moreover, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize granite samples before and after the batch experiments. The experiments showed that the presence of colloids promotes the sorption of Sr in the broken granite system; when goethite, bentonite or humic acid (HA) was present, the sorption capacity percentages were 1.8, 2.13 and 1.93 times higher, respectively, than those in the granite only system. As the initial Sr2+ concentration increased, the sorption of Sr increased, but the sorption percentage decreased; the sorption percentage reached a maximum at pH = 7 and decreased as the acidity or alkalinity of the solution increased. The sorption of granite may be related to the interstitial water of the hydroxyl, quartz, and feldspar, the intergranular water of granite groups and the water molecules attached to the granite. Moreover, the surface of the granite sample was rougher after the sorption experiment.

Effect of a humic acid colloid on the sorption behaviour of Sr onto soil in a candidate high-level radioactive waste geological disposal site.

We explored the effect of the presence or absence of humic acid (HA) on the sorption behaviour of Sr onto soil. We examined three different experimental cases for Sr sorption: (1) sorption in the presence of only colloidal HA, (2) sorption in the presence of only soil and (3) sorption in the presence of both colloidal HA and soil (HS). A batch technique was used to study the influencing factors, including the amount of colloidal HA, solid content, pH, initial concentration of Sr and contact time. The experiments showed that the influencing factors significantly affected the sorption process. For example, in the case of soil and HS, the sorption percentage increased rapidly with increasing solid content at m/V < 20 g/L, changing from 8.35% and 37.54% to 49.09% and 77.03%, respectively. Moreover, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize samples. The kinetics and isotherms of Sr were best described by the pseudo-second-order and Langmuir models, which indicated that the process was controlled by chemisorption and uniform monolayer sorption with constant energy on the outer surface. These findings provide valuable information for predicting strontium migration in radioactive waste disposal sites.

In-situ study of migration and transformation of nitrogen in groundwater based on continuous observations at a contaminated desert site.

The objective of this study was to explore the controlling factors on the migration and transformation of nitrogenous wastes in groundwater using long-term observations from a contaminated site on the southwestern edge of the Tengger Desert in northwestern China. Contamination was caused by wastewater discharge rich in ammonia. Two long-term groundwater monitoring wells (Wells 1# and 2#) were constructed, and 24 water samples were collected. Five key indicators were tested: ammonia, nitrate, nitrite, dissolved oxygen, and manganese. A numerical method was used to simulate the migration process and to determine the migration stage of the main pollutant plume in groundwater. The results showed that at Well 1# the nitrogenous waste migration process had essentially been completed, while at Well 2# ammonia levels were still rising and gradually transitioning to a stable stage. The differences for Well 1# and Well 2# were primarily caused by differences in groundwater flow. The change in ammonia concentration was mainly controlled by the migration of the pollution plume under nitrification in groundwater. The nitrification rate was likely affected by changes in dissolved oxygen and potentially manganese.