P_(2)O_(5)对模拟高放玻璃固化体析晶和抗浸出性能的影响

Effect of P_(2)O_(5) on Crystallization and Leaching Resistance of Simulated High-level Liquid Waste Glass

针对高放废液硼硅酸盐玻璃固化体易析出辉石晶相的问题,本文采用P_(2)O_(5)部分替代硼硅酸盐基础玻璃配方中的MgO和CaO,研究了P_(2)O_(5)掺量(质量分数为0~8%)对玻璃固化体析晶和抗浸出性能的影响。结果表明,当P_(2)O_(5)掺量为0~3%时,样品为无定形态,在850℃热处理6 h后,P_(2)O_(5)掺量为0~2%的样品主要析出辉石晶相,而P_(2)O_(5)掺量为3%的样品析出了少量硅酸钙晶相,辉石晶相基本消失;当P_(2)O_(5)掺量高于3%时,样品析出球形Na_(3)Ca_(6)(PO_(4))_(5)晶体,且析晶度随P_(2)O_(5)掺量的增加而升高。29 Si MAS NMR和^(11)B MAS NMR分析表明,随着P_(2)O_(5)掺量的增加,玻璃网络结构中Q^(3)、Q^(4)和BO_(3)结构单元含量逐渐增加。静态浸泡法(MCC-1)试验结果表明,样品的抗浸出性能随P_(2)O_(5)掺量的增加而逐渐提高,其中P_(2)O_(5)掺量为3%的样品浸泡28 d后,Si、B、Na和Cs元素的归一化浸出率分别为0.508、0.468、0.533、0.280 g/(m^(2)·d)。

Since the glass is matastable from the viewpoint of thermodynamics,the high-level liquid waste glass may crystallize during the process of production,storage,and disposal.Borosilicate glass is used as the matrix for immobilization of high-level liquid waste in China.It is worth noting that pyroxene phase is easy to crystallize in borosilicate waste glass.In order to suppress the crystallization of pyroxene phase,it was proposed that MgO and CaO in the borosilicate glass formula were partially replaced by P_(2)O_(5) in this study.The effect of P_(2)O_(5) content(mass fraction of 0-8%)on the crystallization characteristics and leaching resistance of borosilicate waste glass was mainly investigated.The results show that the waste glass possesses amorphous phase when the content of P_(2)O_(5) is 0-3%.For the samples after heating at 850℃for 6 h,the main crystalline phases are pyroxene when P_(2)O_(5) content is 0-2%.In addition,a small amount of calcium silicate phase appears for the heat treated samples with 3%P_(2)O_(5) content,and pyroxene phase almost disappears.When the content of P_(2)O_(5) is higher than 3%,spherical Na_(3)Ca_(6)(PO_(4))5 crystals precipitate in the glass,and the crystallinity increases with P_(2)O_(5) content.The analyses of 29 Si and ^(11)B MAS NMR show that with the increase of P_(2)O_(5) content from 0 to 6%,the total content of Q^(3) and Q^(4) structural units in the glass network gradually increase from 53.04%to 83.56%,and the content of BO_(3) structural units increases from^(2)9.43%to 38.22%.The increase of P_(2)O_(5) content improves the densification of the overall network structure of the waste glass.The results of the static leaching method(MCC-1)show that the normalized leaching rates LR_(Si),LR_(B),LR_(Na) and LR_(Cs) of the waste glasses gradually decrease with the increase of P_(2)O_(5) content.After 28 d,LR_(Si),LR_(B),LR_(Na) and LR_(Cs) of the waste glass with 3%P_(2)O_(5) content are 0.508,0.468,0.533 and 0.280 g/(m^(2)·d),respectively,which can satisfy the requirements(<1 g/(m^(2)·d))of nuclear industry standard in China.These results suggest that the incorporation of an appropriate amount of P_(2)O_(5) into the borosilicate waste glass may provide an alternative way to solve the problem of crystallization in borosilicate waste glass.