铀在黄壤中的胶体迁移研究

Study on the colloid migration of uranium in loess

利用南方某核生产企业所在地表层黄土和深层黄土,对铀进行了胶体迁移的批试验,分析了溶液中胶体量、胶体载铀量及其影响因素。结果表明,表层土壤较深层土壤产生更多的胶体,单位胶体的载铀量与接触的铀质量浓度呈正相关。铀在胶体上的吸附量与pH值呈非线性关系,表层土单位胶体的载铀量最大为0.17 mg/g,出现在pH=6.0左右;深层土单位胶体的载铀量存在峰值0.51 mg/g,出现在pH=5.0左右。振荡时间对胶体量影响很小,对胶体的载铀量有影响。外加离子和腐殖质会影响土壤胶体量及胶体的载铀量。

The paper intends to present our＇study and analysis of the colloid migration situation quantitatively and qualitatively at various conditions in the surface loess and deeper-layer loess near a nuclear material production enterprise located in south China. We have also done colloid migration batch experiments by analyzing the quantity of colloid in the compound and uranium contained in the colloid. At the same time, we have also investigated the different effects of such factors as the initial concentration of uranium, pH, oscillation time and the additional Fe3＋ , Al3＋ and humic acid on the migration of colloid. The results of our experiments and investigations show that more colloid could be formed with the surface soil than with the deeper one. For example, there has been found over 3 times of colloid containing uranium in the surface soil than in the deeper soil. And, so does there exist more humic acid, plant and animal residues contained in the surface soil than in the deeper soil, which makes the total uranium content in the colloid of surface soil much higher in the surface soil than in the deeper soil. In addition, the uranium loading in the colloid is also positively correlated with the contacted U concentration. Which has been found increased to 0.56 mg/g from 0.198 mg/g with the surface loess and to 0.443 mg/g from the 0.053 mg/g with the deeper-surface of the loess. However, there is not any linear relation between the uranium loading on the colloid and the pH value. What is more, we have found that the uranium adsorption percentage on colloidal tends to increase by pH at 4.0 - 5.0 with the deeper soil and at 4.0 - 6.0 with the surface soil. The greatest amount of unit colloidal uranium that has been found is 0.17 mg/g （2.37 % ） with the surface soil at pH about 6.0 whereas the peak of 0.51 mg/g （1.43%） is to appear just with the deep soil at the pH value of just about 5.0. The quantity of colloidal in the surface soil cart be found decreasing with the increase of pH value in the range of 4.0- 7.0 with the maximum 64.2 mg （2.14 mg/g in the dry soil） . Furthermore, the isolated colloid can be found first increasing and then decreasing with the deeper soil with a peak value of 16.4 mg （0.21 mg/g dry soil） at the pH value of 6.0. However, in the case of high pH, it can be found that H＋ in the hydroxyl and carboxyl groups tends to be dissociated from the surface soil, thus, enhancing the hydrophilic of the colloid and reducing the uranium adsorption of the colloidal. As to the oscillation time, little effect of it has been found on the quantity of the colloid except for its effect on the adsorption weight of uranium. Besides, we have also observed the slight dif- ference of the effects of pH, the total U on the colloidal and its weight in the initial 0 - 32 h. The effect of uranium loading on the colloid has been found increasing from 0.006 7 mg to 0.011 4 mg with the surface loess increasing from 0.004 mg to 0.005 5 mg in comparison with that of the deeper loess, respectively. The additional Fe3 ＋ , Al3＋ and humic acid have been found affecting the amount of soil colloids and uranium loading on the colloid, the adsorption percentage on the soil colloid turned out to be a slight decrease due to the competitive adsorption electrolyte cation with uranyl ion or make changes in the electrostatic potential of the surface, but there is really an increase of the colloid amount.